Growth and development of bambara groundnut (Vigna subterranea) in response to soil moisture: 1. Dry matter and yield

The effect of drought on the growth and development of bambara groundnut (Vigna subterranea (L.) Verdc.) was studied in controlled-environment glasshouses in the UK. There were three landraces (S19-3, DipC and UN from Namibia, Botswana and Swaziland, respectively) and two watering regimes; a control that was irrigated weekly to 90% field capacity and a drought treatment with no irrigation from 49 days after sowing (DAS) until final harvest (147 DAS). Bambara groundnut responded to drought by reducing the rate of leaf area expansion, final canopy size and total dry matter (TDM) during vegetative growth. Drought also caused significant reductions in pod dry matter (PDM), pod number, seed weight and harvest index (HI), leading to a decrease in final pod yield that was different between landraces. Across landraces, drought reduced mean pod yield from 298 g m⁻² to 165 g m⁻², representing 45% yield loss. Despite the reduction in all landraces, the mean pod yield across the droughted treatments that had received no water for almost 100 days indicated the resilience of the species to drought. The three landraces differed in their phenology; S19-3 exhibited a reduced phenology while UN maintained the longest life cycle. The different responses of the landraces reflect their adaptation to their local climates where mean annual rainfall ranges between 365 mm (Namibia) and 1390 mm (Swaziland). We discuss the significance of these results for future breeding programmes on bambara groundnut.     

水稻籼爪交和粳爪交杂种优势的研究Ⅱ.农艺性状的杂种优势分析

研究了籼爪交和粳爪交杂种在长沙、三亚的农艺性状和干物质产量的杂种优势.在长沙的籼爪交杂种在结实率和每穗实粒数方面具有负向超亲优势,在每穗实粒数、结实率、单株粒重和理论产量方面存在负向对照优势,其余性状均为正向优势;粳爪交杂种在千粒重和结实率方面存在负向超亲优势,其余性状为正向超亲优势, 在始穗期、秆高和单     

中华苦荬菜干物质和有效成分积累动态研究

采用称重法测定中华苦荬菜干物质积累程度,UV法测定其总黄酮和总三萜含量,分析中华苦荬菜不同生长发育时期干物质积累及有效成分积累的变化。结果表明,中华苦荬菜的干物质积累呈＂S＂形曲线变化,在4月底至6月初逐渐增加,6月上旬达到高峰,随后降低;总黄酮的含量逐渐增加,在6月初达到顶点;总三萜的含量在4月末最高,之后逐渐降低;适宜采收期在5月末～6月初之间。     

Diversity and production of Ethiopian dry woodlands explained by climate- and soil-stress gradients

Dry woodlands cover about 14% of the total African land surface and represent about 25% of the natural vegetation. They are characterized by a seasonal climate, with a dry season of 4-7 months. Large parts of these ecosystems are degrading due to grazing, fire or exploitation by people. We studied species richness and productivity patterns of dry woodlands in Ethiopia. For such ecosystems, classic productivity and diversity hypotheses predict that species richness and productivity increase as the wet season length increases, and decrease when soil conditions create water stress. We inventoried and measured trees in 18 2-ha plots distributed in two sites, one higher altitude site with a shorter wet season than the lower altitude site. We found that the stand volume per hectare was lower in the site with a shorter wet season. Across all 18 plots we observed that stand volume decreased with soil water stress (estimated from texture and depth). This was in line with the prediction. The species richness was lower in the short-wet-season woodlands, but was unaffected by variation in soil conditions. This suggests that climate driven constraints (wet season length) set the limits to species richness, and not soil conditions. As far as we know, this study is one of the first studies that evaluated these productivity and diversity hypotheses for dry African woodlands.     

Effects of multiple factors on plant diversity of forest fragments in intensive farmland of Northern Portugal

The joint and independent effects of dominant tree species, forest patch spatial attributes, and forest structure and management as drivers of plant species richness and composition in small forest patches scattered within an intensive agricultural landscape were addressed.In a landscape with scattered urban and intensive dairy agricultural areas in north-west Portugal, within which small forest patches (dominated by pines, eucalypts, or both) represent semi-natural habitat islands, 50 small forest patches, with areas ranging between 0.3 and 3 ha, were selected and surveyed for vascular plant diversity, within dairy farming landscape mosaics dominated by annual forage crops. Explanatory variables were composed of three datasets derived either from GIS mapping or field observations: forest type (dominant tree species), forest patch spatial attributes (patch area and shape index), and measures of forest management and structure (diameter at breast height, tree density per hectare, and percentage cover of vegetation strata). Variations in these forest patch attributes were assessed across forest types, and related to measures of plant diversity (total, native, alien, woody, and herbaceous species richness). Redundancy analysis with variance partitioning was applied to evaluate the joint and independent effects of the three sets of variables on species assemblages. The recent shift in canopy dominance from pine to eucalypt observed in the region appears to be related to a (nonsignificant) tendency for the increase of patch area and to the decrease of patch complexity, as well as several changes in forest structure and management, expressed as a trend to denser tree canopies and lower cover of understory plants. Dominant tree species and attributes related to forest structure and management were the most important factors determining plant diversity. The joint effect of the dominant tree species and forest structure and management resulted in lower levels of plant species richness in eucalypt plantations. These were also more prone to invasion by alien species, probably due to decreased biotic resistance from unsaturated native plant assemblages. Our results draw attention to the importance of dominant tree species and management practices for the maintenance of plant diversity levels (species richness and composition) in dairy landscape mosaics, highlighting the importance of the remnants of semi-natural forests as refuges for plant diversity in the landscape context. Nonetheless, forest plant diversity could further be fostered by promoting naturalness of pine stands and the regeneration of native oak woodlands in some forest areas. This would also diversify the range of ecosystem services that could be provided by forest areas in these peri-urban farmlands.     

