模拟大气氮沉降对中国森林生态系统影响的研究进展

人类活动加剧了活性氮的生产和排放,并导致氮沉降日益增加并全球化。目前,人类活动对全球氮循环的干扰已经超出了地球系统安全运行的界限。中国已成为全球氮沉降的高发区域,高氮沉降已经威胁到生态系统的健康和安全,并成为生态文明建设过程中亟待理清和解决的热点问题。对国际上和中国森林生态系统模拟氮沉降研究的概况进行了综述,并从生物学和非生物学两大过程重点阐述模拟氮沉降增加对中国主要森林生态系统影响的研究进展。中国自2000年以后才开始重视大气氮沉降产生的生态环境问题,中国科学院华南植物园在国内森林生态系统模拟氮沉降试验研究上做出了开创性的贡献。模拟氮沉降研究表明,持续高氮输入将会显著改变森林生态系统的结构和功能,并威胁生态系统的健康发展,特别是处于氮沉降热点区域的中国中南部。森林生态系统的氮沉降效应依赖于系统的氮状态、土地利用历史、气候特征、林型和林龄等。最后,对未来的研究提出了一些建议,包括加强长期跟踪研究和不同气候带站点之间的联网研究,特别是在森林生态系统对长期氮沉降响应与适应的过程机制、地下碳氮吸存潜力研究、以及与其他全球变化因子的耦合研究等方面,以期为森林生态系统的可持续发展提供理论基础和管理依据。     

New perspectives on forest soil carbon and nitrogen cycling processes: Roles of arbuscular mycorrhizal versus ectomycorrhizal tree species

Nearly all tree species develop symbiotic relationships with either arbuscular mycorrhizal (AM) or ectomycorrhizal (EM) fungi to acquire nutrients from soils, and hence influence soil carbon (C) and nitrogen (N) cycles in terrestrial ecosystems. It is crucial to understand the differences in soil C and N cycles between AM and EM forests and the underlying mechanisms. In this review, we first compared the differences in the soil C and N cycles between AM and EM forests, and synthesized the underlying mechanisms from perspectives of the inputs, stabilization, and outputs of soil C and N in forest ecosystems. We also compared the responses of soil C and N cycles between AM and EM forests to global changes. In this field, one major research priority is comparing the structure and function (including the soil C and N cycles) between AM and EM forest ecosystems to provide theoretical basis and solid data for improving forest productivity and ecosystem services. The second research focus is deepening the understanding of the effects of interactions between aboveground litter and belowground mycorrhiza and free-living microbes on soil C and N cycles to reveal the potential underlying mechanisms in forests with different mycorrhizal symbioses. Third, the research methodology and new techniques need refining and applying to explicitly focus on scaling up the fine-scale measurements to better expound and predict the C and N cycles in forest ecosystems. Finally, more studies on the stability of soil organic matter among different mycorrhizal forests are needed to precisely assess responses of the structure and function of forest ecosystems to global changes.     

Response and adaptation of terrestrial ecosystem processes to climate warming

陆地生态系统包含一系列时空连续、尺度多元且互相联系的生态学过程。由于大部分生态学过程都受到温度调控, 因此气候变暖会对全球陆地生态系统产生深远的影响。近年来, 全球变化生态学的基本科学问题之一是陆地生态系统的关键过程如何响应与适应全球气候变暖。围绕该问题, 该文梳理了近年来的研究进展, 重点关注植物生理生态过程、物候期、群落动态、生产力及其分配、凋落物与土壤有机质分解、养分循环等过程对温度升高的响应与适应机理。通过定量分析近20年来发表于主流期刊的相关论文, 展望了该领域的前沿方向, 包括物种性状对生态系统过程的预测能力, 生物地球化学循环的耦合过程, 极端高温与低温事件的响应与适应机理, 不对称气候变暖的影响机理和基于过程的生态系统模拟预测等。基于这些研究进展, 该文建议进一步研究陆地生态系统如何适应气候变暖, 更多关注我国的特色生态系统类型, 并整合实验、观测或模型等研究手段开展跨尺度的合作研究。     

A review on the effects of nitrogen and phosphorus addition on tree growth and productivity in forest ecosystems

