Highlights for Agave Productivity

Agaves can grow in marginal arid and semiarid lands where their special ecological and physiological adaptations to environmental conditions give them the potential to produce substantial biomass. Agave americana was the first agave species shown to be a Crassulacean Acid Metabolism plant, with CO₂ uptake occurring primarily at night and with high water‐use efficiency (photosynthesis/transpiration). A. salmiana and A. mapisaga can have high nocturnal net CO₂ uptake rates and high productivities averaging 40 tonnes dry weight ha^?1 yr^?1. Agaves can benefit from the increases in temperature and atmospheric CO₂ levels accompanying global climate change. An Environmental Productivity Index can predict the effects of soil and environmental factors on CO₂ uptake and hence on the regions appropriate for cultivating agaves. In turn, their increased cultivation can support the production of innovative earth‐friendly commodities that can be used as new bioenergy feedstocks.     

Sensitivity analysis of ecosystem CO<Subscript>2</Subscript> exchange to climate change in High Arctic tundra using an ecological process-based model

Arctic terrestrial ecosystems are extremely vulnerable to climate change. A major concern is how the carbon balance of these ecosystems will respond to climate change. In this study, we constructed a simple ecological process-based model to assess how the carbon balance will be altered by ongoing climate change in High Arctic tundra ecosystems using in situ observations of carbon cycle processes. In particular, we simulated stand-level photosynthesis, root respiration, heterotrophic respiration, and hence net ecosystem production (NEP) of a plant community dominated by vascular plants and mosses. Analyses were carried out for current and future temperature and precipitation conditions. Our results showed that the tundra ecosystem was a CO₂ sink (NEP of 2.3–18.9 gC m^?2 growing season^?1) under present temperature conditions. Under rising temperature (2–6 °C), carbon gain is significantly reduced, but a few days’ extension of the foliage period caused by their higher temperatures compensated for the negative effect of temperature on NEP. Precipitation is the major environmental factor driving photosynthetic productivity of mosses, but it had a minor influence on community-level NEP. However, NEP decreased by a maximum 15.3 gC m^?2 growing season^?1 under a 30-day prolongation of the moss-growing season, suggesting that growing season extension had a negative effect on ecosystem carbon gain, because of poorer light conditions in autumn. Because the growing season creates a weak CO₂ sink at present, lengthening of the snow-free season coupled with rising temperature could seriously affect the future carbon balance of this Arctic tundra ecosystem.     

The influence of temperature and labile C substrates on heterotrophic respiration in response to elevated CO2 and nitrogen fertilization

Important effects of elevated [CO₂] on SOM are expected as a consequence of increased labile organic substrates derived from plants. The present study tests the hypotheses that, under elevated [CO₂]: 1) soil heterotrophic respiration will increase due to roots-microbes-soil interactions; 2) the increased labile C will boost soil heterotrophic respiration, depending on N availability; 3) the temperature sensitivity of soil respiration will change, depending on nitrogen inputs and plant activity. To test these hypotheses, we measured the heterotrophic respiration of intact soil cores collected in a poplar plantation exposed to elevated [CO₂] and two nitrogen inputs, at different temperatures. Additional physical (water content, root biomass) and biochemical parameters (microbial biomass, labile C) were determined on the same samples. The soil samples were collected at the POP-EuroFACE experimental site (Italy), where a Populus x euramericana plantation was exposed for 6 years to 550 ppm [CO₂] (Free Air CO₂ Enrichment) at two different nitrogen inputs (none or 290 kg ha^?1). The higher heterotrophic respiration under elevated [CO₂] (+30% on average) was driven by the larger pool of soil labile C (+57% on average). The temperature sensitivity of soil respiration was unaffected by elevated [CO₂], but was positively affected by N fertilization. Our results indicate that only a fraction of the extra carbon fixed by photosynthesis in elevated [CO₂] will contribute to enhanced carbon storage into the soil because of the contemporary stimulation of soil heterotrophic respiration. At the same time, the fraction remaining in the soil will enhance the pool of soil labile C.     

