Concentrations of CO2 were at 400.83ppm in March compared to 398.10ppm in March 2014, the preliminary Noaa data showed. They are are expected to stay above 400pm during May, when levels peak because of CO2 being taken up by plants growing in the northern hemisphere.

Noaa used air samples taken from 40 sites worldwide, and analysed them at its centre in Boulder, Colorado. The agency added that the average growth rate in concentrations was 2.25ppm per year from 2012-2014, the highest ever recorded for three consecutive years.

http://www.theguardian.com/environment/2015/may/06/global-carbon-dioxide-levels-break-400ppm-milestone

Thank you Dr. Anoop Kumar for placing an innovative question and thanks a lot to Barbara for adding High-tech information on the subject. This indicates that how much man can do to explore the hidden treasures of nature. I think Dr. Barbara has explained the subject in a highly innovative way. This subject is new to me. Yes, I agree that significant source of CO2 in soil is the decomposition of organic matter. The dissolved CO2 can produce H2CO3 which can reduce the soil pH temporarily and can prove useful to make available micro nutrients and P in alkaline and neutral soils. The end result will be increase in yields, as explained by Barbara. However, the probable results are soil and plant specific and cannot be generalized for all crops.

Let us wait for our other learned intellectuals who always take the discussion very high by including their experience and expertise. 

Dear Sir,

Thank you very much for raising the important issue. Climate change is very broad topic, let us talk more specifically to the impact of warming and agriculture, especially warming due to elevated CO2, CH4, N2O, chemical fertilization, poor agro waste management, biomass burning are the root cause of the agroecosystem mediated warming and also driving force behind the altered response of crop-plants and soil.  

Answer to first question is Free air CO2 enrichment (FACE) system are more reliable and accurate CO2 delivery system for  studying the soil-plant response to the elevated CO2. 

Answer to second question is C3 crops will be more responsive to the elevated carbon-dioxide concentration because of its distinct physiological pathways than the C4. 

Answer to third question is soil properties like pH, cation exchange capacity, total organic carbon, dissolved organic carbon, nitrogen content, microbial biomass carbon and nitrogen, C/N ratio, soil enzymes like dehydrogenase and other nutrients specific enzymes, greenhouse gases (GHGs)  emission will respond to elevated CO2 prominently. 

Answer to fourth question microbial community structure  and microbial biomass carbon,  CO2 efflux, level of root exudation and rhizodeposits  can be utilized to monitor the early impact of the elevated CO2.

Answer to fifth question since soil is conditionally renewable resource, Some of the soil properties are reversible like pH,CEC, CFU, however other property like CO2 and other GHGs, once release in to the environment  and causes its negative effects on the crops (like loss in cropyield, loss of nutrient from soil and plants) then it would be impossible to regain it by any means.

For more detail kindly see the article after a week or 10 days  "Exploring rhizospheric interactions for agricultural sustainability: The need of integrative research on multi-trophic interactions". which which is recently accepted for publication in Journal of Cleaner Production will be available to you very soon.

For a while, Kindly go through the attachment, it may be helpful to you.

Good Luck.

Highly informative addition by Rama.

Intersting piece of information Barbara about the CO2 dynamics involving soil-plant -environment  tripartite relationship . How different soil microbial communities undergo reorientation in their  structural , functional and metabolic changes in response to change sin atmospheric CO2 concentration , that remains to be seen . if you can further supplement please. Dr Nazir , as usual , provided a strong clue  about the changes in nutrient availability . Hope Dr Nazir continue to participate actively in rest of the discussion to follow. Rama Kant , an excellent piece of information , so appreciative of your collection of literature on the subject . They are so pertinent in the context of the discussion . I will further appreciate , if you can supplement the first part of my response .

This is the exerpts from studies carried out by Barnaby (2012) : DOI: 10.1002/9780470013902.90023718.

Carbon dioxide (CO2) has two unique properties: physically it absorbs in the infra‐red (heat) portion of the spectrum, and plays a role in maintaining global surface temperatures; secondly, it is the source of carbon for plant photosynthesis and growth. Recent, rapid anthropogenic increases in CO2 have been well‐characterised with respect to climatic change; less recognised is that increase in CO2 will also impact how plants supply food, energy and carbon to all living things. At present, numerous experiments have documented the response of single leaves or whole plants to elevated CO2; however, it is difficult to scale up or integrate these observations to plant biology in toto. To that end, a greater emphasis on multiple factor experiments for managed and unmanaged systems, in combination with simulative vegetative modelling, could increase our predictive capabilities regarding the impact of elevated CO2 on plant communities (e.g. agriculture, forestry) of human interest. 

Dear Sir,

Answer to the  first part of the question: There is contradiction between the  Open Top Chamber(OTC) and Free air CO2 (FACE) enrichment system to study the effect of the e CO2 on crop-plants. However practically when we are exposing the crops under OTC then crop-plant always feels restricted environment which is not like natural cropping environment. So to get the actual idea about what will the consequences of the e CO2 on crop-plants in forthcoming future, FACE system are more prominent than the OTC. One demerit of the FACE system is there is more fluctuations in the CO2 concentration under the FACE system however it can be sort out with proper regulatory and monitoring system.

Kindly find the attachment, It may be helpful to you.

Good Luck.

Rama Kant, can you throw some more light why C3 plants are more responsive than C4 plants under high carbon dioxide concentration. 

