Effect of density and species richness of soil mesofauna on nutrient mineralisation and plant growth

The aim of this study was to test the relative importance of changes in density and species richness of soil mesofauna as determinants of nutrient mineralisation and plant growth. The experiment was carried out using microcosms containing a mixture of plant litter and soil in which seedlings of Lolium perenne were planted, and a range of combinations of levels of density and species richness of microarthropods added. Over the duration of the experiment, nutrient release, measured as concentrations of NO₃ ^--N and total N in leachates, increased significantly with increasing microarthropod density, but decreased with increasing species richness. Leachate concentrations of NH₄ ⁺-N, dissolved organic N and C (DON and DOC) were not affected by the faunal treatments. Soil respiration, a measure of microbial activity, decreased with increasing density of microarthropods, whereas microbial biomass was not affected by microarthropods. Increasing density of soil animals had a negative effect on the shoot biomass of L. perenne while the effect of species richness was positive. Neither the species richness nor density of soil microarthropods was found to significantly influence root biomass. We conclude that variations in animal density had a greater influence on soil nutrient mineralisation processes than did species richness. Possible reasons for these opposing effects of animal density and diversity on soil N mobilization are discussed.     

秸秆还田配合化肥减施对潮土作物产量及土壤肥力的影响

我国粮食主产区化肥施用过量,导致肥料利用率降低、土壤质量退化、环境污染风险提高等一系列问题。于黄淮海平原潮土区设置大田试验,研究秸秆还田配合不同比例氮磷减施对土壤养分、作物产量、秸秆养分释放及土壤微生物的影响。结果表明：与常规施肥相比,减氮30%或减磷50%对作物产量及土壤养分含量无显著影响;秸秆降解率在第一季达43.33%～53.11%,减氮30%或减磷50%降解率可增加12.40%,两年后达到63.41%～75.62%;减氮100%显著降低细菌真菌丰度、物种丰富度和多样性,而减磷影响较弱;减氮30%和减磷50%主要增加细菌中芽单胞菌门（Gemmatimonadetes）Longimicrobiaceae科和变形菌门（Proteobacteria）亚硝化单胞菌科（Nitrosomonadaceae）相对丰度,增加真菌中壶菌门（Chrytridiomycota）GS13纲相对丰度,降低子囊菌门（Ascomycota）粪壳菌纲（Sordariomycetes）和被孢霉门（Mortierellomycota）被孢霉纲（Mortierellomycetes）相对丰度;冗余分析表明,影响细菌和...     

Soil carbon pools, plant biomarkers and mean carbon residence time after afforestation of grassland with three tree species

Afforestation of grassland has been globally identified as being an important means for creating a sink for atmospheric carbon (C). However, the impact of afforestation on soil C is still poorly understood, due to the paucity of well designed long-term experiments and the lack of investigation into the response of different soil C fractions to afforestation. In addition, little is known about the origins of soil C and soil organic matter (SOM) stability after afforestation. In a retrospective study, we measured C mass in the soil light and heavy fractions in the first 10 years after afforestation of grassland with Eucalyptus nitens, Pinus radiata and Cupressus macrocarpa. The results suggest that C mass in the soil heavy fraction remained stable, but the C mass in the light fraction decreased at year 5 under three species. Soil δ¹³C analysis showed that the decrease in the light fraction may be due to reduced C inputs from grassland species litter and low inputs from the still young trees. After the initial reduction, the recovery of soil C in the light fraction depended on tree species. At year 10, an increase of 33% in light fraction soil C was observed at the 0-30 cm depth under E. nitens, compared to that under the original grassland (year 0). Planting P. radiata restored light fraction soil C to the original level under grassland, whereas planting C. macrocarpa led to a decrease of 33%. We concluded that the increase of light fraction soil C between year 5 and 10 is most likely due to C input from tree residues. Most of the increased C was derived from root turnover under pine and from both root and leaf turnover under E. nitens, as indicated by plant C biomarkers such as lignin-derived phenols and suberin and cutin-derived compounds in the 0-5 cm soil layer. Modelling of soil ?¹⁴C‰ suggested that SOM had a greater mean residence time at year 10 than year 0 and 5 due to increased relative abundance of recalcitrant plant biopolymers.     

