Long-term litter type treatments alter soil carbon composition but not microbial carbon utilization in a mixed pine-oak forest

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.

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

“…First, the formation of new SOM is offset by the accelerated decomposition of older SOM via priming effects (5.3%, Figure S8; Chen & Chen, 2018; Lajtha et al, 2018). Second, litter addition could enhance microbial turnover and decrease microbial C use efficiency via increasing soil C:N ratio and microbial N limitation (relative to C), consequently leading to more microbial respiration (Figure 2a) and slower SOC formation and accumulation (Guo et al, 2021; Sinsabaugh et al, 2016). Third, soils in some forests likely have a finite capacity to sequester additional SOC (particularly mineral‐associated fraction) and might be saturated (Lajtha, Townsend, et al, 2014; Mayzelle et al, 2014; Sayer et al, 2019).…”

“…Given that POC is mainly made up of newly inputted and relatively‐undecomposed plant residues, it tends to have the fastest turnover rate and is more vulnerable to loss (Cusack et al, 2011; Lavallee et al, 2020). Therefore, the addition or removal of litter and/or roots can directly affect the accumulation of POC in both short and long term (Guo et al, 2021; Pierson et al, 2021). This was confirmed by our results that POC increased after addition of litter and declined after removal of litter or both litter and roots (Figure 4).…”

“…This Lajtha et al, 2018). Second, litter addition could enhance microbial turnover and decrease microbial C use efficiency via increasing soil C:N ratio and microbial N limitation (relative to C), consequently leading to more microbial respiration (Figure 2a) and slower SOC formation and accumulation (Guo et al, 2021;Sinsabaugh et al, 2016).…”

Effects of Mixed Decomposition of Pinus sylvestris var. mongolica and Morus alba Litter on Microbial Diversity

“…The interactions of mixed decomposition of litters from different tree species during decomposition have become an important indicator to measure interspecific relationships [28], which will directly affect litter decomposition, nutrient release, soil nutrient balance, and enzyme activity [29], which thus affect the nutrient cycles of mixed forest ecosystems [30]. A large number of studies have proven that the mixed decomposition of litter and leaves exhibits complex nonadditive effects [31,32] and that mixed decomposition of different tree species results in different decompositions and releases of different nutrient components [33]. The litter of coniferous species and broad-leaved tree species have different decomposition rates due to the differences in their substrates.…”