Dear Sikha, 

Response of C3 and C4 both  to elevated CO2 is mainly dependent upon the associated photosynthetic process  of the crops. C4 plants like (maize, sugarcane, sorghum, millet) are belong to have specific physiology (Kranz anatomy) and distinct photosynthetic process which is  already CO2 saturated at ambient CO2 concentration. Whereas in C3 crops like (wheat, rice, barley, oat, and rye, soybean, peanut, various beans, potato, cassava, sweet potato, sugar beet, most oil-seed crops) process of CO2 fixation happen at faster rate under elevated CO2 concentration. This result in faster rate of photosynthesis and  crop biomass in C3 under elevated CO2.  Again this enhanced crop biomass will enhances all the belowground rhizospheric process like more root exudation, rhizodeposits, enhanced  microbial activity and altered microbial community. Further these changes become the  root cause of the changed soil quality and crop productivity. 

These are the differences behind the different response of C3 and C4 to elevated CO2 and their consequences in short.

For more detail kindly find the attachment. It may be helpful to you.

Good Luck.

Freinds, my question is how many years of data are required there is a change in climate thats my first question. My second question is what kind of climatic constants should we use for such studies so that such studies find much wider application.

The atmospheric CO2 concentration was 270 ppm for  1000 years before the start of the industrial revolution. Then it has been accumulating in the atmosphere at an accelerating rate. Now, the global atmospheric CO2 concentration has reached 400 ppm, which has been projected to surpass 550 ppm by the middle of this century. Elevated CO2 stimulates photosynthetic carbon gain and net primary production over the long term. Studies indicated that elevated CO2 improves N use efficiency, but decreases water use at both the leaf and canopy scale. On the other hand, elevated CO2 does not directly stimulate C4 photosynthesis, but can indirectly stimulate carbon gain during drought time. According to previous studies yield stimulation by elevated CO2 in crop species is smaller than expected. Genetic factors can also play an important role in photosynthetic response to elevated CO2. This may be explained with fast-growing Populus trees exposed to elevated CO2. For example, research findings suggest that photosynthetic capacity does not change in soybeans grown under elevated CO2. Photosynthetic capacity acclimates to elevated CO2 in C3 plants and the scale of down-regulation differs with genetic and environmental factors. However, despite acclimation of photosynthetic capacity, carbon gain will be greater by 19–46% in plants grown at the CO2 anticipated for the middle of this century.

Carbon sequestration may be a climate change mitigation option in agricultural soils as most of cultivated soils are depleted of soil organic carbon and far from saturation. The management practices, most frequently suggested to increase soil organic carbon content have variable effects depending on soil and climatic conditions and have to be applied for a long time periods to maintain their sink capacity. For instance, the turnover of soil applied organic matter in tropical soils is much faster than in temperate soils. Effective mitigation of greenhouse gases emission requires the exploration of a range of alternatives in agricultural sector, which is the cause of one third of greenhouse gas emissions. Carbon sequestration in agricultural soils can be considered as a good option to potentially store vast amount of carbon in soils. Improved soil tillage practices, crop rotation system, application of manure, crop residue, compost and cover and deep-rooting crops may increase soil organic carbon content (SOC) via increased carbon input and reduced decomposition rates. But the adoption of these practices may be limited due to the uncertainty of carbon sequestration rates across arrange of soil and climatic conditions. The use of biochar can be good option as soil amendment to achieve such large carbon sequestration.

Excellent piece of information , you have added Dr Getachew. I appreciate it . Our friends will enjoy reading it.

 I am bringing to you another marvel piece of work by Cure and Acock ( 1986) who   identify the  strengths and weaknesses in the knowledge base for modelling plant responses to CO2. It is based on an extensive tabulation of published information on responses of ten leading crop species to elevated CO2. The response variables selected for examination were: (a) net carbon exchange rate, (b) net assimilation rate, (c) biomass accumulation, (d) root:shoot ratio, (e) harvest index, (f) conductance, (g) transpiration rate and (h) yield. The results were expressed as a predicted percentage change of the variable in response to a doubled CO 2 concentration. In most instances, a linear model was used to fit the response data. Overall, the net CO2 exchange rate of crops increased 52% on first exposure to a doubled CO2 concentration, but was only 29% higher after the plants had acclimatized tothe new concentration. For net assimilation rate, the increases were smaller, but fell with time in a similar way. The C4 crops responded very much less than C3 crops. The responses of biomass accumulation and yield were similar to that for carbon fixation rate.

Yield increased on average 41% for a doubling of CO2 concentration. The variation in harvest index was small and erratic except for soybean, where it decreased with a doubling of CO2 concentration. Conductance and transpiration were both inversely related to CO2 concentration. Transpiration decreased 23% on average for a doubling of CO 2 . Crop responses to CO2 during water stress were variable probably because high CO2 both increased leaf area (which increases water use) and reduced stomatal conductance(which decreases water use). However, low nutrient concentrations limited the responses of most crops to CO 2 . The absolute increase in photosynthetic rate in response to high CO 2 concentration was always greater in high light than in low light, but this was not necessarily true of the relative increase. In all except one study, responses to CO2 were larger at high temperature than at low. Most of these studies were done in high light intensity. In low light intensity, the effect of temperature on the CO2 response was smaller .

Kindly find enclosed the required PDF for further reading

Concentrations of CO2 were at 400.83ppm in March compared to 398.10ppm in March 2014, the preliminary Noaa data showed. They are are expected to stay above 400pm during May, when levels peak because of CO2 being taken up by plants growing in the northern hemisphere.

