潮虫消耗木本植物凋落物的可选择性试验

Abstract

A growing number of researchers are investigating the impact of exotic plant invasion on soil ecological processes.This includes the mechanisms of feedback,especially in litter degradation and nutrient cycling.Recent studies indicate that the litter of exotic plants potentially decomposes faster and releases more nutrients if they are nitrogen-fixing plants,or if their leaves have a higher specific leaf area and maintaining higher concentration of nutrients.But slower decomposition of alien species than native species is found when alien plants have higher lignin content,higher C/N ratio and/or unique secondary compounds.However,few studies have concentrated on the comparison between native plant species and different levels of invasive exotic plant such as non-invasive alien species or invasive alien species.In addition,it is not clear whether local soil organism present consumption differences in their litter and food preference.Nor is it clear if generalist decomposers show any associations with the invasion status or particular plant traits. Therefore,we tested leaf litter palatability for ten native plant species,five non-invasive alien species and five invasive alien woody plant species in Switzerland by a selective food-feeding experiment in the laboratory.The generalist consumer used was Porcellio scaber(Isopoda) which is typically employed as a primary generalist decomposer in forest leaf litter decomposition.Each plant species underwent 42 times replications during the test,and the percentage of mass loss determined the consumption rate.Meanwhile,initial traits including lignin,cellulose,hemicellulose,carbon and nitrogen for each plant species were measured for comparison with their consumption rates.Leaf litter compounds were analyzed for the percentage of dry matter and the C/N ratio was calculated afterwards. First and most importantly,our results showed that there are no significant consumption differences(P0.05) among native,non-invasive alien and invasive alien species as food resources for the woodlice in our study.However,taking the architectural form as a functional group,the consumption rate was significantly higher in shrubs than in trees(P0.01).However,the comparison of lignin,cellulose,hemicellulose,carbon and nitrogen content among native,non-invasive alien and invasive alien species or between trees and shrubs did not show any significant differences.And over all the traits,only nitrogen concentration of litter was positively correlated with consumption rate(R2=0.358). Our conclusion therefore emphasizes that the consumption rate of woody species is not necessarily associated to the plants′ invasion status.But nitrogen content or any forms of nitrogen composition may play an important role and may affect the biological processes of invasion to in some extent. Functionally speaking,an increasing presence of alien woody plants should not influence the decomposition of plant material and matter flux negatively.Ecosystem dynamics are altered through a variety of interacting,mutually reinforcing mechanistic pathways,and additional studies on the ecosystem-scale impacts of invasions are needed.