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Knowledge about the elevational patterns of soil microbial biomass and communities can facilitate accurate prediction of the responses of soil biogeochemical processes to climate change. However, previous studies that have considered intra‐ and inter‐annual variations have reported inconsistent results on the one hand, and they have paid little attention to the effect of soil layer on the other hand. We, therefore, conducted a 4‐year in situ soil core incubation experiment along a 2431‐m elevational gradient across the dry valley shrubland, valley‐montane ecotone forest, subalpine coniferous forest, alpine coniferous forest, and alpine meadow in an ecologically fragile alpine‐gorge region on the eastern edge of the Qinghai‐Tibetan Plateau. Soil microbial biomass and community composition in the organic and mineral layers were measured using the phospholipid fatty acids (PLFA) method at five critical periods each year. Our results indicated that soil microbial biomass in the organic layer was the highest in the subalpine coniferous forest, followed by the alpine meadow, alpine coniferous forest, and valley‐montane ecotone forest. In contrast, soil microbial biomass in the mineral layer was significantly higher in the alpine meadow than in the other sites. Soil microbial biomass exhibited differential seasonal fluctuations at different elevations, resulting in their elevational patterns being strongly intra‐annual and inter‐annual dependent. Our results revealed that elevation and seasonality significantly affected soil microbial communities. Seasonality had a more substantial effect than elevation on soil microbial communities during the first 3 years of incubation, whereas the relative importance of seasonal and elevational effects on microbial communities was reversed in the organic layer with incubation time. These results are mainly attributed to the magnitude and direction of effect of environmental variables on soil microbial biomass and communities vary with elevation, soil layer, and sampling time. Briefly, the elevational patterns and dominant factors of soil microbial biomass and communities have intense soil layer and temporal specificity, implying that differential responses of soil biochemical processes to climate change might be observed at different elevations. [ABSTRACT FROM AUTHOR]

Previous studies showed that bark cover at early‐decay stage had profound control on the invertebrate assemblages of bark and wood, with possible consequence for the decomposition process. However, previous experimental designs could not disentangle how bark versus wood traits affect the invertebrate assemblage process in bark and/or wood separately because wood traits of different tree species may vary independently from bark traits. Furthermore, we do not know whether such tree species‐specific bark trait effects are still influential at mid‐decay stage.To unravel whether and how bark and wood traits influence invertebrate communities in tree logs at mid‐decay stage, we introduce reciprocal bark transplantation within pairs of different tree species as a new method. We applied this method to two pairs of phylogenetically contrasting species of gymnosperms (pair I: Araucaria araucana and Cryptomeria japonica, pair II: Picea abies and Thuja plicata) and another gymnosperm (Chamaecyparis lawsoniana) set as disturbance control to test for potential bark manipulation artefacts on invertebrate community composition.Our bark exchange experiment revealed that both bark and wood host abundant and divergent subsets of invertebrates on mid‐decay logs of different tree species. We further documented that the invertebrate community composition was predominantly shaped by the traits of host tissue per se, while also being significantly but less strongly affected by the traits of the other tissue, that is, the adjacent bark or wood. Our results indicated that bark trait effects faded with time and how long bark trait effects persist greatly depends on bark thickness.Synthesis. Our study suggests that maintaining deadwood heterogeneity related to variation between tree species and bark versus wood, is important for nursing a large biodiversity of invertebrates. Combined with bark removal methodology, our bark exchange method can be further extended to more decay stages and more forest biomes to track bark trait effects and bark induced priority effects on deadwood decomposition, and its associated invertebrate and microbial communities. [ABSTRACT FROM AUTHOR]

Epixylic vegetation may be important in dead wood decay by altering the microenvironment and, thereby, microbial communities in logs. However, the interaction between epixylic vegetation and dead wood microbial communities remains poorly known. Therefore, repeated experimental epixylic (bryophyte-dominated) vegetation removal (ERM) from logs of the fir Abies faxoniana across a wide range of decay classes (I–V) was conducted on the eastern Tibetan Plateau. The dynamics of the microbial community were separately measured in heartwood, sapwood and bark using the phospholipid fatty acid analysis (PLFA) method. Our results showed that the effects of ERM on the microbial community depended greatly on the three log components and sampling seasons but less on decay class. (1) The absence of epixylic vegetation generally enhanced the total microbial biomass and Sørensen similarity in bark, whereas it had a more complicated effect on those in heartwood and sapwood. Specifically, the response to ERM became progressively stronger from winter until the late growing season. (2) ERM increased the total percentage of Gram-negative bacteria and fungi in heartwood and upper side sapwood and decreased their percentages in bark. (3) The moisture content and pH of the logs were good predictors and likely drivers of the dynamic patterns of the microbial community composition. Our findings demonstrate strong and partly consistent interactions between epixylic vegetation and microbial communities. Further in-depth research should reveal how these interactions feed back to the decomposition process of logs and thereby to carbon and nutrient cycles in the alpine forest ecosystem. [ABSTRACT FROM AUTHOR]

