Second generation bioenergy crops and climate change: a review of the effects of elevated atmospheric CO2 and drought on water use and the implications for yield

Second-generation, dedicated lignocellulosic crops for bioenergy are being hailed as the sustainable alternative to food crops for the generation of liquid transport fuels, contributing to climate change mitigation and increased energy security. Across temperate regions they include tree species grown as short rotation coppice and intensive forestry (e.g. Populus and Salix species) and C₄ grasses such as miscanthus and switchgrass. For bioenergy crops it is paramount that high energy yields are maintained in order to drive the industry to an economic threshold where it has competitive advantage over conventional fossil fuel alternatives. Therefore, in the face of increased planting of these species, globally, there is a pressing need for insight into their responses to predicted changes in climate to ensure these crops are 'climate proofed' in breeding and improvement programmes. In this review, we investigate the physiological responses of bioenergy crops to rising atmospheric CO₂ ([Ca]) and drought, with particular emphasis on the C₃ Salicaceae trees and C₄ grasses. We show that while crop yield is predicted to rise by up to 40% in elevated [Ca], this is tempered by the effects of water deficit. In response to elevated [Ca] stomatal conductance and evapotranspiration decline and higher leaf–water potentials are observed. However, whole-plant responses to [Ca] are often of lower magnitude and may even be positive (increased water use in elevated [Ca]). We conclude that rising [Ca] is likely to improve drought tolerance of bioenergy crop species due to improved plant water use, consequently yields in temperate environments may remain high in future climate scenarios.     

Elevated CO2 alters belowground exoenzyme activities in tussock tundra

A three-year exposure to a CO2 concentration of 680 mol mol-1 altered the enzymic characteristics of root surfaces, associated ectomycorrhizae, and in soils surrounding roots in a tussock tundra ecosystem of north Alaska, USA. At elevated CO2, phosphatase activity was higher on Eriophorum vaginatum root surfaces, ectomycorrhizal rhizomorphs and mantles associated with Betula nana roots, and in Oe and Oi soil horizons associated with plant roots. Also, endocellulase and exocellulase activities at elevated CO2 were higher in ectomycorrhizal rhizomorphs and lower in Oe and Oi soil horizons associated with roots. These results suggest that arctic plants respond to raised CO2 by increasing activities associated with nutrient acquisition, e.g. higher phosphatase activities on surfaces of roots and ectomycorrhizae, and greater cellulase activity in ectomycorrhizae. Changes in enzyme activities of surrounding soils are consistent with an increase in carbon exudation from plant roots, which would be expected to inhibit cellulase activities and stimulate phosphatase activities of soil microflora. These data were used to modify existing simulation models describing tussock phosphatase activities and litter decay. Model projections suggest that observed increases in phosphatase activities at 680 mol mol-1 CO2 could augment total annual phosphorus release within tussocks by more than 40%, at present levels of root and ectomycorrhizae biomass. This includes a nearly three-fold increase in potential phosphatase activity of E. vaginatum roots, per unit of surface area. Observed reductions in cellulase activities could diminish cellulose turnover by 45% in soils within rooting zones, which could substantially increase mineral nitrogen availability in soils due to lowered microbial immobilization.     

CO2浓度升高对大豆干旱胁迫的缓解效应

CO2浓度升高和干旱带来的气候变化势必对大豆的生长造成影响.目前,CO2浓度升高对干旱胁迫下大豆生理生化的影响研究较少.本试验研究了不同CO2浓度(400、600 pumol ? mol-1)和水分处理下(正常水分:叶片相对含水量为83％-90％;干旱:叶片相对含水量为64％-70％)大豆开花期的光合能力、光合色素积累...     

干旱胁迫下CO2浓度升高对转StAPX番茄植株耐旱能力的影响

在干旱胁迫伴随大气CO2浓度以及升高的CO2浓度（加倍）条件下,以过量表达番茄类囊体膜抗坏血酸过氧化物酶基因（StAPX）的转基因番茄为试材,探明干旱胁迫TCO2浓度升高对转基因及其野生型番茄植株清除活性氧及耐旱能力的影响。结果表明：升高的CO2浓度明显增加了干旱胁迫下植物的光合水平;升高的CO2浓度明显降低了干旱导致的植物体内H2O2．和O2的积累,影响了干旱胁迫下番茄植株的水．水循环系统的活性氧清除酶活性和小分子抗氧化物质含量;干旱胁迫下即使伴随升高的CO2浓度,测试番茄植株体内的渗透调节物质含量变化也不太明显;升高的CO2浓度明显降低了干旱胁迫下的植物细胞膜伤害程度;干旱胁迫下,升高的CO2浓度对转基因番茄株系比对野生型植株的影响更加明显。结果证明干旱逆境下,升高的CO2浓度能够在一定程度上进一步提高转基因番茄植株的耐旱性。     

