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On the other hand, the simulation of elevated CO2 on canopy photosynthesis leveled off with time.
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where SL, ML, BL and LL are stomatal, mesophyll, biochemical and light limitation, respectively. The fact that the contribution of different limitations calculated by this method can be be treated additively () allows straightforward interpretation and allows the computation of the photosynthetic limitation at canopy levels by summing up the limitations of all leaves of a plant. For example, the stomatal limitation of a plant with n leaves (SLp, μmol CO2 per plant s–1) can be calculated by:
When sea levels rise as dramatically as they did in the Cretaceous, coral reefs will be buried under rising waters and the ideal position, for both photosynthesis and oxygenation, is lost, and reefs can die, like burying a tree’s roots. About 125 mya, reefs made by , which thrived on , began to displace reefs made by stony corals. They may have prevailed because they could tolerate hot and saline waters better than stony corals could. About 116 mya, an , probably caused by volcanism, which temporarily halted rudist domination. But rudists flourished until the late Cretaceous, when they went extinct, perhaps due to changing climate, although there is also evidence that the rudists . Carbon dioxide levels steadily fell from the early Cretaceous until today, temperatures fell during the Cretaceous, and hot-climate organisms gradually became extinct during the Cretaceous. Around 93 mya, , perhaps caused by underwater volcanism, which again seems to have largely been confined to marine biomes. It was much more devastating than the previous one, and rudists were hit hard, although it was a more regional event. That event seems to have , and a family of . On land, , some of which seem to have , also went extinct. There had been a decline in sauropod and ornithischian diversity before that 93 mya extinction, but it subsequently rebounded. In the oceans, biomes beyond 60 degrees latitude were barely impacted, while those closer to the equator were devastated, which suggests that oceanic cooling was related. shows rising oxygen and declining carbon dioxide in the late Cretaceous, which reflected a general cooling trend that began in the mid-Cretaceous. Among the numerous hypotheses posited, late Cretaceous climate changes have been invoked for slowly driving dinosaurs to extinction, in the “they went out with a whimper, not a bang” scenario. However, it seems that dinosaurs did go out with a bang. A big one. Ammonoids seem to have been brought to the brink with nearly marine mass extinctions during their tenure on Earth, and it was no different with that late-Cretaceous extinction. Ammonoids recovered once again, and their lived in the late Cretaceous, but the end-Cretaceous extinction marked their final appearance as they went the way of and other iconic animals.
Photosynthesis - an overview | ScienceDirect Topics
Maximizing photosynthesis at the canopy level is important for enhancing crop yield, and this requires insights into the limiting factors of photosynthesis. Using greenhouse cucumber (Cucumis sativus) as an example, this study provides a novel approach to quantify different components of photosynthetic limitations at the leaf level and to upscale these limitations to different canopy layers and the whole plant.
Improving productivity is a major goal in crop production. This can be achieved by genetic crop improvement or by the optimization of the cropping system. Important tasks to optimize the cropping system are to maximize crop photosynthesis at the canopy level (; ; ) and to optimize the photosynthetic resource distribution within the canopy (). However, since it is difficult to measure canopy photosynthesis, modelling approaches are necessary for its study (). To date, several approaches for modelling canopy photosynthesis have been proposed: (1) big leaf models, where the whole canopy is assumed to consist of one leaf (); (2) sunlit–shaded models, where a plant canopy is represented by two leaves and where one of which is shaded by the other (; ); (3) multilayer models, where the plant canopy is divided into leaf clusters exposed to different light environments (); and (4) functional–structural plant models (FSPMs), where the plants and the canopy are constructed spatially explicitly at the organ level with geometry and topology, and the physiological functions of plants, e.g. photosynthesis, and interactions between canopy structure and environmental factors, such as light, are described (; ). A key feature of FSPMs is that the heterogeneities of microclimate, especially local light conditions, can be simulated and used to compute photosynthesis at the leaf level and upscale it to the canopy level (; ; ; ).
influenced in situ leaf-level photosynthesis rates in the ..
where ML,k, BL,k and LL,k are the mesophyll, biochemical and light limitations of leaf k. This upscaling approach may provide insights into the sources of photosynthetic limitations in the cropping system. Since it is almost impossible to measure all of the parameters (light interception by the leaves, FvCB model parameters, stomatal and mesophyll conductance) required for the quantitative limitation analysis of all leaves of a plant, a modelling approach would be desirable for investigating the photosynthetic limitation of both different canopy layers and the whole plant. We suggest combining a structural model and the FvCB model, as has been done in several studies (; ; ; ), to quantify different components of photosynthetic limitation at the canopy level.
