Altered litter inputs modify carbon and nitrogen storage in soil organic matter in a lowland tropical forest

Abstract

Soil organic matter (SOM) in tropical forests is an important store of carbon (C) and nutrients. Although SOM storage could be affected by global changes via altered plant productivity, we know relatively little about SOM stabilisation and turnover in tropical forests compared to temperate systems. Here, we investigated changes in soil C and N within particle size fractions representing particulate organic matter (POM) and mineral-associated organic matter (MAOM) after 13 years of experimental litter removal (L−) and litter addition (L+) treatments in a lowland tropical forest. We hypothesized that reduced nitrogen (N) availability in L− plots would result in N-mining of MAOM, whereas long-term litter addition would increase POM, without altering the C:N ratio of SOM fractions. Overall, SOM-N declined more than SOM-C with litter removal, providing evidence of N-mining in the L− plots, which increased the soil C:N ratio. However, contrary to expectations, the C:N ratio increased most in the largest POM fraction, whereas the C:N ratio of MAOM remained unchanged. We did not observe the expected increases in POM with litter addition, which we attribute to rapid turnover of unprotected SOM. Measurements of ion exchange rates to assess changes in N availability and soil chemistry revealed that litter removal increased the mobility of ammonium-N and aluminium, whereas litter addition increased the mobility of nitrate-N and iron, which could indicate SOM priming in both treatments. Our study suggests that altered litter inputs affect multiple processes contributing to SOM storage and we propose potential mechanisms to inform future work.

Different responses of soil respiration to environmental factors across forest stages in a Southeast Asian forest

“…Thus, the organic matter content in the soil was the main energy source for microbial activity that determined soil CO 2 efflux in the dry period of these forests. As previously mentioned, this period corresponded to high litter addition to the forest floor, which may stimulate soil microbial activity as shown in greater soil CO 2 release (Bréchet et al, 2017;Sayer et al, 2019Sayer et al, , 2020. Large variations in OM were observed across forest stages, which may be explained by different quantity and quality of litter input (i.e., litterfall and roots) and different rates of litter decomposition in each stage.…”

Soil carbon storage is related to tree functional composition in naturally regenerating tropical forests

“…We demonstrate that soil C stocks were highest in stands with a greater relative influence of light-demanding ACC tree species (Figure 5), of which many have 'high-quality' litter (Bakker et al, 2011; Figure 3), representing a substantial source of labile C compounds and nutrients for soil microbes. This major role of leaf litter decomposition in tropical forest soil carbon storage (Sayer et al, 2021) would also explain why we only observed a significant relationship between soil C stocks and tree functional composition at the soil surface (0-10 cm; Figure 5a). Thus, our results suggest that high-quality plant inputs may play a key role in soil C accumulation during secondary succession in these forests.…”

Changes in plant inputs alter soil carbon and microbial communities in forest ecosystems

“…DOC and microbial biomass account for only a small proportion (often <2%) of SOC pool (Guo et al, 2020; Xu, Thornton, et al, 2013), whereas MAOC is a dominant portion (often >50%) of SOC pool and cannot be easily used by soil microbes because of physical and chemical protection (Cotrufo et al, 2019; Lavallee et al, 2020). Therefore, the increased or decreased DOC and microbial biomass and its newly‐formed necromass C under altered plant inputs will not have a significant effect on MAOC in the short term (Wu et al, 2018), and it may take a long time to observe the considerable detritus‐treatment effects on MAOC (Lajtha, Townsend, et al, 2014; Sayer et al, 2021).…”