How macro- and mesofauna contribute to decomposition of single- and mixed-species litter assemblages in a shrub-encroached wetland?

Abstract

Background

Soil macro- and mesofauna play a critical role in regulating (mixed-)litter decomposition. In shrub-encroached temperate graminoid wetlands, shrub and graminoid litters, with contrasting chemical quality, often interact to affect decomposition. However, little is known about how fauna contribute to decomposition and mixing effects in situ.

Methods

We collected litters of two graminoid species (Deyeuxia angustifolia and Carex schmidtii) and two shrubs (Betula fruticosa and Salix floderusii) in a shrub-encroached wetland. By a one-year field microcosm experiment involving 8 mm- and 0.5 mm-mesh sizes to control soil fauna sizes in B. fruticosa and S. floderusii islands, we measured litter mass loss of graminoid species, shrubs, and their mixtures.

Results

In both islands, the 8-mm treatment increased mass loss by 11.4% ~ 35.9% relative to the 0.5-mm, irrespective of monospecific and mixed-species litter. For mixed-species litter, positive non-additive effects on mass loss were common, especially in the 8-mm treatment (in three of four mixtures in the S. floderusii island, and in all mixtures in the B. fruticose island). Specifically, graminoid litters generally had greater mass loss in the shrub-graminoid mixtures than that decomposing alone, with a higher incidence in the 8-mm treatment. For the mixtures, the mesh size explained most variation (26.9%, followed by species composition and litter chemical dissimilarity) in mass loss.

Conclusions

This study provides field evidences for the critical role of macro- and mesofauna in regulating litter decomposition in freshwater wetlands. Following shrub encroachment, the fauna contributes greatly to positive mixing effects on decomposition of shrub-graminoid litter assemblages.