河岸带对陆地水体氮素输入的截流转化作用

氮素是陆地水体的重要污染物之一,相邻高地土壤中的氮素经非点源途径通过河岸带进入水体.河岸带是高地和水体之间的过渡带,健康的河岸带系统能够通过物理的、生物的和生物化学的过程,实现对氮素的截留转化.本文系统地介绍了氮素进入陆地水体的主要途径和河岸带对陆地水体氮素污染物截留转化的机制,并从河岸带水文过程、土壤特征、植被状况、人为活动等方面,论述了影响河岸带氮素截留转化作用的因素;在此基础上,对目前河岸带研究中存在的问题进行了讨论,并对我国开展河岸带的研究提出了建议.     

短期放牧干扰对黄土丘陵区生物结皮土壤氮素累积的影响

通过野外调查结合室内分析,研究了黄土丘陵区模拟放牧干扰半年和一年后生物结皮土壤全氮、速效氮和微生物生物量氮累积的变化,以期揭示生物结皮土壤氮素对干扰响应的敏感性.结果表明: 生物结皮土壤氮素对干扰响应敏感,短期干扰可导致土壤全氮、速效氮和微生物生物量氮含量降低.干扰半年后,生物结皮层全氮和速效氮含量较不干扰分别下降0.17～0.39 g·kg^-1、1.78～5.65 mg·kg^-1;干扰一年后,分别下降0.13～0.40 g·kg^-1、11.45～32.68mg·kg^-1,生物结皮层微生物生物量氮下降69.99～330.97 mg·kg^-1,0～2 cm土壤微生物生物量氮增加25.51～352.17 mg·kg^-1.干扰对生物结皮土壤氮素累积的影响与干扰强度有关,20%和30%干扰强度下生物结皮层氮素累积变化不显著,40%和50%干扰强度下生物结皮层氮素累积显著降低.短期干扰降低了生物结皮层氮素累积,但表层5 cm土壤氮素含量变化不显著.     

尕海湿地草甸土退化过程土壤氮矿化演变特征

氮矿化是生态系统循环的重要环节之一,影响着生态系统功能和氮素生物地球化学循环,因此研究高寒湿地退化过程中土壤氮矿化演变特征,对揭示气候变化和人为活动干扰背景下的湿地土壤氮素循环过程具有重要意义。以尕海湿地4种不同退化梯度(未退化、轻度退化、中度退化、重度退化)土壤为研究对象,采用野外树脂芯原位培养方法,通过对植物生长季不同生长阶段(生长初期、生长盛期、枯萎期)土壤氮素矿化作用研究,分析湿地退化演替过程中土壤氮矿化时空变化特征及其与土壤环境因子和酶活性之间的关系。结果表明：尕海湿地退化对土壤氮矿化过程有显著抑制作用,与未退化(0.143 mg kg^-1 d^-1)相比,轻度退化、中度退化、重度退化的土壤净氮矿化速率分别减小了0.018 mg kg^-1 d^-1、0.025 mg kg^-1 d^-1、0.020 mg kg^-1 d^-1;随着退化程度加剧,土壤净氨化速率逐渐减小或者不变,而净硝化速率却增大。随时间推移,各退化...     

