Influence of soil and microclimate on species composition and grass encroachment in heath succession

Aims and Methods Mostly due to land use changes, European heathlands have become increasingly rare. In addition, the increasing amount of atmospheric nitrogen deposition has resulted in an encroachment of grasses and a loss in species diversity. Despite many investigations, information about the precise environmental parameters that determine the development and maintenance of heathland vegetation is still insufficient. In order to determine the environmental factors that control heath succession and grass encroachment, and to develop appropriate management schemes, we studied the influence of several soil and microclimate parameters on species composition and vegetation characteristics in five successional stages in a coastal heathland on the island of Hiddensee, north-east Germany, where the encroachment of Carex arenaria has become a major problem.Important findings We recorded the highest plant species richness in grey dune and birch forest plots, while the encroachment of C. arenaria let to a significant decline in plant species richness. The most important environmental factors influencing species richness and distribution of single species were microclimate, soil moisture, soil pH and the C/N ratio. While many studies reported the importance of differences in nutrient availability, we found no significant correlations between soil nutrient availability and vegetation pattern. Environmental conditions in dense C. arenaria stands, especially soil properties (e.g. soil pH), showed great differences in comparison to the other successional stages. However, no correlations between the encroachment of C. arenaria and single environmental factors were found. Our results show that not only soil nutrients are important abiotic factors in heaths but that also microclimate and soil moisture play an important role and that many factors are involved in heath succession and in the promotion of grass encroachment. Management plans for the conservation and restoration of heathlands should therefore focus on the specific site conditions and should take several abiotic and biotic factors into account.     

Environmental factors influencing herb layer productivity in Central European oak forests: insights from soil and biomass analyses and a phytometer experiment

Habitat productivity and vegetation biomass are important factors affecting species diversity and ecosystem function, but factors determining productivity are still insufficiently known, especially in the forest herb layer. These factors are difficult to identify because different methods often yield different results. We sampled the herb layer biomass and assessed soil nutrients, moisture and light availability in 100 m² plots in Czech oak forests. Habitat productivity was estimated independently from nutrient content in the soil, herb layer biomass and using a bioassay experiment (growing phytometer plants of Raphanus sativus under standardised conditions in soil samples taken from forest plots). The generalised linear model for herb layer biomass showed it to increase with light, soil phosphorus and moisture availability, but only 10.7% of its variation was explained by these factors. The phytometer biomass increased mainly with soil pH and phosphorus availability; together with soil C/N ratio these factors explained 56.1% of the phytometer biomass variability. Combined evidence based on different approaches indicates that canopy shading and soil phosphorus tend to be the most important factors influencing the herb layer productivity of the studied oak forests.     

Variation in nutrient availability and plant species diversity across forb and graminoid zones of a Northern New England high salt marsh

Plant zonation patterns across New England salt marshes have been investigated for years, but how nutrient availability differs between zones has received little attention. We investigated how N availability, P availability, and plant N status varied across Juncus gerardii, Spartina patens, and mixed forb zones of a Northern New England high salt marsh. We also investigated relationships between several edaphic factors and community production and diversity across the high marsh. P availability, soil salinity, and soil moisture were higher in the mixed forb zone than in the two graminoid zones. NH⁺ ₄-N availability was highest in the J. gerardii zone, but NO^– ₃-N availability and mid season net N mineralization rates did not vary among zones. Plant tissue N concentrations were highest in the mixed forb zone and lowest in the S. patens zone, reflecting plant physiologies more so than soil N availability. Community production was highest in the J. gerardii zone and was positively correlated with N availability and negatively correlated with soil moisture. Plant species diversity was highest in the mixed forb zone and was positively correlated with P availability and soil salinity. Thus, nutrient availability, plant N status, and plant species diversity varied across zones of this high marsh. Further investigation is needed to ascertain if soil nutrient availability influences or is a result of the production and diversity differences that exist between vegetation zones of New England high salt marshes.     

