Plant invasions differentially affected by diversity and dominant species in native‐ and exotic‐dominated grasslands

Plant invasions are an increasingly serious global concern, especially as the climate changes. Here, we explored how plant invasions differed between native‐ and novel exotic‐dominated grasslands with experimental addition of summer precipitation in Texas in 2009. Exotic species greened up earlier than natives by an average of 18 days. This was associated with a lower invasion rate early in the growing season compared to native communities. However, invasion rate did not differ significantly between native and exotic communities across all sampling times. The predictors of invasion rate differed between native and exotic communities, with invasion being negatively influenced by species richness in natives and by dominant species in exotics. Interestingly, plant invasions matched the bimodal pattern of precipitation in Temple, Texas, and did not respond to the pulse of precipitation during the summer. Our results suggest that we will need to take different approaches in understanding of invasion between native and exotic grasslands. Moreover, with anticipated increasing variability in precipitation under global climate change, plant invasions may be constrained in their response if the precipitation pulses fall outside the normal growing period of invaders.     

Bayesian Insight into a Robust Test for Linear Contrast Based on Asymmetric Censored Samples

A robust test for linear contrast using modified maximum likelihood estimators based on symmetrically censored samples proposed by Tiku (1973, 1982a) is studied in this paper from the Bayesian point of view. The effects of asymmetric censoring on this testing procedure is investigated and a good approximation to its posterior distribution in this case is worked out. We also present an example which illustrates the method of obtaining the highest posterior density interval for the linear combination of the unknown location parameters.     

Water‐use efficiency in response to climate change: from leaf to ecosystem in a temperate steppe

Water‐use efficiency (WUE) has been recognized as an important characteristic of ecosystem productivity, which links carbon (C) and water cycling. However, little is known about how WUE responds to climate change at different scales. Here, we investigated WUE at leaf, canopy, and ecosystem levels under increased precipitation and warming from 2005 to 2008 in a temperate steppe in Northern China. We measured gross ecosystem productivity (GEP), net ecosystem CO₂ exchange (NEE), evapotranspiration (ET), evaporation (E), canopy transpiration (T_c), as well as leaf photosynthesis (P_max) and transpiration (T_l) of a dominant species to calculate canopy WUE (WUE_c=GEP/T), ecosystem WUE (WUE_gep=GEP/ET or WUE_nee=NEE/ET) and leaf WUE (WUE_l=P_max/T_l). The results showed that increased precipitation stimulated WUE_c, WUE_gep and WUE_nee by 17.1%, 10.2% and 12.6%, respectively, but decreased WUE_l by 27.4%. Climate warming reduced canopy and ecosystem WUE over the 4 years but did not affect leaf level WUE. Across the 4 years and the measured plots, canopy and ecosystem WUE linearly increased, but leaf level WUE of the dominant species linearly decreased with increasing precipitation. The differential responses of canopy/ecosystem WUE and leaf WUE to climate change suggest that caution should be taken when upscaling WUE from leaf to larger scales. Our findings will also facilitate mechanistic understanding of the C–water relationships across different organism levels and in projecting the effects of climate warming and shifting precipitation regimes on productivity in arid and semiarid ecosystems.     

The −1082A/G polymorphism in the Interleukin-10 gene and the risk of rheumatoid arthritis: A meta-analysis

A large number of studies have shown that the −1082A/G polymorphism (rs1800896) in the Interleukin-10 gene (IL-10) is implicated in the susceptibility to rheumatoid arthritis (RA). However, the results are inconsistent and inconclusive. The aim of this study is to analyze the association between the −1082A/G polymorphism in the IL-10 gene and the RA risk by meta-analysis. A total of 1480 cases and 1413 controls in 10 case–control studies were included in this meta-analysis. The results indicated that the G allele carriers (GG + GA) had a 25% decreased risk of RA, when compared with the homozygote AA (odds ratio (OR) = 0.75, 95% confidence interval (CI): 0.59–0.93). In the analysis in Europeans, significant decreased risks were associated with the G allele carriers (OR = 0.73 and 95% CI: 0.57–0.93 for GG + GA vs. AA). The results from this meta-analysis provide evidence for the association between the IL-10 −1082A/G polymorphism and the risk of RA. To further evaluate gene × gene and gene × environment interactions between the polymorphisms in the IL-10 gene and RA risk, more studies with large groups of patients are required.     

蛹虫草子实体多糖的分离纯化

目的:研究人工培养蛹虫草子实体多糖的分离纯化方法.方法:多糖经脱色、醇析、除蛋白及乙醇分级沉淀,采用Seph-adex G100柱层析纯化.结果:60℃脱色9h脱色率达70.72％.醇析最优条件为:无水乙醇,24h,4倍乙醇.Sevag法抽提30min重复6次除蛋白率达84.09％;抽提lh重复3次、6次除蛋白率分别为81.14％、84.47％,多糖损失率分别为27.03％、43.16％.木瓜蛋白酶除蛋白最优条件为70℃,1:10,2h,除蛋白率为25.67％.粗多糖经乙醇分级沉淀得2种粗多糖成分,分别经Sephadex G100柱层析可进一步纯化为3种较纯多糖成分.结论:采用乙醇分级沉淀及Sephadex G100柱层析纯化粗多糖可得到3种较纯多糖成分,纯化效果较好.     