古尔班通古特沙漠生物土壤结皮对氨氧化微生物生态位的影响

生物结皮作为荒漠地表的重要覆被类型, 在荒漠生态系统的氮素循环中扮演重要角色。融雪期为古尔班通古特沙漠生物结皮的复苏和生长提供了充足的水分, 也成为该沙漠氮素固定和转化的重要时期, 但该时期生物结皮如何影响驱动氨氧化转化的微生物群落动态尚未明确。因此, 我们利用荧光定量PCR (fluorescent quantitative PCR, qPCR)方法分析融雪期生物结皮与去除结皮不同土层(0-2, 2-5, 5-10和10-20 cm)氨氧化菌群丰度特征, 结合潜在硝化速率和土壤理化参数, 探究融雪期生物结皮对荒漠土壤氮素转化作用。结果表明: 氨氧化古菌(ammonia-oxidizing archaea, AOA)是古尔班通古特沙漠土壤优势氨氧化菌, 生物结皮对0-2 cm层土壤中AOA、氨氧化细菌(ammonia-oxidizing bacteria, AOB) amoA基因丰度具有显著抑制作用(P < 0.01), 对10-20 cm层土壤中AOA amoA基因丰度具有显著促进作用(P < 0.01)。冗余分析(redundancy analysis, RDA)表明, AOA、AOB amoA基因丰度主要受土壤含水量和铵态氮含量的影响, 占总条件效应的54.90%。氨氧化速率分析发现, 去除生物结皮显著降低古尔班通古特沙漠土壤硝化作用潜力(P < 0.001), 证实生物结皮对荒漠土壤氮素转化具有重要的调控作用。综上所述, 古尔班通古特沙漠氨氧化微生物的分布规律受环境因子调控, 特别是生物结皮可以通过调节土壤含水量和铵态氮含量影响AOA和AOB的空间生态位分化, 促进沙漠土壤的硝化作用。     

中国典型生态脆弱区生态化学计量学研究进展

在人类活动和自然环境变化的相互作用下,生态脆弱区生态系统随之变迁,荒漠化、盐碱化、水土流失、植被生产力下降等是生态脆弱区面临的重要问题。生态化学计量学作为当前多学科交叉研究的热点领域,强调从生态系统能量与元素平衡角度,揭示元素生物地球化学循环和生态系统对环境变化的调控机制。为了促进对生态脆弱区碳（C）、氮（N）、磷（P）生态化学计量的深入理解,本文重点总结了近年来有关我国典型生态脆弱区植物、凋落物、土壤和土壤微生物量C、N、P生态化学计量及其对环境变化响应的研究成果,并展望未来研究方向,以期促进生态化学计量学的发展和生态脆弱区生态保护与恢复研究。研究表明,植物-凋落物-土壤-土壤微生物系统C、N、P化学计量具有较强相关性,并受土壤因子、气候因子、生物因子和人类活动的显著影响。在生态脆弱区,我国北方荒漠及荒漠化地区由于较高的N∶P比值易受P限制,而青藏高原脆弱区、西南岩溶石漠化地区和黄土高原脆弱区等生态脆弱区更易受N限制;随着植被恢复,养分限制逐渐由N限制向P限制转变。生态脆弱区相对较低的养分含量和C∶N∶P比值或许可在一定程度上解释植被生产力较低的原因,而具有较高N、P化学计量内稳性的植物在贫瘠环境中具有较强竞争力和更高稳定性。今后可加强多尺度、不同生态系统植物-凋落物-土壤-土壤微生物系统生态化学计量和长期、多因子交互控制实验的研究。     

牲畜排泄物返还对草地土壤氮转化和氧化亚氮(N2O)排放的影响研究进展

牲畜排泄物返还被认为是对草地的一种天然的施肥措施,也是草地养分归还的一种重要途径,对于维持土壤肥力和植被生产力具有十分重要的生态学意义。论述了放牧牲畜粪便和尿液自身降解及其氮素变化、粪尿返还对草地土壤氮转化和氧化亚氮(N₂O)排放的作用机制及影响效应,指出排泄物氮输入使粪尿斑块成为草地土壤氮转化和N₂O排放的活跃点,且不同排泄物类型、土壤理化特性和气候条件等使土壤氮素矿化、固持、硝化及反硝化等关键过程具有复杂性和差异性,进而导致不同类型草地生态系统N₂O排放对牲畜排泄物返还的响应不尽相同。建议未来在全球气候变化背景下,应加强草地牲畜排泄物-植被-土壤体系氮素生物地球化学循环过程的系统研究,进一步加深天然草地关键氮素转化过程和N₂O排放的微生物作用机制方面的认识,从而有助于为优化放牧牲畜排泄物的管理模式、制定科学合理的草地土壤养分调控策略和维持草地生态系统可持续发展提供科学有效的理论指导。     

