The effect of elevated atmospheric CO2 and drought on sources and sinks of isoprene in a temperate and tropical rainforest mesocosm

Isoprene is the most abundant volatile hydrocarbon emitted by many tree species and has a major impact on tropospheric chemistry, leading to formation of pollutants and enhancing the lifetime of methane, a powerful greenhouse gas. Reliable estimates of global isoprene emission from different ecosystems demand a clear understanding of the processes of both production and consumption. Although the biochemistry of isoprene production has been studied extensively and environmental controls over its emission are relatively well known, the study of isoprene consumption in soil has been largely neglected. Here, we present results on the production and consumption of isoprene studied by measuring the following different components: (1) leaf and soil and (2) at the whole ecosystem level in two distinct enclosed ultraviolet light‐depleted mesocosms at the Biosphere 2 facility: a cottonwood plantation with trees grown at ambient and elevated atmospheric CO₂ concentrations and a tropical rainforest, under well watered and drought conditions. Consumption of isoprene by soil was observed in both systems. The isoprene sink capacity of litter‐free soil of the agriforest stands showed no significant response to different CO₂ treatments, while isoprene production was strongly depressed by elevated atmospheric CO₂ concentrations. In both mesocosms, drought suppressed the sink capacity, but the full sink capacity of dry soil was recovered within a few hours upon rewetting. We conclude that soil uptake of atmospheric isoprene is likely to be modest but significant and needs to be taken into account for a comprehensive estimate of the global isoprene budget. More studies investigating the capacity of soils to uptake isoprene in natural conditions are clearly needed.     

Rapid appearance of 13C in biogenic isoprene when 13CO2 is fed to intact leaves

Biogenic isoprene substantially affects atmospheric chemistry, but it is not known how or why many plants, especially trees, make isoprene. We fed ¹³CO₂ to leaves of Quercus rubra and monitored the incorporation of ¹³C into isoprene by mass spectrometry. After feeding ¹³CO₂ for 9 min we found all possible labelling patterns from completely unlabelled to fully labelled isoprene. By 18 min, 84% of the carbon atoms in isoprene were ¹³C. Labelling of the last 20% of the carbon atoms was much slower than labelling of the first 80%. The rate of labelling of isoprene was similar to that reported for phosphoglyceric acid indicating that there is a close linkage between the carbon source for isoprene synthesis and the photosynthetic carbon reduction pathway.     

Interactive effects of elevated CO2 and soil fertility on isoprene emissions from Quercus robur

The effects of global change on the emission rates of isoprene from plants are not clear. A factor that can influence the response of isoprene emission to elevated CO₂ concentrations is the availability of nutrients. Isoprene emission rate under standard conditions (leaf temperature: 30°C, photosynthetically active radiation (PAR): 1000 μmol photons m^?2 s^?1), photosynthesis, photosynthetic capacity, and leaf nitrogen (N) content were measured in Quercus robur grown in well‐ventilated greenhouses at ambient and elevated CO₂ (ambient plus 300 ppm) and two different soil fertilities. The results show that elevated CO₂ enhanced photosynthesis but leaf respiration rates were not affected by either the CO₂ or nutrient treatments. Isoprene emission rates and photosynthetic capacity were found to decrease with elevated CO₂, but an increase in nutrient availability had the converse effect. Leaf N content was significantly greater with increased nutrient availability, but unaffected by CO₂. Isoprene emission rates measured under these conditions were strongly correlated with photosynthetic capacity across the range of different treatments. This suggests that the effects of CO₂ and nutrient levels on allocation of carbon to isoprene production and emission under near‐saturating light largely depend on the effects on photosynthetic electron transport capacity.     

尖峰岭热带山地雨林生态系统的水文生态效应

根据尖峰岭热带山地雨林３个对比集水区的研究,天然更新４０ａ山地雨林生态系统在５￣９月份,蓄养降水资源的５１．８％;１０￣翌年２月份,补枯径流水量１４３．５ｍｍ;特大暴雨的径流响应从３２．７％￣６２．５％、随系统蓄满程度变化。集水区降雨、径流水体ＣＯＤ、氨氮、酚、Ｚｎ、Ｃｕ、Ｐｂ、Ｃｄ、Ｎｉ的浓度含量远低于地面水环境质量Ⅰ类标准;山地雨林系统对降雨中氨氮、酚、Ｐｂ、Ｃｄ、Ｚｎ浓度贮滤强度分别达２３．     