Nitrogen (N) and phosphorus (P) inputs induced by anthropogenic activities and atmospheric N and P deposition have largely increased the availability of soil N and P in terrestrial ecosystems, which have considerably affected terrestrial carbon cycling processes. Tree growth and productivity in forest ecosystems play an important role in global carbon cycling, and determine the magnitude and direction of terrestrial carbon sequestration. Currently, a large number of field manipulation experiments have been conducted to investigate the effects of N and/or P addition on tree growth and forest productivity, but the results from these studies were inconsistent. Such inconsistent results might be affected by multiple factors, including biological, environmental and experimental variables. Here, we reviewed the present research status of the effects of N and P addition on tree growth and forest productivity in forest ecosystems based on three aspects, including the number of publications and experiments with field N and P addition, and the global distributions of these experiments. Then, we summarized the methods for assessing tree growth and forest productivity at ecosystem level in forest ecosystems, including relative growth rate and absolute increment. According to the related results, we reviewed the regulating factors that affect tree growth and productivity, and the potential mechanisms for such factors, including climate, tree size and stand age, plant functional traits (including type of tree-associated mycorrhizal fungi, N-fixation property of trees, and conservative and acquisitive functional traits), plant-microbe interaction, ambient nutrient (i.e., N and P) deposition rate, and experimental variables. Finally, we summarized the current studies, and pointed out five aspects that are urgently needed to provide further insights in future studies, including the physiological mechanism of how tree growth responds to N and P addition, the tradeoff and allocation among growth of various parts of tree under N and P addition, the role of plant functional traits in regulating and predicting the responses of tree growth to N and P addition, how the competition among trees regulates the responses of tree growth to N and P addition, and conducting long-term and coordinated distributed field experiments investigating the effects of N and P addition on tree growth and forest productivity at the global scale.     

Global change and ecosystems research progress and prospect

全球变化与生态系统研究是一个宏观与微观相互交叉、多学科相互渗透的前沿科学领域, 重点研究生态系统结构和功能对全球变化的响应及反馈作用, 其目标是实现人类对生态系统服务的可持续利用。《植物生态学报》的《全球变化与生态系统》专辑在对国内外全球变化研究进行历史回顾和综合分析的基础上, 总结了全球变化与生态系统研究的阶段性重大进展及存在的主要问题, 并对全球变化研究的前沿方向进行展望和建议。根据研究内容和对象, 该专辑系统地综述了不同全球变化因子, 包括CO₂和O₃浓度升高、气候变暖、降水格局改变、氮沉降增加、土地利用变化等对陆地植物生理生态、群落结构及生态系统功能等的影响以及全球变化对海洋生态系统的影响; 探讨生态系统关键过程以及生物多样性的变化; 在明确全球变化生态效应的基础上, 阐明这些影响对气候和环境变化的反馈机制, 为构筑全球变化的适应对策提供生态学理论基础。     

Impacts of elevated carbon dioxide concentration on terrestrial ecosystems: problems and prospective

理解生态系统对过去、现在和未来CO₂浓度变化的响应,对于在生态进化的时间尺度上认识和预测全球变化的后果至关重要。过去三十多年来CO₂浓度升高相关的科学问题主要集中在对植物生长和生产力的影响, 碳氮周转, 生态系统渐进式氮限制(PNL)形成, 与其他胁迫因子(O₃污染、氮沉降、升温、干旱)之间的交互作用等方面。尽管生态学家在数据累积、基础理论上取得了一定进展, 但是仍然存在较大不确定性和大量未知有待解决。该文探究了近30年来CO₂浓度升高对陆地生态系统影响研究的国际研究进展、重点领域及热点, 回顾了CO₂浓度升高对植物影响的模拟实验研究发展, 重点论述了CO₂浓度升高对粮食产量及品质、碳固定、水分利用效率、生态系统氮利用和土壤微生物响应等国际前沿动态研究中存在的主要问题与不足, 在此基础上展望了未来研究中值得关注的前沿研究方向。     

水分再分配对土壤-植物系统养分循环的生态意义

水分再分配(hydraulic redistribution, HR)作为一个普遍存在的生物物理过程, 在缓解植物干旱胁迫、调节植物种间关系和群落组成、影响生态系统水碳平衡等方面具有重要的生态意义。近年来, 同位素标记示踪技术的应用促进了HR的深入研究, 该文综述了HR对土壤-植被系统养分循环的影响。HR能改善干燥土层的水分状况, 防止根系栓塞, 促进细根存活与生长, 提高微生物活性, 从而促进植物对表层土壤养分(尤其是氮)的吸收; HR还通过水分下传作用促进植物对深层土壤中磷和金属离子的吸收。HR促进土壤养分库的上下交换与流动, 调节植物与土壤的氮磷比, 因此其影响可能具有全球意义。在全球变化(如氮沉降)背景下, 有必要深入探索HR在生物地球化学循环过程中的影响和作用, 并将其纳入生态系统模型中。     