湿地氮素传输过程研究进展

综述了湿地氮素传输过程的研究进展。湿地氮素传输过程包括物理过程、化学过程和生物过程 ,与土壤、植物的发生、发育紧密联系在一起 ,并形成了空气 -水 -土 -生命系统中物质循环和能量流动的复杂网络。湿地硝态氮的淋失直接威胁着湿地地下水水质安全 ,N2 O源汇转变受土壤和水体等环境因子的制约 ,氨挥发则与水体 p H值密切相关排放。湿地氮素的化学转化过程是矿质养分供给和 N2 O产生的主要机制 ,受环境因子和人类活动干扰的影响 ;动力学模型可用于描述氮素的化学转化过程。湿地植物的吸收和累积以及微生物的分解过程是湿地氮素循环的重要环节。最后分析了当前国内外研究中存在的不足 ,并对未来研究的重点领域进行了展望     

毛乌素沙地区域尺度生物结皮有机碳

生物结皮在旱区荒漠养分循环和碳氮固存等生态系统功能方面发挥着重要作用,尤其能通过光合作用固定CO₂,从而提高土壤有机碳含量。目前有关区域尺度生物结皮土壤有机碳认知的缺乏在一定程度上制约了土壤碳库的精准预测。本研究选取毛乌素沙地全域(4.22万km²)内45个样地,测算了藓结皮和藻结皮两类典型生物结皮及其下土壤的有机碳含量(SOC)和密度(SOCD),并结合气候、土壤和植被等指标,深入探讨了区域尺度下生物结皮有机碳的空间分布特征及其主控因素。结果表明: 1)与裸沙相比,生物结皮显著提升了土壤有机碳含量和密度,且藓结皮及其下土壤有机碳含量(4.93 g·kg^-1)和密度(0.41 kg·m^-2)均高于藻结皮(1.89 g·kg^-1、0.18 kg·m^-2)。2)区域尺度上,生物结皮的有机碳含量和密度具有明显的空间分布特征,呈现出由东北-中部、西部-东南方向递减的带状分布与块状镶嵌分布。3)生物结皮及其下土壤有机碳含量和密度主要受气候、土壤和植被的综合影响,并因生物结皮类型而异,藓结皮主要受年均最高温和蒸散力的影响,而藻结皮主要受水蒸气分压的影响。     

土壤氮素转化的关键微生物过程及机制

微生物是驱动土壤元素生物地球化学循环的引擎.氮循环是土壤生态系统元素循环的核心之一,其四个主要过程,即生物固氮作用、氨化作用、硝化作用、反硝化作用,均由微生物所驱动.近10年来,随着免培养的分子生态学技术和高通量测序技术等的发展,在硝化微生物多样性及其作用机理、厌氧氨氧化过程和机理等研究方面取得了突破性进展.本文重点阐述了我国有关土壤硝化微生物方面的研究进展,在此基础上,简要介绍了反硝化微生物和厌氧氨氧化及硝酸盐异化还原成铵作用的研究进展,并对今后的研究工作提出了展望.今后土壤氮素转化微生物生态学的研究,应瞄准国际微生生态学发展的前沿,加强新技术新方法的应用,结合我国农业可持续发展、资源环境保护和全球变化研究的重大需求,重点开展以下几方面的工作:(1)开展大尺度上土壤硝化作用及氨氧化微生物分布的时空演变特征及驱动因子的研究;(2)加强氮素转化关键微生物过程与机理的研究,并与相关过程的通量(如氨挥发、N2O释放)和反应速率(如矿化速率、硝化速率)关联起来;(3)在特定生态系统中系统研究各个氮转化过程的耦合关系,构建相关氮素转化和氮素平衡模型,为定向调控土壤氮素转化过程,提高氮素利用效率并减少其负面效应提供科学依据.     