P uptake by arbuscular mycorrhizal hyphae: effect of soil temperature and atmospheric CO2 enrichment

Mycorrhizas are ubiquitous symbioses that may have an important role in the movement of C from air to soil. Studies on the effects of climate change factors on mycorrhizas have been concentrated on the effects of atmospheric [CO₂] whereas temperature effects have been neglected. Based on previous results showing no effect of varying atmospheric [CO₂] on the development and P uptake of the arbuscular mycorrhizal fungi (AMF) colonizing plants growing in controlled conditions, we hypothesized that soil temperature would have a higher impact on AMF development and nutrient uptake than the effects of [CO₂] on the host plant. Pea plants were grown in association with either a single isolate of Glomus caledonium or AMF from field soil in factorial combination with the corresponding current (10 °C) or elevated (15 °C) soil temperatures at current (350 p.p.m) or elevated (700 p.p.m) atmospheric [CO₂]. ³³P uptake by extraradical AMF hyphae was measured independently from root P uptake in a root exclusion compartment. Intraradical colonization developed well at both soil temperatures and almost duplicated from 10 to 15 °C. Extraradical mycelium developed only at 15 °C in the root exclusion compartment and hyphal P uptake could therefore be studied at 15 °C only. Hyphal P uptake differed markedly between inoculum types, but was not altered by growing the host plants at two atmospheric [CO₂] levels. No significant [CO₂] × soil temperature interactions were observed. The results suggested that, in the system tested, AMF development and function is likely more influenced by the temperature component of climate change than by its [CO₂] component. We suggest that much more attention should be paid to temperature effects in future studies.     

Genotypes of Brassica rapa respond differently to plant-induced variation in air CO2 concentration in growth chambers with standard and enhanced venting

Growth chambers allow measurement of phenotypic differences among genotypes under controlled environment conditions. However, unintended variation in growth chamber air CO₂ concentration ([CO₂]) may affect the expression of diverse phenotypic traits, and genotypes may differ in their response to variation in [CO₂]. We monitored [CO₂] and quantified phenotypic responses of 22 Brassica rapa genotypes in growth chambers with either standard or enhanced venting. [CO₂] in chambers with standard venting dropped to 280 μmol mol^?1 during the period of maximum canopy development, ~80 μmol mol^?1 lower than in chambers with enhanced venting. The stable carbon isotope ratio of CO₂ in chamber air (δ¹³C_air) was negatively correlated with [CO₂], suggesting that photosynthesis caused observed [CO₂] decreases. Significant genotype × chamber-venting interactions were detected for 12 of 20 traits, likely due to differences in the extent to which [CO₂] changed in relation to genotypes’ phenology or differential sensitivity of genotypes to low [CO₂]. One trait, ¹³C discrimination (δ¹³C), was particularly influenced by unaccounted-for fluctuations in δ¹³C_air and [CO₂]. Observed responses to [CO₂] suggest that genetic variance components estimated in poorly vented growth chambers may be influenced by the expression of genes involved in CO₂ stress responses; genotypic values estimated in these chambers may likewise be misleading such that some mapped quantitative trait loci may regulate responses to CO₂ stress rather than a response to the environmental factor of interest. These results underscore the importance of monitoring, and where possible, controlling [CO₂].     

Plasticity of rice tiller production is related to genotypic variation in the biomass response to elevated atmospheric CO2 concentration and low temperatures during vegetative growth

Appropriate resource partitioning to either production of new tillers or growth of individual tillers is a critical factor for increasing rice biomass production and facilitating adaptation to climate change. We examined the contributions of genotypic variation to the tiller number and individual tiller growth of 24 rice cultivars in response to an elevated atmospheric CO₂ concentration [CO₂] (control + 191 μmol mol⁻¹) and a low air temperature (control minus 4.7 °C) during 56 days of vegetative growth after transplanting. For all genotypes combined, biomass increased by 27% under elevated [CO₂] and decreased by 34% at low temperature, with a significant genotype × temperature interaction. The increase caused by elevated [CO₂] resulted from increased tiller number, and the decrease caused by low temperature resulted from decreased growth of individual tillers. Despite the different overall responses to elevated [CO₂] and low temperature, most of the genotypic variation in biomass at elevated [CO₂] and low temperature was explained by the responses of tiller number rather than by individual tiller growth. The genotypes with the highest biomass response to elevated [CO₂] had a smaller reduction of biomass under low temperature. These results highlight the greater importance of genotypic variation in tiller number than in individual tiller growth in the response of biomass to environmental change.     

