Net ecosystem carbon exchange in two experimental grassland ecosystems

Increases in net primary production (NPP) may not necessarily result in increased C sequestration since an increase in uptake can be negated by concurrent increases in ecosystem C losses via respiratory processes. Continuous measurements of net ecosystem C exchange between the atmosphere and two experimental cheatgrass (Bromus tectorum L.) ecosystems in large dynamic flux chambers (EcoCELLs) showed net ecosystem C losses to the atmosphere in excess of 300 g C m^?2 over two growing cycles. Even a doubling of net ecosystem production (NEP) after N fertilization in the second growing season did not compensate for soil C losses incurred during the fallow period. Fertilization not only increased C uptake in biomass but also enhanced C losses through soil respiration from 287 to 469 g C m^?2, mainly through an increase in rhizosphere respiration. Fertilization decreased dissolved inorganic C losses through leaching of from 45 to 10 g C m^?2. Unfertilized cheatgrass added 215 g C m^?2 as root‐derived organic matter but the contribution of these inputs to long‐term C sequestration was limited as these deposits rapidly decomposed. Fertilization increased NEP but did not increase belowground C inputs most likely due to a concurrent increase in the production and decomposition of rhizodeposits. Decomposition of soil organic matter (SOM) was reduced by fertilizer additions. The results from our study show that, although annual grassland ecosystems can add considerable amounts of C to soils during the growing season, it is unlikely that they sequester large amounts of C because of high respiratory losses during dormancy periods. Although fertilization could increase NEP, fertilization might reduce soil C inputs as heterotrophic organisms favor root‐derived organic matter over native SOM.     

Ecological effects of atmospheric reactive nitrogen deposition on semi-natural terrestrial ecosystems

Evidence that enhanced reactive nitrogen deposition is affecting semi-natural terrestrial ecosystems comes from historic increases in plant tissue N concentrations, correlations between tissue N concentrations and present-day total atmospheric N deposition, changes in plant amino-acid composition and effects on N assimilation. The ecological significance of such changes in biomarkers is uncertain. This paper explores the ecological significance of reactive atmospheric N deposition through a review of previous experimental findings and new experimental evidence from an acidic and a calcareous grassland, both showing phosphorus limitation, and a N-limited Calluna vulgaris (L.) Hull heathland in upland Britain. Nitrogen addition in the range 0–20 g N m⁻² yr⁻¹ initially (years 0–4) increased the growth of Calluna and a decline in some subordinate species. In subsequent years, shoot extension was not stimulated, but winter injury was observed from 1993 onwards, suggesting a strong interaction between N supply and climatic conditions. By contrast, the grasslands showed a small decrease in the cover of higher plants in later years (6–7) of the experimental treatments (0–14 g N m⁻² yr⁻¹) and no growth stimulation. All N treatments reduced the bryophyte cover in the acidic grassland. There were marked effects on below-ground processes, including a sustained stimulation of N mineralization in the grassland soils, and an increase in the bacterial utilization of organic substrates in the heathland, as measured in BIOLOG plates. The results strongly suggest the importance of atmospheric N deposition on microbially driven processes in soils, and are discussed in relation to the scale of potential ecosystem changes and their reversibility by pollution abatement.     

西南岩溶生态系统土壤微生物的初步研究

探讨微生物在岩溶作用中的作用 ,需要考察土壤微生物在岩溶地区的生态分布和特性。本文对采自中国西南 4个不同岩溶地区 (重庆金佛山、六盘水米苏嘎、广西弄拉和桂林丫吉村岩溶试验场 )生态系统土壤样品中的细菌、放线菌和真菌进行了数量测定 ,结果表明 ,微生物的数量和组成与赋予不同地形和植被特征的岩溶生态系统的特性高度相关。本文还分析了马山弄拉和岩溶试验场的优势细菌 ,并且进行了初步鉴定 ,结果显示 ,固氮菌科细菌在两个岩溶生态系统土壤中都占优势 ,表明其土壤肥力都在改善。     

