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Knowledge of the patterns in the degradation of cellulose and lignin in decaying logs under different climatic conditions is necessary to understand the carbon cycling in forest ecosystems since cellulose and lignin are the dominant carbon fractions in decaying logs. However, the effects of the environmental heterogeneity by variation in canopy cover on the degradation of cellulose and lignin in decaying logs remain unknown. To evaluate the effect of forest gaps, we measured the concentration and mass loss of cellulose and lignin in experimentally exposed decaying logs in gaps, at the edge of gaps, and under the closed canopy during a four-year in situ log incubation experiment in a subalpine Minjiang fir (Abies faxoniana) forest on the eastern Qinghai-Tibet Plateau, China. We found the lowest cellulose concentration in gaps for all wood tissues, while we observed the opposite for lignin except for bark. Based on the linear relationship between cellulose and lignin concentrations, the rate of lignin enrichment in bark and heartwood was slowest in gaps and fastest under closed canopy, while in sapwood gaps had almost no influence. The mass loss of cellulose was highest in gaps for all wood tissues in any decay classes. The gap effect on lignin mass loss in decaying logs showed high variability with wood tissues and decay classes. Our results show that forest gaps accelerate the degradation of cellulose and lignin during the decomposition of logs by increasing cellulose mass loss and slowing lignin enrichment. The observed gap effects were mediated by wood tissues but not by decay classes. [ABSTRACT FROM AUTHOR]

Soil fungi are crucial drivers of log decomposition in forest ecosystems, but how soil fungal community composition varies during the process of log decomposition remains poorly understood. We conducted an experiment incubating decaying logs in a subalpine coniferous forest on the eastern Qinghai‐Tibet Plateau, China. Five classes of decaying Minjiang fir (Abies faxoniana) logs were incubated on the forest floor, and the composition and diversity of fungal communities in soils underneath decaying logs were measured using high‐throughput sequencing. A total of 4321 operational taxonomic units (OTUs) were detected by Illumina NovaSeq sequencing analysis. Soil fungal diversity differed significantly during the process of log decomposition and was highest in decay classes III or IV. Basidiomycota and Ascomycota were dominant phyla regardless of log decay classes. Moreover, the proportion of arbuscular mycorrhiza, wood saprotroph and saprotrophs increased during the process of log decomposition, but that of ectomycorrhiza decreased. The structure of soil fungal community underneath decaying logs varied greatly with decay classes. Different decay classes of logs favour special fungal groups, implying that the ecological effects of logs at differing decay classes on soil fungal communities were different. Highlights: Effects of logs at differing decay classes on soil fungal community were different.Soil fungal diversity was highest in decay classes III or IV.Basidiomycota and Ascomycota were dominant phyla regardless of decay classes.Soil fungi groups on guilds and relative abundance of genera differed by decay classes. [ABSTRACT FROM AUTHOR]

To reveal the changes in the interactions between invertebrates and microbes in decomposing litter with seasonal rainfall, litterbags containing camphor (Cinnamomum longepaniculatum) and Masson pine (Pinus massoniana) litter were therefore in situ incubated on the floor of Masson pine-camphor mixed plantations in the subtropical region of China. Different mesh sizes of litterbags were used to control the access of the invertebrates. The invertebrates in litterbags were collected by funnel method, and microbial communities were detected by phospholipid fatty acid (PLFA) method in slightly rainy season (SRS; November 1–December 24), micro rainy season (MRS; December 25–March 7), early rainy season (ERS; March 8–June 15) and rainy season (RS; June 16–October 31) during two decomposition years. The abundance and composition of microbial and invertebrate communities varied significantly with seasonal rainfall and tree species. Invertebrate exclusion generally decreased the bacterial and fungal biomass, and the biomass of Gram-positive bacteria and Gram-negative bacteria in Masson pine needle litter, but generally increased these indices in camphor foliar litter. Invertebrate exclusion decreased the mass loss rate of Masson pine litter, but increased the mass loss rate of camphor litter. Total microbial biomass and bacterial biomass in both foliar litters were generally higher in SRS and MRS than these in ERS and RS during the first decomposition year, whereas the situation reversed during the second decomposition year. The abundance of invertebrates increased gradually from the first SRS to the second SRS and decreased gradually afterwards. Briefly, the interactions between invertebrate and microbial communities varied greatly with litter types and seasons. Positive and negative interactions between invertebrate and microbes were respectively observed in Masson pine and camphor litters, and differential responses of microbial biomass and mass loss rate to invertebrate exclusion were found in two litter types. In turn, the interactions between invertebrates and microbes run the litter decomposition. • Interactions between invertebrates and microbes varied with litter types and seasons. • Positive and negative interactions were respectively observed in Masson pine and camphor litter. • Differential responses of microbial biomass and mass loss to invertebrate exclusion were observed in two litters. • The interactions between invertebrates and microbes run the litter decomposition. [ABSTRACT FROM AUTHOR]

• Carbon sequestration of decaying logs via humification is determined by wood trait. • Wood trait has a stronger effect on the humification of heartwood and sapwood than on bark. • The humified carbon in sapwood is in favour of organic carbon accumulation in nutrient-poor soil. Deadwood is an indispensable component of forest ecosystems, with important consequences for global carbon cycling. Although research into carbon release from decaying logs and its response to wood traits has increased, little attention has been paid to how wood traits affect the potential of carbon sequestration in decaying logs through humification. To evaluate the wood trait effects, we measured the concentrations (mg g−1) and content (mg cm−3) of humus, including humic substrates, humic acid, and fulvic acid, and the degree of humification (%) separately in bark, sapwood, and heartwood in a four-year log decomposition experiment in a subalpine Minjiang fir forest on the eastern Qinghai-Tibet Plateau, China. We found the highest humus concentrations and humification degree in bark and the lowest in sapwood. The humus mass had a net loss in bark and did not change in sapwood over time. As decomposition proceeded, the humus mass in heartwood firstly accumulated and then decreased. In addition, wood traits strongly affected the humification of sapwood and heartwood compared to bark. Lignin and its interactions with cellulose and N concentrations were associated with sapwood humification. Nutrient conditions like N and P concentrations and the C/N ratio were related to heartwood humification. These findings suggest that wood traits can determine the potential of carbon sequestration of decaying logs through humification and that the large proportion of sapwood in decaying logs has a positive effect on long-term and stable carbon sequestration in poor soils in subalpine forests. [ABSTRACT FROM AUTHOR]