海北高寒草甸土壤有机碳同位素组成及C3/C4碳源的变化

通过对高寒嵩草草甸土壤剖面不同深度(0～5cm,5～15cm,15～25cm,25～35cm,35～50cm,50～65cm)有机碳稳定性碳同位素的测定发现,土壤有机碳稳定性同位素(δ^13C)随土壤深度的增加而变大。表层土壤(0～5cm,定义为现代土壤)的δ^13C值最小,基本上接近现代植被的碳同位素特征。在土层5～10cm深度以下(粗略地定为古土壤),土壤有机碳稳定性同位素骤然上升,与表层土壤的同位素特征明显不同。考虑到影响土壤碳同位素的诸多因素,通过稳定性碳同位素的质量平衡模型计算,得出初步结果：来自C4(或CAM)植物的碳源随土壤深度的增加而增大。进一步推测,该地区植被可能经历由C4植物占优势的群落向C3植物占优势的群溶演化的过程。在这个过程中,大气碳同位素的变化和土壤有机质的形成过程(有机质淋溶过程)等也会引起土壤碳同位素的升高,因此质量平衡模型可能会过多地估算C4组分,而低估C3组分。     

华南亚热带山地土壤有机质更新特征及其影响因子

选择鼎湖山自然保护区及中国科学院华南植物研究所小良生态站6个土壤剖面,根据土壤有机质碳稳定同位素特征、^14C放射性水平、有机质含量、粒度特征,研究土壤有机质更新特征及其制约因素。结果表明,土壤有机质分解呈明显阶段性：有机质快速分解发生在0－100a之内,自地表向下,有机质含量急剧降低,因碳同位素分馏效应,有机质δ^13C值迅速增加;至170／240a,有机质δ^13C值达最大;自170／240－800／1400a,有机质分解速度变慢,有机质含量缓慢降低,因高δ^13C值组分分解,δ^13C值逐渐减小;约在1500a之后,有机质含量变化甚微,δ^13C值趋于稳定。对比研究表明,粘粒对有机质赋存状态及其更新有直接影响,粒度是制约土壤有机质动态的重要因子;地表植被类型及其发育特征直接影响土壤有机质更新,在植被类型相似情况下,植被覆盖史对土壤剖面有机质动态有明显影响。     

典型滨岸草地生态系统碳稳定同位素组成及分布特征

通过测定上海市青浦区东风港百慕大、白花三叶草、高羊茅和白茅等4种典型滨岸草本植物各组织以及不同垂直深度土壤有机质δ¹³C值,对滨岸草地生态系统的植物-土壤碳稳定同位素特征进行了分析.结果表明: 白花三叶草、高羊茅属于C3植物,百慕大、白茅属于C4植物,其茎叶、凋落物和根系各组织间δ¹³C值无显著差异.C3和C4植物样带表层土壤有机质δ¹³C值随着土壤深度递增而呈现截然不同的变化特征,这与样带本底δ¹³C值以及碳稳定同位素分馏效应有关,同时还受植物根系分布深度的影响.植物输入是土壤有机碳(SOC)的最主要来源,植物有机体δ¹³C组成对土壤有机质δ¹³C值有直接影响,植物各组分δ¹³C值与土壤有机质δ¹³C值均存在极显著相关.4种草本植物样带SOC含量与δ¹³C值均呈极显著相关,其中,C3植物样带SOC含量与δ¹³C值呈线性负相关,C4植物样带SOC含量与δ¹³C值呈线性正相关.     

