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 (RamÃrez 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.