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991.
半干旱地区植被恢复过程中林下植被生态位特征的研究 总被引:9,自引:0,他引:9
应用生态位理论,以黄土半干旱区6个不同密度林分林下草本层植被为研究对象,以林分密度作为资源轴,以物种重要值为生态位计测的状态指标,对林下植被进行生态位计测和分析,揭示林内资源环境利用状况。结果表明:林下植被的生态位宽度值普遍较小,其中阿尔泰紫婉、铁杆蒿等生态位宽度较大,这与无林地相似,同时物种间生态位重叠并不普遍,重叠度普遍不大,各种对间对资源的共享趋势不明显,生态位发生分离,显示了林下植被状况差。 相似文献
992.
993.
该本文采用三因素三水平正交试验设计,就笼底材料、饲养密度、不同性别组群下3~6周龄AA肉仔鸡的生产性能及其胴体品质进行研究。结果表明:竹竿和塑料笼底下肉仔鸡的胴体品质以及笼养密度11 ~14只/m2下的生产性能较高,以塑料笼底、低密度和公鸡单饲组的肉仔鸡总增重最高,达1.82kg。笼底材料对增重、饲料转化率、屠宰率、腹脂率以及胸肌纤维直径没有影响,但铁丝笼底会导致胸囊肿发病率升高。高饲养密度下能显著降低肉鸡增重和饲料转化率,但肉仔鸡的屠宰率有所增加;而低饲养密度有利于胸肌纤维直径的增加。单饲母鸡的腹脂率显著高于单饲公鸡和公母混群饲养鸡的腹脂率。 相似文献
994.
Variation of enzyme activities, CO2 evolution and redox potential in an Eutric Histosol irrigated with wastewater and tap water 总被引:1,自引:0,他引:1
M. Brzezinska S. C. Tiwari Zofia Stepniewska M. Nosalewicz R. P. Bennicelli A. Samborska 《Biology and Fertility of Soils》2006,43(1):131-135
An Eutric Histosol soil was irrigated for 4 years with municipal wastewater to compare its characteristics with a soil under natural rainfall that had never received wastewater and a soil that was irrigated with normal tap water. Four years irrigation of the soil with wastewater caused significant (P<0.001) increase in dehydrogenase, urease, acid and alkaline phosphate activities and CO2 evolution, and reduced the redox potential (P<0.05). The influence of treatments and plant cover on soil properties were significant (P<0.05) under both salix and grasses, except for few properties (redox potential and urease and alkaline phosphatase activities). It is suggested that, although different toxicants, e.g. heavy metals, may accumulate in wastewater-treated soils, enrichment of soil with organic substances and nutrients stimulated CO2 evolution and enzyme activities in the irrigated soil. 相似文献
995.
996.
Factors affecting the compaction susceptibility of South African forestry soils were assessed. Two traditional measures of compaction susceptibility were used: maximum bulk density (ρmbd) determined by the standard Proctor test, defined compactibility, and the compression index using a simple uni-axial test, defined compressibility. Soils were chosen from a broad range of geological and climatic regions and they varied greatly in texture (8 to 66 g 100 g−1 clay) and organic matter content (0.26 to 5.77 g 100 g−1 organic carbon). Soils showed a wide range in ρmbd values, from 1.24 to 2.00 Mg m−3, and this reflected the wide range of particle size distributions and organic matter contents of the soils. Very good correlations were achieved between measures of particle size distribution, particularly clay plus silt and both compactibility and compressibility. Both compactibility and compressibility were significantly correlated with loss-on-ignition (LOI) which is a measure reflecting the combined effects of soil texture and organic matter on soil physical properties. Indices of compaction susceptibility were influenced more by particle size distribution than by organic carbon content. Clear effects of organic carbon on compaction behaviour were only evident for soils with low clay contents (< 25 g 100 g−1. No clear relationship between compactibility and compressibility was found. Compactibility generally increased with decreasing clay plus silt content, whereas compressibility increased up to about 70 g 100 g−1 clay plus silt before decreasing again. It is difficult to define compaction susceptibility solely in terms of indices of compactibility or compressibility particularly as there is no clear relationship between these two properties. A classification system for compaction risk assessment is presented, based on the relationship between compactibility (ρmbd) and LOI, and between clay plus silt content and compressibility. 相似文献
997.
Juan Carlos Moreno Saiz Felipe Dom?&#x;nguez Lozano Helios Sainz Ollero 《Biological conservation》2003,113(3):419-431
The transfer of legal responsibilities from the Central Government to the Autonomous Communities ended a tradition of paying little attention to endangered Spanish flora. The studies undertaken to implement the European Natura 2000 network, and to prepare regional ‘Red Data Books’ and lists of protected flora offered a much better view of which species were really at risk. As a consequence, a growing number of botanists is now involved in different aspects of conservation biology. The recent publication of a new Spanish Red List of vascular flora has provided the groundwork for the so-called ‘Threatened Flora Atlas’ project, which will update and homogenise the information on 500 taxa at risk. This project will produce a new Spanish Red Book and monitor the status of 40 selected species. The Spanish strategy for plant conservation is discussed, pointing out some deficiencies, such as the neglect of non-vascular taxa, the uneven and sometimes uncoordinated local policies and the uncertain future of some current initiatives. 相似文献
998.
重庆市土壤有机碳库的估算及其空间分布特征 总被引:22,自引:2,他引:22
基于重庆市第二次土壤普查的1411个土壤剖面数据,结合重庆市土壤图、土地利用现状图和行政区划图,在地理信息系统技术的支持下,对重庆市土壤有机碳密度及储量进行了估算、同时引入有机碳丰度指数这一指标,对有机碳在不同土壤、不同区域以及不同景观中的分布特征进行了分析。结果表明:重庆市20cm和100cm深度的土壤有机碳储量分别为0.27Tg和1.0Tg;20cm深度的土壤有机碳密度介于0.33~30.36kg/m^2之间.100cm深度的土壤有机碳密度介于1.27~72.69kg/m^2之间;重庆市土壤有机碳库在不同土壤、不同区域以及不同景观的分布具有高度的空间变异性,100cm深度的土壤、区域和景观有机碳丰度指数分别为0.58~1.95,0.55~1.39和0.46~1.58.与气候、植被、人类活动等因素密切相关。 相似文献
999.
通过建立观测样地,研究广西陆川县湿地松工程林的生长过程和经济效益,基本情况是林分生长正常,投资项目可行,但经济效益不够理想.其主要原因是:(1)过林密度小,每公顷仅1667株,(2)投入偏低;导致林分单位面积蓄积量少,按林价计算的单位面积产值较低. 相似文献
1000.
The wide distribution of Scots pine (Pinus sylvestris L.) in Europe includes two relict populations in southern Spain (Sierra Nevada and Sierra de Baza), belonging to the subspecies nevadensis. These populations are isolated in high mountains, which tends to protect them from the attack of a severe defoliating Mediterranean pest, the pine processionary moth Thaumetopoea pityocampa. However, as a consequence of climate change, the pine processionary caterpillar has increasingly attacked populations of this pine in recent years. This work describes the detrimental effects of defoliation by the pine processionary caterpillar in P. sylvestris subsp. nevadensis in Sierra Nevada. Defoliation strongly reduced pine growth as well as all the reproductive parameters measured (female and male cone production, mature cone size, seed production and seed weight), in addition to some deaths. If winter temperatures continue to increase, the pine processionary caterpillar will have a dangerous impact in these relict pine populations, by further reducing the pine's weak regeneration capacity. We suggest some mitigation actions based on managing habitat structure, in order to reduce or avoid such negative impacts. 相似文献