Resource quality and trophic responses to simulated throughfall: Effects on decomposition and nutrient flux in a no-tillage agroecosystem

Abstract

Effects of simulated throughfall additions on microbial and microfaunal abundances, decomposition and N, P, Ca, Mg and K flux from winter rye ( Secale cereale L.) and crimson clover ( Trifolium incarnatum L.) residues in a no-tillage agroecosystem were quantified during the summer of 1986. Clover residues, with higher initial nutrient concentrations and lower C-to-element ratios, had a greater rate of decomposition, greater net mineralization and higher mean concentrations of all five elements than rye. Overall mean densities of both fungi and bacteria were also greater on clover and these in turn supported greater overall mean densities of fungivore microarthropods and bacterivore nematodes. Throughfall additions to low resource quality rye residues enhanced microbial immobilization of N, P and Ca in the absence of high grazer abundances. Microfloral densities and nutrient retention were diminished under higher grazer-fauna densities. No consistent throughfall effects were observed for the higher resource quality crimson clover residues. Significantly lower net N mineralization from rye (0.95 mgg −1 of initial litter) vs clover (12.69 mgg −1 of initial litter) and enhanced N retention in throughfall-treated rye suggest the limiting nature of this element. The additional amounts of N and P retained in throughfall-treated rye residues over controls were greater than could be accounted for by throughfall inputs and suggest that low level nutrient additions may stimulate immobilization of elements from other sources.