Physiological ecology of desert biocrust moss following 10 years exposure to elevated CO₂: evidence for enhanced photosynthetic thermotolerance

In arid regions, biomes particularly responsive to climate change, mosses play an important biogeochemical role as key components of biocrusts. Using the biocrust moss Syntrichia caninervis collected from the Nevada Desert Free Air CO₂ Enrichment Facility, we examined the physiological effects of 10 years of exposure to elevated CO₂, and the effect of high temperature events on the photosynthetic performance of moss grown in CO₂‐enriched air. Moss exposed to elevated CO₂ exhibited a 46% decrease in chlorophyll, a 20% increase in carbon and no difference in either nitrogen content or photosynthetic performance. However, when subjected to high temperatures (35–40°C), mosses from the elevated CO₂ environment showed higher photosynthetic performance and photosystem II (PSII) efficiency compared to those grown in ambient conditions, potentially reflective of a shift in nitrogen allocation to components that offer a higher resistance of PSII to heat stress. This result suggests that mosses may respond to climate change in markedly different ways than vascular plants, and observed CO₂‐induced photosynthetic thermotolerance in S. caninervis will likely have consequences for future desert biogeochemistry.     

Warming Reduces Carbon Losses from Grassland Exposed to Elevated Atmospheric Carbon Dioxide

The flux of carbon dioxide (CO₂) between terrestrial ecosystems and the atmosphere may ameliorate or exacerbate climate change, depending on the relative responses of ecosystem photosynthesis and respiration to warming temperatures, rising atmospheric CO₂, and altered precipitation. The combined effect of these global change factors is especially uncertain because of their potential for interactions and indirectly mediated conditions such as soil moisture. Here, we present observations of CO₂ fluxes from a multi-factor experiment in semi-arid grassland that suggests a potentially strong climate – carbon cycle feedback under combined elevated [CO₂] and warming. Elevated [CO₂] alone, and in combination with warming, enhanced ecosystem respiration to a greater extent than photosynthesis, resulting in net C loss over four years. The effect of warming was to reduce respiration especially during years of below-average precipitation, by partially offsetting the effect of elevated [CO₂] on soil moisture and C cycling. Carbon losses were explained partly by stimulated decomposition of soil organic matter with elevated [CO₂]. The climate – carbon cycle feedback observed in this semiarid grassland was mediated by soil water content, which was reduced by warming and increased by elevated [CO₂]. Ecosystem models should incorporate direct and indirect effects of climate change on soil water content in order to accurately predict terrestrial feedbacks and long-term storage of C in soil.     

Climate change and ocean acidification effects on seagrasses and marine macroalgae