Do large‐seeded herbs have a small range size? The seed mass–distribution range trade‐off hypothesis

We aimed to introduce and test the “seed mass–distribution range trade‐off” hypothesis, that is, that range size is negatively related to seed mass due to the generally better dispersal ability of smaller seeds. Studying the effects of environmental factors on the seed mass and range size of species, we also aimed to identify habitats where species may be at risk and need extra conservation effort to avoid local extinctions. We collected data for seed mass, global range size, and indicators for environmental factors of the habitat for 1,600 species of the Pannonian Ecoregion (Central Europe) from the literature. We tested the relationship between species’ seed mass, range size, and indicator values for soil moisture, light intensity, and nutrient supply. We found that seed mass is negatively correlated with range size; thus, a seed mass–distribution range trade‐off was validated based on the studied large species pool. We found increasing seed mass with decreasing light intensity and increasing nutrient availability, but decreasing seed mass with increasing soil moisture. Range size increased with increasing soil moisture and nutrient supply, but decreased with increasing light intensity. Our results supported the hypothesis that there is a trade‐off between seed mass and distribution range. We found that species of habitats characterized by low soil moisture and nutrient values but high light intensity values have small range size. This emphasizes that species of dry, infertile habitats, such as dry grasslands, could be more vulnerable to habitat fragmentation or degradation than species of wet and fertile habitats. The remarkably high number of species and the use of global distribution range in our study support our understanding of global biogeographic processes and patterns that are essential in defining conservation priorities.     

Abundance of trees and grasses in a woodland savanna in relation to environmental factors

The relationships of plant species associations and underlying environmental factors in a woodland savanna in South Africa were investigated. 40 plots were included with 25 tree and 17 grass species dominating the arboreal and ground cover. Correspondence Analysis described the relationships between soil moisture retention, soil nutrients and the abundance of trees and grasses. Dry matter indices represented the accumulated effects of rainfall, fire and grazing of the herbaceous layer. Variations in the abundance of plants corresponded to well-defined gradients of soil nutrients. The distribution of grass and tree species along the ordination axes indicated that soils with high water retention capacity and high nutrient contents provided a suitable substrate for many of the tree species sampled. However, grass species abundance was high in plots with porous soils and poor nutrient availability.     

A site classification for Scottish native woodlands

Summary

The proposed site classification should assist in choice when creating or rehabilitating native woodlands on site types of different quality. Eight climatic zones are defined by warmth and wetness factors. Eight soil moisture regimes are defined by water table depth and the amount of available water in summer. Six soil nutrient regimes are defined by soil acidity and nitrogen availability. Woodland and scrub sub-communities of the National Vegetation Classification are ordinated by their preferences for soil moisture and soil nutrients, using Ellenberg ecological indicator values. After stratification by climatic zone, the communities are then located on the grid of soil moisture and nutrient regimes. The actual and relative positions of the communities and sub-communities are discussed in relation to existing knowledge of their distribution in relation to climate and soil types.     

Relative Roles of Soil Moisture,Nutrient Supply,Depth, and Mechanical Impedance in Determining Composition and Structure of Wisconsin Prairies

