| The intensity of nutrient substance metabolism in pond mud will affect the nutrients supply to overlying water and the decomposition of residual feeds and fecal matter at the bottom of the pond,which will affect the aquaculture production further.Pond mud enzymes,which are a kind of extracellular secretions of microorganisms in pond mud,can decompose and mineralize the macromolecule organic matter in the pond mud and promote the transportation of the nutrients to the water body.Their activities can reflect the ability of pond mud to metabolize nutrient substance.However,the activities of pond mud enzymes were influenced by the nutritional status and physicochemical properties of pond mud.Different purple soils are developed from different parent material,so they have different nutritional status and physicochemical properties,which may affect the enzyme activity of pond mud and even impact the fishery when the purple soil as pond mud.Based on above,four kinds of typical purple soils(Jiaguan group(S1),Shaximiao group(S2),Penglai town group(S3)and Suining group(S4))were used to analog study the changes and correlation of the enzyme activity and the physicochemical properties of pond mud,which under the conditions of soil submerged(S1,S2,S3,S4)and soil submerged with fish feeding in the overlying water(CS1,CS2,CS3,CS4)respectively.This study has been aimed to find out the key factors that limit the enzyme activity of purple soil pond mud,and provide a basis for the evaluation of "fishery feasiblity" in the purple soil area.The results are as follows:(1)The content of major elements(N+P+K+Ca+Mg+S)in four groups was: S4 > S3 > S2 > S1,while microelements(Fe+Zn+Mn+Cu+B)was: S2 > S4 > S1 > S3.The contents of organic matter,available nitrogen,available phosphorus,available potassium,total nitrogen,total phosphorus and calcium in S1 were significantly lower than in S2,S4 and S3,respectively.Whereas the content of total potassium of S1 was significantly higher than of S2,S4 and S3.The activity of alkaline phosphatase in S1 was the lowest,and there was no significant difference among S2,S4 and S3.The activity of sucrase was significantly different in the four groups,which S1 was the highest and S4 lowest.The urease activity was significantly different as well,the highest in S3,and the lowest in S1.The difference of alkaline protease activity was significant,the highest in S4,and lowest in S2.The activity of catalase was significantly different,which S1 was the lowest while S2 and S3 were higher.(2)After water overlying,the physicochemical properties and the enzymatic activity of the four purple soil ponds vary depending on the soil type.The pH of S2,S3 and S4 were approaching to neutral,while there was no significant change in S1.During the experiment period,the contents of organic matter,total nitrogen,total phosphorus,available phosphorus and calcium in S2,S3,S4 were significantly higher than those in S1 but total potassium content was significantly lower than S1.The catalase and alkaline phosphatase activity in S1 were significantly lower than the other three groups.The results indicated that the pond mud qualities and nutrient status after water overflying were mainly affected by the original soil properties and nutrients.The results of redundant analysis showed that the importance of influence factors,except total nitrogen,on the pond mud enzyme activities was as follows: available phosphorus>pH>available potassium>organic matter>calcium>available nitrogen>total potassium>total phosphorus.The available P and pH were very significantly correlated with the pond mud enzyme activity(P < 0.01),and the available potassium and organic matter were significantly correlated with pond mud enzyme activity(P<0.05).S1 contributed less to the nutrient of overlying water becacuse it has a low background value in its pH,available phosphorus,available potassium and organic matter,which affects the pond mud enzyme activity.(3)After feeding fish,the contents of nutrient in the 4 groups were increased to diffirent level compared with the original soil samples.The pH of all groups gradually approached to neutral.During the experiment,CS2 the organic matter content in CS2 was significantly higher than than in CS1.And the content of total phosphorus in CS3 was significantly higher than that in CS1.The content of calcium in CS1 was significantly higher than that in CS2,CS3 and CS4.Other nutrients content were not significantly different increased with time.The results indicated that the contribution of residual feeds and feces to pond mud nutrient was greater than that of soil background nutrient after feeding fish.As time increasing,the catalase and alkaline phosphatase activities in CS2 and CS3 were significantly higher than those in CS1,and the urease activitiy was significantly higher than CS4.CS3 sucrosease activity was significantly higher than that in CS1,CS2 and CS4.The enzyme activities in CS1 were higher after feeding fish compared to the only water overlying condition,but they were still lower than those in the other groups.Moreover,the content of organic matters in CS1 was higher than that in other groups.The results of redundancy analysis showed that the importance effect of environmental factors on the anzyme ctivity of pond mud was as follows:pH>total nitrogen>total potassium>calcium>available phosphorus>organic matter>available potassium>available nitrogen.The pH was very significantly correlated with the pond mud enzyme activity.Total nitrogen,total potassium and calcium contents were significantly correlated with pond mud enzyme activity.There was no significant correlation between the other factors and pond mud enzyme activity. |
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