Invertebrate phenology modulates the effect of the leaf economics spectrum on litter decomposition rate across 41 subtropical woody plant species

Abstract

Litter quality and decomposers are critical to carbon and nutrient cycling through litter decomposition. However, how relationships between litter quality and invertebrate detritivores change litter mass loss through time is poorly known. Species’ initial leaf litter quality, as a legacy of their position on the ‘leaf economics spectrum’ (LES), may determine the invertebrate contribution to litter mass loss. This contribution may change through time, as both population peaks of invertebrate detritivores and litter quality of given species will change through time. Here we introduce invertebrate phenology into a conceptual model of drivers of litter mass loss. We hypothesized that in the early decomposition period, LES can predict litter decomposability with or without a strong invertebrate contribution, that is, litter with higher nutrient content would decompose faster. But in the later decomposition period, when higher quality litter will already have decomposed too much and lower quality litters have still been less degraded, a strong invertebrate peak would coincide with relatively more consumption of initially lower quality litters; this would lead to a humpback relationship between leaf litter mass loss and initial LES position in this period. We tested our hypothesis through a 1‐year field decomposition experiment using leaf litter of 41 woody species in each of two sites in subtropical forest in China; only one of these sites had a strong late peak of leaf litter‐feeding moth larvae in the litter layer. LES score of litter species had a positive linear relationship with litter mass loss before the key invertebrate consumer peaks in the litter layer. However, with the invertebrates peaking later into the decomposition process, the invertebrate consumption peaked at initially lower quality litters, which altered the species’ decomposability trajectory on the LES, consistent with the hypothesized humpback relationship between leaf litter mass loss and LES. This phenomenon resulted in a strongly reduced slope of cumulative mass loss on initial LES score across species. Our finding highlights the importance of considering interactions between the timing of detritivore activities and the timing of litter quality for better understanding the relationships between soil animals and ecosystem carbon and nutrient cycling. A free Plain Language Summary can be found within the Supporting Information of this article.

Dynamic feedbacks among tree species traits, termites and an endangered mammal via deadwood turnover

“…While, without the involvement of invertebrate decomposers wood decomposition rates were predicted by initial values along the WES, when termites participated in the decomposition process they actively altered the species' ranking in terms of the WES through time and moved in abundance and activity from initially high WES species to initially medium WES species. These findings have an interesting parallel with a recent study that found a modulating effect of invertebrate consumption on leaf mass loss rankings along an axis of initial litter quality, i.e., the leaf economics spectrum, over time (Guo et al 2019). However, in that study the modulation was due to a single outbreak by detritivorous moth larvae, while in this study the decomposing invertebrates (i.e., termites) were present in considerable abundance through time in the studied forests, but changed their relative abundance and contribution to decomposition among tree species as decomposition progressed.…”

Influences of the bark economics spectrum and positive termite feedback on bark and xylem decomposition

“…2018, Guo et al. 2019), while to our knowledge no such clear pattern has been found for roots as yet (Fujii et al. 2018).…”

Increasing temperatures reduce invertebrate abundance and slow decomposition

“…Additionally, red maple can decompose quickly [ 33 , 34 ], thus enabling the assessment of early decay dynamics. We collected healthy fresh rather than senesced leaves directly from living trees to standardize the initial conditions of the substrate, an experimental approach that can be used to compare among treatments [ 35 ]. The same day of collection, the leaves were dried in an industrial oven at 70º C for 24h to measure the initial dry-weight ( M 0 ).…”

“…In this study we only capture the early stages of leaf litter loss, though acknowledge that early decomposition dynamics are different from those in the late decomposition period [ 35 ]. Nonetheless, in studies that evaluate decomposition for longer periods, the importance of invertebrate exclusion becomes evident after 30 days (e.g.…”