中国荒漠化潜在发生范围的修订

为了客观反映中国荒漠化发生区域,按照联合国防治荒漠化《公约》的定义,利用1950-1990年间全国671个气象站的长时间序列气象数据,分别采用Thornthwaite和Penman计算可能蒸散量的方法计算了湿润指数的分布,然后根据中国气候区划和中国植被区划以及中国荒漠化发生的特点等对计算结果进行了调整,对中国荒漠化潜在发生范围进行了修订,明确了荒漠化各气候类型区的地理涵义。研究结果表明：①《公约》定义的荒漠化潜在发生范围及各气候类型区的划分标准不完全适用于中国。②中国的荒漠化发生在极干旱区、干旱区、半干旱区和亚湿润干旱区。极干旱区对应极旱荒漠,干旱区对应典型荒漠、草原化荒漠以及荒漠草原,半干旱区对应典型草原,亚湿润干旱区对应草甸草原中偏干旱的部分。③修订后中国荒漠化潜在发生范围总面积约4 524 089.1 km²,约占国土总面积的47.1％,其中亚湿润干旱区、半干旱区、干旱区和极干旱区分别占12.6％、28.8％、34.4％和24.2％。荒漠化潜在发生范围修订后比修订前增加1 207 056.9 km²,其中亚湿润干旱区面积减少,半干旱区、干旱区和极干旱区面积增加。     

Pedotransfer functions to estimate soil bulk density for Northern Africa: Tunisia case

Countries should provide regularly national inventories of greenhouse gas emissions and sinks and, and for the agriculture and forestry sectors this comprise national estimates of soil organic carbon (C) stocks. Estimation of soil C stock requires soil bulk density (D_b) values. However, direct measurement of D_b is often lacking mainly for soils in arid and semi-arid conditions. Much effort has been made in finding alternative solution to predict D_b, either improving in situ determinations, either improving estimation procedures based on other soil properties. Regression models or pedotransfer functions (PTFs) based on easily measured soil properties constitute an adequate tool to assess D_b, since it needs a minimum data set of indicators. A forward stepwise multiple linear regression routine was used to predict D_b from physico-chemical soil properties. In this study, a soil database was organised from published and unpublished data from Tunisia. The database consisted of 238 soil profiles corresponding to 707 soil horizons from Tunisia. A general regression model fitted with all the data showed that OC, Clay, coarse-Sand and pH were the principal contributors to D_b prediction (R² = 0.55, standard error of prediction = 0.14). Additional models based on different set of variables are also provided providing alternative solutions for different levels of soil information. Predictions of the models were often improved when the data were partitioned into groups by soil depth (0–40 and 40–100 cm) and soil orders. This study also showed that CaCO₃ might be an important predictor for deeper soil horizon. The proposed PTFs for Tunisia might be useful for a larger range of soil from arid and sub arid regions.     

Biomass production, evapotranspiration and water use efficiency of arid rangelands in the Northern Cape, South Africa

Annual above-ground net primary production (ANPP), evapotranspiration (ET) and water use efficiency (WUE) of rangeland have the potential to provide an objective basis for establishing pricing for ecosystem services. To provide estimates of ANPP, we surveyed the biomass, estimated ET and prepared a water use efficiency for dwarf shrublands and arid savanna in the Riemvasmaak Rural Area, Northern Cape, South Africa. The annual production fraction was surveyed in 33 MODIS 1 km² pixels and the results regressed against the MODIS f_PAR product. This regression model was used to predict the standing green biomass (kg DM ha⁻¹) for 2009 (dry year). Using an approach which combines potential evapotranspiration (ET₀) and the MODIS f_PAR product, we estimated actual evapotranspiration (ET_a). These two models (greening standing biomass and ET_a) were used to calculate the annual WUE for 2009. WUE was 1.6 kg DM mm⁻¹ ha⁻¹ yr⁻¹. This value may be used to provide an estimate of ANPP in the absence of direct measurements of biomass and to provide a comparison of the water use efficiency of this rangeland with other rangeland types.     