Interactive effects of tree species and soil moisture on methane consumption

Methane consumption by temperate forest soils is a major sink for this important greenhouse gas, but little is known about how tree species influence CH₄ uptake by soils. Here, we show that six common tree species in Siberian boreal and temperate forests significantly affect potential CH₄ consumption in laboratory microcosms. Overall, soils under hardwood species (aspen and birch) consumed CH₄ at higher rates than soils under coniferous species and grassland. While NH₄⁺ addition often reduces CH₄ uptake, we found no effect of NH₄⁺ addition, possibly because of the relatively high ratio of CH₄-to-NH₄⁺ in our incubations. The effects of soil moisture strongly depended on plant species. An increase in soil moisture enhanced CH₄ consumption in soils under spruce but had the opposite effect under Scots pine and larch. Under other species, soil moisture did not affect CH₄ consumption. These results could be explained by specific responses of different groups of CH₄-oxidizing bacteria to elevated moisture.     

人为干扰对高黎贡山社区森林树种多样性的影响

研究人为干扰活动对高黎贡山社区森林树种多样性的影响结果表明 ,人为干扰对该社区森林有明显的负面影响 ,减少了群落树种多样性和破坏森林群落结构 ,降低森林资源量。当地居民对森林树种选择性的砍伐 ,使群落优势种组成发生变化 ,导致某些树种种群减小 ,物种生存受到极大威胁。并提出减少人为干扰的策略。     

A mixture of grass and clover combines the positive effects of both plant species on selected soil biota

The introduction of N₂-fixing white clover (Trifolium repens) in grassland is a management measure that may contribute to sustainable grassland systems by making them less dependent on inorganic fertilizers. However, little is known about the impact of this measure on soil biota and ecosystem services. We investigated earthworms, nematodes, bacteria and fungi in an experiment in which white clover-only and a mixture of grass and white clover without fertilization were compared with grass-only with and without fertilization.In comparison with grass-only, white clover-only had a lower total root biomass and a lower C/N-ratio in the above- and below-ground plant biomass. These plant characteristics resulted in a lower bacterial biomass, a lower fungal biomass, a higher proportion of bacterivorous nematode dauerlarvae, a lesser proportion of herbivorous nematodes and a greater abundance of earthworms in clover-only.The quantity and quality (C/N-ratio) of the above- and below-ground plant biomass in the mixture of grass and white clover (20–30% clover in the DM) was comparable with grass fertilized with 150 kg N ha⁻¹ of inorganic fertilizer. Differences between these treatments might show specific clover effects in the grass–clover mixture on soil biota other than quantity and C/N-ratio of the litter. However, the only differences were a higher proportion of bacterivorous nematode dauerlarvae and a different nematode community composition in grass–clover.The soil structure in white clover-only showed a higher proportion of angular blocky elements, a lower penetration resistance, a higher number of earthworm burrows, a higher potential N-mineralization and respiration than the soil in grass-only. This suggests that clover stimulates the ecosystem services of water infiltration and supply of nutrients, but is less conducive to soil structure maintenance. The grass–clover mixture differed from grass-only in a higher respiration and from clover-only in a higher percentage of soil crumbs. We suggest that when clover is introduced in grassland to reduce the reliance on inorganic fertilizer, the mixture of grass and clover maintains the positive impact of grass roots on soil structure and increases the supply of nutrients via the soil food web. Thus, a grass–clover mixture combines the agronomic benefits of the two plant types.     

