Increasing dominance of large lianas in Amazonian forests

Ecological orthodoxy suggests that old-growth forests should be close to dynamic equilibrium, but this view has been challenged by recent findings that neotropical forests are accumulating carbon and biomass, possibly in response to the increasing atmospheric concentrations of carbon dioxide. However, it is unclear whether the recent increase in tree biomass has been accompanied by a shift in community composition. Such changes could reduce or enhance the carbon storage potential of old-growth forests in the long term. Here we show that non-fragmented Amazon forests are experiencing a concerted increase in the density, basal area and mean size of woody climbing plants (lianas). Over the last two decades of the twentieth century the dominance of large lianas relative to trees has increased by 1.7-4.6% a year. Lianas enhance tree mortality and suppress tree growth, so their rapid increase implies that the tropical terrestrial carbon sink may shut down sooner than current models suggest. Predictions of future tropical carbon fluxes will need to account for the changing composition and dynamics of supposedly undisturbed forests.     

Pervasive alteration of tree communities in undisturbed Amazonian forests

Amazonian rainforests are some of the most species-rich tree communities on earth. Here we show that, over the past two decades, forests in a central Amazonian landscape have experienced highly nonrandom changes in dynamics and composition. Our analyses are based on a network of 18 permanent plots unaffected by any detectable disturbance. Within these plots, rates of tree mortality, recruitment and growth have increased over time. Of 115 relatively abundant tree genera, 27 changed significantly in population density or basal area--a value nearly 14 times greater than that expected by chance. An independent, eight-year study in nearby forests corroborates these shifts in composition. Contrary to recent predictions, we observed no increase in pioneer trees. However, genera of faster-growing trees, including many canopy and emergent species, are increasing in dominance or density, whereas genera of slower-growing trees, including many subcanopy species, are declining. Rising atmospheric CO2 concentrations may explain these changes, although the effects of this and other large-scale environmental alterations remain uncertain. These compositional changes could have important impacts on the carbon storage, dynamics and biota of Amazonian forests.     

氟苯尼考对海洋沉积物中氮循环的影响

为了评估抗生素对海洋沉积物氮素循环的影响,采用室内模拟实验研究了氟苯尼考存在下沉积物中氮素含量的变化.实验结果表明:氟苯尼考在低质量分数(1 mg/kg和10 mg/kg)下对沉积物间隙水中NH4—N含量的影响不显著,只有在较高质量分数(100 mg/kg和500 mg/kg)下才出现显著的NH4—N积累.培养前期,添加氟苯尼考可导致沉积物间隙水中NO2—N含量迅速降低,而培养后期氟苯尼考又表现为刺激NO2—N含量增加.培养的第2天,沉积物间隙水中NO3—N的含量有短时间的积累;培养4 d以后,高质量分数(500 mg/kg)的氟苯尼考又表现为对硝化作用的抑制.同时,实验表明:高质量分数(100 mg/kg和500 mg/kg)的氟苯尼考可抑制沉积物的氧化还原电位的变化.     

Amino-acid cycling drives nitrogen fixation in the legume-Rhizobium symbiosis

The biological reduction of atmospheric N2 to ammonium (nitrogen fixation) provides about 65% of the biosphere's available nitrogen. Most of this ammonium is contributed by legume-rhizobia symbioses, which are initiated by the infection of legume hosts by bacteria (rhizobia), resulting in formation of root nodules. Within the nodules, rhizobia are found as bacteroids, which perform the nitrogen fixation: to do this, they obtain sources of carbon and energy from the plant, in the form of dicarboxylic acids. It has been thought that, in return, bacteroids simply provide the plant with ammonium. But here we show that a more complex amino-acid cycle is essential for symbiotic nitrogen fixation by Rhizobium in pea nodules. The plant provides amino acids to the bacteroids, enabling them to shut down their ammonium assimilation. In return, bacteroids act like plant organelles to cycle amino acids back to the plant for asparagine synthesis. The mutual dependence of this exchange prevents the symbiosis being dominated by the plant, and provides a selective pressure for the evolution of mutualism.     

