The importance of macro- and micro-nutrients over climate for leaf litter decomposition and nutrient release in Patagonian temperate forests

Abstract

Temperate forests play an important role in the global carbon (C) cycle. Extensive research on litter decomposition in temperate forests in the Northern Hemisphere have greatly contributed to our conceptual framework of the controls of C cycling, where climate and litter lignin/N ratio have played a dominant role. However, there is a noteworthy lack of basic information on southern temperate forests, which have unique characteristics demonstrated by differences in ecosystem functioning and their response to human impact when compared to their northern counterparts. Patagonian forests are the most extensive temperate forests in South America and offer the opportunity to evaluate the importance of climate and litter traits in old growth forests with relatively little human impact. We compared litter decomposition of 10 dominant native tree species and of two non-native tree species (used as common substrates) in two native forests with varying precipitation and tree species composition: a Nothofagus mesic mixed forest (2200 mm MAP) and an Austrocedrus open dry forest (1350 mm MAP). In addition to rainfall, these forest types differed markedly in tree species composition and leaf litter traits that resulted in 1.5 times larger soil carbon and nitrogen pool in Austrocedrus open dry forest and 5 times higher soil inorganic nitrogen than in Nothofagus mesic forests. Nevertheless, decomposition of common litter substrates was similar between both forest types. In contrast, native tree species litter showed up to 10-fold differences in their decomposition rates in a common forest site. Litter mass loss and nitrogen dynamics were strongly associated with magnesium (Mg) and manganese (Mn) content of the litter, respectively. In contrast to dominant control of climate and litter lignin/N, our results demonstrate that native tree species traits may be more important than climate and its effects on plant-soil interactions in Patagonian forests. Our study also highlights the importance of macro- and micro-nutrients (Mg and Mn) in litter that are generally overlooked as determinants of litter decomposition in terrestrial ecosystems. These native Patagonian forests show distinctive controls of litter decomposition compared with other temperate forests of the world. They also highlight the importance of considering how management that affects tree species identity and composition may have far-reaching effects on ecosystem functioning that are currently not being considered.