Background and aimsSoil microbes play crucial roles in regulating soil nutrient cycling and shaping plant community structure in forest ecosystems. Compared with our understanding of plant community succession and soil nutrient changes, the succession of soil microbial communities and functional guilds after deforestation remains unclear.MethodsWe used 16S rRNA gene and internal transcribed spacer amplicon sequencing to investigate the microbial diversity and community composition in surface (0-10 cm) and subsurface (10-20 cm) mineral soils along a secondary succession after logging in Korean pine forests. Topological structures of microbial co-occurrence networks were also assessed.ResultsFungal diversity, community composition, and network structure, rather than bacterial, significantly changed with successional stages. Specifically, the diversity of ectomycorrhizal fungi (EcMF) in subsurface and whole soil layers, and saprotroph diversity in the subsurface, increased monotonically with increasing time since logging, while the relative abundances of plant pathogenic fungi decreased significantly with successional stages in surface and whole soil layers. Fungal network complexity (i.e., average degree) increased monotonically with increasing time since logging. Successional stages were the strongest driver of fungal community composition. In the subsurface layer, successional stages affected fungal diversity strongly and positively by increasing fungal network complexity.ConclusionsThis study revealed distinct successional trajectories for soil fungal and bacterial communities following forest logging. Compared with bacteria, fungi and their functional guilds (i.e., EcMF, saprotrophs, and plant pathogens) exhibited stronger responses to successional stages, indicating a more important role for facilitating the restoration of broad-leaved Korean pine forests after disturbance.

The potential improvement of biological nitrogen fixation (BNF) in legumes and edaphic factors affecting BNF remain unclear following biochar application to Ultisols. In this study, the effects of biochars derived from different feedstocks on BNF in soybean and soil properties were examined in an Ultisol. Straw biochar and manure biochar were applied at different rates (0, 24, and 48 t ha(-1)). The percentage of soybean N derived from BNF was determined by the N-15 isotope dilution method. Manure biochar and straw biochar increased BNF by 130% and 79% over the control when pooled across two application rates, respectively. However, biochar's improvement in BNF showed a decreasing trend with the application rates. Only manure biochar application at 48 t ha(-1) significantly stimulated N uptake in soybean from soil by 89% over the control. Manure biochar increased soil pH, total nitrogen, and soil available nutrients (P, K, Ca, Mg, Cu, Zn, and Mo) and reduced soil available Al to a greater extent than straw biochar. Soil pH, total nitrogen, and available nutrients (P, K, Ca, Mg, Cu, and Mo) could explain 34.5%-54.6% of the BNF variations. Among these edaphic factors, the improvement in soil available Mo induced by biochar was the most crucial to promoting BNF based on the random forest model analysis. In conclusion, biochar prompted BNF in soybean in the Ultisol, which could be attributed to the increase in soil available nutrients and the liming effect of biochar.

The role of biophysical variables in constructing community structure changes with the time since fire. The major objective of this study is to verify the transition stage and its underlying variables for the postfire forest and soil microbial function in the boreal forested area of China. A 50-year fire chronosequence was presented, and biomass of forbs, shrubs and woody plants was separately weighted to assess their contribution to the whole community with the year since fire (YSF). Simultaneously, soil biophysical properties were measured for stands in different time periods after fire. Soil microbial functions, i.e. growth efficiency (GE) and carbon use efficiency (CUE), were calculated based on ecoenzymatic and soil nutrient stoichiometry. In terms of vegetative structure, forbs' proportion decreased from 75% to 1.5%, but the proportion of woody plants increased from 0.04% to 70% across this fire chronosequence. GE and CUE of soil microorganisms averaged 0.242 and 0.236 and were significantly higher in 9, 15 and 31 YSF than in 2 and 3 YSF. Soil metal content was significantly increased at the late stage of this fire chronosequence, and soil calcium content showed a positive correlation with woody plant biomass and a negative correlation with soil microbial function. Overall, the present work highlights that the time period of 15 and 31 YSF is a hallmark stage for aboveground vegetative structure and soil microbial function to change in different trends and that the calcium content may partly account for these two divergent trajectories.

