The Leaching Characteristics Of Soil Organics Carbon In Tea Plantations

The carbon cycle of ecosystem is one of core content in climate change currently and regional sustainable development, it affects all aspects of economic and social development. Evaluating accurately leaching rule and quantifying carbon leaching fluxes of tea plantation ecosytem, are a difficute matter in the research of carbon balance and carbon cycle. Tea plantations as a ecosystem dominated by human, it has a extremely important significance to explore soil carbon content, carbon leaching rule and leaching flux, which benefit to reduce carbon emissions, increase storage of soil organic carbon and develope low carbon economy of tea plantation.We took soil samples from tea plantations of adjacent forests as a control,5 yr old,10 yr old,20 yr old,33 yr old, and 56 yr old (adjacent samples are grassland accompanied by a few trees)and as deep as 120 cm (each 20 cm is a soil layer) in the soil profile. The methods of undisturbed soil column leaching carbon simulation experiment and the carbon isotope tracer were used to study leaching fluxes of soil carbon, the rule of leaching in tea plantations, and traced the source of organic carbon in each soil layer. The mechanism of leaching was analyzed by measuring soil carbon isotope (513C), soil organic carbon content (SOC), soil bulk density (BD), soil pH, total nitrogen (TN) and ammonium nitrogen (NH4+-N), and contrasting the change rule of SOC and δ13C in the scales of space and time from different tea cultivation ages and different soil layers. The results showed that:(1)The SOC concentration and SOC density decreases with soil depth in tea plantations, total soil carbon density is 109.48 Mg C/ha in the layers of 0-120 cm.(2)After native forests are substituted by planted tea trees, SOC turned into a loss in the establish process, and SOC recoverable process was divided in two phases:when tea pantations were established among 10 years, soil organic carbon has a rapid recovery phase in the layer of 40-120 cm, however, organic carbon did not recover to carbon concentration level of adjacent forests in the same soil layer when tea plantations were established in 33 years; after planting 20 years, the recover and the accumulate of soil organic carbon mainly accured in the topsoil layer of 0-60 cm.(3)By analyzing soil organic carbon δ13C ratio, we found that the approach of carbon leaching in soil of tea plantations exists really. The location of the slopes is a factor to influent soil carbon leaching fluxes of tea plantation. The loss of carbon leaching of tea plantation in the summit could be neglected, the speed of migration in the mid-slope was slow, and the loss is large in the foot-slope.(4)The SOC leaching flux in the layer of 0-20 cm was greater than in the soil layer of 0-40 cm, their average values are 5607.78 mg/m2,4358.27 mg/m2, respectively; ie 22.3% of organic carbon content lost in the soil layer of 0-20 cm was trapped in the layer of 20-40 cm, but there are a lot SOC content was leached to the deeper layers through 40 cm soil layer. The SOC leaching fluxes of tea plantations with different cultivation ages are smaller than forests in the soil layers of 0-20 cm and 0-40 cm, which illustrated that soil carbon in tea plantations has few losses after cutting native forestes. Whereas the leaching fluxes in the 20-40 cm soil layer had significant negative correlation with tea planting age (P<0.05), it illustrated the extension of tea cultivation age reduce the losses of SOC and benefit storage of soil carbon.(5)When planting density of 10000 plants/ha, there were significant linear positive correlations between tea cultivation period and soil pH in the 0-20 cm and 20-40 cm layers, with acidification rates of 0.0158/yr and 0.0140/yr, respectively; Soil pH in the 40-80 cm layer did not change significantly. There was a significant linear negative correlation in the 80-100 cm and 100-120 cm layers, with acidification rates of-0.0161/yr and -0.0245/yr, respectively. Soil in tea plantations have showed no acidification at lower planting density of 5000 plants/ha (P>0.05), and reducing planting density can reduce acidification.(6)There is no found that SOC leaching fluxes effected by soil background concentration of soil organic carbon, pH, nitrogen and ammonium nitrogen in our study (P>0.05).