Does litter leachate diversity lead to non-additive effect on litter decomposition and soil microbial activity?

François-Xavier Joly1, Nathalie Fromin1, Michael Scherer-Lorenzen2, Stephan Hättenschwiler1
1 Centre d'Ecologie Fonctionnelle et Evolutive (CNRS), Montpellier, France
2 Faculty of Biology - Geobotany, University of Freiburg, Germany

O 5.1 in Linking biodiversity and biogeochemistry

15.07.2014, 11:00-11:20, H19

In tree species-rich forests, the mixing of leaf litter results often in faster decomposition than expected from component species decomposing singly. Among the proposed mechanisms underlying these diversity effects on decomposition, are the passive transfer of nutrients and/or carbon compounds between litter species, and resource complementarity in microbial communities colonizing species rich litter.

Soluble litter components that easily leach from litter during the initial stage of decomposition may play a critical role in nutrient transfer and complementary resource use in litter mixtures, but this has not specifically been studied so far. Depending on litter species identity, leaching can contribute up to 30% of overall litter mass loss over the first few weeks of decomposition. Moreover, the leachates vary greatly in composition and overall quality among litter species. This initial leaching of a diverse group of compounds has important consequences for microbial activity and community composition and may prime litter decomposition beyond the initial stage of decomposition. We hypothesized that leachate diversity resulting from litter mixtures are an important driver of litter diversity effects on microbial decomposers and subsequent litter mass loss and microbial activity in the underlying soil.

We tested this hypothesis using litter leachates from the four co-occurring temperate forest tree species Acer pseudoplatanus, Fagus sylvatica, Abies alba, and Picea abies. Leaf litter leachates from these species were added singly (4 treatments) and in all possible combinations (11 mixtures) to soil from a forest where all four tree species are present within plasma flasks under controlled laboratory conditions. On top of the soil we placed cellulose discs as a standardized simple substrate for microbial decomposers. Cellulose discs and soil were watered with the 15 different leachates (5 replicates per leachate) and incubated at constant temperature (20°C) over two weeks. During the incubation, we regularly measured the respiration rate, and at the end of the experiment, we measured the mass loss of the cellulose and the catabolic capacity (Microresp™) of the soil microbial community. Leachate quality of leaf litter from each tree species was characterized by dissolved organic carbon, nitrogen, total phosphorus, aromaticity, pH.

According to our hypothesis, preliminary analyses indicate that some mixtures of leachates from the four studied tree species affected cellulose decomposition non-additively. Likewise, the combined respiration of cellulose and underlying soil in some mixed leachate treatments deviated from the values expected from the addition of leachates from single litter species. Ongoing analyses aim at distinguishing the relative contribution of leachate mean traits and functional trait dissimilarity to the observed non-additive leachate effects. Our results point to an important role of leachates diversity on decomposers activity.

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last modified 2014-06-19