Ecologists have long classified Midwestern prairies based on compositional variation assumed to reflect local gradients in moisture availability. The best known classification is based on Curtis’ continuum index (CI), calculated using the presence of indicator species thought centered on different portions of an underlying moisture gradient. Direct evidence of the extent to which CI reflects differences in moisture availability has been lacking, however. Many factors that increase moisture availability (e.g., soil depth, silt content) also increase nutrient supply and decrease soil mechanical impedance; the ecological effects of the last have rarely been considered in any ecosystem. Decreased soil mechanical impedance should increase the availability of soil moisture and nutrients by reducing the root costs of retrieving both. Here we assess the relative importance of soil moisture, nutrient supply, and mechanical impedance in determining prairie composition and structure. We used leaf δ¹³C of C₃ plants as a measure of growing-season moisture availability, cation exchange capacity (CEC) x soil depth as a measure of mineral nutrient availability, and penetrometer data as a measure of soil mechanical impedance. Community composition and structure were assessed in 17 remnant prairies in Wisconsin which vary little in annual precipitation. Ordination and regression analyses showed that δ¹³C increased with CI toward “drier” sites, and decreased with soil depth and % silt content. Variation in δ¹³C among remnants was 2.0‰, comparable to that along continental gradients from ca. 500–1500 mm annual rainfall. As predicted, LAI and average leaf height increased significantly toward “wetter” sites. CI accounted for 54% of compositional variance but δ¹³C accounted for only 6.2%, despite the strong relationships of δ¹³C to CI and CI to composition. Compositional variation reflects soil fertility and mechanical impedance more than moisture availability. This study is the first to quantify the effects of soil mechanical impedance on community ecology.     

Low soil water and nutrient availability below New Zealand kauri (<Emphasis Type="Italic">Agathis australis</Emphasis> (D. Don) Lindl.) trees increase the relative fitness of kauri seedlings

Tree species can affect the soil they are growing on and this might influence their fitness. The New Zealand gymnosperm tree species kauri (Agathis australis (D. Don) Lindl.) which grows in mixed angiosperm–gymnosperm forests has a substantial effect upon the soil. We studied the hypotheses that: (1) low soil moisture availability below mature kauri trees hampers growth of kauri seedlings and angiosperm seedlings, (2) low nutrient availability below kauri trees hampers only angiosperm seedlings, and (3) angiosperm seedlings are hampered more than kauri seedlings by the conditions below kauri trees. We tested these hypotheses by planting seedlings of kauri and mapau (Myrsine australis (A. Rich) Allan) under kauri trees and applying the following treatments: removal of herbs, removal of litter, removal of nutrient limitation, and elimination of root competition of mature kauri trees. The results indicate that low soil moisture availability, or the combination of low soil moisture availability and low nutrient fertility, hampers the growth of kauri as well as mapau seedlings below kauri trees. The mapau seedlings are hampered relatively more than the kauri seedlings which might result in an increased relative fitness of the latter.     

Succession in Inland Sand Ecosystems: Which Factors Determine the Occurrence of the Tall Grass Species Calamagrostis epigejos (L.) Roth and Stipa capillata L.?

In many successional series, grass species play an important role in mid-successional stages. Using calcareous sand ecosystems in the northern upper Rhine valley (Germany) as a model, we analyzed successional trajectories and the factors that determine their direction. A 5- to 7-year study of 23 permanent plots is presented. Polar ordination revealed that succession starts with pioneer communities (dominated by Corynephorus canescens and cryptogams) and can eventually lead to relatively stable Calamagrostis epigejos or Stipa capillata tall grass stands. At some sites, Cynodon dactylon can play a major role, but we focused on the two previously mentioned species. Gradient analyses of their ecological amplitudes by means of principal components and regression analysis were carried out in order to elucidate the factors determining the successional trajectories. Soil analyses of 71 plots established significantly positive linear relations for C. epigejos with respect to total nitrogen, extractable phosphate and potassium, as well as soil moisture indicator values. C. epigejos is not able to spread if the stress factors nutrient deficiency and dryness are combined. Lower tolerance limits are presented. In contrast, S. capillata shows negative relations to phosphate, declining strongly at P contents > 20 mg kg(-1). At a moisture indicator value of around 3.2 (indicating dry sites), S. capillata reaches its optimum. S. capillata is a model for a tall grass species which, even with low nutrient levels and dry soil conditions, can be successful in mid-successional phases; but it is displaced by C. epigejos if soil moisture increases or phosphate/potassium supply is higher. Regarding a general framework, the successional phases are characterized by processes such as replacement of species, facilitation, and inhibition.     

