Abstract:

Background and Aims The influence of soil fauna on litter decomposition is rarely explored in tropical rain forest. This study examined the effect of soil fauna on the decomposition of mixed substrate by litter bag technical at two tropical seasonal rain forest plots in Xishuangbanna, SW China in year of 2000. The following questions were considered in the present study: 1) What roles do soil fauna play in regulating litter mass loss and decomposition rate? 2) How do soil fauna influence litter nutrient release?

Methods In order to examine the role of soil macro-mesofauna in mass loss and nutrient release of litter, litter bags with both fine mesh size (0.15 mm) that excludes the soil macro-mesofauna population from litter and coarse mesh size (2 mm) that allows soil fauna access to litter were used in this experiment. Mass loss and C, N, P, S, K, Ca, and Mg concentrations of leaf litter were determined from the litter in two different mesh size litterbags at monthly intervals. The soil fauna were extracted by hand and by heating the samples.

Key Results Higher relative density and taxonomic diversity of total soil fauna were found in the bags with 2 mm mesh size (22.3-21.77 individuals and 2.67-2.83 orders per g of dry litter) compared to the bags with 0.15 mm mesh size (2.88-2.77 individuals and 0.27-0.28 orders per g of dry litter). Collembola and Acari were the most abundant group, and Hymenoptera(ant), Coleoptera, Hemiptera, Diptera, Diplopoda, Isopoda, Araneae, Pseudoscorpiones were common groups of soil fauna in litter bags with 2 mm mesh size. There were very few individuals of Collembola and Acari in the 0.15 mm litter bags. Our results suggested that soil macro-mesofauna contributed more to the decomposition of leaf litter in 2 mm litter bags than that in 0.15 mm litter bags. The higher mass loss rate (around 71%), decomposition rate (k=1.88-2.44), and nutrient release in litter bags with 2 mm mesh size than in litter bags with 0.15 mm mesh size (34%-35%, k=0.48-0.58) indicated a significant influence of soil macro-mesofauna on mass loss and nutrient release in tropical seasonal rain forest. The release rates of N, S and Ca that could be attributable to the soil macro-mesofauna were higher than other elements whereas K release rate that could be attributable to the soil macro-mesofauna was the lowest. Soil macro-mesofauna caused greater decreases in C/N and C/P ratios in litter bags with 2 mm mesh size than litter bags with 0.15 mm mesh size. There were negative relationships of the percentage of litter mass remaining with order richness and individuals abundance of soil fauna. However, a positive relationship between Shannon-Wiener index of soil fauna and the decomposition rate was found.

Conclusions This study suggests that the presence of soil fauna accelerated plant litter decomposition in the tropical seasonal rain forest. The litter mass loss attributable to the soil macro-mesofauna was about 46%. The effects of soil macro-mesofauna on the nutrient release rates were different among elements. The diversity of soil fauna may have important ecosystem consequences, particularly in tropical rain forest.

Key words: Leaf litter decomposition, Litter bag, Mesh size, Nutrient, Soil macro-mesofauna