不同放牧强度对赛罕乌拉草原蜘蛛多样性的影响

蜘蛛作为草原生态系统中的主要消费者, 对维系草原生物多样性和生态系统功能具有重大意义。放牧是人类利用草原最普遍的方式, 了解放牧对蜘蛛多样性的影响具有重要生态学意义。本研究调查了内蒙古赛罕乌拉草原上5个不同放牧强度样地中的蜘蛛多样性, 通过单因素方差分析(one-way analysis of variance)比较各样地中的蜘蛛多样性, 非度量多维标度分析(non-metric multidimensional scale, NMDS)和相似性分析(analysis of similarities, ANOSIM)比较各样地间的蜘蛛物种组成相似性, 再结合相关性分析探讨了植被高度对蜘蛛多样性的影响。结果表明: 重度放牧强度样地的蜘蛛多样性显著低于其他未放牧及轻度放牧样地; 具体到常见科上, 放牧强度对织网型的园蛛物种数和个体数影响显著, 而对游猎型的狼蛛、跳蛛却不明显; 织网型蜘蛛主要受植被结构影响, 而游猎型蜘蛛更可能受潜在猎物可得性的影响。NMDS分析表明不同放牧强度下, 蜘蛛类群的物种组成呈现明显的梯度变化, 放牧强度越低, 物种组成和未放牧样地越相近。相关性分析表明草原植被高度与蜘蛛多样性总体上呈正相关关系, 即植被高度越高, 蜘蛛多样性越高。其中依靠植物构建蛛网的园蛛科和在植物上层伏击猎物的蟹蛛科、逍遥蛛科等与植被高度显著相关。这说明植物资源及其空间异质性可能对草原蜘蛛多样性起着主导作用。因此, 降低放牧强度有助于保护草原蜘蛛群落的多样性, 特别有利于织网型蜘蛛。     

草地利用方式对温性典型草原优势种植物功能性状的影响

当外界环境发生变化后植物能够改变自身功能性状及时调整适应策略, 因此植物功能性状能够有效地反映植物对草地利用变化的响应, 然而在内蒙古草原从植物功能性状角度开展草地利用方式影响的研究略少。该研究以内蒙古典型草原大针茅(Stipa grandis)、羊草(Leymus chinensis)、糙隐子草(Cleistogenes squarrosa)和冷蒿(Artemisia frigida) 4种主要优势种为研究对象, 探讨在长期自由放牧、割草、短期围封和长期无干扰的影响下优势种植物功能性状的差异, 以期从功能性状视角, 揭示植物在受到外界干扰后的适应策略, 旨为天然草地的可持续管理提供基础数据支持和科学依据。结果表明: 1)除糙隐子草外, 在长期放牧后内蒙古典型草原优势植物植株高度、根长和植物碳氮含量降低, 这些性状的变化能够使植物个体小型化, 适口性降低, 表明植物通过逃避放牧的策略适应长期自由放牧的干扰; 在割草管理方式下, 优势种的高度和比叶面积有增加的趋势, 其中冷蒿的氮含量对割草响应最敏感, 其根、茎、叶中的氮含量均在割草样地最低; 围封和长期无干扰处理下植物的碳氮含量增加, 表明在干扰强度降低后, 植物通过功能性状的改变从资源获取策略向资源储藏策略转变。2)对优势种功能性状集合分析表明, 糙隐子草具有较低的植株高度和较高的比叶面积, 冷蒿具有较高的木质素含量和氮含量, 这些性状能够使两种植物被家畜采食量减少, 并保证其具有较强的再生能力, 这可能是糙隐子草和冷蒿耐牧的原因; 大针茅具有最高的植株高度、最大的叶片干物质含量, 以及最高的茎、叶纤维素含量, 说明大针茅是非常典型的竞争物种, 在干扰较低的条件下, 大针茅采取竞争策略对其他物种产生较大的竞争压力可能是其占优势的重要原因。     