Mapping global soil acidification under N deposition

Soil pH is critically important in regulating soil nutrients and thus influencing the biodiversity and ecosystem functions of terrestrial ecosystems. Despite the ongoing threat of nitrogen (N) pollution especially in the fast-developing regions, it remains unclear how increasing N deposition affects soil pH across global terrestrial ecosystems. By conducting a global meta-analysis with paired observations of soil pH under N addition and control from 634 studies spanning major types of terrestrial ecosystems, we show that soil acidification increases rapidly with N addition amount and is most severe in neutral-pH soils. Grassland soil pH decreases most strongly under high N addition while wetlands are the least acidified. By extrapolating these relationships to global mapping, we reveal that atmospheric N deposition leads to a global average soil pH decline of −0.16 in the past 40 years and regions encompassing Eastern United States, Southern Brazil, Europe, and South and East Asia are the hotspots of soil acidification under N deposition. Our results highlight that anthropogenically amplified atmospheric N deposition has profoundly altered global soil pH and chemistry. They suggest that atmospheric N deposition is a major threat to global terrestrial biodiversity and ecosystem functions.     

Advances in the effect of nitrogen deposition on grassland litter decomposition

Atmospheric nitrogen deposition has increased in the last several decades due to anthropogenic activities and global changes. Increasing nitrogen deposition has become an important factor regulating carbon cycle in grassland ecosystems. Litter decomposition, a key process of carbon and nutrient cycling in terrestrial ecosystems, is the main source of soil carbon pool and the basis of soil fertility maintenance. Elevated nitrogen deposition could affect litter decomposition by raising soil nitrogen availability, increasing the quantity and quality of litter inputs, and altering soil microorganism and soil conditions. Litter decomposition are complex biological, physical and chemical processes, which were affected by abiotic, biological factors and their interactions. The effects of nitrogen deposition on litter decomposition and the underlying mechanisms were discussed in this paper, including the aspactes of soil nitrogen availability, litter production, litter quality, microclimate, soil microorganism and enzyme activities. The main research contents, directions, methods and existing problems of litter decomposition in grasslands were discussed. We also discussed the prospect of future directions to study the interaction and feedback between nitrogen deposition and grassland ecosystem carbon cycling process.     

土壤微生物对气候变暖和大气N沉降的响应

气候变暖和大气N沉降是近一、二十年来人们非常关注的全球变化现象,它们所带来的一系列生态问题已成为全球变化研究的重要议题。它们不仅影响地上植被生长和群落组成,还直接或间接地影响土壤微生物过程,而土壤微生物对此做出的响应正是生态系统反馈过程中非常重要的环节。该文分别从气候变化对土壤微生物的影响(土壤微生物量、微生物活动和微生物群落结构)和土壤微生物对气候变化的响应(凋落物分解、养分利用与循环以及养分的固持与流失)两个角度,综述近期土壤微生物对气候变暖和大气N沉降响应与适应的研究进展。气候变暖和大气N沉降对土壤微生物的影响更多地反映在微生物群落的结构和功能上,而土壤微生物量、微生物活动和群落结构的变化又会通过改变凋落物分解、养分利用和C、N循环等重要的土壤生态系统功能和过程做出响应,形成正向或负向反馈,加强或削弱气候变化给整个陆地生态系统带来的影响。然而,到目前为止土壤微生物的响应对陆地生态系统产生的最终结果仍是未决的关键性问题。     

大气氮沉降影响草地植物物种多样性机制研究综述

大气氮沉降对草地生态系统结构和功能的影响已成为全球变化生物学研究重点。大气氮沉降导致草地群落物种多样性降低已成为全球普遍现象,但其生物学机制还不清楚,因此有必要系统梳理大气氮沉降对全球不同草地生态系统的研究结果,以便在氮沉降背景下为我国草地生态系统的研究和管理制定科学决策。系统综述了氮沉降降低草地群落物种多样性的可能机制,主要包括资源竞争排斥、群落更新限制、土壤酸化及其离子毒害、养分失衡、氮素本身的毒害、次生胁迫。氮沉降导致草地物种多样性降低是多种机制综合作用的结果,每种机制在不同时空具有不同的相对贡献。同时,与欧洲酸性土壤草地和美国高草草原相比,我国草地土壤类型和植被属性具有明显差异。因此,应根据我国草地生态系统的特征、不同植物功能利用养分策略,从土壤养分变化、根系养分吸收转运、叶片生理过程等方面的整合研究思路,探讨氮沉降影响我国草地群落物种多样性的生物学机制,为我国草地生态系统的科学管理提供理论依据。     

