1. Plant traits affect wood decomposition. Far less acknowledged, wood trait-decay relationships may vary with environmental conditions that alter the spatiotemporal distribution of decomposer activities. Unfavorable environments can suppress decomposer activities and weaken the wood trait-decay relationships. We hypothesize that waterlogged soils in the valley during rainy season may decrease termite activities and decomposition rates, especially of palatable deadwood. By comparison, wood trait-decay relationships could be less affected at the ridge and hilltop during rainy season.
2. We conducted wood decay experiments of 137 tree species in three sites (valley/ridge/hilltop) differing in microclimate in a 50-ha plot in a subtropical forest. Eight physical and chemical traits were measured to determine the most influential wood properties for termite feeding activities and wood decomposition rates. Samples were harvested after the rainy or after a whole year (rainy-plus-dry season). Mass loss and volume loss (i.e. termite feeding activities) of the first harvest were attributed to the rainy season, while the difference between two harvests were attributed to the dry season.
3. We found that termite feeding activities and wood mass loss during the rainy season were decreased by soil waterlogging in the valley but not on the ridge or hilltop. Wood density predominantly controlled termite feeding and wood mass loss, but its negative effects appeared at the ridge and hilltop only during rainy season, and in the valley only during the dry season. Notably, warmer soil temperatures in the valley accelerated termite activities during the dry season, causing similar final wood mass loss as higher-elevation sites.
4. Synthesis. Our study reveals that environmental effects on wood decomposition are not only mediated by trait changes directly, but also via the spatiotemporal variations of wood trait-decay relationships indirectly. Moreover, wood decomposition does not strictly follow the elevational temperature gradients due to the negative effects of rainfall at lower elevation. Notably, future droughts may reduce soil waterlogging and accelerate termite activities and the decomposition of lower-density wood, particularly in valleys. We are concerned that deadwood carbon stocks once waterlogged by rainfall could become C source under future droughts, especially in regions where termites are dominant decomposers.