Carbon Balance Of Tea Plantation Ecosystem In China

Plantations are expanding globally in recent decades at the expense of forest and other natural ecosystems and altering the original ecosystem functions. This conversion may alter the original carbon balance of the system, and the anthropogenic management of plantation system, such as fertilizer application, pruning, tillage and harvesting which change the carbon fluxes of the system may affect the regional carbon cycle.Tea is one of three beverages (coffee, tea and cocoa) in the world, and the plantations cover approximately 3 million hectares (about 3 million ha).In China, tea plantations occupies～50% of world's tea cultivating area (1.64 million ha) and has expanded 900% in past six decades.We divided tea plantation in China into these three producing zone:The western zone, the southern zone and the eastern zone. We sampled 45 plots from 15 sites from 12 provinces which are the main tea producing area (5 to 50 years old). A full carbon cycle approach was developed for this study to investigate the carbon balance of tea plantations supplanted from existing forests by measuring biomass production and net primary production (NPP) and estimating soil organic carbon from collected data. Based on the data from field investigations and the literature data, we estimated biomass, litterfall production, NPP and carbon storage in these three tea producing zone. Additionally, we compare the carbon sequestration and storage of tea plantation with that of adjacent forests and evaluate the contribution and impact of tea plantation expansion on regional carbon budget. The main results are summarized as follows:1) Vegetation carbon storage was 83.29 Tg in entire China tea plantation. For the tea plantation, the biomass carbon density in the three areas varied between 48.93 and 52.89 with a mean value of 50.90 Mg C ha-1 in China, and there were no significant differences among the areas (p>0.05), but lower than that of forest.2) Soil carbon storage was 235.47 Tg. Soil carbon density for three areas varied between 132.27 and 158.70 and with a mean value of 143.90 Mg C ha-1, and there were no significant differences among the areas (p>0.05). The soil carbon stocks in new constructed tea plantations could be gradually recovered at an annually rate of 0.68 Mg C ha-1. After 42 years the soil carbon could be restored to the original level of the forest. At present, the average rotation length was 35-year, the average carbon density was lower than that of adjacent forests. Therefore, in tea cultivation management, it is not desirable to frequently renew tea plantations. Under the prerequisite of guarantee economic income, we should elongate the rotation length as long as possible.3) The NPP (9.56 Mg C ha-1 yr-1) of tea plantations in access of five years in age was greater than adjacent evergreen broadleaved forests of similar age (from eight to 50 years old) by a magnitude of two (4.18 Mg C ha-1 yr-1). High tea stand density (from 24,000 to 67,000 plants ha-1), intensive pruning, and fertilization are the primary reasons for the elevated NPP found in tea plantations.4) Total carbon density (including soil, biomass and litter layer) for three areas in China was varied between 185.98 and 217.10 Mg C ha-1 with the average mean values of 199.72 Mg C ha-1, and 326.80 Tg C in entire China. This study found that 72.87% of the carbon stored in the soil,24.51% in the vegetation and 2.62% in the litter layer. Soil carbon accounted for a large proportion of the total carbon stocks of the ecosystem carbon budget in Chinese tea plantation.5) The NEP of tea plantation still keeps positive (i.e. tea plantation is a carbon sink), because large amount of prunings and litters returned to soil can more than counterbalance for the organic carbon loss, which lead to net carbon accumulation. The high NPP and heterotrophic respiration indicated that tea plantation ecosystems were high carbon flux systems, which have higher carbon inputs and outputs compared with the forests in the similar regions. Although the total tea plantation area is only 1.19% of forested area and 0.49% of grassland area, its total net ecosystem production (NEP) accounts for 3.56% of forested area and 26.31% of grassland area. That is, the mean NEP of tea plantation is 3 and 50 times of that of forests (0.7 Mg C ha-1) and grasslands (0.04 Mg C ha-1) in China, respectively. This indicates that tea plantations in themselves possess considerable economic advantages while also acting as carbon sinks. The contribution of tea plantations to the regional carbon balance must be investigated further in light of their overwhelming potential benefits.6) Based on the analysis of tea plantation systems, it has recently been suggested that a win-win situation exists for carbon balance and economic performance.