全球气候变化对陆地植物碳氮磷生态化学计量学特征的影响

全球气候变化背景下生物地球化学循环的响应规律和陆地植物适应对策已受到广泛关注.本文在分析气候变暖和降水变化对不同生态系统植物C∶N∶P的影响、CO₂浓度升高对不同光合途径物种元素的影响,以及氮沉降对土壤 植物元素影响的短期和长期效应等基础上,从植物生理特性和土壤有效营养元素变化等方面揭示了其可能存在的内在机理,以期为研究C、N、P化学元素在土壤 植物之间传递与调节机制、陆地生态系统结构和功能,以及生物地球化学元素循环对气候变化的响应提供理论依据.最后提出了该领域研究中存在的问题及对今后研究的展望.     

Influence of multiple global change drivers on terrestrial carbon storage: additive effects are common

The interactive effects of multiple global change drivers on terrestrial carbon (C) storage remain poorly understood. Here, we synthesise data from 633 published studies to show how the interactive effects of multiple drivers are generally additive (i.e. not differing from the sum of their individual effects) rather than synergistic or antagonistic. We further show that (1) elevated CO₂, warming, N addition, P addition and increased rainfall, all exerted positive individual effects on plant C pools at both single‐plant and plant‐community levels; (2) plant C pool responses to individual or combined effects of multiple drivers are seldom scale‐dependent (i.e. not differing from single‐plant to plant‐community levels) and (3) soil and microbial biomass C pools are significantly less sensitive than plant C pools to individual or combined effects. We provide a quantitative basis for integrating additive effects of multiple global change drivers into future assessments of the C storage ability of terrestrial ecosystems.     

哀牢山中山湿性常绿阔叶林两种优势幼苗C、N、P化学计量特征及其对N沉降增加的响应

N沉降对不同森林生态系统的影响是当今全球变化生态学研究的一个热点问题。山地湿性常绿阔叶林是我国西部高海拔地区重要的森林植被类型之一。该文以云南哀牢山中山湿性常绿阔叶林为对象, 研究了其林下优势树种多花山矾(Symplocos ramosissima)和黄心树(Machilus gamblei)幼苗不同器官中C、N、P含量和生态化学计量特征及其对N沉降增加的响应。结果表明: 两种幼苗C、N、P含量的差异均达到了显著性水平(p < 0.05), 多花山矾的C含量较低, N和P含量较高。N处理对植物幼苗元素含量及其比值影响极显著(p < 0.01), 且与物种和器官之间存在显著的交互作用。N处理提高了幼苗体内N含量, 导致不同器官N:P值有不同程度的增加。随N处理水平的升高, 多花山矾幼苗P含量下降, 黄心树幼苗P含量整体升高, 幼苗间P含量差异减小。在一定范围内, 植物幼苗N含量与土壤无机N含量之间存在极显著的相关性(p < 0.01)。不同器官之间相比, 植物幼苗根和茎的N内稳性比叶片更高, 即植物叶片对N沉降的响应更为敏感。     

氮添加对荒漠草原植物群落组成与微生物生物量生态化学计量特征的影响

大气氮(N)沉降增加加速了土壤N循环, 引起微生物生物量碳(C):N:磷(P)生态化学计量关系失衡、植物种丧失和生态系统服务功能降低等问题。开展N添加下植物群落组成与微生物生物量生态化学计量特征关系的研究, 可为深入了解N沉降增加引起植物多样性降低的机理提供新思路。该文以宁夏荒漠草原为研究对象, 探讨了N添加下植物生物量和群落多样性的变化趋势, 分析了微生物生物量C:N:P生态化学计量特征独立及其与其他土壤因子共同对植物群落组成的影响。结果表明: N添加下猪毛菜(Salsola collina)生物量呈显著增加趋势, 牛枝子(Lespedeza potaninii)生物量呈逐渐降低趋势, 其他植物种生物量亦呈降低趋势但未达到显著水平; 沿N添加梯度, Shannon-Wiener多样性指数、Simpson优势度指数和Patrick丰富度指数均呈先略有增加后逐渐降低的趋势; N添加提高了微生物生物量N含量和N:P, 降低了微生物生物量C:N; 植物群落组成与微生物生物量N含量、微生物生物量C:N、微生物生物量N:P、土壤NO₃ ^--N浓度、土壤NH₄ ⁺-N浓度以及土壤全P含量有较强的相关关系; 微生物生物量C:N:P生态化学计量特征对植物种群生物量和群落多样性变化的独立解释力较弱, 但却与其他土壤因子共同解释了较大变差, 意味着N添加下微生物生物量C:N:P生态化学计量特征对植物群落组成的影响与其他土壤因子高度相关。     

