Ecosystem Carbon Stock Influenced by Plantation Practice: Implications for Planting Forests as a Measure of Climate Change Mitigation

Uncertainties remain in the potential of forest plantations to sequestrate carbon (C). We synthesized 86 experimental studies with paired-site design, using a meta-analysis approach, to quantify the differences in ecosystem C pools between plantations and their corresponding adjacent primary and secondary forests (natural forests). Totaled ecosystem C stock in plant and soil pools was 284 Mg C ha−1 in natural forests and decreased by 28% in plantations. In comparison with natural forests, plantations decreased aboveground net primary production, litterfall, and rate of soil respiration by 11, 34, and 32%, respectively. Fine root biomass, soil C concentration, and soil microbial C concentration decreased respectively by 66, 32, and 29% in plantations relative to natural forests. Soil available N, P and K concentrations were lower by 22, 20 and 26%, respectively, in plantations than in natural forests. The general pattern of decreased ecosystem C pools did not change between two different groups in relation to various factors: stand age (<25 years vs. ≥25 years), stand types (broadleaved vs. coniferous and deciduous vs. evergreen), tree species origin (native vs. exotic) of plantations, land-use history (afforestation vs. reforestation) and site preparation for plantations (unburnt vs. burnt), and study regions (tropic vs. temperate). The pattern also held true across geographic regions. Our findings argued against the replacement of natural forests by the plantations as a measure of climate change mitigation

Effects of irrigation on the soil CO2 efflux from different poplar clone plantations in arid northwest China

Soil respiration in forest plantations can be greatly affected by management practices such as irrigation. In northwest China, soil water is usually a limiting factor for the development of forest plantations. This study aims to examine the effects of irrigation intensity on soil respiration from three poplar clone plantations in this arid area. The experiment included three poplar clones subjected to three irrigation intensities (without, low and high). Soil respiration was measured using a Li-6400-09 chamber during the growing season in 2007. Mean soil respiration rates were 2.92, 4.74 and 3.49 mu mol m(-2) s(-1) for control, low and high irrigation treatments, respectively. Soil respiration decreased once soil water content was below a lower (14.8 %) or above an upper (26.2 %) threshold. When soil water content ranged from 14.8 % to 26.2 %, soil respiration increased and correlated with soil temperature. Fine root also played a role in the significant differences in soil CO2 efflux among the three treatments. Furthermore, the three poplar hybrid clones responded differently to irrigation regarding fine root production and soil CO2 efflux. Irrigation intensity had a strong impact on soil respiration of the three poplar clone plantations, which was mainly because fine root biomass and microbial activities were greatly influenced by soil water conditions. Our results suggest that irrigation management is a main factor controlling soil carbon dynamics in forest plantation in arid regions

Decomposition of Organic Carbon in Fine Soil Particles Is Likely More Sensitive to Warming than in Coarse Particles: An Incubation Study with Temperate Grassland and Forest Soils in Northern China

It is widely recognized that global warming promotes soil organic carbon (SOC) decomposition, and soils thus emit more CO(2) into the atmosphere because of the warming; however, the response of SOC decomposition to this warming in different soil textures is unclear. This lack of knowledge limits our projection of SOC turnover and CO(2) emission from soils after future warming. To investigate the CO(2) emission from soils with different textures, we conducted a 107-day incubation experiment. The soils were sampled from temperate forest and grassland in northern China. The incubation was conducted over three short-term cycles of changing temperature from 5°C to 30°C, with an interval of 5°C. Our results indicated that CO(2) emissions from sand (>50 µm), silt (2–50 µm), and clay (<2 µm) particles increased exponentially with increasing temperature. The sand fractions emitted more CO(2) (CO(2)-C per unit fraction-C) than the silt and clay fractions in both forest and grassland soils. The temperature sensitivity of the CO(2) emission from soil particles, which is expressed as Q(10), decreased in the order clay>silt>sand. Our study also found that nitrogen availability in the soil facilitated the temperature dependence of SOC decomposition. A further analysis of the incubation data indicated a power-law decrease of Q(10) with increasing temperature. Our results suggested that the decomposition of organic carbon in fine-textured soils that are rich in clay or silt could be more sensitive to warming than those in coarse sandy soils and that SOC might be more vulnerable in boreal and temperate regions than in subtropical and tropical regions under future warming