土地利用变化对陆地生态系统碳贮量的影响

陆地生态系统是重要的碳库之一,在碳素生物地球化学循环中起着重要作用．本文就森林、农田生态系统,综述了土地利用变化对陆地生态系统碳贮量的影响及其可能的作用机制．土地利用变化显著地影响陆地生态系统的结构和功能,造成系统碳贮量的变化,这很大程度取决于生态系统类型和土地利用方式的改变．森林砍伐后变为农田和草地,使生态系统中植被和土壤碳贮量大大降低．土壤碳含量的降低主要是由于凋落物输入的减少,有机质分解速度的提高,以及耕种措施对有机质物理保护的破坏造成的．土壤碳损失主要发生在森林砍伐后较短的时期内,而其降低速率取决于诸多因素以及土壤理化和生物过程．农田和草地弃耕恢复为森林,以及农田保护性管理措施的利用．能够使大气中的碳在植被和土壤中得到汇集．森林恢复过程中植被可以大量汇集大气中的碳,而由于农田耕种历史不同以及土壤空间异质性。导致土壤碳汇集速率差异极大．保护性农田管理措施(诸如免耕、合理的种植制度、化肥的施用等)可以影响土壤理化特性、作物根系生长以及残茬数量和质量、土壤微生物数量和活性,维持和提高土壤碳含量水平．     

半干旱黄土小流域不同植被类型植物与土壤生态化学计量特征

生态化学计量学是研究生态系统元素平衡与能量流动的有效方法,明确不同植被恢复类型下植物与土壤化学计量特征对揭示黄土高原植被恢复中生态系统养分循环具重要意义,可为黄土高原植被恢复类型的选择提供可行性依据。以典型半干旱黄土小流域3种植被恢复方式下（天然荒草、自然恢复、人工恢复）的5种植被类型（长芒草草地、赖草草地、苜蓿草地、柠条灌丛、山杏林）为研究对象,分析不同植被类型下叶、茎、根及土壤碳（C）、氮（N）、磷（P）含量及化学计量特征。结果表明：1）植物不同器官和植被类型对植物生态化学计量特征都具有显著影响,C、N、P含量在5种典型植被中均表现为叶>茎>根。人工恢复植被各器官C、N含量及N ∶ P均显著高于天然荒草地,与自然恢复植被无显著差异;其中,在人工恢复植被中山杏各器官C含量最高,柠条各器官N含量最高。叶、茎、根的C ∶ N则表现为自然恢复植被显著高于人工恢复植被与天然荒草地。P含量、C ∶ P则在不同植被恢复类型间无显著差异。2）不同植被恢复类型下土壤C、N、P含量及化学计量特征具一定差异。人工恢复植被土壤C、N、P含量及C ∶ P、N ∶ P均为最高,显著高于自然恢复植被土壤;人工恢复植被中柠条土壤C、N含量及C ∶ P、N ∶ P均显著高于其他植被土壤。土壤C ∶ N在各植被类型间无显著差异。3）不同植被恢复类型下C、N、P含量在植物叶片与土壤间的相关性存在差异,说明植物自身生长特性影响着养分在植物与土壤间转化与传递。以5种典型植被整体来看,植物叶、茎、根的生态化学计量特征在彼此间均呈显著正相关。在植物与土壤间,植物各器官N含量与土壤C、N、P含量呈显著正相关,植物各器官N ∶ P与土壤N ∶ P呈显著正相关,表明该黄土小流域生态系统中植物与土壤生态化学计量特征的变化是相互制约,相互影响的。     

碳同位素示踪技术及其在陆地生态系统碳循环研究中的应用与展望

碳同位素示踪技术具有高度的专一性和灵敏度,经过几十年的发展,形成了一系列成熟的标记方法,在陆地生态系统碳循环过程的研究中已得到广泛应用。目前,自然丰度法、与13C贫化示踪技术结合的自由空气中气体浓度增加(FACE)实验、脉冲与连续标记法以及碳同位素高丰度底物富集标记法是研究陆地生态系统碳循环过程常用的碳同位素示踪方法;通过将长期定位实验和室内模拟实验结合,量化光合碳在植物-土壤系统的传输与分配特征,明确植物光合碳对土壤有机质的来源、稳定化过程的影响及其微生物驱动机制;阐明土壤碳动态变化(迁移与转化)和新碳与老碳对土壤碳库储量的相对贡献,评估有机碳输入、转化与稳定的生物与非生物微观界面过程机制。然而,生态系统碳循环受气候、植被、人为活动等多因素影响,碳同位素技术需要结合质谱、光谱技术实现原位示踪,结合分子生物学技术阐明其微生物驱动机制,从而构建灵敏、准确、多尺度、多方位的同位素示踪技术体系。因此,该文以稳定碳同位素为主,综述了碳同位素示踪技术的原理、分析方法和在陆地生态系统碳循环过程中的应用进展,归纳总结了碳同位素示踪技术结合原位检测技术和分子生物学技术的研究进展和应用前景,并对碳同位素示踪技术存在的问题进行了分析和展望。     