草地生态系统中土壤氮素矿化影响因素的研究进展

氮素是各种植物生长和发育所需的大量营养元素之一,也是牧草从土壤吸收最多的矿质元素．土壤中的氮大部分以有机态形式存在,而植物可以直接吸收利用的是无机态氮．这些有机态氮在土壤动物和微生物的作用下。由难以被植物直接吸收利用的有机态转化为可被植物直接吸收利用的无机态的过程就是土壤氮的矿化．氮素矿化受多种因子的影响,这些因子可以归结为生物因子和非生物因子．生物因子包括：土壤动物、土壤微生物和植物种类．土壤动物可以促进土壤有机质的矿化;土壤微生物种类、结构及功能与氮的分解、矿化有密切的关系;不同的植物种类对土壤氮素的矿化作用是不相同的,一般来说。有豆科植物生长的土壤比其它种类土氮素矿化的作用大．非生物因素一般可以分为环境因子和人类活动干扰．环境因子中土壤温度和含水量对土壤氮素矿化的影响是国内外众多科学家研究的方向．尽管如此,在此方面的研究还没有取得一致意见,仍然需要进行这方面的研究,而在其他诸如：不同的土壤质地与土壤类型方面,研究报道的结论也很不一致,草地生态系统中人类活动对土壤氮素矿化的影响主要包括,不同强度的放牧,割草以及施肥、火烧强度等．非生物因子对氮素矿化的影响非常直接和明显,尤其是人类活动．本文综述了近年来影响草地生态系统土壤氮素矿化有关因素的一些进展．     

草地土壤固碳潜力研究进展

土壤固碳功能和固碳潜力已成为全球气候变化和陆地生态系统研究的重点。草地土壤有机碳库,作为陆地土壤有机碳库的重要组成部分,其较小幅度的波动,将会影响整个陆地生态系统碳循环,进而影响全球气候变化。因此,深入研究草地土壤固碳功能和固碳潜力对于适应和减缓气候变化具有重要意义。在土壤固碳潜力相关概念界定基础上,结合《2006年IPCC国家温室气体清单指南》,从样点及区域尺度上综述了目前关于草地土壤固碳潜力的一般估算方法,同时对各类方法的特点及适用性进行了评述,提出了草地生态系统固碳潜力研究概念模型。最后在对草地土壤固碳的影响因素及固碳措施总结的基础上,阐明了草地土壤有机碳固定研究中存在的问题和发展前景。     

Models of sulfur dynamics in forest and grassland ecosystems with emphasis on soil processes

The major S constituents in terrestrial ecosystems include inorganic SO ₄ ^2– , C-bonded S and ester sulfate with the organic fractions constituting the major soil S pools. Conceptual models of S dynamics link inorganic SO ₄ ^2– flux to organic sulfur transformations and other elements such as N and C. Mass balance models have been useful in ascertaining whether a system is at steady-state with respect to adsorption processes and/or nutritional demands of vegetation for S. Chemical equilibrium/surface complexation models have been used to evaluate the effects of a complex of factors, including effects of pH on SO₄ ^– adsorption and precipitation; these models have not generally been integrated into ecosystem models of S dynamics. Models such as ILWAS, Birkenes, Storgama, Trickle-Down and MAGIC were developed to ascertain surface water acidification processes within watersheds; these models incorporated SO₄ ^2– adsorption in some formulation combined with hydrological considerations. None of these models explicitly treat organic S transformations and fluxes. In contrast, grassland ecosystem models detail organic S transformations, but give little attention to adsorption and hydrologic factors. More detailed simulation models of S transformations in forest and grassland soils have recently been developed, but these results have yet to be incorporated into ecosystem and watershed models.     

