Effects Of Pinus Sylvestris Var. Mongolica Forest On Soil Fertility And Plant Community Species Diversity In Yulin Sand Area

Pinus sylvestris var. mongolica forest，which resistants to drought and barren, is one ofthe most important sand-fixation tree species in Yulin sand area. For the purpose of revealingthe effect of P. sylvestris var. mongolica forest on soil fertility and its plant communityspecies diversity, with investigation, sampling in the field and inside analysis, this paper tookP. sylvestris var. mongolica of different stand ages in Yulin sand area as study objects,researched on soil physical properties, chemical properties, enzymatic activities, plant speciesrichness and soil fertility. The main conclusions are as follows:(1) Bulk density(BD) in0～20soil layers were higer than that in20～40cm, whiletotal porosity (TP)were in an order of0～20cm>20～40cm. Compared with drift sand, thegrowth of Pinus sylvestris var. mongolica can reduce BD and improve TP in two soil layerssignificantly. With stand age increasing, BD of five woodlands in two soil layers firstlyincreased then decreased, while the variation trends of TP were opposite to BD.(2) pH in0～20cm was mostly higher than that in20～40cm, however, soilorganicmatter(SOM), available nitrogen(AN), available phosphorus(AP) and available kalium(AK)(except for drift land) of six sample plots were in an order of0～20cm>20～40cm. pH ofsix sample plots, most of which in two soil layers had no significant difference, wasalkalescence. pH of two soil layers performed fluctuating trends as stand age increasing.Compared with drift sand, most of SOM and AK content of five woodlands in two soil layerswere significantly increased and decreased, respectively. The content of AN in0～20cmmostly significantly lower than that in drift sand land, while, most of AP content in the samesoil layer had no significant difference. The content of AN and AP of all woodlands in20～40cm were lower than that in drift lands. Except for SOM and AK in0～20cm added asstand age increasing, soil nutrient in other layers performed volatility trends.(3) The activities of invertase, urease, catalase and alkaline phosphatase of fivewoodlands in two soil layers were in an order of0～20cm>20～40cm. Invertase activities inall woodlans were higher than that in drift sand. The growth of P. sylvestris var. mongolicawas limited in improving the urease activities, and most of which in20～40cm showednegative growth. Compared with drift sand, alkaline phosphatase activities and catalase activities in0～20cm increased significantly, while catalase activities of20～40cm mostlyhad no significant difference, but most of alkaline phosphatase activities were higher thandrift sand. As the growth of P. sylvestris var. mongolica, the activities of four enzymesperformed volatility trends.（4）AN and AP play dominant roles in modulating the activities of invertase andphosphatase, however, SOM has strong indirect effects on these two enzyme activities. SOMis the main factor of catalase activity. Both of pH and AK are not the main factors of soilenzyme activities. The direct impacts of five soil chemical properties upon urease activity arelargely minimized by the indirect effects.(5) With single species composition, P. sylvestris var. mongolica community wascomposed of17vascular plants, which belonged to8families and15genuses. With stand ageincreasing, Margalef index and Shannon-Wienner index firstly increased followed bydecreasing then increased again, however, Pielou index showed a volatility trend. RDAanalysis showed that Margalef index, Shannon-Wienner index and Pielou index had largercorrelation indexes with nutrient contents than that with soil physical properties. SOM wasthe most important nutrient factor of species diversity. The better habitat conditions, thehigher species richness. Margalef index and Shannon-Wienner index had close relations withcatalase and invertase activities, and pH had larger influence on Margalef index.(6) TP, SOM, AN, AP and invertas activities were chose as the soil fertility indicators ofstudy area. Compared with drift sand, integrated fertility index（IIF）, the variation range ofwhich was0.4434~0.5164, increased by6.21%~23.69%. On the basis of IIFtransformationlaw, soil fertility increased in7to15years and20to32years, and decreased in15to20years, while overall, it performed an increasing trend.