Ecological ramifications of the direct foliar uptake of nitrogen

The foliar incorporation of various reactive forms of nitrogen (N) has been identified and studied for nearly 30 years. However, the ecosystem-level ramifications of this uptake pathway have only recently been considered by the scientific community. In this review, I present our current understanding of the foliar uptake process and then discuss why this pathway of N addition to ecosystems should be considered separately from the bulk deposition of N to the soil surface. Direct foliar uptake is a direct addition of N to plant metabolism and could potentially more readily influence plant growth compared to soil-deposited N. Current ecosystem process models do not partition reactive N between foliar and soil entry pathways and the influence of N deposition on ecosystem C sequestration is likely inadequately represented in most models. I also outline several research priorities for the future understanding of the ecological consequences of foliar uptake of reactive N.     

Changes of the relationships between soil and microbes in carbon,nitrogen and phosphorus stoichiometry during ecosystem succession

AimsThe carbon (C), nitrogen (N) and phosphorus (P) stoichiometry (C:N:P) of soil profoundly influences the growth, community structure, biomass C:N:P stoichiometry, and metabolism in microbes. However, the relationships between soil and microbes in the C:N:P stoichiometry and their temporal dynamics during ecosystem succession are poorly understood. The aim of this study was to determine the temporal patterns of soil and microbial C:N:P stoichiometry and their relationships during ecosystem succession.MethodsAn extensive literature search was conducted and data were compiled for 19 age sequences of successional ecosystems, including 13 forest ecosystems and 6 grassland ecosystems, from 18 studies published up to May 2016. Meta-analyses were performed to examine the sequential changes in 18 variables that were associated with soil and microbial C, N and P contents and the stoichiometry. Important findings (1) There was no consistent temporal pattern in soil C:N along the successional stages, whereas the soil C:P and N:P increased with succession; the slopes of the linear relationships between soil C:N:P stoichiometry and successional age were negatively correlated with the initial content of the soil organic C within given chronosequence. (2) There was no consistent temporal pattern in microbial C:N:P stoichiometry along the successional stages. (3) The fraction of microbial biomass C in soil organic C (qMBC), the fraction of microbial biomass N in soil total N, and the fraction of microbial biomass P in soil total P all increased significantly with succession, in consistency with the theory of succession that ecosystem biomass per unit resource increases with succession. (4) The qMBC decreased with increases in the values of soil C:N, C:P, or N:P, as well as the stoichiometric imbalances in C:N, C:P, and N:P between soil and microbes (i.e., ratios of soil C:N, C:P, and N:P to microbial biomass C:N, C:P, and N:P, respectively). The C:N, C:P, and N:P stoichiometric imbalances explained 37%-57% variations in the qMBC, about 7-17 times more than that explainable by the successional age, illustrating the importance of soil-microbial C:N:P stoichiometry in shaping the successional dynamics in qMBC. In summary, our study highlights the importance of the theories of ecosystem succession and stoichiometry in soil microbial studies, and suggests that appropriately applying macro-ecological theories in microbial studies may improve our understanding on microbial ecological processes.     

Effects of extreme drought on terrestrial ecosystems: review and prospects

作为地球表层重要的组成部分, 陆地生态系统是人类生存和发展的重要场所。进入21世纪以来, 气候变化导致干旱事件发生的强度、频度和持续时间显著增加, 对陆地生态系统带来深远的影响, 严重制约甚至威胁人类社会的可持续发展。因此, 开展极端干旱对陆地生态系统影响的研究并评估其生态风险效应, 是当前全球变化领域研究的重点问题。该文从植物生理生态过程、生物地球化学循环、生物多样性以及生态系统结构和功能4个方面综述了极端干旱对陆地生态系统的影响, 并对当前的研究热点进行探讨, 深度剖析当前研究中存在的难点问题和未来可能的发展方向, 以期为未来开展干旱对陆地生态系统影响的观测与预测研究提供参考, 为在未来干旱影响下加强陆地生态系统风险评估和管理提供新思路。     

