Distribution Of Organic Phosphorus Associated With Aggregate In Soil From Cold Temperate Forest

As the basic component of soil structure,soil aggregates directly affect the interface process and behavior of elements in soil.The dynamics and availability of soil phosphorus pool are significantly related to the fractions and behavior of organic phosphorus(OP)in aggregates.The Greater Khingan area is the only cold temperate forest in China.The characteristics of soil OP in the Greater Khingan area is an indispensable part to compare the environmental behavior in different types of forest soil.In this work,the soil samples were classified by different thinning intensity,different restoration ages after severe forest fire and different geographical locations were collected from the Greater Khingan area.According to the stability of carbon pool,soil aggregates in different particle sizes(4 sizes and 7 fractions)were obtained by wet sieving method,and the distribution of OP fractions associated with soil and aggregates in the Greater Khingan area were extracted by the sequential extraction.Further 31P-NMR were also used to analyze the differences of OP compounds in soil and aggregates under different environments.The key driving mechanism of OP redistribution in soil aggregates under different conditions by varied protective effect of aggregates were discussed.This work was of great significance to understand the environmental geochemical cycle and ecological effects of OP in cold temperate forest,and to enrich the protection mechanism of different types of forest soil aggregates on OP.The main results and conclusions were as follows:1.The fraction of 250?2000 ?m was the predominant fractions accounting for 43% of the total soil mass in the Greater Khingan area.The distribution of OP in different aggregates(cPOM,LF,iPOM,dSilt,?Silt,dClay and ?Clay)in the three types of soil samples presented significant grain-size effects.2.The distribution of soil OP pool was as follows: Moderately Labile Organic Phosphorus(MLOP)> Nonlabile Organic Phosphorus(NLOP)>Labile Organic Phosphorus(LOP).Fulvic Acid OP(FA-OP)and Residual OP(Re-OP)were the dominant fractions of TOP.3.The aggregate stability was the strongest with thinning intensity at10% and the weakest with thinning intensity at 30%;in the burned area,the aggregate stability had a positive correlation with the restoration ages;the soil structure stability in the middle altitude(450?590 m)was higher than that in high altitude(605?1090 m)and low altitude(230?438 m).The changing trend of OP concentration was similar to that of structure stability,indicating that the soil OP distribution in the forest was affected by the stability of soil structure,and the stronger the stability was,the higher the OP content was.4.The results of the RDA and structural equation model indicated that the increasing of restoration ages led to the increase of OP concentration,by increasing TOC concentration and crown density;the increase of altitude led to the increase of litter depth,the decrease of pH and the increase of TOC concentration,and the increasing concentration of TOP in soil.It was the joint effects of the above factors influencing the characteristic of OP in the Greater Khingan area.5.The positive correlation between TOC and TOP suggested aggregates had protective effect on soil TOP.The order of protection intensity was as follows: physical-chemical-biochemically protection >chemically protection > physically protection > non-protection.6.31P-NMR results showed that orthophosphate monoester the dominated compound of OP in forest soil from the Greater Khingan area.The fraction extracted by NaOH-EDTA was the highest in the aggregates with unprotected mechanism(250?2000 ?m),indicating that the potential of macroaggregates to supply phosphorus were relative higher.