Noaa used air samples taken from 40 sites worldwide, and analysed them at its centre in Boulder, Colorado. The agency added that the average growth rate in concentrations was 2.25ppm per year from 2012-2014, the highest ever recorded for three consecutive years.

http://www.theguardian.com/environment/2015/may/06/global-carbon-dioxide-levels-break-400ppm-milestone

 Earlier , i responded to the question , how plant responds to higher  CO2 .  In my  next response , please see , how plant roots react to elevated CO2. This review covers current knowledge on the impact of increasing CO2 concentration on root dynamics of plants in terms of growth, root/shoot (R/S) ratio, root biomass, root length, root longevity, root mortality, root distribution, root branching, root quality, and the response of these root parameters to management practices including soil water and nutrients. The effects of CO2 concentration on R/S ratio are contradictory due to complexity in accurate underground biomass estimation under diverse crops and conditions. Roots become more numerous, longer, thicker, and faster growing in crops exposed to high CO2 with increased root length in many plant species. Branching and extension of roots under elevated CO2 may lead to altered root architecture and ability of roots to acquire water and nutrients from the soil profile with exploration of the soil volume. Root turnover is important to the global C budget as well as to nutrient cycling in ecosystems and individual plants. Agricultural management practices have a greater impact on root growth than rising atmospheric CO2 since management practices influence soil physical, chemical, and biological properties of soil, consequently affects root growth dynamics in the belowground. Less understood are the interactive effects of elevated CO2 and management practices including drought on root dynamics, fine-root production, and water-nutrient use efficiency, and the contribution of these processes to plant growth in water and nutrients limited environments. Enclosed the concerned PDF for further reading friends .

I think amongst soil properties, soil microbial communities undergo most immediate change, while properties like pH could be difficult to induce change under elevated carbon dioxide conditions. 

Dear Sikha,

Your prior question that is how many years of data are required there is a change in climate that my first question. My second question is what kind of climatic constants should we use for such studies.

Answer to your first question: if you are planing to do some climate modelling then definitely you have to take data of minimum 30 years.  if you wish to see the effect practically it will appears within in year, whereas to conclude something there must be repetition of 4-5 years experimentation.  

Answer to your second question:   In climatic factor temperature, rainfall , humidity  will be most regulatory factor to study the effect of elevated CO2. Now  in your last answer pH will also respond to elevated CO2 because of CO2 and H2O reaction and H2CO3 reaction and their association.

Good Luck. 

The problem facing our planet seems a bit complex and challenging. I think a special multidisciplinary effort involving plant breeders, plant physiologists, soil scientists, agronomists, environmentalists and others including policy makers is necessary to generate technologies that may acclimate to the changing climatic conditions and sustain agricultural productivity while mitigating environmental pollution and global warming.

The problem facing our planet seems a bit complex and challenging. I think a special multidisciplinary effort involving plant breeders, plant physiologists, soil scientists, agronomists, environmentalists and others including policy makers is necessary to generate technologies that may acclimate to the changing climatic conditions and sustain agricultural productivity while mitigating environmental pollution and global warming.

The problem facing our planet seems a bit complex and challenging. I think a special multidisciplinary effort involving plant breeders, plant physiologists, soil scientists, agronomists, environmentalists and others including policy makers is necessary to generate technologies that may acclimate to the changing climatic conditions and sustain agricultural productivity while mitigating environmental pollution and global warming.

The problem facing our planet seems a bit complex and challenging. I think a special multidisciplinary effort involving plant breeders, plant physiologists, soil scientists, agronomists, environmentalists and others including policy makers is necessary to generate technologies that may acclimate to the changing climatic conditions and sustain agricultural productivity while mitigating environmental pollution and global warming.

The problem facing our planet seems a bit complex and challenging. I think a special multidisciplinary effort involving plant breeders, plant physiologists, soil scientists, agronomists, environmentalists and others including policy makers is necessary to generate technologies that may acclimate to the changing climatic conditions and sustain agricultural productivity while mitigating environmental pollution and global warming.

Dear Getachew Agegnehu.

You are absolutely right.  Present day agricultural sustainability is the need of hour to feed the burgeoning global population equitably. 

1. Free Air CO2 enrichment (FACE) experiments.

2. C3 > C4 due to rubisco. Among C3 plants, there are no particular species more responsive than others. The CO2 response depends on other co-limiting factors. For example, if water or nutrients are limiting, plants cannot use the extra CO2 to grow further.

3.Nitrogen availability is the most important limiting factor to CO2 on earth (Hungate et al. 2003 Science), specially in the northern hemisphere. N-availability is greatly determined by pH. Artificially you can increase N-availability by adding nitrogen to the soil, and if N was limiting in the soil, the response to CO2 will be higher (Reich & Hobbie 2013 Nature Climate Change).

I am more willing to see how organic carbon changes when carbon dioxide concentration is high. Is carbon dioxide response induced increase in root biomass various rhizodeposition etc. leading to improvements in organic carbon. How does this fraction of organic carbon become permanent soil carbon pool?

Interesting.Lets listen from other colleagues.

Highly esteemed Anup Kumar Srivastava and colleagues. Very good, competent response gave Dr. Rama Kant Dubey, apparently the most fully reflect the state of affairs at the present stage of research. But if we look closely, it turns out that this is not enough either in the experimental or theoretical (conceptual) sense.

Let me give you the following observations in the course of numbering issues.

1) The system FACE is an open. So, it is a priori can not be effective for studying the response of a complex object "soil-plant" to increase of CO2 in the atmosphere. After all, we need a balance of carbon in the soil and vegetation, with known concentrations (or flows) in the atmosphere. Only then will we be able to say whether the sequestration (sink) or emissions of CO2. It is difficult count the balance in an open system. Part of the CO2 in the atmosphere will go in different directions, and some - absorbed by the soil, not just the surface, but also in the volume through the roots respiration. CO2 - a heavy gas and its possible convective gravitational downward flow at relief and in soils with sufficient porosity. Sprinkler irrigation or rainfall will also remove some of the gas from the atmosphere. Even if the sensor of CO2 is located in the soil at different depths, it will then be very difficult to assess the response of soils to changes in atmospheric concentrations. However, FACE does not provide for soil studies. Therefore, the FACE system is hardly suitable for quantitative studies. Here we need to start a closed system such as phytotron.