Uncovering the different scales in deer–forest interactions

Deer are regarded to be a keystone species as they play a crucial role in the way an ecosystem functions. Most deer–forest interaction studies apply a single scale — process of analyzing ecological interactions by only taking into account one dependent variable — to understand how deer browsing behavior shapes different forest components, but they overlook the fact that forests respond to multiple scales simultaneously. This research evaluates the effect of browsing by wild deer on temperate and boreal forests at different scales by synthesizing seminal papers, specifically (a) what are the effects of deer population density in forest regeneration? (b) What are the effects of deer when forests present diverging spatial characteristics? (c) What are the effects on vegetation at different temporal scales? and (d) What are the hierarchical effects of deer when considering other trophic levels? Additionally, a framework based on modern technology is proposed to answer the multiscale research questions previously identified. When analyzing deer–forest interactions at different scales, the strongest relationships occur at the extremes. For example: when deer assemblage occurs in low or high density and is composed of a mix of small and large species. As forests on poor soils remain restrained in size, isolated and chronically browsed. When forests harbor incomplete trophic levels, the effects spill over to lower trophic levels. To better understand the complexities in deer–forest interactions, researchers should combine technology‐based instruments like fixed sensors and drones with field‐tested methods such observational studies and experiments to tackle multiscale research questions.     

Incorporation of mineral nitrogen into the soil food web as affected by plant community composition

Although nitrogen (N) deposition is increasing globally, N availability still limits many organisms, such as microorganisms and mesofauna. However, little is known to which extent soil organisms rely on mineral‐derived N and whether plant community composition modifies its incorporation into soil food webs. More diverse plant communities more effectively compete with microorganisms for mineral N likely reducing the incorporation of mineral‐derived N into soil food webs. We set up a field experiment in experimental grasslands with different levels of plant species and functional group richness. We labeled soil with ¹⁵NH₄ ¹⁵NO₃ and analyzed the incorporation of mineral‐derived ¹⁵N into soil microorganisms and mesofauna over 3 months. Mineral‐derived N incorporation decreased over time in all investigated organisms. Plant species richness and presence of legumes reduced the uptake of mineral‐derived N into microorganisms. In parallel, the incorporation of mineral‐derived ¹⁵N into mesofauna species declined with time and decreased with increasing plant species richness in the secondary decomposer springtail Ceratophysella sp. Effects of both plant species richness and functional group richness on other mesofauna species varied with time. The presence of grasses increased the ¹⁵N incorporation into Ceratophysella sp., but decreased it in the primary decomposer oribatid mite Tectocepheus velatus sarekensis. The results highlight that mineral N is quickly channeled into soil animal food webs via microorganisms irrespective of plant diversity. The amount of mineral‐derived N incorporated into soil animals, and the plant community properties affecting this incorporation, differed markedly between soil animal taxa, reflecting species‐specific use of food resources. Our results highlight that plant diversity and community composition alter the competition for N in soil and change the transfer of N across trophic levels in soil food webs, potentially leading to changes in soil animal population dynamics and community composition. Sustaining high plant diversity may buffer detrimental effects of elevated N deposition on soil biota.     

Fine roots and ectomycorrhizas as indicators of environmental change

Abstract

Human-induced and natural stress factors can affect fine roots and ectomycorrhizas. Therefore they have potential utility as indicators of environmental change. We evaluated, through meta-analysis, the magnitude of the effects of acidic deposition, nitrogen deposition, increased ozone levels, elevated atmospheric carbon dioxide, and drought on fine roots and ectomycorrhizal (ECM) characteristics. Ectomycorrhizal colonization was an unsuitable parameter for environmental change, but fine root length and biomass could be useful. Acidic deposition had a significantly negative impact on fine roots, root length being more sensitive than root biomass. There were no significant effects of nitrogen deposition or elevated tropospheric ozone on the quantitative root parameters. Elevated CO₂ had a significant positive effect. Drought had a significantly negative effect on fine root biomass. The negative effect of acidic deposition and the positive effect of elevated CO₂ increased over time, indicating that effects were persistent contrary the other factors. The meta-analysis also showed that experimental conditions, including both laboratory and field experiments, were a major source of variation. In addition to quantitative changes, environmental changes affect the species composition of the ectomycorrhizal fungal community.     