Controls on microbial CO2 production: a comparison of surface and subsurface soil horizons

Although a significant amount of the organic C stored in soil resides in subsurface horizons, the dynamics of subsurface C stores are not well understood. The objective of this study was to determine if changes in soil moisture, temperature, and nutrient levels have similar effects on the mineralization of surface (0–25 cm) and subsurface (below 25 cm) C stores. Samples were collected from a 2 m deep unsaturated mollisol profile located near Santa Barbara, CA, USA. In a series of experiments, we measured the influence of nutrient additions (N and P), soil temperature (10–35°C), and soil water potential (?0.5 to ?10 MPa) on the microbial mineralization of native soil organic C. Surface and subsurface soils were slightly different with respect to the effects of water potential on microbial CO₂ production; C mineralization rates in surface soils were more affected by conditions of moderate drought than rates in subsurface soils. With respect to the effects of soil temperature and nutrient levels on C mineralization rates, subsurface horizons were significantly more sensitive to increases in temperature or nutrient availability than surface horizons. The mean Q₁₀ value for C mineralization rates was 3.0 in surface horizons and 3.9 in subsurface horizons. The addition of either N or P had negligible effects on microbial CO₂ production in surface soil layers; in the subsurface horizons, the addition of either N or P increased CO₂ production by up to 450% relative to the control. The results of these experiments suggest that alterations of the soil environment may have different effects on CO₂ production through the profile and that the mineralization of subsurface C stores may be particularly susceptible to increases in temperature or nutrient inputs to soil.     

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。     

The effects of glacial atmospheric CO2 concentrations and climate on isoprene emissions by vascular plants

Isoprene (C₅H₈) emissions by terrestrial vegetation vary with temperature and light intensity, and play an important role in biosphere–chemistry–climate interactions. Such interactions were probably substantially modified by Pleistocene climate and CO₂ cycles. Central to understanding the nature of these modifications is assessment and analysis of how emissions changed under glacial environmental conditions. Currently, even the net direction of change is difficult to predict because a CO₂‐depleted atmosphere may have stimulated emissions compensating for the negative impacts of a cooler climate. Here, we address this issue and attempt to determine the direction of change from an experimental standpoint by investigating the interaction between isoprene emissions and plant growth of two known isoprene‐emitting herbaceous species (Mucuna pruriens and Arundo donax) grown at glacial (180 ppm) to present (366 ppm) CO₂ levels. We found a significant enhancement of isoprene emissions per unit leaf area in M. pruriens under subambient CO₂ concentrations relative to ambient controls but not for A. donax. In contrast, canopy emissions remained unaltered for both plant species because enhanced leaf emissions were offset by reductions in biomass and leaf area. Separate growth experiments with M. pruriens revealed that lowering day/night temperatures by 5°C decreased canopy isoprene emissions irrespective of the CO₂ level. Incorporation of these results into a simple canopy emissions model highlights their potential to attenuate reductions in the total isoprene flux from forests under glacial conditions predicted by standard models.     

Potential effects of elevated CO2 and changes in temperature on tropical plants

Abstract. Very little attention has been directed at the responses of tropical plants to increases in global atmospheric CO₂ concentrations and the potential climatic changes. The available data, from greenhouse and laboratory studies, indicate that the photosynthesis, growth and water use efficiency of tropical plants can increase at higher CO₂ concentrations. However, under field conditions abiotic (light, water or nutrients) or biotic (competition or herbivory) factors might limit these responses. In general, elevated atmospheric CO₂ concentrations seem to increase plant tolerance to stress, including low water availability, high or low temperature, and photoinhibition. Thus, some species may be able to extend their ranges into physically less favourable sites, and biological interactions may become relatively more important in determining the distribution and abundance of species. Tropical plants may be more narrowly adapted to prevailing temperature regimes than are temperate plants, so expected changes in temperature might be relatively more important in the tropics. Reduced transpiration due to decreased stomatal conductance could modify the effects of water stress as a cue for vegetative or reproductive phenology of plants of seasonal tropical areas. The available information suggests that changes in atmospheric CO₂ concentrations could affect processes as varied as plant/herbivore interactions, decomposition and nutrient cycling, local and geographic distributions of species and community types, and ecosystem productivity. However, data on tropical plants are few, and there seem to be no published tropical studies carried out in the field. Immediate steps should be undertaken to reduce our ignorance of this critical area.     