张掖绿洲农田防护林可持续经营评价指标体系研究

以可持续发展理论为指导 ,结合森林可持续经营的思想 ,从森林生态学和森林经理学的角度出发 ,在张掖绿洲农田防护林的基本特征和经营状况的基础上 ,进行了系统的阐述和分析 ,提出了张掖绿洲农田防护林可持续经营的思想内涵。并运用数学方法 ,从社会发展指标、经济发展指标、生态功能指标、政策、技术保障功能指标等 6个方面构建了张掖绿洲农田防护林可持续发展的指标体系 ,计算结果表明 ,张掖绿洲农田防护林可持续发展力指数为 0 .4 780 ,为基本不可持续发展。同时提出了农田防护林可持续经营的对策和建议     

坐标旋转订正对农田林网水热通量测算精度的影响

农田防护林的特殊结构使附近农田地表大气运动形成了特有的动力学和热力学效应,影响着周边物质和能量交换过程。坐标旋转订正方法的选择成为提高农田防护林水热通量测算精度的核心问题,选取2012年3月9日至5月7日共60 d的防护林网内农田的涡动相关观测数据,对相关湍流特征及能量闭合率等关键参数进行坐标旋转订正并进行比较,结果表明:(1)在整个试验过程中,采用平面拟合法进行坐标旋转时,当订正参数的计算周期小于15 d时,x-z平面内旋转角度有一定的波动,而在计算周期大于15 d后,则基本维持在-2.8°左右。采用二次旋转法订正的x-z平面内旋转角度受原始水平风向的影响始终很大;(2)2种坐标旋转方法对于三维风速的处理结果基本一致,在风速较大的情况下,需要考虑坐标旋转方法的选择对结果的影响。二次旋转方法订正后的垂直风速全部为零,平面拟合方法订正后的垂直风速接近于0;(3)平面拟合订正后摩擦风速基本与订正前一致,而二次旋转方法订正后的结果增大了将近5%;(4)平面拟合方法对显热通量及潜热通量的订正误差较小,二次旋转方法则分别将原始测得值提高了5%左右;(5)防护林网通量的能量闭合率经过平面拟合订正后提高了17%,而经过二次旋转法订正后则提高了30%。总之,坐标旋转方法可以对观测设备倾斜引起的误差进行订正,订正后的结果比订正前更精确。二次坐标旋转方法因为可以订正较短时间段内的单组数据,比较适用于下垫面情况变化较快时的观测;平面拟合方法适用于观测系统及其周围环境在整个测量过程中相对稳定时的观测。二次旋转方法对防护林网水热通量订正更好。     

论退耕还林与耕地保护的辨证关系

从辨证唯物主义的角度深入分析了当前我国实行的耕地保护和退耕还林的辨证关系,指出退耕还林与耕地保护均是构筑国土安全的重要组成部分,退耕还林是改善生态环境、维护国土生态安全的重要举措;耕地保护则是保障国家耕地和粮食安全,维系大局稳定的战略性问题。耕地保护是退耕还林的基础和前提,退耕还林是耕地保护的辅助和保障。要实现耕地保护和退耕还林的协同发展,必须正确认识和处理好二者的辨证关系,统筹规划,是耕地保护与退耕还林协同发展的基础;切实保护农民权益,是耕地保护与退耕还林协同发展的关键;因时、因地、因势制宜,是耕地保护与退耕还林协同发展的保障。     

退耕还林地域选择研究——以内蒙古武川县为例

采用地理信息系统分析工具与手段,从生态需求进行系统分析,提出和确定出武川县退耕还林地域选择标准为:坡度级大于25°的耕地;重度沙化的耕地;轻微沙化或未沙化无灌溉条件且年降雨量不足300mm的耕地。最终确定出该县退耕还林面积为7 18万hm2,占全县农耕地面积的50 18%。