稳定同位素技术在植物水分利用研究中的应用

近20a稳定同位素技术在植物生态学研究中的应用得到了长足发展,使得对植物与水分关系也有了更深一步的了解。介绍稳定同位素性碳、氢、氧同位素在研究植物水分关系中的应用及进展,以期能为国内植物水分利用研究提供参考。由于植物根系从土壤中吸收水分时并不发生同位素分馏,对木质部水分同位素分析有助于对植物利用水分来源,生态系统中植物对水分的竞争和利用策略的研究,更好地了解生态系统结构与功能。稳定碳同位素作为植物水分利用效率的一个间接指标,在不同水分梯度环境中,及植物不同代谢产物与水分关系中有着广泛的应用。同位素在土壤-植被-大气连续体水分中的应用,有助于了解生态系统的水分平衡。随着稳定同位素方法的使用,植物与水分关系的研究将取得更大的进展。     

碳同位素技术在森林生态系统碳循环研究中的应用

碳同位素技术对碳素在生态系统中的迁移动态具有很好的示踪作用,在生态学各领域研究中应用广泛。土壤、大气、植物是森林生态系统的重要碳库,植物是大气和土壤交换碳元素的重要介质。本文简要总结了碳同位素技术在研究碳元素在植物体内以及植物、土壤、大气碳库之间的迁移规律和生态学过程中的应用,展望了该技术在森林界面学中的应用前景。     

碳同位素示踪技术及其在陆地生态系统碳循环研究中的应用与展望

碳同位素示踪技术具有高度的专一性和灵敏度, 经过几十年的发展, 形成了一系列成熟的标记方法, 在陆地生态系统碳循环过程的研究中已得到广泛应用。目前, 自然丰度法、与¹³C贫化示踪技术结合的自由空气中气体浓度增加(FACE)实验、脉冲与连续标记法以及碳同位素高丰度底物富集标记法是研究陆地生态系统碳循环过程常用的碳同位素示踪方法; 通过将长期定位实验和室内模拟实验结合, 量化光合碳在植物-土壤系统的传输与分配特征, 明确植物光合碳对土壤有机质的来源、稳定化过程的影响及其微生物驱动机制; 阐明土壤碳动态变化(迁移与转化)和新碳与老碳对土壤碳库储量的相对贡献, 评估有机碳输入、转化与稳定的生物与非生物微观界面过程机制。然而, 生态系统碳循环受气候、植被、人为活动等多因素影响, 碳同位素技术需要结合质谱、光谱技术实现原位示踪, 结合分子生物学技术阐明其微生物驱动机制, 从而构建灵敏、准确、多尺度、多方位的同位素示踪技术体系。因此, 该文以稳定碳同位素为主, 综述了碳同位素示踪技术的原理、分析方法和在陆地生态系统碳循环过程中的应用进展, 归纳总结了碳同位素示踪技术结合原位检测技术和分子生物学技术的研究进展和应用前景, 并对碳同位素示踪技术存在的问题进行了分析和展望。     

稳定碳同位素技术在土壤-植物系统碳循环中的应用

碳作为重要的生命元素,在土壤-植物系统物质循环中发挥重要作用.作为一种天然的示踪物,稳定碳同位素（13C）较放射性同位素具有安全、无污染、易控制的优点,在土壤-植物生态系统碳循环研究中得到广泛应用.通过检测土壤-植物体系中稳定碳同位素的自然丰度或采用稳定碳同位素标记有机材料,能够较真实地了解植物的光合特性、光合产物在土壤-植物体系中的运转及其在土壤中的分解、转化等过程.本文概述了稳定碳同位素技术在植物光合作用及光合产物运转、古气候重建、土壤有机质周转以及植物-根际微生物相互作用等方面的研究进展,并针对当前研究中存在的问题提出了今后的研究展望.     