西双版纳热带雨林聚果榕隐头果的昆虫群落结构与多样性

聚果榕(Ficus racemasa)是西双版纳热带雨林生态系统中的一个优势种群,在聚果榕隐头果内外,形成了为聚果榕传粉、传播种子和在榕果上取食、栖息、繁衍后代的昆虫群落,在西双版纳勐仑国家自然保护区、植物园沟谷雨林、植物园江边次生林等样地内,对聚果榕隐头果中的昆虫群落结构、动态和多样性进行了研究,样地内采集到184 264号昆虫标本。隶属5个目,19个科,36属,51种;论种类和个体数量,膜翅目最为丰富,占聚果榕隐头果昆虫总数的37．3％,尤其传粉榕小蜂。种群数量在昆虫群落中占绝对优势。其传粉行为影响着聚果榕种群的构建和稳定;鳞翅目占昆虫总数的31．4％;鞘翅目、同翅目和双翅目三类仅占聚果榕隐头果昆虫总数的31．3％,3个样地的多样性指数、均匀度和种类丰富度。以勐仑国家自然保护区最高,其次是沟谷雨林保护区,再次是植物园次生林。资料分析表明,热带雨林片断化使聚果榕隐头果上的昆虫种类呈明显下降趋势,常见种个体数量增加,特有种数量减少。     

CO2浓度升高和干旱对春小麦生长和水分利用的生态效应

利用开顶式气室对春小麦进行了一个生长季的CO2倍增盆栽实验,土壤水分控制为3个水平(分别为田间持水量(FWC)的80%、60%、40%).结果显示,CO2倍增显著提高小麦的光合速率.但在相同的CO2测定浓度下, 生长在加倍CO2浓度下的小麦的光合速率比当前CO2浓度下小麦低22%.高CO2浓度显著促进小麦生长,相对增加幅度在适宜水分下最大,为14.8%.80%FWC水分条件下高CO2使植株的干重/高度比增加15.7%.高CO2条件下,小麦的蒸腾速率降低、累积耗水量减少、水分利用效率(WUE)提高,WUE的提高幅度在适宜水分下最大,为30%.干旱(40%FWC)使小麦地上干重和WUE在当前CO2条件下分别降低72%和19%,加倍CO2条件下降低幅度较大,分别为76%和23%.根据以上结果得出结论: (1) 高CO2条件下, 小麦的光合速率、地上生物量和水分利用效率提高;(2) 植物长期生长于高CO2浓度导致光合能力降低;(3) 高CO2对植物侧向生长的促进作用大于垂直生长,即高CO2下植株将相对粗壮;(4) 高CO2对植物的生态效应依赖于土壤水分,在适宜水分下相对较大;(5) 在未来高CO2条件下,干旱引起的减产和水分利用效率减低幅度将会更大.     

CO2浓度增加对长白山森林土壤甲烷氧化影响

大气CO2浓度升高可能对森林土壤的甲烷(CH4)氧化速率产生影响.本文采用开顶箱技术,对连续6年高浓度CO2(500 μmol·mol-1)处理的长白山森林典型树种蒙古栎树下土壤CH4氧化速率进行研究,并利用CH4氧化菌的16S rRNA特异性引物以及CH4单加氧酶功能基因引物分析了土壤中CH4氧化菌的群落结构与数量.结果表明:CO2浓度增高后,生长季土壤甲烷氧化量与对照和裸地相比分别降低了4％和22％;基于16S rRNA特异性引物的DGGE分析表明,CO2浓度增高导致两类甲烷氧化菌的多样性指数降低;CO2浓度增高对土壤中Ⅰ类甲烷氧化菌数量无显著影响,而使土壤中Ⅱ类甲烷氧化菌数量显著减少,功能基因pmoA拷贝数与对照和裸地相比分别降低了15％和46％.CO2浓度增高导致森林土壤甲烷氧化菌数量与活性降低,土壤含水量的增加可能是导致这一现象的主要原因.     