Although seagrasses and marine macroalgae (macro‐autotrophs) play critical ecological roles in reef, lagoon, coastal and open‐water ecosystems, their response to ocean acidification (OA) and climate change is not well understood. In this review, we examine marine macro‐autotroph biochemistry and physiology relevant to their response to elevated dissolved inorganic carbon [DIC], carbon dioxide [CO₂], and lower carbonate [CO₃^2?] and pH. We also explore the effects of increasing temperature under climate change and the interactions of elevated temperature and [CO₂]. Finally, recommendations are made for future research based on this synthesis. A literature review of >100 species revealed that marine macro‐autotroph photosynthesis is overwhelmingly C₃ (≥ 85%) with most species capable of utilizing HCO₃^?; however, most are not saturated at current ocean [DIC]. These results, and the presence of CO₂‐only users, lead us to conclude that photosynthetic and growth rates of marine macro‐autotrophs are likely to increase under elevated [CO₂] similar to terrestrial C₃ species. In the tropics, many species live close to their thermal limits and will have to up‐regulate stress‐response systems to tolerate sublethal temperature exposures with climate change, whereas elevated [CO₂] effects on thermal acclimation are unknown. Fundamental linkages between elevated [CO₂] and temperature on photorespiration, enzyme systems, carbohydrate production, and calcification dictate the need to consider these two parameters simultaneously. Relevant to calcifiers, elevated [CO₂] lowers net calcification and this effect is amplified by high temperature. Although the mechanisms are not clear, OA likely disrupts diffusion and transport systems of H⁺ and DIC. These fluxes control micro‐environments that promote calcification over dissolution and may be more important than CaCO₃ mineralogy in predicting macroalgal responses to OA. Calcareous macroalgae are highly vulnerable to OA, and it is likely that fleshy macroalgae will dominate in a higher CO₂ ocean; therefore, it is critical to elucidate the research gaps identified in this review.     

Crop residue incorporation negates the positive effect of elevated atmospheric carbon dioxide concentration on wheat productivity and fertilizer nitrogen recovery

Background and purpose

Rapid increases in atmospheric carbon dioxide concentration ([CO₂]) may increase crop residue production and carbon: nitrogen (C:N) ratio. Whether the incorporation of residues produced under elevated [CO₂] will limit soil N availability and fertilizer N recovery in the plant is unknown. This study investigated the interaction between crop residue incorporation and elevated [CO₂] on the growth, grain yield and the recovery of ¹⁵N-labeled fertilizer by wheat (Triticum aestivum L. cv. Yitpi) under controlled environmental conditions.

Methods

Residue for ambient and elevated [CO₂] treatments, obtained from wheat grown previously under ambient and elevated [CO₂], respectively, was incorporated into two soils (from a cereal-legume rotation and a cereal-fallow rotation) 1 month before the sowing of wheat. At the early vegetative stage ¹⁵N-labeled granular urea (10.22 atom%) was applied at 50 kg?N ha^?1 and the wheat grown to maturity.

Results

When residue was not incorporated into the soil, elevated [CO₂] increased wheat shoot (16 %) and root biomass (41 %), grain yield (19 %), total N uptake (4 %) and grain N removal (8 %). However, the positive [CO₂] fertilization effect on these parameters was absent in the soil amended with residue. In the absence of residue, elevated [CO₂] increased fertilizer N recovery in the plant (7 %), but when residue was incorporated elevated [CO₂] decreased fertilizer N recovery.

Conclusions

A higher fertilizer application rate will be required under future elevated [CO₂] atmospheres to replenish the extra N removed in grains from cropping systems if no residue is incorporated, or to facilitate the [CO₂] fertilization effect on grain yield by overcoming N immobilization resulting from residue amendment.     

Vulnerability of riparian ecosystems to elevated CO2 and climate change in arid and semiarid western North America

Riparian ecosystems, already greatly altered by water management, land development, and biological invasion, are being further altered by increasing atmospheric CO₂ concentrations ([CO₂]) and climate change, particularly in arid and semiarid (dryland) regions. In this literature review, we (1) summarize expected changes in [CO₂], climate, hydrology, and water management in dryland western North America, (2) consider likely effects of those changes on riparian ecosystems, and (3) identify critical knowledge gaps. Temperatures in the region are rising and droughts are becoming more frequent and intense. Warmer temperatures in turn are altering river hydrology: advancing the timing of spring snow melt floods, altering flood magnitudes, and reducing summer and base flows. Direct effects of increased [CO₂] and climate change on riparian ecosystems may be similar to effects in uplands, including increased heat and water stress, altered phenology and species geographic distributions, and disrupted trophic and symbiotic interactions. Indirect effects due to climate‐driven changes in streamflow, however, may exacerbate the direct effects of warming and increase the relative importance of moisture and fluvial disturbance as drivers of riparian ecosystem response to global change. Together, climate change and climate‐driven changes in streamflow are likely to reduce abundance of dominant, native, early‐successional tree species, favor herbaceous species and both drought‐tolerant and late‐successional woody species (including many introduced species), reduce habitat quality for many riparian animals, and slow litter decomposition and nutrient cycling. Climate‐driven changes in human water demand and associated water management may intensify these effects. On some regulated rivers, however, reservoir releases could be managed to protect riparian ecosystem. Immediate research priorities include determining riparian species' environmental requirements and monitoring riparian ecosystems to allow rapid detection and response to undesirable ecological change.     

