Ammonium uptake, transport and nitrogen economy in forest trees

AMMONIUM UPTAKE, TRANSPORT AND NITROGEN ECONOMY IN FOREST TREES Francisco M. Cánovas, Concepción Avila, Fernando N. de la Torre, Rafael A. Cañas, Belén Pascual, Vanessa Castro- Rodríguez, Jorge El-Azaz Departamento de Biología Molecular y Bioquímica, Facultad de Ciencias, Universidad de Málaga, Spain. Email: canovas@uma.es Forests ecosystems play a fundamental role in the regulation of global carbon fixation and preservation of biodiversity. Forest trees are also of great economic value because they provide a wide range of products of commercial interest, including wood, pulp, biomass and important secondary metabolites. The productivity of most forest ecosystems is limited by low nitrogen availability and woody perennials have developed adaptation mechanisms, such as ectomycorrhizal associations, to increase the efficiency of N acquisition and metabolic assimilation. The efficient acquisition, assimilation and economy of nitrogen are of special importance in trees that must cope with seasonal periods of growth and dormancy over many years. In fact, the ability to accumulate nitrogen reserves and to recycle N is crucial to determine the growth and production of forest biomass. Ammonium is the predominant form of inorganic nitrogen in the soil of temperate forests and many research efforts are addressed to study the regulation of ammonium acquisition, assimilation and internal recycling for the biosynthesis of amino acids, particularly those relevant for nitrogen storage. In our laboratory, we are interested in studying nitrogen metabolism and its regulation in maritime pine (Pinus pinaster L. Aiton), a conifer species of great ecological and economic importance in Europe and for which whole-transcriptome resources are available. The metabolism of phenylalanine plays a central role in the channeling of carbon from photosynthesis to the biosynthesis of phenylpropanoids and the regulation of this pathway is of broad significance for nitrogen economy of maritime pine. We are currently exploring the molecular properties and regulation of genes involved in the biosynthesis and metabolic fates of phenylalanine in maritime pine. An overview of this research programme will be presented and discussed. Research supported by Spanish Ministry of Economy and Competitiveness and Junta de Andalucía (Grants BIO2015-69285-R, BIO2012-0474 and research group BIO-114).

Climate change and forests in India

Forests play a critical role in addressing climate change concerns in the broader context of global change and sustainable development. Forests are linked to climate change in three ways. i) Forests are a source of greenhouse gas (GHG) emissions: ii) Forests offer mitigation opportunities to stabilise GHG concentrations: iii) Forests are impacted by climate change. This paper reviews studies related to climate change and forests in India: first, the studies estimating carbon inventory for the Indian land use change and forestry sector (LUCF), then the different models and mitigation potential estimates for the LUCF sector in India. Finally it reviews the studies on the impact of climate change on forest ecosystems in India, identifying the implications for net primary productivity and bio-diversity. The paper highlights data, modelling and research gaps relevant to the GHG inventory, mitigation potential and vulnerability and impact assessments for the forest sector in India.

Tree mortality and deadwood dynamics in late-successional boreal forests

Here I aimed at quantifying the main components of deadwood dynamics, i.e. tree mortality, deadwood pools, and their decomposition, in late-successional boreal forests. I focused on standing dead trees in three stand types dominated by Picea mariana and Abies balsamea in eastern Canada, and on standing and down dead trees in Picea abies-dominated stands in three areas in Northern Europe. Dead and living trees were measured on five sample plots of 1.6-ha size in each study area and stand type. Stem disks from dead trees were sampled to determine wood density and year of death, using dendrochronological methods. The results were applied to reconstruct past tree mortality and to model deadwood decay class dynamics. Site productivity, stand developmental stage, and the occurrence of episodic tree mortality influenced deadwood volume and quality. In all study areas tree mortality was continuous, leading to continuity in deadwood decay stage distribution. Episodic tree mortality due to either autogenic or allogenic causes influenced deadwood volume and quality in all but one study area. However, regardless of productivity and disturbance history deadwood was abundant, accounting for 20 53% of total wood volume in European study areas, and 15 27% of total standing volume in eastern Canada. Deadwood was a persistent structural component, since its expected residence time in early- and midstages of decay was 18 yr even in the area with the most rapid decomposition. The results indicated that in the absence of episodic tree mortality, stands may eventually develop to a steady state, in which deadwood volume fluctuates around an equilibrium state. However, in many forests deadwood is naturally variable, due to recurrent moderate-severity disturbances. This variability, the continuous tree mortality, and variation in rates of wood decomposition determine the dynamics and availability of deadwood as a habitat and carbon storage medium in boreal coniferous forest ecosystems.