The foliar endophytic fungal community composition in Cirsium arvense is affected by mycorrhizal colonization and soil nutrient content

Foliar fungal endophytes are ubiquitous, but understudied symbionts of most plant species; relatively little is known about the factors affecting their occurrence, diversity and abundance. We tested the effects of soil nutrient content and arbuscular mycorrhizal (AM) colonization on the occurrence of foliar endophytic fungi in Cirsium arvense in two field studies. In the first study, we assessed relationships between soil moisture, organic matter, carbon and nitrogen content and plant water, nitrogen and carbon content and AM colonization and the occurrence of foliar endophytic fungal species. In the second study, we manipulated soil nutrient content and AM colonization of potted seedlings and identified differences in endophytic fungal species composition of the leaves and stems. The results reveal that endophytes can occur either more or less frequently, depending on soil nutrient and plant water content and AM colonization. We propose that these patterns were the result of differences in fungal growth responses to nutrient availability in the leaves, which can be affected by resources obtained from the soil or symbiotic fungi in the roots.     

中亚热带不同森林更新方式生态酶化学计量特征

了解土壤生态化学计量特征对预测不同生态系统养分变化、功能以及植物生产力具有重要意义。森林更新是维持中亚热带森林生态系统可持续发展的重要手段。选取福建省三明市陈大林业采育场3种不同森林更新方式进行研究,包括米槠次生林（SF）、米槠人工促进天然更新林（AR）和杉木人工林（CF）,测定其土壤理化性质及土壤3种酶,计算酶化学计量。结果显示：1）AR的土壤总氮、全磷、铵态氮含量以及含水量最高（P < 0.05）,土壤有效磷的含量则是CF最高（P < 0.05）;2）生态酶化学计量结果表明AR的土壤微生物处于氮限制状态,CF的土壤微生物处于磷限制状态;3）冗余分析表明,土壤含水量和铵态氮是驱动不同森林更新方式土壤生态酶化学计量变异的重要环境因子。研究表明,人促更新方式更有利于土壤有效氮的积累,而人工林则有利于土壤有效磷积累,这可能与造林树种有关。土壤生态酶化学计量更易受到土壤含水量以及有效性养分的驱动,而与土壤化学计量未呈现良好的耦合性。     

植物的养分利用效率(NUE)及植物对养分胁迫环境的适应策略

提高养分利用效率（ＮＵＥ）是植物适应贫瘠生境的一种重要的竞争策略。养分利用效率的概念从提出到现在,曾用多个参数描述,其间经历了一个不断完善的发展过程。通过综述近年来相关的研究结果,可以初步得出以下结论：⑴不同种,不同生活型植物,乃至同株植物不同器官的ＮＵＥ存在不同程度的差异。⑵ＮＵＥ受多种因素影响。其中,养分有效性的影响研究较多,但争议较大,综合考虑,它对ＮＵＥ的影响不甚显著;叶片脱落持续时间的影     

Calibrating Ellenberg indicator values for moisture,acidity, nutrient availability and salinity in the Netherlands

A general calibration of Ellenberg indicator values for moisture, acidity, nutrient availability and salinity was carried out on a large database of relevées and environmental variables from a variety of ecosystems in the Netherlands.Satisfying relationships with Ellenberg indicator values for moisture, acidity and salinity were found for mean groundwater level in spring time, soil pH and chloride concentration in groundwater. For mean groundwater level in spring and chloride concentration in groundwater subdivision of the database led to clearer relationships with indicator values. For the Ellenberg indicator value for nutrient availability satisfying calibration results were only achieved with data on standing crops and N stock in standing crop. The relationship with soil chemical variables was less clear.Although the correlation between indicator and measured values is obvious, the variation around the regression lines is considerable. However, because of the size and composition of the database, it is unlikely that our calibration results can be much improved by adding more (Dutch) data.The calibration results will be applied in the multi-stress model SMART-MOVE, developed to predict changes in species composition due to acidification, eutrophication and the effects of lowering groundwater.     

