Study On Fallen Wood Storage And Nutrient Release In Castanopsis Eyrei Forest

As a key medium and link between vegetation and soil ecosystem interfaces in forest ecosystems,fallen wood is an indispensable functional element that links above-ground and below-ground nutrient cycles.In this study,we used a "spatial for temporal gradient" methodology to investigated the characteristics and storage capacity of fallen wood,soil nutrients and soil fungal community under fallen wood in two natural forests of Castanopsis eyrei at different elevations in the subtropical region by using field survey,laboratory experiments and microbial high-throughput sequencing.The above study can provide an understanding of the pattern of nutrient release to soil from fallen woods in Castanopsis eyrei forests and how the soil is affected by nutrient release from fallen woods.Our study shed light on the nutrient and storage characteristics of fallen wood in the study area and the effect of fallen wood on soil fungal communities.The main findings are as follows:(1)Decay of fallen wood significantly reduced its water content and organic carbon content,while the contents of organic carbon,total nitrogen and total phosphorus increased significantly;the contents of potassium,calcium and magnesium decreased with decomposition at high altitudes and increased with decomposition at low altitudes;iron and manganese elements had no obvious change pattern.The carbon to nitrogen ratio and carbon to phosphorus ratio of fallen wood at different altitudes showed a decreasing trend with the deepening of decomposition,while the nitrogen to phosphorus ratio showed an increase and then a decrease.The fallen wood in the high-elevation sample site mainly consisted of lightly decayed and moderately decayed fallen wood,and the diameter class was generally large,while the distribution of fallen wood in the lower elevation was closer to each decay class.The total storage capacity of fallen wood in sweet chink forest at high elevation was 18.52 t/hm2,while that at low elevation was 1.75 t/hm2.The storage capacity of each nutrient was uniformly shown that the higher the decay grade,the lower the storage capacity.(2)Except for water content,decomposition of fallen wood had significant effects on soil physicochemical factors.The organic carbon,total nitrogen and carbon to nitrogen ratio decreased and then increased with decomposition of fallen wood;total phosphorus,iron and manganese showed an increasing trend with decomposition of fallen wood;nitrogen to phosphorus ratio showed a decreasing trend with decomposition of fallen wood;potassium and carbon to phosphorus ratio varied inconsistently with decomposition of fallen wood at different altitudes.In the horizontal distance,pH increased with increasing distance from the fallen wood,organic carbon and total nitrogen decreased with increasing distance from the fallen wood,and the rest of physicochemical factors did not have obvious change pattern in the horizontal distance.(3)A total of 2818 fungal species were detected in this study,but few species were shared among different samples.Fungal species were mainly classified in three phyla,Basidiomycota,Ascomycota and Mucoromycota,with Agaricomycetes accounting for the largest proportion at the phylum taxonomic level,followed by Dothideomycetes,and this phylum was mainly detected in the soil beneath moderately decomposed fallen wood.The fungal Shannon and Pielou indices decreased and then increased with decomposition of fallen wood at high elevations,and showed a continuous decrease at low elevations,while the Simpson and Chao1 indices did not differ significantly among samples.The decay of fallen wood was the dominant factor in the variation of soil fungal community structure.Soil fungal community structure was significantly affected mainly by soil iron,carbon to phosphorus ratio,calcium,soil capacitance,and significantly by total phosphorus,water content of fallen wood,organic carbon of fallen wood,iron of fallen wood,and nitrogen to phosphorus ratio of fallen wood.Nutrients of fallen wood(R2.Adj=0.5898,P=0.002)had greater explanation and higher significance for the community structure of fungi compared to soil nutrients(R2.Adj=0.4531,P=0.026).(4)There was a highly significant positive correlation between total nitrogen and phosphorus content of fallen wood,and a strong positive correlation between potassium,calcium,magnesium and manganese elements;there was a highly significant positive correlation between soil organic carbon,total nitrogen and total phosphorus,but only nitrogen and phosphorus elements of fallen wood nutrients were significantly positively correlated;organic carbon of fallen wood was significantly positively correlated with soil capacity,soil organic carbon,total nitrogen,total phosphorus,carbon to nitrogen ratio and carbon to phosphorus ratio were significantly positively correlated with most of the nutrient indicators of fallen wood;fungal abundance was significantly positively correlated with soil pH and manganese elements,and fungal diversity index was significantly correlated with calcium and carbon to phosphorus elements.The abundance of fungi was significantly and positively correlated with soil pH and manganese,and the diversity index of fungi was significantly and positively correlated with calcium and carbon,nitrogen and phosphorus;most of the species significantly correlated with soil nutrients belonged to the Basidiomycota.In summary,1)decomposition of fallen wood significantly changes its own physicochemical properties,and nutrient elements are released with decomposition of fallen wood,but the release patterns of different elements are not consistent;2)the storage and distribution of fallen wood at different altitudes are significantly different;3)decomposition of fallen wood has a significant impact on soil nutrients,but different nutrient elements have different trends,and some soil nutrient elements will in turn affect 4)fallen wood had a greater impact on soil fungal communities than soil,and decomposition of fallen wood significantly changed the structure and diversity of fungal communities,while the diversity and dominant species of fungi also contributed to the increase of soil nutrients.This study can provide a theoretical basis for the study of nutrient cycling and energy flow within subtropical forest ecosystems,and provide effective help for scientific management of Castanopsis eyrei natural forest.