三峡库区消落带重建植被下土壤微生物生物量碳氮含量特征

为探究三峡库区消落带植被重建后,土壤微生物生物量含量特征及影响因素,对忠县消落带人工重建植被土壤及裸地土壤(作为对照)微生物生物量碳氮含量进行了调查研究。结果表明:(1)在消落带165-175 m高程土壤微生物生物量碳含量草地林地农耕地裸地,微生物生物量氮含量规律与微生物生物量碳一致,农耕地明显提高;土壤微生物生物量总体呈现出草地最高、林地和农耕地次之,裸地最低的趋势,表明进行消落带植被恢复对土壤微生物生物量有显著的促进作用。(2)不同植被类型下,土壤微生物生物量碳氮比变化范围为8.02-10.25,土壤微生物生物量碳、氮占土壤有机碳、全氮的百分比范围分别是2.40%-4.60%和2.13%-3.58%,其中林地对土壤碳、氮库贡献显著高于裸地(P0.05)。(3)土壤微生物生物量碳、氮与土壤有机碳、全氮和pH值呈现显著相关性,与土壤含水量呈现极显著相关性,说明消落带重建植被土壤的这些理化性质对土壤微生物生物量碳、氮含量有强烈的影响。因此,在三峡库区消落带进行植被恢复重建能显著提高土壤微生物生物量及土壤质量,对加强三峡库岸生态系统的稳定性具有重要意义。     

Woody Vegetation Removal Stimulates Riparian and Benthic Denitrification in Tallgrass Prairie

Expansion of woody vegetation into areas that were historically grass-dominated is a significant contemporary threat to grasslands, including native tallgrass prairie ecosystems of the Midwestern United States. In tallgrass prairie, much of this woody expansion is concentrated in riparian zones with potential impacts on biogeochemical processes there. Although the effects of woody riparian vegetation on denitrification in both riparian soils and streams have been well studied in naturally wooded ecosystems, less is known about the impacts of woody vegetation encroachment in ecosystems that were historically dominated by herbaceous vegetation. Here, we analyze the effect of afforestation and subsequent woody plant removal on riparian and benthic denitrification. Denitrification rates in riparian soil and selected benthic compartments were measured seasonally in naturally grass-dominated riparian zones, woody encroached riparian zones, and riparian zones with woody vegetation removed in two separate watersheds. Riparian soil denitrification was highly seasonal, with the greatest rates in early spring. Benthic denitrification also exhibited high temporal variability, but no seasonality. Soil denitrification rates were greatest in riparian zones where woody vegetation was removed. Additionally, concentrations of nitrate, carbon, and soil moisture (indicative of potential anoxia) were greatest in wood removal soils. Differences in the presence and abundance of benthic compartments reflected riparian vegetation, and may have indirectly affected denitrification in streams. Riparian soil denitrification increased with soil water content and NO₃ ^?. Management of tallgrass prairies that includes removal of woody vegetation encroaching on riparian areas may alter biogeochemical cycling by increasing nitrogen removed via denitrification while the restored riparian zones return to a natural grass-dominated state.     

Ecosystem response to removal of exotic riparian shrubs and a transition to upland vegetation

Understanding plant community change over time is essential for managing important ecosystems such as riparian areas. This study analyzed historic vegetation using soil seed banks and the effects of riparian shrub removal treatments and channel incision on ecosystem and plant community dynamics in Canyon de Chelly National Monument, Arizona. We focused on how seeds, nutrients, and ground water influence the floristic composition of post-treatment vegetation and addressed three questions: (1) How does pre-treatment soil seed bank composition reflect post-treatment vegetation composition? (2) How does shrub removal affect post-treatment riparian vegetation composition, seed rain inputs, and ground water dynamics? and (3) Is available soil nitrogen increased near dead Russian olive plants following removal and does this influence post-treatment vegetation? We analyzed seed bank composition across the study area, analyzed differences in vegetation, ground water levels, and seed rain between control, cut-stump and whole-plant removal areas, and compared soil nitrogen and vegetation near removed Russian olive to areas lacking Russian olive. The soil seed bank contained more riparian plants, more native and fewer exotic plants than the extant vegetation. Both shrub removal methods decreased exotic plant cover, decreased tamarisk and Russian olive seed inputs, and increased native plant cover after 2 years. Neither method increased ground water levels. Soil near dead Russian olive trees indicated a short-term increase in soil nitrogen following plant removal but did not influence vegetation composition compared to areas without Russian olive. Following tamarisk and Russian olive removal, our study sites were colonized by upland plant species. Many western North American rivers have tamarisk and Russian olive on floodplains abandoned by channel incision, river regulation or both. Our results are widely applicable to sites where drying has occurred and vegetation establishment following shrub removal is likely to be by upland species.     

