Earthworm and microbe response to litter and soils of tropical forest plantations with contrasting C:N:P stoichiometric ratios

1

The stoichiometry of resources is increasingly acknowledged as a major control of consumer activity and abundance. Chemical properties of litter, the main source of food for decomposers, are likely to be important drivers of decomposer activity.

2

Theory predicts a high control of resource stoichiometry on the abundance of consumer organisms that maintain strict homeostasis, due to costs associated with the regulation of nutrient balance in their body tissue. Decomposer efforts in nutrient acquisition should be related to imbalances in resource stoichiometry.

3

A 21 year old experimental plantation of monospecific plots of trees with leaves of contrasting chemistry was used to test four hypotheses: (i) soil and litter nutrient stoichiometry (C, N, P) are linked; (ii); soil enzyme activity ratios and stoichiometry are linked; (iii) earthworms’ tissue stoichiometry does not depend on soil and litter stoichiometry (homeostasis); (iv) earthworm density is dependent upon phosphorus availability, the most limiting nutrient in soils at this site, and, to a lesser extent, to nitrogen availability.

4

We found (i) no relationship between litter and soil stoichiometry, (ii) microbial activity was linked to soil stoichiometry, (iii) earthworms showed strict homeostasis in their tissue and (iv) earthworm abundance increased with P availability.

5

We discuss the mechanisms that might lead to these patterns.