is plant habit one of the factors determining photosynthesis light response? can we say trees generally have curve with bigger slope compared to herbs?
For sure , there will be conspicuous difference...
Photosynthetic responses to light in seedlings of selected Amazonian and Australian rainforest tree species
Summary : Seedlings of the Caesalpinoids Hymenaea courbaril, H. parvifolia and Copaifera venezuelana, emergent trees of Amazonian rainforest canopies, and of the Araucarian conifers Agathis microstachya and A. robusta, important elements in tropical Australian rainforests, were grown at 6% (shade) and 100% full sunlight (sun) in glasshouses. All species produced more leaves in full sunlight than in shade and leaves of sun plants contained more nitrogen and less chlorophyll per unit leaf area, and had a higher specific leaf weight than leaves of shade plants. The photosynthetic response curves as a function of photon flux density for leaves of shade-grown seedlings showed lower compensation points, higher quantum yields and lower respiration rates per unit leaf area than those of sun-grown seedlings. However, except for A. robusta, photosynthetic acclimation between sun and shade was not observed; the light saturated rates of assimilation were not significantly different. Intercellular CO2 partial pressure was similar in leaves of sun and shade-grown plants, and assimilation was limited more by intrinsic mesophyll factors than by stomata. Comparison of assimilation as a function of intercellular CO2 partial pressure in sun- and shade-grown Agathis spp. showed a higher initial slope in leaves of sun plants, which was correlated with higher leaf nitrogen content. Assimilation was reduced at high transpiration rates and substantial photoinhibition was observed when seedlings were transferred from shade to sun. However, after transfer, newly formed leaves in A. robusta showed the same light responses as leaves of sun-grown seedlings. These observations on the limited potential for acclimation to high light in leaves of seedlings of rainforest trees are discussed in relation to regeneration following formation of gaps in the canopy.Source ; Oecologia,August 1984, Volume 63, Issue 2, pp 215–224
Shape of leaf photosynthetic electron transport versustemperature response curve is not constant along canopy light gradients in temperate deciduous trees
Responses of foliar light-saturated net assimilation rate (Amax), capacity for photosynthetic electron transport (Jmax) and mitochondrial respiration rate (Rd) to long-term canopy light and temperature environment were investigated
in a temperate deciduous canopy composed of Populus tremula L. in the upper (17–28 m) and of Tilia cordata Mill. in the lower canopy layer (4–17 m). Climatic
measurements indicated that seasonal average daily maximum air temperature (Tmax) was 5·5 °C (range 0·7–10·5 °C) higher in the top than in the bottom of the canopy, and strong positive correlations were observed between Tmax and seasonal average integrated quantum flux density (Qint), as well as between seasonal average daily mean temperature and Qint. Because of changes in leaf dry mass and nitrogen per unit area, Amax, Jmax, and Rd scaled positively with Qint in both species at a common leaf temperature (T). According to Jmax versus T response curves and dark chlorophyll fluorescence transients, photosynthetic electron transport was less heat resistant in P. tremulawith optimum temperature of Jmax, Topt, of 33·5 ± 0·6 °C than in T. cordata with Topt of 40·7 ± 0·6 °C. This difference was suggested to manifest evolutionary adaptation of photosynthetic electron transport to cooler environments in P. tremula, the range of which extends farther north than that in T. cordata. Possibly because of acclimation to long-term canopy temperature environment, Topt was positively related to Qint in P. tremula, foliage of which was also exposed to higher irradiances and temperatures, but not in T. cordata, in the canopy of which quantum flux densities and temperatures were lower, and gradients in the environmental factors less pronounced. Parallel to changes in Topt, the activation energy for photosynthetic electron transport decreased with increasing Qint in P. tremula, indicating that Jmax of leaves acclimated to colder environment was more responsive to T in lower temperatures than that of high T acclimated leaves. Similar alterations in the activation . Source :Plant, Cell and Environment (1999) 22, 1497–1513
The leaf economics spectrum and the prediction of photosynthetic light–response curves by Giancarlo Marino, Marouane Aqil, Bill Shipley ,
DOI: 10.1111/j.1365-2435.2009.01630.x '
Trees invest on structure and their frame is permanent. This cost enters in respiration budget but tree dominance can be supported by creating deep shades. Herbs and annuals have got a better light response if the daily integral is cconsidered. further a real tree canopy operates under water friction drwback and electron trasport rate at an osmotic pressure is lower than in herbs.
C3, C4 and CAM photosynthesis occurs in small plants but only C3 in trees :)
its just that i compared canna indica (herb) and morus alba (tree) and canna indica has smaller slop.
Photosynthesis-irradiance curves are species-specific, and are influenced by a variety of factors, such as nutrient concentration, temperature, and the physiological capabilities of the individual plants :)
Herbs and trees differ so heavily , because of their perenniality ( Perennial framework is so extensively developed in trees compared to herbs)l , thereby , bringing a huge difference in physiology of the two contrasting plant types. Difference in the length of their growth period also define the pattern of dry matter accumulation and their partitioning as well...
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