Regional aboveground biomass equations for North American arid and semi-arid forests

Calculations of dry tree, plot and regional aboveground biomass, M, and assessments of complex diverse forests remain key challenges in the implementation of conventional and sustainable projects. This study reports a set of robust regional equations and the application of several allometric tree and plot M equations in Mexican arid and semi-arid forest communities. The data were collected from 1084 tree M fitting models, and 195 arid and semi-arid and 206 mesquite trees and 55 plot datasets were used to validate the models. Theoretical, semi-empirical and empirical models with exogenous variables, as well as wood specific gravity, diameter, top height, and form-factor values, were used to evaluate aboveground biomass. Empirical computer-based equations projected more consistently similar tree M assessments than did semi-empirical or theoretical models. Therefore, empirical models are recommended for assessments of tree and plot M, and future allometry research should properly address independent variables in more theoretical models. The large sample size, model richness, economic and ecological importance, and wide coverage of this dataset make it useful for estimating several biogeochemical and bioenergy density parameters and contribute to the body of knowledge regarding heterogeneity in dry forest stand structures.     

A tool for estimating impacts of woody encroachment in arid grasslands: Allometric equations for biomass,carbon and nitrogen content in Prosopis velutina

Regression equations were developed to estimate above ground biomass and carbon and nitrogen mass of foliage and stem size fractions from plant size dimensions (basal diameter, canopy area, height, canopy volume) for a tall shrub species (Prosopis velutina) that has increased in abundance in arid and semi-arid grasslands in the southwestern United States and northwestern Mexico. Regression equations were also developed to describe relationships among the dimensions of plant size. All equations were significant (p < 0.001); and all but two had r² values >0.72. In addition to species-specific information, we found support for the global patterns of foliar biomass increasing to the ¾ power of stem biomass and height increasing to the ½ power of stem diameter. We provide a comprehensive report of all equations, which can support a variety of in situ (ground-based), modeling, and remote-sensing objectives related to quantifying changes in ecosystem function and carbon sequestration accompanying changes in woody plant abundance. We advocate that comprehensive reporting should become more common for arid and semi-arid woody species in order to support a broad spectrum of users while laying the foundation for the development of global generalizations similar to those available for forest trees.     

Ecophysiological studies inHesperaloe funifera(Agavaceae): a potential new CAM crop. The effect of light availability on photosynthesis and growth

Hesperaloe funifera(Agavaceae) is being investigated as a new specialty-fiber crop for arid lands. The objective of this study was to examine the effects of reduced solar radiation on photosynthesis and growth in this CAM species.Peak CO₂uptake integrated through 24 h was found to be highest during the fall. Although shading greatly reduced CO₂uptake in fall and winter, the decrease was not statistically significant for the spring and summer. Total biomass was significantly different for the three light treatments, with average fresh weights of 5243 g, 4488 g, and 3671 g for the full-sun, 53%-sun, and 20%-sun treatments, respectively. The greatest differences were found in the crown growth, which would affect future production of both leaves and flower stalks.Photosynthesis and growth results suggest that the cultivation ofHesperaloe funiferawill be favored in well-lit environments characteristic of arid or semi-arid climates.     

两种干湿气候类型评价方法在内蒙古地区应用比较

Holdridge可能蒸散率(PER)和徐文铎湿润指数(HI)在内蒙古地区的应用结果表明:两种干湿气候类型划分差异主要体现在半干旱和亚(半)湿润区,其余气候类型地域分布比较一致。其年代变化的共同点是半干旱区+干旱区+极干旱区面积逐年增加,亚(半)湿润区+湿润区面积逐年减少。PER分类与降水量分布规律明显,而HI分类更多体现了温度和降水的综合影响。在考虑下垫面特征的情况下,徐文铎湿润指数更符合内蒙古地区干湿气候带划分。30 a温度与降水相关分析表明:温度呈显著增加趋势,而降水的下降趋势属正常气候波动。     

干旱半干旱区农田土壤风蚀特征及参数化研究进展

干旱半干旱地区是中国的农业后备战略基地,然而近年来该地区农田土壤风蚀现象严重,沙/尘释放量显著增大,威胁农业的可持续发展和生态系统平衡。目前绝大部分的天气和气候模式仅考虑了沙漠地表起沙,忽视退化农田的土壤风蚀起沙,导致起沙通量模拟存在很大的不确定性。对20世纪50年代以来干旱半干旱区农田土壤风蚀起沙特征及参数化做了详细的分析总结,回顾并梳理了干旱半干旱区农田土壤风蚀观测和数值模拟的研究脉络以及存在的问题,为提高农田起沙的模拟精度提供了有效参考,对中国干旱半干旱区农田土壤风蚀防治、土地荒漠化治理以及理解未来土地利用改变对大气污染的影响具有重要意义。     

Global greenhouse gas implications of land conversion to biofuel crop cultivation in arid and semi-arid lands – Lessons learned from Jatropha