Responses of soil microbial communities to clonal variation of Norway spruce

In boreal forests, microorganisms have a pivotal role in nutrient and water supply of trees as well as in litter decomposition and nutrient cycling. This reinforces the link between above-ground and below-ground communities in the context of sustainable productivity of forest ecosystems. In northern boreal forests, the diversity of microbes associated with the trees is high compared to the number of distinct tree species. In this thesis, the aim was to study whether conspecific tree individuals harbour different soil microbes and whether the growth of the trees and the community structure of the associated microbes are connected. The study was performed in a clonal field trial of Norway spruce, which was established in a randomized block design in a clear-cut area. Since out-planting in 1994, the spruce clones showed two-fold growth differences. The fast-growing spruce clones were associated with a more diverse community of ectomycorrhizal fungi than the slow-growing spruce clones. These growth performance groups also differed with respect to other aspects of the associated soil microorganisms: the species composition of ectomycorrhizal fungi, in the amount of extraradical fungal mycelium, in the structure of bacterial community associated with the mycelium, and in the structure of microbial community in the organic layer. The communities of fungi colonizing needle litter of the spruce clones in the field did not differ and the loss of litter mass after two-years decomposition was equal. In vitro, needles of the slow-growing spruce clones were colonized by a more diverse community of endophytic fungi that were shown to be significant needle decomposers. This study showed a relationship between the growth of Norway spruce clones and the community structure of the associated soil microbes. Spatial heterogeneity in soil microbial community was connected with intraspecific variation of trees. The latter may therefore influence soil biodiversity in monospecific forests.

Climate change, sustainable development and India: Global and national concerns

Climate change is one of the most important global environmental challenges, with implications for food production, water supply, health, energy, etc. Addressing climate change requires a good scientific understanding as well as coordinated action at national and global level. This paper addresses these challenges. Historically, the responsibility for greenhouse gas emissions' increase lies largely with the industrialized world, though the developing countries are likely to be the source of an increasing proportion of future emissions. The projected climate change under various scenarios is likely to have implications on food production, water supply, coastal settlements, forest ecosystems, health, energy security, etc. The adaptive capacity of communities likely to be impacted by climate change is low in developing countries. The efforts made by the UNFCCC and the Kyoto Protocol provisions are clearly inadequate to address the climate change challenge. The most effective way to address climate change is to adopt a sustainable development pathway by shifting to environmentally sustainable technologies and promotion of energy efficiency, renewable energy, forest conservation, reforestation, water conservation, etc. The issue of highest importance to developing countries is reducing the vulnerability of their natural and socio-economic systems to the projected climate change. India and other developing countries will face the challenge of promoting mitigation and adaptation strategies, bearing the cost of such an effort, and its implications for economic development.

Impact of climate change on Indian forests: a dynamic vegetation modeling approach

We make an assessment of the impact of projected climate change on forest ecosystems in India. This assessment is based on climate projections of the Regional Climate Model of the Hadley Centre (HadRM3) and the dynamic global vegetation model IBIS for A2 and B2 scenarios. According to the model projections, 39% of forest grids are likely to undergo vegetation type change under the A2 scenario and 34% under the B2 scenario by the end of this century. However, in many forest dominant states such as Chattisgarh, Karnataka and Andhra Pradesh up to 73%, 67% and 62% of forested grids are projected to undergo change. Net Primary Productivity (NPP) is projected to increase by 68.8% and 51.2% under the A2 and B2 scenarios, respectively, and soil organic carbon (SOC) by 37.5% for A2 and 30.2% for B2 scenario. Based on the dynamic global vegetation modeling, we present a forest vulnerability index for India which is based on the observed datasets of forest density, forest biodiversity as well as model predicted vegetation type shift estimates for forested grids. The vulnerability index suggests that upper Himalayas, northern and central parts of Western Ghats and parts of central India are most vulnerable to projected impacts of climate change, while Northeastern forests are more resilient. Thus our study points to the need for developing and implementing adaptation strategies to reduce vulnerability of forests to projected climate change.

Climate change and Indian forests

An assessment of the impact of projected climate change on forest ecosystems in India based on climate projections of the Regional Climate Model of the Hadley Centre (HadRM3) and the global dynamic vegetation model IBIS for A1B scenario is conducted for short-term (2021-2050) and long-term (2071-2100) periods. Based on the dynamic global vegetation modelling, vulnerable forested regions of India have been identified to assist in planning adaptation interventions. The assessment of climate impacts showed that at the national level, about 45% of the forested grids is projected to undergo change. Vulnerability assessment showed that such vulnerable forested grids are spread across India. However, their concentration is higher in the upper Himalayan stretches, parts of Central India, northern Western Ghats and the Eastern Ghats. In contrast, the northeastern forests, southern Western Ghats and the forested regions of eastern India are estimated to be the least vulnerable. Low tree density, low biodiversity status as well as higher levels of fragmentation, in addition to climate change, contribute to the vulnerability of these forests. The mountainous forests (sub-alpine and alpine forest, the Himalayan dry temperate forest and the Himalayan moist temperate forest) are susceptible to the adverse effects of climate change. This is because climate change is predicted to be larger for regions that have greater elevations.