阴离子洗涤剂废液中三氯甲烷的回收再利用

通过对三氯甲烷废液的回收实验,并用样品阴离子洗涤剂的测定作为萃取液对比,得到回收的三氯甲烷与纯三氯甲烷实验结果一致,经检验,二者无显著性差异。回收后的三氯甲烷不仅能取得良好的实验结果,且具有一定的经济效益和环境效益。     

电子网板显影废液中铬的回收与利用研究

针对彩虹集团电子网板厂的含铬废水进行研究。先用氢氧化钠调节废液的pH值为7．5，使其沉淀抽滤。清液在酸性介质下，用蔗糖还原，使废液中的Cr^6 还原为Cr^3 ，将其配制成鞣革液，应用于皮革工业的鞣革，所鞣制的猪皮蓝湿革，各项技术指标已达到标准铬粉的同等水平，从而使含铬废水回收利用，在含铬废水处理上，从环境保护和应用方面开辟一条新的途径。     

氮在柠条不同刈割处理后补偿生长中的作用

柠条对外界的扰动具有一定的忍耐能力.在地上组织破坏后,从根颈或剩余枝条产生大量的萌蘖枝.本文对柠条刈割处理分6种:对照(CK),去除主枝长度的30%,60%,去除主枝分枝数的25%,50%,100%.刈割处理植株当年生枝生物量显著高于对照;100%RSN处理没有开花结果,其他处理植株籽粒生物量、果荚生物量和所有刈割处理叶生物量高于对照或与对照差异不显著.籽粒氮质量分数、果荚氮质量分数、一年生枝氮质量分数与对照相似,但生长后期叶片氮质量分数高于对照.除100%RSN处理外,刈割处理植株在座果期根系氮质量分数低于对照,表明植物将大量的根系储存的氮供应地上组织生长.在果实采收期刈割植株根系氮质量分数迅速增加,可能是根系固氮能力或吸收能力增强的结果.在整个生长季节中,刈割植株向地上组织氮的输出量高于对照.     

安徽省农业现代化与农产品物流互促机制研究

农产品物流是实现农业现代化的动能和保障。本文从农业投入水平、农业产出水平、农村社会化水平和农业可持续化发展水平四个维度建立农业现代化评价指标体系,采用变异系数法确定各评价指标权重后,计算并评价2006-2015年安徽省农业现代化水平综合得分,然后与农产品物流总额建立起回归方程。研究表明:安徽省农业现代化水平稳步提高,农业投入水平、农业产出水平、农村社会发展水平均取得明显进步,但农业可持续化发展水平有待提高;农产品物流业快速发展的同时,对农业现代化发展起到了明显促进作用。     

Host specificity of Lepidoptera in tropical and temperate forests

For numerous taxa, species richness is much higher in tropical than in temperate zone habitats. A major challenge in community ecology and evolutionary biogeography is to reveal the mechanisms underlying these differences. For herbivorous insects, one such mechanism leading to an increased number of species in a given locale could be increased ecological specialization, resulting in a greater proportion of insect species occupying narrow niches within a community. We tested this hypothesis by comparing host specialization in larval Lepidoptera (moths and butterflies) at eight different New World forest sites ranging in latitude from 15 degrees S to 55 degrees N. Here we show that larval diets of tropical Lepidoptera are more specialized than those of their temperate forest counterparts: tropical species on average feed on fewer plant species, genera and families than do temperate caterpillars. This result holds true whether calculated per lepidopteran family or for a caterpillar assemblage as a whole. As a result, there is greater turnover in caterpillar species composition (greater beta diversity) between tree species in tropical faunas than in temperate faunas. We suggest that greater specialization in tropical faunas is the result of differences in trophic interactions; for example, there are more distinct plant secondary chemical profiles from one tree species to the next in tropical forests than in temperate forests as well as more diverse and chronic pressures from natural enemy communities.     