Growth and onto-morphogenesis of soybean (Glycine max Merril) in an open, naturally CO2-enriched environment

Springs emitting carbon dioxide are frequent in Central Italy and provide a way of testing the response of plants to CO₂ enrichment under natural conditions. Results of a CO₂ enrichment experiment on soybean at a CO₂ spring (Solfatara) are presented. The experimental site is characterized by significant anomalies in atmospheric CO₂ concentration produced by a large number of vents emitting almost pure CO₂ (93%) plus small amounts of hydrogen sulphide, methane, nitrogen and oxygen. Within the gas vent area, plants were grown at three sub-areas whose mean CO₂ concentrations during daytime were 350,652 and 2370 μmol mol^-1, respectively. Weekly harvests were made to measure biomass growth, leaf area and ontogenetic development. Biomass growth rate and seed yield were enhanced by elevated CO₂. In particular, onto-morphogenetic development was affected by elevated CO₂ with high levels of CO₂ increasing the total number of main stem leaf nodes and the area of the main stem trifoliolate leaves. Biochemical analysis of plant tissue suggested that there was no effect of the small amounts of H₂S on the response to CO₂ enrichment. Non-protein sulphydryl compounds did not accumulate in leaf tissues and the overall capacity of leaf extracts to oxidize exogenously added NADH was not decreased. The limitations and advantages of experimenting with crop plants at elevated CO₂ in the open and in the proximity of carbon dioxide springs are discussed.     

Stomatal behaviour, photosynthesis and transpiration under rising CO2

Definitions of the variables used and the units are given in Table 1

The literature reports enormous variation between species in the extent of stomatal responses to rising CO₂. This paper attempts to provide a framework within which some of this diversity can be explained. We describe the role of stomata in the short-term response of leaf gas exchange to increases in ambient CO₂ concentration by developing the recently proposed stomatal model of Jarvis & Davies (1998 ). In this model stomatal conductance is correlated with the functioning of the photosynthetic system so that the effects of increases in CO₂ on stomata are experienced through changes in the rate of photosynthesis in a simple and mechanistically transparent way. This model also allows us to consider the effects of evaporative demand and soil moisture availability on stomatal responses to photosynthesis and therefore provides a means of considering these additional sources of variation. We emphasize that the relationship between the rate of photosynthesis and the internal CO₂ concentration and also drought will have important effects on the relative gains to be achieved under rising CO₂.  

  Table 1 . Abbreviations     

8.

Seasonal acclimation of leaf respiration in Eucalyptus saligna trees: impacts of elevated atmospheric CO2 and summer drought     

KRISTINE Y. CROUS  JOANA ZARAGOZA‐CASTELLS  MARKUS LÖW  DAVID S. ELLSWORTH  DAVID T. TISSUE  MARK G. TJOELKER  CRAIG V. M. BARTON  TERESA E. GIMENO  OWEN K. ATKIN 《Global Change Biology》2011,17(4):1560-1576

Understanding the impacts of atmospheric [CO₂] and drought on leaf respiration (R) and its response to changes in temperature is critical to improve predictions of plant carbon‐exchange with the atmosphere, especially at higher temperatures. We quantified the effects of [CO₂]‐enrichment (+240 ppm) on seasonal shifts in the diel temperature response of R during a moderate summer drought in Eucalyptus saligna growing in whole‐tree chambers in SE Australia. Seasonal temperature acclimation of R was marked, as illustrated by: (1) a downward shift in daily temperature response curves of R in summer (relative to spring); (2)≈60% lower R measured at 20^oC (R₂₀) in summer compared with spring; and (3) homeostasis over 12 months of R measured at prevailing nighttime temperatures. R₂₀, measured during the day, was on average 30–40% higher under elevated [CO₂] compared with ambient [CO₂] across both watered and droughted trees. Drought reduced R₂₀ by≈30% in both [CO₂] treatments resulting in additive treatment effects. Although [CO₂] had no effect on seasonal acclimation, summer drought exacerbated the seasonal downward shift in temperature response curves of R. Overall, these results highlight the importance of seasonal acclimation of leaf R in trees grown under ambient‐ and elevated [CO₂] as well as under moderate drought. Hence, respiration rates may be overestimated if seasonal changes in temperature and drought are not considered when predicting future rates of forest net CO₂ exchange.     

9.

