Litter type and termites regulate root decomposition across contrasting savanna land‐uses

Abstract

Decomposition is a vital ecosystem process, increasingly modified by human activity. Theoretical frameworks and empirical studies that aim to understand the interplay between human land‐use, macro‐fauna and decomposition processes have primarily focused on leaf and wood litter. For a whole‐plant understanding of how land‐use and macro‐fauna influence decomposition, investigating root litter is required. Using litterbags, we quantified rates of root decomposition across contrasting tropical savanna land‐uses, namely wildlife and fire‐dominated protected areas and livestock pastureland without fire. By scanning litterbags for termite intrusion, we differentiated termite and microbial driven decomposition. Root litter was buried underneath different tree canopies (leguminous and non‐leguminous trees) and outside canopies to account for savanna landscape effects. Additionally, we established a termite cafeteria‐style experiment and common garden to explore termite selectivity of root litter and root trait relationships, respectively. After one year, we found no significant differences in root litter mass loss between wildlife dominated areas and pastureland. Instead, we found consistent species differences in root litter mass loss across land‐uses and additive and non‐additive effects of termites on root decomposition across plant species. Termite selectivity for root litter species occurred for both root and leaf litter buried near termite mounds, but was not explained by root traits measured in the common garden. Termite foraging was greater under leguminous tree canopies than other canopies; however, this did not influence rates of root decomposition. Our study suggests that land‐use has a weak direct effect on belowground processes in savannas. Instead, changes in herbaceous species composition and termite foraging have stronger impacts on belowground decomposition. Moreover, termites were not generalist decomposers of root litter, but their impact varies depending on plant species identity and likely associated root traits. This root litter selectivity by termites is likely to be an important contributor to spatial heterogeneity in savanna nutrient cycling.

Teatime in the Serengeti: macrodetritivores sustain recalcitrant plant litter decomposition across human-modified tropical savannahs

“…However, prior work in the Serengeti found that termites eat through nylon litterbags to access plant litter creating holes~0.55 mm 2 in size (Smith et al 2019). To quantify the contributions of macrodetritivores to litter decomposition, we used a stainless steel metal mesh treatment with an aperture size of 0.3 mm designed to exclude the head-width of the smallest foraging termites (Smith et al 2019;Teo et al 2020). Our litterbag approach targeted termites, but could equally apply to other savannah macrodetritivores with strong mandibles such as beetle larvae, millipedes and woodlice.…”

“…or on the diets of insectivorous mammals, for example aardwolf consumption of Trinervitermes spp. termites (de Visser et al 2015;Freymann et al 2008;Freymann et al 2007;Freymann et al 2010;Kruuk and Sands 1972;Smith et al 2019). Inside wildlife protected areas, the majority of wild herbivores (including elephants, buffalos, impalas and various species of antelope) occur at low densities, with the exception of migratory wildebeest and zebra (Hopcraft et al 2015;Sinclair et al 2007).…”

“…Litterbag material was made of woven nylon with a mesh size of 0.25 mm, allowing access to soil microbes, microdetritivores and roots, but not macrodetritivores. However, prior work in the Serengeti found that termites eat through nylon litterbags to access plant litter creating holes~0.55 mm 2 in size (Smith et al 2019). To quantify the contributions of macrodetritivores to litter decomposition, we used a stainless steel metal mesh treatment with an aperture size of 0.3 mm designed to exclude the head-width of the smallest foraging termites (Smith et al 2019;Teo et al 2020).…”

“…However, this is not always the case in tropical ecosystems. Detritivores continue to remove plant litter in human managed landscapes, for example under regulated burning or livestock grazing (Davies et al 2013;Smith et al 2019). Quantifying the contribution of detritivores to plant litter decomposition remains a key knowledge gap in tropical ecosystems increasingly modified by humans.…”

“…We used a modified version of the Tea Bag Index (Keuskamp et al 2013), decomposing standardized labile green and recalcitrant rooibos tea litter in the wet and dry season. Meshed litterbags were used to determine the contribution of macrodetritivores >0.3 mm body width, targeting the exclusion of termites (Smith et al 2019;Teo et al 2020). Other standardized litter types, e.g.…”