Challenges in vulnerability assessment of forests under climate change

Forest-management goals in the context of climate change are to reduce the adverse impact of climate change on biodiversity, ecosystem services and carbon stocks. For developing an effective adaptation strategy, knowledge on nature and sources of vulnerability of forests is necessary to conserve or enhance carbon sinks. However, assessing the vulnerability of forest ecosystems is a challenging task, as the mechanisms that determine vulnerability cannot be observed directly. In this article, we list the challenges in forest vulnerability assessments and propose an assessment of inherent vulnerability by using process-based indicators under the current climate. We also suggest periodic assessment of vulnerability, which is necessary to review adaptation strategies for the management of forests and forest carbon stocks.

The Costs of Ecosystem Adaptation: Methodology and Estimates for Indian Forests

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Relação entre pluviosidade efetiva e estoque de matéria orgânica de superfície na ciclagem de nutrientes em floresta ombrófila urbana: Parque Nacional da Tijuca - RJ

O estoque de matéria orgânica de superfície refere-se a todo material orgânico decomposto ou em decomposição sobreposto ao solo mineral, bem como ao material orgânico misturado às partículas minerais do horizonte A. Este serve como indicador da funcionalidade e integridade de ecossistemas florestais quando o analisamos sob a perspectiva das "Formas de Húmus". Nesta perspectiva o material orgânico se presenta como disposto em camadas internas que variam no peso e espessura de acordo com a atuação dos agentes decompositores locais, e expressa a ciclagem de nutrientes que se dá a partir dos dois principais processos que sintetizam e/ou modulam o funcionamento dos ecossistemas, a produção e a decomposição da matéria orgânica. O modelo de formas de húmus segue uma classificação desenvolvida na Europa que não se aplica perfeitamente às áreas tropicais pela alta variabilidade de ambientes. Estima-se que fatores locais e particulares como características edáficas, estrutura e composição da vegetação, relevo e o microclima podem distorcer esta classificação e diferir significativamente do modelo global. Esta pesquisa buscou o refinamento deste modelo, buscando entender de que modo a pluviosidade efetiva (chuva que atravessa a copa das árvores e chega ao solo), como fenômeno de natureza microclimática, se relaciona com o estoque de matéria orgânica de superfície (sob a perspectiva das formas de húmus) em ambiente de floresta ombrófila montanhosa urbana.Para tal foram executadas análises físicas sobre o estoque de matéria orgânica de superfície, monitoramento da pluviosidade efetiva com pluviômetro experimentais adaptados para esta demanda e análises químicas sobre a água da chuva após lixiviação da matéria orgânica. Foi montada uma estrutura composta de quinze pluviômetros experimentais em uma encosta florestada no Parque Nacional da Tijuca (Rio de Janeiro - RJ) e instalação de pluviômetros eletrônicos em ambientes de céu aberto em áreas adjacentes a esta encosta pertencentes à área do parque. Os resultados indicam que da chuva que cai na floresta, cerca de 15% é interceptada pelas copas e o restante, parte é interceptada pela matéria orgânica do solo. A camada MFB (ou H) é a que retém mais água, indicando que, florestas que a decomposição é rápida no processo de fragmentação e lenta na mineralização, terão mais água retida no estoque de matéria orgânica. As diferentes camadas vão nutrir o solo de maneira diferenciada quando este processo deriva da lixiviação, como o cálcio que é liberado em a maior quantidade pelas camadas mais fragmentadas como a F e a MFB, o potássio e magnésio têm maior disponibilização quando deriva da camada L, indicando que durante este processo estes nutrientes são mais consumidos do que liberados. Foi perceptível que o sódio é bastante abundante na chuva antes mesmo de atingir a matéria orgânica, confirmando estudos anteriores. A utilização deste sistema proposto de pluviômetros experimentais possibilitou entender como esta estratificação interna do estoque de matéria orgânica de superfície acumula água, pois os métodos tradicionais não se baseiam no modelo de formas de húmus, e possibilitou ainda, o a análise do processo de lixiviação e liberação de nutrientes para o solo.