内蒙古地带性针茅植物对CO2和气候变化的适应性研究进展

收集了1992—2013年关于模拟CO2浓度升高及气候变化(温度升高、降水变化)对内蒙古地带性草原群落的5个建群种针茅植物(贝加尔针茅、本氏针茅、大针茅、克氏针茅、短花针茅)影响的实验研究结果表明,模拟CO2浓度升高、增温和增雨将提高针茅植物的光合作用和株高生长,但CO2处理时间延长会导致光合适应;温度和降雨变化将改变针茅植物的物候进程,但物种之间反应有差异;CO2浓度升高有助于针茅植物生物量增加,增温和干旱则相反,CO2浓度升高对干旱的影响具有补偿作用;干旱和涝渍胁迫将提高针茅植物植株C/N,CO2浓度升高将加剧水分胁迫下针茅植物植株C/N的增加效应,导致牧草品质下降。由于当前在适应性指标、针茅植物对气候变化协同作用的适应机理及其敏感性研究等方面存在的不足,导致目前无法全面比较各针茅植物对CO2和温度、降水变化的响应差异及其敏感性,因而无法预测未来在全球变化背景下,这几种针茅植物的动态变化及其在地理分布上的迁移替代规律。为科学应对气候变化,未来应加强内蒙古地带性针茅植物的适应性指标、针茅植物对多因子协同作用的适应机理及敏感性研究。     

The effect of elevated CO2 on photochemistry and antioxidative defence capacity in wheat depends on environmental growing conditions – A FACE study

The present study examines photosynthesis, photochemistry and low weight molecular antioxidants (ascorbic acid and glutathione) of two Triticum aestivum L. cultivars (H45 and Yitpi) in response to growth under two CO₂ concentrations (elevated CO₂, e[CO₂] vs. ambient CO₂, a[CO₂]), two sowing times (time of sowing 1, TOS1, less stressful growing conditions vs. time of sowing 2, TOS2, more stressful growing conditions) and two water treatments (rain-fed vs. irrigated). The objective was to evaluate (1) if growth under e[CO₂] will alleviate climate stresses such as higher temperature and/or limited water supply thereby reducing the need for photoprotection and concentrations of low weight molecular antioxidants and (2) cultivar-specific responses to combined climate change factors which may be useful to identify intra-specific variation in stress tolerance for future breeding. We compared gas exchange, chlorophyll fluorescence and antioxidative defence compounds (ascorbic acid, glutathione) of flag leaves of Australian Grains Free Air Carbon dioxide Enrichment (AGFACE) grown wheat. When plants were grown under the less stressful growing conditions of TOS1, e[CO₂] increased light saturated net assimilation rates (A_sat) and quantum yield of PSII electron transport (ΦPSII) but decreased thermal energy dissipation (indicated by increased efficiency of open PSII centres, Fv′/Fm′), while antioxidant concentrations did not change. Under the more stressful growing conditions of TOS2, e[CO₂] also increased A_sat (like at TOS1), however, photochemical processes were not affected while antioxidant concentrations (especially ascorbic acid) were decreased. Cultivar specific responses also varied between sowing dates: Only at TOS2 and additional irrigation, antioxidant concentrations were lower in e[CO₂] grown H45 as compared to Yitpi indicating decreased photo-oxidative pressure in H45. These results suggest a photo-protective role of e[CO₂] as well as some intra-specific variability between investigated cultivars in their stress responsiveness, all strongly modified by environmental growing conditions.     