Quantifying nitrogen-fixation in feather moss carpets of boreal forests

Biological nitrogen (N) fixation is the primary source of N within natural ecosystems, yet the origin of boreal forest N has remained elusive. The boreal forests of Eurasia and North America lack any significant, widespread symbiotic N-fixing plants. With the exception of scattered stands of alder in early primary successional forests, N-fixation in boreal forests is considered to be extremely limited. Nitrogen-fixation in northern European boreal forests has been estimated at only 0.5 kg N ha(-1) yr(-1); however, organic N is accumulated in these ecosystems at a rate of 3 kg N ha(-1) yr(-1) (ref. 8). Our limited understanding of the origin of boreal N is unacceptable given the extent of the boreal forest region, but predictable given our imperfect knowledge of N-fixation. Herein we report on a N-fixing symbiosis between a cyanobacterium (Nostoc sp.) and the ubiquitous feather moss, Pleurozium schreberi (Bird) Mitt. that alone fixes between 1.5 and 2.0 kg N ha(-1) yr(-1) in mid- to late-successional forests of northern Scandinavia and Finland. Previous efforts have probably underestimated N-fixation potential in boreal forests.     

Low beta diversity of herbivorous insects in tropical forests

Recent advances in understanding insect communities in tropical forests have contributed little to our knowledge of large-scale patterns of insect diversity, because incomplete taxonomic knowledge of many tropical species hinders the mapping of their distribution records. This impedes an understanding of global biodiversity patterns and explains why tropical insects are under-represented in conservation biology. Our study of approximately 500 species from three herbivorous guilds feeding on foliage (caterpillars, Lepidoptera), wood (ambrosia beetles, Coleoptera) and fruit (fruitflies, Diptera) found a low rate of change in species composition (beta diversity) across 75,000 square kilometres of contiguous lowland rainforest in Papua New Guinea, as most species were widely distributed. For caterpillars feeding on large plant genera, most species fed on multiple host species, so that even locally restricted plant species did not support endemic herbivores. Large plant genera represented a continuously distributed resource easily colonized by moths and butterflies over hundreds of kilometres. Low beta diversity was also documented in groups with differing host specificity (fruitflies and ambrosia beetles), suggesting that dispersal limitation does not have a substantial role in shaping the distribution of insect species in New Guinea lowland rainforests. Similar patterns of low beta diversity can be expected in other tropical lowland rainforests, as they are typically situated in the extensive low basins of major tropical rivers similar to the Sepik-Ramu region of New Guinea studied here.     

Control of cation concentrations in stream waters by surface soil processes in an Amazonian watershed

The chemical composition of ground waters and stream waters is thought to be determined primarily by weathering of parent rock. In relatively young soils such as those occurring in most temperate ecosystems, dissolution of primary minerals by carbonic acid is the predominant weathering pathway that liberates Ca2+, Mg2+ and K+ and generates alkalinity in the hydrosphere. But control of water chemistry in old and highly weathered soils that have lost reservoirs of primary minerals (a common feature of many tropical soils) is less well understood. Here we present soil and water chemistry data from a 10,000-hectare watershed on highly weathered soil in the Brazilian Amazon. Streamwater cation concentrations and alkalinity are positively correlated to each other and to streamwater discharge, suggesting that cations and bicarbonate are mainly flushed from surface soil layers by rainfall rather than being the products of deep soil weathering carried by groundwater flow. These patterns contrast with the seasonal patterns widely recognized in temperate ecosystems with less strongly weathered soils. In this particular watershed, partial forest clearing and burning 30 years previously enriched the soils in cations and so may have increased the observed wet season leaching of cations. Nevertheless, annual inputs and outputs of cations from the watershed are low and nearly balanced, and thus soil cations from forest burning will remain available for forest regrowth over the next few decades. Our observations suggest that increased root and microbial respiration during the wet season generates CO2 that drives cation-bicarbonate leaching, resulting in a biologically mediated process of surface soil exchange controlling the streamwater inputs of cations and alkalinity from these highly weathered soils.     

建立农业高校农学类实验教学质量保障长效机制的研究与实践

构建高等农业院校本科实验教学质量保障的长效机制,对贯彻国家中长期教育改革与发展计划精神具有重要的意义。提高本科实验教学质量应把实验教学示范中心引领到实验教学改革和实验室建设的方向。山东农业大学国家级实验教学示范中心,创新性地提出了"学校—专业主任—实验教师—实验中心"四位一体的实验教学管理模式,起到了国家级实验教学示范中心辐射带动其他实验教学中心,从而全面带动本科实验教学改革纵深发展的作用。通过几年来的运行,取得了良好的实践效果。     

中国农作物水灾风险分析

水灾是造成中国农作物产量损失的主要因素之一,对农作物水灾风险进行分析可有效防治农作物水灾灾情,减少农作物因水灾造成的损失.本文基于正态信息扩散风险分析模型,在灾情指标及农作物播种面积的基础上,详细分析了我国各省农作物水灾风险,并从宏观上对全国农作物水灾风险强度进行分级阐述,最后从灾情范围和灾情程度两方面进一步讨论了全国农作物水灾风险情况,为我国农作物种植规划及水灾防治提供理论参考,为中国农作物水灾风险的进一步深入分析奠定基础.     