Nutrient Vectors and Riparian Processing: A Review with Special Reference to African Semiarid Savanna Ecosystems

Abstract This review article describes vectors for nitrogen and phosphorus delivery to riparian zones in semiarid African savannas, the processing of nutrients in the riparian zone and the effect of disturbance on these processes. Semiarid savannas exhibit sharp seasonality, complex hillslope hydrology and high spatial heterogeneity, all of which ultimately impact nutrient fluxes between riparian, upland and aquatic environments. Our review shows that strong environmental drivers such as fire and herbivory enhance nitrogen, phosphorus and sediment transport to lower slope positions by shaping vegetative patterns. These vectors differ significantly from other arid and semiarid ecosystems, and from mesic ecosystems where the impact of fire and herbivory are less pronounced and less predictable. Also unique is the presence of sodic soils in certain hillslopes, which substantially alters hydrological flowpaths and may act as a trap where nitrogen is immobilized while sediment and phosphorus transport is enhanced. Nutrients and sediments are also deposited in the riparian zone during seasonal, intermittent floods while, during the dry season, subsurface movement of water from the stream into riparian soils and vegetation further enrich riparian zones with nutrients. As is found in mesic ecosystems, nutrients are immobilized in semiarid riparian corridors through microbial and plant uptake, whereas dissimilatory processes such as denitrification may be important where labile nitrogen and carbon are in adequate supply and physical conditions are suitable—such as in seeps, wallows created by animals, ephemeral wetlands and stream edges. Interaction between temporal hydrologic connectivity and spatial heterogeneity are disrupted by disturbances such as large floods and extended droughts, which may convert certain riparian patches from sinks to sources for nitrogen and phosphorus. In the face of increasing anthropogenic pressure, the scientific challenges are to provide a basic understanding of riparian biogeochemistry in semiarid African savannas to adequately address the temporal and spatial impact of disturbances, and to apply this knowledge to better regional land and water management. An integrated, multidisciplinary approach applied in protected as well as human-disturbed ecosystems in southern Africa is essential for underpinning a strong environmental basis for sustainable human-related expansion.     

Tracing Si–N–P ecosystem-pathways: is relative uptake in riparian vegetation influenced by soil waterlogging,mowing management and species diversity?

Despite the growing concern about the importance of silicon (Si) in controlling ecological processes in aquatic ecosystems, little is known about its processing in riparian vegetation, especially compared to nitrogen (N) and phosphorus (P). We present experimental evidence that relative plant uptake of N and P compared to Si in riparian vegetation is dependent on mowing practices, water-logging and species composition. Results are obtained from a controlled and replicated mesocosm experiment, with a full-factorial design of soil water logging and mowing management. In our experiments, the Si excluding species Plantago lanceolata was dominant in the mown and non-waterlogged treatments, while Si accumulating meadow grasses and Phalaris arundinacea dominated the waterlogged treatments. Although species composition, management and soil moisture interacted strongly in their effect on relative Si:N and Si:P uptake ratios, the uptake of N to P remained virtually unchanged over the different treatments. Our study sheds new light on the impact of riparian wetland ecosystems on nutrient transport to rivers. It indicates that it is essential to include Si in future studies of the impact of riparian vegetation on nutrient transport, as these are often implemented as a measure to moderate excessive N and P inputs.     