The influence of field shape, area and surrounding landscape on plant species richness in grazed ex-fields

Over the past 100 years species-rich semi-natural grasslands have decreased dramatically in Western Europe, where former arable fields (ex-fields) are used instead as pasture. The disappearance of semi-natural grasslands has caused a threat to the biodiversity in agricultural landscapes. Many typical grassland plants are dispersal limited, thus grazed ex-fields can be used to investigate if species spontaneously colonise these new grassland habitats. We examined the relationship between surrounding landscape, field area, shape, distance between edge and centre, and plant species diversity in ex-fields that had been grazed for 15-18 years. The results showed that there were 35% more plant species in fields surrounded by commercial forestry production compared to those surrounded by open agricultural landscape. Area and shape did not influence species richness, although there was increasing number of species in the centre with decreasing distance from the edge. Twenty-five percent of the species where typical grassland species, and ex-fields surrounded by forest had 91% more grassland species compared to those in the open landscape. It is possible to increase grassland plant occurrences by grazing ex-fields surrounded by forest or other grassland remnant habitats, particularly in landscapes where grazed semi-natural grasslands are scarce.     

Management effects on the vegetation and soil seed bank of calcareous grasslands: An 11-year experiment

Calcareous grasslands, most of which are man made and therefore depend on some kind of human interference for their maintenance, are among the most species-rich communities on Earth at a small scale. For many centuries, most of these grasslands have been used as extensive pasture. However, after 1900, and particularly from 1940 onwards, livestock grazing has declined throughout Europe leading to the abandonment of low intensity grasslands over large areas. To conserve the remaining grasslands or to restore recently abandoned grasslands, better insights about the effects of grassland management on above and belowground species diversity are needed. Here, we describe the results of an 11-year experiment to investigate the role of grassland management (grazing, mowing and abandonment) in determining species composition and diversity both in the aboveground vegetation and the seed bank of a calcareous grassland in Belgium. Species diversity declined by about 60% 11 years after abandonment, from 29 species m⁻² to as few as 12 species m⁻². Plots that were grazed remained constant in species richness, whereas mown sites lost about 20% of their original species. Abandoned plots were largely dominated by a few grass species, in particular Festuca rubra. Concomitant with changes in the aboveground vegetation, both the number of species found in the seed bank and seed density (number of seeds m⁻²) had changed significantly 11 years after abandonment. Species diversity and seed density were significantly lower in abandoned plots than in grazed or mown plots. We conclude that abandonment of calcareous grasslands may lead to rapid decline of plant species diversity both in the aboveground vegetation and in the seed bank. As a result, seed banks probably have a limited role to play in the restoration of recently abandoned grasslands.     

武夷山天然常绿阔叶林林隙物种多样性比较研究

对武夷山不同常绿阔叶林发育阶段林隙样地更新层物种多样性变化规律研究结果表明 ,林隙物种多样性指数大于非林隙样地 ,而生态优势度则相反 ;不同大小扩展林隙物种多样性指数不同 ,<10 0m2 面积林隙物种多样性指数最大 ,而≥ 30 0m2 的林隙则最小 ;>1.5m的林隙物种丰富度指数、Shannon Wienner多样性指数、均匀度指数和均优多指数随发育阶段的变化趋势基本一致 ,均以林隙形成时间为 10～ 2 0年达最大 ,而 <10年的则最小 ;更新层树种平均各林隙内SW多样性指数、均匀度指数和均优多指数以林隙形成 10～ 2 0年为最小 ,至 30年后有所增加 ,4 0～ 5 0年时达最大 ,5 0年后呈缓慢减少趋势。林隙形成为不同树种更新提供了动力 ,林业生产适当培育林隙对物种多样性保护极其重要。     

择伐作业对常绿阔叶林乔木层树种结构及物种多样性的影响

研究4种不同强度择伐作业(弱度13.0%、中度29.1%、强度45.8%和极强度67.1%)对常绿阔叶林林分结构及乔木层物种多样性的影响结果表明,轻度与中度择伐对林分结构的影响较小,原林分乔木层优势树种的地位仍保持甚至略有提高;而强度择伐和极强度择伐则引起林分结构一定的变化,一些优势树种的地位削弱,而另一些树种的优势地位上升。但采伐作业不利于常绿阔叶林物种多样性的发展,尤其是林冠强度破坏对物种多样性的影响最大,而轻度与中度择伐作业有利于原有物种保持与恢复,这可能与不同强度择伐作业引起林地光照条件、温度和湿度等环境因子的不同变化有关。     

