Defence‐related traits drive leaf litter decomposition more than growth‐related or size and shape traits in a subtropical climate

Abstract Functional traits reflecting leaf structure and functions can show tradeoff or synergetic patterns. How these patterns exert an ‘afterlife’ effect on litter decomposition, or how such an effect is mediated by soil fauna, remains poorly understood. Here, using litter traits reflecting leaf growth, defence, size and shape, we tested a hypothetical framework addressing (i) the relationships between decomposition rate ( k ) and trait patterns (growth versus defence, chemical versus structural defence and size versus shape) and (ii) how the access of soil macro‐ and mesofauna to the litter alters these relationships. We conducted a litterbag decomposition experiment of 18 tree species in subtropical Hunan, China, for 13 months. Litterbags with mesh sizes of 0.07, 2 and 5 mm were used to mimic the cases of (i) excluding meso‐ and macrofauna, (ii) excluding macrofauna and (iii) including all fauna. For each species, 14 litter traits related to leaf growth and defence and 8 traits related to leaf size and shape were measured. We found a growth‐defence space and a size‐shape space among species: the former was driven by two orthogonal trait gradients reflecting the tradeoffs between mechanical and chemical defences, and between growth and overall defence, respectively; the latter was driven by two orthogonal trait gradients of size and shape, respectively. Among the four gradients, the defence category gradient spanning species with varying relative investments in mechanical versus chemical defences was the only one showing significant relationships with k , mainly due to the significant relationships between mechanical traits and k . The presence of meso‐ and macrofauna significantly increased k but could not significantly change the slope of the relationship between k and any of the trait gradients. Synthesis . We reveal that defence‐related traits predominate over growth‐related or size and shape traits in driving litter decomposition and that soil fauna play a marginal role in modifying such relationships, thereby enhancing our holistic understanding of trait‐decomposition relationships. Our findings indicate that the contribution of relative investments in chemical versus mechanical defence to interspecific variation in leaf litter decomposition deserves broad investigation in different ecosystems.