2) I often ask this question in lectures to students. What plants bind the most CO2? When no one answers correctly, I take out the mirror and show them. Same as you, that is - young, growing, those who have not yet reached a steady state. I think the answer would be useful here. Stationary ecosystem regardless of species composition of plants (C4, C3), however do not give a meaningful response to changes in the concentration of CO2 in the atmosphere. First absorb, but then during respiration and decomposition go back. But the young (planting perennials, young forests, shrubs) can be a sink, proportional to the concentration in the atmosphere and individual physiological characteristics of binding CO2.

3) This question is complex and the beginning of the need to decide what it means to «elevated concentration» ?. If the 400-600 ppm, I think, no properties of the soil are not directly respond. Soil air contains tens or hundreds of times more CO2, so it means that for all soil processes the level of 400-600 ppm is disparagingly small.Therefore it can work only indirect mechanisms - through changes in vegetation productivity, revenue organic litter and root respiration, and after that - microbial activity. Assume productivity increased two-fold. Hence microbial activity of the same amount must increase, and since the root respiration increased two times, the total biogenic flux of carbon from the soil to the atmosphere also increases 2 times, if the ecosystem stationary. However soil system will respond to an increase in productivity with a delay, especially in our boreal climate. You tropical system likely quite rapidly formed a new equilibrium state with higher emission flow (q) from the soil. If the flow is predominantly convective (wetlands) q = Cs * v, Cs - concentration of the gas in the soil, v - velocity of the flow. If it is a diffusion (conventional aerated soil) q = -D * dC / dz, D - the effective diffusion coefficient, z - depth of soil, dC = Cs-Ca, Ca - concentration in the atmosphere. Since Cs >> Cao, while Ca = 400-600 ppm, then q = D * Cs / dz. This means for both convective and diffusive transport in the steady state flow of CO2 emission increase 2 times requires increasing soil concentration (Cs) 2 times, if not change the permeability characteristics of the medium (v, D). What happens if the concentration of CO2 in soil air permanently (irreversibly) will increase by 2 times? First, as in the ocean, will react carbonate buffer system. Due to buffering the increase in concentration in the soil air in 2 times will lead only to a relatively small (10-20%) increase in the final total inorganic carbon in the soil solution. A significant part of the CO2 is adsorbed solid phase, in particular humus (Henry constant for adsorption of 10-40 or more). By buffering, no significant changes in pH, and therefore the movable elements for alkaline soils of arid likely will not. Finally, part of the CO2 will flow deep into the soil and there is dissolved in groundwater or restock carbonates. Microorganisms, as living beings will react Shelford curve with a maximum (extremum). And here is what kinds of activities will increase, for others - a decline, but on average, after appropriate microbial succession, the system will come to a new steady state with a twofold increase in destructive activity, otherwise there will be a balance with productivity. Rising productivity and plant litter in 2 times may be accompanied by an increase in the coefficients of humification in 1.3-2 times, and hence the flow of organic carbon in the long-term reservoir. Therefore, it is reasonable to expect some increase in organic carbon content of soils, but is also probably small (less than 10%), as the stock will be compensated by increasing biodegradation. This is an ideal, equilibrium picture, which will complement the kinetics. However, in contrast to the ocean with the depths of 5-6 km, the soil quickly come to a new steady state during the time commensurable with the growth of vegetation (productivity). So, the overall conclusion on the question №3. The properties of the soil will not change or will have a small response with an increase in the CO2 content of the atmosphere.

4) Hence, the answer to the question №4 - no parameters. Maybe only a very specific microflora, and even then is unlikely.

5) I think the question is not correct for complex systems with many processes and different time scales.

Yours sincerely, prof. A.V/ Smagin.

An excellent account of responses , so authortatively defined.But biggest question is again the diagnostic criteria to define such responses.

Despite so many early responses in plant and soil undergoing some distinct changes cant we designate some responses as a part guiding principles of response of elevated carbon dioxide like our earlier colleagues Rama Kant , Nazir, Getachew all responded.

I endorse your response Dr Deka. We  need early signals of both plant and soil behaviour for even modelling such responses .

We always decode the plant response to elevated carbon dioxide concentration on the basis of C3 and C4 plant type. The basis of such responses of C3 being more responsive than C4 plants. What are the exact mechanistic insights about such physiological crop responses which can be decoded into developing early warning signals. This is what Dr Srivastava is perhaps looking at if I have understood correctly.

The elevation of Carbon dioxide is something that there is not argument about.

In one part of your question there is the idea that Carbon dioxide enrichment  is not irreversible. Indeed the geological record would support that climate changes are reversible.

The global systems seeks equilibrium or homeostasis. With the increase knowledge we have we can probably influence the stabilization of our climate change if we decide to and make that a priority. Our management of our agriculture can play a role both in reduction of emissions in our practices and more importantly greatly increasing terrestrial sequestration at the same time we reduce emissions.

Another part of the question stressed the positive application of Carbon dioxide supplementation which is done in greenhouse environments and would be useful for crops such as tomatoes grown in Greenhouses. The injection of critical amounts in the drip lines would also help in maintaining the irrigation system. yield and quality would be increased and this has been proven but largely not applied in major extent.

Research on mycorrhizae would suggest the enrichment of Carbon dioxide would lead to better nutrition of mycorrhizal fungi which I would lead to greater soil organic matter and the soil parameters related to that. Higher rates of photosynthesis will provide greater liberation of Carbon to mycorrhizae in roots. Mycorrhizae Carbon portions such as Glomalin are highly resistant and will contribute to improved soil organic matter contents.

Although C3 photosynthesis is more favored at enriched Carbon dioxide environments  the C4 and other PS systems which are more efficient in hotter and drier environments will probably mean C4 weeds will proliferate and the evergreen conifers will suffer as a result of Carbon dioxide enrichment.

Some thoughts.