Biofuels are considered as a climate-friendly energy alternative. However, their environmental sustainability is increasingly debated because of land competition with food production, negative carbon balances and impacts on biodiversity. Arid and semi-arid lands have been proposed as a more sustainable alternative without such impacts. In that context this paper evaluates the carbon balance of potential land conversion to Jatropha cultivation, biofuel production and use in arid and semi-arid areas. This evaluation includes the calculation of carbon debt created by these land conversions and calculation of the minimum Jatropha yield necessary to repay the respective carbon debts within 15 or 30 years.The carbon debts caused by conversion of arid and semi-arid lands to Jatropha vary largely as a function of the biomass carbon stocks of the land use types in these regions. Based on global ecosystem carbon mapping, cultivated lands and marginal areas (sparse shrubs, herbaceous and bare areas) show to have similar biomass carbon stocks (on average 4–8 t C ha⁻¹) and together cover a total of 1.79 billion ha. Conversion of these lands might not cause a carbon debt, but still might have a negative impact on other sustainability dimensions (e.g. biodiversity or socio-economics). Jatropha establishment in shrubland (0.75 billion ha) would cause a carbon debt of 24–28 t C ha⁻¹ on average (repayable within 30 year with yield of 3.5–3.9 t seed ha⁻¹ yr⁻¹). Land use change in the 1.15 billion ha of forested area under arid and semi-arid climates could cause a carbon debt between 70 and 118 t C ha⁻¹. This debt requires 8.6–13.9 t seed production ha⁻¹ yr⁻¹ for repayment within 30 years. If repayment is required within 15 years, the necessary minimum yields almost double. Considering that 5 t seed ha⁻¹ yr⁻¹ is the current maximum Jatropha yield, conversion of forests cannot be repaid within one human generation. Repayment of carbon debt from shrubland conversions in 30 years is challenging, but feasible. Repayment in 15 year is currently not attainable.Based on this analysis the paper discusses the carbon mitigation potential of biofuels in arid and semi-arid environments.     

Effects of land cover and soil properties on denitrification potential in soils of two semi-arid grasslands in Inner Mongolia,China

High N₂O emissions have been observed in semi-arid grasslands, especially during freeze/thaw periods, when denitrification might be the main process of N₂O production. However, there have been few denitrification studies in semi-arid grassland. This study was designed to determine the denitrification potential of four representative land cover types (typical steppe, meadow steppe, marshland, arid steppe) in two grasslands in Inner Mongolia, China. We found that soils from different land cover types exhibited significantly different denitrification potentials, with highest rates in marshland and lowest rates in arid steppe. Denitrification potentials were maximal in the upper layer and generally decreased with depth for all soils. Soil water content, soil carbon and nitrogen availability, and C/N ratio were found to be significantly correlated with denitrification potentials in all soils. Addition of glucose or/and nitrate significantly increased denitrification activities throughout the profile for all soils, suggesting that both bioavailable carbon and nitrogen were limiting factors of denitrification in these grasslands soils. However, further field studies are needed to translate the denitrification potentials determined in laboratory measurements to denitrification rates under field conditions.     

The effect of PET method on Reconnaissance Drought Index (RDI) calculation

Drought severity is conventionally assessed by drought indices. Several drought indices with varying complexity have been used in many geographical areas. Recently, a powerful drought index, the Reconnaissance Drought Index (RDI), is gaining wide acceptance mainly in the arid and semiarid climatic regions. Since RDI is based both on precipitation and potential evapotranspiration (PET), it is interesting to assess the effect of the PET calculation method on the drought severity characterisation obtained by RDI. This paper compares the results of RDI for various reference periods using some popular empirical PET methods with minimum data requirements. The selected methods are: Hargreaves, Thornthwaite, Blaney–Criddle and FAO Penman–Monteith (only temperature). The FAO Penman–Monteith method is used as reference method. The data used are from meteorological stations in Greece representing the mountainous and the coastal Mediterranean climatic conditions. No significant influence on RDI was detected by using the selected PET methods. However, the Hargreaves and FAO P–M (only T) methods performed relatively better. This supports the opinion that RDI is a robust drought index, not dependent upon the PET calculation method.     