暖温带山地森林生态系统水分问题研究

本文的研究是中国科学院院重大项目“暖温带森林生态系统结构、功能及生产力持续发展”的主要内容之一。作者以详实的第一手资料，从森林小气候及环境特征、森林降水的水文学效应及降水化学、森林的热量平衡及蒸发散、树木个体的水分生理生态学几个方面阐述、分析了暖温带山地森林生态系统主要林分的水分及其相关生态学问题。 在森林小气候及环境特征一章，作者从不同季节的日变化和生长季的月际变化两个视角，以落叶阔叶混交林和油松林为研究对象，考察了林冠上和林下四个不同梯度的风速、气温、湿度、地温的时空动态。 在森林降水的水文学效应和降水化学一章，笔者以1993、1994年试验年度的83次降雨观测资料为基础，分析了暖温带落叶阔叶混交林、辽东栎林、油松林、落叶松林、次生灌丛降水总量与各降水分量的关系，建立了单次降雨与各降雨分量的经验模型，并给出了生长季林冠作用层和林地作用层的水量分配的月际动态。在探讨上述水量关系的同时，作者还分析了前四类林分大气降水及各降水分量中N、K、Ca、S、Mg、P、Al七种元素的浓度及含量变化，就不同树种对上述元素的选择性交换作了探讨，比较了不同林分的降水化学效应差异。 在第四章，作者以落叶阔叶混交林和油松林为研究对象，分析了两类林分在94试验年度生长季辐射平衡、显热通量、潜热通量、蒸发散以及土壤热通量的季节变化和日变化特征。 在树木个体的水分生理生态部分，作者应用压力室一容积技术测定了暖温带落叶阔叶林、油松林和次生灌丛10种主要树种的水分生理指标：日最低水势值、最大膨压时的渗透势、膨压为零时的渗透势、初始质壁分离时渗透水的相对含量、初始质壁分离时的相对含水量、质外体水的相对含量、细胞最大弹性模量，并比较了不同树种间上述指标与抗旱性的关系。此外，作者还应用Li-1600稳态气孔计测定了上述林分中主要树种的日均蒸腾强度的季节动态，并比较了上下两面叶片蒸腾特性的差异。最后，作者采用九种水分生理指标对10种主要树种的抗旱性作了主分量分析，给出了综合性抗旱指标。 在第六章，作者应用热脉冲技术系统地研究了暖温带山地森林主要乔木树种的树干液流的时空变化特征，并应用时序分析方法对上述树种的树液流量变化建立了自回归模型，在此基础上提出了生理惯性指标，给予了生理学解释。

