Abstract
Changes in litter and nutrient inputs into soil could have significant consequences on forest carbon (C) dynamics via controls on the structure and microbial utilization of soil organic C (SOC). In this study, we assessed changes in physical fractions (250–2000 μm, 53–250 μm, and < 53 μm soil aggregates) and chemical fractions (labile, intermediate and recalcitrant pools) of SOC in the top 20 cm mineral soil layer and their influences on microbial substrate utilization after eight years of experiment in a mixed pine-oak forest. The litter treatments included: control (Lcon), litter removal (Lnil), fine woody litter addition (Lwoody), leaf litter addition (Lleaf) and a mix of leaf and fine woody litter (Lmix). Nitrogen (N) addition (application rates of 0, 5 and 10 g N m−2 year−1, respectively) was also applied. We found that complete removal of forest-floor litter (Lnil) significantly reduced the pool sizes of all SOC fractions in both the physical and chemical fractions compared with treatments that retained either leaf litter (Lleaf) or mixture of leaves and fine woody materials (Lmix). The type of litter was more important in affecting SOC fractions than the quantity of inputs; neither the level of N addition rate nor its interaction with litter treatment had significant effects on both physical and chemical SOC fractions. Microbial respiration differed significantly among the treatments of varying litter types. However, the effectiveness of microbial C utilization inferred by microbial C use efficiency and biomass-specific respiration was not affected by either the litter treatments or N addition. These results suggest that despite significant changes in SOC composition due to long-term treatments of forest-floor litter and N addition in this mixed pine-oak forest of temperate climate, microbial C utilization strategies remain unaffected.
Highlights
The amount of carbon (C) stored in soil worldwide far exceeds the amount of carbon stored in plants and the atmosphere combined (Scharlemann et al 2014), and it is very sensitive to global change factors, such as CO2 fertilization effect-enhanced plant growth and nitrogen (N) deposition-induced changes in soil nutrient availability (Thornton et al 2007)
Plant litter play a vital role in determining soil organic C (SOC) storage and cycling in forest ecosystems, as some of them are translocated to mineral soil as particulate or dissolved organic matter, and transformed to various physical components and chemical fractions (Schmidt et al 2011; Cotrufo et al 2013)
An apparent phenomenon was that both total SOC (TOC) and DOC under Lnil and Lwoody
Summary
The amount of carbon (C) stored in soil worldwide far exceeds the amount of carbon stored in plants and the atmosphere combined (Scharlemann et al 2014), and it is very sensitive to global change factors, such as CO2 fertilization effect-enhanced plant growth and nitrogen (N) deposition-induced changes in soil nutrient availability (Thornton et al 2007). The effects of litter on SOC dynamics are inconsistent, depending on litter quantity and quality and soil conditions (von Haden et al 2019). Fresh litter inputs may cause soil priming (Kuzyakov et al 2000), such that soil C replenishment by new litter input may be offset by the primed decomposition of native soil C (Sayer et al 2011; Cotrufo et al 2013; Lajtha et al 2018). It remains an open question if the litter inputs of differential quality and quantity would affect the stability of soil carbon storage through modification of the SOC composition. Elucidation of the associations of litter inputs with various physical and chemical SOC fractions will help gain better insight in the regulation of SOC dynamics by litter production and variations
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