Photo-thermal regulation of seed germination in natural populations of Eruca sativa Miller (Brassicaceae)

Populations of the winter annual Eruca sativa in Israel are distributed along a climatic gradient, from Mediterranean mesic habitats in the north to semi-arid and arid habitats in the south. Seed cohorts of five populations sampled across the gradient were produced in a common-garden experiment, and their germination was tested under continuous light or darkness at 5–35 °C, as well as with alternating 30/20 and 25/15 °C temperatures under a 12/12 h photoperiod. Germination was enhanced by light and by increasing temperature. Under constant temperatures maximal germination of arid and semi-arid populations was lower than in the mesic populations, suggesting on higher levels of primary dormancy with increasing aridity. Seeds that did not germinate in darkness or at low temperatures in light, germinated almost fully when exposed to GA₃ at 25 °C, indicating that imbibition under less favorable conditions induces secondary dormancy in E. sativa. Daily alternating temperatures did not affect or even reduced seed germination compared to constant 25 and 30 °C in continuous light. Exposure of dry seeds to 30 °C before imbibition increased germination to ≥80% in seed cohorts of all populations. These responses to light and temperature indicate that adaptation of E. sativa to the Mediterranean environment is associated with the ability to germinate under the relatively warm autumn temperatures, and is enhanced by exposure to high temperature during the dry summer.     

汉江上游郧县段黄土古土壤序列风化成壤特征以及成壤环境演变

对汉江上游进行野外实地详细调查,在湖北省郧县尚家河台地前沿发现了典型的全新世黄土-古土壤沉积剖面,通过粒度、磁化率、吸湿水和烧失量分析表明,黏粒、细粉砂、磁化率、吸湿水和烧失量在古土壤层S₀出现高值,在L₁、L_t、L₀为低值;而粗粉砂、细砂粒和粗砂粒在S₀为低值,在L₁、L_t、L₀为高值。这些指标的变化说明了全新世以来的气候和成壤环境的变化特征,即在古土壤S₀形成时期,气候温暖湿润,成壤作用非常强烈;黄土堆积时期气候相对干旱,成壤作用较弱。     

Climatic response of thick leaf spruce (Picea crassifolia) tree-ring width at different elevations over Qilian Mountains, northwestern China

Tree-ring cores of thick leaf spruce (Picea crassifolia) taken from four sites at different elevations, in the middle of the Qilian Mountains, in the arid and semi-arid region of northwestern China, were used to develop four tree-ring width chronologies using standard dendrochronological methods. Results indicate that with increasing altitude the chronologies’ year-to-year variations decreased. Hence, the sensitivity of the tree-ring chronologies to climate decreases with altitude. Further analysis showed that the significant limiting factor on tree growth is spring precipitation. Measurements of stomata density and leaf dry weight suggest the species’ ecological adaptation strategy changes with elevation. At high elevation the metabolic rate of thick leaf spruce decreases, thus showing the effect of the climate.     

江河源区生态环境范围的探讨

The Tibetan Plateau, as the origin of the Yangtze and Yellow rivers, is the region of climate variation and is very sensitive to climate change in China (Feng etal., 1998). The runoff in the upper reaches of the Yellow River has been decreasing at a rate of 9.8 m3/s per decade due to rapid climate warming in the Tibetan Plateau since the mid- and late 1980s (Zhang etal., 2000). Eco-environmental change is also extremely substantial in the source regions of the Yangtze and Yellow rivers. T…     

Spatial carbon and nitrogen distribution and organic matter characteristics of biological soil crusts in the Negev desert (Israel) along a rainfall gradient

In arid and semi-arid areas biological soil crusts are main contributors to C and N-cycles and the origin of organic matter. Nevertheless systematic studies on the spatial distribution of total organic carbon (TOC) and nitrogen (N) and a characterization of crust organic matter composition are missing. To describe the spatial distribution of TOC and N we examined three soil depths and three relief positions along a steep rainfall gradient. In addition the molecular composition of organic matter was characterized by Pyrolysis-field ionization mass spectrometry.TOC and N concentrations decreased with increasing depth, the effects of the relief followed no clear trend. Surprisingly the amount of TOC and N decreased with increasing rainfall. Stable organic matter compounds were reduced with increasing rainfall. Topcrusts (0–2 mm) showed a relative enrichment in bacteria, as indicated by proportionally larger contents in N-acetylmuramic acid (m/z 167 + 276) than the subcrusts (2–40 mm). These were enrichment in cyanobacteria, as indicated by proportionally larger contents of hexadecadienoic acid (m/z 252).We conclude that the spatial distribution of TOC and N is related to sampling depth and annual precipitation. Organic matter composition and the main biomass contributors in crusts are successfully identified by pyrolysis-field ionization mass spectrometry.     