放牧对全球草地生态系统碳氮磷化学计量特征影响的Meta分析

为明确全球尺度下放牧管理措施对草地生态系统碳(C)、氮(N)、磷(P)化学计量特征的影响,提高草地生态系统管理水平,本研究选取国内外83篇中英文文献进行Meta分析,并通过亚组分析探讨了放牧家畜组合(羊单牧、牛单牧和牛羊混牧)和放牧强度(轻度、中度、重度)对草地生态系统叶片、凋落物、根系,以及土壤C、N、P化学计量特征的影响。结果表明: 放牧会显著降低叶片和凋落物C含量、C/N、C/P,增加N、P含量及N/P;显著降低根系和土壤C、N含量,C/P和N/P,增加P含量和C/N。叶片、凋落物化学计量特征变化对牛、羊单独放牧响应更为明显,而根系、土壤化学计量特征变化则对混牧响应更为明显,重度放牧会对草地生态系统化学计量特征产生更大的影响。放牧会降低土壤N含量,增加P含量,表明放牧对草地N、P含量的影响路径不同。进一步研究N、P含量变化对放牧活动不平衡响应机制,将放牧方式、强度的影响纳入草地生态系统预测、管理模型,能够有效提高草地生态系统管理水平。     

Silicon supply modifies C:N:P stoichiometry and growth of Phragmites australis

Silicon is a non-essential element for plant growth. Nevertheless, it affects plant stress resistance and in some plants, such as grasses, it may substitute carbon (C) compounds in cell walls, thereby influencing C allocation patterns and biomass production. How variation in silicon supply over a narrow range affects nitrogen (N) and phosphorus (P) uptake by plants has also been investigated in some detail. However, little is known about effects on the stoichiometric relationships between C, N and P when silicon supply varies over a broader range. Here, we assessed the effect of silicon on aboveground biomass production and C:N:P stoichiometry of common reed, Phragmites australis, in a pot experiment in which three widely differing levels of silicon were supplied. Scanning electron microscopy (SEM) showed that elevated silicon supply promoted silica deposition in the epidermis of Phragmites leaves. This resulted in altered N:P ratios, whereas C:N ratios changed only slightly. Plant growth was slightly (but not significantly) enhanced at intermediate silicon supply levels but significantly decreased at high levels. These findings point to the potential of silicon to impact plant growth and elemental stoichiometry and, by extension, to affect biogeochemical cycles in ecosystems dominated by Phragmites and other grasses and sedges.     

Patterns and potential drivers of intraspecific variability in the body C,N, and P composition of a terrestrial consumer,the snowshoe hare (Lepus americanus)

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Interactive effects of global change factors on soil respiration and its components: a meta‐analysis

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.     