西北旱寒区地理、地形因素与降雨量及平均温度的相关性——以甘肃省为例

地理、地形因素是影响西北旱寒区农业种植结构和生态保育的重要因素之一。以甘肃为例,在遥感和GIS技术支持下,选取该地区122个气象站点的1980、1990、2000年3个年份各月降雨量和平均气温作为数据源,分析了各月降雨量和平均气温与经纬度、海拔、坡向、坡度之间的相关关系。结果表明,降雨量与经度、纬度和海拔3个地理、地形因子相关性较大,与坡度和坡向无显著性相关;降雨量和纬度之间存在普遍的显著性负相关,平均偏相关系数在0.5以上。另外,月平均气温与经度、海拔具有很高的显著性负相关,其中平均气温与海拔之间的偏相关系数达到0.9以上,但与坡度和坡向的相关性不显著。更进一步,分析了3个年度各月的月平均气温与纬度之间的关系,虽然气温和纬度之间存在一定的相关性,但随着年份的变化,温度与纬度具有显著性相关的月份数在减少,并且在存在相关性的月份中,气温同纬度之间的偏相关系数也在逐年减小,纬度对温度的空间分布的影响正逐渐变弱。研究结果支持了中国西北干旱区范围正向东南扩展的结论,并为全球变化下旱区农业生态系统管理提供理论潜力。     

贵阳市大气降水中汞的分布特征

于2008年7-9月对贵阳市中心城区采集的21个大气降水进行了总汞、甲基汞及阴、阳离子浓度的测定,分析了大气降水中总汞与阴阳离子间的相互关系.结果表明:大气降水中总汞的平均含量为18 ng·L-1,变化范围为0.4～57.4 ng·L-1;甲基汞的平均含量为0.07 ng·L-1,变化范围为0.02～0.2 ng·L-1.大气降水中的阴离子以SO2-4和NO-3为主,其浓度平均值分别为151和145 mol·L-1;阳离子主要以Ca2+为主,平均浓度达到了123 mol·L-1,变化范围为3.7～560 mol·L-1,其次是NH4+和Mg2+,其浓度平均值分别为52.2和20.4 mol·L-1.通过分析降水中总汞和阴阳离子之间的相互关系,发现总汞和阴离子SO2-4具有显著的相关性,与F-有一定的相关性,而与NO-3不具有相关性.由此初步判定,大气降水中的总汞主要来源于燃煤等人为释放源.     

南丰蜜桔可溶性固形物近红外检测的多元线性回归变量筛选

文章采用反向区间偏最小二乘法结合连续投影算法,筛选南丰蜜桔近红外检测的多元线性回归变量。对南丰蜜桔近红外光谱进行多元散射校正后,利用反向间隔偏最小二乘法,从500～1750 nm中初选出7个光谱区间,用于多元线性回归变量筛选。利用通过遗传算法和连续投影算法筛选出的变量建立了多元线性回归模型。经比较发现,利用反向区间偏最小二乘法结合连续投影算法筛选出的变量建立的多元线性回归模型,预测结果最优,模型预测相关系数为0.937,模型预测均方根误差为0.613 oBrix。结果表明,反向区间偏最小二乘法结合连续投影算法,可以有效地筛选近红外光谱的多元线性回归变量,提高南丰蜜桔可溶性固形物模型的预测精度。     

Effect of precipitation variability on net primary production and soil respiration in a Chihuahuan Desert grassland

Precipitation regimes are predicted to become more variable with more extreme rainfall events punctuated by longer intervening dry periods. Water‐limited ecosystems are likely to be highly responsive to altered precipitation regimes. The bucket model predicts that increased precipitation variability will reduce soil moisture stress and increase primary productivity and soil respiration in aridland ecosystems. To test this hypothesis, we experimentally altered the size and frequency of precipitation events during the summer monsoon (July through September) in 2007 and 2008 in a northern Chihuahuan Desert grassland in central New Mexico, USA. Treatments included (1) ambient rain, (2) ambient rain plus one 20 mm rain event each month, and (3) ambient rain plus four 5 mm rain events each month. Throughout two monsoon seasons, we measured soil temperature, soil moisture content (θ), soil respiration (R_s), along with leaf‐level photosynthesis (A_net), predawn leaf water potential (Ψ_pd), and seasonal aboveground net primary productivity (ANPP) of the dominant C₄ grass, Bouteloua eriopoda. Treatment plots receiving a single large rainfall event each month maintained significantly higher seasonal soil θ which corresponded with a significant increase in R_s and ANPP of B. eriopoda when compared with plots receiving multiple small events. Because the strength of these patterns differed between years, we propose a modification of the bucket model in which both the mean and variance of soil water change as a consequence of interannual variability from 1 year to the next. Our results demonstrate that aridland ecosystems are highly sensitive to increased precipitation variability, and that more extreme precipitation events will likely have a positive impact on some aridland ecosystem processes important for the carbon cycle.