Interacting effects of temperature, soil moisture and plant biomass production on ecosystem respiration in a northern temperate grassland

Chamber measurements of total ecosystem respiration (TER) in a native Canadian grassland ecosystem were made during two study years with different precipitation. The growing season (April–September) precipitation during 2001 was less than one-half of the 30-year mean (1971–2000), while 2002 received almost double the normal growing season precipitation. As a consequence soil moisture remained higher in 2002 than 2001 during most of the growing season and peak aboveground biomass production (253.9 g m⁻²) in 2002 was 60% higher than in 2001. Maximum respiration rates were approximately 9 μmol m⁻² s⁻¹ in 2002 while only approximately 5 μmol m⁻² s⁻¹ in 2001. Large diurnal variation in TER, which occurred during times of peak biomass and adequate soil moisture, was primarily controlled by changes in temperature. The temperature sensitivity coefficient (Q₁₀) for ecosystem respiration was on average 1.83 ± 0.08, and it declined in association with reductions in soil moisture. Approximately 94% of the seasonal and interannual variation in R₁₀ (standardized rate of respiration at 10 °C) data was explained by the interaction of changes in soil moisture and aboveground biomass, which suggested that plant aboveground biomass was good proxy for accounting for variations in both autotrophic and heterotrophic capacity for respiration. Soil moisture was the dominant environmental factor that controlled seasonal and interannual variation in TER in this grassland, when variation in temperature was held constant. We compared respiration rates measured with chambers and that determined from nighttime eddy covariance (EC) measurements. Respiration rates measured by both techniques showed very similar seasonal patterns of variation in both years. When TER was integrated over the entire growing season period, the chamber method produced slightly higher values than the EC method by approximately 4.5% and 13.6% during 2001 and 2002, respectively, much less than the estimated uncertainty for both measurement techniques. The two methods for calculating respiration had only minor effects on the seasonal-integrated estimates of net ecosystem CO₂ exchange and ecosystem gross photosynthesis.     

Using traits of species to understand responses to land use change: Birds and livestock grazing in the Australian arid zone

The expansion of the artificial water-point network and livestock grazing in arid and semi-arid Australia has significantly increased access to water by water limited herbivores and thus has potential to seriously negatively affect the unique endemic flora and fauna. We examined the effects of the expansion of the water-point network on the arid and semi-arid zone bird community, using data from the Atlas of Australia bird surveys of 1977-1981 and 1996-2001. We examined whether traits of species could be used to uncover the critical ecological processes altered by this land use change. We detected large scale declines in individual species. Species reliant on water for nesting and feeding declined more than other groups in the presence of high water-point density, likely through direct effects of livestock degrading habitat of both natural and artificial water points. The arid zone has no natural hoofed animals and livestock have significant impacts. Species that forage and nest on the ground also showed large declines, likely because of trampling and removal of vegetation by livestock and potentially through the indirect effect of water limited predators, dingos and foxes, expanding their ranges in response to the expanding network of water points in the landscape. This result was also apparent at large spatial scales so that these local-scale responses to water points translate into continental-scale population declines. Using traits of species to understand declines of bird species helped us to uncover which critical changes associated with the expansion of the water-point network most affected the bird community and therefore which species are most at risk.     

