Dynamic assessments of plant biomass and carbon storage during the production cycle of tea gardens

Abstract

Tea(Camellia sinensis)is a kind of evergreen shrub or tree,which has been widely planted as an important economic crop in mountainous tropical and subtropical regions of China.Tea gardens are considered both ecologically friendly and economically profitable due to their high plant standing biomass and important role in soil and water conservations.Though it is recognized that the carbon sequestration potential should be huge in the plant and soil of tea gardens,few researches have been carried to quantify their carbon storage and balance.In the tea producing regions of China,tea garden area occupies a large proportion of the total forest area(e.g.3.1% in Zhejiang Province).Tea gardens might play an important role in the carbon sink of forest ecosystems in those areas.Based on publications between 1950 and 2011 on tea plant growth in China,regression models on the relationship between tea stand biomass and tea plant age or tea yield were established to find out how its carbon storage capacity changes and how much its carbon storage capacity can achieve during aproduction cycle of a common double-row tea garden.An exponential growth model was established between tea plant aboveground biomass(Ba)and its age(t):Ba =-14.95+56.3×(1-e-0.27t).Modeling results showed that tea biomass increased rapidly during the first 10 years and then slowly after the first 15years.Carbon(C)mass of 10 and 15year-old tea plants was 92% and 98% of that(30.6t/m2)of 25 year-old tea plants respectively.Carbon accumulation rate was(4.5±0.4)t/(hm2·a) for tea plants of 1-4year-old and was(0.95±0.05)t/(hm2·a)for those of 5-15year-old.When the shoot/root biomass ratio ranged from 1.68 to 2.34,the C mass of 15-year-old tea plants ranged from 31.31 to 28.02t/hm2.A model for C storage in tea garden was set up based on potential photosynthetic productivity of tea plants and tea yield,thus C storage capacity of tea plants in various tea production regions was estimated.With an efficiency of solaremergy utilization of 0.5% currently,the corresponding total C storage was amount to(9.1±1.4)t/hm2 in the tea gardens of China.As for 15-year-old tea plants,the C mass of 60t/hm2 given by the exponential model was close to the theoretical value(56.41t/hm2)with an efficiency of solar emergy utilization of 2%,and the C mass could be up to 70.5t/hm2 in tea gardens if tea yield was increased.In a word,it is important to quantify the carbon stock through modeling on the changes of biomass C accumulation with tea plant age rather than based on limited field sampling data.It is also noted that plant C pool of tea gardens is one of main agroforestry C pools in tea production regions and tea garden has a high plant C sequestration potential in China.