Climate warming interacts with other global change drivers to influence plant phenology: A meta-analysis of experimental studies

Shifts in plant phenology influence ecosystem structures and functions, yet how multiple global change drivers interact to affect phenology remains elusive. We conducted a meta-analysis of 242 published articles to assess interactions between warming (W) and other global change drivers including nitrogen addition (N), increased precipitation (IP), decreased precipitation (DP) and elevated CO₂ (eCO₂) on multiple phenophases in experimental studies. We show that leaf out and first flowering were most strongly affected by warming, while warming and decreased precipitation were the most pronounced drivers for leaf colouring. Moreover, interactions between warming and other global change drivers were common and both synergistic and antagonistic interactions were observed: interactions W + IP and W + eCO₂ were frequently synergistic, whereas interactions W + N and W + DP were mostly antagonistic. These findings demonstrate that global change drivers often affect plant phenology interactively. Incorporating the multitude of interactions into models is crucial for accurately predicting plant responses to global changes.     

Marine nitrogen: Phosphorus stoichiometry and the global N:P cycle

Nitrogen supply is often assumed to limitmarine primary production. A global analysis of totalnitrogen (N) to phosphorus (P) molar ratios shows thattotal N:P is low (<16:1) in some estuarine andcoastal ecosystems, but up to 100:1 in open oceans.This implies that elements other than N may limitmarine production, except in human impacted, estuarineor coastal ecosystems. This pattern may reconcileconflicting enrichment studies, because N additionfrequently increases phytoplankton growth where totalN:P is expected to be low, but P, Fe, or Si augmentphytoplankton growth in waters where total N:P ishigh. Comparison of total N:P stoichiometry betweenmarine and freshwaters yields a model of the form ofthe aquatic N:P cycle.     

陆地生态系统植被氮磷化学计量研究进展

因化学功能的耦合和元素的不可替代性, 植物对N、P的需求和利用存在严格的比例。植物N、P化学计量在不同功能群、生长地区、生长季、器官之间以及环境梯度下存在明显的变化规律。多数研究从N、P浓度、N:P及N、P间异速指数等角度分析了植物化学计量变化规律, 并探讨其在全球范围内的具体数值。为增进对植物响应全球变化的理解, 该文综述了N、P化学计量的影响因素及其机理的最新研究进展, 并指出未来拟重点研究的方向。     

全球环境变化对森林凋落物分解的影响

全球环境变化将对森林生态系统凋落物的分解和养分循环产生直接和间接的多重影响.就全球环境变化如全球变暖、大气CO2浓度升高、UV-B辐射增强、氮沉降等对凋落物分解影响的研究进展进行了综合述评.影响凋落物分解的内部因素为凋落物基质质量,外部因素包括生物因素(微生物和动物)和非生物因素(温度、水分和土壤性质等).全球变暖对凋落物分解的非生物作用有正效应,也有负效应.全球变暖对凋落物化学组成虽然只有轻微的影响,但可以通过影响植被的物种组成来间接改变凋落物的产量、化学性质和分解.全球变暖对凋落物分解生物作用的主要影响是增强土壤微生物活性,从而加速凋落物的分解.CO2浓度上升将增加凋落物产量,并通过影响凋落物质量(提高C/N比、木质素/N比等)和生物环境(微生物的数量和活性)而影响分解过程.UV-B辐射和大气N沉降的增加亦对凋落物分解产生直接和间接的影响,但影响效果尚不很清楚,有待进一步的研究.总起来看,全球环境变化将通过影响凋落物的分解速率而对全球碳循环产生重要影响,但由于气候变化和凋落物分解响应的复杂性以及各因子之间的相互作用,气候变化对凋落物分解的总效应尚需更深入的研究来定量化.     