Effects of grazing intensity on soil carbon stocks following deforestation of a Hawaiian dry tropical forest

The effects of forest-to-pasture conversion on soil carbon (C) stocks depend on a combination of climatic and management factors, but factors that relate to grazing intensity are perhaps the least understood. To understand the long-term impact of grazing in converted pastures, methods are needed that accurately measure the impact of grazing on recent plant inputs to soil C in a variety of pasture management and climate settings. Here, we present an analysis from Hawai'i of changes in vegetation structure and soil organic carbon (SOC) along gradients of grazing intensity and elevation in pastures converted from dry tropical forest 100 years ago. We used hyperspectral remote sensing of photosynthetic vegetation, nonphotosynthetic vegetation (NPV) and exposed substrate to understand the effects of grazing on plant litter cover, thus, estimating recent plant inputs to soils (the NPV component). Forest-to-pasture conversion caused a shift from C3 to C4 plant physiology, thus the δ ¹³C method was used in soil cores to measure the fraction of SOC accumulated from pasture vegetation sources following land conversion. SOC decreased in pasture by 5–9 kg C m⁻², depending upon grazing intensity. SOC derived from C3 (forest) sources was constant across the grazing gradient, indicating that the observed variation in SOC was attributable to changes in C inputs following deforestation. Soil C stocks were also reduced in pastures relative to forest soils. We found that long-term grazing lowers SOC following Hawaiian forest-to-pasture conversion, and that these changes are larger in magnitude that those occurring with elevation (climate). Further we demonstrate a relationship between remotely sensed measurements of surface litter and field SOC measurements, allowing for regional analysis of pasture condition and C storage where limited field data are available.     

林火干扰对森林生态系统土壤有机碳的影响研究进展

林火干扰是森林生态系统特殊而重要的生态因子,可改变生态系统的养分循环与能量传递。研究林火干扰对森林生态系统土壤有机碳的影响,有助于理解森林生态系统中土壤碳固持和碳循环过程,为制定科学合理的旨在减缓全球变化的林火管理策略具有重要意义。从4个方面阐述了林火干扰对森林生态系统土壤有机碳的影响及内在机制:分别从大尺度和小尺度两个方面阐述了林火干扰对土壤有机碳的影响及对森林生态系统碳循环与碳平衡的作用机制;探讨了不同林火干扰类型和林火干扰强度下,土壤活性有机碳对林火干扰的响应机制;阐明了林火干扰对土壤惰性有机碳的影响及作用机制;论述了林火干扰主要通过改变土壤有机碳的输入和输出过程进而影响土壤有机碳的稳定性及内在机制。最后提出了提高林火干扰对森林生态系统土壤有机碳影响定量化研究的4种路径选择:(1)全面比较研究不同林火干扰类型对土壤有机碳循环及其碳素再分配过程的功能特征;(2)进一步阐明林火干扰通过改变植被结构进而影响土壤生物群落结构,剖析土壤碳库循环的内在机制;(3)完善不同时空尺度下林火干扰对森林生态系统土壤碳库周转过程的定量化研究;(4)加强不同林火干扰类型土壤碳库稳定性差异的研究。     

Temperature and substrate controls on intra-annual variation in ecosystem respiration in two subarctic vegetation types

