Responses Of Soil Phosphorus Fractionation And Availability To Throughfall Manipulation In A Planted Robinia Pseudoacacia Forest On Loess Plateau

Precipitation is changing with climate change and affects the nutrient cycling of terrestrial ecosystems despite large cross-regional differences.To date,there are no reports on how manipulated throughfall influences soil phosphorus fractionation in planted forest ecosystems on Loess Plateau,a highland area in northern and central China.My study investigated the responses of soil total and available phosphorus,the fractionation of phosphorus and alkaline phosphatase activity via a manipulative throughfall experiment.This thesis aimed to explore how soil phosphorus responded to changing precipitation in a planted Robinia pseudoacacia forest on Loess Plateau.The primary results were listed bellow:?1?The soil total phosphorus in the study area was 547-750 mg kg^-1,and the average available phosphorus accounted for 0.597%of total phosphorus.The total inorganic and organic phosphorus and residual phosphorus accounted for 71.6,15.8 and 12.6%of total extracted phosphorus,respectively.Manipulated throughfall didn't significantly affect soil total phosphorus or total organic phosphorus.However,it had a significant effect on soil available phosphorus.No significant correlations were found among soil total phosphorus,inorganic phosphorus,soil moisture and pH.Available phosphorus was positively correlated with soil moisture but negatively correlated with pH.Changing throughfall affected soil available phosphorus likely due to its impacts on soil moisture and pH.Total phosphorus was found to be positively correlated with total inorganic phosphorus.There was a significant positive correlation between available phosphorus and total organic phosphorus in the 0-20cm layer.Organic phosphorus,a part of available phosphorus,was more abundant in the surface layer.?2?Soil Dil.HCl-P_i?67.4%?was the largest proportion of total inorganic phosphorus,while Conc.HCl-P_o?76.1%?was the largest proportion of total organic phosphorus.Throughfall manipulation significantly affected the contents of resin-P,NaHCO₃-Po,and NaHCO₃-Pi in 0-20 and 20-40 cm layers and NaOH-Po in 40-60 cm layer.However,the contents of NaOH-Pi,Dil.HCl-Pi,Conc.HCl-Pi,Conc.HCl-Po or residual-P was not significantly affected by changing throughfall.Both resin-P and NaHCO₃-Pi contents decreased at low throughfall and increased thereafter.There was no clear pattern of soil NaHCO₃-Po content with increasing throughfall,likely due to the increasing soil microbial biomass.NaOH-Po content declined with increasing throughfall which reduced the proportion of Dil.HCl-Pi in soil total phosphorus and increased the proportion of NaHCO₃-Po.In addition,there were negative correlations among Dil.HCl-Pi,resin-Pi and NaHCO₃-Pi.There was no correlation between HCl-Pi and available phosphorus.In contrast,significant correlations were found among the other phosphorus fractionations and available phosphorus.Because HCl-Pi in soil mainly includes Ca-P and apatite,the expression of the availability of them is very limited.?3?The phosphatase activity in rhizosphere soils ranged from 103 to 513 mg·kg·h^-1,and the phosphatase activity in non-rhizosphere soils ranged from 78.7 to 443 mg kg h^-1.Increased throughfall enhanced the phosphatase activities in rhizosphere soils of 0-20 and20-40 cm layers by 55.9 and 88.3%,respectively.Increased throughfall also enhanced the phosphatase activities in non-rhizosphere soils in 0-20 and 20-40 cm layers by 109 and121%,respectively.Increasing throughfall increased soil phosphatase activity.The response of phosphatase activity in non-rhizosphere soils to the increase of throughfall was stronger than that in rhizosphere soils.Soil phosphatase activity was positively correlated with soil moisture,organic phosphorus and the biomass of Rosaceae.These results indicated that changing throughfall affected soil phosphatase activity through its impacts on soil moisture,organic phosphorus and aboveground vegetation.Overall,the increase of precipitation tended to result in the loss of soil phosphorus,but this effect was not significant in my studied planted Robinia pseudoacacia forest on Loess Plateau,suggesting that soil total phosphorus was not mainly affected by short-term precipitation changes.In contrast,changing precipitation affected the content of phosphorus fractionation and their proportion of total phosphorus,the activity of phosphatase through its impact on soil moisture,microbial activity and aboveground vegetation.NaHCO₃-Po has the strongest response than the other phosphorus fractionation to precipitation change,with significant influence up to 60 cm layer.Changing precipitation affected soil phosphatase activity through its impact on the phosphorus fractionation.This study is of great significance to understand the effect of precipitation change on the availability of soil phosphorus and its influence mechanism in a planted Robinia pseudoacacia Forest on Loess Plateau.