I put crop litter in the field soils under a gradient of long-term N addition (N0, N1, N2). I measured the rate of litter decomposition and found that the rate is lowest in the treatment (N1) of medial N amount addition. This is different from previous studies who reported high N addition decease the rate of litter decomposition.
How to explain my results? I speculated that it may be N limitation in N0 but C limitaion in N2, resulting in their greater rate of litter decomposition compared to N1. For N1 treatment, it was neither C limitation nor N limitation. Is this explanation reasonable?
How to prove C or N limitation? I want to sample the soils under different treatments and incubate them with addition of C ( glucose ) or N ( ammonium or nitrate) substrates. Then, I measure the change of enzyme activities and microbial activities. I hypothesis that soil microbe was more sensitive to N addition in N0 treatment but more sensitive to C addition in N2 treatment.
Is my design reasonable? Are there some documents providing how to test C and N limitation for soil microbes (direct evidence)?
Thanks!
Dear Fan
Check this link to access article entitled:
Carbon and nitrogen limitations of soil microbial biomass in desert ecosystems.
Hope be useful.
Article Carbon and nitrogen limitations of soil microbial biomass in...
In the organic matter decomposition process in the absence of nitogen application C:N ratio generally wide about 1:100; so immobilisation of nitrogen in bacterial body cells to plant nutrition occur .So, amount of nitogen to required to check immobilisation of nitogen by microoganisms cell known as nitogen factor should be evaluated by application of nitrogen to check immobilised nitogen in bacterial body cells.
Limitation of carbon in microbal body cell may be estimated by estimation of microbial body carbon.Total carbon percent may be estimated by gravimetric method by burning of soil at 400 ton500 degree centigrade in muffle furnace or by Walkly and Black rapid titration method ( 1934 ) Total Nitogen estimation by Kjeldahl method.( Method prescribed in Soil chemical analysis ,M.L.Jackson 1973 )
Microbial carbon may be estimated by sterilization of soil with toluine and estimation of soil.carbon percent before after sterilization and difference in carbon percent may estimate total carbon and microbial carbon percent in soil.
Dear Fan Ding,
Determining if a state of C limitation exists:
The best way to do this is to use the opposing stable isotope (C or N). Add 15N labelled NH4NO3 to your soils with/without a labile carbon source and observe the contrast... (be sure to measure intra- and extracellular products of anabolism). Your hypothetically C limited microbial biomass will not generate any substantial anabolic products containing 15N (if your hypothesis is correct).
EXAMPLES: "Soil organic matter and the extracellular microbial matrix show contrasting responses to C and N availability"Article Soil organic matter and the extracellular microbial matrix s...
NOTE: there are small amounts of C fixed from the atmosphere even in the dark. However, our results also demonstrate that "dark-CO2 fixation" was negligible in these arable soils over a short (10 day) incubation.
Best wishes,
Marc
General process of observation carbon and nitrogen limitation of microbes by determination of C:N of soil.
In this respect carbon and nitrogen limitation of microbe generaly happen in wide C:N from 100 to 200 compare to optimum C:N from10 to 25..
Nitrogen immobilzation and mineralisation generally happen in two different conditions of cultivated soil . In optimum temperature generally 25 to 35 degree centigrade with mososture at field capacity and favorable pH of soil generally 6 to 8 in which nitrogen transforming microbial populations with the help of nitrogenase enzymes mineralised organic nitrogen R-NH2 transform to nitrite by nitrosomnous bacteria and to nitrate by nitrobacter in optimum C:N ratio generally from 10 to 25.
In wide C:N ratio generally from 100 to 200 nitrogen immobilzation takes place in cultivated soil due to dificiency of mineralizable nitrogen in soil for nitrogen transforming microbial populations and this stage of Organic matter transformation in soil known as immobilzation of nitrogen in bacterial cell. So, amount of nitrogen required to check immobilization is known as nitogen factor.
Organic carbon may be estimated by Walkly and Black rapid titration method(1939).
Total nitrogen may be estimated nby Kjeldahl method.
Nitrogen mineralization of organicmatter nitrogen generally happen in cultivated soil RNH2 to NO2 by nitrosomnous bacteria with nitrite reductutase enzyme and NO2 to NO3 by nitrobacter bacteria with the help of nitrate reductase enzyme.
Cultivated soil should be sterilized with phenol and microbial carbon should be estimated by standard method.
Very useful answers and so many new scientific approach could be known regarding nitrogen mineralization in soil. I like to thank everybody.
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