Soil-atmosphere exchange of greenhouse gases in subtropical plantations of indigenous tree species

Indigenous broadleaf plantations are increasingly developing as a prospective silvicultural management approach for substituting in place of large pure conifer plantations in subtropical China. However, little information is known about the effects of tree species conversion on soil-atmosphere greenhouse gas (GHG) exchanges. Four adjacent monospecific plantations were selected in subtropical China to examine the effects of tree species on soil-atmosphere exchanges of N₂O, CH₄ and CO₂. One coniferous plantation was composed of Pinus massoniana (PM), and the three broadleaf plantations were Castanopsis hystrix (CH), Michelia macclurei (MM) and Mytilaria laosensis (ML). We found that mean soil N₂O and CO₂ emissions in the PM plantation were 4.34 μg N m^?2?h^?1 and 43.25 mg C m^?2?h^?1, respectively, lower than those in the broadleaf plantations (>5.25 μg N m^?2?h^?1 and >56.38 mg C m^?2?h^?1). The PM plantation soil had higher mean CH₄ uptake (39.03 μg C m^?2?h^?1) than the broadleaf plantation soils (<32.67 μg C m^?2?h^?1). Variations in soil N₂O emissions among tree species could be primarily explained by the differences in litter C:N ratio and soil total N stock. Differences in soil CH₄ uptake among tree species could be mostly attributed to the differences in mean soil CO₂ flux and water filled pore space (WFPS). Litter C:N ratio could largely account for variations in soil CO₂ emissions among tree species. This study confirms that there is no GHG benefit of converting PM plantation to broadleaf plantations in subtropical China. Therefore, the future strategy of tree species selection for substituting in place of large coniferous plantations in subtropical China needs to consider the potential effects of tree species on soil-atmosphere GHG exchanges.