太白山针叶林的数量分类与排序

应用模糊聚类和ＰＣＡ排序方法对太白山针叶林进行了分类和排序，利用多元回归分析将排序值与环境参数相联系而给出群落的定量环境解释．分析表明，太白山针叶林的类型及分布主要取决于海拔、降水和热量．模糊聚类的截取水平选在模糊关系变化较大之处，可得到较为合理的聚类结果     

土壤动物对森林凋落物分解的影响

凋落物分解是森林生态系统中物质和能量交换的重要生态学过程。土壤动物在森林凋落物的分解过程中起着非常重要的作用。可以通过物理的或化学的方法研究土壤动物对凋落物分解的影响。笔者综合了目前该领域研究中常用的方法,如分解网袋法、化学试剂排除法、电击法、数学模型法等,分析了各种方法的特点和局限性,指出了今后研究的方向。     

华北地区农业干旱灾害变化特征?

采用干旱灾情数据,以县域为单位,运用受旱率及干旱灾害频率2个指标,分析了华北4省(河南、河北、山东、山西)1949—2000年农业干旱灾害变化特征.研究表明:华北4省农业干旱灾害受旱率52年间呈上升趋势,20世纪80年代之后,中度及中度以上程度干旱灾害发生频率明显增加;干旱灾害频率分布格局有较为明显的东西差异,高频区集中在河南省东北部、山西省北部、山西省西南部及晋中地区;52年间河南省大部及山东省青岛市干旱灾害发生频率有增加的趋势.本研究从灾情记录角度识别了华北4省农业干旱灾害高发区及严重干旱年份,能够为干旱灾害的风险防范及国家防灾减灾工作提供理论支持.     

语音技术在农业智能化中的应用展望

针对农业智能装备工作环境复杂、操作不便捷与作业效率低的问题,对语音技术在农业智能化中应用的前景进行了展望,并提出农业装备中语音系统软硬件整体架构,把语音技术分为语音提示、语音报警、语音控制、视觉语音4部分.在ROS开发环境中,运用python编译语言建立控制软件系统框架,将成套控制软件分为农作物信息检测单元、作业信息检测单元、接收语音信号单元、作业命令控制单元、语音播报-报警单元,把各功能单元进行模块化编程,实现整套系统的多功能同步协调运行.以葡萄采摘机器人为例,分别实现采摘机器人作业信息语音提示功能、语音控制采摘机器人运动功能、田间葡萄品种与成熟度信息识别储存并语音播报功能,对推进语音技术在农业智能化中的应用具有一定价值.     

Respiration as the main determinant of carbon balance in European forests

Carbon exchange between the terrestrial biosphere and the atmosphere is one of the key processes that need to be assessed in the context of the Kyoto Protocol. Several studies suggest that the terrestrial biosphere is gaining carbon, but these estimates are obtained primarily by indirect methods, and the factors that control terrestrial carbon exchange, its magnitude and primary locations, are under debate. Here we present data of net ecosystem carbon exchange, collected between 1996 and 1998 from 15 European forests, which confirm that many European forest ecosystems act as carbon sinks. The annual carbon balances range from an uptake of 6.6 tonnes of carbon per hectare per year to a release of nearly 1 t C ha(-1) yr(-1), with a large variability between forests. The data show a significant increase of carbon uptake with decreasing latitude, whereas the gross primary production seems to be largely independent of latitude. Our observations indicate that, in general, ecosystem respiration determines net ecosystem carbon exchange. Also, for an accurate assessment of the carbon balance in a particular forest ecosystem, remote sensing of the normalized difference vegetation index or estimates based on forest inventories may not be sufficient.