Tree age and soil phosphorus conditions influence N2-fixation rates and soil N dynamics in natural populations of Acacia senegal

Acacia senegal, an important leguminous tree in arid and semi-arid environments, has shown promise as a multipurpose species, including gum production and soil fertility improvement, linked with N₂-fixation capabilities. Of particular interest are ontogenetic and edaphic effects on A. senegal performance in natural populations. Our research objectives were to investigate the effect of tree age and site phosphorus conditions on (1) tree N₂-fixation and (2) soil N and C dynamics in natural stands of A. senegal var. senegal, Baringo District, in the Rift Valley, Kenya. Sites consisted of A. senegal saplings (9 months) and mature A. senegal trees (7 years) along an edaphic gradient of soil P availability. A single-tree neighborhood approach was employed using a two by two factorial design: site conditions [high and low soil P contents] and tree age class [juvenile and mature]. Soil (N and C pools and fluxes) and plant metrics were quantified. A soil transfer experiment was also employed to confirm age and site effects on soil N mineralization. On the high soil P site, A. senegal had significantly lower foliar (¹⁵N levels than neighboring non-leguminous species (Balanites aegyptiaca), while foliar δ¹⁵N values in A. senegal on the low P site exhibited no significant difference with our reference plant, B. aegyptiaca. Across P sites, B. aegyptiaca had similar foliar δ¹⁵N values. These results indicate that the rate of N₂-fixation of A. senegal trees, as determined with foliar ¹⁵N natural abundance methodology, increased with increasing soil P availability in these natural populations. However, N₂-fixation rates declined with age. Although soil texture and soil CO₂ efflux did not differ between sites or across ages, soils under mature A. senegal at the high P site exhibited significantly greater total N content and total C content in comparison to soils at the low P site and under juvenile plants. Furthermore, under mature A. senegal trees, soil N mineralization rates were significantly greater as compared to under saplings. Soil transplants confirmed that soil microbial activity may be stimulated under mature trees as N mineralization rates were 2-3 fold greater compared to under A. senegal saplings. Our findings suggest that tree age and soil P availability are important factors in the nitrogen budget of natural populations of A. senegal, determining N₂-fixation rates, and potentially influencing soil total N and C pools and soil mineral N. This study provides information regarding the adaptation of A. senegal under differing edaphic conditions thus increasing accuracy of management support for A. senegal populations as productive agroforests.     

仰角可调摇臂式喷头水力性能试验

在不改变喷头原有结构的基础上,设计了一种由上支撑杆、下支撑杆、限位杆、柔性波纹管组件、内螺纹空心轴、定位螺钉、调节螺钉等组成的喷头仰角调节机构,实现喷头仰角在13°、18°、23°、30°4个角度的调节,并对安装了该机构的喷头进行了水力性能试验。结果表明,喷头仰角为23°时,不同工作压力下喷头的射程均最大;在23°与30°时组合均匀度系数相对较大,最利于组合喷灌。不同工作压力下,平均喷灌强度随着喷头仰角的减小而增大。喷头仰角由23°减小到13°时,喷头喷洒水滴的飘移损失减小,平均喷灌强度增加,因此喷头仰角减小可以增强其抗风、抗坡能力。仰角越小,喷头射程末端降水量变化越剧烈,导致喷头喷洒降水量分布不均,所以仰角调节不宜过小。安装了仰角调节机构的喷头在各象限的转动误差均小于±10%,其转动均匀性符合要求。     

基于GIS土壤酸碱度的Kriging和Cokriging估值研究

应用地统计学的半方差函数和克立格法,在仪征地区利用高程这一辅助变量把土壤pH和成土母质联系起来,分析了土壤pH的半方差和不同高程土壤pH的交互半方差特征,比较了土壤pH的Kriging和Cokriging估值.研究表明,预测值与实测值之间的相关系数协同克立格法比普通克立格法提高了39.00%,使估值的结果进一步精确.     

桑科植物水分运输阻力生物物理模型研究

根据枸树导管解剖结构，用统计学方法建立了桑科植物水分长距离运输阻力的生物物理模型。结果表明，枸树水分长距离运输阻力与导管长度倒数呈极显著的线性关系，这与实际情况相符。     

Soil and climate are better than biotic land cover for predicting home-range habitat selection by endangered burrowing owls across the Canadian Prairies

Statistical models that describe species-environmental relationships are important components within many wildlife conservation strategies. These models are typically developed from studies conducted on small geographic scales (hundreds of square kilometres), representing a relatively small range in environmental conditions. Such local models from local studies are often then extrapolated to predict the suitability of other unsampled regions. The value of many models would be increased by considering larger-scale processes that might be structuring spatial patterns across species distributions. We examined home-range habitat selection by burrowing owls throughout the mixed prairie grassland region of western Canada (180,000 km²) to determine whether owl selection for biotic factors changes along abiotic gradients. Specifically, we classified 37 explanatory variables into five categories (geography, grassland fragmentation, land-use, soil, and climate), created models for each set of variables, and evaluated the predictive ability of each model. We then examined interaction effects to determine if the relationship between land cover variables and the probability of owl home-range selection varied within large-scale abiotic criteria. Our results showed that soil and climate produce the most predictive models of burrowing owl home-range selection and create unique environmental conditions for owls which are independent of land cover at this scale. This study provides new insight into burrowing owl habitat requirements, and strengthens the case for considering large-scale abiotic gradients when prioritizing areas for species conservation.     