    

Michell L. Thomey  Rebecca A. Slattery  Iris H. Khler  Carl J. Bernacchi  Donald R. Ort 《Global Change Biology》2019,25(12):4352-4368

Elevated atmospheric CO₂ concentration ([CO₂]) generally enhances C₃ plant productivity, whereas acute heat stress, which occurs during heat waves, generally elicits the opposite response. However, little is known about the interaction of these two variables, especially during key reproductive phases in important temperate food crops, such as soybean (Glycine max). Here, we grew soybean under elevated [CO₂] and imposed high‐ (+9°C) and low‐ (+5°C) intensity heat waves during key temperature‐sensitive reproductive stages (R1, flowering; R5, pod‐filling) to determine how elevated [CO₂] will interact with heat waves to influence soybean yield. High‐intensity heat waves, which resulted in canopy temperatures that exceeded optimal growth temperatures for soybean, reduced yield compared to ambient conditions even under elevated [CO₂]. This was largely due to heat stress on reproductive processes, especially during R5. Low‐intensity heat waves did not affect yields when applied during R1 but increased yields when applied during R5 likely due to relatively lower canopy temperatures and higher soil moisture, which uncoupled the negative effects of heating on cellular‐ and leaf‐level processes from plant‐level carbon assimilation. Modeling soybean yields based on carbon assimilation alone underestimated yield loss with high‐intensity heat waves and overestimated yield loss with low‐intensity heat waves, thus supporting the influence of direct heat stress on reproductive processes in determining yield. These results have implications for rain‐fed cropping systems and point toward a climatic tipping point for soybean yield when future heat waves exceed optimum temperature.     

10.

Isoprene emissions from plants are mediated by atmospheric CO2 concentrations     

MALCOLM POSSELL  C. NICHOLAS HEWITT 《Global Change Biology》2011,17(4):1595-1610

The tropical African tree species Acacia nigrescens Oliv. was grown in environmentally controlled growth chambers at three CO₂ concentrations representative of the Last Glacial Maximum (～180 ppmv), the present day (～380 ppmv), and likely mid‐21st century (～600 ppmv) CO₂ concentrations. Isoprene (C₅H₈) emissions, per unit leaf area, were greater at lower‐than‐current CO₂ levels and lower at higher‐than‐current CO₂ levels relative to controls grown at 380 ppmv CO₂. Changes in substrate availability and isoprene synthase (IspS) activity were identified as the mechanisms behind the observed leaf‐level emission response. In contrast, canopy‐scale emissions remained unaltered between the treatments as changes in leaf‐level emissions were offset by changes in biomass and leaf area. Substrate concentration and IspS activity‐CO₂ responses were used in a biochemical model, coupled to existing isoprene emission algorithms, to model isoprene emissions from A. nigrescens grown for over 2 years at three different CO₂ concentrations. The addition of the biochemical model allowed for the use of emission factors measured under present day CO₂ concentrations across all three CO₂ treatments. When isoprene emissions were measured from A. nigrescens in response to instantaneous changes in CO₂ concentration, the biochemical model satisfactorily represented the observed response. Therefore, the effect of changes in atmospheric CO₂ concentration on isoprene emission at any timescale can be modelled and predicted.     

11.

30 years of free‐air carbon dioxide enrichment (FACE): What have we learned about future crop productivity and its potential for adaptation?     

Elizabeth A. Ainsworth  Stephen P. Long 《Global Change Biology》2021,27(1):27-49

Free‐air CO₂ enrichment (FACE) allows open‐air elevation of [CO₂] without altering the microclimate. Its scale uniquely supports simultaneous study from physiology and yield to soil processes and disease. In 2005 we summarized results of then 28 published observations by meta‐analysis. Subsequent studies have combined FACE with temperature, drought, ozone, and nitrogen treatments. Here, we summarize the results of now almost 250 observations, spanning 14 sites and five continents. Across 186 independent studies of 18 C₃ crops, elevation of [CO₂] by ca. 200 ppm caused a ca. 18% increase in yield under non‐stress conditions. Legumes and root crops showed a greater increase and cereals less. Nitrogen deficiency reduced the average increase to 10%, as did warming by ca. 2°C. Two conclusions of the 2005 analysis were that C₄ crops would not be more productive in elevated [CO₂], except under drought, and that yield responses of C₃ crops were diminished by nitrogen deficiency and wet conditions. Both stand the test of time. Further studies of maize and sorghum showed no yield increase, except in drought, while soybean productivity was negatively affected by early growing season wet conditions. Subsequent study showed reduced levels of nutrients, notably Zn and Fe in most crops, and lower nitrogen and protein in the seeds of non‐leguminous crops. Testing across crop germplasm revealed sufficient variation to maintain nutrient content under rising [CO₂]. A strong correlation of yield response under elevated [CO₂] to genetic yield potential in both rice and soybean was observed. Rice cultivars with the highest yield potential showed a 35% yield increase in elevated [CO₂] compared to an average of 14%. Future FACE experiments have the potential to develop cultivars and management strategies for co‐promoting sustainability and productivity under future elevated [CO₂].     

