| Crop straw is one kind of biomass resource that contains large amounts of organic matter,nitrogen,phosphorus,potassium,and other trace elements necessary for plant growth.In the terrestrial ecosystem,straw decomposition is an important source of soil organic matter.The rate of straw decomposition in the soil is not only related to the material composition of the straws itself,but also to the environmental conditions such as temperature,moisture,and soil properties.Microorganisms are an important part of the geochemical cycle and play a very important role in the straw decomposition process.Various straws characteristics and environmental factors could lead to distinct microbial community structures and functional diversities.In this work,the mesh bag method was used to explore howplant straws decompose in fields with three long-term field experiments(Farmland,Peach orchard and Vineyards)in Guanzhong of Shann'xi Province.Combining with soil properties,Biolog,and soil enzymes analysis,soil microbial community diversities were investigated under various straws decomposings in different land uses.The effect of environmental factors,soil types,and straws properties was explored to find out the relationships between straw properties and microbial communities decomposing straws.The results will apply the basic research data for maximally benefiting from straw biomass energy and provide the scientific basis for soil organic carbon conversion and reasonable use of long-term experimental fields.The main results are listed as follows:Results showed that with the decomposition time increasing,the residue rate of fresh plant straws did not varied much.The three long-term field experiments showed the similar trend,with an order of FB(Fresh bean stalk)> FCN(Fresh corn stalk + nitrogen fertilizer)> FC(Fresh corn stalk).The decomposition process was divided into two stages: 0-10d(decreased rapidly)and 10-360d(slow decline).The residue rate of straws in all treatments decreased to 17.61-30.43%,when decomposition completed.The residue rate of dried milled straw varied among different treatments,with the order of DB(Dry bean stalk)> DC(Dry corn stalk)> DCN(Dry corn stalk + nitrogen fertilizer).The whole decomposition process was divided into three phases: 0-10d(decreased rapidly),10-270d(slow decreases),and 270-360d(stable).When decomposition completed,the residue rate of straws in all treatments decreased to 36.11-47.24%.With the increase of decomposition time,the residue rate of drying straws was higher than fresh straws.Regardless of fresh or dry straws,the volume size,and C / N how,the stalk straws showed the more rapid decomposition rate compared with the soybean straws.Soil temperature significantly affected the residue rate of straw decomposition in different experimental fields.Soil temperature deviation affected the stability of soil microbial activity and thereby resulted in distinct decomposing residue rate in different experimental fields.Soil water content did not significantly affect the straws decomposition rate.When the hard decomposing component accumulated gradually,slowing greatly the rate of straw decomposition in experimental fields.The water content of straws affected the straw decomposition residue,especially for the high-quality of plant residues was more obvious.By comparing with dry straw decomposing residue rate,we founded that high water content of straws did not necessarily speed up the decomposition rate,which need more complex chemical reaction to complete the straw decomposition process.In terms of soil microbial community activity(average well color development,AWCD),the microbial community stability of three long-term experiments followed an order of Vineyard > Peach orchard > Farmland.With the extension of the time of the straw decomposition,the soil microbial carbon metabolism of the three experimental soil was similar,and the dominant population was basically shown as the carbohydrate metabolism group,and the second was polymer.The diversity index results showed that with the increase of decay time,the species richness of microorganisms in three land uses soil decreased and the dominance of common species increased slightly.Meanwhile,the evenness also decreased,indicating the possible occur of some dominant population decomposition of straw.The aromatic compound metabolism group was the weakest carbon metabolism group in all tested soils.The diversity index analysis indicated that with the increase of decomposition time,the microbial species richness in straw FB treatment in farmland soil reduced,while the dominance species were stable.It was indicated that some decomposition straw dominant population occur,resulting in the decomposing rate significantly changed among different straw treatment in farmland soil.For the straw FB treatment in orchard soil,microbial community richness increased with the decomposing time and the dominance remained the same or lower,which need to be studied further to find out which microorganism affecting decomposing.With the increase of decomposing time,the microbial community function showed some regularity and the convergence trend.The utilization orders of the 6 kinds of carbon sources by microbial community in different land uses soils were not consistent.However,the dominant species were mainly composed of sugars and polymers with the aromatic compounds accumulation gradually in the middle of decomposing process,which indicating the weakest use of aromatic compounds.The results showed that the soil catalase activity significantly affected residual rate of straw decomposing in different experimental fields.Soil temperature also influenced the soil catalase activities.With the extension of the straw decomposition time,orchard soil with grass coverage would maintain and improve the activities of soil urease and invertase,while reduced the activities of soil urease and invertase in farmland.The soil catalase activity decreased with the decomposition time increased and showed the similar valuesin all soils with different land uses(P>0.05).Due to the different management practices and fertilization methods in different experimental fields,the activities of soil enzyme had changed with different trends,particularly between soil urease and invertase in the orchard.The pasture cover did not show the advantages of nitrogen fixation and affected the rate of decomposition straws.Different straw treatments had different sensitivities to environmental factors,which affecting the growth environment of microorganisms and resulting in different diversity of microbial communities in the process of straw decomposition.The results showed that there was no significant correlation among the dominance of straw microbe,the utilization of sugars,and aromatic compounds.Soil pH had extremely significant negative correlation with the soil urease and sucrose.Soil organic matter was significant positive correlated with soil catalase.Soil available phosphorus and potassium were very significant positive correlated with soil catalase,indicating that the soil pH,organic matter,and available potassium significantly affected the soil enzyme activity.We selected southern red soil(typical acidic soil)and the north Lou soil(calcareous soil)to explore the affect of 5 kinds of heavy metal(Cd,Cr,Pb,Hg,As)on soil enzymes at the different stages of two straw decomposition(wheat straw and corn straw)by indoor cultivation experiments.The results showed that compared with red soils,the catalase,urease,and sucrose enzyme activities were higher than Lou soils.The catalase activity in Lou soils was more sensitive to Pb and Cr than in red soils.The catalase activity in red soil was more sensitive to Cr.The soil urease activity showed sensitive change on heavy metal Hg stress.The addition of Pb obviously increased on the soil sucrose enzyme activity.The total enzyme activity of red soil was the most sensitive to Cr,while for Lou soil,it was most sensitive to Hg. |
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