Impact of drought and increasing temperatures on soil CO2 emissions in a Mediterranean shrubland (gariga)

In arid and semiarid shrubland ecosystems of the Mediterranean basin, soil moisture is a key factor controlling biogeochemical cycles and the release of CO₂ via soil respiration. This is influenced by increasing temperatures. We manipulated the microclimate in a Mediterranean shrubland to increase the soil and air night-time temperatures and to reduce water input from precipitation. The objective was to analyze the extent to which higher temperatures and a drier climate influence soil CO₂ emissions in the short term and on an annual basis. The microclimate was manipulated in field plots (about 25 m²) by covering the vegetation during the night (Warming treatment) and during rain events (Drought treatment). Soil CO₂ effluxes were monitored in the treatments and compared to a control over a 3-year period. Along with soil respiration measurements, we recorded soil temperature at 5 cm depth by a soil temperature probe. The seasonal pattern of soil CO₂ efflux was characterized by higher rates during the wet vegetative season and lower rates during the dry non-vegetative season (summer). The Warming treatment did not change SR fluxes at any sampling date. The Drought treatment decreased soil CO₂ emissions on only three of 10 occasions during 2004. The variation of soil respiration with temperature and soil water content did not differ significantly among the treatments, but was affected by the season. The annual CO₂ emissions were not significantly affected by the treatments. In the semi-arid Mediterranean shrubland, an increase of soil CO₂ efflux in response to a moderate increase of daily minimum temperature is unlikely, whereas less precipitation can strongly affect the soil processes mainly limited by water availability.     

Potential effects of interaction between CO2 and temperature on forest landscape response to global warming

Projected temperature increases under global warming could benefit southern tree species by providing them the optimal growing temperature and could be detrimental to northern species by exposing them to the supra optimal growing temperatures. This benefit-detriment trade-off could increase the competitive advantage of southern species in the northern species range and cause the increase or even dominance of southern species in the northern domain. However, the optimum temperature for photosynthesis of C3 plants may increase due to CO₂ enrichment. An increase in the optimum temperature could greatly reduce the benefit-detriment effect. In this study, we coupled a forest ecosystem process model (PnET-II) and a forest GAP model (LINKAGES) with a spatially dynamic forest landscape model (LANDIS-II) to study how an optimum temperature increase could affect forest landscape response due to global warming. We simulated 360 years of forest landscape change in the Boundary Water Canoe Area (BWCA) in northern Minnesota, which is transitional between boreal and temperate forest. Our results showed that, under the control scenario of continuing the historic 1984–1993 mean climate (mainly temperature, precipitation and CO₂), the BWCA will become a spruce-fir dominated boreal forest. However, under the scenario of predicted climatic change [the 2000–2099 climates are predicted by Canadian Climate Center (CCC), followed by 200 years of continuing the predicted 2090–2099 mean climate], the BWCA will become a pine-dominated mixed forest. If the optimum temperature increases gradually with [CO₂] (the increase in optimum temperature is assumed to change gradually from 0 °C in year 2000 to 5 °C in year 2099 when [CO₂] reaches 711 ppm and stabilizes at 5 °C after year 2099), the BWCA would remain a fir-dominated boreal forest in areas with relatively high water-holding capacity, but not in areas with relatively low water-holding capacity. Our results suggest that the [CO₂] induced increases in optimum temperature could substantially reduce forest landscape change caused by global warming. However, not all tree species would be able to successfully adapt to future warming as predicted by CCC, regardless of optimum temperature acclimations.     

