Effects Of Legumes Intercropping And Nitrogen Fertilization On Soil Phosphorus Availability In A Camellia Oleifera Agroforestry

Phosphorus is the limiting nutrient element second only to nitrogen in the growth of camellia oleifera.Scientific management mode of camellia oleifera forest can effectively improve soil nutrient utilization efficiency.Relevant research is of great significance to the improvement of agricultural economy and ecological environment.Legume intercropping and nitrogen fertilization are both common management measures of camellia oleifera forest.Compared with nitrogen fertilization which may cause soil degradation and environmental pollution,legume intercropping is considered as a sustainable development approach to improve the production efficiency of camellia oleifera forest.Most previous studies focused on the comparison of biological nitrogen fixation effects of intercropping legume plants and the effects of nitrogen fertilization on soil nitrogen availability,but few studies explored the difference of effects of the two measures on soil phosphorus availability and their mechanisms of action.In order to improve the understanding of this problem,six treatments were set up:Cassia seed(CS),peanut(CP),Camellia monoculture +low nitrogen(LN),camellia monoculture+high nitrogen(HN),camellia monoculture weed control(CK)and camellia monoculture without weed control(CG).Hedley phosphorus classification,fluorescence quantitative PCR and functional gene microarray were used to quantify the dynamic changes of soil phosphorus availability,major microbial groups and the abundance of carbon,nitrogen and phosphorus functional genes,and to explore the internal mechanism of the effect of legume intercropping and nitrogen fertilization on phosphorus conversion.The results show that:(1)Intercropping of legumes significantly increased pH,available phosphorus,and nitrogen and phosphorus contents of camelia oleifolia leaves(p<0.05).In July,the available phosphorus content increased by 31%and 70%under CS and CP treatments,in September,the available phosphorus content increased by 9.5%and decreased by 4%under CS and CP treatments.In July,Nitrogen fertilization reduced pH,total phosphorus and available phosphorus contents,while in September,nitrogen fertilization increased pH,and LN treatment increased soil available phosphorus content by 185%compared with CK,suggesting that nitrogen fertilization in July increased soil acidity and reduced the dissolution of soil inorganic phosphorus.However,in September,soil total phosphorus increased,indicating that with the growth of crops and the increasing demand for soil phosphorus,worthy plants have explored a new phosphorus acquisition strategy,and LN treatment can improve soil phosphorus activity more effectively.(2)The contents of active phosphorus(Resin-Pi,NaHCO3-Pi,NaHCO3-Po)and moderately active phosphorus(NaOH-Pi,NaOH-Po)in soil were improved by intercropping of leguminous plants.In July,Resin-Pi and NaHCO3-Pi increased by 50%and 94%under CS treatment,and 96%and 47%under CP treatment.In September,Resin-Pi and NaHCO3-Pi increased 321%and 168%respectively under CS treatment,and 173%and 143%respectively under CP treatment.Resin-Pi content decreased by 64%and 45%under LN and HN treatments in July,and increased by 140%and 61%under LN and HN treatments in September.In addition,the contents of NaHCO3-Pi,NaOH-Pi and NaOH-Po were significantly increased by LN treatment in September(p<0.05),indicating that appropriate nitrogen fertilization could promote soil phosphorus conversion.(3)Intercropping of leguminous plants increased Soil microbial biomass phosphorus(MBP)content and acid phosphatase activity(APA).Under CS and CP treatment,MBP increased by 29%and 32%,APA increased by 98%and decreased by 9.7%,respectively,in July;MBP increased by 57%and decreased by 19%,and APA increased by 44%and 37%,respectively,in September;Legume intercropping increased the abundance of soil bacteria and fungi.Under CS treatment,AMF and archaea abundance increased significantly(p<0.05),the abundance of hemicellulosic(abfA)hydrolysis gene and inorganic phosphorus hydrolysis gene was increased Compared with CK,but not significantly(p>0.05).However,the abundance of AMF and archaea decreased under CP treatment,while the abundance of organic phosphate mineralization and nitrogen functional genes increased compared with CK treatment.LN treatment increased MBP content and APA activity,while HN treatment increased MBP content and decreased APA activity.The abundance of soil bacteria and fungi increased under LN treatment,while the abundance of AMF and archaea decreased.Under HN treatment in September,the abundances of functional genes of C,N,P,were the highest.Under different treatments,APA decreased in September compared with July,while the abundances of soil fungi and AMF increased in September compared with July.(4)Correlation analysis showed that active phosphorus in July was positively correlated with pH,organic carbon,carbon hydrolysis and carbon fixation genes,and negatively correlated with ammonia nitrogen and nitrate nitrogen.APA was positively correlated with AMF and archaea,and MBP was positively correlated with denitrification and inorganic phosphorus hydrolysis genes.In September,soil active phosphorus was positively correlated with APA,MBP,SOC and pH,APA was significantly positively correlated with bacteria,and functional genes of C,N and P were weakly correlated with soil phosphorus components.These results indicated that soil biological factors and abiotic factors were important regulators of soil phosphorus components.In conclusion,In acidic soil,both legume intercropping and nitrogen fertilization can promote soil P conversion and improve the absorption of soil active P by plants.The soil P utilization efficiency is higher under legume intercropping,but the mechanism of promoting P conversion between them is slightly different.Among them,legume intercropping can promote soil phosphorus conversion through the regulation of soil physical and chemical environment and microorganisms,while nitrogen fertilization can improve available phosphorus mainly by affecting microorganisms(bacteria,AMF,fungi.),and the efficiency is higher in LN treatment.