森林生态系统的养分循环-一个温带落叶阔叶林生态系统的研究

l、有机质和全N在草甸土壤的不同层次之间呈现明显的差异，表现力随着土壤深度的增加，含量逐渐降低。无机N包括NH4+-N和No3--N在土层之闻的差异并没有象全N和有机质那么显著。NH4+-在表面30Cm的土壤中明显高于NO3--N的。全P在各层土壤中的含量差异并不显著，但有效p在三层土壤中表现出明显的差异，表现为随土壤深度的增加而降低。 K、Na、Ca、Mg、Fe和AI等6种金属元素的可交换成分在革甸土壤中的含量除K表现出明显的土层间的差异外，在表层30cm的土壤中并没有明显的随土壤深度变化的趋势。 有机质和全N在东灵山地区主要森林土壤中的含量以0~lOcm土层中的显著高于10~20cm的土层中的。20cm的土层中无机N中也以NH4+-为主，这与草甸土壤中的一致。全p和有效P在两个土层之间的差异并不十分显著，而以0^lOcm土层略高于10～20Cm土层的。 K、Na、Ca、Mg、Fe和AI等6种金属元素的可交换成分在不同土层间的差异以K和Ca较为明显，K和Ca在O—1Ocm的土层中要高于lO-20cm的。 森林土壤中的有机质、全N（包括NH4+-N）、全p（包括有效P)都表现为低于亚高山草甸土壤中的，主要原因是亚高山革甸分布于海拔1800cm至2300m，而主要森林类型则基本分布在海拔120m至1500m，亚高山草甸较为恶劣的气候条件明显不利于有机质的矿化，因而分解速率较低，积聚了较多的有机质．而森林土壤中较低的NH4+-N和有效P则可能是由于森林中旺盛的生命活动，尤其是微生物的活动，而大量被植物和微生物固持，因而，即使在森林土壤中有较高的矿化速率，但仍具有较低的NH4+-N和有效p的含量． 不同类型的森林土壤之间各化学成分并没有发现有明显的变化趋势，即使森林类型差异较大的落叶阔叶林和针叶林之间也并没有发现十分显著的差异，这说明各森林类型土壤之间养分特征的一致性。两种针叶林均为人工林，林龄不超过30，而在这之前推测也是以落叶阔叶林为主，森林土壤在这30年间并没有发生十分明显的变化。 在l100m至I500m之间的各种森林类型的土壤也没有表现出十分明显的与海拔高度的相关性。同一森林土壤在不同时间的采样之间，各化学成分也没有表现出明显的差异。 2、降水引起的树干茎流水分中全N的含量在降水季节的初期的含量略高于大量降水期间的。而在降水季节后期，随着每次降雨量的减少，降水间隔时间的增加，树干茎流中N的含量明显地有很大幅度的升高。NO3-N在树干茎流中的含量也同样受到了降水量的影响，表现在后期也发生显著的升高，但升高的幅度没有全N的大。受到降水量影响的元素还有S。 全p在树干茎流水分中含量随降水时间的变化，在各个树种之间有很大的差异。 其它几种元素的可交换态在茎流水分中的含量以K的含量为最高;其次是S、ca、Mg，AI在所有分析的元素中含量最低。不过，AI在降水初期(6月22日)的取样中，含量在几个树种的茎流水分样品中普遍较高，Ca和Mg也被发现有类似的情形。 穿透雨中全N的含量在降水初期略高于降水中期的，而至降水末期时又略有升高，这种格局与树干茎流水分中的具有一致性。全P、K、Ca、Mg、S．ＡＩ等包括全N及其无视成分与树干茎流中的含量的差异并不显著． 地表径流中的全N含量在去除枯枝落叶层的径流场的变化格局与树干茎流和穿透雨中的较为一致．表明这三者之间存在一定的相关性．但与未去除枯枝落叶层的径流场的径流水分中全N和NO３－Ｎ的含量并不十分一致，全N和NO３－N的含量有时较高． 取自马牙石沟流水堰口的集水区水样中全N和NO３-N的含量均变化在l～3ｍｇ／L之间;而取自南沟流水堰口的集水区水样中的全N和N03-N的含量均在l～2mg／L之间，但在这两者之间并没有十分显著的差异，说明取自两个集水区溪流水分中的全N和N03-N的含量基本一致。 3、通过对三个森林立地乔木层生物量的两次调查（相隔6年），发现尽管以辽东栎为主要优势树种的暖温带落叶阔叶混交林（91- 03）第一次调查的生物量低于辽东栋林（91 - 02）和桦木林（91 - 04)的，但在生长6年后，该立地的乔木层生物量已明显超过桦木林的，其增长速率在三个样地中为最高。 根据两次调查的结果，三个样地中出现的11种乔木树种胸径的增加可以分成两组，第一组包括北京花楸、糠椴、白桦和辽东栎，另一组则由山杨、五角枫、棘皮桦、大叶白蜡、蒙椴、黄花柳和沙涞组成。6年中，第一组树种的胸径增加量在1.O～l.4em之间，而第二组的增量在0.2~O.9cm之间，两者之间具有显著的差异。 常用的生物量预测模型包括两个因子，即胸径(D)和树高(H)。D通常可以实测得到，但H大部分只能估计得到。本研究通过比较6年前后两次树高的实际估测结果，证明用D和H共同建立的模型预测结果可能会产生较大的人为误差，建议改用D的单因子预测模型。 无论是实测结果还是树木年轮分析结果，都表明处于目前径级水平的暖温带地区分布的这几个树种还处在不断生长的过程中，随着年龄的增加，表现为胸径还有很大程度的增加，因为这些树种目前的大径级个体的年平均增加速率大于小径级的． 树木年龄与胸径的相互关系的分析结果表明，树木年龄和胸径可以很好地用饱和模型Y=a-be－ｃｘ来拟合． 4、通过近5年对辽东栎枝条( D<0.5cm)和叶片凋落物分解的观察和分析，发现辽东栎枝条的总失重率达到了43%，分解速率常数k为2.713x10－3／周，而叶的总失重率则可以达到70%，分解速率常数k为6.234xl0-3/周. 枝条分解过程中的有机质含量变化可以分为三种类型，一种是单调上升型的，如蛋白质，其含量从3.5%增加到约6%;-种是单调下降型的，如半纤维素，约从15%降低至7%;另一种则是相对变化不大，如粗纤维（包括纤维素和木质素），粗纤维的含量变化在58％±3%，木质素变化在56%±2.5%，纤维素则变化在1%～3%之间。 用Olson指数方程拟合，结果表明粗纤维、木质素和半纤维素三者的分解以半纤维素为最快，分解速率常数为5.693xl0-3／周，其次是木质素和粗纤维，分别为2.461x10-3/周和2.352xl0-3／周．而蛋白质和纤维素的拟合结果较差或根本无法拟合． 用Olsoｎ指数方程拟合的结果表明，有些元素在凋落物分解过程中可以很好地用该方程拟合，如K，Na、Mn和C，p和N，Mg，Zn，而一些元素如Ca和Cu没有取得很好的拟合效果。 几种元素在叶片凋落物分解过程过程的丢失速率也以K为最快，其它元素的顺序为，e，N，p，Na，Mn，Mg和Ca（Ca的拟合效果较差），而Cu、Zn也不能很好地用Olson指数方程拟合。 5、根据对东灵山地区6年(199l~1997)的气象观测结果，可得到该地区的年平均降水量和总降水量，用1994年分析的降水中养分含量的数据可以近似计算得东灵山地区每年通过降水进入该暖温带落叶阔叶林生态系统的几种养分输入量。同理可以计算降水输入养分在树干茎流和穿透雨中的分配，还可以计算养分从地表径流中的输出。通过对这几个水分循环的主要环节中养分输入或输出量的计算，发现每年通过降水而进入系统的养分，大部分将积累在系统中，而输出份额只占很小的一部分。 K和Mg两种养分元素在降水通过林冠和树干表面时，将产生大量的淋溶，而Ca的淋溶较小．N、P和AI则产生少量的吸附或吸收。对于S来说，淋溶和吸收或吸附作用相当，或两者都很小。 通过生物量的年平均增量和生物量中的养分含量可以计算得到每年积累在生物量中的养分量即存留量，同理可以计算年凋落物中的养分量、归还量及生物系统从土壤中吸收的养分量，每年养分的存留率．通过以上计算，发现该落叶阔叶林对养分的存留率较低，这可能是由于该落叶阔叶林森林生态系统每年具有较高的养分归还量，对于一些元素来说，还具有较高的淋溶量，尤其是K和Mg．