Effects of exotic plant invasion on soil nitrogen availability

外来植物入侵对土壤氮循环和氮有效性的影响是入侵成功或进一步加剧的重要原因。通过对比相同研究地点入侵区域和无入侵区域的土壤原位氮状态差异, 探讨了外来植物入侵对土壤氮有效性的影响程度和生理生态学机制。基于107篇相关研究文献数据的整合, 发现植物入侵区域相对于无入侵区域土壤总氮、铵态氮、硝态氮、无机氮、微生物生物量氮含量显著增加, 增幅分别为(50 ± 14)%、(60 ± 24)%、(470 ± 115)%、(69 ± 25)%、(54 ± 20)%。土壤硝态氮含量增幅较大反映硝化作用增强, 这可能增加入侵植物硝态氮利用以及喜硝植物的共存。温带地区植物入侵后土壤的硝态氮含量增幅显著高于亚热带地区。固氮植物入侵后土壤的总氮和无机氮含量增幅均显著高于非固氮植物入侵。木本和常绿植物入侵后土壤的总氮含量增幅分别高于草本和落叶植物入侵; 而土壤铵态氮含量的增幅没有显著差异且与固氮入侵植物占比无明显关系; 然而硝态氮含量的增幅普遍较高且与固氮入侵植物占比显著正相关。外来入侵植物固氮功能以及凋落物质量和数量是影响土壤氮矿化和硝化过程的关键因素。该研究为理解外来植物入侵成功和加剧的机制以及入侵植物功能性状与土壤氮动态之间的关系提供了新的见解。     

华北盐渍化草地土壤净氮矿化速率对不同水平氮添加的响应

对于养分贫瘠的盐渍化草地生态系统, 大气氮沉降如何影响土壤氮循环过程是一个目前尚未解决的问题。该研究在位于华北地区山西省右玉县境内的盐渍化草地建立了一个模拟氮沉降的试验平台, 设置8个氮添加水平, 分别为0、1、2、4、8、16、24、32 g·m^-2·a^-1 (N0、N1、N2、N4、N8、N16、N24、N32), 生长季5-9月, 每月月初以喷施的方式等量添加NH₄NO₃。从2017年5月到2019年10月, 运用顶盖PVC管法每月一次进行净氮矿化速率的测定同时计算了净氮矿化速率对不同水平氮添加的敏感性。主要结果表明: (1)高水平氮添加(N16、N24、N32)显著增加土壤无机氮库; (2)该盐渍化草地土壤氮矿化以硝化作用为主, 经过3年氮添加以后, 高氮添加(N24、N32)显著促进了土壤净硝化速率, 并且不同氮添加水平在不同的月份和年份中表现出差异性响应; (3)不同氮添加水平对土壤净氮矿化敏感性的影响在不同降水年份差异显著, 短期低水平氮添加提高了土壤净氮矿化的敏感性, 而高水平氮添加降低土壤净氮矿化敏感性; (4)盐渍化草地土壤净氮矿化速率与土壤温度和水分呈正相关关系, 与土壤pH呈负相关关系。因此, 在当前氮沉降增加的背景下, 北方盐渍化草地土壤氮矿化速率对低氮添加的敏感性较高, 结合氮沉降的特点, 未来模型预测应该同时考虑氮沉降对盐渍化草地的可能影响。     

Research progress on the effects of grazing on grassland ecosystem

全球草地占据30%左右的陆地面积, 在全球气候变化、碳氮及养分循环、保持水土、调节畜牧业生产等方面具有重要的作用。目前草地的主要利用方式之一就是放牧, 不同的牲畜种类、放牧强度、年限、历史和制度等, 会影响草地植物群落、生物多样性及土壤微生物, 进而影响草地生态系统结构、功能和过程。该文围绕放牧对草地生态系统结构、功能和过程的影响, 1)回顾了20世纪50年代到现在各个历史阶段放牧对草地生态系统影响的研究; 2)利用文献计量分析的方法, 剖析了放牧对草地影响研究的热点内容、重要区域和关键词等; 3)阐明了放牧对草地植物生长、群落特征、碳氮及养分循环、生产力及土壤质量等的各方面影响的研究进展及国内相关研究的优势及存在的主要问题和不足; 4)基于上述分析, 从草地放牧精准管理、经典假说验证、放牧和全球变化研究相结合等方面, 提出未来研究的前沿方向和优先领域。该文在系统总结放牧对草地生态系统影响的研究进展、研究优势及存在问题的基础上, 提出未来的研究应与全球变化相结合, 为我国的草地放牧生态学研究、适应性管理和可持续利用等提供科学基础。     