辽宁西部地区的气候变化及干湿状况年代际变化特征

辽宁西部(简称辽西)是气候及生态环境脆弱区,因其特殊性使之成为相关科研人员关注的焦点,在全球气候变暖背景下增温显著的辽西地区气候及地表干湿气候界线如何变化是本文研究的问题。应用1961—2004年辽宁省内52个气象站的温度、降水、湿度、风、日照等气候资料,分析了辽西近50 a来的气候变化特点,采用改进的Penman模型计算潜在蒸发量,讨论了其时空代表性及分布特征;进一步计算了干燥度指数,并在10 a代际尺度上详细分析了辽西干湿气候变化特征。研究表明:辽西地区近44 a的总体气候变化趋势是气温升高、降水减少。20世纪60年代以来该区域干湿气候界线波动显著,呈现出整体移动、南北异相波动的特征。干湿气候年代际变化特征为60年代最湿润;70年代北部明显变干,南部不明显;80年代干湿气候存在一次突变,半干旱与半湿润界线明显东移,为最干期;90年代又跳跃性西移,明显变湿,尤其在北部表现更为显著,接近60年代。辽西的气候干湿年代际变化与西太平洋副热带高压和东南季风波动有较好的对应关系。     

Relationship between species richness of small mammals and primary productivity of arid and semi-arid grasslands in north China

We studied the relationship between primary productivity and species richness of small mammals at both large and small spatial scales in the arid and semi-arid grasslands of north China. The productivity (x)–species richness (y) pattern at a large spatial scale can be described by a unimodal quadratic regression curve (y=7·41+0·1^*x−0·0003^*x²,p =0·008, r²=0·788). At a small spatial scale, however, neither linear nor quadratic regression fit the data for 1980 and 1994 (p>0·25). Primary productivity may not be an appropriate predictor of the species richness of small mammals at a small spatial scale. We conclude, therefore, that the primary productivity–species richness pattern of small mammals may be scale-dependent in the arid and semi-arid grasslands of north China. Landscape complexity should be considered in future studies of productivity–richness relationships.     

Evapotranspiration of a Populuseuphratica Oliv. forest and its controlling factors in the lowerHeihe RiverBasin, Northwest China

Evapotranspiration (ET) within an ecosystem is crucial for the water-limited environment that currently lacks adequate quantification in the arid region of Northwest China, mainly covered by phreatophytes, such as the Populus euphratica Oliv. tree and the Tamarix ramosissima Ledeb. shrub species. Accordingly, ET was measured for an entire year using eddy covariance (EC) in P. euphratica stands in the lower Heihe River Basin, Northwest China. During the growing season, the total ET was 850 mm, with a mean of 4.0 mm/d, which is obviously more than that observed at tree-level and standlevel scales, which was likely due to the different level of soil evaporation induced by irrigation via water conveyance. Factors associated with ET fall into either environmental or plant eco-physiological categories. Environmental factors account for at least 79% variation of ET, and the linear relationship between ET and the groundwater table (GWT) revealed the potential water use of P. euphratica forests under the non-water stress condition with the GWT less than 3 m deep. Plant eco-physiological parameters, specifically the leaf area index (LAI), have direct impact on the seasonal pattern of ET, which provides a valuable reference to the wide-area estimates of ET for riparian forests by using LAI. In conclusion, P.euphratica forests have high water use after water conveyance, which may be the result of long-term adapting to local climates and limited water availability.     

中国内陆干旱、半干旱区苦咸水分布特征

通过大量野外调查、水样采集和化验分析,对中国内陆干旱、半干旱区的苦咸水和高氟水分布特征进行了初步研究。采集到的地表和地下水样中,分别有51.0%和41.5%属于苦咸水;55%和59%水样氟化物含量超标,属于高氟水。研究区的苦咸水以Cl^--Na⁺和HCO₃^--Na⁺为主要离子类型,SO₄^2--Mg²⁺和SO₄^2--Ca²⁺为次要离子类型。苦咸水和高氟水主要分布在内陆河流域下游尾闾、封闭内流区低洼湖盆低地、北部准平原化干燥剥蚀低山残丘间冲积洼地、沙漠低洼湖盆和黄土高原中西部径流系数较小的河流及部分露头潜水等区域,并具有区域富集性分布特点。季节性降水、季节性河流或渠系灌溉对苦咸水的季节性或年际间变化和空间分布有较大影响。较高浓度基质含盐量、水文地质结构、气候条件和特定的水文地球化学环境是苦咸水和高氟水形成与富集分布的主要原因。