Assessing the Spatiotemporal Dynamic of Global Grassland Water Use Efficiency in Response to Climate Change from 2000 to 2013

Water use efficiency (WUE), which is a ratio of net primary production (NPP) to evapotranspiration (ET), is an important index representing the relationship between carbon and water cycles. This study evaluates the spatiotemporal dynamics of global grassland WUE from 2000 to 2013 to reveal the different responses of each grassland type to climate variations. Their correlations with climate variables are also investigated to reflect their dependence on climate. The average annual WUE of different grassland types follows an order of: closed shrublands > woody savannas > savannas > open shrublands > non‐woody grasslands. Although the NPP of all grassland types has increased from 2000 to 2013, 37.89 % of grassland ecosystems globally experienced a decreased WUE, in which 3.34 % has extremely significantly decreased. The WUE of open shrublands, woody savannas and non‐woody grasslands shows an overall descending trend because of the exceeding increasing rate of ET. By contrast, the decreased ET contributes to the overall ascending trend of the WUE of closed shrublands and savannas over this period. Moreover, the WUE of each grassland type reacts differently to climate variations in the northern and southern hemispheres. The grassland WUE dynamic is more controlled by precipitation than temperature at a global scale.     

冻融交替对水稻土水溶性有机碳含量及有机碳矿化的影响

冻融交替影响土壤水分的有效性及土壤团聚体稳定性,进而影响土壤中微生物的活性及土壤有机碳的矿化。通过室内冻融模拟(即分别在-7℃和28℃下处理土壤)及培养实验,研究了不同冻融交替循环处理下土壤水溶性有机碳(WSOC)、微生物生物量及土壤有机碳矿化的变化规律。结果表明,1到3次冻融交替处理会增加土壤中水溶性有机碳的含量,其中经过1次冻融交替处理的2种土壤其WSOC含量分别增加了25%,20%;但在本实验条件下如果继续增加冻融交替次数则会使土壤水溶性有机碳含量减少。冻融交替处理降低土壤微生物生物量,因此也会影响土壤有机碳的矿化。冻融交替处理对培养第1天的土壤有机碳矿化具有激发效应,激发能力:1次冻融交替>3次冻融交替>6次冻融交替,经过1次冻融交替处理后的土壤其呼吸速率与对照相比增加了17%～40%;其后,冻融交替处理土壤呼吸速率迅速下降,在培养后期甚至低于对照处理。     

泥沙来源“指纹”示踪技术研究综述

泥沙来源"指纹"示踪技术是综合研究流域土壤侵蚀和泥沙输移的新方法。泥沙来源"指纹"示踪技术基于流域侵蚀产沙过程划分潜在物源类型,根据物源特性筛选具有诊断能力的"指纹"性质,通过定量转换模型建立流域出口泥沙与内部潜在物源间的"指纹"联系,定量描述各潜在物源对流域出口产沙的相对贡献;结合悬移质或沉积泥沙通量监测,定量分析各潜在物源对流域产沙的绝对贡献量及流域侵蚀产沙时、空变化特征。通过综述泥沙来源"指纹"示踪技术的理论基础及实施框架,流域尺度潜在物源类型,泥沙"指纹"因子类别、分布特点及诊断能力,泥沙来源复合"指纹"示踪技术的研究进展,指出泥沙来源"指纹"示踪技术的局限性,并对泥沙来源"指纹"示踪技术进行展望。     

速生阶段第二代杉木人工林生物地球化学循环动态

对速生阶段第二代杉木人工林生态系统的生物地球化学循环进行了研究 .结果表明 :第二代杉木人工林生态系统大气降水输入的 N、P、K总量为 3 9.970 kg· hm- 2 a- 1 ,径流输出 9.883 kg· hm - 2 a- 1 ,净变化率为 75 .3 % .在整个系统中以 N的净积累最高 ,变化率为 83 .5 4% ;N、P主要以地质输入为主 ;K以降雨输入为主 .N、P、K的生物地球化学循环遵循 N>K>P的顺序 ,循环速率分别为 0 .3 87、0 .3 89、0 .476.此外 ,建立了速生阶段第二代杉木人工林生态系统养分循环的动态模型 ,该模型可用于杉木林生态系统速生阶段养分动态的模拟和预测 .     

Nutrient cycling in a clonal stand of Eucalyptus and an adjacent savanna ecosystem in Congo: 3. Input–output budgets and consequences for the sustainability of the plantations

Clonal plantations of Eucalyptus have been introduced since 1978 on savanna soils of the coastal plains of Congo. Atmospheric deposition, canopy exchange and transfer through the soil were estimated on the whole rooting depth (6 m) over 3 years, in an experimental design installed in a native savanna and an adjacent 6-year-old Eucalyptus plantation. Complementary measurements after planting the experimental savanna made it possible to establish input–output budgets of nutrients for the whole Eucalyptus rotation and to compare them with the native savanna ecosystem.

In this highly-weathered soil, atmospheric deposits and symbiotic N fixation by a legume species balanced the nutrient budgets in savanna, despite large losses during annual burnings. After afforestation, weeding in the Eucalyptus stands eliminated the leguminous species responsible for a N input by symbiotic fixation of about 20 kg ha⁻¹ year⁻¹. Whereas the budgets of P, K, Ca and Mg were roughly balanced, the current silviculture led to a deficit of about 140 kg N ha⁻¹ in the soil, throughout a 7-year rotation. This deficit was large relative to the pool of total N in the upper soil layer (0–50 cm), which was about 2 t ha⁻¹. Therefore, the sustainability of Congolese plantations will require an increase in N fertilizer inputs over successive rotations to balance the N budget. These results were consistent with field trials of fertilization. Practical consequences of these budgets were identified, in order to: (i) direct field trials of fertilization, (ii) select appropriate methods of soil preparation, weed control and harvest, (iii) highlight the importance of fire prevention in this area, and (iv) support the implementation of field trials aiming at introducing a biological nitrogen fixing understorey in Eucalyptus stands.     