东灵山森林生态系统若干水分问题的研究

东灵山地区年均降水量659.7mm，单次降水以雨量小、雨强低的降水为主。水汽压（年均17.7mb）、相对湿度（年均66％）的季节变化呈现生长季高、冬季低的趋势。年均蒸发量1019.5mm;气温、风速、日照时间和水压与月蒸发量和日蒸量相关显著;气温、日照时间和水压分别在11-6月、7－8月和9－10月为决定蒸发量的首要因子。枯枝落叶层、土壤层湿度主要受前十日降水量和坡向影响。 植物体含水量生长季节较高，冬季较低;含水量随径级的增大而降低。六个灌木树种的平均含水量大小顺序为：毛榛（48.62%）最高荆条（36.32%）最低;七个乔木树种水分含量为油松，56.14%;蒙椴，54.19%;华北落叶松，52.91%;五角枫，43.64%;辽东栎，41.87%;棘皮桦，41.13%;大叶白腊，37.79%。几种植被类型的储水量为：辽东栎林，82.08mm;华北落叶松林，47.35mm;混交林，34.60mm;油松林，31.33mm;灌丛，12.40mm。各树种叶片日最低水势的季节均值为：辽东栎，-16.1bar;五角枫，-15.8bar;大叶白腊，-15.1bar;糠椴，-13.4bar;棘皮桦，-12.3bar;蒙椴，-12.2bar。叶片水势的日间变化均呈一“V”形曲线;光照在叶片水势的日间变化中起着决定性作用。 96年各树种平均单株树干茎流量为辽东栎，30.3mm(4.19%);华北落叶松，16.1mm(2.22%);油松，8.9mm(1.23%);棘皮桦，2.9mm(0.40%)。两个生长季各林分冠层的水量平衡为：辽东栎林，树干流茎量101.87mm(9.18%)，穿透降水量823.08mm(74.15%)，截留量185.05mm(16.67%);华北落叶松林，树干径流量66.88mm(6.03%)，穿透降水量836.92mm(75.40%)，截留量206.20mm(18.58);混交林，树干径流量50.13(4.52%)，穿透降水量846.78mm(76.29%)，截留量212.20mm(19.12%);油松林，树干径流量33.90mm(3.05%)，穿透降水量934.88mm(84.22%)，截留量141.22mm(12.72%)。多元回归分析表明，树干流茎量S与降水量P和前24小时降水量P_1呈显著正相关关系;穿透降水量T与降水量P和最大雨强M正相关显著。附加截留量与降水时间成正比。 枯枝落叶层的生物量为：油松林，25.56t/hm~2;华北落叶松林20.01t/hm~2;辽东栎林，8.31t/hm~2;混交林，7.98t/hm~2。枯枝落叶层的平均实际持水量和有效持水量均以油松林最大，其次是华北落叶松林，而混交林和辽东栎林较低;枯枝落叶层的实际持水量和有效持水量的季节变化分别与前十日降水量P10成正相关和负相关关系。枯枝落叶层的截留量为油松林＞华北落叶松林＞辽东栎林＞混交林;油松林（145.632mm和90.800mm）混交林(61.816mm和54.504mm)。油松林、辽东栎林、混交林和华北落叶松林去除枯枝落叶层后，土壤入渗量比对照平均降低100mm以上;表层土壤含水量分别比对照土壤下降了6.26、18.26、15.06和15.07个百分点。地表径流量分别增加了，辽东栎林34.299mm(603%)和15.816mm(525%);油松林14.593mm(732%)和10.584mm(1321%);混交林12.004mm(181%)和7.275mm(364%);华北落叶松林3.555mm(118%)，3.275mm(229%)。96年生长季，各土壤流失量分别增加了：油松林172.751t/hm~2(124倍);辽东栎林836.500t/hm~2(119倍);混交林172.499t/hm~2(47倍);华北落叶松林11.557t/hm~2(11倍)。表层土壤容重分别增加了：油松林15.0%和20.6%，辽东栎林18.4%和28.2%，混交林11.5%和38.5%，华北落叶松林4.3%和17.1%。 0-60cm深度土壤容重平均值的大小顺序为：草地>灌丛>辽东栎林>油松林>混交林>华北落叶松林;而土壤孔隙度的大小顺序为华北落叶松林>混交林>油松林>辽东栎林>灌丛>草地。两个生长季为土壤实际储水量的均值：油松林，124.45mm，78.62mm;辽东栎林，131.23mm，87.72mm;混交林，180.41mm，113.90mm;华北落叶松林，165.53mm，127.95mm;灌丛，172.50mm，89.81mm;草地，152.92mm，89.59 mm分别比干旱年份97年高出45.83mm、43.51mm、51.63mm、37.58mm、82.69mm和63.33mm。两个生长季的地表径流量为草地，30.930mm(2.79%);灌丛，16.321mm(147%);油松林，2.911mm(0.26%);辽东栎林，8.703mm(0.78%);混交林，8.625mm(0.78%);华北落叶松林，4.447mm(0.40%)。油松林、混交林和华北落叶松林地表径流量与降水量P(mm)和最大雨强(mm/h)正相关显著;而辽东栎林、灌丛和草地的地表径流量则与降水量P(mm)、平均雨强Q(mm/hr)和最大雨强M(mm/hr)三者之间呈显著正相关关系。与草地相比(1220.093kg/hm~2，100％)，灌丛、辽东栎林、混交林、油松林和华北落叶松林96年生长季的土壤流失量分别降低了85.05%、94.26%、96.99%、98.86和99.14%。 降水量是影响小流域径流量时间变化的主要因素;南沟和马牙石沟96年的径流量分别是97年的8.19倍和7.87倍，而径流深(46.25mm，52.75mm)分别比97年(5.65mm,6.70mm)高出40.60mm和46.05mm。两个小流域由于面积的差异而使南沟两年的径流量分别比马牙石沟高出2773.136m~3(13.15%)和235.434m~3(8.79%)。96年和97年马牙石沟径流深比南沟高出6.5mm(14.05%)和1.05mm(18.58%)。在地处大陆性季风气候区的东灵山地区，用0.010m~3/min/km~2/hr能较好地分割小流域的洪峰和基流。在五次暴雨水文曲线中，马牙石沟的快速径流量分别比南沟高出25.00%到143.33%。五次洪水水文响应R的平均值南沟为0.218%，马牙石沟为0.404%;与海洋性气候地区相比，东灵山地区小流域的R值要低一到两个数量级。马牙石沟洪峰流量Qp的平均值为418.772L/min要比南沟(281.191L/min)大48.9%。东灵山地区小流域的洪水径流过程可分为三种类型。