12.

    

Issmat I. Kassem  Puneet Joshi  Von Sigler  Scott Heckathorn  Qi Wang 《植物学报(英文版)》2008,50(11):1406-1415

Our understanding of the effects of elevated atmospheric CO2, singly and In combination with other environmental changes,on plant-soil interactions is incomplete. Elevated CO2 effects on C4 plants, though smaller than on C3 species, are mediated mostly via decreased stomatal conductance and thus water loss. Therefore, we characterized the interactive effect of elevated CO2 and drought on soil microbial communities associated with a dominant C4 prairie grass, Andropogon gerardii Vitman. Elevated CO2 and drought both affected resources available to the soil microbial community. For example, elevated CO2 increased the soil C:N ratio and water content during drought, whereas drought alone decreased both. Drought significantly decreased soil microbial biomass. In contrast, elevated COz increased biomass while ameliorating biomass decreases that were induced under drought. Total and active direct bacterial counts and carbon substrate use (overall use and number of used sources) increased significantly under elevated CO2. Denaturing gradient gel electrophoresis analysis revealed that drought and elevated CO2, singly and combined, did not affect the soil bacteria community structure.We conclude that elevated CO2 alone increased bacterial abundance and microbial activity and carbon use, probably in response to increased root exudation. Elevated CO2 also limited drought-related impacts on microbial activity and biomass,which likely resulted from decreased plant water use under elevated CO2. These are among the first results showing that elevated CO2 and drought work in opposition to modulate plant-associated soil-bacteria responses,which should then Influence soil resources and plant and ecosystem function.     

13.

Using the output from global circulation models to predict changes in the distribution and abundance of cereal aphids in Canada: a mechanistic modeling approach   总被引：1，自引：0，他引：1  

JONATHAN A. NEWMAN 《Global Change Biology》2006,12(9):1634-1642

Climate change will alter the abundance and distribution of species. Predicting these shifts is a challenge for ecologists and essential information for the formation of public policy. Here, I use a mechanistic mathematical model of the interaction between grass growth physiology and aphid population dynamics, coupled with the climate change projections from the UK's Hadley Centre HadCM3 global circulation model (GCM) and Canada's Center for Climate Modeling and Analysis CGCM2 GCM to predict the changes in the abundance and distribution of summer cereal aphid populations in wheat-growing regions of Canada. When used with the HadCM3 projections, the model predicts a latitudinal shift northward in abundances but there is longitudinal variation as well. However, when used with the CGCM2 projections the model predicts that continental regions will see a decline while coastal regions will see an increase in summer cereal aphid populations. These effects are stronger under the higher emissions scenarios.     

14.

The effects of increasing CO₂ on crop photosynthesis and productivity: a review of field studies   总被引：8，自引：13，他引：8  

D. W. LAWLOR  R. A. C. MITCHELL 《Plant, cell & environment》1991,14(8):807-818

Abstract. Only a small proportion of elevated CO₂ studies on crops have taken place in the field. They generally confirm results obtained in controlled environments: CO₂ increases photosynthesis, dry matter production and yield, substantially in C₃ species, but less in C₄, it decreases stomatal conductance and transpiration in C₃ and C₄ species and greatly improves water-use efficiency in all plants. The increased productivity of crops with CO₂ enrichment is also related to the greater leaf area produced. Stimulation of yield is due more to an increase in the number of yield-forming structures than in their size. There is little evidence of a consistent effect of CO₂ on partitioning of dry matter between organs or on their chemical composition, except for tubers. Work has concentrated on a few crops (largely soybean) and more is needed on crops for which there are few data (e.g. rice). Field studies on the effects of elevated CO₂ in combination with temperature, water and nutrition are essential; they should be related to the development and improvement of mechanistic crop models, and designed to test their predictions.     

15.

短期CO₂浓度升高和干旱胁迫对白羊草土壤碳氮和微生物根际效应的影响     

肖列  刘国彬  李鹏  薛萐 《生态学杂志》2017,28(10):3251-3259

采用人工气候室和盆栽控水试验研究黄土丘陵区典型草本植物白羊草在倍增CO₂浓度(800 μmol·mol^-1)下和充分供水(75%～80%的田间持水量)、轻度干旱胁迫(55%～60%的田间持水量)和重度干旱胁迫(35%～40%的田间持水量)下根际和非根际土壤碳氮含量和微生物群落结构及其根际效应.结果表明: CO₂浓度升高和干旱胁迫对白羊草根际和非根际土壤有机碳、全氮和水溶性有机碳(DOC)含量及其根际效应均无显著影响.轻度干旱胁迫下CO₂浓度升高显著促进了根际土壤水溶性有机氮(DON)的消耗,导致DOC/DON升高,提高了DON的负根际效应和DOC/DON的正根际效应.干旱胁迫和CO₂浓度升高对土壤总磷脂脂肪酸(总PLFA)和细菌PLFA的根际效应无显著影响.CO₂浓度升高条件下干旱胁迫显著提高了根际土壤G⁺/G^- PLFA,降低了非根际土壤G⁺/G^- PLFA,导致其根际效应显著提高,表明根际微生物群落由自养微生物群落向异养微生物群落的转变.     

