Abstract:

The concentration, accumulation, spatial distribution and bioloigcal cycling of 7 microelements (Fe, Cu, Zn, Mn,Pb, Ni and Cd) as well as their changes with growth of stands in Pinus massoniana plantation of 4 different age classes were studied. The results showed that concentration of Fe was the highest among 7 microelements, followed by Mn and that of Cd was the lowest in the soil. Irespetive of age classes, microelements concentration decreased with increasing of the soil depth. Microelements of Fe, Cu, Zn, Mn, Pb and Ni had a higher rate of decomposition than element of Cd in the litter floor. The order of microelements concentration in different organs of Masson Pine was as follow: root>Needle>branch>bark>stem. Regardless of organs, concentrations of 7 microelements was in the order of Fe>Mn>Zn>Cu>Pb>Ni>Cd, and concentrations of Pb and Cd in root were higher than those in other organs. Microelements concentration varied remarkedly with the stands growth, especially for Fe element. The total storage of microelements in the plantations ranged from 8.818 kg·hm^-2 to 103 825 kg·hm^-2 and increased with the biomass accumulation in the process of the stands growth. The storage in bark and stem was the highest and accounted for 40% to 46%. The annual absorption of microelements in 4 age classes plantations were 3. 846, 12.558, 18.753 and 13.234 kg·hm^-2, respectively. The annual returns equaled to 2.733, 9.866, 14. 866 and 9.935 kg·hm^-2, respectively. The annual retention were 1.113, 2.692, 3.887 and 3.299 kg·hm^-2, respectively. The microelement utilization coefficient, cycling coefficient and recycling period were estimated to be 0.127～0 436, 0.711～0 793 and 3.226～10.450 In early stage stands, microelement use efficiency in Masson Pine plantation was lower but recycling rate was higher and turnover period was shorter. Mature stands had a lower microelement recycling rate and a longer turnover period, so the trees extract more microelement from soil. Hence measures should be taken to faciltate the successional process to reach a stable zonal community.

Key words: Masson Pine plantation, Age classes, Microelement, Biological cycling