北京东灵山暖温带典型植被类型物种构成及物种多样性对氮素转化过程的影响

通过调查东灵山地区7个典型植被类型的物种多样性，并测定各林型中植物叶片养分特征，凋落物品质，土壤理化特性，豆科植物的生物固氮作用以及土壤有机质的净N矿化与硝化作用，研究了不同林型及其物种多样性对氮素转化过程的可能影响。结果表明： 1) 各林型乔灌草三层13个物种多样性指数之间都不同程度存在差异，且都表现基本一致的大小顺序，各样地乔灌草三层3个丰富度指数和5个多样性指数之间大都表现草本层>灌木层>乔木层的大小顺序。 2) 林型对植物叶片养分特征、叶片凋落物品质指标、土壤的大多数理化特性都有显著影响，其中，落叶阔叶林与针叶林之间的差异最为明显，优势种不同的针叶林之间也不同程度地存在差异。各林型物种多样性对植物叶片养分特征，凋落物品质和土壤理化特性也都不同程度存在显著影响，且乔灌草三层的物种多样性的影响不同。我们的结果支持物种多样性对生态系统过程存在显著影响的观点。 3) 胡枝子(Lespedeza bicolor)％FNDA值较低，在0～53.3％之间，与国外学者对某些木本豆科固氮植物的研究结果接近，但低于三叶草、野豌豆等草本豆科固氮植物。胡枝子生物固氮具有明显的季节差异，不同样地生境对胡枝子％FNDA值也存在显著影响，大都都表现铁塔辽东栎样地>重力点样地>站下灌丛样地>垭口样地的趋势。除胡枝子之外的其他豆科植物的％FNDA都高于胡枝子，且存在种间差异，以三籽两型豆(Amphicarpaea capillipes)最高(100％)，歪头菜(Vicia unijuga)最低(平均66.4％)，这些结果与国外相关研究接近。不同林型之间和同一林型不同样地之间也影响豆科植物的％FNDA。东灵山地区有相当数量的植物种具有和固氮植物相近的δ15N值和全N含量，具有潜在的生物固氮能力。6个林型中所有豆科植物的％FNDA平均值主要受乔木层和草本层物种多样性的影响，乔木层和草本层物种多样性提高，豆科植物的％FNDA将随之显著降低。 4) 气温、土壤温度和降水量显著影响各林型净氮硝化速率的季节动态，都表现为温度升高，降水量增加，净氮硝化速率也随之增大。 5) 在不同取样时间，不同林型在土壤NH4+、N03-含量，矿化、硝化速率以及年度总净矿化、硝化量之间均不同程度存在显著差异，其中，以辽东栎落叶阔叶林与针叶林之间，常绿针叶林与落叶针叶林之间，纯林与混交林之间的差异最为明显。 6) 土壤初始N0_3含量与年度总净硝化量，年度总净矿化量及其占TKN的百分比呈显著正相关关系;植物叶片全N浓度与净氮矿化、硝化作用呈显著负相关：植物叶片凋落物的品质指标与净氮矿化、硝化作用没有显著相关。 7) 胡枝子固氮作用(％FNDA值)越强，土壤有机氮的净硝化量就越大，胡枝子在从大气中获取大量N，的同时，很可能会增加氮素的淋溶损失量。胡枝子固氮作用(％FNDA值)与净氮矿化量不存在显著相关关系。 8) 只有乔木层和草本层部分种多样性指数对净氮矿化、硝化量存在显著影响。乔木层均匀度提高，土壤净氮碳化量将随之增大;而草本层物种多样性提高，均匀度提高，净氮矿化、硝化作用将随之降低，草本层植物对土壤氮素矿化作用具有显著抑制作用。 9) 落叶阔叶林与针叶林的供氮能力和维持无机氮素的能力之间存在比较明显的差异，而不同针叶林的矿化／硝化作用也有所差别。其中，辽东栎落叶阔叶林的供氮能力和维持氮素能力均高于针叶林和山杏灌丛;油松林的供氮能力与防止氮素损失的能力显然要强于落叶松林和山杏灌丛。 10) 尽管箭叶锦鸡儿灌丛植物叶片与凋落物中全N、全P浓度在大多数取样点上都低于硕桦(高于草甸)，但表层土中全N浓度高于硕桦和草甸，且其土壤有机质的供氮能力以及维持氮素能力都高于硕桦林和草甸，表明，锦鸡儿灌丛为侵入草甸和硕桦入侵提供了良好的养分条件，在该演替序列的发展过程中起了一定的推动作用。

