ObjectiveBy studying the vegetation biomass and root characteristics through the field investigation and laboratory tests, the study can provide scientific basis for the selection of afforestation tree species and the restoration of vegetation in Beijing soil stone mountain area.

Method Regarding the chronosequence of Pinus tabuliformis plantation (35, 40 and 57 years old) and Platycladus orientalis plantation (20, 40, 57 and 100 years old), which located at the Hongmengchuan Catchment in the northeast of Miyun County of Beijing, using full mow and drying method hold the undergrowth plant biomass, using the root auger drilling core, which will be back to the indoor soil core samples, the water immersion, rinse clean, using a magnifying glass, scissors, tweezers and other tools manual pick out root system, analyzing the characteristic of the root system, this study researched the distribution characteristics and influencing factors of roots under different plantations.

ResultThe results showed that: the mean root biomass differed significantly among the natural shrub, Pinus tabuliformis and Platycladus orientalis plantation, the highest ((6.84±1.35) t/ha) root biomass was found in natural shrub land, followed by Platycladus orientalis plantation ((4.65±0.90) t/ha), and Pinus tabuliformis plantation ((3.33±0.93) t/ha), the root biomass showed the same regularity in different soil layers in varied forestlands. Root length density, root surface area density decreased gradually with diameter increased, 0-0.1 mm diameter root was most widely distributed in forestland, followed by 0.1-0.2 mm diameter root. Different diameter root length density, root surface area density and root biomass decreased with the increasing stand age in Platycladus orientalis and Pinus tabuliformis forest, but they were significantly lower than nature shrub. The aspect had an important impact on root biomass, root biomass of half shady slope was significantly higher than that of sunny slope and shady slope (P < 0.05). Root length density and root surface area density had a significant negative correlation with sand content (P < 0.05), 0-0.1 mm and 0.2-0.5 mm diameter root were particularly evident; root biomass also had a significant negative correlation with soil bulk density (P < 0.05), especially 0.2-0.5 mm diameter root.

Conclusion The study revealed the root characteristics and their influencing factors and the results indicate that the selection of afforestation tree in soil and stone mountain should not only refer to local environmental conditions and soil characteristics, but also consider the growth characteristics of afforestation tree.