Chemical composition and diversity influence non-additive effects of litter mixtures on soil carbon and nitrogen cycling: Implications for plant species loss

Diverse plant litter mixtures frequently decompose differently than expected compared to the average of the component species decomposing alone, and it remains unclear why decomposition may respond non-additively to diversity. Here, we hypothesized that litter chemical composition and chemical diversity would be important determinants of the strength and direction (synergistic versus antagonistic) of non-additive soil carbon (C) and nitrogen (N) cycling responses to litter mixtures. To test this, we performed a soil incubation experiment using litter mixtures comprised of up to four plant species, and we measured three components of decomposition: respiration, net N mineralization, and microbial biomass N accumulation. We used nine chemical traits to calculate the chemical composition and diversity of the litter mixtures. First, we found that respiration responded as the average of the individual species in the mixture (i.e. additively), rather than non-additively as initially predicted. Second, litter mixtures stimulated significantly more net N immobilization than expected in 64% of cases, and non-additive responses were highly dependent on mixture chemical composition, and were influenced to a lesser degree by chemical diversity. Specifically, concentrations of tannins and certain low molecular weight phenolics in the mixtures were positively correlated with greater N immobilization than expected. Non-additive N mineralization responses were poorly correlated with traditional measures of litter chemistry like N concentration, C:N, lignin:N, and phenolic:N. Our results also show that non-additive N mineralization responses were affected by loss of some species significantly more than others, and the effects of species loss could depend on 1) whether a species contains compounds with strong effects on non-additive responses; and 2) whether those compounds are also found in other species. Finally, litter mixtures stimulated more microbial biomass N than expected in 45% of cases, but non-additive responses were only weakly dependent on the litter chemistry variables that we measured.     

Effect of long‐term cattle grazing on seasonal nitrogen and phosphorus concentrations in range forage species in the fescue grassland of southwestern Alberta

Numerous studies have examined the nutritive quality of fodder plants in different seasons but few have related this seasonal response to long‐term grazing intensity. Our objective was to examine the effect of long‐term grazing on the concentrations of total nitrogen, δ¹⁵N, and total phosphorus in selected forage species from the fescue grassland near Stavely, Alberta. Plants were selected from paddocks that had been stocked at 0 (control), 2.4 (moderate grazing), and 4.8 (heavy grazing) animal unit months ha^–1 for 58 years. Plant material from ten species was sampled and analyzed at monthly intervals from May to September in 2007. Total N and P concentrations were not (p > 0.05) affected by grazing for most species, but total N and P concentrations in Poa. pratensis L. were higher (p < 0.05) in grazed treatments than in the control. These results reflect an altered plant phenology through defoliation and illustrate delayed phenology in P. pratensis when grazed. The higher δ¹⁵N concentration for most species in the grazed treatments than the control is an indication of accelerated nitrogen cycling through dung and urine deposition.     

Rapid effects of plant species diversity and identity on soil microbial communities in experimental grassland ecosystems

Changes in plant community structure, including the loss of plant diversity may affect soil microbial communities. To test this hypothesis, plant diversity and composition were experimentally varied in grassland plots cultivated with monocultures or mixtures of 2, 3 or 4 species. We tested the effects of monocultures versus mixtures and of plant species composition on culturable soil bacterial activity, number of substrates used and catabolic diversity, microbial biomass N, microbial respiration, and root biomass. These properties were all measured 10 months after seeding the experiment. Soil bacterial activity, number of substrates used and catabolic diversity were measured in the different plant communities using BIOLOG GN and GP microplates, which are redox-based tests measuring capacity of soil culturable bacteria to use a variety of organic substrates. Microbial biomass N, microbial respiration, and root biomass were insensitive to plant diversity. Culturable soil microbial activity, substrates used and diversity declined with declining plant diversity. Their activity, number of substrates used and diversity were significantly higher in plots with 3 and 4 plant species than in monocultures and in plots with 2 species. There was also an effect of plant species composition. Culturable soil microbial activity and diversity was higher in the four-species plant community than in any of the plant monocultures suggesting that the effect of plant diversity could not be explained by the presence of a particular plant species. Our results showed that changes in plant diversity and composition in grassland ecosystems lead to a rapid response of bacterial activity and diversity.     

