Effects Of Coastal Reclamation On Soil Enzymes

With the rapid development of economy and urbanization,land demand increase,reclamation development become an important way for costal regional to access land,this makes good for alleviating the shortage of land resources and the problem of human land contradiction,in the new period,the coastal development strategy is put forward,which will inevitably lead to a new round of development upsurge of reclamation.As a big province with rich tidal flat resources,Jiangsu has a long history of reclamation,the reclamation of which is mainly oriented by agricultural land use,how the soil quality changes after reclamation is worth studying.As an index which indicates microbial activity,soil enzyme takes part in all the biochemical processes of the soil system,and has close relationship with soil fertility;research on soil enzyme activity is helpful to understand nutrient cycling of C,N and P in soil ecosystem.This paper selects the barren wetland and four typical type of reclamation in Rudong County,Jiangsu Province as study objects to study the process that soil physicochemical properties and enzyme activity change on a long time scale,the distribution rule of soil enzyme activity in soil profile,and the response of soil enzyme activity to different land use patterns,to explore the key factor influencing soil enzyme activity,in order to provide reference for later scientific research and the development and utilization of tidal flat,we get the following main conclusions:(1)With the increase of reclamation years,the physical and chemical environment of soil improved gradually as well,showed mainly the decrease of soil alkalinity and the increase of soil nutrient(TN,TP,SOC).The improvement of the physical and chemical properties of soil can be divided into the following four stages:A sharp drop of soil salinity in the preceding 10 years,changed from inshore saline soil to moderate saline soil,and the soil nutrient content promoted a level rapidly;in 10-30 reclamation years,soil salinity dropped continuously,changed from moderate saline soil to non-saline soil,the soil desalinate completely,the soil nutrient content promoted a level continuously,but the rate of soil salinity decrease and the improvement level of soil nutrient are both below the first 10 years of reclamation;in 30-40 reclamation years,the soil physical and chemical properties improves a little,but not obvious,in a relatively stable state;in 40-60 reclamation years,the soil nutrient content improved a level continuously.Overall,the improvement of soil physical and chemical properties experienced a stage from a sharp boost?quick promotion?relatively stable?slow ascension.(2)This paper studies the changes of superficial soil enzyme activity under different reclamation years,the result shows that with the increase of reclamation years,the superficial soil urease,acid phosphatase and alkaline phosphatase activity increased gradually,the change rule of which corresponds to that of soil physical and chemical properties,that is,sharp increase in the first 10 reclamation years?rapid increase in 10-30 reclamation years?relatively stable in 30-40 reclamation years?slow raise in 40-60 reclamation years.Soil enzyme activity can be influenced only at the beginning of reclamation,when soil environmental conditions changed dramatically,with the gradually improvement and stabilization of soil physical and chemical properties,the reaction of amylase activity is not sensitive,and the influence of reclamation to it is not obvious.Soil dehydrogenase is in a sharp boost phase in the first 10 reclamation years,but the rate slows down in 10-30 reclamation years.The alkaline phosphatase activity is higher than the activity of acid phosphatase in different reclamation area of this study zone,approximately 2-3 times of the acid phosphatase content,the reason is that the alkalescent soil of the reclamation zone gives full play of alkaline phosphatase activity in favor.(3)Soil enzyme activity reduce gradually with the depth increase of the section,in 10-30cm layer,the enzyme activity dropped significantly,in 30-60cm layer,the difference of enzyme activity is not obvious.Coefficient of variation analysis shows that the change rule of soil enzyme in profile generally performs as following:10 years reclamation>mudflats>30 years reclamation>40 years reclamation>60 years reclamation,the sectional enzyme changes most severely in 10 reclamation years,with the increase of reclamation years,the changes of profile enzyme tend to be more uniform and stable.The difference is that soil dehydrogenase is uniformly distributed in mudflats,this may be linked to the fact that the soil is in a long reducing state when tidal flats are submerged under water for a long time.The change rule of soil enzyme activity in the same soil depth but different reclamation years generally performs as following:60 years reclamation>40 years reclamation>30 years reclamation>10 years reclamation>non-reclamation,the same as that the surface enzyme activity changes with times.(4)Under different land use ways,the soil enzyme activity of wheat,rape,bean in farmland ecosystem has little differences,the soil enzyme activity of bean is a little higher than that of wheat,which makes important affect though the process that N,P nutrient elements transform and circulate effectively in the farmland soil ecosystem.The soil moisture content and salt in farmed fish ponds are significantly higher than that in farmland ecosystem;the soil nutrient content has little difference with which in farmland ecosystem,however,the soil enzyme activity of soil dehydrogenase,urease,and acid phosphatase is significantly higher than that in farmland ecosystem,this may be related to different microbial community structure under water system,and this illustrates that the landuse way of farmed fish ponds has best tolerance degree to coastal soil salinization.(5)The study about the vertical distribution of soil enzyme activity under different land utilization way shows that with the increase of soil depth,the enzyme activity of wheat,broad bean and soil will decrease,the most pronounced part of which the soil enzyme activity declines is 10-3 0cm depth,the soil enzyme activity of depth 30-60cm has a rather small change.The profile distributions rule of fishponds soil enzyme activity is different;it declines as an s-shaped type with the increase of soil depth,a downward trend on layer 10-20cm,the enzyme activity increases on layer 20-30cm and 30-40cm,and sharply decreases on layer 40-60cm,this is connected with the rich humus on black peat soil layer of 30-40cm.(6)The research of path coefficient analysis indicate that the key factor which has an influence on soil urease is soil organic carbon,other factors which have effect on urease achieve their impact by influencing the formation and accumulation of soil organic carbon.The main limiting factors in the study area are pH and salt,the ascension of soil organic carbon and improvement of salinization are both important reasons which make an increase of urease activity.The key factor affecting acid phosphatase activity of soil physical and chemical properties is pH,major nutrient factor TN makes its.promotion for acidic phosphatase by weakening the inhibitory effect of pH,the stress effect of salt and pH together on acid phosphatase is a factor which cannot be ignored.The important factor influence soil alkaline phosphatase activity is TN;on the one hand,TN directly affects the activity of soil alkaline phosphatase,on the other hand,the other key limiting factors such as pH and salt which inhibit alkaline phosphatase work by affecting the content of TN.Thus increase soil TN content in the study area is the key to increase soil alkaline phosphatase.The key physical and chemical factor which affects soil dehydrogenase activity is soil organic carbon,the increase of organic carbon content can directly promote the activity of dehydrogenase;soil moisture content and TN content are important factors to improve the activity of amylase;soil salinity is a key limiting factors inhibiting the activity of amylase.To sum up,elevated levels of soil organic carbon and total nitrogen and improvement of salinity is key to promoting the soil enzyme activity in reclamation zone.