Effects of repeated drought on soil microarthropod communities in the northern Chihuahuan Desert

 Soil microarthropods were sampled in plots centered on creosotebushes (Larrea tridentata) and in plots centered on mesquite (Prosopis glandulosa) coppice dunes. Nine plots in each area were covered by rain-out shelters with greenhouse plastic roofs which excluded natural rainfall and nine plots received natural rainfall. There were differences in the abundance of several mite taxa in soils from the mesquite coppice dune plots. Some taxa (Stigmaeidae, Nanorchestidae, and Entomobryidae) occurred in significantly lower numbers in the soils of the drought plots. Other taxa (Tarsonemidae and Cunaxidae) were more abundant in the drought plots in the mesquite coppice dunes. There were no significant differences in the abundance of any of the dominant taxa of soil microarthropods in the drought and control plots centered on creosotebush. In the creosotebush habitat, there were significantly fewer Prostigmata in the plots exposed to drought. In an area with both creosotebush and mesquite, there were no significant differences in microarthropod population responses to drought and in recovery from drought. The differences in responses of soil microarthropods to drought in creosotebush and mesquite habitats are attributed to the differences in soil stability, litter accumulations, and microclimate associated with the shrubs. Received: 29 December 1997     

Monitoring soil restoration in an open-pit mine in northern Italy

Mining causes significant damage to the environment: the removal of top layers of soil causes loss of structure and functionality, with a subsequent reduction in biodiversity. Soil communities are important for soil formation, they contribute to the improvement of several characteristics of soils and they play key roles in many processes that enhance the success of restoration. Unfortunately, soil fauna are poorly monitored even though they represent a good tool for assessing soil quality. The “La Speranza” quarry in northern Italy was studied from the start of the restoration process in 2008 until 2012. Six sites were selected and monitored annually. Microarthropods were extracted from three replicates of soil drawn from each site, identified to order level and then counted. Both the abundances of taxa and the soil biological indices applied (Shannon diversity index (H’), Pielou's evenness index (J), the Acari to Collembola ratio (A/C) and the QBS-ar index) revealed a good level of soil recovery over the years studied. Furthermore, the edaphic organisms that are generally associated with stable conditions in the soil (e.g. Symphyla, Protura, Chilopoda), appeared in the most recent of the years.     

Reducing the dimensionality of soil microinvertebrate community datasets using Indicator Species Analysis: Implications for ecosystem monitoring and soil management

Soil microinvertebrates are closely associated with soil decomposition and nutrient cycles and may be particularly responsive indicators for soil management practices. However, identification of appropriate bioindicator species for many systems has been severely limited by a lack of information on species taxonomy, distribution, and functional role. We evaluated Indicator Species Analysis (ISA) as an objective method for assessing the indicator potential of different taxa without regard to their ecological role or expected management response. Restricting ordination and site classification to significant indicator morphotaxa reduced the dimensionality of the community data matrix by 69% while only slightly decreasing the efficiency of unsupervised classification (from 87.2 to 84.4%); the percentage of total variability explained by first two PCA axes increased following ISA. When these same indicator morphotaxa were used to classify an independent set of samples, the percentage of total variability explained by the first two PCA axes increased from 55.3 to 65.2%; cluster analysis of the test dataset correctly classified 47 out of 50 plots by cover type (94% accuracy). However, restriction of analysis to indicator morphotaxa alone reduced detection of differences between sampling dates relative to the complete dataset. Although care needs to be taken to ensure that the dataset used for indicator selection is fully representative of underlying temporal and spatial variability, ISA appears to overcome many of the limitations associated with parametric and multivariate approaches for identifying indicator morphotaxa and has the potential to greatly reduce the taxonomic expertise and labor costs associated with sorting and identification of soil microarthropods.     

Species diversity and seasonal abundance of Collembola in turfgrass ecosystems of North America

In North America, lawns are the most widely used plantings in urban areas. However, despite the ubiquity and ecological roles of turfgrass soil arthropods, many aspects of their composition and diversity have been neglected. We investigated assemblages of Collembola and their seasonal fluctuations in a newly established lawn and a 10-year old lawn located in Québec City, Canada. Collembola were sampled every month from May to October in 2003 and 2004 by extracting individuals from soil cores using a modified Berlese funnel. A total of 21 species representing 17 genera and nine families were identified. Four species are new records for the province of Quebec: Brachystomella parvula, Mesaphorura simplex, Isotomodes productus, and Sphaeridia pumilis. Turfgrass supports mainly three cosmopolitan species from the Isotomidae family, which represent 73.5% of all Collembola collected during the survey: Parisotoma notabilis, Isotoma viridis, and Cryptopygus thermophilus. Collembola were twice more abundant at the newly established site, but there were minor differences in species diversity between sites and years. No clear patterns of seasonal relative abundance were observed for the whole Collembola populations, as well as for the three dominant species. Turfgrass ecosystem provides a suitable habitat for epedaphic and hemiedaphic Collembola, such as the Isotomidae, most likely because turfgrass mowing and natural leaf, stem and root replacement produces large amounts of decaying organic matter.     

