Effects of different land use types on infiltration capacity in a catchment in the highlands of Ethiopia

Infiltration capacity is an important variable for understanding and predicting a range of soil processes. This study investigated for different slope positions the effects of forest conversion to cultivation and grazing on soil infiltration capacity. Infiltration capacity was measured in the field in each land use type using a double‐ring infiltrometer. A total of 108 soil samples (3 slope positions × 3 land use types × 4 soil profiles × 3 soil depths) were collected to determine the variables that affect infiltration capacity viz. particle size distribution, organic carbon content, dry bulk density and soil moisture content. The results showed that in the cultivated and grazed land compared with forest, infiltration capacity and soil moisture content were 70 and 45% smaller respectively, and dry bulk density was 13–20% larger. Changes in soil structure caused by surface soil compaction because of tillage and animal trampling coupled with a smaller soil organic carbon content, are likely to be the principal factors causing the decline in infiltration capacity and soil moisture content after conversion of forest to cultivation and grazing.     

实验性犬细小病毒感染及其病理形态学研究

取2～3月龄大13只(10只肠道驱虫),禁食24h后,分组分别经口鼻、静脉、肌肉接种TCID_(50)/ml为4×10~(5·75)的犬细小病毒(CPV)第四代猫肾细胞培养毒11.5或25.0m1/kg,再禁食48h。结果,各犬均于接种后第4d起陆续典型发病,粪便HA试验阳性,负染见CPV粒子。主要病理学变化是,小肠出血性坏死性炎,心肌灶状出血和颗粒变性;胸腺皮质的胸腺细胞及淋巴结皮质的淋巴细胞死亡、减少;在一些小肠隐窝上皮细胞、淋巴结的淋巴细胞和网状细胞以及胸腺的胸腺细胞和上皮性网状细胞核内见嗜酸性、嗜硷性或两染性包涵体;3只3月龄犬膈肌灶状出血。小肠粘膜扫描电镜观察,粘液增多,绒毛肿胀。其上的横沟变钱或消失。杯状细胞开口扩张,数目增加。电镜观察,在小肠隐窝上皮未分化细胞的核内见直径为27nm的CPV粒子,并对其形态发生作了描述。     

青海河卡牧场硒的季节变化及盈缺分析

试验研究了青海共和盆地河卡牧场夏、冬两季牧草草地系统(水、土壤、牧草、绵羊)中硒的含量变化.结果表明,河卡牧场夏季土壤和牧草严重缺硒,绵羊血浆中硒浓度低于临界水平,夏冬两季绵羊被毛中硒含量低于毛硒含量临界值.     

拟南芥PLDα1突变体的繁殖及形态和生理特性分析

对拟南芥野生型Ws及其突变体PLDα1(phospholipase D)的种植方法和形态特征进行了比较,并研究了ABA处理对其抗氧化酶系活力和丙二醛含量的差异。结果表明,与野生型相比,突变体形态上发生了较大的变化,并表现出对ABA反应敏感性的降低。ABA处理24 h后,野生型的SOD酶和POD酶活迅速发生变化,丙二醛含量迅速升高,而突变体变化较平缓,叶绿素含量的变化相似。     

肉桂人工林土壤速效养分与酶活性的季节变化

研究了广西高峰林场林龄为3年和6年的肉桂人工林土壤速效养分(水解N、速效P、速效K)和土壤酶活性(过氧化氢酶、脲酶、酸性磷酸酶)的季节变化规律及其相互关系。结果表明：两种林地土壤速效养分含量和土壤酶话性均表现出明显的季节动态．：E壤速效N、P、K含量和L壤脲酶活性均以肉桂生长初期(3月中旬)最高．其次是第一个生长高峰期(6月中旬)或第二个生长高峰期(9月中旬)，最低是生长未期(12月中旬)；而土壤过氧化氢酶和酸性磷酸酶活性以第一个生长高峰期或第二个生长高峰期最高．其次是生长初期,最低是生长末期；士壤速效养分与土壤酶活性的季节变化密切相关。因此，生长初期至第一个生长高峰期是肉桂林地施用N、P、K肥的适当时期。     

