Abstract:

Root biomasses, of average individual tree, and in rhizosphere between rows in 20-year-old Pinus massoniana forests with five different planting densities were measured by total root excavating and soil auger methods. The results showed that total root biomass of the average individual tree decreased with increasing planting density. Biomasses of different root diameter classes ranked as root stake > thick-root > large-root > medium-root > small-root, among which root stake and thick-root accounted for more 90% of total root biomass. Root Biomass of different diameter classes in rhizosphere between rows ranked as medium-root >fine-root >small-root. The effect of planting density on biomass decreased gradually from medium-root, small-root to fine-root. Under the five planting densities, major roots distributed in 0-30 cm upper soil, accounted for more than 82% of total root biomass. Root biomass in rhizosphere between rows decreased with increased soil depth in all planting densities. Mathematic models showed that root biomasses of different classes of average individual tree were correlated to stand average breast diameter, average height and planting density. The correlation coefficients were all above 0.8 except for small-root. The root biomass of different classes in rhizosphere between rows was also correlated to planting density.

Key words: Pinus massoniana, plantation, planting density, root biomass, distribution pattern