海氏桨角蚜小蜂新疆种群形态特征及其与烟粉虱的时空动态比较

为了解烟粉虱的寄生蜂海氏桨角蚜小蜂的特征、发生规律,观察了其新疆种群的形态特征,于2012年在田间比较了该寄生蜂在棉花、甜瓜、茄子和辣椒上与烟粉虱的时空动态。结果表明,在辣椒上海氏桨角蚜小蜂成虫发生期最早,7月5日始见成虫;在4种作物上海氏桨角蚜小蜂和烟粉虱成虫分别在茄子和甜瓜上的发生数量最多,单叶虫口数量最高分别为16.12和66.47头;除辣椒外,在其它作物上成蜂的发生期比烟粉虱成虫约晚20 d,而被寄生的烟粉虱若虫与未被寄生的若虫时空动态较吻合;烟粉虱和海氏桨角蚜小蜂在植株上的成虫数量均表现出明显的上部中部下部的分布特征。研究表明,与烟粉虱比较,海氏桨角蚜小蜂新疆种群的时空动态表现出明显的滞后性和跟随效应,且其可能对寄主植物有一定的选择性。     

四种不同种植模式茶园节肢动物的群落组成

为了解浙江省不同种植模式茶园节肢动物的群落组成,于2013—2014年对松阳县4种茶园的节肢动物群落数量、时空格局和茶丛上层益害生物比及其动态进行了调查。结果表明:林间茶园害虫、天敌物种数和总物种数显著大于其它3种茶园;林间茶园天敌个体数最多,丰产茶园害虫个体数和总个体数最多。在垂直分布上,天敌个体数在母穗园、林间茶园中以上层最多,在丰产茶园和两行密植茶园中以中层最多;害虫个体数在丰产茶园、母穗园和林间茶园以中层最多,在两行密植茶园以下层最多,分别占其全株的60%、56%、42%和51%;4种茶园益害个体数比皆以上层最多。在水平分布上,害虫个体数在丰产茶园、两行密植茶园、林间茶园皆以朝北方向最多,分别占其全株的35.0%、26.0%和26.3%;害虫个体数以茶丛内层较多,天敌个体数以外层较多;地上部分林间茶园益害个体数比约是丰产茶园的2倍。表明种植模式可改变群落空间格局和益害比。     

Groundwater contributions in water-salt balances of the lakes in the Badain Jaran Desert,China

Groundwater-fed lakes are essential for the ecology in arid and semiarid regions.As a typical arid region,the Badain Jaran Desert (BJD) is famous in the world for the presence of a large number of groundwater-fed saline lakes among the mega dunes.Based on the up to date geological surveys and observations,this study analyzed the groundwater contributions in water-salt balances of the lakes in the desert.We found different types of springs,including the sublacustrine springs that indicate an upward flow of groundwater under the lakebed.A simplified water balance model was developed to analyze the seasonal variations of water level in the Sumu Barun Jaran Lake,which revealed an approximately steady groundwater discharge in the lake and explained why the amplitude of seasonal changes in lake level is less than 0.5 m.In addition,a salt balance model was developed to evaluate the salt accumulations in the groundwater-fed lakes.The relative salt accumulation time is 800–7,000 years in typical saline lakes,which were estimated from the concentration of Cl-,indicating a long history evolution for the lakes in the BJD.Further researches are recommended to provide comprehensive investigations on the interactions between the lakes and groundwater in the BJD.     

Comparison of three evapotranspiration models with eddy covariance measurements for a Populus euphratica Oliv. forest in an arid region of northwestern China

The accurate estimation of evapotranspiration(ET) in arid regions is important for improving the water use efficiency of vegetation. Based on successive observations from May to October of 2014, we estimated the ET of a Populus euphratica Oliv. forest during the growing season in an extremely arid region using the PM(Penman-Monteith), SW(Shuttleworth-Wallace) and SSW(an improved canopy transpiration model) models. Estimated ET values were compared with those of the eddy covariance measurements. Results indicated that the actual ET of the P. euphratica forest was always overestimated by the PM model. The accuracy of the SW model was higher than that of the PM model. However, some data were not easily obtained because of the complicated structure of the SW model. The newly proposed SSW model gave the most accurate ET values, and its accuracy was higher at hourly than at daily time scale. In conclusion, the SSW model is more suitable for sparse vegetation system at large scales in extremely arid regions.     

