Relative effects of macroinvertebrates and habitat on the chemistry of litter during decomposition

Abstract

Summary During the decomposition of terrestrial leaf litter, the concentrations of lignin, tannin, cellulose, hemicellulose, nitrogen, and carbon are known to change. These chemical changes have been associated with subsequent colonization and activity of decomposer flora and fauna. Here, we report that chemical changes in litter during the first twelve months of decomposition are affected by macroinvertebrate activity. Moreover, chemical changes are associated most closely with the activities of invertebrate predators. Using litter bags that either excluded (fine mesh) or allowed access by (coarse mesh) macroinvertebrates, we followed the concentrations of lignin, tannin, cellulose, hemicellulose, nitrogen, and carbon in the litter of Liriodendron tulipifera, Quercus prinus and Rhododendron maximum in a North Carolina forest ecosystem. We also compared chemical changes in these litters at a riparian site and an upland site within the forest. The exclusion of macroinvertebrates decreased concentrations of nitrogen and total phenolics in the litter of L. tulipifera, increased concentrations of cellulose and condensed tannin in Q. prinus litter, and increased the concentrations of condensed tannin in R. maximum litter in the riparian zone. Although fine mesh bags excluded most macroinvertebrates, the greatest effects of exclusion were upon ants and spiders, not macroinvertebrate decomposers. Our data therefore suggest that predator-mediated changes in the decomposer communities were responsible for observed shifts in litter chemistry. Predator effects on litter chemistry were likely mediated by their interactions with fungivorous and bacterivorous fauna. For example, Collembola populations were 34% higher in litter bags from which macroinvertebrates were excluded. Litter chemistries also differed between the riparian and upland sites. For both L. tulipifera and R. maximum, effects of habitat were limited to higher concentrations of condensed tannin in the upland site. In contrast, habitat effects upon the litter chemistry of Q. prinus were pervasive. Specifically, Q. prinus litter in the upland habitat exhibited slower increases in lignin, more stable concentrations of cellulose, slower increases in hemicellulose, higher concentrations of total phenolics, and higher concentrations of hydrolysable tannins than did litter in the riparian habitat. Overall, our data provide the first evidence that predators in the litter of deciduous forests can influence the chemistry of litter during the decomposition process.