Soil Organic Carbon Sequestration Potential in Nectarine Orchards under Different Reclamation Systems

The Red Soil Hilly Region in South China, where there is a high capacity of carbon(C), and the land use and vegetation cover change greatly, is an important ecological area in the world, and has an important impact on the global carbon cycle and the seasonal fluctuation of atmospheric CO_2. To better evaluate the effects of reclamation systems in orchards converted from grasslands on soil carbon sequestration, we investigated soil organic carbon(SOC) content and stable C isotope(δ^(13)C)composition in three nectarine orchards at Yuchi Experimental Station in South China. Compared with the sloping clean tillage orchard and terraced clean tillage orchard, SOC content in the terraced orchard with grass cover was increased by 14.90% to 38.49%, and 7.40% to 15.33%, respectively. During the 14 years after orchard establishment, the soil organic matter sources influenced both δ^(13)C distribution with depth and carbon replacement. SOC turnover of the upper soil layer in the terraced orchard with grass cover(a mean 63.05% of replacement in the 20 cm after 14 years) was 1.59 and 1.41 times larger than that of the sloping clean tillage orchard and terraced clean tillage orchard under subtropical conditions, respectively. The equilibrium value of soil organic carbon in the three treatments ranged from 16.067 to 25.608 g/kg under the experimental conditions. The equilibrium value of soil organic carbon in the surface layer under grass cover was 54.801 t/hm^2, and the carbon sequestration potential was 24.695 1 t/hm^2.

Soil Organic Carbon Stocks of Citrus Orchards in Yongchun County Fujian Province China

Studies related to the quantitation and distribution of soil organic carbon(C) under different land use types can help to fill the knowledge gaps regarding estimation of the amount of C stored in soils at a global scale. Orchards are an important land use type in southern China; the total area(1.15 × 10~7 ha) of orchards in China comprises approximately 20.5% of the area of all orchards worldwide. We assessed soil organic C stocks(SOCS) in citrus orchards in Yongchun County(consisting of 22 towns), Fujian Province,China in 1982 and 2010. The southeastern part of the county, an area featuring extensive citrus farming with a gently sloping landscape and low rates of water erosion, had the highest SOCS. In contrast, the lowest SCOS was observed in the northern part of the county,where steep hills with severe erosion problems are common and citrus orchards are sparsely distributed. From 1982 to 2010, the mean SOCS in citrus orchards increased from 22.1 to 41.7 Mg ha^(-1), which indicated that current management practices such as fertilization,irrigation, and cultivation enhanced soil C stocks. Further in-depth studies on the effects of these practices on C sequestration would be worthwhile and surveys of SOCS throughout Fujian Province are needed, to support efforts to mitigate global C emission.

Sensitivity to Abscisic Acid Modulates Positive Interactions between Arabidopsis thaliana Individuals

The ability of abscisic acid （ABA） to modulate positive interactions between Arabidopsis thaliana individuals under salinity stress was investigated using abi1-1 （insensitive to ABA）, era1-2 （hypersensitive to ABA） mutant and wild type plants. The results showed that sensitivity to ABA affects relative interaction intensity （RII） between Arabidopsis thaliana individuals. The neighbor removal experiments also confirmed the role of phenotypic responses in linking plant-plant interactions and sensitivity to ABA. For abil-1 mutants, the absolute value differences between neighbor removal and control of stem length, root length, leaf area, leaf thickness, flower density, above biomasslbelowground biomass （A/U）, photosynthetic rate, stomatal conductance, leaf water content and water-use efficiency were smaller than those of the wild type, while for era1-2 mutants, these absolute value differences were larger than those of the wild type. Thus, it is suggested that positive interactions between Arabidopsis thaliana individuals are at least partly modulated by different sensitivity to ABA through different physiological and phenotypic plasticity.