森林生态系统中养分循环特征的比较研究

　通过研究都江堰地区三个不同林型下（般若寺亚热带常绿阔叶林、龙池杉木林、月亮湾楠木林）土壤氮素分布的异质性及其矿化动态、凋落物的分解，得出以下结论： 　　1. 在野外用顶盖埋管法培养土壤，测定土壤中的速效氮含量变化，我们发现，尽管铵态氮含量在三种林型下都大于硝态氮含量，但只有在龙池杉木纯林下净氨化速率和净硝化速率基本持平，其它两种林型下，净硝化速率都远远大于净氨化速率。净硝化速率的增强，暗示着土壤的退化程度的加剧。 　　2. 净氨化速率和净氮矿化速率在三种林型下均和土壤温度呈现一定程度的负相关，其中净氨化速率在龙池杉木纯林下和土壤温度达到了显著的负相关。而硝化速率在三种林型下均和土壤温度呈一定程度的正相关。这说明，虽然温度是影响净硝化速率、净氨化速率和净氮矿化速率的最重要的环境因子之一，但温度是通过影响土壤微生物的种群、数量和活力等来影响上述过程的，而由于生长环境的巨大差异性，温度的影响效果会出现很大的差异。另外，土壤含水量对三种林型下的净硝化速率、净氨化速率和净氮矿化速率也有很大的影响，但均没有达到显著的相关。 　　3. 不同的林型下具有不同物种多样性，而物种多样性会通过凋落物的质量和数量，土壤微生物类群的组成和性质以及植被盖度等角度对森林生态系统的土壤氮素循环产生深刻的影响。生物多样性的丧失会导致土壤无机氮（特别是硝态氮）流失的潜力增加，导致无机氮库的逐渐缩小。速效氮含量迅速降低。 　　4.铵态氮和硝态氮共同组成了土壤无机氮的绝大部分。但由于硝态氮易于淋溶, 从地表径流中流失，易被植物吸收，也可能通过反硝化损失掉，因此硝态氮的含量常常表现出较大的波动性，而且硝态氮的含量要远低于铵态氮的含量。但硝态氮占总速效氮的比例在不同的研究地点和时间上有很大的差别。 　　5 通过地统计学的变异函数和时间序列分析，我们发现，全氮和铵态氮在整个研究区域的异质性很大，并且异质性随着时间的推移发生了很大的变化，其中全氮和铵态氮的自相关尺度变化不大，但空间自相关度随着时间的推移变化明显，这说明，随着时间的推进，全氮和铵态氮的空间格局在大尺度上的变化很小，在小尺度的却发生了很大的变化。本研究还发现，对于全氮和铵态氮的空间异质性格局进行地统计学分析时，最小取样间隔应小于5米，并且铵态氮由于其自身的不稳定性，其在小尺度的空间异质性格局更明显，而其取样间隔应小于全氮的取样间隔。 　　6. 应用网袋法进行凋落物分解的实验，发现混合凋落物的分解速率在第一年就比按各组分混合比例计算的理论值更低。说明在本实验中几种凋落物——黄牛奶树、青冈栎、栲树和润楠的混合对分解没有促进作用。 　　7. 土壤湿度和凋落物干物质分解密切相关，而不同林地的温度差异对干物质分解影响不大。但对于具体元素（本文中的C和N）的分解而言，分解受更复杂的机制调节，其中可能包括不同林型土壤中的分解微生物群落以及土壤理化性质的差异，相比之下，土壤湿度影响就不重要了。 　　8. 初始凋落物中的C/N浓度的比值显著影响分解速率，和腐解率呈显著负相关。因此可以用它来预测分解。在N的分解中，初始凋落物中的N浓度也会影响分解，具体反映在初始N浓度和实验截止时的N浓度成正比。 　　9. 亚热带气候下，凋落物的分解比在暖温带分解要快，并且初始凋落物中N元素的含量普遍较高，因而在分解中没有出现大量富集。 　　10.凋落物质量本身分解较快的树种，有机质的分解并没有相应快，说明在凋落物干物质降解过程中占主要地位的不是有机质。