Effects Of Long-term Fertilization On Soil Organic Matter And Soil Microbial Functional Diversity In Jiangxi Paddy Soil

Soil organic matter(SOM)pools play important role in maintaining crop productivity,improving soil quality and sequestrating C.The study on the change of SOM pools in rice agriculture soil is not only related to the sustainability of China’s food security and the development of agricultural system,but also has scientific guiding significance for the formulation and implementation of China’s agriculture policy and measures to address climate change.As the vital organism in the soil environment,soil microbes participate in a series of important ecosystem processes,including soil carbon,nitrogen conversion and recycling in soil ecosystems.It is important to study the microbial indexes such as the change of microbial function diversity and the improvement of soil fertility and regulation of ecosystems by long-term fertilization on microbial functional diversity.Based on the a 35-year paddy soil of long-term fertilization experiment,by using physical-chemical fractionation method,separated the non-protected SOM pool,the physical protected pool,the physical-chemical protection pool,the physical-biochemical protection pool,the chemical protection pool and the biochemical protection pool.we investigated the effects of long-term fertilization on soil functional SOM fraction mass,the soil organic carbon(SOC)and total nitrogen(TN)contents in each fraction,Response of SOM to long-term fertilization;The functional diversity of soil microbial community was analyzed by BIOLOGECO micro-plate method;The mechanism of functional diversity of microbial communities to different functional soil organic matter pools was explored by studying the functional diversity of SOM-soil microbes under different fertilization treatments with the multivariate statistical analysis.Results showed that:(1)Long-term application of NPKM significantly increased the percentages of non-protected SOM pool(cPOM and fPOM)and physical protected pool(iPOM).Meanwhile,long-term application of NPKM significantly increased the SOC and TN content in non-protected and physical protected SOM pools as compared with other treatments.The SOC and TN content in non-protected SOM pool is the highest under the treatment with NPKM,up to 35.9%and 33%.This shows that this SOM pool is the major storage pool for SOC and TN.As compared with the control(CK),application of NPKM significantly decreased the contents of biochemical protected pool NH-dSlit and NH-dClay fractions by 15%and 9.5%,respectively.The influences of long-term fertilization on the mass of physical-chemical protected SOM pool,physical-biochemical protected SOM pool and chemical protected SOM pool content were not significant.This indicates that these three types of functional SOM pools are currently relatively stable,and the capacity of SOC and TN may have been close to saturation.(2)Long-term fertilization affected the activities of soil microbial metabolism,and the AWCD values under the long-term fertilization showed an increasing trend.The result indicated that the ability of soil microbial biomass to use carbon source increased with time,but the increasing speeds had sufficiently different in different time periods.Compared with other treatments,AWCD treated with organic and inorganic fertilizer(NPKM)was significantly higher than other treatments in the rapid utilization(12-60 H)during the culture.Analysis of 60H data tested on BIOLOGECO micro-plate showed that the soil microbes of different treatments had the highest metabolic activity against carbohydrate carbon source,followed by the utilization of amino acids and carboxylic acid carbon sources,while the utilization of amines and polymers and other mixtures were lower.The enrichment of soil microbial community under the treatment with NPKM was higher than other treatments,followed by nitrogen fertilizer,NPK,and the CK was the lowest.The result of uniformity index also showed that NPKM treatment was the highest,but there was no significant difference between NPKM and N treatments.Also the results showed that there was no significant difference between NPK and CK treatments.The utilization index of carbon source under the treatment with NPKM was significantly higher than that of N fertilizer,and slightly higher than other treatments,but the difference was not significant between NPK and CK treatments.Principal components analysis for carbon utilization of soil microbial communities in different treatments showed that(PC1)can explain 36.6%of variance of all variables,and the second principal component(PC2)can explain 21.9%of the variance of all variables.The results showed that different fertilization treatments had a significant effect on the utilization pattern of carbon sources.Species scores of different carbon source utilization of the principal components analysis showed that sugars,carboxylic acids,amino acids,and polymers were the main carbon sources for microbial utilization.(3)The changes of microbial metabolism in soil were affected by different functional SOM contents,SOC content and TN content:The content of SOM components,SOC content and TN content of different functional pools explained 61.8%,73.4%and 67.0%of microbial metabolism variance.The content of non-protected SOM pool explained 25.7%of the variation,and the content of physical protected SOM pool explained 21.3%.The SOC content of non-protected SOM pool explained 29.1%of the variation,and the SOC content of physical protected SOM pool explained 15.7%.The TN content of non-protected SOM pool explained 28.6%,and the SOC content of physical protected SOM pool explained 27.9%of the variation(p<0.05).The treatment under NPKM of microbial metabolic function has strong correlations with the component contents of non-protected SOM pool and physical protected SOM pool and its SOC content and TN content.Soil macro-aggregates and micro-aggregates organic matter components may have a significant effect on the metabolic functional diversity of soil microbes.Above all,this study indicates that different functional SOM pools response to long-term fertilization differently.NPKM is the optimum fertilization measure to enhance the quantity and quality of red paddy soil SOM,especially for the non-protected and physical protected SOM pools.At the same time,it’s a significant role in promoting and maintaining the functional diversity of soil microbial communities.