Since enhanced CO2 significantly increased biomass of rice stems and panicles, increase in canopy respiration caused diminishment of CO2 stimulation in canopy net photosynthesis, keaf nitrogen in the canopy level decreased with CO2 concentration and may eventually hasten CO2 stimulation on canopy photosynthesis.
Increases in photosynthesis of leaves remaining ..
Redesigning photosynthesis to sustainably meet global …
01/12/1998 · HOW ENVIRONMENTAL CONDITIONS AFFECT CANOPY LEAF-LEVEL ..
at the canopy level to maximize the potential for light ..
20/12/2017 · Request (PDF) | Canopy-level photosy..
National Academy of Sciences
Canopy Photosynthesis: From Basics to Applications
Our novel model approach, combining an FSPM with quantitative limitation analysis of photosynthesis, allows us to quantify the different photosynthetic limitations at the leaf level and to upscale them to the canopy level. Under non-stressed conditions, the biochemical capacity is the most prominent limitation in the lower canopy, whereas light interception is the most important factor limiting photosynthesis in the upper canopy and diffusional limitations contribute less to total limitation. Methods for maintaining the biochemical capacity of the middle–lower canopy and optimizing the vertical leaf area profile would be promising strategies to improve canopy photosynthesis. Further analyses using our model approach would provide insights into the influence of horticultural practices on canopy photosynthesis and the design of optimal cropping systems.
Photosynthesis and respiration - Plant Factory - Chapter 9
Moreover, implementing this analysis in a dynamic structural model (; ) would enable us to explore the effect of developmental stage on photosynthetic limitations at the canopy level.
Spectral dependence of photosynthesis and light absorptance in ..
Perhaps a few hundred million years after the first mitochondrion appeared, as the oceanic oxygen content, at least on the surface, increased as a result of oxygenic photosynthesis, those complex cells learned to use oxygen instead of hydrogen. It is difficult to overstate the importance of learning to use oxygen in respiration, called . Before the appearance of aerobic respiration, life generated energy via and . Because oxygen , aerobic respiration generates, on average, about per cycle as fermentation and anaerobic respiration do (although some types of anaerobic respiration can get ). The suite of complex life on Earth today would not have been possible without the energy provided by oxygenic respiration. At minimum, nothing could have flown, and any animal life that might have evolved would have never left the oceans because the atmosphere would not have been breathable. With the advent of aerobic respiration, became possible, as it is several times as efficient as anaerobic respiration and fermentation (about 40% as compared to less than 10%). Today’s food chains of several levels would be constrained to about two in the absence of oxygen. Some scientists have and oxygen and respiration in eukaryote evolution. is controversial.
on the spectral dependence of photosynthesis and ..
We would like to stress that our results may not be generalized to all plant species, although we suppose that similar results may be obtained by analysing other greenhouse crops (e.g. melon, tomato, pepper and aubergine). However, our approach, combining FSPM and quantitative limitation analyses (for both saturating and non-saturating light conditions), can be applied to all plant species and we merely use cucumber as a model plant to demonstrate this approach. It will be fruitful to apply this analysis to investigate other plant species and the influence of horticultural practices on canopy photosynthesis or to search the optimal cropping systems for yield maximization, e.g. row distance, plant density and training system. Another question might be the necessity for supplemental lighting and the efficiency of its energy use. Furthermore, implementing the physiological responses to temperature would aid in revealing the importance of temperature to canopy photosynthesis. It is very likely that temperature is the key factor determining whether photosynthesis is at the Rubisco-limited or RuBP-limited phase in the FvCB model (). also showed that temperature strongly affects the position of the transition point (Cctr) in the FvCB model. However, temperature changes the reference photosynthesis rate and this makes the comparison difficult. It would be interesting to implement stress responses of gsc and gm into the model to investigate the changes in DL on the canopy level under stress. In general, gsc and gm decrease under stress conditions. These decreases may result in (1) an increase in DL, (2) a decrease in Cc and (3) a higher leaf temperature due to a lower gsc and transpiration. Since photosynthesis tends to be Rubisco limited at low Cc and high temperature and DL is more prominent at the Rubisco-limited phase (see above), DL would be significantly higher under stress conditions.
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