Altitude and temperature dependence of change in the spring vegetation green-up date from 1982 to 2006 in the Qinghai-Xizang Plateau

Research in phenology change has been one heated topic of current ecological and climate change study. In this study, we use satellite derived NDVI (Normalized Difference Vegetation Index) data to explore the spatio-temporal changes in the timing of spring vegetation green-up in the Qinghai-Xizang (Tibetan) Plateau from 1982 to 2006 and to characterize their relationship with elevation and temperature using concurrent satellite and climate data sets. At the regional scale, no statistically significant trend of the vegetation green-up date is observed during the whole study period (R² = 0.00, P = 0.95). Two distinct periods of green-up changes are identified. From 1982 to 1999, the vegetation green-up significantly advanced by 0.88 days year⁻¹ (R² = 0.56, P < 0.001). In contrast, from 1999 to 2006, a marginal delaying trend is evidenced (R² = 0.44, P = 0.07), suggesting that the persistent trend towards earlier vegetation green-up in spring between 1980s and 1990s was stalled during the first decade of this century. This shift in the tendency of the vegetation green-up seems to be related to differing temperature trends between these two periods. Statistical analysis shows that the average onset of vegetation green-up over the Qinghai-Xizang Plateau would advance by about 4.1 days in response to 1 °C increase of spring temperature. In addition, results from our analysis indicate that the spatial patterns of the vegetation green-up date and its change since 1982 are altitude dependent. The magnitude of the vegetation green-up advancement during 1982-1999, and of its postponement from 1999 to 2006 significantly increases along an increasing elevation gradient.     

Association between biogeographical factors and boreal lake fish assemblages

Abstract  Five regions in insular Newfoundland Canada, comprising 152 lakes, were studied to identify associations between species composition (presence and absence), geographical location and environmental variables (pH, area, depth, alkalinity, secchi disc depth and shoreline development factor). Correspondence analysis and canonical variate analysis were used to distinguish regional patterns. Five biologically and environmentally distinct areas were identified. The degree of association between biological, environmental and geographical distances were contrasted using Mantel's test. Regional fish community structure was significantly correlated with large-scale geographical distance but not with environmental parameters or small scale distance. It was proposed that large scale processes such as post-glacial dispersion, climate and recent species introductions are important determinates in structuring regional fish assemblages. Differences in individual lake character were important determinates in intraregional variability in fish assemblage type. Sampling strategies for regional modelling and management are discussed.     

不同海拔高度温、湿度对土壤养分的影响

本研究选择不同海拔的高寒草甸为研究对象,对不同海拔梯度温度、湿度及土壤养分进行了研究,研究结果显示:随着海拔的逐渐升高,地表温度逐渐降低,土壤湿度逐渐增大,土壤养分含量总体变化规律不明显,土壤全钾含量与温度呈负相关关系,且达到显著水平。     

海拔高度对茶园环境及茶叶品质的影响

[目的]研究不同海拔高度对山地茶园环境和茶叶内含成分的影响。[方法]对黄山市徽州区不同海拔高度的茶园生态环境和茶叶生化品质(包括氨基酸、咖啡碱、茶多酚、酚氨比、茶水浸出物、叶绿素)进行研究。[结果]茶园小气候因子和茶叶品质性状在不同海拔高度的变异存在很大差异。海拔每增加100 m,年均气温下降0.65℃,降水量增加36.3 mm,相对湿度增加3.85%。茶园日光照强度曲线呈一个开口向下的抛物线变化趋势,峰值出现在12:00。通过对茶叶产量及其构成要素的分析表明,随着海拔的上升,芽叶密度呈明显的下降趋势;产量最高值在海拔400 m的茶园。随着海拔的增加,氨基酸和咖啡碱含量均增加,茶多酚和水浸出物含量均是海拔600 m的茶园最高,酚氨比与海拔呈明显负相关。叶片中叶绿素a、叶绿素b及叶绿素总量随海拔增加呈先上升后先下降的变化规律,在海拔达到400 m时,茶树叶片中叶绿素a、叶绿素b含量最高分别为6.32和2.68 mg/g;而叶绿素a/b值随着海拔增加呈下降趋势,且下降速率随着海拔增加而逐渐减缓。[结论]该研究可为建立复合生态茶园优化管理技术体系提供科学依据。     

DGT技术在测定汞离子及其化合物中的发展与应用

汞及其化合物是环境中关注度较高的具有较强神经毒性的污染物,但其在环境中的浓度较低,传统监测方法存在操作过程复杂、较难检出等问题。梯度扩散薄膜（DGT）技术作为一种快速发展的原位采样技术能够实现汞等多种重金属污染物的高效监测。本文详细阐述了DGT装置测定Hg的原理、材料的发展、应用场景和使用中存在的问题,并结合文献计量学方法梳理研究热点与不同国家/地区的使用情况。Hg-DGT材料发展经历了从单一材料到纳米复合材料的过程,本文重点列举了不同材料的使用条件。DGT技术的环境应用主要包括监测水体中各种化学形态Hg、监测土壤和沉积物中Hg的空间分布信息、对生物有效性评价研究及其与DIFS模型结合评估Hg迁移潜力。DGT技术在应用中主要存在溶解性有机质、生物膜、Hg纳米颗粒和边界扩散层的干扰。在系统性梳理之后,提出未来Hg-DGT发展的三个方向。