武夷山黄山松群落物种多样性与种群空问格局的研究

对武夷山黄山松群落物种多样性和种群空间格局的研究结果表明 ,低海拔地区由于受人为干扰影响较大而物种多样性与种群空间分布格局未表现出明显规律性 ,高海拔地区群落物种多样性指数、丰富度和均匀度均有不同程度下降 ,黄山松种群空间格局均呈集群分布 ,且随海拔高度升高而黄山松种群生长受到一定抑制     

Nonadditive effects of litter mixtures on decomposition and correlation with initial litter N and P concentrations in grassland plant species of northern China

We studied the occurrence of nonadditive effects of litter mixtures on the decomposition (the deviation of decomposition rate of litter mixtures from the expected values based on the arithmetic means of individual litter types) of litters from three plant species (i.e., Stipa krylovii Roshev., Artemisia frigida Willd., and Allium bidentatum Fisch. ex Prokh. & Ikonn.-Gal.) endemic to the grassland ecosystems of Inner Mongolia, northern China and the possible role of initial litter N and P on such effects. We mixed litters of the same plant species that differed in N and P concentrations (four gradients for each species) in litterbags and measured mass losses of these paired mixtures after 30 and 80 days under field conditions. We found the occurrence of positive, nonadditive effects of litter mixtures and showed that the magnitude of the nonadditive effects were related to the relative difference in the initial litter N and P concentrations of the paired litters.     

人工林对土壤地力的影响过程及其调控研究进展

土壤是支撑人工林健康生长的基础资源,是营养物质转化和生物多样性保护的主要场所。目前,我国人工林经营中土壤地力衰退问题突出,是制约我国林业生产可持续经营、增大生态安全屏障脆弱性的重要因素。因此,有必要深入认识和理解人工林对土壤地力的影响过程,同时开发保障人工林健康和初级生产力的关键调控技术。本文从土壤物理化学环境、土壤生物群落特性及功能等方面,系统论述了人工林土壤地力的维持机制,重点探讨了林龄结构、林分密度、树种类型等影响人工林地力的地下生态学过程。未来需要关注环境变化下人工林土壤理化性质与生物学性质的耦合机制。现阶段大面积人工林土壤病原菌积累特征不清,土壤病害影响人工林健康的障碍机理也亟待揭示。因此,今后需进一步量化林木健康、土壤生物以及环境之间的互作关系模型,形成从造林配置、过程经营、症状诊断及土壤地力调控等全方位的人工林健康定向调控体系,保障人工林可持续、多目标经营。     

京郊桃园养分投入对土壤养分和桃果品质的影响

以绿化9号品种为调查对象,2006年调查了平谷区141个桃园的施肥现状及其对土壤养分和桃果品质的影响。结果表明:所调查的桃园施用的有机肥以鸡粪、羊粪、猪粪、牛粪为主,化肥投入以复合肥居多;与2004年的调查结果相比,2006年来自有机肥和化肥的总N投入数量下降,但是P、K投入总量增加;由于桃园多年的过量养分投入,2006年桃园土壤有机质、全氮、碱解氮、有效磷和速效钾含量比1981年第二次土壤普查结果均有大幅度提高;调查结果还显示,养分投入为适宜等氮素投入水平(100～200kghm-2)、中磷素投入水平(20～100kghm-2)和低钾素投入水平(50kghm-2)的桃园桃果实单果重较大,可溶性固形物含量较高,因此,桃园要进行合理的养分管理以保证产量和品质的形成,以及桃园的可持续发展。     

Conservation of beetles in boreal pine forests: the effects of forest age and naturalness on species assemblages

The effort of boreal forest conservation has emphasised the preservation of old-growth forests while the role of young successional stages in maintaining biodiversity has remained largely unstudied. We compared the richness of beetle species and composition of species assemblages between managed and seminatural forests in five stages of forest succession. The sites were in boreal sub-xeric pine-dominated forests in eastern Finland. Seminatural study sites, especially the recently burned sites, were important habitats for threatened and near-threatened species. We propose that young stages of natural succession should be included in the network of protected forest areas. On the other hand, the composition of saproxylic species assemblages in seminatural forests differed from the assemblages in managed forests, indicating also the need to improve the forest management guidelines so that they better address the requirements of species protection. Regeneration methods applied should resemble or mimic the natural disturbances more closely.