Aim There have been numerous studies of forest-soil microbial biogeography, but an integrated view of edaphic factors, plant, climatic factors, and geographic distance in determining the variation of bacterial community and assembly processes remains unclear at large spatial scales. Here, we analysed the factors affecting the biogeographic pattern and assembly processes of soil bacterial communities under 58 tree species in five natural mountain forests. Location Eastern China. Major taxa studied Bacterial communities. Methods Hierarchical partitioning analysis and distance decay models were performed to evaluate the relative contributions of plant phylogeny, environmental, and spatial variables to the composition of bacterial communities. We applied the nearest taxon index (NTI), beta-nearest taxon index (beta NTI), and the modified Raup-Crick metric to reveal the mechanisms of bacterial assembly processes. Results We found that plant phylogeny accounted for a significant, but minor, fraction (0.7%) of the variation in composition of bacterial communities. In contrast, soil pH was the primary determinant of bacterial diversity and community composition, independently explaining 68.6 and 69.9% of the variation, respectively. Based on the NTI analysis, bacterial community assembly was more phylogenetically clustered with increasing soil pH. Variable selection was the predominant process explaining bacterial community assembly when differences in soil pH were >= 0.83, whereas homogenizing dispersal dominated when differences in soil pH were <0.83. However, there was no significant relationship between plant phylogenetic distance and beta NTI. Main conclusions Our findings provide strong evidence that soil pH predominantly determines bacterial distribution and mediates the relative impact of stochasticity and determinism in soil bacterial community assembly. This suggests that climate-change associated forest soil acidification could have a dramatic impact on soil bacterial diversity, composition, and function.

Understanding the effects of thinning on forest productivity under climate change is vital to adaptive forest management. In the present study, the 3-PG m i x model was applied to simulate the thinning effects on productivity of Lartx olgensis plantations under climate change using 164 sample plots collected from the 6th, 7th and 8th National Forest Inventories in Jilin Province, northeast China. Climate scenarios of RCP 4.5 and RCP 8.5 were adopted from 2011 to 2100 with corresponding reference years (1981-2010). We simulated four cutting intensities: no-thinning, NT; low intensity thinning with 10% stem removal, LT; moderate thinning with 20% stem removal, MT and heavy thinning with 30% stem removal, HT for three times with 5- and 10-year thinning intervals. The results indicated that the mean net primary productivity (NPP) during the simulated 90 years was increased under RCP 4.5 and RCP 8.5. The LT and MT had positive but HT had negative effects on the mean NPP for the same climate scenario. Increased thinning intensity facilitated the positive effects of climate change on NPP but without a significant interaction effect. During the simulation, LT had the highest NPP value and HT had the biggest NPP increase under future climate change. We also discussed the management of larch plantations under climate change and advocated low intensity thinning with 10-year thinning interval to gain maximum NPP for mitigating climate change.

Soil fungi represent a major component of below-ground biodiversity that determines the succession and recovery of forests after disturbance. However, their successional trajectories and driving mechanisms following wildfire remain unclear.We examined fungal biomass, richness, composition and enzymes across three soil horizons (Oe, A1 and A2) along a near-complete fire chronosequence (1, 2, 8, 14, 30, 49 and c. 260 yr) in cold-temperate forests of the Great Khingan Mountains, China. The importance of soil properties, spatial distance and tree composition were also tested.Ectomycorrhizal fungal richness and beta-glucosidase activity were strongly reduced by burning and significantly increased with 'time since fire' in the Oe horizon but not in the mineral horizons. Time since fire and soil C : N ratio were the primary drivers of fungal composition in the Oe and A1/A2 horizons, respectively. Ectomycorrhizal fungal composition was remarkably sensitive to fire history in the Oe horizon, while saprotroph community was strongly affected by time since fire in the deeper soil horizon and this effect emerged 18 years after fire in the A2 horizon.Our study demonstrates pronounced horizon-dependent successional trajectories following wildfire and indicates interactive effects of time since fire, soil stoichiometry and spatial distance in the reassembly of below-ground fungal communities in a cold and fire-prone region.

