the National Natural Science Foundation of China(41877029,41961130383);Royal SocietyNewton Advanced Fellowship(NAF\R1\191017);Wuhan Science and Technology Bureau(2019020701011469).

Due to the tremendous diversity of microbial organisms in topsoil,the estimation of saturated richness in a belowground ecosystem is still challenging.Here,we intensively surveyed the 16S rRNA gene in four 1 m2 sampling quadrats in a typical grassland,with 141 biological or technical replicates generating over 11 million sequences per quadrat.Through these massive data sets and using both non-asymptotic extrapolation and non-parametric asymptotic approaches,results revealed that roughly 15919±193,27193±1076 and 56985±2347 prokaryotic species inhabited in 1 m2 topsoil,classifying by DADA2,UPARSE(97%cutoff)and Deblur,respectively,and suggested a huge difference among these clustering tools.Nearly 500000 sequences were required to catch 50%species in 1 m2,while any estimator based on 500000 sequences would still lose about a third of total richness.Insufficient sequencing depth will greatly underestimate both observed and estimated richness.At least~911000,~3461000,and~1878000 sequences were needed for DADA2,UPARSE,and Deblur,respectively,to catch 80%species in 1 m2 topsoil,and the numbers of sequences would be nearly twice to three times on this basis to cover 90%richness.In contrast,α-diversity indexes characterized by higher order of Hill numbers,including Shannon entropy and inverse Simpson index,reached saturation with fewer than 100000 sequences,suggesting sequencing depth could be varied greatly when focusing on exploring differentα-diversity characteristics of a microbial community.Our findings were fundamental for microbial studies that provided benchmarks for the extending surveys in large scales of terrestrial ecosystems.

Soil microbiome mediated nutrients decline during forest degradation process

Degradation succession in forests is an important and serious land use/cover change problem in ecology,and during these processes soil microbial communities mediate the recycling of most important nutrients.To reveal the effect of degradation succession processes on soil microbial community diversity,structure,and species interrelationships,we collected abundant samples(21 per vegetation type)in broad-leaved forest,coniferous forest,and meadow to observe the microbial community dynamics.The results showed that diversity and structure of soil prokaryotic and fungal communities responded differently to different forest degradation processes,diversity of soil microbial communities increased during degradation processes.Soil microbial communities abundance changes may indicate that prokaryotic communities showed a living strategies change as an ecological adaption to harsh conditions during forest degradation process.While for fungal communities,their abundance changes may indicate that environmental selection pressure and plant selectivity during forest degradation process.Changes in soil prokaryotic communities and fungal communities were both correlated with soil carbon and nitrogen loss.The soil microbial interaction network analysis indicated more complex species interrelationships formed due to the loss of soil nutrients during degradation succession processes,suggesting soil microbial communities might form more complex and stable networks to resist the external disturbance of soil nutrient loss.All results suggested soil microorganisms,including bacteria,archaea and fungi,all involved in the soil nutrient decline during the forest degradation process.