重点国有林区森林资源管理政策变革措施分析

重点国有林区天然林资源保护工程实施5年后,工程区内各级森林资源管理部门仍然沿用既往政策,已不适应新时期林业发展的趋势,更不利于森林资源的保护与利用。文中对尽快实施森林分类经营、规范林权流转、适度采伐人工商品林等森林资源管理政策提出了变革建议与对策。     

Management effects on carbon stocks and fluxes across the Orinoco savannas

Across the physiognomic types of the Orinoco llanos, periodic inventories and changes in land-use between 1982–1992 are estimated. Results indicate that the area under pastures and forest plantations is increased by 0.005337×10⁶ km², whilts reducing the area of croplands by 0.000119×10⁶ km². This is a net increase of 0.005218×10⁶ km². The gross carbon release is 174.66 Tg C per year to the atmosphere and transferring from cultivated and native vegetation to wood products (1.62 Tg C per year) and slash (1.18 Tg C per year). The processes of land preparation contribute 1.40 Tg C per year to the atmosphere. From the tree savannas, woodlands and forests 0.73 Tg C per year are estimated to have been transferred to the soil following clearance and burning over this period, and 1.05 Tg C per year from herbaceous savannas when were buried and decomposed at 0.84 Tg C per year. The estimate of carbon balance here by inventories and changes in land-use approach indicates that the Orinoco llanos is a sink of −17.53 Tg C per year. The carbon turnover time in the Orinoco system is 68 years, which provides a limited route for carbon sequestration. The calculated potential of the Orinoco llanos for storing carbon is 8300 Tg C. Ecological options to achieve this potential value are addressed. However, nutrient deficiency and seasonal water supply are serious drawbacks to take into account for increasing carbon accretion. These results are particular for the Orinoco llanos, even though described processes could be similar to world-wide savannas, where a gradient of carbon heterogeneity exists.     

甘肃竹林资源的历史变迁与发展建议

根据历史文献和实地考察资料，论述了甘肃省竹林资源的历史分布变迁和特点以及现在竹资源现状，对今后甘肃省的竹林发展提出了一些建设性建议。     

香椿组织培养与快速繁殖的研究

香椿试管苗在不同培养条件下增殖速度明显不同.太行山香椿试管苗的最佳增殖条件为改良MS十SBA1.0十GA_32.0+IAA0.0;燕山香椿试管苗则为WPM+6BA1.0+GA_32.0+IAA0.0。试管苗的生根能力在IBA0.2～1.0的范围内逐渐提高.增殖倍数不同试管苗其K的摄入量、碳水化合物含量以及POD和EST同工酶图谱亦有明显差别。     

从澳大利亚引进的两种相思植物光合速率和蒸腾效率的初步研究

以LCA-4光合蒸腾测定系统进行大腺相思和多花相思叶片气体交换过程的测定。结果如下：（1）净光合速率日变化明显，且变化趋势大体一致，即10：00-13：00具有较高的光合速率，其它测定时间相对较低。（2）两树种净光合速率存在差异。大腺相思高于多花相思，其最大值分别为19.6(10:00),16.1(13:00)μmolm^-2s^-1，日平均值分别为11.9,9.8μmolm^-2s^-1，反映了大腺相思的生长速度较多花相思快。（3）大腺相思和多花相思蒸腾速率日变化明显，正午前后较高，13：00达到最大，日平均值多花相思略高于大腺相思，分别为3.3,3.0mmolm^-2s^-1，表明在相同的环境条件下大腺相思的耗水量低于多花相思。（4）两树种蒸腾效率的日变化趋势大体上也类似，即在9：00-11：00较高，此期间大腺相思和多花相思和多花相思的平均值分别为5.51,4.21μmolCO2/mmolH2O。日平均值大腺厢思和多花相思分别为3.84,2.88μmolCO2/mmolH2O,表明消耗等量的水分大腺相思比多花相思能固定更多的CO2量，即有更高的水分利用效率。