Environmental filtering vs. resource-based niche partitioning in diverse soil animal assemblages

Terrestrial invertebrates constitute most of described animal biodiversity and soil is a major reservoir of this diversity. In the classical attempt to understand the processes supporting biodiversity, ecologists are currently seeking to unravel the differential roles of environmental filtering and competition for resources in niche partitioning processes: these processes are in principle distinct although they may act simultaneously, interact at multiple spatial and temporal scales, and are often confounded in studies of soil communities. We used a novel combination of methods based on stable isotopes and trait analysis to resolve these processes in diverse oribatid mite assemblages at spatial scales at which competition for resources could in principle be a major driver. We also used a null model approach based on a general neutral model of beta diversity. A large and significant fraction of community variation was explainable in terms of linear and periodic spatial structures in the distribution of organic C, N and soil structure: species were clearly arranged along an environmental, spatially structured gradient. However, competition related trait differences did not map onto the distances separating species along the environmental gradient and neutral models provided a satisfying approximation of beta diversity patterns. The results represent the first robust evidence that in very diverse soil arthropod assemblages resource-based niche partitioning plays a minor role while environmental filtering remains a fundamental driver of species distribution.     

Positive relationship between herbaceous layer diversity and the performance of soil biota in a temperate forest

The current decline in biodiversity is particularly pronounced in the herbaceous layer of forest ecosystems. We explored the relationship between a naturally occurring plant diversity gradient in the understory vegetation of a deciduous forest and several above-and belowground ecosystem processes. We show that particularly soil microbial parameters and microarthropod densities are positively correlated with plant species richness. These results confirm recent findings in grassland ecosystems and highlight the intimate interconnectance between the diversity and functioning of above-and belowground compartments. We conclude that irrespective of a potential causal relationship between plant species richness and belowground processes, it is essential to consider the performance of soil biota in order to understand the relationship between herbaceous layer composition and ecosystem function.     

不同种植年限转基因抗虫棉对土壤中小型节肢动物的影响

2007~2008年,在分别于1999年、2002年和2006年种植Cry1Ac基因抗虫棉的棉田中,于棉花的苗期、蕾期、花铃期和吐絮期采集土壤样品,采用改良的Tullgren法收集土壤中的中小型节肢动物,以监测长期种植转基因抗虫棉对土壤节肢动物群落的影响。2年8次采样共获得12类中小型节肢动物,隶属于节肢动物门中的7纲10目,其中弹尾目、蜱螨目、蜘蛛目为本地区棉田中的优势类群,综合纲、双翅目、半翅目、双尾目、鞘翅目和同翅目为常见类群。广义线性混合模型分析结果表明,随着转基因抗虫棉种植年限的增加,各转基因抗虫棉田中的土壤主要类群中小型节肢动物的个体密度和多样性指数没有产生显著性差异,但是随着采样时期的不同各棉田土壤主要中小型节肢动物的个体密度和群落多样性指数均呈显著性季节变化。主成分分析表明,弹尾目、蜘蛛目、蜱螨目的得分值较高,可作为本地区未来转基因抗虫棉环境影响监测的重要指标生物。     

美国俄勒冈州有机与传统农业生态系统间土壤生物区的比较

Soil samples at 0--10 cm in depth were collected periodically at paired fields in Corvallis, Oregon, USA to compare differences in soil microbial and faunal populations between organic and conventional agroecosystems Results showed that the organic soil ecosystem had a significantly higher (P < 0.05) average number or biomass of soil bacteria; densities of flagellates, amoebae of protozoa; some nematodes, such as microbivorous and predaceous nematodes and plant-parasitic nematodes; as well as Collembola. Greater numbers of Rhabditida (such as Rhabditis spp.), were present in the organic soil ecosystem while Panagrolaimus spp. Were predominant in the conventional soil ecosystem. The omnivores and predators of Acarina in the Mesostigmata (such as Digamasellidae and Laelapid), and Prostigmata (such as Alicorhaiidae and Rhagidiidae), were also more abundant in the organic soil ecosystem. However, fungivorous Prostigmata (such as Terpnacaridae and Nanorchestidae) and Astigmata (such as Acarida) were significantly higher (P < 0.05) in the conventional soil ecosystem, which supported the finding that total fungal biomass was greater in the conventional soil ecosystem. Seansonal variations of the population depended mostly on soil moisture condition and food web relationship. The population declined from May to October for both agroecosystems. However, higher diversities and densities of soil biota survived occurred in the organic soil ecosystem in the dry season.