Little information has been available on the shifts in the microbial community in decaying fallen logs during critical periods in cold forests. Minjiang fir (Abies faxoniana) fallen logs in decay classes I-V were in situ incubated on the forest floor of an alpine forest in the eastern Tibet Plateau. The microbial community was investigated during the seasonal snow cover period (SP), snow thawing period (TP), early growing season (EG) and late growing season (LG) using Phosphorous Lipid Fatty Acid (PLFA) analysis. Total microbial biomass and microbial diversity in fallen logs were much more affected by critical period than decay class, whereas decay class had a stronger effect on microbial diversity than on microbial biomass. Abundant microbial biomass and microbial diversity in logs even without the cover of snow were observed in winter, which could not be linked to thermal insulation by snow cover. The freshly decayed logs functioned as an excellent buffer of environmental variation for microbial organisms during the sharp fluctuations in temperature in winter. We also found distinct decay patterns along with seasonality for heartwood, sapwood and bark, which requires further detailed research. Gram- bacteria mainly dominated the shifts in microbial community composition from SP to EG, while fungi and Gram+ bacteria mainly dominated it from SP to TP. Based on previous work and the present study, we conclude that fallen logs on the forest floor alter ecological processes by influencing microbial communities on woody debris and beneath the soil and litter. Our study also emphasizes the need to maintain a number of fallen logs, especially fresh ones, on the forest floor. [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]

Dead trees are vital structural elements in forests playing key roles in the carbon and nutrient cycle. Stem traits and fungal community composition are both important drivers of stem decay, and thereby affect ecosystem functioning, but their relative importance for stem decomposition over time remains unclear.To address this issue, we used a common garden decomposition experiment in a Dutch larch forest hosting fresh logs from 13 common temperate tree species. In total, 25 fresh wood and bark traits were measured as indicators of wood accessibility for decomposers, nutritional quality and chemical or physical defence mechanisms. After 1 and 4 years of decay, we assessed the richness and composition of wood‐inhabiting fungi using amplicon sequencing and determined the proportional wood density loss.Average proportional wood density loss for the first year was 18.5%, with further decomposition occurring at a rate of 4.3% year−1 for the subsequent 3 years across tree species. Proportional wood density loss varied widely across tree species in the first year (8.7–24.8% year−1) and subsequent years (0–11.3% year−1). The variation was directly driven by initial wood traits during the first decay year, then later directly driven by bark traits and fungal community composition. Moreover, bark traits affected the composition of wood‐inhabiting fungi and thereby indirectly affected decomposition rates. Specifically, traits promoting resource acquisition of the living tree, such as wide conduits that increase accessibility and high nutrient concentration, increased initial wood decomposition rates. Fungal community composition, but not fungal richness explained differences in wood decomposition after 4 years of exposure in the field, where fungal communities dominated by brown‐rot and white‐rot Basidiomycetes were linked to higher wood decomposition rate.Synthesis: Understanding what drives deadwood decomposition through time is important to understand the dynamics of carbon stocks. Here, using a tailor‐made experimental design in a temperate forest setting, we have shown that stem trait variation is key to understanding the roles of these drivers; initially, wood traits explained decomposition rates while subsequently, bark traits and fungal decomposer composition drove decomposition rates. These findings inform forest management with a view to selecting tree species to promote carbon storage. [ABSTRACT FROM AUTHOR]

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]

Information about the seasonal changes in soil enzyme activity along altitudinal gradients is key for understanding the responses of soil biochemical processes to ongoing climate change. Therefore, a 3-year in situ soil core incubation experiment was conducted along a 2431-m altitudinal gradient in an alpine-gorge region on the eastern Qinghai-Tibet Plateau, which includes dry valley shrubland, valley-mountain ecotone forest, subalpine coniferous forest, alpine coniferous forest and alpine meadow. The invertase, urease, and acid phosphatase activities in the soil organic layer (OL) and mineral layer (ML) were measured at five critical periods from 2013 to 2017. Higher soil enzyme activity was observed in the subalpine coniferous forest and alpine meadow, whereas lower activity was observed in the dry valley shrubland and valley-mountain ecotone forest. Overall, the seasonal sensitivity of soil enzyme activity decreased with increases in altitude. In the subalpine and alpine coniferous forests, the seasonal sensitivity of soil enzyme activity was significantly higher in the ML than in the OL. The key drivers of the seasonal variation in soil enzyme activity exhibited marked variation with changes in altitude, and these variations depended on the enzyme type and soil layer. Significant effects of temperature and precipitation on seasonal fluctuations in enzyme activities were observed at lower altitudes, whereas soil freeze-thaw cycles significantly affected the seasonal changes in acid phosphatase activity at higher altitudes. In addition, the seasonal variations in specific enzyme activities differed from those found for enzyme activities, which indicated that microorganisms might have mediated the effects of environmental factors on soil enzyme activity by altering the enzyme production efficiency. Briefly, the seasonal fluctuations in soil enzyme activity and their dominant drivers varied greatly among different altitudes in the alpine-gorge region, implying that soil biochemical processes will exhibit differential responses to ongoing climate change at different altitudes. [ABSTRACT FROM AUTHOR]

The correct calculation equation and unit expression were exhibited as follows: HT ht Graph where mass loss (mg cm SP -3 sp ) is the cellulose or lignin mass losses in decaying logs after the decomposition of four years; I Concentration i SB 2013 sb and I Concentration i SB 2017 sb are the cellulose or lignin concentrations (%) of decaying logs in 2013 and 2017, respectively; I Density i SB 2013 sb and I Density i SB 2017 sb are the density (g cm SP -3 sp ) of decaying logs in 2013 and 2017, respectively; and 10 is the conversion coefficient of the unit. We mistakenly presented the calculation equation and unit expression of cellulose and lignin mass losses in decaying logs. [Extracted from the article]

• 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]