Impact of elevated atmospheric CO2 concentration on soil microbial biomass and activity in a complex, weedy field model ecosystem

Although soil organisms play an essential role in the cycling of elements in terrestrial ecosystems, little is known of the impact of increasing atmospheric CO₂ concentrations on soil microbial processes. We determined microbial biomass and activity in the soil of multitrophic model ecosystems housed in the Ecotron (NERC Centre for Population Biology, Ascot, UK) under two atmospheric CO₂ concentrations (ambient vs. ambient + 200 ppm). The model communities consist of four annual plant species which naturally co-occur in weedy fields and disturbed ground throughout southern England, together with their herbivores, parasitoids and soil biota. At the end of two experimental runs lasting 9 and 4.5 months, respectively, root dry weight and quality showed contradictory responses to elevated CO₂ concentrations, probably as a consequence of the different time-periods (and hence number of plant generations) in the two experiments. Despite significant root responses no differences in microbial biomass could be detected. Effects of CO₂ concentration on microbial activity were also negligible. Specific enzymes (protease and xylanase) showed a significant decrease in activity in one of the experimental runs. This could be related to the higher C:N ratio of root tissue. We compare the results with data from the literature and conclude that the response of complex communities cannot be predicted on the basis of oversimplified experimental set-ups.     

Influence of atmospheric CO2 enrichment on methane consumption in a temperate forest soil

Rates of atmospheric CH₄ consumption of soils in temperate forest were compared in plots continuously enriched with CO₂ at 200 µL L^?1 above ambient and in control plots exposed to the ambient atmosphere of 360 µL CO₂ L^?1. The purpose was to determine if ecosystem atmospheric CO₂ enrichment would alter soil microbial CH₄ consumption at the forest floor and if the effect of CO₂ would change with time or with environmental conditions. Reduced CH₄ consumption was observed in CO₂‐enriched plots relative to control plots on 46 out of 48 sampling dates, such that CO₂‐enriched plots showed annual reductions in CH₄ consumption of 16% in 1998 and 30% in 1999. No significant differences were observed in soil moisture, temperature, pH, inorganic‐N or rates of N‐mineralization between CO₂‐enriched and control plots, indicating that differences in CH₄ consumption between treatments were likely the result of changes in the composition or size of the CH₄‐oxidizing microbial community. A repeated measures analysis of variance that included soil moisture, soil temperature (from 0 to 30 cm), and time as covariates indicated that the reduction of CH₄ consumption under elevated CO₂ was enhanced at higher soil temperatures. Additionally, the effect of elevated CO₂ on CH₄ consumption increased with time during the two‐year study. Overall, these data suggest that rising atmospheric CO₂ will reduce atmospheric CH₄ consumption in temperate forests and that the effect will be greater in warmer climates. A 30% reduction in atmospheric CH₄ consumption by temperate forest soils in response to rising atmospheric CO₂ will result in a 10% reduction in the sink strength of temperate forest soils in the atmospheric CH₄ budget and a positive feedback to the greenhouse effect.     

水分胁迫对冬小麦叶片CO2／H2O交换参数的影响

Changes of CO2/H2O exchange parameters were continually measuredin winter wheat under different water stress stages.The results showed that photosynthesis rate and transpiration rate of winter wheat in water stress conditions were obviously lower than that in non-stress conditions.After water stress,both of them slowly increased and even overtook that on sufficient irrigation treatment. Responses of winter wheat to water stress in different growth stages were different.To some extent, water stress can improve crop water use efficiency,speed up the process of milking.Under water stress condition,stomatal conductance limited diurnal changes of photosynthesis and transpiration in the morning but not in the afternoon.Transpiration is more sensitive to water stress than photosynthesis.     

水分胁迫对冬小麦叶片CO_2/H_2O交换参数的影响

水资源严重匮乏已成为华北平原农业可持续发展的主要障碍因素 [1] ,提高有限水资源的利用效率显得十分重要。以前的研究主要注重农田水平作物与水分的关系 [2 ,4 ] ,利用作物生物学进行节水研究不够 [3,4 ] 。Roa等人认为作物适度的水分亏缺可获得高产 [15] ;Jensen等人认为适度水分胁迫甚至能使作物水分利用效率显著提高 [5,6] ,依此发展了调亏灌溉思想 ,对有限水量在作物生育期内时空最优分配制度进行研究 ,目前已为世界各国广泛关注 [6] 。作物 CO2 /H2 O交换参数包括光合速率、蒸腾速率、水分利用效率等 ,这些是确定作物水分高效利用…     

