森林凋落物分解研究进展

 森林凋落物分解是森林生态系统养分生物循环的重要环节,而分解过程中所释放的CO2是全球碳素收支的重要组分,开展森林凋落物分解研究是充分认识森林生态系统结构和功能的基础。研究认为:凋落物分解的预测指标可分为3类,即环境指标(如实际蒸散量)、凋落物物理质量(如叶抗张强度)和化学质量指标(如C/N比、木质素/N比和C/P比等);凋落物分解过程中养分释放机制极其复杂,养分动态模式主要有淋溶—释放、淋溶—富集—释放和富集—释放3种,并因凋落物种类、分解阶段和元素本身性质的不同而异;凋落物混合分解并非单一树种分解的简单叠加,因树种组成和比例不同,基质的化学组成会发生变化,从而影响分解者的多样性、丰富度和生理活性,进而直接和间接地影响其分解速率;凋落物混合分解中可能存在无效应、促进效应和抑制效应;现有的研究结果显示,凋落物混合分解的适宜比例应与群落中不同树种的种群比例相一致;CO2浓度升高不仅影响凋落物的化学性质,而且与分解环境中土壤的生物活性密切相关,但CO2浓度升高并不改变凋落物质量与分解速率之间的关系;越来越多的研究显示,CO2浓度升高的环境下,植物群落的物种组成会产生变化,这种变化对养分循环速率的影响远大于单纯大气CO2浓度变化的影响。     

太湖地区氮磷肥施用对稻田氨挥发的影响

在太湖地区乌栅土上,采用田间小区试验连续两年研究了施氮(N)量为0、180、255、330kg hm-2,施磷(P2O5)量为0、309、0、180 kg hm-2的6个组合(对照N0P0、低氮N180P90、优化N255P90、低磷N255P30、高磷N255P180、高氮N330P90)以及三个施肥时期对稻田氨挥发损失的影响,氨挥发采用密闭室间歇通气法测定。结果表明,稻田氨挥发损失主要发生在施肥后6d内,基肥和第一次追肥后各处理氨挥发量占施氮量的0.4%~11.5%,而第二次追肥后氨挥发损失比例较大,对照、低氮、优化、低磷、高磷和高氮处理的氨挥发在2002年稻季分别占施氮量的5.8%、9.7%、25.6%、15.6%和11.6%,在2003年稻季则分别为27.4%、26.2%、30.0%、35.1%和27.6%。若施肥后遇阴雨天气或正值水稻拔节孕穗期,氨挥发量便降低。田面水中的NH4 -N浓度是氨挥发的决定因素之一,与氨挥发通量呈正相关。施磷量相同时,氨挥发随施氮量增加而增加;施氮量相同时,高磷和低磷处理氨挥发均高于优化处理,表明在氮磷不平衡施用时,氮肥氨挥发损失会加剧,从氨挥发损失方面考虑,稻田推荐施磷量不宜超过P2O590 kg hm-2。     

FAO可持续土地资源管理综合规划指南及启示

土地资源可持续利用是基于可持续发展的核心内容——资源的可持续利用而形成的，指对人类生存所依赖的物质资源，在追求经济效益最大的同时，维持和改善土地资源的生产条件和环境基础。在当前社会主义市场经济体制下,可持续土地资源管理的任务主要依靠政府严格的土地利用规划事先调节和控制，引导、限制或鼓励人们的土地利用行为，保证土地资源的合理配置和可持续利用。该文试图在分析FAO的土地规划的概念、内容、体系、成功的关键因素、及编制的步骤和方法基础上，展开探讨并对完善我国土地利用规划提出了借鉴意义。     

中国北方典型地区农用地膜污染现状调查及其防治对策

通过对我国北方典型地区的调查，初步探索了该地区土壤农膜残留量和残膜特征。研究表明，河北省典型地区温室大棚、蔬菜田和作物田的农膜土壤残留量平均分别为5.629、7.369和2.822 kg·hm^-2，黑龙江省典型地区温室大棚、蔬菜田和作物田残留量平均分别为4.169、3.682和2.430 kg·hm^-2，各采样点之间存在着较大差异，但普遍较高，均明显高于未使用农膜的对照土壤。两地区之间除作物田的土壤农膜残留量没有明显差异外，河北地区其他两类土壤中的农膜残留量水平明显高于黑龙江地区，这种差异与各地区在农事活动及农膜使用上的差异具有一定的相关性。上述两地区土壤中残留农膜尺寸基本一致，主要集中在10～15 cm之间。该文针对我国目前农膜使用情况及其污染现状，提出了相应的防治对策。     

CO2施肥对黄瓜幼苗矿质营养吸收与分配的影响

以土培和砂培黄瓜幼苗为试材，研究CO₂施肥对植株矿质营养吸收和分配的影响。结果表明：每天上午以1100±100 μl/L CO₂浓度施肥3 h或上、下午各施肥3 h明显降低植株各部位多数矿质元素的含量，CO₂施肥时间延长，降幅增大。CO₂施肥增强了黄瓜对矿质元素的吸收能力，使单株吸收总量显著增加，且施肥时间越长，吸收数量越多。因此，在CO₂施肥的同时应增加矿质营养的供给。     

华南兴国县影响土壤侵蚀时空动力学的环境因素

By using soil erosion maps of four different time periods and a digital elevation model (DEM), in combination with the remote sensing and GIS technologies, soil erosion dynamics in Xingguo County of Jiangxi Province in South China were analyzed on both temporal and spatial scales in soils of different parent materials, altitudes and slopes. The results showed that from 1958 to 2000 severe soil erosion was coming under control with a decreasing percentage of the land under severe erosion. It was also found that the soils developed from Quaternary red clay, granite and purple shale were more susceptible to soil erosion and that areas sitting between 200 to 500 m in altitude with a slope less than 3° or between 7° to 20° where human activities were frequent remained to be zones where soil erosion was most likely to occur. These areas deserve special attention in monitoring and controlling.     