16.

    

Lingyan Zhou  Xuhui Zhou  Junjiong Shao  Yuanyuan Nie  Yanghui He  Liling Jiang  Zhuoting Wu  Shahla Hosseini Bai 《Global Change Biology》2016,22(9):3157-3169

As the second largest carbon (C) flux between the atmosphere and terrestrial ecosystems, soil respiration (Rs) plays vital roles in regulating atmospheric CO₂ concentration ([CO₂]) and climatic dynamics in the earth system. Although numerous manipulative studies and a few meta‐analyses have been conducted to determine the responses of Rs and its two components [i.e., autotrophic (Ra) and heterotrophic (Rh) respiration] to single global change factors, the interactive effects of the multiple factors are still unclear. In this study, we performed a meta‐analysis of 150 multiple‐factor (≥2) studies to examine the main and interactive effects of global change factors on Rs and its two components. Our results showed that elevated [CO₂] (E), nitrogen addition (N), irrigation (I), and warming (W) induced significant increases in Rs by 28.6%, 8.8%, 9.7%, and 7.1%, respectively. The combined effects of the multiple factors, EN, EW, DE, IE, IN, IW, IEW, and DEW, were also significantly positive on Rs to a greater extent than those of the single‐factor ones. For all the individual studies, the additive interactions were predominant on Rs (90.6%) and its components (≈70.0%) relative to synergistic and antagonistic ones. However, the different combinations of global change factors (e.g., EN, NW, EW, IW) indicated that the three types of interactions were all important, with two combinations for synergistic effects, two for antagonistic, and five for additive when at least eight independent experiments were considered. In addition, the interactions of elevated [CO₂] and warming had opposite effects on Ra and Rh, suggesting that different processes may influence their responses to the multifactor interactions. Our study highlights the crucial importance of the interactive effects among the multiple factors on Rs and its components, which could inform regional and global models to assess the climate–biosphere feedbacks and improve predictions of the future states of the ecological and climate systems.     

17.

大气CO2浓度升高对干旱条件下冬小麦叶片光合适应的影响     

宗毓铮  杨琦  常翠翠  勾俊英  张东升  郝兴宇  高志强 《应用生态学报》2021,32(12):4370-4380

大气CO2浓度升高是全球气候变化的主要特征,但大气CO2浓度长期升高条件下冬小麦叶片发生光合适应的机制尚不十分清楚.本研究以盆栽冬小麦'郑麦9023,为试验材料,在人工气候控制室内设置2个CO2浓度(400和600 μmol·mol-1)、2个水分条件(田间持水量的80％±5％和55％±5％),测定拔节期和抽穗期的光合...     

18.

Carbon gains by desiccation-tolerant plants at elevated CO₂     

Z. Tuba  Z. Csintalan  K. Szente  Z. Nagy  & J. Grace 《Functional ecology》1998,12(1):39-44

1. There have been no reports of the long-term responses of the desiccation-tolerant (DT) plants to elevated CO₂. Xerophyta scabrida is a DT woody shrub, which loses chlorophylls and thylakoids during desiccation: a so-called poikilochlorophyllous desiccation-tolerant species (PDT). When the leaves of X. scabria are allowed to desiccate, the species shows many of the normal features of (P)DT plants.
2. However, the duration of photosynthesis in X. scabria is prolonged by 300% when the measurements are made at 700 as opposed to 350p.p.m. CO₂. The implication is that the carboxylating enzymes must still have been active at this time to enable appreciable photosynthetic activity. This response could have far-reaching implications for the success of such species in a future climate.
3. Lichens and mosses, representing the homoiochlorophyllous DTs (HDT), retain their chlorophyll content and photosynthetic apparatus during desiccation. We show the desiccation responses of two common HDT species ( Cladonia convoluta and Tortula ruralis ) to elevated CO₂ for comparison. Both HDT species showed increased net CO₂ uptake in the material grown at high CO₂ by more than 30% in moss and by more than 50% in lichen. It is concluded that desiccation-tolerant plants will be among the main beneficiaries of a high CO₂ future.     

