Microbial-mediated feedbacks of leaf litter on invasive plant growth and interspecific competition

Abstract

Feedbacks between plants and soil microbes can play an important role in competition between potential invaders and the resident community. However, the role of saprophytic soil microbes is poorly understood because research largely focuses on the role of specific soil-borne pathogens. Our aim was to examine the role of plant-saprophyte feedbacks in soil processes (decomposition and enzyme activities) and plant competition. We preconditioned a common soil in microcosms by decomposing litter of four species; two exotic invasive species (Microstegium vimineum and Berberis thunbergii) and two native species (Viburnum acerifolium and Vaccinium corymbosum). We then replaced the litter with either the same species’ litter or a different species’ litter on the preconditioned soil. We measured the effect of preconditioning on subsequent litter decomposition, microbial community structure (phospholipid fatty acids) and function (soil enzyme activities and decomposition). We then grew Berberis and Viburnum seedlings in preconditioned soils under intraspecific and interspecific competition to determine whether litter preconditioning had a feedback effect on competition. Changes in microbial community structure during preconditioning persisted through time and altered subsequent soil enzyme activities and litter decomposition. These changes also affected the growth rate of two shrub species, but because both shrubs grew best in soil that previously contained Berberis litter, competition between these species was not directly affected. Plant litter creates a legacy that influences the future structure of the microbial community even after that litter is gone. This legacy effect has functional consequences on decomposition and plant growth, and could be an important but under-appreciated factor in soil and plant community ecology. Further study is needed to determine how these consequences affect plant community composition and invasibility.