超微细菌Glaciecola多糖的超声提取工艺研究

多糖已作为免疫药物，应用于心血管疾病的临床治疗。研究了超微细菌Glaciecola多糖适宜的提取方法。通过研究常规水浸提法中不同料液比、提取温度和时间对细菌多糖得率、黏度和表面张力的影响，以及超声提取对多糖得率、黏度和表面张力的影响，结果表明：提取时间对多糖得率和多糖黏度均存在着显著的影响(p<0.05)，细菌多糖的适宜提取条件为料水比1∶15，提取温度在100℃左右，提取时间4～6 h。超声强化处理能显著提高超微细菌多糖的得率，降低提取液的表面张力(p<0.05)，超声强化处理后提取2 h的多糖得率，可达未处理前提取6 h的水平；超声提取条件以选择10～15 min、100 W功率，提取4 h为宜。超微细菌Glaciecola多糖的得率可达8.82%。     

Release and activity of allelochemicals from allelopathic rice seedlings

3-Isopropyl-5-acetoxycyclohexene-2-one-1 (1), momilactone B (2), and 5,7,4'-trihydroxy-3',5'-dimethoxyflavone (3) were isolated and identified from an allelopathic rice accession PI312777. These three compounds at low concentrations could inhibit the growth of weeds Echinochloa crusgalli and Cyperus difformis associated with rice, especially mixtures of the compounds had stronger inhibitory activity than did individual compounds. Studies with hydroponic culture, continuous root exudates trapping system (CRETS), and direct resin adsorption methods showed that a total of 7.6 n moles 1, 2, and 3 were exuded from living roots of each seedling into the environment at 10 days after seedlings were transplanted. Furthermore, 1, 2, and 3 were found in the soil growing PI312777 seedlings at day 15 after seedlings emergence and reached a total of 39.5 microg/g soil at day 30. The results indicated that PI 312777 seedlings could release sufficient quantities of 1, 2, and 3 into the environment to act as allelochemicals inhibiting the growth of associated weeds. Investigations on the distribution of 1, 2, and 3 in PI 312777 plant, and its root exudates showed that the levels of 1, 2, and 3 were significantly higher in the shoots and root exudates than in the roots, and only trace 1 was observed in the roots. The results suggest that the roots of rice seedlings are not major site of synthesis or accumulation 1, 2, and 3, but a pathway for their release into the environment. The levels of 1, 2, and 3 in the root exudates were over 2-folds higher under direct resin adsorption than under hydroponic culture and CRETS, and hence, it is the preferred method to collect and identify active allelochemicals in rice exudates in future studies on rice allelopathy.     

Soil volatile fungistasis and volatile fungistatic compounds

Fungistasis is a widespread phenomenon that can be mediated by soil microorganisms and volatile organic compounds (VOCs). The relationship between soil microorganisms and VOCs is still unclear, however, and many fungistatic compounds remain to be identified. We assessed the effects of soils (soil direct fungistasis) and VOCs produced by natural soils (soil volatile fungistasis) on the spore germination of several fungi. Both strong soil direct fungistasis and soil volatile fungistasis were observed in a wide range of soils. Soil fungistasis and VOC fungistasis were significantly correlated (P<0.001). The volatile fungistatic activity of soils stopped after autoclaving. Some VOCs were identified by using solid-phase microextraction-gas chromatography/mass spectrum. VOC composition and in vitro antagonism of relatively pure commercial compounds also were measured. Some VOCs, trimethylamine, 3-methyl-2-pentanone, dimethyl disulfide, methyl pyrazine, 2,5-dimethyl-pyrazine, benzaldehyde, N,N-dimethyloctylamine and nonadecane, were produced by various fungistatic soils. Moreover, antifungal activity test of above VOCs showed that trimethylamine, benzaldehyde, and N,N-dimethyloctylamine have strong antifungal activity even at low levels (4-12 mg l⁻¹).     

长江中下游地区Venlo型温室空气温湿度以及黄瓜蒸腾速率模拟研究

根据温室能量和质量平衡的物理学原理,建立了一个以温室外气候条件(太阳辐射、温度、湿度、风速等)为驱动变量,以温室结构、温室覆盖材料、温室内作物(高度、叶面积指数)为参数的温室小气候模拟模型,并利用上海Venlo型温室的三季试验数据对模型进行了检验。结果表明：模型能较好地预测中国长江中下游地区Venlo型温室内夏季和冬季空气温度、湿度以及作物蒸腾速率。模型对该地区夏干季节(2001年8月,三伏天)、夏湿季节(2002年6月下旬至7月中旬,梅雨季节)和冬季(2002年1月27日~2月5日)温室内空气温度、湿度以及作物蒸腾速率预测值与实际观测值的决定系数(R²)和标准误(SE)分别为：0.89,0.75,0.52;1.1℃,4.4%,0.040 g·m^-2·s^-1;0.80,0.84,0.77;1.5℃,4.4%,0.018 g·m^-2·s^-1;0.84,0.59,0.73;1.6℃,6.0%,0.012 g·m^-2·s^-1。该研究为进一步探讨温室环境的优化调控提供了理论依据和决策支持。