Effects of root dominate over aboveground litter on soil microbial biomass in global forest ecosystems

Background:Inputs of above-and belowground litter into forest soils are changing at an unprecedented rate due to continuing human disturbances and climate change.Microorganisms drive the soil carbon(C)cycle,but the roles of above-and belowground litter in regulating the soil microbial community have not been evaluated at a global scale.Methods:Here,we conducted a meta-analysis based on 68 aboveground litter removal and root exclusion studies across forest ecosystems to quantify the roles of above-and belowground litter on soil microbial community and compare their relative importance.Results:Aboveground litter removal significantly declined soil microbial biomass by 4.9%but root exclusion inhibited it stronger,up to 11.7%.Moreover,the aboveground litter removal significantly raised fungi by 10.1%without altering bacteria,leading to a 46.7%increase in the fungi-to-bacteria(F/B)ratio.Differently,root exclusion significantly decreased the fungi by 26.2%but increased the bacteria by 5.7%,causing a 13.3%decrease in the F/B ratio.Specifically,root exclusion significantly inhibited arbuscular mycorrhizal fungi,ectomycorrhizal fungi,and actinomycetes by 22.9%,43.8%,and 7.9%,respectively.The negative effects of aboveground litter removal on microbial biomass increased with mean annual temperature and precipitation,whereas that of root exclusion on microbial biomass did not change with climatic factors but amplified with treatment duration.More importantly,greater effects of root exclusion on microbial biomass than aboveground litter removal were consistent across diverse forest biomes(expect boreal forests)and durations.Conclusions:These data provide a global evidence that root litter inputs exert a larger control on microbial biomass than aboveground litter inputs in forest ecosystems.Our study also highlights that changes in above-and belowground litter inputs could alter soil C stability differently by shifting the microbial community structure in the opposite direction.These findings are useful for predicting microbe-mediated C processes in response to changes in forest management or climate.

Photosynthate supply drives soil respiration of Fraxinus mandshurica seedlings in northeastern China： evidences from a shading and nitrogen addition experiment

Improved understanding of the link between photosynthesis and below-ground processes is needed to better understand ecosystem carbon （C） cycling and its feedback to climate change. We conducted a short-term shading and nitrogen （N） addition experiment from June to September 2013 to investigate the effect of photosynthate supply by Manchurian Ash （Fraxinus mandshurica） seed- lings on soil respiration （SR）. Shading significantly reduced SR in early and middle growing season, but not in late growing season, leading to a decrease in mean SR by 24 % in N-unfertilized treatments. N addition increased mean SR by 42 % in un-shaded treatment. The stimulation of SR was largely attributed to accelerated autotrophic respiration by increasing photosynthesis, leaf area index and belowground biomass. Shading reduced mean SR by 32 % in N addition treatment. The strengthened shading effect on SR resulted from N addition was because of more photosynthates supply at low soil temperature. Our findings highlight the predominance of photosynthates supply in regulating the responses of C cycling to global change.

Different Decaying Wood Effects on Bacterial Diversity:Insights from Molecular Methods

Decaying wood is a novel key factor required for biodiversity and function of a forest,as it provides a good account of substrate and habitats for various organisms.Herein,the bacterial diversity in decaying wood of Betula platyphylla was discussed through high throughput sequencing.Our results showed that most of the obtained sequences belonged to the phyla Firmicutes,Proteobacteria,Bacteroidetes,Actinobacteria,Acidobacteria and Verrucomicrobia.Bacterial community compositions in samples with higher moisture content were obviously different than that with lower content,which could be reflected by richness estimators,diversity indices,and cluster and heatmap analysis.All three networks were non-random and possessed topological features of complex systems such as small-world and modularity features.However,these networks exhibited distinct topological features,indicating the potential ability of extensive cooperative and competitive interactions in the decayed wood microenvironments.Redundant analysis showed that most bacterial phyla were mainly distributed in highermoisture trunks.The obtained data will increase the knowledge of the complex bacterial diversity associated with dead wood,and lay a foundation for the bioconversion technology of plant cell walls using bacteria.

Influence of tree species on soil microbial residue accumulation and distribution among soil aggregates in subtropical plantations of China

Background Microbial residues are significant contributors to stable soil organic carbon(SOC).Soil aggregates effectively protect microbial residues against decomposition;thus,microbial residue accumulation and distribution among soil aggregates determine long-term SOC stability.However,how tree species influence accumulation and distribution of soil microbial residues remains largely unknown,hindering the chances to develop policies for SOC management.Here,we investigated microbial residue accumulation and distribution in soil aggregates under four subtropical tree species(Cunninghamia lanceolata,Pinus massoniana,Michelia macclurei,and Schima superba)after 29 years of afforestation.Results Accumulation of microbial residues in the 0-10 cm soil layer was 13.8-26.7%higher under S.superba than that under the other tree species.A structural equation model revealed that tree species affected the accumulation of microbial residues directly by altering fungal biomass.Additionally,tree species significantly affected microbial residue distribution and contribution to SOC in the top 20 cm soil.In particular,microbial residue distribution was 17.2-33.4%lower in large macro-aggregates(LMA)but 60.1-140.7%higher in micro-aggregates(MA)under S.superba than that under the other species in the 0-10 cm soil layer,and 14.3-19.0%lower in LMA but 43-52.1%higher in MA under S.superba than that under C.lanceolata and M.macclurei in the 10-20 cm soil layer.Moreover,the contribution of microbial residues to SOC was 44.4-47.5%higher under S.superba than under the other tree species.These findings suggest a higher stability of microbial residues under S.superba than that under the other studied tree species.Conclusions Our results demonstrate that tree species influence long-term microbial persistence in forest soils by affecting accumulation and stabilization of microbial residues.