Straw and biochar strongly affect functional diversity of microbial metabolism in paddy soils

The application of straw and biochar is widely practiced for the improvement of soil fertility.However,its impact on microbial functional profiles,particularly with regard to paddy soils,is not well understood.The aim of this study was to investigate the diversity of microbial carbon use patterns in paddy soils amended with straw or straw-derived biochar in a 3-year field experiment in fallow soil and at various development stages of a rice crop(i.e.,tillering and blooming).We applied the community level physiological profiling approach,with 15 substrates(sugars,carboxylic and amino acids,and phenolic acid).In general,straw application resulted in the greatest microbial functional diversity owing to the greater number of available C sources than in control or biochar plots.Biochar amendment promoted the use of α-ketoglutaric acid,the mineralization of which was higher than that of any other substrate.Principal component analyses indicated that microbial functional diversity in the biochar-amended soil was separated from those of the straw-amended and control soils.Redundancy analyses revealed that soil organic carbon content was the most important factor regulating the pattern of microbial carbon utilization.Rhizodeposition and nutrient uptake by rice plants modulated microbial functions in paddy soils and stimulated the microbial use of N-rich substances,such as amino acids.Thus,our results demonstrated that the functional diversity of microorganisms in organic amended paddy soils is affected by both physicochemical properties of amendment and plant growth stage.

Nitrous Oxide Emissions from a Masson Pine Forest Soil in Subtropical Central China

The forest ecosystem plays a pivotal role in contributing greenhouse gases to the atmosphere.In order to characterize the temporal pattern of nitrous oxide(N_2O) emissions and identify the key factors affecting N_2O emissions from a Masson pine forest in a hilly red-soil region in subtropical central China,we measured the N_2O emissions in Jinjing of Hunan Province using the static chambergas chromatographic method for 3 years(2010-2012) and analyzed the relationships between the N_2O fluxes and the environmental variables.Our results revealed that the N_2O fluxes over the 3 years varied from-36.0 to 296.7 μg N m^(-2) h^(-1),averaging 18.4±5.6 μg N m^(-2) h^(-1)(n=3).The average annual N_2O emissions were estimated to be 1.6±0.3 kg N ha^(-1) year^(-1).The N_2O fluxes exhibited clear intra-annual(seasonal) variations as they were higher in summers and lower in winters.Compared with other forest observations in the subtropics,N_2O emissions at our site were relatively high,possibly due to the high local dry/wet N deposition,and were mostly sensitive to variations in precipitation and soil ammonium N content.In this work,a multiple linear regression model was developed to determine the influence of environmental factors on N_2O emissions,in which a category predictor of "Season" was intentionally used to account for the seasonal variation of the N_2O fluxes.Such a model explained almost 40%of the total variation in daily N_2O emissions from the Masson pine forest soil studied(P<0.001).