| Low nocturnal temperature(LNT)in winter and spring cultivation of protected tomato often leads to growth and development obstacles,which seriously limits the development of protected tomato production in China.LNT caused more growth and development disorders of protected tomato,and one of the most important symptoms was phosphorus(P)deficiency.Previous studies have shown that low temperature can reduce the availability of soil P and limit microbial activities,but how LNT affects soil microorganisms and thus regulates the transformation of soil P fractions remains unclear.In this study,daily/night temperature(25 /15 °C)was used as control,and three LNTs treatments were set(day/night temperature: 25 /12 °C,25 /9 °C and 25/6 °C),and sampled at 10,20 and 40 days(d)of LNT treatment,respectively.P distribution characteristics of protected tomato,dynamic rule of P fractions in soil in tomato and relationship between them were analyzed by measuring protected tomato soil P fractions and plant fractions under LNT.The function and diversity of protected tomato soil bacterial community and metabolome were analyzed.The basic rules of soil nutrient cycling and the response characteristics of bacterial community and metabolites of protected tomato soil under LNT were clarified.Subsequently,the abundance of key P cycling genes(pho D and pqq C)and their microbial community functions and diversity were determined.Their correlation with soil P fractions was analyzed to reveal the transformation process of P fractions in protected tomato soil controlled by P cycling microorganisms under LNT.The main results are as follows:1.In this paper,P uptake in plant and foliar and root P content of tomato were determined and analyzed.The results showed that under the LNTs of 12,9 and 6 °C,the P uptake of whole plant and foliar total P content were significantly lower than that of the control,while under LNT of 6 °C,the root total P content of tomato was significantly higher than that of the control.Under LNT,percentage of metabolic P decreased but percentage of lipid P and nucleic P increased in plant tomato leaves.These results indicated that LNT had stronger P restriction on tomato leaves than on roots.Under LNT,the carbon metabolism of tomato leaves was limited and phosphate was preferentially used to maintain membrane integrity and synthesize enzymes related to carbon metabolism.2.We determined the soil P fractions and analyzed its relationship with plant P fractions.The results showed that under 9 and 6 °C treatment,the content of soil labile inorganic P decreased significantly at 20 and 40 d,while the content of soil labile and moderately labile organic P increased significantly at 40 d.The soil moderately labile inorganic P increased significantly after 20 d of treatment at 6 ℃,but increased significantly after 40 d of treatment at 9 ℃.In addition,structural equation model analysis showed that soil moderately labile P was the largest positive and negative effect factor of foliar and root P fractions.Root and foliar P fractions were the largest positive and negative effect factor of dry matter accumulation in tomato shoots,respectively.These results indicated that LNT of 9 and 6 °C reduced the protected tomato soil P,but LNT of 12 °C had no effect on it.LNT reduced foliar and root P fractions by inhibiting the availability of soil P,and thus decreased dry matter accumulation in plant shoots.3.Soil basic nutrient indexes,functional diversity of bacterial community and metabolome were analyzed.The results showed that at 9 and 6 °C for 40 d,the content of soil organic matter was significantly increased,and the content of available P(AP)and disolve organic carbon(DOC)was significantly decreased.The decrease of soil AP and DOC was the key driving factor for the change of soil bacterial community.Under 6 °C treatment,the relative abundance of genes related to carbohydrate synthesis,translation and ribosome structure in soil microorganisms of protected tomato significantly decreased,and the abundance of genes related to membrane generation and enzyme synthesis and metabolites related to membrane fluidity significantly increased,as well as the abundance of anti-stress metabolites such as linoleic acid,jasmonic acid and brassinosteroids significantly increased.This suggests that LNT alters the function of bacterial communities by limiting soil carbon and P availability in tomato facilities,and that LNT enables bacteria in tomato facilities to allocate resources to the process of cold adaptation and enhances the potential of bacteria and plant resistance.4.The abundance of pho D and pqq C gene was determined,and their related microbial communities were analyzed.The results showed that pqq C gene abundance decreased significantly under 9 and 6 ℃.However,pho D gene abundance only decreased significantly under 6 ℃.pho D microbial community was not significantly separated,while pqq C microbial community was significantly separated.The relative abundance of pqq C(7 species)was significantly higher than that of pho D(3 species)under LNT.This indicated that pqq C gene and its microorganisms had more vigorous response to low night temperature than pho D gene and its microorganisms.5.The abundance of phosphorus cycling-related genes and the phosphorus components in soil of tomato facilities were analyzed and the structural equation model was established.Actinobacteria,Alphaproteobacteria and Betaproteobacteria are the key pho D and pqq Charboring microbial groups that drive the protected tomato soil P fractions changes.The abundance of pqq C gene and the composition of microbial community are the key ways to change the phosphorus content in soil of tomato plant.The reasons for the decrease of soil P availability were as follows: On the one hand,the limited expression of pqq C gene and the change of pqq C-harboring microorganisms community composition limited the dissolution of moderately labile inorganic P to labile inorganic P.Labile inorganic P could not be supplemented and its content decreased.On the other hand,the accumulation of soil labile and moderately labile organic P decreased soil P availability.The main reason of soil labile and moderately labile organic P accumulation is not the decrease of organic P mineralization caused by the decline of phosphatase(pho D gene coding)activity,but the increase of microbial biomass P. |
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