Litter is essential to promote nutrient cycling and maintain the sustainability of forest resources. However, its variability has not been sufficiently studied at the local scale. The prediction of litter amount using ordinary cokriging with Pearson correlation analysis (COKP) and ordinary cokriging with principal component analysis (COKPCA) was compared with that using ordinary kriging (OK) based on cross-validation at the local scale of a 1-ha plot over natural spruce-fir mixed forest in Jilin Province, China. Litter samples in semidecomposed (F) and complete decomposed (H) horizons were collected using an equidistant grid point sampling of 10 m x 10 m. Pearson correlation analysis and principal component analysis (PCA) were used to confirm auxiliary variables. The results showed that the amount of litter was 19.65 t/ha in the F horizon and 10.37 t/ha in the H horizon. The spatial structure variance ratio in the H horizon was smaller than that in the F horizon, indicative of its stronger spatial autocorrelation. Spatial distributions of litter amount in both horizons exhibited a patchy and heterogeneous pattern. Of the selected stand characteristics and litter properties, litter moisture content indicated the strongest relationship with litter amount. Cross-validation revealed that COKPCA using the comprehensive score as an auxiliary variable produced the most accurate map. The average standard error and root-mean-square error between the predicted and measured values were always smaller, the mean error and mean standardized error were much closer to 0, and the root-mean-square standardized error was closer to 1 than COKP using litter moisture and OK. Therefore, a clear advantage of cokriging based on principal component analysis was observed and COKPCA was found to be a very useful approach for further interpolation prediction.

Soil organic carbon (SOC) mineralization is closely related to carbon source or sink of terrestrial ecosystem. Natural stands of Larix olgensis on the Jincang forest farm, Jilin Province were selected to investigate the dynamics of SOC mineralization and its correlations with other soil properties in a young forest and mid-aged forest at soil depths of 0-10, >10-20, >20-40 and >40-60cm. The results showed that compared with a mid-aged forest, the SOC stock in the young forest was 32% higher. Potentially mineralizable soil carbon (C-0) in the young forest was 1.1-2.5gkg(-1), accounting for 5.5-8.1% of total SOC during the 105days incubation period and 0.3-1.5gkg(-1) in the mid-aged forest at different soil depths, occupying 2.8-3.4% of total SOC. There was a significant difference in C-0 among the soil depths. The dynamics of the SOC mineralization was a good fit to a three-pool (labile, intermediate and stable) carbon decomposition kinetic model. The SOC decomposition rate for different stand ages and different soil depths reached high levels for the first 15days. Correlation analysis revealed that the C-0 was significantly positively related with SOC content, soil total N (TN) and readily available K (AK) concentration. The labile soil carbon pool was significantly related to SOC and TN concentration, and significantly negatively correlated with soil bulk density. The intermediate carbon pool was positively associated with TN and AK. The stable carbon pool had negative correlations with SOC, TN and AK.

Litter, as the basic carrier of nutrients, is a link between plants and soil in nutrient cycling and plays a major role in maintaining soil fertility and promoting material cycling and nutrient balance in forest ecosystems. The present study used geostatistics to investigate the spatial heterogeneity of organic carbon (OC) and total nitrogen (TN) in litter and their influencing factors, over four representative 1-ha natural spruce-fir mixed stands in Jilin Province, China. Our results showed that forest litter OC and TN varied in the four stands with an average OC concentration ranging from 378 to 453 g.kg(-1) and average TN concentration ranging from 16.4 to 21.8 g.kg(-1). The nugget-to-sill values were < 25%, revealing that litter OC and TN had a strong spatial autocorrelation. Spatial distributions were estimated using ordinary kriging and showed a distinct strip and patch as the gradient changed. The fractal dimension of litter OC concentration was higher than that of litter TN. This indicated that litter OC had a more complex spatial pattern, whereas litter TN exhibited a better structure and stronger spatial dependence. Stand characteristics (i.e., species number, stem number, biodiversity indices, proportion of conifer species and stems), together with litter properties (i.e., litterfall, litter moisture content and total phosphorous concentration), affected the spatial variation in litter TN concentration, but they had no significant effects on litter OC. Therefore, this study demonstrated the feasibility of using geostatistics to predict litter nutrient concentrations at small scales and provided a theoretical basis for large-scale monitoring of biogeochemical cycles and disturbances in forest ecosystems.