Yes Dr Deka , you are right .  Lets us arrive at some kind of early warning signals which could act  as pre-evaluation parameters for changes in plant and soil undergoing in response to  elevated carbon dioxide concentration. 

Another point i just missed from whole discussion , do we have to keep an eye  on the changes in temperature , since nutrients have huge role in neutralizing the impact of changes in temperature at crop phenophases ?

My response is addressed to Paul and other colleagues. Normally along with CO2 temperature also rises, and under that situation crops belonging to gramineae would respond very aggressively. Weeds for example will be more rampant, how incentive on C3 plants could be better harvested in such situations.

Sir,

We have to keep our eye on weeds, which will dominate during future elevated CO2 concentration. If this concentration reaches beyond 450 ppm, the present day weeds will dominate and crops will be suppressed.  In recent past, within 25-30 years, the CO2 concentration has increased tremendously in the atmosphere, and crossed 350 ppm.  The food crisis may also be one of the problem by this elevated CO2.  The growth of plants will be definitely higher under higher CO2 concentration. Experiments in rice have shown increased yield. But in open atmosphere, weed are going to pose the problem ! 

You are absolutely right Dr Rajakumar . Weeds as C4 plants are going to be highly responsive to higher carbon dioxide concentration . But , why you say food crisis would be problem , since most of the cereals belong to C3 category  , and  they have excellent photosynthetic efficiency ? .

Yes, Anoop Kumar I agree with you. How increase in yield will create food crises as stated by Dr. Rajkumar?

Dear friends!  I think, that in our discussion is not considered a very important factor - the self-regulatory mechanism of soil-plant system as elementary ecosystem. Probably, each plant of providing a quasi-optimal concentration of CO2 in the zone of photosynthesis. This is due to the labile organic matter exudates roots (their quantity and quality), control rhizosphere pH due to the assimilation of NO3 or NH4, the specifics of the rhizosphere microflora and so on.  I want to give an example of controlling the flow of CO2 in the intensive growing of marsh vegetation. This is particularly well documented in the book A. Naumov: “Soil Respiration:components, ecological functions, geographic patterns” (Novosibirsk: Publishing House of SB RAS, 2008. 208 p : in rus.) http://www.sibran.ru/catalog/CBE/144945/.

See fragment from this book:

«Until recently, there was representation among environmentalists that the input of Carbon into the ecosystem is determined by the net primary production. However, direct comparison of the gas streams in the marshes with the estimates, formed during the growing season plant matter, showed a clear discrepancy. Further research has uncovered the main reason: the presence of the “internal cycle”, returning Carbon to the ecosystem, not allowing it to disperse into the atmosphere. As a result of the operation of small cycle in the wetland ecosystem of more than 60 percent of the primary production of Carbon it has an internal origin.

The developed model can be used for peat (organic) soils, and for the mineral. Most of the global models of atmospheric dynamics is built on a common "flowing" pattern. Neglecting the internal cycle will obviously lead to distorted and unreliable results. Analysis of experimental data and work with the model allowed to establish a wide range of stability of the carbon cycle of wetland ecosystems in relation to external influences related to fluctuations in the concentration of carbon dioxide in the atmosphere".

I hope, that this  information will be useful in the context of understanding the complexity of the regulatory mechanisms of photosynthesis, particular in conditions of global warming.

Sir,

My view on weeds and food crops is that when these two individuals get higher CO2 concentration, then C4 will suppress C3, hence shortage of food may become the crisis.

Interesting responses by Dr Hemkalo and Dr Rajakumar , appreciate it . Lets listen other colleagues in response , what they have to say . 

Dear Dr Anoop,

There is an important question, which I believe must also be addressed here. The increase of CO2 will not come alone, but in conjunction with increasing temperature. The majority of plant species is expected to benefit from the individual increase of the CO2 with higher biomass production. However, the increase in temperature may cause a decrease in grain yield. The coffee, for example, aborting its flowers under conditions of high temperatures and decreases its productivity, despite increased biomass growth.

I agree with you Marcos .Its an important addition to the discussion. Increase in carbon dioxide alone will not come.

Let me enclose my PDF entitled Soil Fertility Dynamics in response to Climate Change . Hope , it will be useful for further reading .  Probably,  this will aid in identifying those parameters , we are looking at .

Crop plants responses to elevated CO2 atmospheric levels would be affected in terms of their physiology and yield. A recent study that is under press in Agronomy for Sustainable Development shows that increasing levels of atmospheric CO2 due to various anthropogenic activities will directly influence photosynthesis, transpiration, and respiration, the main processes by which elevated CO2 can be sensed directly by the plants and ecosystems. C3 and C4 plant types exhibit different responses to CO2 enrichment. The current amount of CO2 in the atmosphere is inadequate to saturate the ribulose-1 ,5-biphosphate (RuBisCO) enzyme that drives photosynthesis in C3 plants. Therefore, future increases in CO2 concentrations by 2050 (i.e. various models predict values between 600–800 ppm), will most probably favor C3 plant types. In contrast, C4 type plants are likely to respond less to elevated CO2 levels as they possess an innate concentrating mechanism that increases CO2 level at the site of RuBisCO to 2000 ppm. Hence, predicted increases in atmospheric CO2 concentrations, from a current ambient level of about 370 ppm, are less relevant to the photosynthetic capacity of C4 plants which, most probably, will respond only marginally. The association of photosynthesis rate and intercellular CO2 concentration was compared in soybean (C3) and maize (C4). Photosynthesis in soybean was stimulated by 39 % under elevated CO2 concentration but not in maize.Carbon dioxide is fundamental for plant production, and increases of atmospheric CO2 concentrations have the potential to enhance the productivity of agroecosystems. Elevated CO2 is expected to increase plant yield through root mass and leaf area increases and to alter plant chemical composition, hence the rate of nutrient cycling in soil.