Developing a vision for improved monitoring and reporting of riparian restoration projects

Representatives from agencies involved in natural resource management in the Murray‐Darling Basin gathered for a workshop in November 2010 to develop a vision for improved monitoring and reporting of riparian restoration projects. The resounding message from this workshop was that the effectiveness of riparian restoration depends on having sound, documented and agreed evidence on the ecological responses to restoration efforts. Improving our capacity to manage and restore riparian ecosystems is constrained by (i) a lack of ecological evidence on the effects of restoration efforts, and (ii) short‐termism in commitment to restoration efforts, in funding of monitoring and in expected time spans for ecosystem recovery. Restoration at the effective spatial scope will invariably require a long‐term commitment by researchers, funding agencies, management agencies and landholders. To address the knowledge gaps that constrain riparian restoration in the Basin, participants endorsed four major fields for future research: the importance of landscape context to restoration outcomes; spatio‐temporal scaling of restoration outcomes; functional effects of restoration efforts; and developing informative and effective indicators of restoration. To improve the monitoring and restoration of riparian zones throughout the Basin, participants advocated an integrated approach: a hierarchical adaptive management framework that incorporates long‐term ecological research.     

氮输入对东北土壤碳蓄积氮素利用效率的影响

由于人类活动影响,通过沉降和施肥方式进入生态系统的活性氮显著增加,其对土壤有机碳库产生重要影响。氮素利用效率(NUE)作为深入理解陆地生态系统碳氮耦合关系的重要参数,对NUE时空规律的研究不仅可以评估目前氮输入对陆地生态系统碳汇增加的贡献,同时也有助于预测未来氮输入情况下陆地生态系统的碳平衡。利用生态系统过程模型——CEVSA2模型的模拟结果,分析了东北地区氮输入情况下,土壤碳的氮素利用效率(SNUE)的时空变化规律及其影响因素,结果表明:(1)1961—2010年,氮输入的显著增加促进了土壤碳的蓄积,但SNUE显著下降;(2)森林的平均SNUE最高,农田最低;灌丛的下降速率最大,森林的SNUE变化趋势最不显著;(3)三江平原和长白山地区以及大小兴安岭的部分地区SNUE最大,其次是辽河平原、松嫩平原地区;内蒙古高原、呼伦贝尔高原地区以及大、小兴安岭的部分地区SNUE出现负值,说明在这些地区,外援氮输入抑制了土壤碳的蓄积;(4)氮输入的空间分异和不同生态系统响应氮输入的差异共同决定了SNUE及其变化的空间格局。该研究结果可为进一步分析不同区域氮促汇潜力和预测未来氮输入情景下的区域碳平衡提供参考。     

Plants for nitrogen management in riparian zones: A proposed trait‐based framework to select effective species

Restoring plants to the riparian zone is regarded as management best practice in river restoration and has the potential to reduce the impact of nitrogen (N) pollution on aquatic organisms and improve water quality for human use. Plant characteristics and the interplay of hydrology and biogeochemistry control N retention in the riparian zone. The balance between processes such as denitrification and plant assimilation determines riparian N retention. Plant traits are likely to mediate these N removal processes through variations in root form, growth character, foliage production (quantity, quality and rate of return to the soil) and by altering conditions in the rhizosphere soil. Vegetation can slow N transfer via direct plant uptake of N (during periods of rapid vegetation growth) and changes induced to soil hydrology, nutrient cycling and microbial activity, principally denitrification. Few studies have focused on species‐dependent effects on N movement through soil and across boundaries. We propose a new framework, based on a literature review of plant traits with respect to N cycling, which can be used to select plant species with traits likely to maximise N removal during transport through the riparian zone. In the proposed framework, inter‐specific differences in traits known to influence N mobility: root form, growth rate, foliar characteristics and rhizosphere processes, are used to describe species’ potential impact on N removal. Plant trait data may be drawn from studies outside the riparian zone; for example forest ecology, horticulture or forestry research, and candidate species are scored to predict N removal efficiency. We apply the framework to New Zealand's native riparian plant assemblages to demonstrate the trait‐based approach. This framework can guide restoration management decisions and investment in riparian revegetation in a manner that is not restricted to geographically specific or well‐studied species.     