Arctic ecosystems are important in the context of climate change because they are expected to undergo the most rapid temperature increases, and could provide a globally significant release of CO₂ to the atmosphere from their extensive bulk soil organic carbon reserves. Understanding the relative contributions of bulk soil organic matter and plant‐associated carbon pools to ecosystem respiration is critical to predicting the response of arctic ecosystem net carbon balance to climate change. In this study, we determined the variation in ecosystem respiration rates from birch forest understory and heath tundra vegetation types in northern Sweden through a full annual cycle. We used a plant biomass removal treatment to differentiate bulk soil organic matter respiration from total ecosystem respiration in each vegetation type. Plant‐associated and bulk soil organic matter carbon pools each contributed significantly to ecosystem respiration during most phases of winter and summer in the two vegetation types. Ecosystem respiration rates through the year did not differ significantly between vegetation types despite substantial differences in biomass pools, soil depth and temperature regime. Most (76–92%) of the intra‐annual variation in ecosystem respiration rates from these two common mesic subarctic ecosystems was explained using a first‐order exponential equation relating respiration to substrate chemical quality and soil temperature. Removal of plants and their current year's litter significantly reduced the sensitivity of ecosystem respiration to intra‐annual variations in soil temperature for both vegetation types, indicating that respiration derived from recent plant carbon fixation was more temperature sensitive than respiration from bulk soil organic matter carbon stores. Accurate assessment of the potential for positive feedbacks from high‐latitude ecosystems to CO₂‐induced climate change will require the development of ecosystem‐level physiological models of net carbon exchange that differentiate the responses of major C pools, that account for effects of vegetation type, and that integrate over summer and winter seasons.     

黄土高原天然次生林植被演替过程中土壤团聚体有机碳动态变化

土壤团聚体物理保护是促进有机碳积累主要机制之一。以黄土高原子午岭林区天然次生林植被演替群落为对象,研究从农田、草地（白羊草,Bothriochloa ischaemum）、灌木林（沙棘,Hippophae rhamnoides）、先锋林（山杨,Populus davidiana）到顶级林（辽东栎,Quercus liaotungensis）5个植被演替阶段0-20 cm土壤团聚体稳定性和团聚体有机碳的动态变化,并分析团聚体有机碳的影响因素。结果表明：土壤团聚体稳定性随着植被演替显著提高（P<0.05）,顶级林的团聚体稳定性最高;土壤有机碳含量和各粒径土壤团聚体（> 2 mm、2-0.25 mm、0.25-0.053 mm、<0.053 mm）有机碳含量均随着植被演替而增加。除草地0.25-0.053 mm团聚体有机碳含量最高外,其他演替阶段均为0.25-2 mm粒径最高。根系生物量、凋落物生物量、微生物生物量碳、团聚体稳定性均与团聚体有机碳含量呈显著正相关关系（P<0.05）。总体而言,长期植被演替有助于团聚体稳定性和团聚体有机碳累积。     

Labile Phosphorus in Soils of Forest Fallows and Primary Forest in the Bragantina Region, Brazil

We used the Hedley sequential extraction procedure to measure nine different organic inorganic soil phosphorus fractions in forest soil of the Bragantina region of Para, Brazil. We compared the labile fractions (resin‐extractable P + HCO3‐extractable inorganic and organic P) in Oxisols from three secondary forests (10, 20, and 40 years old) and a primary forest. These stands were located in an area that has supported shifting agriculture for approximately a century. After agricultural use, total P and labile P in soils of young secondary forests are diminished compared to the amounts presents in the primary forest soil. Within each stand, organic carbon content was a good predictor of labile organic and inorganic P, consistent with the large body of research indicating that mineralization of organic matter is important to plant nutrition in tropical ecosystems. During the reorganization of P pools during forest development, the pool of labile organic P (HCO3‐extractable) diminishes more than the other labile fractions, suggesting that it is directly or indirectly an important source of P for the regrowing forest vegetation. Across the four age classes of forest, the soil reservoir of labile P was equal to or greater than the total amount of P in the vegetation. If labile P measured by this method adequately represents P available to plants in the short term (as suggested by the current consensus), we would conclude that plant‐available P is reasonable abundant, and that the effects of agriculture on available P pools are detectable but not sufficient to compromise forest regrowth in this area.     