Microenvironmental changes support evidence of photosynthesis and calcification inhibition in Halimeda under ocean acidification and warming

The effects of elevated CO₂ and temperature on photosynthesis and calcification of two important calcifying reef algae (Halimeda macroloba and Halimeda cylindracea) were investigated with O₂ microsensors and chlorophyll a fluorometry through a combination of two pCO₂ (400 and 1,200 μatm) and two temperature treatments (28 and 32 °C) equivalent to the present and predicted conditions during the 2100 austral summer. Combined exposure to pCO₂ and elevated temperature impaired calcification and photosynthesis in the two Halimeda species due to changes in the microenvironment around the algal segments and a reduction in physiological performance. There were no significant changes in controls over the 5-week experiment, but there was a 50–70 % decrease in photochemical efficiency (maximum quantum yield), a 70–80 % decrease in O₂ production and a threefold reduction in calcification rate in the elevated CO₂ and high temperature treatment. Calcification in these species is closely coupled with photosynthesis, such that a decrease in photosynthetic efficiency leads to a decrease in calcification. Although pH seems to be the main factor affecting Halimeda species, heat stress also has an impact on their photosystem II photochemical efficiency. There was a strong combined effect of elevated CO₂ and temperature in both species, where exposure to elevated CO₂ or temperature alone decreased photosynthesis and calcification, but exposure to both elevated CO₂ and temperature caused a greater decline in photosynthesis and calcification than in each stress individually. Our study shows that ocean acidification and ocean warming are drivers of calcification and photosynthesis inhibition in Halimeda. Predicted climate change scenarios for 2100 would therefore severely affect the fitness of Halimeda, which can result in a strongly reduced production of carbonate sediments on coral reefs under such changed climate conditions.     

Stomatal responses of Douglas-fir seedlings to elevated carbon dioxide and temperature during the third and fourth years of exposure

Two major components of climate change, increasing atmospheric [CO₂] and increasing temperature, may substantially alter the effects of water availability to plants through effects on the rate of water loss from leaves. We examined the interactive effects of elevated [CO₂] and temperature on seasonal patterns of stomatal conductance (g_s), transpiration (E) and instantaneous transpiration efficiency (ITE) in Douglas‐fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings. Seedlings were grown in sunlit chambers at either ambient CO₂ (AC) or ambient + 180 µmol mol^?1 CO₂ (EC), and at ambient temperature (AT) or ambient + 3·5 °C (ET) in a full‐factorial design. Needle gas exchange at the target growth conditions was measured approximately monthly over 21 months. Across the study period and across temperature treatments, growth in elevated [CO₂] decreased E by an average of 12% and increased ITE by an average of 46%. The absolute reduction of E associated with elevated [CO₂] significantly increased with seasonal increases in the needle‐to‐air vapour pressure deficit (D). Across CO₂ treatments, growth in elevated temperature increased E an average of 37%, and did not affect ITE. Combined, growth in elevated [CO₂] and elevated temperature increased E an average of 19% compared with the ACAT treatment. The CO₂ supply and growth temperature did not significantly affect stomatal sensitivity to D or the relationship between g_s and net photosynthetic rates. This study suggests that elevated [CO₂] may not completely ameliorate the effect of elevated temperature on E, and that climate change may substantially alter needle‐level water loss and water use efficiency of Douglas‐fir seedlings.     

Contrasting responses of leaf stomatal characteristics to climate change: a considerable challenge to predict carbon and water cycles

Stomata control the cycling of water and carbon between plants and the atmosphere; however, no consistent conclusions have been drawn regarding the response of stomatal frequency to climate change. Here, we conducted a meta‐analysis of 1854 globally obtained data series to determine the response of stomatal frequency to climate change, which including four plant life forms (over 900 species), at altitudes ranging from 0 to 4500 m and over a time span of more than one hundred thousand years. Stomatal frequency decreased with increasing CO₂ concentration and increased with elevated temperature and drought stress; it was also dependent on the species and experimental conditions. The response of stomatal frequency to climate change showed a trade‐off between stomatal control strategies and environmental factors, such as the CO₂ concentration, temperature, and soil water availability. Moreover, threshold effects of elevated CO₂ and temperature on stomatal frequency were detected, indicating that the response of stomatal density to increasing CO₂ concentration will decrease over the next few years. The results also suggested that the stomatal index may be more reliable than stomatal density for determination of the historic CO₂ concentration. Our findings indicate that the contrasting responses of stomata to climate change bring a considerable challenge in predicting future water and carbon cycles.     

