Consistent response of nematode communities to management of coniferous plantations

Background:Crop-tree thinning (CTT) is a forest management practice aiming at enhancing the growth of target trees in plantations by harvesting neighboring trees. Along with the positive effect on tree growth, thinning represents a disturbance, which likely affects belowground organisms and may feed back to stand productivity.However, the impact of CTT on the belowground food web is poorly understood. Since nematodes are species-rich and abundant belowground organisms, occupying a variety of trophic positions in soil food webs and being sensitive to disturbances, they serve as ecological indicators of ecosystem disturbance.Results:We studied the effect of CTT on the soil nematode community structure in pine (Pinus massoniana Lamb.),Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) and cypress (Cupressus funebris Endl.) plantations in the Sichuan Basin three years after applying CTT. Crop-tree thinning significantly increased the abundance of soil nematodes in each of the plantations. Moreover, CTT significantly increased the relative abundance of herbivorous nematodes in each of the plantations. Furthermore, CTT increased the proportion of stress tolerators (c-p 1)and enrichment opportunists (c-p 2) and reduced the maturity, structure and enrichment indices of nematodes in Chinese fir and cypress plantations, while only subtle changes were observed in pine plantations. Interestingly,across plantations, the effects of CTT on soil nematode communities were mainly due to changes in microbial biomass nitrogen and understory vegetation diversity.Conclusions:Forest management practices resulting in more open canopies uniformly affect soil food webs by changing the quantity and quality of resources associated with increased understory cover and diversity as well as microbial food. These insights increase our understanding of the impacts of forest management on the structure and functioning of belowground communities, which may contribute to management and conservation policies for more sustainable forestry.

Changes in diversity and body size of Onychiurinae(Collembola:Onychiuridae)along an altitudinal gradient in Changbai Mountain,China

Collembola are among the most abundant and diverse soil animals contributing significantly to major ecosystem processes.Global climate changes in temperature and precipitation are likely to affect their community structure and functioning and this is likely to differ along altitudinal gradients.In this study,changes in richness,abundance,and body size of onychiurin Collembola with altitude have been investigated in the Changbai Mountain range of northeast China.Sampling was carried out on a 30 km long transect along forested slopes of the Changbai Mountains.Standardized samples were taken from 800 to 1700 m at seven altitudinal levels.More than 5000 specimens of Onychiurinae representing 13 species were collected,making Onychiuridae(with the sole subfamily Onychiurinae in Changbai)the most abundant Collembolan family in the area.The number of species of Onychiurinae slightly increased along the altitudinal gradient.The average number of species per sample,but not the total abundance,changed significantly but not monotonically with altitude.Body size of Onychiurinae species decreased significantly with increasing altitude contradicting Bergmann’s rule.Furthermore,the abundance of the three body-size groups differentially responded to increasing altitude,with the abundance of the large body-size group decreasing and the abundance of the small body-size group increasing.Our results suggest that the distribution patterns of Collembola along the altitudinal gradient are complicated and may be linked to taxonomic groups and bioclimatic zones.

Biodiversity and belowground interactions mediate community invasion resistance against a tall herb invader

Aims Species-rich plant communities are hypothesized to be more resistant against plant invasions because they use resources in a more efficient way.However,the relative contributions of aboveground competition and belowground interactions for invasion resistance are still poorly understood.Methods We compared the performance of Knautia arvensis transplants growing in plots differing in plant diversity both under full competition and with shoots of neighbors tied back to determine the relative strength of aboveground competition in suppressing this test invader without the confounding effect of shading.In addition,we assessed the effects of belowground competition and soil-borne pathogens on transplant performance.Important Findings Both aboveground competition and plant species richness strongly and independently affected invader performance.Aboveground biomass,height,leaf mass per area and flowering of transplanted individuals of K.arvensis decreased with increasing species richness of the host community.Species-rich and species-poor communities both imposed equally strong aboveground competition on K.arvensis.However,belowground interactions(especially belowground root competition)had strong negative effects on transplant performance.In addition,the presence of grasses in a plant community further reduced the performance of K.arvensis.Our results suggest that belowground competition can render species-rich host communities more suppressive to newly arriving species,thus enhancing community invasion resistance.