Based on several sources, increases in marketable yield of cereals, particularly those that exhibit C3 photosynthetic pathway, range between 8 and 70 %; those of row, cash, and vegetable crops between 20 and 144 %; and those of flowers between 6 and 35 %. The quality of agricultural products may be altered also by elevated CO2. Nitrogen content, for example, in some non-nitrogen fixing plants grown at elevated CO2, was found reduced. These changes could affect the nutritional value, taste, and storage quality of some fruits and vegetables.

Very interesting finding. As you explained C3 plants can benefit from the  elevated CO2 in terms of enhancing photosynthesis and dry matter accumulation, that means increased food production. And as you know main field food crops including wheat are  C3 plants, which may benefit from elevated CO2. But, what is not clear here is that if optimum level of N fertilizer is applied both in organic and inorganic forms, why is the N concentration of grains decreases and the associated nutritional quality? The other question is that if N-uptake of plants decreases how can the photosynthetic activity of C3 plants be increased?

Another controversy that I may see here is that the issue of global warming due to increased greenhouse gas emissions, with the highest contribution from CO2. How could these two contrasting scenarios be compromised and used for maximizing food production without affecting the environment?  

Interesting points raised by Getachew, Two "scenarios" about the effects of elevated CO2 atmospheric concentration on  crop plants are examined. The first one states the effects of elevated CO2 per se on plant physiological and yield responses. In the following scenario CO2, N content, and crop quality has most probably to do with intra-plant N utilization and allocation e.g. cultivars with lower harvest indices. 

Global warming is a consequence of the release into the atmosphere of three major constituents namely CO2, N2O and CH4 all expressed as kg of CO2 equivalent. Although CO2 per se is emitted into the atmosphere in great quantities,  nitrous oxide through nitrification, denitrification of N-based agricultural inputs and residues (e.g. fertilization, slurry respectively)  and methane (e.g. rice cultivation) either as direct or indirect emissions account most for global warming. A holistic approach is needed as interactions concur and affect the outcome of global warming on crops and plants at local, regional and higher degree scales.

Some interesting answers were presented by experts.

Dear Anoop Kumar Srivastava, I am not an expert about the issue you have raised but I could see a huge number of interesting answers were presented by experts. 

The response of crop to CO2 should not be looked in isolation. we should also consider the associated temperature changes also. How do we see the response of perennial fruits to rising global warming. 

Nice response from Abhishek , thank you so much dear . 

Climate change is shifting the habitat ranges of plants and animals , including agricultural crops. For example, as average global temperatures increase, plant and animal populations may move to new latitudes with more favourable climates. It is, therefore, possible that crops that used to be productive in one area may no longer be so or the other way around.

Currently, more than two dozen crop models exist and all of them allow in one way or the other to assess the responses of crops to climate change, all of them mostly agreeing in the direction but not in the extent of the changes. However, as stated before, most of these approaches are developed for annual crops or have only been extensively applied and tested on a limited number of crops.

Sugar beet, onions and cabbages are decreasing their climatic suitability in at least 60% of the areas where they can be grown in Sub-Saharan Africa and India, and in more than 80% of their currently global suitable areas. Oppositely, mangoes are showing an average increase of 1.6% globally, with only 26% of the global suitable areas for mango production being negatively impacted. In the case of coconut, some 40% of the global suitable areas seem to be decreasing their climatic suitability. 

We often debate about the two broad base strategies to combat climate change related issues, the adaptation and mitigation strategies. Shall adaptation and mitigation strategies go hand-in-hand   ?

The Carbon dioxide level is now increasing at 2 ppm per year and will double at that rate from 400 to 800 ppm in 200 years if nothing changes. I am counting on the engagement of energy improvements and the engagement of agriculture to reverse the present trend. 

Carbon dioxide injected into a greenhouse watering system will give increased productivity for high value crops. Residual use of waste Carbon dioxide can be used to close the loop in energy systems producing excess Carbon dioxide.

 This will be an economically valuable way of producing valuable materials. From a greenhouse gas prospective the stablization of residual materials left over would determine the overall impact of that system in relation to net greenhouse gas impact. 

A systems net greenhouse gas impact is not calculated for most of our agricultural activities and in that regard what happens to residual materials is of key importance. 

Interesting and very  informative  response , Paul . No  doubt , carbon dioxide is the key component of such emissions arising out of various agricultural activities, Some of the global strategies to counter carbon dioxide emissions include: enriching soil with organic matter  through various soil management techniquesand  considering total carbon stock ( labile and non-labile pool);crop diversification utilising perennial trees having better carbon trapping ability in their perennial framework; climate friendly livestock production system; maintaining 4 billion ha under forest and 5 billion ha under grasses as a natural reservoir of  global carbon and ;  devising ways and means  for a suitable land use strategy for rehabilitating the degraded lands. 

When  we think about meat we need to consider that all meat is not the same.

The greenhouse gas equation of a feedlot of animals confined and fed corn is completely distinct from the totality of a grass fed corws used for providing milk as example.

Looking at emissions only is critically flawed since an integrated crop animal system maximizes the Carbon and Nitrogen fixation or sequestration and that is a much bigger greenhouse gas ticket in this whole equation that isolated production practices. From a crop production emission view the biggest factor is ammoniated fertilizer use for cereal grains and this can be almost completely avoided through legumes in crop systems and the development of systems aimed at Carbon sequestration as soil organic matter. 

There is more that twice the land in pastures and forests than in crop system and our vision needs to be focused on systematic integration and measurement of responses in real terms such as Carbon equivalence. These hard data can be used to inform better policies to drive our agriculture and food systems.

From a research prospective the critical factors and the trends of practices in integration to systems for our crop and animal production is a good start point and including the potentials for agroforestry in mixed fiber food systems. 