Root dynamics and global change: seeking an ecosystem perspective

Changes in the production and turnover of roots in forests and grasslands in response to rising atmospheric CO₂ concentrations, elevated temperatures, altered precipitation, or nitrogen deposition could be a key link between plant responses and longer-term changes in soil organic matter and ecosystem carbon balance. Here we summarize the experimental observations, ideas, and new hypotheses developed in this area in the rest of this volume. Three central questions are posed. Do elevated atmospheric CO₂, nitrogen deposition, and climatic change alter the dynamics of root production and mortality? What are the consequences of root responses to plant physiological processes? What are the implications of root dynamics to soil microbial communities and the fate of carbon in soil? Ecosystem-level observations of root production and mortality in response to global change parameters are just starting to emerge. The challenge to root biologists is to overcome the profound methodological and analytical problems and assemble a more comprehensive data set with sufficient ancillary data that differences between ecosystems can be explained. The assemblage of information reported herein on global patterns of root turnover, basic root biology that controls responses to environmental variables, and new observations of root and associated microbial responses to atmospheric and climatic change helps to sharpen our questions and stimulate new research approaches. New hypotheses have been developed to explain why responses of root turnover might differ in contrasting systems, how carbon allocation to roots is controlled, and how species differences in root chemistry might explain the ultimate fate of carbon in soil. These hypotheses and the enthusiasm for pursuing them are based on the firm belief that a deeper understanding of root dynamics is critical to describing the integrated response of ecosystems to global change.     

控雨对荒漠草原植物、微生物和土壤C、N、P化学计量特征的影响

以宁夏荒漠草原为研究对象,于2014—2015年设置了降雨量变化(减雨50%、减雨30%、自然降雨、增雨30%和增雨50%)的野外模拟试验,测定了植物、微生物和土壤C、N、P含量,同时调查了植物群落组成和土壤含水量等指标,研究了各组分C、N、P化学计量特征对连续两年降雨量变化的响应,分析了土壤C∶N∶P和含水量分别与植物生长、养分利用以及微生物量积累的相关性。结果表明,控雨改变了植物叶片C∶N∶P,且其影响程度随物种不同而异:减雨50%提高了牛枝子(Lespedeza potanimill)绿叶N和P以及猪毛蒿(Artemisia scoparia)绿叶P摄取能力,增雨(30%和50%)降低了猪毛蒿绿叶N摄取能力。增雨提高了猪毛蒿绿叶C∶N,增雨30%提高了苦豆子(Sophora alopecuroides)绿叶C∶N。增雨降低了猪毛蒿绿叶N∶P,增雨30%降低了白草(Pennisetum centrasiaticum)绿叶N∶P。相比之下,控雨条件下枯叶C∶N∶P的变化幅度较小;随降雨量增加微生物量C、N以及C∶N逐渐增加,但增雨50%使微生物量C和C∶N降低;控雨对土壤C∶N∶P的影响较小,但增雨提高了土壤水分有效性,因此促进了植物和微生物生长;试验期内,相对稳定的土壤C∶N∶P不能很好地指示植物和微生物生长发育的养分受限状况;干旱时提高叶片养分摄取、湿润时增强叶片养分回收,可能解释了牛枝子对降雨量变化的弹性适应能力。     

Climate change and freshwater ecosystems: impacts across multiple levels of organization

Fresh waters are particularly vulnerable to climate change because (i) many species within these fragmented habitats have limited abilities to disperse as the environment changes; (ii) water temperature and availability are climate-dependent; and (iii) many systems are already exposed to numerous anthropogenic stressors. Most climate change studies to date have focused on individuals or species populations, rather than the higher levels of organization (i.e. communities, food webs, ecosystems). We propose that an understanding of the connections between these different levels, which are all ultimately based on individuals, can help to develop a more coherent theoretical framework based on metabolic scaling, foraging theory and ecological stoichiometry, to predict the ecological consequences of climate change. For instance, individual basal metabolic rate scales with body size (which also constrains food web structure and dynamics) and temperature (which determines many ecosystem processes and key aspects of foraging behaviour). In addition, increasing atmospheric CO₂ is predicted to alter molar CNP ratios of detrital inputs, which could lead to profound shifts in the stoichiometry of elemental fluxes between consumers and resources at the base of the food web. The different components of climate change (e.g. temperature, hydrology and atmospheric composition) not only affect multiple levels of biological organization, but they may also interact with the many other stressors to which fresh waters are exposed, and future research needs to address these potentially important synergies.