塔里木河中下游湿地及周边植物群落与环境因子的关系初探

选取塔里木河中下游湿地及周边16个典型植物群落样地调查和环境因子数据,采用主分量分析(PCA)排序技术和回归分析,定量分析湿地及周边植物群落在空间上的分布格局,以及群落结构特征和环境梯度之间的关系.结果表明,影响塔里木河中下游湿地及周边植物群落分布的第1主分量中,土壤水分和盐分影响最大,贡献率为35.70％;在第2主分量中,土壤养分的影响最大,贡献率为25.97％.植物群落分布的生境可分为沼生轻盐中营养生境、湿生中盐中营养生境、中生中盐低营养生境和中旱生重盐低营养生境4种类型.沿不同生境依次分布着沼泽植被、草甸植被、河岸疏林和盐生荒漠 盐化灌丛植被.塔里木河中下游湿地及周边植物群落的生态优势度与土壤水分和盐分复合梯度呈显著的一元线性相关.二元回归分析结果显示,塔里木河中下游湿地及周边土壤水分和盐分复合梯度与多样性指数和生态优势度二元指标呈极显著相关.     

Seasonal and Spatial Controls over Nutrient Cycling in a Pacific Northwest Prairie

West Coast prairies in the US are an endangered ecosystem, and effective conservation will require an understanding of how changing climate will impact nutrient cycling and availability. We examined how seasonal patterns and micro-heterogeneity in edaphic conditions (% moisture, total organic carbon, % clay, pH, and inorganic nitrogen and phosphorus) control carbon, nitrogen, and phosphorus cycling in an upland prairie in western Oregon, USA. Across the prairie, we collected soils seasonally and measured microbial respiration, net nitrogen mineralization, net nitrification, and phosphorus availability under field conditions and under experimentally varied temperature and moisture treatments. The response variables differed in the degree of temperature and moisture limitation within seasons and how these factors varied across sampling sites. In general, we found that microbial respiration was limited by low soil moisture year-round and by low temperatures in the winter. Net nitrogen mineralization and net nitrification were never limited by temperature, but both were limited by excessive soil moisture in winter, and net nitrification was also inhibited by low soil moisture in the summer. Factors that enhanced microbial respiration tended to decrease soil phosphorus availability. Edaphic factors explained 76% of the seasonal and spatial variation in microbial respiration, 35% of the variation in phosphorus availability, and 29% of the variation in net nitrification. Much of the variation in net nitrogen mineralization remained unexplained (R ² = 0.19). This study, for the first time, demonstrates the complex seasonal controls over nutrient cycling in a Pacific Northwest prairie.     

林木细根寿命及其影响因子研究进展

 细根周转要消耗大量的C,它影响森林生态系统C分配格局与过程和养分循环,对生态系统生产力具有重要意义。细根的周转取决于细根的寿命,细根寿命越短,周转越快,根系对C的消耗也越多。大量研究表明,细根的寿命与地上部分C向根系供应的多少有密切关系,同时也与细根直径大小、土壤中N和水分的有效性、土壤温度以及根际周围的土壤动物和微生物的活动有关。本文综述了国外近年来在该领域里的研究进展,特别是对控制细根寿命的机理和主要影响因子进行了评述,目的是引起国内研究者的关注,促进我国根系生态学的研究与发展。     

Vertebrate herbivores and plants in the Arctic and subarctic: effects on individuals, populations, communities and ecosystems

