Opposing Effects of Plant-Community Assembly Maintain Constant Litter Decomposition over Grasslands Aged from 1 to 25 Years

Litterdecomposition is central to ecosystem functioning and depends, under constant abiotic conditions, on litterquality and decomposeractivity. During the assembly of a plant communityfollowing disturbance, litterquality is expected to decrease, due to an increasing proportion of resource-conservative species, whereas decomposeractivity is expected to increase, due to the establishment of decomposerpopulations and their response to local vegetation (“home-field advantage”, HFA). To date, the combined effect of these processes remains poorly understood. We studied 27 seminatural grasslandsin western France, ranging from 1 to 25 years since last cultivation. We measured the functional compositionof plant communitiesusing littertraits ( specific leaf area, leaf dry matter content, C/N ratio, phenolics), characterized the entire community of decomposers(macrofauna, mesofauna, microbes) and performed reciprocal littertransplants to quantify HFA. We found that, overall, decomposition was rapid, and HFA was not evident. While there was substantial among- grasslandvariation in decomposition and HFA, neither changed with grasslandage. Litterquality and decomposerefficiency also remained, overall, unchanged. However, grasslandage determined all measured littertraits and caused soil microbial C/N ratio to decline. Although these changes impacted decomposition individually, together they canceled out each other, resulting in constant decomposition across the chronosequence. Our results suggest that processes driving decomposition differ during grasslandsuccession and suggest that HFA may be lower in communities with high litterquality. Moreover, simultaneous assembly processes have opposing and therefore stabilizing effects on decomposition, possibly explaining the outstanding resilience of primary production in temperate grasslandecosystems.