Effects of grazing intensity on seed production of Caragana stenophylla along a climatic aridity gradient in the Inner Mongolia Steppe,China

As the increases of climatic aridity and grazing intensity,shrubs play an increasingly important role in grassland ecosystem in arid and semi-arid regions,and its abundance also generally increases.However,the effects of climatic aridity and grazing intensity on sexual reproduction of shrubs in grassland remain largely unclear.In order to understand the effects of grazing intensity and climatic drought stress,and their interaction on seed production of shrub species,we examined the seed number,seed weight and seed yield of Caragana stenophylla under three grazing intensities(fenced,mild grazing and severe grazing) across a climatic aridity gradient(semi-arid,arid,very arid and intensively arid zones) in the Inner Mongolia Steppe,northern China during 2012–2013.The seed number,seed weight and seed yield gradually increased from the semi-arid to the very arid zones,but decreased from the very arid to the intensively arid zones in fenced plots.The seed number and seed yield decreased from the semi-arid to the intensively arid zones in mild and severe grazing treatment plots,therefore,grazing enhanced the suppression effect of climatic aridity on seed production of C.stenophylla.The seed number and seed yield gradually decreased as grazing intensity increased.The seed weight was highest in severe grazing plots,followed by the mild grazing plots and then the fenced plots.Precipitation varied interannually during the study period.We observed that the seed number,seed weight and seed yield were lower in the low precipitation year(2013) than in the high precipitation year(2012).As climatic drought stress increased,the negative effects of grazing on seed production of C.stenophylla also gradually increased.Our results indicated that climatic drought stress may contribute to the encroachment of C.stenophylla shrub in arid zones by promoting its seed production.However,grazing had negative effects on sexual reproduction of C.stenophylla,and the combined effects of drought stress and grazing seriously suppressed sexual reproduction of C.stenophylla in the intensively arid zone.     

西安市临潼区土地利用动态变化研究

基于临潼区2001～2006年土地利用现状变更调查数据,对临潼区5年间土地利用在数量结构、利用程度、空间格局等方面的变化进行了较为深入的分析,揭示了临潼区土地利用在变化幅度、变化速度、变化方向、利用深度和广度及空间分布上的特征,为全面掌握临潼区土地利用变化的时空规律、进行未来趋势预测提供了基础。     

欠发达地区农村剩余劳动力转移模式比较及路径选择——城镇化与非农化

通过对城镇化和非农化两个基本概念的辨析,探讨并揭示农村剩余劳动力转移的实质,提出超越城镇化的非农化转移模式,旨在为当下中国农村剩余劳动力转移寻求一条更为切合欠发达地区实际的路径与模式。     

陕西省植被净第一性生产力时空变化研究

利用1981~2000年GloPEM光能利用率模型数据、土地覆盖数据和中国县域行政区划矢量数据,对陕西省植被净第一性生产力(NPP)总量变化、空间分布格局及其变化特征进行了研究。结果表明,陕西省多年平均NPP总量为1.59×1014gC/a,单位面积年均NPP为771 gC/(m2.a)。20年来,陕西省植被年均NPP在波动中虽然有增加但总量仍呈减少趋势,即从1981年的1.55×1014gC/a减少到2000年的1.50×1014gC/a。陕西省单位面积年均NPP的空间分布格局显著,呈现出由南北向中部递增的趋势。陕西省年均NPP的空间变化明显,其中有43.4%的地区年均NPP增加,主要集中在陕南秦巴山区和关中平原;有56.6%的地区年均NPP减少,主要集中在陕北黄土高原。     

Economics of smallholder rubber expansion in Northern Laos

In Northern Laos, as elsewhere in the Southeast Asian uplands, there is an agricultural transition underway from subsistence production based on shifting cultivation to commercial production based on tree crops. In response to demand from China, rubber smallholdings are being established by shifting cultivators in Northern Laos, encouraged by government land-use policy. We examine the bio-economics of smallholder rubber production in an established rubber-growing village and model the likely expansion of smallholder rubber in Northern Laos. Data were obtained from key informants, group interviews, direct observation, and a farm-household survey. Latex yields were estimated using the Bioeconomic Rubber Agroforestry Support System (BRASS). A financial model was developed to estimate the net present value for a representative rubber smallholding. This model was then combined with spatial data in a Geographical Information System (GIS) to predict the likely expansion of rubber based on resource quality and accessibility. Implications are drawn for upland development in the region.     

祁连山土壤呼吸的时空变异及其与影响因子的关系

采用美国Li—cor公司生产的L16400-09土壤呼吸室连接到L16400便携式光合作用测量系统,对祁连山不同植被类型土壤呼吸速率进行了连续1年在生长季的野外测定,并通过多元回归手段对其影响因子进行了分析。结果表明：1）2003年生长季祁连山不同植被类型土壤呼吸速率的季节动态均为一单峰曲线,最大值出现在7月份;2）不同植被类型之间的土壤呼吸及其影响因子都存有一定程度的空间变异,且随着季节的变化,表现出一定规律性;其变异系数分别为：土壤呼吸速率在21．4％-72．18％之间,温度在12．00％-38．67％之间,土壤水分在32．17％．201．34％之间,地上生物量在72％左右;3）CO2释放速率、气温、土壤含水量和生物量之间的关系分析表明约有81％的土壤呼吸量变化是由气温、土壤水分和生物量共同决定的。