19.

  总被引：1，自引：0，他引：1  

JEREMY D. BARNES  JOHN H. OLLERENSHAW  CLARE P. WHITFIELD 《Global Change Biology》1995,1(2):129-142

Two cultivars of spring wheat (Triticum aestivum L. cvs. Alexandria and Hanno) and three cultivars of winter wheat (cvs. Riband, Mercia and Haven) were grown at two concentrations of CO₂ [ambient (355 pmol mol^?1) and elevated (708 μmol mol^?1)] under two O₃ regimes [clean air (< 5 nmol mol^?1 O₃) and polluted air (15 nmol mol^?1 O₃ at night rising to a midday maximum of 75 nmol mol^?1)] in a phytotron at the University of Newcastle-upon-Tyne. Between the two-leaf stage and anthesis, measurements of leaf gas-exchange, non-structural carbohydrate content, visible O₃ damage, growth, dry matter partitioning, yield components and root development were made in order to examine responses to elevated CO₂ and/or O₃. Growth at elevated CO₂ resulted in a sustained increase in the rate of CO₂ assimilation, but after roughly 6 weeks' exposure there was evidence of a slight decline in the photosynthetic rate (c.-15%) measured under growth conditions which was most pronounced in the winter cultivars. Enhanced rates of CO₂ assimilation were accompanied by a decrease in stomatal conductance which improved the instantaneous water use efficiency of individual leaves. CO₂ enrichment stimulated shoot and root growth to an equivalent extent, and increased tillering and yield components, however, non-structural carbohydrates still accumulated in source leaves. In contrast, long-term exposure to O₃ resulted in a decreased CO₂ assimilation rate (c. -13%), partial stomatal closure, and the accumulation of fructan and starch in leaves in the light. These effects were manifested in decreased rates of shoot and root growth, with root growth more severely affected than shoot growth. In the combined treatment growth of O₃-treated plants was enhanced by elevated CO₂, but there was little evidence that CO₂ enrichment afforded additional protection against O₃ damage. The reduction in growth induced by O₃ at elevated CO₂ was similar to that induced by O₃ at ambient CO₂ despite additive effects of the individual gases on stomatal conductance that would be expected to reduce the O₃ flux by 20%, and also CO₂-induced increases in the provision of substrates for detoxification and repair processes. These observations suggest that CO₂ enrichment may render plants more susceptible to O₃ damage at the cellular level. Possible mechanisms are discussed.     

20.

    

Jürgen Knauer  Snke Zaehle  Martin G. De Kauwe  Nur H. A. Bahar  John R. Evans  Belinda E. Medlyn  Markus Reichstein  Christiane Werner 《Global Change Biology》2019,25(5):1820-1838

Mesophyll conductance (g_m) is known to affect plant photosynthesis. However, g_m is rarely explicitly considered in land surface models (LSMs), with the consequence that its role in ecosystem and large‐scale carbon and water fluxes is poorly understood. In particular, the different magnitudes of g_m across plant functional types (PFTs) are expected to cause spatially divergent vegetation responses to elevated CO₂ concentrations. Here, an extensive literature compilation of g_m across major vegetation types is used to parameterize an empirical model of g_m in the LSM JSBACH and to adjust photosynthetic parameters based on simulated A_n ? C_i curves. We demonstrate that an explicit representation of g_m changes the response of photosynthesis to environmental factors, which cannot be entirely compensated by adjusting photosynthetic parameters. These altered responses lead to changes in the photosynthetic sensitivity to atmospheric CO₂ concentrations which depend both on the magnitude of g_m and the climatic conditions, particularly temperature. We then conducted simulations under ambient and elevated (ambient + 200 μmol/mol) CO₂ concentrations for contrasting ecosystems and for historical and anticipated future climate conditions (representative concentration pathways; RCPs) globally. The g_m‐explicit simulations using the RCP8.5 scenario resulted in significantly higher increases in gross primary productivity (GPP) in high latitudes (+10% to + 25%), intermediate increases in temperate regions (+5% to + 15%), and slightly lower to moderately higher responses in tropical regions (?2% to +5%), which summed up to moderate GPP increases globally. Similar patterns were found for transpiration, but with a lower magnitude. Our results suggest that the effect of an explicit representation of g_m is most important for simulated carbon and water fluxes in the boreal zone, where a cold climate coincides with evergreen vegetation.     