Effects of the nematofauna on microbial energy and matter transformation rates in European grassland soils

The effect of the nematofauna on the microbiology and soil nitrogen status was studied in 6 major European grassland types (Northern tundra (Abisko, Sweden), Atlantic heath (Otterburn, UK), wet grassland (Wageningen, Netherlands), semi-natural temperate grassland (Linden, Germany), East European steppe (Pusztaszer, Hungary) and Mediterranean garigue (Mt. Vermion, Greece). To extend the range of temperature and humidity experienced locally during the investigation period, soil microclimates were manipulated, and at each site 14 plots were established representing selected combinations of 6 temperature and 6 moisture levels. The investigated soils divided into two groups: mineral grassland soils that were precipitation fed (garigue, wet grassland, seminatural grassland, steppe), and wet organic soils that were groundwater fed (heath, tundra). Effects of the nematofauna on the microflora were found in the mineral soils, where correlations among nematode metabolic activity as calculated from a metabolic model, and microbial activity parameters as indicated by Biolog and ergosterol measurements, were significantly positive. Correlations with bacterial activity were stronger and more consistent. Microbial parameters, in turn, were significantly correlated with the size of the soil nitrogen pools NH4, NO3, and Norganic. Furthermore, model results suggested that there were remarkable direct effects of nematodes on soil nitrogen status. Calculated monthly nematode excretion contributed temporarily up to 27% of soluble soil nitrogen, depending on the site and the microclimate. No significant correlation among nematodes and microbial parameters, or nitrogen pools, were found in the wet organic soils. The data show that the nematofauna can under favourable conditions affect soil nitrogen status in mineral grassland soils both directly by excretion of N, and indirectly by regulating microbial activity. This suggests that the differences in nitrogen availability observed in such natural grasslands partly reflect differences in the activity of their indigenous nematofauna. This revised version was published online in June 2006 with corrections to the Cover Date.     

农田土壤线虫多样性研究现状及展望

目前土壤生物多样性已成为土壤生态学研究的热点问题之一。土壤生物以不同的方式改变着土壤的物理、化学和生物学特性。在农田生态系统中, 土壤动物是分解作用和养分矿化作用等生态过程的主要调节者。线虫作为土壤中数量最丰富的后生动物, 其生活史和取食类型多样, 在生态系统中发挥着重要作用。本文介绍了农田生态系统中影响线虫多样性的主要因素; 回顾了土壤线虫的物种多样性、营养类群多样性、生活史多样性和功能多样性的研究现状; 并提出了今后农田生态系统线虫多样性研究的重点。建议通过综合土壤线虫的生活史策略和营养类群等信息, 深入了解其生物多样性和土壤生态系统功能, 从而更好地发挥土壤线虫对农田生态系统变化的生物指示作用。     

Pattern and process in above-ground and below-ground components of grassland ecosystems

Abstract. This paper describes patterns of below-ground components in grassland ecosystems. It provides estimates of the contribution of below-ground organs to the total phytomass of the community and of different species to the below-ground phytomass; it describes the distribution of above- and below- ground organs of different species and the spatial and temporal correlation between above-ground and below-ground phyto-mass – both total standing crop and net primary production. 10 Siberian grasslands (meadows and steppes) were investigated during 15 yr. Ca. 70 % of the living phytomass is located in the soil and no less than 70 % of the net primary production is allocated in below-ground organs. Phytomass distribution in the soil layer is more homogeneous than above-ground. For some species the spatial distribution within 1-m² plots of the green and below-ground phytomass is similar, for others it is quantitatively or qualitatively different. According to the dominance-diversity curve, the above-ground size hierarchy is much stronger than the below-ground one. The active growth of above- and below-ground organs of a species may occur at different times of the season and it varies from year to year. Allocation of organic substances to rhizomes and roots occurs simultaneously and with proportional intensity.     

