4.1 Influence of recovery period on SOC stability of larch plantations
This study shows that the recovery time of larch trees affects the microorganisms in the soil, and soil properties and microbial communities change with increasing stand age, with bacteria and fungi responding differently to increase in age with the stand. There is a very strong link between soil microbial communities and soil properties in plantations. The DOM quality of the soil, especially the source of DOM and the level of humification, strongly influenced the structural and functional diversity of bacteria and fungi.
Changes in soil microbial diversity ware controlled by the quality of soil carbon in silvicultural ecosystems, and resource use by soil microorganisms was largely dependent on the availability of organic matter, and previous studies had shown a strong relationship between soil carbon content and microbial community diversity (Shen et al., 2019).
The variation in soil microbial community diversity among different pine stand ages varied between soil depths, which may be due to differences in the quantity and quality of soil organic matter. Overall, the HIX index decreased with the increase of soil depth, which indicated that the increase of forest age DOM was more humified in the surface soil and the accumulated humus was gradually transformed by microbial decomposition with soil depth. In contrast, a large amount of newly generated organic matter was buried in the deep soil environment of the 10 years forest due to the influence of anthropogenic activities and the input of organic fertilizers and crop straw (Kramer and Gleixner, 2008). Along with this perennial plant residue lingering on the soil surface, which may increase anaerobic microsites and affect soil moisture and temperature and thus the decomposition of plant residues (Ramírez et al., 2020a), making a higher proportion of lignin and aromatic compounds in the surface soil, when the SOC is more difficult to be decomposed (Li et al., 2021). As restoration time and soil depth increased, humification in the soil would decrease, carbon from plants will increase, and organic matter in the soil will be more difficult to decompose.