Seasonal acclimation of leaf respiration in Eucalyptus saligna trees: impacts of elevated atmospheric CO2 and summer drought

Understanding the impacts of atmospheric [CO₂] and drought on leaf respiration (R) and its response to changes in temperature is critical to improve predictions of plant carbon‐exchange with the atmosphere, especially at higher temperatures. We quantified the effects of [CO₂]‐enrichment (+240 ppm) on seasonal shifts in the diel temperature response of R during a moderate summer drought in Eucalyptus saligna growing in whole‐tree chambers in SE Australia. Seasonal temperature acclimation of R was marked, as illustrated by: (1) a downward shift in daily temperature response curves of R in summer (relative to spring); (2)≈60% lower R measured at 20^oC (R₂₀) in summer compared with spring; and (3) homeostasis over 12 months of R measured at prevailing nighttime temperatures. R₂₀, measured during the day, was on average 30–40% higher under elevated [CO₂] compared with ambient [CO₂] across both watered and droughted trees. Drought reduced R₂₀ by≈30% in both [CO₂] treatments resulting in additive treatment effects. Although [CO₂] had no effect on seasonal acclimation, summer drought exacerbated the seasonal downward shift in temperature response curves of R. Overall, these results highlight the importance of seasonal acclimation of leaf R in trees grown under ambient‐ and elevated [CO₂] as well as under moderate drought. Hence, respiration rates may be overestimated if seasonal changes in temperature and drought are not considered when predicting future rates of forest net CO₂ exchange.     

Isoprene emissions from plants are mediated by atmospheric CO2 concentrations

The tropical African tree species Acacia nigrescens Oliv. was grown in environmentally controlled growth chambers at three CO₂ concentrations representative of the Last Glacial Maximum (～180 ppmv), the present day (～380 ppmv), and likely mid‐21st century (～600 ppmv) CO₂ concentrations. Isoprene (C₅H₈) emissions, per unit leaf area, were greater at lower‐than‐current CO₂ levels and lower at higher‐than‐current CO₂ levels relative to controls grown at 380 ppmv CO₂. Changes in substrate availability and isoprene synthase (IspS) activity were identified as the mechanisms behind the observed leaf‐level emission response. In contrast, canopy‐scale emissions remained unaltered between the treatments as changes in leaf‐level emissions were offset by changes in biomass and leaf area. Substrate concentration and IspS activity‐CO₂ responses were used in a biochemical model, coupled to existing isoprene emission algorithms, to model isoprene emissions from A. nigrescens grown for over 2 years at three different CO₂ concentrations. The addition of the biochemical model allowed for the use of emission factors measured under present day CO₂ concentrations across all three CO₂ treatments. When isoprene emissions were measured from A. nigrescens in response to instantaneous changes in CO₂ concentration, the biochemical model satisfactorily represented the observed response. Therefore, the effect of changes in atmospheric CO₂ concentration on isoprene emission at any timescale can be modelled and predicted.     

30 years of free‐air carbon dioxide enrichment (FACE): What have we learned about future crop productivity and its potential for adaptation?

Free‐air CO₂ enrichment (FACE) allows open‐air elevation of [CO₂] without altering the microclimate. Its scale uniquely supports simultaneous study from physiology and yield to soil processes and disease. In 2005 we summarized results of then 28 published observations by meta‐analysis. Subsequent studies have combined FACE with temperature, drought, ozone, and nitrogen treatments. Here, we summarize the results of now almost 250 observations, spanning 14 sites and five continents. Across 186 independent studies of 18 C₃ crops, elevation of [CO₂] by ca. 200 ppm caused a ca. 18% increase in yield under non‐stress conditions. Legumes and root crops showed a greater increase and cereals less. Nitrogen deficiency reduced the average increase to 10%, as did warming by ca. 2°C. Two conclusions of the 2005 analysis were that C₄ crops would not be more productive in elevated [CO₂], except under drought, and that yield responses of C₃ crops were diminished by nitrogen deficiency and wet conditions. Both stand the test of time. Further studies of maize and sorghum showed no yield increase, except in drought, while soybean productivity was negatively affected by early growing season wet conditions. Subsequent study showed reduced levels of nutrients, notably Zn and Fe in most crops, and lower nitrogen and protein in the seeds of non‐leguminous crops. Testing across crop germplasm revealed sufficient variation to maintain nutrient content under rising [CO₂]. A strong correlation of yield response under elevated [CO₂] to genetic yield potential in both rice and soybean was observed. Rice cultivars with the highest yield potential showed a 35% yield increase in elevated [CO₂] compared to an average of 14%. Future FACE experiments have the potential to develop cultivars and management strategies for co‐promoting sustainability and productivity under future elevated [CO₂].     

