Study On The Effect Of Straw Mulch On Critical Nitrogen Transformation In Camellia Oleifera-peanut Intercropped Soil

Camellia oleifera is an important major economic forest tree species in China,especially widely planted in southern regions such as Hunan,Zhejiang and Jiangxi.Soil nitrogen plays a crucial role in the growth and development of C.oleifera,and the effective use of straw mulch is considered to be a key factor for the high quality development of the current oil tea industry and an effective input method for nitrogen addition.The effect of straw mulch on soil N transformation in C.oleifera-peanut intercropping system is still unclear.In this study,three different straw mulching treatments,powder mulching(W),whole straw mulching(S)and no mulching(CK),were set at three different time periods(T1:50 days of mulching,T2:100 days of mulching and T3:150 days of mulching)in the C.oleifera-peanut intercropping system.Soil properties,nitrogen content and enzyme activities were measured,and nitrogen conversion rates were calculated,and N functional microbial(AOA,nirK and nirS)communities were characterized by high-throughput sequencing,in order to investigate the effects of straw mulching on N conversion in C.oleifera-peanut intercropping system.The main results were as follows:(1)Compared with CK,straw mulches treatments did not significantly affect soil water content,soil bulk density and soil pH,and there was no significant difference between soil layers in these treatments.With the increase of straw mulching time,soil water content and soil bulk density increased.With the increase of mulching time,total N content showed a trend of decreasing and then increasing,and soil organic carbon and total phosphorus content slightly decreased.Soil organic carbon,total N and total phosphorus content decreased with the increasing soil depth.The variation of soil protease activity ranged from 26.41-80.35 mg·g-1·d-1,and straw mulching significantly increased the activity of soil proteases during period of T1(p<0.05).In addition,the effects of straw mulching on soil protease activity were more strong in the topsoil layer than in the deep soil layer.Soil nitrate reductase activity increased with the increase of mulching time,and increased first and then decreased with the increase of soil depth.The overall variation range was 0.01-1.34 μmol·kg-1· d-1.The overall variation range of soil nitrite reductase activity was 0.14-2.92 μmol·kg1·d-1.The straw mulching treatment had an enhancing effect on nitrite reductase activity of C.oleifera-peanut intercropped soil,and there was no significant trend of soil layer on soil nitrite reductase activity.(2)The seasonal changes in contents of N components were found in different straw mulching treatments.The overall variation of soil effective N content ranged from 6.30-40.60 mg · kg-1,nitrate N content ranged from 0.25-8.77 mg · kg-1,ammonium N content ranged from 0.01-20.84 mg · kg-1,and microbial biomass N content ranged from 0.02-9.83 mg·kg-1.Straw mulching did not affect soil available effective N and nitrate N contents.Straw powder mulching significantly affected soil ammonium N content,and straw mulching significantly affected soil microbial biomass N content.Soil mineralization rate did not increase in the first period of straw mulching treatment,and was significantly higher in the later period of the study(mean mineralization rate of 0.234 mg · kg-1·d-1)than in the first period(mean mineralization rate of-0.007 mg·kg-1·d-1),and significantly higher in the later period of the study(mean ammonification rate of 0.152 mg·kg-1·d-1)than in the first period(mean ammonification rate of-0.006 mg·kg-1·d-1),and significantly higher in the later period of the study(mean nitrification rate of 0.082 mg·kg-1·d-1)than in the first period(mean nitrification rate of-0.001 mg·kg-1·d-1)(p<0.05).The changes in soil ammonification rate and soil nitrification rates showed the same trend as the soil mineralization rate.Under different straw mulching treatments,the transformation rate of soil key N was significantly positively correlated with soil available N and nitrite reductase(p<0.05),but was significantly negatively correlated with soil organic carbon.(3)Straw mulching had a general positive effect on the Alpha diversity of soil N functional microbial community,among which the most obvious changes were found in the straw powder mulching treatments.Under different straw mulching treatments,the Beta diversity of AOA gene,nirK gene and nirS gene community structure differed significantly,especially during the T3 mulching period.The straw powder mulching treatment had the most significant effect on the community composition among the various straw mulching treatments(p<0.05).Although the community composition of N-functional microorganisms was the same under the genus category for different straw mulching treatments,the percentage of different genera in soil Nfunctional microorganism community structure was affected by the straw mulching treatments.The relationship between soil N-functional microorganisms and environmental factors was analyzed redundantly,Results showed that the straw powder mulching was positively correlated with soil environmental factors,while straw whole-pole mulching was positively correlated with Alpha diversity of Nfunctional microorganisms(p<0.05).In conclusion,straw mulching improved the nutrients in the soil of C.oleiferapeanut intercropping system,accelerated the rate of soil N conversion,and enriched the diversity and structural functions of soil N-functional microbial communities.Therefore,straw mulching is an effective way to improve soil quality.Among the straw mulching,and the straw powder mulching with the T3 mulching period is the most effective straw mulching practice.This study provides basic information and scientific reference for the disposal of crop straw residues,the application of straw mulching technology in the C.oleifera-peanut intercropping systems,and the sustainable management of C.oleifera forest ecosystem.