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.

Aims This study aimed to determine the influence of tree species on soil microbial community structure. Methods We conducted a litter and root manipulation and a short-term nitrogen (N) addition experiment in 19-yearold broadleaf Mytilaria laosensis (Hamamelidaceae) and coniferous Chinese fir (Cunninghamia lanceolata) plantations in subtropical China. Phospholipid fatty acid (PLFA) analysis was used to examine treatment effects on soil microbial community structure. Redundancy analysis (RDA) was performed to determine the relationships between individual PLFAs and soil properties (soil pH, carbon (C) and N concentration and C:N ratio). ResultsSoil C:N ratio was significantly greater in M. laosensis (17.9) than in C. lanceolata (16.2). Soil C:N ratio was the key factor affecting the soil microbial community regardless of tree species and the litter, root and N treatments at our study site. The fungal biomarkers, 18:1ω9 and 18:2ω6,9 were significantly and positively related to soil C:N ratio and the abundance of bacterial lipid biomarkers was negatively related to soil C:N ratio. N addition for 8 months did not change the biomass and structure of the microbial community in M. laosensis and C. lanceolata soils. Soil nutrient availability before N addition was an important factor in determining the effect of N fertilization on soil microbial biomass and activity. PLFA analysis showed that root exclusion significantly decreased the abundance of the fungal biomarkers and increased the abundance of the Gram-positive bacteria. Rootless plots had a relatively lower Gram-positive to Gram-negative bacteria ratio and a higher fungi to bacteria ratio compared to the plots with roots under both M. laosensis and C. lanceolata. The response of arbuscular mycorrhizal fungi (16:1ω5) to root exclusion was species-specific. Conclusions These observations suggest that soil C:N ratio was an important factor in influencing soil microbial community structure. Further studies are required to confirm the long-term effect of tree species on soil microbial community structure.

No abstract

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

This article uses a case study in Southeast China to demonstrate how the substantial changes in rural livelihoods have been driven by a combination of ''pull'' forces from external economic development, and ''push'' forces from local areas, leading to a shift in rural household economic activities: household outmigration and de-population of the countryside, changes in energy consumption, and most importantly, changes in land uses and eventually, ecological restoration. Such dramatic changes are becoming common across the Chinese countryside. It is pointed out that economic development has generally caused a deterioration of the environment at least at the early period of economic growth, but the positive impacts, especially in some ecosystem in rural areas, have become more apparent.

Aim Forest soils contain large amounts of terrestrial organic carbon (C), but the formation pathway of soil organic C (SOC) remains unclear. Recent evidence suggests that microbial necromass is a significant source of SOC, yet a global quantitative assessment across the whole soil profile is lacking. We aimed to assess the vertical distribution and control of microbial‐derived SOC in forest soils. Location Global forests. Time period 1996–2019. Major taxa studied Soil microbial necromass carbon. Methods We evaluated the proportions of fungal and bacterial necromass C in total SOC in the litter layer, O horizon soil, and various depths of mineral soil in forests using microbial biomarker (glucosamine and muramic acid) data. Results The total microbial necromass C increased significantly with soil depth, ranging from 30% of SOC in O horizon soil to 62% of SOC in mineral soils below 50 cm. However, only bacterial necromass C followed this increasing trend with soil depth; fungal necromass C showed little variation across the whole soil profile. Higher fungal and bacterial necromass C was observed in soils with lower C/N ratios and smaller aggregate sizes. Soil C/N ratio and microbial biomass C dominantly determined microbial necromass C in surface soil (above 20 cm), but soil clay content was the primary factor in subsoil (below 20 cm). Main conclusions Microbial necromass C accounted for high percentages of the total SOC in forest soils (particularly at depths >20 cm), but its long‐term stabilization may be governed by different mechanisms at different soil horizons. Substrate quality regulates microbial activity and then controls biomass turnover in surface soil, while aggregate occlusion facilitates mineral protection of microbial necromass C in subsoil. These differential controls of microbial‐derived organic C could be applied in Earth system studies for predicting soil organic C dynamics in forests.

-Fine root (< 2 mm in diameter) distribution, seasonal pattern and net production were studied during 1999-2001 in 33 year-old plantations of two coniferous trees, Chinese fir (Cunninghamia lanceolata, CF) and Fokienia hodginsii (FH) and two broadleaved trees, Ormosia xylocarpa (OX) and Castanopsis kawakamii (CK), and compared with that of an adjacent natural forest of Castanopsis kawakamii (NF, ~150 year old) in Sanming, Fujian, China. Fine root biomass and necromass were determined by soil coring at a bimonthly interval. Soil cores were divided into 10 depths: 0 ~ 10, 10 ~ 20, 20 ~ 30, 30 ~ 40, 40 ~ 50, 50 ~ 60, 60 ~ 70, 70 ~ 80, 80 ~ 90, and 90 ~ 100 cm. Litter bags (18 × 18 cm 2 size, 0.25 mm mesh) were used in determination the decay rates of fine roots (< 0.5 mm, 0.5-1 mm, and 1-2 mm). Mean annual fine-root production, mortality, decomposition and turnover rate were calculated by the compartment-flow method. Mean fine-root biomass ranged from 1.49 Mg ha -1 in the CF to 4.94 Mg ha -1 in the NF, and decreased in the following order: NF > CK > FH > OX > CF. There were significant seasonal changes of biomass and necromass in all stands (P < 0.05), while no significant yearly fluctuations were detected (P > 0.05). In all stands, an early spring (March) peak of fine root biomass was found, and the minimum value occurred mainly in dry summer or cold winter. For the NF, 59.8% of fine root biomass was found in the top soil of 0-10 cm, a layer that maximum difference of depth distribution among all stands occurred, where fine root biomass of the NF was 2.37 times, 3.55 times, 8.12 times, and 7.12 times as much as those of the CK, FH, CF, and OX, respectively. Percentages of original mass lost during the first year of decomposition ranged from 43% to 56% for the FH to 68% to 80% for the NF. Mean annual root decomposition, mortality and production ranged from 8.47 Mg ha -1 a -1 , 8.63 Mg ha -1 a -1 and 9.5 Mg ha -1 a -1 in the NF to 2.50, 2.49 and 2.51 Mg ha -1 a -1 in the CF, ranked as NF > CK > FH > OX > CF. The mean root turnover rate ranged from 1.48 a -1 in the FH to 1.78 a -1 in the NF. On a utilisé des sacs à litière (18 × 18 cm 2 , maille de 0,25 mm) pour déterminer le taux de décomposition des radicelles (< 0,5 mm, 0,5-1 mm, 1-2 mm). Les taux de production moyenne annuelle, de mortalité, de décomposition et de turnover des radicelles ont été calculés par la méthode de « compartment flow ». La biomasse moyenne de radicelles va de 1,49 Mg/ha dans le CF à 4,94 Mg/ha pour le NF ; elle décroît dans l'ordre suivant : NF > CK > FH > OX > CF. On a enregistré des différences significatives de biomasse et nécromasse, selon les saisons dans tous les peuplements (P < 0,05), tandis qu'aucune fluctuation n'a pu être mise en évidence entre années (P > 0,05). Pour tous les peuplements, on enregistre un pic de biomasse de radicelles au début du printemps (mars), les valeurs minimum intervenant au cours d'étés secs ou d'hivers froids. Pour le NF, 59,8 % de la biomasse de radicelles se situe dans la zone superficielle ...