祁连山区典型草地生态系统土壤抗冲性影响因子

为探索祁连山区典型草地生态系统土壤抗冲性的影响因子及其效应,采用野外实地放水冲刷法,以一定体积的冲刷水流含沙量为指标,对土壤抗冲性进行了研究,并调查了海拔、坡度、植被高度、植被覆盖度、地上生物量、根系密度、生物多样性、土壤质地等因子,利用通径分析研究了各因子与土壤抗冲性的关系。结果表明:(1)土壤抗冲性与海拔、植被覆盖度、根系密度和土壤砂粒体积分数呈极显著正相关(P0.01),而与坡度和土壤粉粒体积分数呈极显著负相关(P0.01),与地上生物量和物种丰富度呈显著正相关(P0.05),与植被高度不具备显著相关性;(2)通径分析结果显示,植被覆盖度和根系密度是影响祁连山区典型草地生态系统土壤抗冲性的主导因素,植被覆盖度对土壤抗冲性的影响主要表现为强烈的直接作用(0.660),而根系密度对土壤抗冲性的直接作用相对较小(0.286),有较大一部分影响表现为间接作用(0.174);(3)径流含沙量随植被覆盖度和根系密度的增加明显减少,植被覆盖度与径流含沙量间的关系可用指数或对数形式表达,根系密度与径流含沙量间的关系可用指数形式表达。研究显示,在祁连山区典型草地生态系统,与海拔、坡度、地上生物量、植物多样性、土壤质地等因素相比,植被覆盖度和根系密度对土壤抗冲性的影响作用更突出,提高植被覆盖度与根系密度能够有效增强土壤抗冲性。该研究可为祁连山区的土壤侵蚀规律研究及效益评价提供依据。     

增温增水对草地生态系统碳循环关键过程的影响

生态系统碳循环是生态系统过程的重要组成部分,对碳循环关键过程机理的研究有助于更好地理解生态系统过程。目前,气候变化（全球变暖、降水时空格局变化）对草地生态系统过程产生了重要的影响。综述了气候变化（温度和降水变化）对草地生态系统碳循环关键过程（植物生产力、植物物候、植物根系周转、生态系统呼吸和生态系统净碳交换）的影响,在此基础上指出了目前气候变化（温度和降水变化）控制试验研究的不足,并进一步提出了今后应该加强研究的方向。     

Elevated [CO2], temperature increase and N supply effects on the accumulation of below-ground carbon in a temperate grassland ecosystem

The effects of elevated [CO₂] (700 μl l⁻¹ [CO₂]) and temperature increase (+3 °C) on carbon accumulation in a grassland soil were studied at two N-fertiliser supplies (160 and 530 kgN ha⁻¹ year⁻¹) in a long-term experiment (2.5 years) on well established ryegrass swards (Lolium perenne L.,) supplied with the same amounts of irrigation water. For all experimental treatments, the C:N ratio of the top soil organic matter fractions increased with their particle size. Elevated CO₂ concentration increased the C:N ratios of the below-ground phytomass and of the macro-organic matter. A supplemental fertiliser N or a 3 °C increase in elevated [CO₂] reduced it. At the last sampling date, elevated [CO₂] did not affect the C:N ratio of the soil organic matter fractions, but increased significantly the accumulation of roots and of macro-organic matter above 200 μm (MOM). An increased N-fertiliser supply stimulated the accumulation of the non harvested plant phytomass and of the OM between 2 and 50 μm, without positive effect on the macro-organic matter >200 μm. Elevated [CO₂2] increased C accumulation in the OM fractions above 50 μm by +2.1 tC ha⁻¹, on average, whereas increasing the fertiliser N supply led to an average supplemental accumulation of +0.8 tC ha⁻¹. There was no significant effect of a 3 °C temperature increase under elevated [CO₂] on C accumulation in the OM fractions above 50 μm. This revised version was published online in June 2006 with corrections to the Cover Date.     