川西亚高山不同森林生态系统碳氮储量及其分配格局

森林采伐和恢复是影响森林碳氮储量的重要因素。以川西亚高山岷江冷杉原始林、粗枝云杉阔叶林、天然次生林和粗枝云杉人工林为研究对象,采用样地调查和生物量实测的方法,研究了不同森林生态系统各组分碳、氮储量及其分配特征。结果表明岷江冷杉原始林、粗枝云杉阔叶林、天然次生林和粗枝云杉人工林生态系统碳储量分别为611.18、252.31、363.07 tC/hm~2和239.06 tC/hm~2;氮储量分别为16.44、12.11、15.48 tN/hm~2和8.92 tN/hm~2。恢复林分与原始林碳储量在土壤—植被的分配格局发生了变化,而氮储量未发生变化。岷江冷杉原始林以植被碳储量为主,恢复林分以土壤为主,氮储量均以土壤为主。乔木层碳储量分别占生态系统总储量的56.65%、17.63%、13.57%和22.05%,土壤层(0—80 cm)分别占32.03%、69.87%、76.20%和72.12%;土壤层氮储量占生态系统总储量的76.80%—92.58%。植物残体碳氮储量分别占生态系统总储量的4.40%—9.83%和2.94%—7.08%,林下植被所占比例最小。空间格局上,岷江冷杉原始林植被部分具有较高的碳储量,应进行保护。3种恢复林分具有较高的碳汇潜力,且地上/地下碳储量较低,表明其碳汇潜力尤其表现在地上部分。天然次生林利于土壤有机碳的积累,而人工林乔木层碳储量较高。     

林火干扰对广东木荷林生态系统碳库的影响

森林碳库在调节CO₂浓度及减缓温室效应中发挥重要作用。选择广东木荷林为研究对象,通过相邻样地法,进行植被生物量、凋落物生物量和土壤样品的采样与分析,研究不同林火干扰强度对生态系统各碳库(植被、凋落物和土壤有机碳)及生态系统碳库产生的变化规律和空间分布格局及其影响因素。结果表明:(1)植被碳密度随着林火干扰强度增强而减少,但不同组分的植被碳密度表现不同,乔木碳密度在不同林火干扰强度下变化与植被碳密度变化一致,而草本碳密度则呈现相反的变化趋势。相同林火干扰强度下,植被各组分碳密度均以乔木层降低幅度最大。林火干扰均显著降低了凋落物碳密度(P<0.05),并随林火干扰强度的增加其降低幅度增大,但不同林火干扰强度对凋落物碳密度的影响有所差异。林火干扰降低了土壤有机碳密度,且降低幅度随土层深度增加而逐渐变小。(2)林火干扰有效改变了生态系统碳库的空间分布格局。对照样地木荷林土壤有机碳库占比为61.59%,重度林火干扰后,土壤有机碳库占比为70.96%呈上升趋势,占生态系统碳库的优势地位,而植被和凋落物碳库占比呈下降趋势,处于生态系统碳库的次要地位。(3)双因素方差分析表明,林火干扰强度和土层深度及其交互作用均对土壤有机碳密度有显著影响。林火干扰强度解释了土壤有机碳密度变异的8.78%,土层深度解释了土壤有机碳密度变异的70.29%,林火干扰强度和土层深度之间的交互作用解释了土壤有机碳密度变异的8.16%。研究发现:林火干扰降低了生态系统碳库,且随林火干扰强度增加,生态系统碳库减少幅度增大。轻度林火干扰对森林生态系统碳库的影响差异不显著,而中度和重度林火干扰对森林生态系统碳库的影响差异显著。研究结果对深化亚热带森林固碳效应的影响机制提供理论支撑。     

Soil Organic Matter Dynamics Along a Vertical Vegetation Gradient in the Gongga Mountain on the Tibetan Plateau

