Effects Of Carbon Input Changes On Soil Phosphorus Fractions In Larix Principis-rupprechtii Plantation Under Different Management Measures

Phosphorus(P)is one of the important elements for plant growth.Soil phosphorus is the main phosphorus source for plant uptake,and plays an important role in maintaining the stability of ecosystem functions.In the process of forest management,the biogeochemical cycle of forest ecosystems will be disrupted,resulting in carbon inputs changes from aboveground and underground,thus affecting the availability of soil phosphorus.In recent years,many reports have been reported that temperate forest ecosystems are limited by soil phosphorus.Understanding the effects of forest management practices(e.g.,thinning)on soil phosphorus fractions is important for sustainable development in forest ecosystems.In this study,We conducted a Detritus Input and Removal Treatments(DIRT)experiment in plantations of Larix principis-rupprechtii in Taiyue Mountain,Shanxi,China(i.e control,CK;exclusion litter,NL;addition litter,DL;exclusion litter and roots,NRL),a modified Hedley phosphorus fractionation method was used to sequentially extract soil samples and investigate the characteristics of soil phosphorus fractions with different thinning intensities(control,T0;Low thinning,T15;Moderate thinning,T35;Heavy thinning,T50),different forest ages(young forest,15years,15a;middle-aged forest,15years,26a)and successive crops in a Larix principis-rupprechtii plantation and addressed its determining factors.The main conclusions are as follows:(1)Soil labile phosphorus(Resin-Pi,NaHC03-Pi and NaHC03-Po),soil microbial biomass phosphorus,and acid phosphatase activity increased first and then decreased with the increase of thinning intensity,and the maximum appeared in T35.DL treatment significantly increased the content soil labile phosphorus(Resin-Pi,NaHC03-Pi and NaHC03-Po),soil microbial biomass phosphorus,and acid phosphatase activity.The stable P phosphorus(HCl-Pi,concentrated HCl-Pi and concentrated HCl-Po)and residual phosphorus(Residual-P)were not affected by thinning or litter treatments.The redundancy analysis indicated that the changes in phosphorus fractions were mainly driven by soil microbial biomass phosphorus,acid phosphatase activity,and soil organic carbon in the surface soil of the Larix principis-rupprechtii plantation.The results suggested that moderate thinning and increased litter could significantly improve the activation of phosphorus in the surface soil of the Larix principis-rupprechtii plantation.(2)There were significant differences in soil phosphorus fraction,soil microbial biomass P and acid phosphatase activity between 15a and 26a of Larix principis-rupprechtii conifer and broad-leaved forest(P<0.05).Compared with the 15 a mixed forest,the content of soil labile P(Resin-Pi,NaHCO3-Pi,NaHCO3-Po)in the 26a mixed forest increased significantly,and the content of NaOH-Po in the 26a mixed forest decreased significantly(P<0.05).Compared with the CK treatment,DL treatment significantly increased the content of soil labile P(Resin-Pi,NaHCO3-Pi and NaHCO3-Po)and middle labile P(NaOH-Pi and NaOH-Po)(P<0.05).NL and NRL treatment significantly reduced the content of soil Resin-Pi,NaHC03-Pi,NaHCO3-Po,NaOH-Pi and NaOH-Po(P<0.05).There was no significant difference in stable P(dilute HCl-Pi,concentrated HCl-Pi and concentrated HCl-Po)and residual P under different forest ages and litter treatments(P>0.05).The redundancy analysis indicated that the changes in P fractions were mainly driven by soil microbial biomass P,acid phosphatase activity,plant growth(average basal area)and organic carbon under different ages forests and litter treatments.(3)Soil total P content did not differ between the Larix principis-rupprechtii crop rotations in surface soil layers.Successive Larix principis-rupprechtii cultivation significantly reduced the contents of Resin-Pi,NaHCO3-Po,NaOH-Pi and NaOH-Po,but the content of stable P and Residual-P content were not sensitive to successive Larix principis-rupprechtii cultivation.Correlation analysis showed that soil organic carbon,soil moisture content,microbial biomass phosphorus and acid phosphatase activities were significantly correlated with soil phosphorus fractions(P<0.05).Our result highlighted that the decline of soil organic carbon,soil moisture content,soil microbial biomass and acid phosphatase activity after successive Larix principis-rupprechtii cultivation may be the reasons for the decrease of soil phosphorus availability.