Abstract
Global changes and human disturbances can strongly affect the quantity of aboveground litter entering soils, which could result in substantial cascading effects on soil biogeochemical processes in forests. Despite extensive reports, it is unclear how the variations in litter depth affect soil carbon and nitrogen cycling. The responses of soil carbon and nitrogen to the variability of litter inputs were examined in a coniferous–broadleaf mixed forest of Central China. The litter input manipulation included five treatments: no litter input, natural litter, double litter, triple litter, and quadruple litter. Multifold litter additions decreased soil temperature but did not affect soil moisture after 2.5 years. Reductions in soil pH under litter additions were larger than increases under no litter input. Litter quantity did not affect soil total organic carbon, whereas litter addition stimulated soil dissolved organic carbon more strongly than no litter input suppressed it. The triggering priming effect of litter manipulation on soil respiration requires a substantial litter quantity, and the impacts of a slight litter change on soil respiration are negligible. Litter quantity did not impact soil total nitrogen, and only strong litter fluctuations changed the content of soil available nitrogen (nitrate nitrogen and ammonium nitrogen). Litter addition enhanced soil microbial biomass carbon and nitrogen more strongly than no litter input. Our results imply that the impacts of multifold litter inputs on soil carbon and nitrogen are different with a single litter treatment. These findings suggest that variability in aboveground litter inputs resulting from environmental change and human disturbances have great potential to change soil carbon and nitrogen in forest ecosystems. The variability of aboveground litter inputs needs to be taken into account to predict the responses of terrestrial soil carbon and nitrogen cycling to environmental changes and forest management.
Highlights
Aboveground litter plays a critical role in regulating soil carbon and nitrogen cycling between plants and soils in forest ecosystems, and the litter layer mediates the soil microclimate by buffering the soil surface and atmosphere [1]
There was a greater decrease in soil temperature under triple litter (TL) and quadruple litter (QL) compared to L, but no differences in soil temperature between other litter treatments were detected
These findings are consistent with reports of a low-strength litter manipulation experiment in central South China [33], but a meta-analysis detected that litter addition decreased soil temperature, whereas litter removal increased it [18]
Summary
Aboveground litter plays a critical role in regulating soil carbon and nitrogen cycling between plants and soils in forest ecosystems, and the litter layer mediates the soil microclimate by buffering the soil surface and atmosphere [1]. Terrestrial ecosystems are undergoing changes from human disturbances that coincide with environmental changes [2]. Those alterations may strongly affect forest net primary productivity and change the aboveground litter inputs to soils. Forests 2019, 10, 188 such as an elevated atmospheric CO2 concentration [3], climate warming [4], atmospheric nitrogen deposition [5], and increased precipitation [6], were found to increase plant productivity. Changes in plant productivity will shift the amounts of aboveground litter moving into soils, which subsequently affects biogeochemical processes by changing soil carbon and nitrogen inputs, soil biotic activity, and the soil microenvironment [1]. Future extreme events (i.e., wildfire, hurricane, sandstorm) can result in sudden and dramatic changes in litter inputs [11,12]
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