Our knowledge about soil organic matter (SOM) dynamics is limited although this is an important issue in the study of responses of ecosystems to global climate changes. Twelve sampling plots were set up every 200 m from 1 700 to 3 900 m along the vertical vegetation gradient along the east slope of Gongga Mountain. Samples were taken from all 12 plots for SOM content measurement, although only 5 of the 12plots were subjected to radiocarbon measurements. A radiocarbon isotope method and a time-dependent model were used to quantify the SOM dynamics and SOM turnover rates along the vertical vegetation gradient. The results showed that the SOM turnover rate decreased and turnover time increased with soil depth for all vegetation types. The litter layer turnover rates presented a clear trend along the gradient. The litter layer turnover rates decreased with an increase in elevation, except that the litter layer turnover rate of mixed forest was higher than that of evergreen forest. Climatic factors, such as temperature and precipitation,were the main factors influencing the surface soil carbon dynamics. The turnover rates of the subsoil (including the A, B, and C horizons in the soil profiles) along the vertical gradient had no clear trends. The SOM of subalpine shrub and meadow turned over more slowly than that of the forest types in almost all soil horizons. The characteristic of short roots distributing in the upper part of the soil profile leads to different SOM dynamics of shrub and meadow compared with the forest types. Coniferous and mixed forests were susceptible to carbon loss from the young carbon pool, but their long and big roots resulted in high △14C values of the deep soil profiles and increased the input of young carbon to the deep soil. In evergreen forest,the carbon cumulative ability from the B horizon to the C horizon was weak. The different vegetation types,together with their different modes of nutrient and carbon intake, may be the mechanism conditioning the subsoil organic matter dynamics.     

The Role of Revegetation for Rehabilitation of Sodic Soils in Semiarid Subtropical Forest, India

A 40‐year‐old rehabilitated forest developed on a sodic wasteland at Banthra, Lucknow, north India, was studied for the performance of various species in different vegetation strata as well as their overall impact in soil amelioration. The plant communities of the three selected stands (S1, S2, and S3) of this forest were categorized into three vegetation strata: overstory trees, understory trees and shrubs, and a ground layer with scattered herbs and tree seedlings. The three stands contained 44, 19, and 8 species in each stratum, respectively, and three climber species. Importance value index (IVI) and basal area/cover did not show a clear dominance for particular species, and this is identified as a mixed forest with deciduous as well as evergreen species. Therefore, dominant species in each layer were categorized according to an IVI value of 10 and greater than 10% relative basal area. Within each stratum, species richness and plant population density decreased with an increase in plant size. Both species diversity and productivity were relatively high compared to the reference site because of protection from biotic disturbances, which cannot be controlled on the reference site. Creation of new forest on the barren land has contributed significant soil amelioration in the degraded sodic soil of the Indogangetic plains. The soil properties of the three stands did not vary much, although different tree species dominated the stands. Maximum soil amelioration was recorded for total N, followed by mineralized N, available N, and organic carbon contents for the nutritional properties. With regard to chemical properties, exchangeable sodium was greatly reduced in comparison to other properties viz pH, electrical conductivity, cation exchange capacity, and exchangeable Ca content. During 40 years of growth and development of the diverse vegetation in the revegetated forest, microbial C increased to about five times that of the surrounding barren sodic soils. There were no significant changes in soil structure even though the water‐holding capacity of the soil improved to about 53% of the once barren land due to a 7‐fold increase in organic carbon content.     

森林生态系统碳循环对全球氮沉降的响应

森林土壤和植被储存着全球陆地生态系统大约46%的碳,在全球碳平衡中起着非常重要的作用。过去几十年来,森林生态系统的碳循环和碳吸存受到了全球氮沉降的深刻影响,因为氮沉降改变了陆地生态系统的生产力和生物量积累。以欧洲和北美温带森林区域开展的研究为基础,综述了氮沉降对植物光合作用、土壤呼吸、土壤DOM及林木生长的影响特征和机理,探讨了森林生态系统碳动态对氮沉降响应的不确定性因素。热带森林C、N循环与大部分温带森林不同,人为输入的氮对热带生态系统过程的影响也可能不同,因此指出了在热带地区开展碳氮循环耦合研究的必要性和紧迫性。