Assessing the impact of land-use changes on soil respiration (R S ) is of vital significance to understand the interactions between belowground metabolism and regional carbon budgets. In this study, the monthly in situ R S was examined between 09:00 and 12:00 hours over a 3-year period within a representative land-use sequence in the subtropical region of China. The land-use sequence contained natural forest (control treatment), secondary forest, two plantations, citrus orchard and sloping tillage land. Results showed that the R S exhibited a distinct seasonal pattern, and it was dominantly controlled by the soil temperature. After the land-use conversion, the apparent temperature sensitivity of R S (Q 10 ) was increased from 2.10 in natural forest to 2.71 in sloping tillage land except for an abnormal decrease to 1.66 in citrus orchard. Contrarily, the annual R S was reduced by 32% following the conversion of natural forest to secondary forest, 46-48% to plantations, 63% to citrus orchard and 50% to sloping tillage land, with the average reduction of 48%. Such reduction of annual R S could be explained by the decrease of topsoil organic carbon and light-fraction organic carbon storages, live biomass of fine root ( o2 mm) and annual litter input, which indirectly/directly correlated with plant productivity. Our results suggest that substrate availability (e.g., soil organic carbon and nutrients) and soil carbon input (e.g., fine root turnover and litterfall) through plant productivity may drive the R S both in natural and managed ecosystems following strong disturbance events.

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SummaryUnderstanding the allocation of gross primary production (GPP) and its response to climate is essential for improving terrestrial carbon (C) modelling.Here, we synthesize data on component GPP fluxes from a worldwide forest database to determine the allocation patterns of GPP across global gradients in climate and nitrogen deposition (N dep ).Our results reveal that allocation of GPP is governed in an integrated way by allometric constraints and by three trade-offs among GPP components: wood production (NPP wood ) vs fine-root production (NPP froot ), NPP wood vs foliage production (NPP foliage ), and autotrophic respiration (R a ) vs all biomass production components. Component fluxes were explained more by allometry, while partitioning to components was related more closely to the tradeoffs. Elevated temperature and N dep benefit long-term woody biomass C sequestration by stimulating allometric partitioning to wood. N dep can also enhance forest C use efficiency by its effects on the R a vs biomass production trade-off. Greater precipitation affects C allocation by driving the NPP wood vs NPP foliage trade-off toward the latter component.These results advance our understanding about the global constraints on GPP allocation in forest ecosystems and its climatic responses, and are therefore valuable for simulations and projections of ecosystem C sequestration.

Soil labile fractions play an