Soil organic carbon stocks and CO2 effluxes of native and exotic pine plantations in subtropical China

Abstract

The selection of tree species is critical for soil organic carbon (SOC) stock and dynamics under afforestation. Exotic tree species were widely introduced and have been considered as a form of human-induced global change. However, how exotic tree species, as compared with native ones, affect SOC storage and soil respiration (Rs) has not been sufficiently investigated. Here we studied this issue in an even-aged (22years) plantation composed by native Masson pine (Pinus massoniana Lamb.) (MP) and exotic slash pine (Pinus elliottii Engelm.) (SP) in subtropical China. A trenching method was used to partition Rs into heterotrophic (Rh) and autotrophic respiration (Ra). Rs and Rh were measured approximately biweekly during August 2007 to December 2009. Our results showed that seasonal patterns of Rs and Rh in both pine forests were mainly affected by soil temperature and moisture (R2=0.56–0.78, P<0.001). There was no difference in SOC stock (forest floor+mineral soil of 0–40cm), Rh and turnover rate (Rh/SOC stock) between MP and SP forests. However, annual Rs, Ra and Ra/Rs of MP were significantly 24%, 119% and 74% higher than those of SP, respectively. In contrast, even though MP and SP had similar fine and coarse root biomass, MP had significant higher ratios of Ra/fine root biomass and Ra/coarse root biomass than SP, suggesting a higher respiration rate in native pine species on a root biomass basis. We concluded that the exotic SP, as compared with indigenous MP, did not alter SOC stock, Rh and turnover rate but depressed Ra and Rs. Therefore, both pine species were recommended in case of reforestation in terms of SOC sequestration.