基于土壤线虫群落成熟度指数的拉沙山土壤生态系统稳定性评价及可行性研究

土壤生态系统被誉为是生物圈的能量储存介质,稳定健康的土壤生态系统是维持陆地生态系统生产力的关键,但系统内部各种生物作用和复杂过程很难直接观测,很难利用陆地生态系统的评价体系评价其稳定性。近年来土壤线虫群落成熟度指数作为土壤生态系统稳定性的指示类群被广泛认可和利用,拟通过拉沙山区域13个固定大样地中的52个样方的土壤线虫成熟度指数对区域土壤生态系统稳定性进行评价,并对评价的可行性进行验证。采用宏基因技术共获取线虫扩增子序列变体(Amplicon Sequence Variant, ASV)963个,隶属于2纲10目41科67属,群落结构以食细菌线虫和捕食-杂食类线虫为主,群落以K-策略者(c-p 3-5)生活类群为主导。研究结果表明,土壤线虫的成熟度指数均值为3.24±0.32,评价结果认为拉沙山区域土壤生态系统整体较为稳定,且土壤线虫成熟度指数在空间上不存在统计差异(P>0.05)。通过利用样地监测获得的人为干扰强度与利用土壤线虫成熟度指数所评价出的结果呈现显著的负相关关系(P<0.05),表明稳定性较低的样地其人类活动干扰也较大;同时对土壤线虫成熟度指数的评价结果与样地地表生态系统现状验证结果显示,在中海拔的区域主要因其河谷较深,同时两侧山体陡峭且时有塌方发生导致土壤生态系统的不稳定且土壤线虫成熟度指数偏低,评价结果与实际地表生境状态相符,所以利用土壤线虫成熟度指数评价区域大样地是可行的,该研究为未来区域的土壤生态系统健康评价完善提供了新的指标。     

Lagged climatic effects on carbon fluxes over three grassland ecosystems in China

Aims The plasticity of ecosystem responses could buffer and postpone the effects of climates on ecosystem carbon fluxes, but this lagged effect is often ignored. In this study, we used carbon flux data collected from three typical grassland ecosystems in China, including a temperate semiarid steppe in Inner Mongolia (Neimeng site, NM), an alpine shrub-meadow in Qinghai (Haibei site, HB) and an alpine meadow steppe in Tibet (Dangxiong site, DX), to examine the time lagged effects of environmental factors on CO₂ exchange.Methods Eddy covariance data were collected from three typical Chinese grasslands. In linking carbon fluxes with climatic factors, we used their averages or cumulative values within each 12-month period and we called them 'yearly' statistics in this study. To investigate the lagged effects of the climatic factors on the carbon fluxes, the climatic 'yearly' statistics were kept still and the 'yearly' statistics of the carbon fluxes were shifted backward 1 month at a time.Important findings Soil moisture and precipitation was the main factor driving the annual variations of carbon fluxes at the alpine HB and DX, respectively, while the NM site was under a synthetic impact of each climatic factor. The time lagged effect analysis showed that temperature had several months, even half a year lag effects on CO₂ exchange at the three studied sites, while moisture's effects were mostly exhibited as an immediate manner, except at NM. In general, the lagged climatic effects were relatively weak for the alpine ecosystem. Our results implied that it might be months or even 1 year before the variations of ecosystem carbon fluxes are adjusted to the current climate, so such lag effects could be resistant to more frequent climate extremes and should be a critical component to be considered in evaluating ecosystem stability. An improved knowledge on the lag effects could advance our understanding on the driving mechanisms of climate change effects on ecosystem carbon fluxes.     

臭氧对生态系统地下过程的影响

对流层中高浓度的臭氧是一种严重危害植物的大气污染物,臭氧浓度的升高会对作物、林木等产生一系列的损害。本文综述了大气臭氧浓度升高对生态系统地下过程的影响,包括植物根系、根系分泌物、菌根、土壤-根呼吸、土壤酶以及土壤微生物的影响研究进展;阐述了目前研究中存在的争论以及今后需要研究的领域和方向。     

植被恢复方式对松嫩草原重度退化草地土壤线虫群落特征的影响

应用类群属数、个体密度、多样性指数和功能类群指数等群落参数,研究植被恢复方式对松嫩草原重度退化草地土壤线虫群落特征的影响．结果表明：围栏封育和种植碱茅均能明显改善重度退化草地土壤线虫群落环境,但种植碱茅较围栏封育更能显著提高土壤线虫的个体密度和群落多样性．各处理样地线虫个体密度和类群属数表聚性明显,其中碱茅样地个体密度表聚性更强．对功能类群指数的统计表明,种植碱茅和围栏封育均显著改变了土壤线虫群落中r-选择和k-选择植物寄生线虫的比例．与自由生活线虫相比,植物寄生线虫对重度退化草地植被恢复更敏感．种植碱茅更利于松嫩草原重度退化草地土壤线虫群落的恢复与重建．