I have no problem with looking at emissions reduction but in relation to net greenhouse gas equation always knowing the big impact will be on our ability to increase and keep CN in our soils not the atmosphere. 

We need to develop climatic analogues in relation to different growth stages for different crops under elevated CO2 conditions. 

You are right Deka!

Thats a very good point Dr Deka , something agronomic crop modelling . But , such modelling in response to elevated carbon dioxide along with  an elevated temperature  will be quite different . That is the reason , we often keep saying , climate change mitigation adaptation strategies must go hand-in-hand. 

Most of the fruit crops being a C3 plants are considered to be responsive to carbon dioxide. Can perennial framework of these fruit crops act as carbon sink ?

Kudos to Parameshwar Shirgure, The elevated carbon dioxide can be blessing in that as a central core material for enhanced photosynthesis. In the framework of fruit crops their positive carbon footprint is enhanced by a floor management which would focus on legume for inter row covering eliminating need for nitrogen input which would otherwise be a major carbon requirement and recycling wastes in the form of compost ideally to give the overall nutrition of the fruit crop.  The use of biological pest control would be another important consideration. The fruit farmer can also soil and tissue test to optimize nutrition and set goals for soil organic matter which overtime lower the effects of periodic drought and stimulate better plant health and nutritional quality. The major limiting crop nutrient is not usually carbon dioxide or nitrogen or phosphorus it is water. When we manage to optimize soil organic matter we not only reduce the need for supplemental water as we are taking carbon dioxide out of the air of a greenhouse gas with potential climate change issues and resetting the negative effect on the positive effect of improved soil fertility. 100 units of soil which is dry can absorb less than 30 units of water with 5% soil organic matter which soils are capable of generating the same 100 units of dry soil can capture over 200 units of water more than 6 times the depleted state. In addition with soil organic matter is optimized the common issues with nutrient toxicity and deficiency are generally resolved. Management for soil organic matter is something that floats all our agricultural boats and needs be our ultimate agriculture goal. As Confucius said our survival ultimately depends on one foot of top soil and the bounty of rainfall. This is still true today. 

Well said , and as usual your responses are always more than brain tonic to all of us . I was wondering with the feedback from Dr Shirgure , somewhere it is true also. Perennial fruits have so much of  yield potential ,  crops like apple , citrus , mango, have not only perennial framework acting as potential sink for atmospheric carbon , but these crops divert a significant proportion of assimilated carbon towards the  under-ground root system , thereby , catalyzing the microbial proliferation , a driving force for better microbial diversity in rhizosphere . Just feel net primary productivity of these crops, far more than many of the evergreen forests. imagine carbon footprint of these perennial crops  growing for 50-60 years on an average , how much robust carbon footprint , they generate and scavenge the atmospheric carbon dioxide . But , we hardly define the carrying capacity of any perennial crop in terms of such carbon footprint and try to earn carbon credits for international carbon trade through better management of these perennial fruits..?. 

My question is addressed to Paul, is there any study on root carbon footprint of perennial crops versus annual crops ? 

Dear Parameshwar Shirgure, The root footprint of perennial crops is superior to annual crops. The carbon equation is not just about what is produced by photosynthesis but also what is lost be respiration. The highest net Photosynthesis which is Photosynthesisis maximized and minus the Respiration is minimized. This is found in grasslands naturally based on massive ability to transform soil through accumulation of resistant roots. This incremental look is a dynamic one with accumulates and will reach a state of equilibrium and diminishing returns. Top soils however where most soil organic accumulates however do indeed have capacity to expand in depth and quanity. Rather than look at the aboveground which is easy and quick we need to look below the surface at the continuing root systems to see the net effects in term of greenhouse gases. The perennial plants are very important because the accumulation of the Carbon and Nitrogen in the system is related to the time. For studying this we can look at soil change over time and also at early indicators which predict these changes. Usually these very important impacts are only clearly understood from long term systematic studies. Just looking at Carbon gas liberation for fields without having the incremental accumulation in the soil does not tell the whole story. In our agriculture systems will need to clearly map out both the energetic or carbon inputs but also have good ability to determine the net effects where all the benefits lie over the long term.  

I hope this give some useful insights. PRH

Interesting feedback Paul, appreciate your remarks...

BUWALDA J. G. The carbon costs of root systems of perennial fruit crops. ENVIRONMENTAL AND

EXPERIMENTAL BOTANY 33, 131--140, 1993. The carbon requirements for growth and maintenance of root systems of perennial fruit crops are discussed with reference to the definition and costs of an 'optimum' root system. For mature plants, root growth is shown to be a relatively small sink for carbon, but very sensitive to variations in assimilate supply. The carbon lost due to respiration directly associated with ion uptake is also very small, although it may represent a significant sink at certain times of the year. Root maintenance, however, represents a large sink, perhaps accounting for more than 50% of the carbon utilized within the root system. The carbon losses to root associations (e.g. mycorrhiza) and via leakage are difficult to quantify, but are considered as sinks of intermediate dimensions. Stress effects on root carbon costs are considered, using water (deficit and excess) as an example. Adaptation to stress may involve increased growth of the root system, constituting an immediate carbon cost and subsequently higher maintenance costs for the increased biomass. With increasing likelihood of stress, the 'optimum' root system will have larger dimensions, and hence increased carbon costs. A functional basis for considering the carbon costs of root systems of perennial fruit crops is presented. It enables integration of root system costs in terms of the whole-plant carbon economy.

PDF enclosed for further reading, friends ..an excellent article to read...

Dear Anoop Kumar Srivastava,

I believe that this papers would be very useful to you: 

Lobell DB, Field CB (2007) Global scale climate–crop yield relationships and the impacts of recent warming. Environ Res Lett 2:004000;

Lobell DB, Schlenker W, Costa-Roberts J (2011) Climate trends and global crop production since 1980. Science 333: 616–620

Perhaps the second is the most important (Science). You will see that three major crops for global food security (rice, wheat, soybean) have responded strongly to CO2 atmospheric enrichment (fertilization) after 1980, at global scale. 