Responses of growth of four desert species to different N addition levels

Aims The increase in atmospheric N deposition has accelerated N cycling of ecosystems, thus altering the structure and function of ecosystems, especially in those limited by N availability. Studies on the response of plant growth to artificial N addition could provide basic data for a better understanding of how the structure of grasslands in northern China responds to increasing N deposition. Methods We investigated the seasonal dynamics of plant growth of four species after 2-year multi-level N addition in a field experiment conducted in a desert steppe of Ningxia in 2011. Plant biomass and the relative growth rate (RGR) of the studied species were measured and their relationships with C:N:P ratios of plants (community and leaf levels) and soils were analyzed. Important findings Results in 2012 showed that 2-year N addition promoted the growth of the four species and the effects were different among growth forms and were species-specific. In general, the plant biomass of the studied species was significantly correlated with leaf N concentration, leaf N:P ratio, community N pool, soil total N content and soil N:P ratio, while only weak relationships were observed between plant biomass and C:N and C:P ratios of plants and soils. In contrast, there was a significant linear relationship between RGR and N:P ratios both of plants and soils.Our results suggest that short-term N addition promoted the accumulation of plant biomass, and the species-specific responses to stimulated N addition can directly affect the structure of the desert steppe ecosystem. Plant N:P ratio and soil N:P ratio could indicate nutrient limitation of plant growth to a certain extent: N addition increased soil N content and N:P ratio, and thus relieved N limitation gradually. Once more N is available to plants, the growth of plants and the accumulation of community N was stimulated in turn.     

氮添加对森林植物磷含量的影响及其机制

氮沉降对森林生态系统磷循环产生了不可忽视的影响, 尤其是加剧了植物生长的磷限制, 从而使得氮沉降背景下植物磷含量变化备受关注。该文综述了氮添加对森林植物磷含量的影响, 认为氮添加通过促进土壤磷酸酶活性进而提高土壤有效磷含量, 有利于植物的磷吸收并增加植物磷含量。同时, 森林植物磷含量对氮添加的响应还受物种、生活型以及施氮时间长短等因素的影响。基于森林植物磷含量对氮添加响应的差异性, 该文进一步探讨氮富集背景下森林植物磷含量变化的可能机制: 1)外源氮输入通过改变土壤中有效磷含量从而对植物磷的来源产生影响; 2)通过影响植物的根系分泌物、菌根共生和根系形态结构等进而影响植物的磷吸收能力; 3)通过影响植物的磷养分再分配、磷养分重吸收对植物磷利用效率产生影响。综上所述, 外源氮输入使植物磷含量发生改变, 首要原因是土壤有效磷含量的改变, 其次是植物磷吸收能力和磷利用效率的改变起调控作用。     

氮添加对中国陆地生态系统植物-土壤碳动态的影响

近年来,中国大气氮沉降水平不断增加,过量的活性氮输入深刻影响了我国陆地生态系统碳循环。虽然已有大量的研究报道了模拟氮添加实验对我国陆地生态系统碳动态的影响,但是由于复杂的地理条件和不同的施氮措施,关于植物和土壤碳库对氮添加的一般响应特征和机制仍存在广泛争议。因此,采用整合分析方法,收集整理了172篇已发表的中国野外氮添加试验结果,在全国尺度上探究氮添加对我国陆地生态系统植物和土壤碳动态的影响及其潜在机制。结果表明,氮添加显著促进了植物的碳储存,地上和地下生物量均显著增加,且地上生物量比地下生物量增加得多。同时,氮添加显著增加了凋落物质量,但对细根生物量没有显著影响。氮添加显著降低了植物叶片、凋落物和细根的碳氮比。总体上,氮添加显著增加了土壤有机碳含量并降低了土壤pH值,但对可溶性有机碳、微生物生物量碳和土壤呼吸的影响并不显著。在不同的地理条件下,土壤有机碳含量对氮添加的响应呈现增加、减少或不变的不同趋势。回归分析表明,地上生物量与土壤有机碳含量之间,以及微生物生物量碳与土壤有机碳含量之间呈负相关关系。虽然氮添加通过增加凋落物质量显著促进了植物碳输入,但同时也会通过刺激微生物降解来增加土...