黄土高原植被建设与土壤干燥化:问题与展望

黄土高原大规模植被建设有效减少了水土流失、改善了区域生态环境,大规模人工植被种植也造成了土壤水分的过度消耗,导致了土壤干燥化,成为当前黄土高原生态恢复的重要制约因素,威胁区域生态系统健康与稳定。系统综述了黄土高原地区人工植被恢复对土壤干燥化的作用机制,植被群落特征与土壤干燥化的耦合关系,多尺度土壤干燥化时空分异规律及其影响因素,明确了当前大规模人工植被恢复过程中土壤水分持续利用面临的问题与挑战。建议今后加强植被动态对水文过程影响的研究,明确多尺度植被格局与土壤干燥化时空分异的耦合关系,系统开展变化环境下不同尺度植被与土壤水分相互作用的模拟研究,探讨基于植被格局优化的土壤水分调控机制,维护黄土高原地区土壤安全,提升区域生态系统服务功能。     

Soil microbes of an urban remnant riparian zone have greater potential for N removal than a degraded riparian zone

Soils in the riparian zone, the interface between terrestrial and aquatic ecosystems, may decrease anthropogenic nitrogen (N) loads to streams through microbial transformations (e.g., denitrification). However, the ecological functioning of riparian zones is often compromised due to degraded conditions (e.g., vegetation clearing). Here we compare the efficacy of an urban remnant and a cleared riparian zone for supporting a putative denitrifying microbial community using 16S rRNA sequencing and quantitative polymerase chain reaction of archaeal and bacterial nitrogen cycling genes. Although we had no direct measure of denitrification rates, we found clear patterns in the microbial communities between the sites. Greater abundance of N-cycling genes was predicted by greater soil ammonium (N-NH₄), organic phosphorus, and C:N. At the remnant site, we found positive correlations between microbial community composition, which was dominated by putative N oxidisers (Nitrosomonadaceae, Nitrospiraceae and Nitrosotaleaceae), and abundance of ammonia-oxidizing archaea (AOA), nirS, nirK and nosZ, whereas the cleared site had lower abundance of N-oxidisers and N cycling genes. These results were especially profound for the remnant riparian fringe, which suggests that this region maintains suitable soil conditions (via diverse vegetation structure and periodic saturation) to support putative N cyclers, which could amount to higher potential for N removal.     

土壤有机质对土壤水分保持及其有效性的控制作用

如何基于常规测定因子评估森林在土壤水分保持方面的生态效益, 并建立森林固碳效益与水文效益的联系等科学问题, 在综合评估森林生态效益方面有着重要意义。该文以南亚热带地区的3种不同演替阶段的森林生态系统(人工恢复的马尾松针叶林(Pinus massoniana coniferous forest, PF)、马尾松针阔叶混交林(mixed Pinus massoniana-broad-leaved forest, PBF)和季风常绿阔叶林(monsoon evergreen broad-leaved forest, MBF))为研究对象, 通过分析其土壤有机质及土壤水分状况在林内及林型间的分布格局差异, 探讨土壤有机质对土壤水分保持的控制作用。结果表明: 由PF至地带性顶级群落MBF的3种林分虽然相距很近且有关环境因子一致, 但0-30 cm土层的土壤含水量差异显著, MBF的最高, PBF其次; 3种林型林内土壤水分分布格局迥异, MBF的土壤水分随土层加深而递减的趋势明显, PBF土壤各层水分较为均一, PF则土壤表层水分含量较低, 与土壤有机质的状况一致。土壤水分特征曲线显示, 0-40 cm土层在相同基质吸力条件下的土壤水分含量: MBF > PBF > PF, MBF的保水性最好。进一步分析发现, 土壤孔隙度对土壤含水量的影响最大, 饱和含水量、土壤有机质次之, 同时, 考虑到土壤孔隙度和土壤饱和含水量对土壤有机质的高度依赖性, 我们认为土壤有机质控制着土壤含水量及其有效性( p= 0.014)。作为常规测定指标的土壤有机质, 不仅是森林固碳效益的关键指标, 而且可用来量度土壤水分保持及其有效性, 可以作为评价森林生态系统服务功能的一个综合指标。