Responses of Senna reticulata,a legume tree from the Amazonian floodplains,to elevated atmospheric CO2 concentration and waterlogging

Key message

The Amazonian tree Senna reticulata showed an increase in photosynthesis and starch content under elevated [CO ₂ ] that led an increment in biomass after 90 days. Elevated [CO ₂ ] was also capable of reducing the negative effect of waterlogging.

Abstract

Tree species from the Amazonian floodplains have to cope with low oxygen availability due to annual pulses of inundation that can last up to 7 months. Species capable of adapting to flooding and/or waterlogged conditions usually partition their storage to favor starch and allocate it to roots, where carbohydrates are used to maintain respiration rates during waterlogging. In spite of climate change, virtually nothing is known about how elevated atmospheric CO₂ concentration ([CO₂]) will affect plants when combined with waterlogging. In this work, we used open top chambers to evaluate the effect of elevated [CO₂] during a period of terrestrial phase and in subsequent combination with waterlogged conditions to determine if the surplus carbon provided by elevated [CO₂] may improve the waterlogging tolerance of the fast-growing Amazonian legume tree Senna reticulata. During the terrestrial phase, photosynthesis was ca. 28 % higher after 30, 45 and 120 days of elevated [CO₂], and starch content in the leaves was, on average, 49 % higher than with ambient [CO₂]. Total biomass was inversely correlated to the starch content of leaves, indicating that starch might be the main carbohydrate source for biomass production during the terrestrial phase. This response was more pronounced under elevated [CO₂], resulting in 30 % more biomass in comparison to ambient [CO₂] plants. After 135 days at elevated [CO₂] an inversion has been observed in total biomass accumulation, in which ambient [CO₂] presented a greater increment in total biomass in comparison to elevated [CO₂], indicating negative effects on growth after long-term CO₂ exposure. However, plants with elevated [CO₂]/waterlogged displayed a greater increment in biomass in comparison with ambient [CO₂]/waterlogged that, unlike during the terrestrial phase, was unrelated to starch reserves. We conclude that S. reticulata displays mechanisms that make this species capable of responding positively to elevated [CO₂] during the first pulse of growth. This response capacity is also associated with a “buffering effect” that prevents the plants from decreasing their biomass under waterlogged conditions.     

Interactive direct and plant‐mediated effects of elevated atmospheric [CO2] and temperature on a eucalypt‐feeding insect herbivore

Understanding the direct and indirect effects of elevated [CO₂] and temperature on insect herbivores and how these factors interact are essential to predict ecosystem‐level responses to climate change scenarios. In three concurrent glasshouse experiments, we measured both the individual and interactive effects of elevated [CO₂] and temperature on foliar quality. We also assessed the interactions between their direct and plant‐mediated effects on the development of an insect herbivore of eucalypts. Eucalyptus tereticornis saplings were grown at ambient or elevated [CO₂] (400 and 650 μmol mol^?1 respectively) and ambient or elevated ( + 4 °C) temperature for 10 months. Doratifera quadriguttata (Lepidoptera: Limacodidae) larvae were feeding directly on these trees, on their excised leaves in a separate glasshouse, or on excised field‐grown leaves within the temperature and [CO₂] controlled glasshouse. To allow insect gender to be determined and to ensure that any sex‐specific developmental differences could be distinguished from treatment effects, insect development time and consumption were measured from egg hatch to pupation. No direct [CO₂] effects on insects were observed. Elevated temperature accelerated larval development, but did not affect leaf consumption. Elevated [CO₂] and temperature independently reduced foliar quality, slowing larval development and increasing consumption. Simultaneously increasing both [CO₂] and temperature reduced these shifts in foliar quality, and negative effects on larval performance were subsequently ameliorated. Negative nutritional effects of elevated [CO₂] and temperature were also independently outweighed by the direct positive effect of elevated temperature on larvae. Rising [CO₂] and temperature are thus predicted to have interactive effects on foliar quality that affect eucalypt‐feeding insects. However, the ecological consequences of these interactions will depend on the magnitude of concurrent temperature rise and its direct effects on insect physiology and feeding behaviour.