Effects of seasonal snow on the growing season of temperate vegetation in China

Variations in seasonal snowfall regulate regional and global climatic systems and vegetation growth by changing energy budgets of the lower atmosphere and land surface. We investigated the effects of snow on the start of growing season (SGS) of temperate vegetation in China. Across the entire temperate region in China, the winter snow depth increased at a rate of 0.15 cm yr^?1 (P = 0.07) during the period 1982–1998, and decreased at a rate of 0.36 cm yr^?1 (P = 0.09) during the period 1998–2005. Correspondingly, the SGS advanced at a rate of 0.68 day yr^?1 (P < 0.01) during 1982–1998, and delayed at a rate of 2.13 day yr^?1 (P = 0.07) during 1998–2005, against a warming trend throughout the entire study period of 1982–2005. Spring air temperature strongly regulated the SGS of both deciduous broad‐leaf and coniferous forests, whereas the winter snow had a greater impact on the SGS of grassland and shrubs. Snow depth variation combined with air temperature contributed to the variability in the SGS of grassland and shrubs, as snow acted as an insulator and modulated the underground thermal conditions. In addition, differences were seen between the impacts of winter snow depth and spring snow depth on the SGS; as snow depths increased, the effect associated went from delaying SGS to advancing SGS. The observed thresholds for these effects were snow depths of 6.8 cm (winter) and 4.0 cm (spring). The results of this study suggest that the response of the vegetation's SGS to seasonal snow change may be attributed to the coupling effects of air temperature and snow depth associated with the underground thermal conditions.     

Diel patterns of autotrophic and heterotrophic respiration among phenological stages

Improved understanding of the links between aboveground production and allocation of photosynthate to belowground processes and the temporal variation in those links is needed to interpret observations of belowground carbon cycling processes. Here, we show that combining a trenching manipulation with high‐frequency soil respiration measurements in a temperate hardwood forest permitted identification of the temporally variable influence of roots on diel and seasonal patterns of soil respiration. The presence of roots in an untrenched plot caused larger daily amplitude and a 2–3 h delay in peak soil CO₂ efflux relative to a root‐free trenched plot. These effects cannot be explained by differences in soil temperature, and they were significant only when a canopy was present during the growing season. This experiment demonstrated that canopy processes affect soil CO₂ efflux rates and patterns at hourly and seasonal time scales, and it provides evidence that root and microbial processes respond differently to environmental factors.     

Restoration of indigenous dominance in exotic grassland by the establishment of juvenile Microlaena stipoides plants

Two experiments were conducted to determine the establishment success of reintroducing Microlaena stipoides (pātītī, weeping rice grass) into existing high‐fertility grassland on the volcanic cones of the Auckland Isthmus. The first experiment monitored the survival and development of juveniles planted in a factorial design including two planting densities, two slope classes and two aspects across three cones. Plant survival during establishment was consistently over 90%. Maximum M. stipoides cover after 2 years (>80%) was achieved on north‐facing steep slopes (>25°) at the greater planting density (40 plants/m²). However, results were particularly idiosyncratic to specific cone/topographical combinations. The second experiment, on a flat site on one cone, monitored the survival and development of juveniles planted across four post‐planting treatments designed to suppress resident vegetation recovery. Plant survival after 6 months was relatively low (50%), and none of the treatments achieved greater than 5% cover of M. stipoides after 1 year. The chosen post‐planting treatments were unable to suppress vigorous recovery of competitive exotic grasses on a moist fertile site. Overall, juvenile planting was shown to be a potentially successful method of Microlaena establishment and could restore indigenous dominance to exotic grassland in this environment, but individual site factors and the high cost of establishment must be considered.