Abstract:

Robinia pseudoacacia is one of the major planting tree species in the Shaanxi Loess Plateau.Changwu county and Ansai County lie in the semihumid and semiarid region of the area,respectively.In this paper,the fine root vertical distributions of R.pseudoacacia growing at the two counties were studied,using soil auger method.The results showed that the fine root vertical distribution had distinct differences in these two regions.The mean depth of fine root vertical distribution was 250 cm in Ansai County,and only 200 cm in Changwu County.The average fine root surface area(cm²·dm^-3)on shady and sunny slope of Ansai County was 5.06 and 8.29 times over the value of Changwu County,respectively.Both on shady and sunny slope of the two counties,the maximum value of fine root surface area presented soil surface(0～20 cm)and then decrease slowly in Ansai County.However,the maximum value appeared on 60 cm in Changwu County.About 80 percent fine root of R.pseudoacacia distributed in 0～150 cm soil layer in Ansai County,and in 0～100 cm in Changwu County.In addition,the fine root was richer on shady slope than sunny slope both in Ansai and Changwu County.The fine root vertical distribution characteristics was significantly related to soil water,which was a key factor to influence fine root distribution.The model S=Ah^B(C+Dh+Eh²+Fh³)can well described R.pseudoacacia's fine root vertical distribution in these two regions,the fit decide coefficient(R²)more than 0.94 in Ansai and more than 0.80 in Changwu County.The research of R.pseudoacacia's fine root vertical distribution under different soil water environment will help to further explore the relationship between fine root system and soil water and the reason of soil drification in the Leoss Plateau.

Key words: Leoss Plateau, Robinia pseudoacacia, fine root surface area, fine root vertical distribution, model