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Are functional traits and litter decomposability coordinated across leaves, twigs and wood? A test using temperate rainforest tree species

Authors


B. G. Jackson, Dept of Forest Ecology and Management, Swedish Univ. of Agricultural Sciences, SE-901 83 Umeå, Sweden. E-mail: benjamin.jackson@slu.se

Abstract

Synthesis

This study compared the decomposability of leaf, twig and wood litter from 27 co-occurring temperate rainforest tree species in New Zealand. We found that interspecific variation in decomposition was not coordinated across the three litter types. Analysis of the relationships between functional traits and decomposition revealed that traits predictive of wood decomposition varied among the species independently from traits predictive of the decomposition of leaf and twig litter. We conclude that efforts to understand how tree species influence C, N and P dynamics in forested ecosystems through the decomposition pathway need to consider the functional traits of multiple plant structures.

Plant functional traits are increasingly used to evaluate changes in ecological and ecosystem processes. However our understanding of how functional traits coordinate across different plant structures, and the implications for trait-driven processes such as litter decomposition, remains limited. We compared the functional traits of green leaves and leaf, twig and wood litter among 27 co-occurring tree species from New Zealand, and quantified the loss of mass, N and P from the three litter types during decomposition. We hypothesised that: a) the functional traits of green leaves, and leaf, twig and wood litter are co-ordinated so that species which produce high quality leaves and leaf litter will also produce high quality twig and wood litter, and b) the decomposability of leaf, twig and wood litter is coordinated because breakdown of all three litter types is driven by similar combinations of traits. Trait variation across species was co-ordinated between leaves, twigs and wood when angiosperm and gymnosperm species were considered in combination, or when angiosperms were considered separately, but trait coordination was poor for gymnosperms. There was little coordination among the three litter types in their decomposability, especially when angiosperms and gymnosperms were considered separately; this was caused by the decomposability of each of the three litter types, at least partially, being driven by different functional traits or trait combinations. Our findings indicate that although interspecific variation in the functional traits of trees can be coordinated among leaves, twigs and wood, different or unrelated traits predict the decomposition of these different structures. Furthermore, leaf-level analyses of functional traits are not satisfactory proxies for function of whole trees and related ecological processes. As such, efforts to understand how tree species influence C, N and P dynamics in forested ecosystems through the decomposition pathway need to consider functional traits of other plant structures.

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