Rainfall reduction consequences on litter decomposition of two species of Quercus

Abstract

Litter decomposition is a fundamental process for biogeochemical cycles in forest ecosystems. Among the main drivers of litter decomposition, several studies have shown that the key activity of soil fauna is modulated by climatic conditions, which implies that climate change is likely modifying this relationship. However, the magnitude and sign of the effect is yet unclear. Here we performed a litter decomposition study for two Quercus tree species under natural conditions on a mixed forest in South Spain, where we established 6 permanent 15x20 m plots, and experimentally simulated a reduction in 30% of total rainfall in 3 of them. We used two types of litterbags with different mesh sizes to allow and exclude mesofauna, and filled them with dried litter of Quercus suber and Q. canariensis. Litter mass loss was estimated after 3, 9 and 18 months (2 bags, 3 times, 43 trees= 258 litterbags). We then performed a linear mixedeffect model to test the single effects and the interactions between rainfall reduction, fauna exclusion and tree species on litter mass loss. Rainfall reduction, faunal exclusion and tree species significantly affected litter mass loss (litter mass * time interaction) but we did not observe further interactive effects. Unexpectedly, drier conditions contributed disproportionally more to litter decomposition rates of both Quercus species, and the presence of mesofauna enhanced this process by 6%. Regarding both species, the temporal dynamics were different, Q. canariensis litter decayed faster than Q. suber at earlier stages but these differences disappeared at the end of the experiment. Our results suggest that climate change will have an important role in litter decomposition, potentially speeding-up biogeochemical cycles, but this effect is mainly direct and not mediated by a change in the role of soil litter fauna on litter decomposition