Plants in the Arctic and subarctic face the problems posed by herbivory in addition to short growth seasons, low temperatures and low nutrient availability. Herbivores control plant performance by removing biomass, by altering resource availability, by altering the physical environment, and by changing the balance of competition. The main difference between effects of herbivores in the Arctic and at lower latitudes may be the relatively greater importance of changes in resource availability and the physical environment resulting from herbivore activity, and their consequences for plant competitive abilities.Species responses to defoliation depend primarily on growth form. Artificial defoliation of graminoids has negative effects on most species, but in the field total effects of herbivores are often neutral or even positive, resulting in increased nitrogen concentrations in shoots in many species. Shrubs are less able to respond positively to herbivory than graminoids, and although there is some evidence that deciduous shrubs recover faster than evergreen ones, the difference is not great. However, effects of herbivores on shrubs are little studied, despite their importance in the herbivore diet.Responses of individual species to increased nutrient availability vary greatly, even within a growth form. Some graminoids and shrubs show strong positive responses to fertilization while others show little or no response. These species-specific effects suggest that herbivores can alter interspecific relationships through differential responses to fertilization. Herbivores may alter plant population dynamics by altering flower or seed production, by consuming seedlings, or by altering the availability of microsites. However, no study has adequately examined this for any arctic species.Changes in community composition following removal of herbivores are the result not only of selective removal of some plant species, but also of changes in microsite availability, nutrient availability, litter accumulation, and soil characteristics. Thus, the view that abiotic factors are the overwhelming determinants of community structure in low-productivity environments is compatible with the view that herbivores exercise their influence to a large extent by altering abiotic factors.Arctic herbivores often increase total above-ground nitrogen availability (and therefore food quality) in the plant community, but increased productivity as a result of herbivores is rare. The increase in nutrient availability is probably due in part to changes in soil temperature and soil moisture following a reduction in litter accumulation.Although our knowledge of effects of herbivory on individual plants and on communities is extensive, we lack information on effects at the population level. We also do not have an adequate understanding of impacts of herbivores at different spatial and temporal scales, something which is needed to be able to make predictions about longer-term impact of herbivores in these systems.     

Soil Nematodes in Terrestrial Ecosystems

There has been much work on plant-feeding nematodes, and less on other soil nematodes, their distribution, abundance, intrinsic properties, and interactions with biotic and abiotic factors. Seasonal variation in nematode fauna as a whole is correlated with factors such as moisture, temperature, and plant growth; at each site nematode distribution generally reflects root distribution. There is a positive correlation between average nematode abundance and primary production as controlled by moisture, temperature, nutrients, etc. Soil nematodes, whether bacterial feeders, fungivores, plant feeders, omnivores, or predators, all influence the populations of the organisms they feed on. Although soil trematodes probably contribute less than 1% to soil respiration they may play an important role in nutrient cycling in the soil through their influence on bacterial growth and plant nutrient availability.     

Soil animal responses to moisture availability are largely scale,not ecosystem dependent: insight from a cross‐site study

Climate change will result in reduced soil water availability in much of the world either due to changes in precipitation or increased temperature and evapotranspiration. How communities of mites and nematodes may respond to changes in moisture availability is not well known, yet these organisms play important roles in decomposition and nutrient cycling processes. We determined how communities of these organisms respond to changes in moisture availability and whether common patterns occur along fine‐scale gradients of soil moisture within four individual ecosystem types (mesic, xeric and arid grasslands and a polar desert) located in the western United States and Antarctica, as well as across a cross‐ecosystem moisture gradient (CEMG) of all four ecosystems considered together. An elevation transect of three sampling plots was monitored within each ecosystem and soil samples were collected from these plots and from existing experimental precipitation manipulations within each ecosystem once in fall of 2009 and three times each in 2010 and 2011. Mites and nematodes were sorted to trophic groups and analyzed to determine community responses to changes in soil moisture availability. We found that while both mites and nematodes increased with available soil moisture across the CEMG, within individual ecosystems, increases in soil moisture resulted in decreases to nematode communities at all but the arid grassland ecosystem; mites showed no responses at any ecosystem. In addition, we found changes in proportional abundances of mite and nematode trophic groups as soil moisture increased within individual ecosystems, which may result in shifts within soil food webs with important consequences for ecosystem functioning. We suggest that communities of soil animals at local scales may respond predictably to changes in moisture availability regardless of ecosystem type but that additional factors, such as climate variability, vegetation composition, and soil properties may influence this relationship over larger scales.