Net assimilation rate

Kershaw, K.A. (1972). The relationship between moisture content and net assimilation rate of lichen thalli and its ecological significance. Canadian Journal of Botany, 50, 543-55. 

Fig.4 Net Assimilation rate, Ac, vs. stomatal conductance, gc, for a t3rpical day. Each symbol corresponds to different leaves.

Poorter, H. Remkes, C. (1990). Leaf Area Ratio and Net Assimilation Rate of 24 Wild Species Differing in Relative Growth Rate. Oecologia, Vol.83, No.4, (July 1990), pp. 553-559. 

It has been nearly a century and a half since Boussingault (1868) presented the hypothesis that the accumulation of assimilates in an illuminated leaf may be responsible for a reduction in the net photosynthetic rate of that leaf. According to the Munch hypothesis for phloem transport, the greater the sink strength, the greater the depression in solute concentration in the phloem at the sink. This increases the concentration differential between the source and sink, creating the hydrostatic pressure head that drives the system. 

We will now develop an analytical framework to represent CO2 fixation in photosynthesis and its evolution in respiration and photorespiration (Fig. 8-16). The net flux of C02 into a leaf, Jcch> indicates the apparent (net) CO2 assimilation rate per unit leaf area by photosynthesis (see Fig. 8-1 for a measurement technique). The gross or true rate of photosynthesis, ygv minus the rate of CO2 evolution by respiration and photorespiration per unit leaf area, 7, equals Jcch-... 

Epron D., Godard D., Comic G., and Genty B. (1995) Limitation of net CO2 assimilation rate by internal resistances to CO2 transfer in the leaves of 2 tree species (Fagus Sylvaticah and Castanea-sativa Mill). Plant Cell Environ. 18(1), 43-51. 

Fig. 4.45. The phosphorus residence time, the uptake rates of phytoplankton and zooplankton and POC export fluxes at three sampling stations in the ECS. (a) Residence time for TDP, suspended matter, and net-plankton (b) The phosphorus assimilation rates and carbon assimilation fluxes of phytoplankton (c) The phosphorus grazing rates and carbon grazing fluxes of zooplankton (d) POC export fluxes from the upper 35 m (Zhang et al., 2004) (With permission from Elsevier s Copyright Clearance Center)...

Aminotriazole (2mM) was applied through the transpiration stream of excised pea seedlings held in a water-jacketed glass cuvette. Rates of net CO2 assimilation (A) and transpiration (E) were measured by conventional gas exchange techniques under different CO2 and O2 concentrations, with or without PGA added to the transpiration stream. Photosynthetic photon flux density (PPFD) was maintained at 500 /nmol m s temperature at 24 2°C and atmospheric vapour deficit at 1 kPa. Results were normalized to steady state assimilation rates prior to commencement of treatment. 

CO2- assimilation rate The net CO assimilation rate (PN) was measured in a leaf chamber in which one of the leaves was... 

Significant differences in net photosynthetic assimilation of carbon dioxide are apparent between C, C, and CAM biomass species. One of the principal reasons for the generally lower yields of C biomass is its higher rate of photorespiration if the photorespiration rate could be reduced, the net yield of biomass would increase. Considerable research is in progress (ca 1992) to achieve this rate reduction by chemical and genetic methods, but as yet, only limited yield improvements have been made. Such an achievement with C biomass would be expected to be very beneficial for foodstuff production and biomass energy appHcations. 

The subsequent fate of the assimilated carbon depends on which biomass constituent the atom enters. Leaves, twigs, and the like enter litterfall, and decompose and recycle the carbon to the atmosphere within a few years, whereas carbon in stemwood has a turnover time counted in decades. In a steady-state ecosystem the net primary production is balanced by the total heterotrophic respiration plus other outputs. Non-respiratory outputs to be considered are fires and transport of organic material to the oceans. Fires mobilize about 5 Pg C/yr (Baes et ai, 1976 Crutzen and Andreae, 1990), most of which is converted to CO2. Since bacterial het-erotrophs are unable to oxidize elemental carbon, the production rate of pyroligneous graphite, a product of incomplete combustion (like forest fires), is an interesting quantity to assess. The inability of the biota to degrade elemental carbon puts carbon into a reservoir that is effectively isolated from the atmosphere and oceans. Seiler and Crutzen (1980) estimate the production rate of graphite to be 1 Pg C/yr. 

Data compiled by Hanks (1983) show that, contrary to earlier notions, the m coefficient in Equation 1 may be affected by the genotype. A relatively greater net gain of carbon for the same rate of transpiration under stress may be reflected in the m coefficient (Equation 1), in the ratio between assimilation and transpiration (assimilation ratio) or in the agronomic index, WUE (Equation 2). 

Wheeler, P. A. (1993). New production in the subarctic Pacific Ocean net changes in nitrate concentrations, rates of nitrate assimilation and accumulation of particulate nitrogen. Prog. Oceanogr. 32, 137-161. 

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