Using the output from global circulation models to predict changes in the distribution and abundance of cereal aphids in Canada: a mechanistic modeling approach

Climate change will alter the abundance and distribution of species. Predicting these shifts is a challenge for ecologists and essential information for the formation of public policy. Here, I use a mechanistic mathematical model of the interaction between grass growth physiology and aphid population dynamics, coupled with the climate change projections from the UK's Hadley Centre HadCM3 global circulation model (GCM) and Canada's Center for Climate Modeling and Analysis CGCM2 GCM to predict the changes in the abundance and distribution of summer cereal aphid populations in wheat-growing regions of Canada. When used with the HadCM3 projections, the model predicts a latitudinal shift northward in abundances but there is longitudinal variation as well. However, when used with the CGCM2 projections the model predicts that continental regions will see a decline while coastal regions will see an increase in summer cereal aphid populations. These effects are stronger under the higher emissions scenarios.     

The effects of increasing CO2 on crop photosynthesis and productivity: a review of field studies

Abstract. Only a small proportion of elevated CO₂ studies on crops have taken place in the field. They generally confirm results obtained in controlled environments: CO₂ increases photosynthesis, dry matter production and yield, substantially in C₃ species, but less in C₄, it decreases stomatal conductance and transpiration in C₃ and C₄ species and greatly improves water-use efficiency in all plants. The increased productivity of crops with CO₂ enrichment is also related to the greater leaf area produced. Stimulation of yield is due more to an increase in the number of yield-forming structures than in their size. There is little evidence of a consistent effect of CO₂ on partitioning of dry matter between organs or on their chemical composition, except for tubers. Work has concentrated on a few crops (largely soybean) and more is needed on crops for which there are few data (e.g. rice). Field studies on the effects of elevated CO₂ in combination with temperature, water and nutrition are essential; they should be related to the development and improvement of mechanistic crop models, and designed to test their predictions.     

短期CO2浓度升高和干旱胁迫对白羊草土壤碳氮和微生物根际效应的影响

采用人工气候室和盆栽控水试验研究黄土丘陵区典型草本植物白羊草在倍增CO₂浓度(800 μmol·mol^-1)下和充分供水(75%～80%的田间持水量)、轻度干旱胁迫(55%～60%的田间持水量)和重度干旱胁迫(35%～40%的田间持水量)下根际和非根际土壤碳氮含量和微生物群落结构及其根际效应.结果表明: CO₂浓度升高和干旱胁迫对白羊草根际和非根际土壤有机碳、全氮和水溶性有机碳(DOC)含量及其根际效应均无显著影响.轻度干旱胁迫下CO₂浓度升高显著促进了根际土壤水溶性有机氮(DON)的消耗,导致DOC/DON升高,提高了DON的负根际效应和DOC/DON的正根际效应.干旱胁迫和CO₂浓度升高对土壤总磷脂脂肪酸(总PLFA)和细菌PLFA的根际效应无显著影响.CO₂浓度升高条件下干旱胁迫显著提高了根际土壤G⁺/G^- PLFA,降低了非根际土壤G⁺/G^- PLFA,导致其根际效应显著提高,表明根际微生物群落由自养微生物群落向异养微生物群落的转变.     

大气CO2浓度升高对干旱条件下冬小麦叶片光合适应的影响

大气CO2浓度升高是全球气候变化的主要特征,但大气CO2浓度长期升高条件下冬小麦叶片发生光合适应的机制尚不十分清楚.本研究以盆栽冬小麦'郑麦9023,为试验材料,在人工气候控制室内设置2个CO2浓度(400和600 μmol·mol-1)、2个水分条件(田间持水量的80％±5％和55％±5％),测定拔节期和抽穗期的光合...     

Carbon gains by desiccation-tolerant plants at elevated CO2

1. There have been no reports of the long-term responses of the desiccation-tolerant (DT) plants to elevated CO₂. Xerophyta scabrida is a DT woody shrub, which loses chlorophylls and thylakoids during desiccation: a so-called poikilochlorophyllous desiccation-tolerant species (PDT). When the leaves of X. scabria are allowed to desiccate, the species shows many of the normal features of (P)DT plants.
2. However, the duration of photosynthesis in X. scabria is prolonged by 300% when the measurements are made at 700 as opposed to 350p.p.m. CO₂. The implication is that the carboxylating enzymes must still have been active at this time to enable appreciable photosynthetic activity. This response could have far-reaching implications for the success of such species in a future climate.
3. Lichens and mosses, representing the homoiochlorophyllous DTs (HDT), retain their chlorophyll content and photosynthetic apparatus during desiccation. We show the desiccation responses of two common HDT species ( Cladonia convoluta and Tortula ruralis ) to elevated CO₂ for comparison. Both HDT species showed increased net CO₂ uptake in the material grown at high CO₂ by more than 30% in moss and by more than 50% in lichen. It is concluded that desiccation-tolerant plants will be among the main beneficiaries of a high CO₂ future.