Effects of plant coverage on shrub fertile islands in the Upper Minjiang River Valley.

The patchy distribution of vegetation in dry land results in well-documented "fertile islands". However, the response of shrub fertile islands to plant recovery and the underlying mechanisms, such as the linkage plant and soil properties, remain unknown. We sampled soils from areas with three different plant coverages (25%, 45%, and 75%) and three of their adjacent inter-plants to investigate soil physicochemical and microbial properties in the upper Minjiang River arid valley. The results showed that these factors were influenced by the persistence of plants that contrasted with the inter-plant interspaces. We found fertile islands in under-plant soil that were enhanced with increasing plant coverage, from 25% to 45% and 75%; however, there were no significant differences between 45% and 75% plant coverage apart from the soil clay content and the fungi to bacteria ratio. The soil microbial communities in under-plant soil were strongly influenced by the total soil carbon (TC), soil organic carbon (SOC), and available nitrogen (AN), whereas the microbial communities in inter-plant soil were primarily constrained by the AN and available phosphorous (AP). Moreover, the inter-plant soil properties, including gravimetric soil water content, pH, electrical conductivity (EC), and soil C:N ratio, were also strongly influenced by adjacent vegetation, which suggested that fertile islands may be beneficial for plant recovery in this region.

Contrasting elevational diversity patterns for soil bacteria between two ecosystems divided by the treeline.

Above- and below-ground organisms are closely linked, but how elevational distribution pattern of soil microbes shifting across the treeline still remains unknown. Sampling of 140 plots with transect, we herein investigated soil bacterial distribution pattern from a temperate forest up to a subalpine meadow along an elevational gradient using Illumina sequencing. Our results revealed distinct elevational patterns of bacterial diversity above and below the treeline in responding to changes in soil conditions: a hollow elevational pattern in the forest (correlated with soil temperature, pH, and C:N ratio) and a significantly decreasing pattern in the meadow (correlated with soil pH, and available phosphorus). The bacterial community structure was also distinct between the forest and meadow, relating to soil pH in the forest and soil temperature in the meadow. Soil bacteria did not follow the distribution pattern of herb diversity, but bacterial community structure could be predicted by herb community composition. These results suggest that plant communities have an important influence on soil characteristics, and thus change the elevational distribution of soil bacteria. Our findings are useful for future assessments of climate change impacts on microbial community.

Ecological risk assessments and context-dependence analysis of heavy metal contamination in the sediments of mangrove swamp in Leizhou Peninsula, China.

Sediments in eight types of mangroves were sampled in the Leizhou Peninsula. Heavy metals were analyzed to investigate the effects on metal distribution of mangrove communities, to evaluate contamination levels, identify sources and relationships between the two. Results showed that mangrove communities have effects on most heavy metal distributions in sediments, especially in the sediment with shrub communities of Aegiceras corniculatum where the contents of many metals are highest. As, Cr and Ni were identified as metal pollutants of primary concern, while Cd was of no concern. Zn, Pb, As mainly originated from anthropogenic source while the other metals are geogenic. Heavy metal distributions were affected by the independent and joint effects of landscape and sediment context; landscape context explains more variations in heavy metals than does sediment physicochemical variables. Total sulfur, total phosphorus and total potassium in sediment, and the existence of paddy field and forest land within 2000m around the sampling sites are significant variables also.

[Influence of soil moisture, nitrogen and phosphorus contents on Bauhinia faberi seedlings growth characteristics in arid valley of Minjiang River].

To study the influence of resources thresholds on plant growth is a major theme in restoration ecology. Based on the simulation of the natural thresholds of soil moisture, nitrogen (N), and phosphorus (P) under drought condition in the arid valley of Mingjiang River, a full factorial experiment was designed to study the dynamics of Bauhinia faberi seedlings survival rate, growth, biomass production, and resources use efficiency across one growth season. High soil moisture (40% field water capacity), high soil P (24 mg P x kg(-1)), and low N (100 mg N x kg(-1)) increased the seedlings survival rate, and promoted the seedlings growth, biomass production, and water use efficiency. There was a significant coupling effect between soil N and P, but the interactions between soil moisture and soil N and P were not obvious. High N (240 mg N x kg(-1)) restrained the seedlings growth markedly, while high P mitigated the negative effects of high N via increasing root area, root length, and root mass to promote the seedlings N and P uptake. The N and P use efficiency across one growth season kept steady, and had significant positive correlation with root/shoot mass ratio. The combination of high soil moisture, low N, and high P promoted the seedlings growth effectively, while that of low soil moisture, low P, and high N inhibited the seedlings growth markedly.

Characterising biocomplexity and soil microbial dynamics along a smelter-damaged landscape gradient.

Soil micro-organisms are an integral but often underestimated part of plant and soil ecosystems. Long-term industrial air pollution in the Sudbury, Ontario region has altered vegetation and soil, and therefore, possibly, soil microbial function. This study focuses on the historical pollution gradient resulting from a decommissioned smelter near Sudbury, and aims to determine the effect of contaminant concentrations (such as soil heavy metals) and environmental variables (such as soil moisture and vegetation cover) on soil microbial populations and diversity. Results suggest that increasing distance from the pollution source did not correlate well with increasing micro-organism population or diversity. Metal concentrations also did not correlate with microbial dynamics. Only soil nutrient abundance showed a significant relationship, and revealed that phosphorous may be the rate-limiting influence. Secondary affects of pollution such as soil erosion and removal of plant litter are suggested to be important causes. The study reinforces the complex nature of landscape scale recovery and shows that recovery pathways are not linear or dependent upon single variables.