The Contributions of Soil Fauna to the Accumulation of Humic Substances during Litter Humification in Cold Forests

Abstract

Litter humification is an essential process of soil carbon sequestration in forest ecosystems, but the relationship between soil fauna and humic substances has not been well understood. Therefore, a field litterbag experiment with manipulation of soil fauna was carried out in different soil frozen seasons over one year in cold forests. The foliar litter of four dominated tree species was selected as Birch (Betula albosinensis), Fir (Abies fargesii var. faxoniana), Willow (Salix paraplesia), and Cypress (Juniperus saltuaria). We studied the contribution of soil fauna to the accumulation of humic substances (including humic acid and fulvic acid) and humification degree as litter humification proceeding. The results showed that soil fauna with litter property and environmental factor jointly determined the accumulation of humic substances (humic acid and fulvic acid) and humification degree of four litters. After one year of incubation, the contribution rates of soil fauna to the accumulation of humic substances were 109.06%, 71.48%, 11.22%, and −44.43% for the litter of fir, cypress, birch, and willow, respectively. Compared with other stages, both growing season and leaf falling stage could be favorable to the contributions of soil fauna to the accumulation of humic substances in the litter of birch, fir, and cypress rather than in willow litter. In contrast, the contribution rates of soil fauna to humification degree were −49.20%, −7.63%, −13.27%, and 12.66% for the litter of fir, cypress, birch, and willow, respectively. Statistical analysis indicated that temperature changes at different sampling stages and litter quality exhibited dominant roles in the contributions of soil fauna on the accumulation of humus and litter humifiaction degree in the cold forests. Overall, the present results highlight that soil fauna could play vital roles in the process of litter humification and those strengths varied among species and seasons.

Fire-Derived Charcoal Attracts Microarthropods in the Litter of Boreal Deciduous Forest

“…However, previous research indicates the critical role of microarthropods in organic matter transformation, even without visible impact on mass loss [11,21,49]. For example, an experiment on decomposition in tallgrass prairies showed that a reduction in the number of microarthropods (collembola and acari) led to a decrease in the input of carbon from litter into the soil and a significant narrowing of the C/N ratio of organic matter derived from litter, which in the long term (based on a model) will slow down soil organic matter accumulation [11].…”

“…For example, an experiment on decomposition in tallgrass prairies showed that a reduction in the number of microarthropods (collembola and acari) led to a decrease in the input of carbon from litter into the soil and a significant narrowing of the C/N ratio of organic matter derived from litter, which in the long term (based on a model) will slow down soil organic matter accumulation [11]. Also, a field "litter-bag" experiment in cold alpine forests showed that soil fauna, dominated by collembola, contributes significantly to the accumulation of humic substances in the soil during litter decomposition (more in coniferous forests), promoting soil carbon sequestration [49]. Furthermore, the presence of collembola led to greater availability of C from litter for the soil microbial community and transport of compounds obtained from alder (chlorophyll and its breakdown product pheophytin) into the soil, indicating that collembola modifies soil organic matter at a molecular level [21].…”