Contribution of nitrification and denitrification to the emission of N2O in a freeze‐thaw event in an agricultural soil

The amounts of N₂O released in freeze‐thaw events depend on site and freezing conditions and contribute considerably to the annual N₂O emissions. However, quantitative information on the N transformation rates in freeze‐thaw events is scarce. Our objectives were (1) to quantify gross nitrification in a Luvisol during a freeze‐thaw event, (2) to analyze the dynamics of the emissions of N₂O and N₂, (3) to quantify the contribution of nitrification and denitrification to the emission of N₂O, and (4) to determine whether the length of freezing and of thawing affects the C availability for the denitrification. ¹⁵NO was added to undisturbed soil columns, and the columns were subjected to 7 d of freezing and 5 d of thawing. N₂O emissions were determined in 3 h intervals, and the concentrations of ¹⁵N₂O and ¹⁵N₂ were determined at different times during thawing. During the 12 d experiment, 5.67 mg NO ‐N (kg soil)^–1 was produced, and 2.67 mg NO ‐N (kg soil)^–1 was lost. By assuming as a first approximation that production and loss occurred exclusively during thawing, the average nitrate‐production rate, denitrification rate, and immobilization rate were 1.13, 0.05, and 0.48 mg NO ‐N (kg soil)^–1 d^–1, respectively. Immediately after the beginning of the thawing, denitrification contributed by 83% to the N₂O production. The ratios of ¹⁵N₂ to ¹⁵N₂O during thawing were narrow and ranged from 1.5 to 0.6. For objective (4), homogenized soil samples were incubated under anaerobic conditions after different periods of freezing and thawing. The different periods did not affect the amounts of N₂ and N₂O produced in the incubation experiments. Further, addition of labile substrates gave either increases in the amounts of N₂O and N₂ produced or no changes which suggested that changes in nutrient availability due to freezing and thawing are only small.     

CO2 and N2O emissions from gleyic soils in the Russian tundra and a German forest during freeze-thaw periods—a microcosm study

Knowledge is scarce on mineralization of soil organic carbon (SOC) in and N₂O emissions from tundra soils in periods of alternate freezing and thawing. Our objectives were to study the CO₂ and N₂O emissions from two silty gleyic soils formed in different climate zones (a gleyic Cryosol located in the Russian tundra, and a stagnic Gleysol located in an oak stand in central Germany) during freeze-thaw events. Soils were adjusted to a matric potential of −0.2 kPa and emissions were measured in 3-h intervals during an incubation period of 50 days including three freeze-thaw cycles. CO₂ emissions from the German oak forest soil were twofold higher than those of the tundra soil. The ratios of the mean CO₂ production rate before the freezing to the mean CO₂ production rate after thawing ranged from 0.63 to 0.73 for the forest soil and from 0.85 to 0.89 for the tundra soil. The specific CO₂-C production rate (CO₂-C/SOC) was 0.16 for the tundra soil and 0.57 for the forest soil. The results indicate that bioavailability of SOC was markedly smaller in the tundra soil than in the forest soil. Large N₂O emissions were found for the German forest soil, but no N₂O emissions were observed for the tundra soil. The main reason for the absence of N₂O emissions was most likely the negligible availability of nitrate for denitrification. There was some indication that the initial increase in mineralization of SOC induced by freezing and thawing differs between soils from various climatic regions, probably mainly due to a differing bioavailability of the SOC and differing releases of nutrients after thawing.     

交替浸渍矿化丝胶膜表面沉积的矿化物及对丝胶膜结构的改变

丝胶蛋白中含有的大量羧基、羟基等活性基团与生物矿化有着密切的联系。以家蚕丝胶膜为模板,采用氯化钙和磷酸氢二钠溶液交替浸渍的方法,研究经不同矿化周期处理丝胶膜上的矿化物沉积及对丝胶膜结构的改变情况。通过红外吸收光谱(FTIR)仪、X射线衍射(XRD)仪、扫描电子显微镜(SEM)和X射线能谱(EDX)仪对表面沉积矿化物的丝胶膜进行微观形貌与结构表征,可见矿化物能快速有效地在丝胶膜表面沉积和生长,随着矿化周期的增加,矿化物的沉积量不断增加,丝胶膜表面的结晶度略有提高,沉积的矿化物呈龟裂、薄板状,主要成分为无定形磷酸钙盐。采用氯化钙和磷酸氢二钠溶液交替矿化的方法并增加矿化周期可促进无定形磷酸钙盐在丝胶膜表面的沉积,有望进一步开发出丝胶蛋白/磷酸钙盐复合支架材料应用于骨组织工程。     

Nematode feeding and activity: the importance of development stages

Summary Nematodes have four juvenile stages and there is significant growth during development. The stages may differ in their respiratory and metabolic rates, and one stage may have significantly greater resistance to environmental stress. The mode of life of successive stages may vary from migratory to sessile. In both the Diplogasterida and Mononchida initial stages may be bacterial-feeding and later stages predatory on protozoa or nematodes. If the role of nematode species in promoting mineralization of nutrients is to be fully understood it is necessary to determine the trophic and metabolic characters of each stage under field conditions.Dedicated to the late Prof. Dr. M.S. Ghilarov