Linking changes in the soil microbial community to C and N dynamics during crop residue decomposition

Crop residues are among the main inputs that allow the organic carbon(C)and nutrients to be maintained in agricultural soil.It is an important management strategy that can improve soil fertility and enhance agricultural productivity.This work aims to evaluate the extent of the changes that may occur in the soil heterotrophic microbial communities involved in organic matter decomposition and C and nitrogen(N)mineralization after the addition of crop residues.Soil microcosm experiments were performed at 28℃ for 90 days with the addition of three crop residues with contrasting biochemical qualities:pea(Pisum sativum L.),rapeseed(Brassica napus L.),and wheat(Triticum aestivum L.).Enzyme activities,C and N mineralization,and bacterial and fungal biomasses were monitored,along with the bacterial and fungal community composition,by the highthroughput sequencing of 16 S rRNA and ITS genes.The addition of crop residues caused decreases in β-glucosidase and arylamidase activities and simultaneous enhancement of the C mineralization and net N immobilization,which were linked to changes in the soil microbial communities.The addition of crop residues decreased the bacterial and fungal biomasses 90 days after treatment and there were shifts in bacterial and fungal diversity at the phyla,order,and genera levels.Some specific orders and genera were dependent on crop residue type.For example,Chloroflexales,Inquilinus,Rubricoccus,Clitocybe,and Verticillium were identified in soils with pea residues;whereas Thermoanaerobacterales,Thermacetogenum,and Hypoxylon were enriched in soils with rapeseed residues,and Halanaerobiales,Rubrobacter,and Volutella were only present in soils with wheat residues.The findings of this study suggest that soil C and N dynamics in the presence of the crop residues were driven by the selection of specific bacterial and fungal decomposers linked to the biochemical qualities of the crop residues.If crop residue decomposition processes showed specific bacterial and fungal operational taxonomic unit(OTU)signatures,this study also suggests a strong functional redundancy that exists among soil microbial communities.

Soil under dead or live organic matter systems:Effect of European shag(Phalacrocorax aristotelis L.)nesting on soil nematodes and nutrient mineralization

Here we studied whether soil systems differ if they are under the influence of live(plants)or dead organic matter systems(nest)in terms of C and N mineralization,microbiological characteristics and nematode trophic group structure.We analyzed physicochemical and microbiological properties of soils inside and outside nests of the European shag(Phalacrocorax aristotelis L.)on the Cies Islands(NW Spain).We sampled fresh soil below dead(nests)and live organic matter(plants)(paired samples,n=7).Soil of nests had lower organic matter and higher electric conductivity and dissolved organic C and extractable N contents than the soil of plants.Microbial biomass and activity were greater in soil of nests than in soil of plants.The abundance of nematode trophic groups(bacterivores,fungivores,omnivores and herbivores)differred between soils of nests and plants,and the soil of plants supported a more abundant and diverse nematode community.The present results points to that source of organic matter promote differences in the decomposer community,being more efficient in soil of nests because C mineralization is greater.Further,this occurred independently of the complexity of the systems,higher in the soil of plants with more groups of nematodes.