https://botanika.prf.jcu.cz/suspa/pdf/2007_Garnieretal_AnnBot.pdf

Assessing the effects of land-use change on plant traits, communities and ecosystem functioning in grasslands: a standardized methodology and lessons from an application to 11 European sites.

Carbon stocks in vegetation have a key role in the climate system. However, the magnitude, patterns and uncertainties of carbon stocks and the effect of land use on the stocks remain poorly quantified. Here we show, using state-of-the-art datasets, that vegetation currently stores around 450 petagrams of carbon. In the hypothetical absence of land use, potential vegetation would store around 916 petagrams of carbon, under current climate conditions. This difference highlights the massive effect of land use on biomass stocks. Deforestation and other land-cover changes are responsible for 53-58% of the difference between current and potential biomass stocks. Land management effects (the biomass stock changes induced by land use within the same land cover) contribute 42-47%, but have been underestimated in the literature. Therefore, avoiding deforestation is necessary but not sufficient for mitigation of climate change. Our results imply that trade-offs exist between conserving carbon stocks on managed land and raising the contribution of biomass to raw material and energy supply for the mitigation of climate change. Efforts to raise biomass stocks are currently verifiable only in temperate forests, where their potential is limited. By contrast, large uncertainties hinder verification in the tropical forest, where the largest potential is located, pointing to challenges for the upcoming stocktaking exercises under the Paris agreement.

/pdf/unexpectedly-large-impact-of-forest-management-and-grazing-ovu4klgjv8.pdf

Unexpectedly large impact of forest management and grazing on global vegetation biomass

Chlorophyll (Chl) fluorescence is a subtle reflection of primary reactions of photosynthesis. Intricate relationships between fluorescence kinetics and photosynthesis help our understanding of photosynthetic biophysical processes. Chl fluorescence technique is useful as a non-invasive tool in eco-physiological studies, and has extensively been used in assessing plant responses to environmental stress. The review gives a summary of some Chl fluorescence parameters currently used in studies of stress physiology of selected cereal crops, namely water stress, heat stress, salt stress, and chilling stress.

http://bio.sfu-kras.ru/files/1162_Sayed_2004_Photosynthetica.pdf

Chlorophyll fluorescence as a tool in cereal crop research

The effect of the rate of mixing on productivity of algal mass in relation to photon flux density and algal concentration was quantitatively evaluated in cultures ofSpirulina platensis grown in a newly designed flat-plate photobioreactor. Special emphasis was placed on elucidating the principles underlying efficient utilization of high photon flux density for maximal productivity of algal-mass. Whereas the rate of mixing exerted little influence on productivity and photosynthetic efficiency in cultures of relatively low algal density, its effect became ever more significant as algal concentration was increased. Maximal mixing-enhanced cell concentrations and productivity of biomass were obtained at the highest light intensity used. At each level of incident light intensity, maximum productivity and photosynthetic efficiency could be achieved only when algal concentration and mixing rates were optimized. The higher the intensity of the light source, the higher became the optimal culture density, highest algal concentrations and productivity of biomass being obtained at the highest light intensity used. The rate of mixing required careful optimization: when too low, maximal productivity resulting from the most efficient utilization of light could not be obtained. Too high a rate of mixing resulted in cell damage and reduced output rate.

Productivity and photosynthetic efficiency of Spirulina platensis as affected by light intensity, algal density and rate of mixing in a flat plate photobioreactor

Regulated thermal dissipation of absorbed light energy within the photosystem II antenna system helps protect photosystem II from damage in excess light. This reversible photoprotective process decreases the maximum quantum yield of photosystem II (Fv)/Fm) and CO2 assimilation (phiCO2), and decreases the convexity of the non-rectangular hyperbola describing the response of leaf CO2 assimilation to photon flux (theta). At high light, a decrease in phiCO2 has minimal impact on carbon gain, while high thermal energy dissipation protects PSII against oxidative damage. Light in leaf canopies in the field is continually fluctuating and a finite period of time is required for recovery of phiCO2 and when light drops below excess levels. Low phiCO2) and can limit the rate of photosynthetic carbon assimilation on transfer to low light, an effect prolonged by low temperature. What is the cost of this delayed reversal of thermal energy dissipation and phiCO2 recovery to potential CO2 uptake by a canopy in the field? To address this question a reverse ray-tracing algorithm for predicting the light dynamics of 120 randomly selected individual points in a model canopy was used to describe the discontinuity and heterogeneity of light flux within the canopy. Because photoprotection is at the level of the cell, not the leaf, light was simulated for small points of 10(4) micro m rather than as an average for a leaf. The predicted light dynamics were combined with empirical equations simulating the dynamics of the light-dependent decrease and recovery of phiCO2 and and their effects on the integrated daily canopy carbon uptake (A'c). The simulation was for a model canopy of leaf area index 3 with random inclination and orientation of foliage, on a clear sky day (latitude 44 degrees N, 120th day of the year). The delay in recovery of photoprotection was predicted to decrease A'c by 17% at 30 degrees C and 32% at 10 degrees C for a chilling-susceptible species, and by 12.8% at 30 degrees C and 24% at 10 degrees C for a chilling-tolerant species. These predictions suggest that the selection, or engineering, of genotypes capable of more rapid recovery from the photoprotected state would substantially increase carbon uptake by crop canopies in the field.

http://sippe.ac.cn/gh/papers/zhuxinguang/Zhu,%20et.al.%202004%20Journal%20of%20Expeimental%20Botany.pdf

The slow reversibility of photosystem II thermal energy dissipation on transfer from high to low light may cause large losses in carbon gain by crop canopies: a theoretical analysis

H. R. Bolhàr-Nordenkampf

Papers

Photosynthesis and Production in a Changing Environment