More exactly, in the 1980–2008 period, climate changes generated globally, through temperature (mainly) and precipitation dynamics, significant diminutions of the major agricultural productions of wheat (-5.5 %), maize (-3.8 %), soy (-1.7 %) and rice (-0.1 %). However, these decreases have been canceled / attenuated following the CO2 atmospheric fertilization, which determined increases of about 3 % in wheat, soy and rice yields over the last 30 years (considering that the atmospheric CO2 concentration increased in this period by 47 ppm, and every ppm determined yield increases for the three cultures by 0.065 %, according to the free-air CO2 enrichment experiments). 

Given that maize is immune from carbon fertilization, this major crop is probably most threatened by climate change. For more details, you can investigate the papers, which will provide some of the necessary answers, in my opinion.

I hope my answer is useful you! 

With kind regards,

Pravalie Remus

Dear Pravalie Remus, You bring up that modeling is showing while in some cases the enrichment of Carbon dioxide could be favorable but when higher temperatures are linked with greater drought this would counteract the stimulation for increased potential photosynthesis. Maize is very sensitive to high temperatures at pollinization and this can be an issue as you note. A crop like oats is much more sensitive than maize and global warming would do a number on it as well as crops such as tomatoes which are already stymied by warm tropical summer temperatures. These crops which are eaten directly and have critical nutritional qualities are maybe more important than feed grains. If we are to better feed our growing population more vegetables and fresh fruits are the ways to address the deteriorating diets which result in unsupportable health costs. Climate change is quite a challenge no matter how you look at it. 

Good publication Anoop Sir, informative one.

I agree with Sikha Deka.

Dear Paul Reed Hepperly,

I totally agree that climate change is a big problem for the agricultural systems, if we consider their negative "net" effect on crops. These effects are felt  also in Romania, even if this country is less affected by climate change compared to other countries in the world (from my own research experience, I can say that, for example, maize has suffered a decline in the vast areas of the country up to 1.7 t/ha/yr for a

1 degree celsius temperature rise in the last two decades). 

In the previous comment I have noted that some crops may have a benefic response to the direct carbon emissions, but that does not mean that crop yields will be higher, taking into account the climatic or pedological parameters perturbations of warming. 

Do you mean, yield of most of the crops will decline with climate change , regardless of whether the crop is C3 or C4.

Although C3 plants in particular can be stimulated at prevailing increased carbon dioxide concentration increases, the most limiting factor for overall crop and plant growth is usually water and its distribution. If higher temperature leads to more periodic drought and agricultural practices continuing to maintain low soil organic matter will cause problems in the crop yields.In general agriculture will be compromised. In the United State 80% of all crop insurance claims are from drought effects. Certain crops such as oats which are very sensitive to high temperatures at pollination may be very much affected by climate change and there area of reliable production could change in a Northern or Southern migration to cooler temperatures. To this day the vast majority of world crop production is under rainfall conditions and the ability to effectively capture and use rainfall can greatly determine crop productivity. This is very much associated with soil organic matter.  The agricultural systems which maintain and increase soil organic matter allow for better capture and use of scarce water resources an d the ability to have the negative potential climate change impacts will depend on how we can stimulate better soil conservation and organic matter management. Increase and conservation of soil organic matter is the best tool we have to deal with climate change and its effect. 

* What kind of soil-plant response parameters could be effectively used as an early warning signals under elevated concentration of CO2?.

I propose to use isotopic analysis in 13C to know the main source of CO2

Although C3 plants in particular can be stimulated at prevailing increased carbon dioxide concentration increases, the most limiting factor for overall crop and plant growth is usually water .

Good point Issam. It will give some fruitful insightful discussion. 

If we look at this cottonwood tree experiment the doubling of ambient carbon dioxide would triple cottonwood growth amazing. Also inteteresting also that at 3 times the carbon dioxide the growth rate is doubled. Finally the proportion of roots to aboveground increases significantly at triple carbon dioxide. The system itself seems to adjust itself to favor taking the excess carbon dioxide out of the air and repatriating it into the ground through the roots. I would expect that increased rooting would cause a much better drought reaction and that carbon sequestration would increase since the turnaround for roots is much slower than for aerial parts. Interesting article. 

Which kind of crops are more responsive to elevated CO2 concentration ?

Dear sir, based on my research experience on tropical tuber crops (except potato), i can say that tropical tuber crops showed positive response to eCO2. Analysis of data has shown that rate of Pn under eCO2 was significant and increment rate (%) in Pn under eCO2 was significant upto 600-800 ppm as compared to 400 ppm. Pn rate at 1000 ppm was the highest but increment rate was very less as compared to 600 and 800 ppm. Ci and stomatal conductance had linear to quadratic correlation with Pn. Conclusively, under eCO2 tropical tuber crops recorded 1.5 to 2 times higher Pn rates at 600,800 and 1000 ppm as compared to ambient 400 ppm concentration.

Dear A. Raj Yes the increase carbon dioxide will increase photosynthesis as you confirm. In some ways the idea of nitrogen limitation is moot in my mind as in legume crops nitrogen can be provided for both the legume crop and for crops in rotation in an optimized cropping system. After all is said about 80% of our atmosphere is nitrogen gas and that makes Nitrogen deficiency somewhat artificial. The issue of overall effect or raised carbon dioxide would include the weather modeling suggested to confront high heat and periodic drought will become more frequent. There would need to thoughtful analysis of the net benefits of increased photosynthesis against the increased issues related to heat and increased periodic drought issues. In a hotter world these issues need much closer consideration and thought.