加气灌溉对不同施氮水平的设施甜瓜土壤CO2和N2O排放的影响

为探讨不同加气灌溉施氮模式下设施甜瓜土壤CO₂和N₂O排放的动态变化规律及其与土壤温度、湿度的关系,本研究采用密闭静态箱-气相色谱法对加气灌溉不同施氮水平下土壤CO₂和N₂O排放进行监测,并分析了加气灌溉对不同施氮量下土壤CO₂和N₂O排放的影响.试验采用加气灌溉(AI)和不加气灌溉(CK)两种灌溉方式,施氮量设不施氮(N₁)、传统施氮量的2/3(150 kg·hm^-2,N₂)和传统施氮量(225 kg·hm^-2,N₃)3个施氮水平.结果表明:加气灌溉土壤CO₂和N₂O排放量高于不加气灌溉处理,但是差异不显著;相同灌溉模式下,CO₂和N₂O排放量随施氮量的增加而显著增加,施氮量是土壤CO₂和N₂O排放的主要影响因素.加气灌溉条件下,不同施氮处理N₂O排放通量与土壤温度和湿度呈显著正相关,CO₂排放通量与土壤温度呈显著正相关.加气减氮处理在氮肥减少1/3的情况下,甜瓜产量提高了6.9%,温室气体排放引起的增温潜势值从9544.82 kg·hm^-2下降到9340.72 kg·hm^-2.综上,通过加气灌溉减少氮肥施用量来抑制农业生产系统中温室气体排放是可行的.     

Effects of elevated atmospheric CO2 concentration on C and N pools and rhizosphere processes in a Florida scrub oak community

The effect of elevated atmospheric CO₂ concentration (C_a) on soil carbon and nitrogen accumulation and soil microbial biomass and activity in a native Florida scrub oak community was studied. The plant community, dominated by Quercus myrtifolia Willd. and Q. geminata Small, was exposed for 2 years to elevated C_a in open‐top chambers. Buried subsoil bags were retrieved after 1 year of exposure to elevated C_a. In addition, soil cores were taken twice from the chambers within two weeks in July 1998 (the first after a long dry spell and the second after 25 mm of rainfall) and divided into rhizosphere and bulk soil. Soil organic matter accumulation (excluding roots) into the buried subsoil bags was lower in elevated than in ambient C_a. Concentrations of soluble carbon and ninhydrin‐reactive nitrogen (N_ninh) in the rhizosphere soil were reduced by elevated C_a for the first sampling date and unaffected for the second sampling date. Microbial activity, measured as fluorescein diacetate (FDA) hydrolysis, decreased in elevated C_a for the first sampling date. Microbial biomass carbon and nitrogen in the bulk soil were unaffected by elevated C_a. There was no effect of elevated C_a on bacterial numbers in the rhizosphere.     

CO2浓度升高和干旱对春小麦生长和水分利用的生态效应

利用开顶式气室对春小麦进行了一个生长季的CO2倍增盆栽实验,土壤水分控制为3个水平（分别为田间持水量（FWC）的80％,60％,40％）。结果显示,CO2倍增显提高小麦的光合速率。但在相同的CO2测定浓度下,生长在加倍CO2浓度下的小麦的光合速率比当前CO2浓度下小麦低22％。高CO2浓度显促进小麦生长,相对增加幅度在适宜水分下最大为14．8％。80％FWC水分条件下高CO2使植株的干重／高度比增加15．7％,高CO2条件下,小麦的蒸腾速率降低,累积耗水量减少,水分利用效率（WUE）提高,WUE的提高幅度在适宜水分下最大,为30％。干旱（40％FWC）使小麦地上干重和WUE在当前CO2条件下分别降低72％和19％,加倍CO2条件下降低幅度较大,分别为76％和23％。根据以上结果得出结论：（1）高CO2条件下,小麦的光合速率,地上生物量和水分利用效率提高;（2）植物长期生长于高CO2浓度导致光合能力降低;（3）高CO2对植物侧向生长的促进作用大于垂直生长,即高CO2下植株将相对粗壮;（4）高CO2对植物的生态效应依赖于土壤水分,在适宜水分下相对较大;（4）在未来高CO2条件下,干旱引起的减产和水分利用效率减低幅度将会更大。