Carbon Storage And Its Allocation Of Rubber Plantation In Xishuangbanna, Southwest China

Forests play an important role in the global carbon cycle, because they store large quantities of carbon in vegetation and soil as well as exchange carbon with atmosphere through photosynthsis and respiration. It is of theoretically importance to understand carbon storage in forest ecosystems.Rubber plantation is one of the main forest types in Xishuangbanna, southwest China. However, there is little information available on carbon storage dynamics and allocation in the rubber plantation with different stand ages. In order to asses the allocation of biomass, carbon storage and its dynamics with different stand ages,15 plots were established at 5 different stand ages, there were 3 repeat plots in each stand age. Regression models relating tree biomass to DBH (diameter at breast height,1.3 m) and height were developed to estimate the tree biomasses. Carbon concentration of different rubber organs and soil layers were analyzed by the Biogeochemical Laboratory in XTBG. The carbon storage of rubber trees and soil were studied based on the biomass data and the carbon concentration data.The results and conclusions were drawn as follows:1. Biomass regression models of tree relating to its DBH (diameter at breast height,1.3 m) and height were developed and a power-law allometric relationship of the form W= a Db and W=a (D2 H)b were used to estimate the tree biomass, where W is the biomass of a species (kilogram for leaves, branches, stems or roots); a and b are constants; D is the DBH (cm); H is the tree height(m). the correlation coefficient of these two models were in 0.928～0.990 (p< 0.001). The two models both can be used to assess the biomass of rubber plantation. The tree height is not very useful in increase the precision of biomass estimation.2. The rubber plantation biomass included trees and litterfall biomass. Total biomass of 7-,13-,19-,25- and 47-year-old rubber plantation was 26.72 t·hm-2, 71.63 t·hm-2,155.62 t·hm-2,176.86 t·hm-2 and 255.91 t·hm-2, respectively. The biomass of trees accounted for the greatest proportions, which was 89.75% of the total in 7-year-stand,93.40% in 13-years-tand,96.63% in 19-year-stand,96.76% in 25-year-stand and 97.77% in 47-year-stand. The allocation of biomass to different organs followed different orders with different stand ages.7-,13- and 19-year-old rubber plantation followed the order:stems> roots> branches> leaves, however, the 25- and 47-year-old rubber plantation showed the other order: stems> branches> roots> leaves. The litterfall biomass account for less than 11% of the total biomass, and decreased from 10.25% in the 7-year-stand to 2.23% in the 47-year-stand. The litterfall biomass of 7-,13-,19-,25- and 47-year-old rubber plantation were 2.74 t·hm-2,4.72 t·hm-2,5.25 t·hm-2,5.74t·hm-2 and 5.70 t·hm-2, respectively.3. The carbon concentrations varied largely among different rubber organs. They followed the decreasing order: leaves> branches> stems> roots, the mean carbon concentration was 511.83 g·kg-1 in leaves,483.51 g·kg-1 in branches,482.73 g·kg-1 in stems and 467.27 g·kg-1 in roots. The soil carbon concentration decreased with soil depths in rubber plantation with different stand age. The soil carbon concentration of 0～10 cm increased continually before 25- year-old rubber plantation and decreased after that. The mean soil carbon concentration decreased with stand age, which was 20.22 g·kg-1 in 7-year-stand,19.29 g·kg-1 in 13-year-stand,19.89 g·kg-1 in 19-year-stand,18.70 g·kg-1 in 25-year-stand and 10.20 g·kg-1 in 47-year-stand.4. The carbon storage of rubber trees was increased with stand age. Trees carbon storage of 7-,13-,19-,25- and 47-year-old rubber plantation were 11.76 t·hm-2, 32.34 t·hm-2,71.70 t·hm-2,84.94 t·hm-2 and 121.33 t·hm-2, respectively. The stem made up over 50% of trees carbon storage and increases with stand age. The allocation of carbon storage to different tree organs followed the order:stems> roots > branches> leaves in 7-,13- and 19-year-old rubber plantation, and followed the order:stems> branches> roots> leaves in 25- and 47-year-old rubber plantation.5. The soil carbon storage of 7-,13-,19-,25- and 47-year -old rubber plantation was 251.65 t·hm-2,230.35 t·hm-2,246.14 t·hm-2,223.87 t·hm-2 and 129.17 t·hm-2, respectively. The carbon storage was highest on the top 10 cm soil layer and decreased with soil depths, most of the soil carbon storage were in the top 40 cm soil layer.6. The carbon storage of rubber plantation was composed of living plant carbon storage, litterfall carbon storage and soil carbon storage. The total carbon storage of 7-, 13-,19-,25- and 47-year-old rubber plantation were 262.89 t·hm-2,261.30 t·hm-2, 315.33 t·hm-2,306.50 t·hm-2 and 256.02 t·hm-2, respectively. The proportion of plant carbon storage and litterfall carbon storage increased with stand age, conversely, and that of the soil carbon storage decreased with stand age.