Effects of stand density and site types on root characteristics of Platycladus orientalis plantations in Beijing mountainous area

Soil coring was applied to investigate the root characteristics of Platycladus orientalis plantations in Beijing mountainous area.Results showed that the stand density,site types and their interaction affected root production and root vertical distribution of planted P.orientalis stands obviously,and stand density was the most intensive factor to influence root characteristics.The root length density(P<0.05) and root surface area density(P<0.001) in surface soil layer increased with the increase of stand density,but this trend declined with soil layer going to deeper.The phenomenon of that,the proportion of root length density in diameter of <1 mm,the root surface area density and root volume density in diameter of <1 mm and 1-2 mm remarkably increased with the increase of stand density,indicated that P.orientalis plantations would forage limit soil resources by increasing fine root production when intraspecific competition occurred.The root length density and root surface area density were evidently declined with the improvement of site quality.But the differences of root length density and root surface area density among sites were weakened in the deeper soil layers.In general,the root length density and root surface area density were 20.4% and 20.9% higher in the site of sun-oriented aspect and shallow soil than those of the sun-oriented aspect site and deep soil.This phenomenon suggests that P.orientalis plantations take wider root absorption range as their strategy to implore the limited soil resources when trees growing in infertile sites.