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.     

氮沉降对微生物分解森林地上凋落物过程的影响

森林生态系统凋落物被微生物分解的过程影响整个土壤碳库的碳来源及稳定性,在氮沉降全球化的趋势下因试验树种、试验方法、试验时间等不同因素导致森林地上凋落物分解产生了促进、抑制和无影响等3种响应。氮沉降对凋落物分解的影响主要通过3种机制实现:①不同浓度的氮沉降对凋落物中纤维素和木质素分解的影响不一致,原因可能是外加低浓度氮时,与之相关的真菌和细菌的生物量、活性会升高,高氮时则反之; 也有部分研究表明氮沉降一般促进含木质素少抑制含木质素较多的凋落物的分解; ②氮沉降对微生物产生的胞外酶活性影响也不一致,所以微生物酶对凋落物分解速率影响不同; ③通过对微生物的生物量、多样性、群落组成以及生态化学计量比等的影响,氮沉降也会影响凋落物分解木质素、纤维素等化学物质的过程。     

氮肥对毛竹林土壤硝化和反硝化作用的影响

【目的】探究氮肥对毛竹林土壤硝化和反硝化作用的影响,并分析其与主要土壤因子的相关关系,为毛竹林的抚育管理及可持续经营提供理论依据。【方法】以不施氮肥毛竹林为对照,应用气压过程分离(BaPS)方法,分季节测定施氮肥条件下毛竹林土壤总硝化和反硝化速率。【结果】施氮肥条件下毛竹林土壤总硝化和反硝化速率从春季到冬季变化规律相似,均呈现先升高后降低趋势,施肥毛竹林土壤总硝化和反硝化速率均以7月最高,当月相比分别比未施肥毛竹林高27.50%和44.60%; 最低值分别出现在1月和10月,当月相比分别比未施肥毛竹林高45.58%和402.56%。【结论】施氮肥可以促进毛竹林土壤硝化和反硝化作用,提高土壤硝态氮和微生物生物量氮含量,氮肥和季节对总硝化和反硝化速率存在显著交互作用,土壤温度、含水率与土壤总硝化、反硝化速率均呈显著正相关。     

不同油茶林分联合固氮菌的分离及固氮效能分析

通过对湖南省6种有代表性的油茶林分联合固氮菌的调查,研究了不同林地根际联合固氮菌的分布规律,筛选出了优良的固氮菌株并对其固氮效能进行了测定分析。结果表明：不同油茶林分根际联合固氮菌的数量存在显著差异,野生林较人工林高,山地较圃地高,青壮林较幼龄林高;根据固氮效能分析可知,从油茶林分中可分离到高效固氮菌株,高效固氮菌株在野生青壮林根内部分布最多。     

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。     

氮磷添加对亚热带常绿阔叶林凋落物产量及其养分含量的影响

【目的】凋落物是森林净生产量的重要组分,探讨森林凋落物生产及其养分归还量对氮磷添加的响应,为亚热带常绿阔叶林可持续经营提供科学依据。【方法】选择安徽池州亚热带常绿阔叶林,包括甜槠(Castanopsis eyrei)老龄林和苦槠(C. sclerophylla)中龄林,开展氮磷添加试验,设置3个处理,即氮[N 100 kg /(hm²·a)]、氮+磷[N 100 kg /(hm²·a) +P 50 kg /(hm²·a)]和对照(CK,无氮磷添加)。采用凋落物收集框法,对林分凋落物生产量及其养分归还量进行了为期1年的监测(2017年5月至2018年4月)。【结果】N+P处理下,苦槠林和甜槠林总凋落物量最高值分别为9.502、7.120 t/(hm²·a);其次是N处理,分别为8.393、7.041 t/(hm²·a);CK林分分别为7.724和6.697 t/(hm²·a),氮磷添加提高了总凋落物量,但不同处理间没有显著差异。在N处理和对照条件下,两林分凋落物各组分所占比例由大到小顺序均为:落叶、落枝、碎屑、落花落果。但在N+P处理的苦槠林中由大到小依次为:落叶、落枝、落花落果、碎屑。N处理下,苦槠林和甜槠林凋落物年均氮含量分别为14.199和13.648 g/kg,N+P处理分别为13.863和13.650 g/kg,CK林分分别为13.384和13.094 g/kg。各处理下苦槠林和甜槠林凋落物年均磷含量由大到小顺序为N+P、CK、N处理。两林分凋落物的氮磷含量和年归还量不同处理间差异均不显著;不同处理间的苦槠林和甜槠林凋落物的氮磷比均无明显差异。【结论】氮沉降提高了苦槠和甜槠林凋落物产量,磷添加具有一定的增效作用,表明磷添加缓解了氮沉降引起的磷限制作用。     

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。     

模拟氮磷沉降和凋落物处理对两种林型红松林土壤有机碳组分的影响

【目的】阐明模拟氮(N)磷(P)沉降和凋落物处理对两种林型红松(Pinus koraiensis)林土壤有机碳(SOC)组分的影响,为该地区红松林的合理施肥提供参考。【方法】以黑龙江省伊春市带岭区凉水国家级自然保护区红松人工林与阔叶红松林为对象,每个林型设置3块20 m×30 m样地,每块样地间隔20 m,每块样地内布设12个样方,共计72个样方。每个样方实施两种处理：(1)凋落物处理：2017年10月进行该处理的去除(R)、添加(A)和原状(CK1)3个水平的试验,每个水平设定3个重复;(2)模拟氮磷沉降处理：2018年与2019年的5—10月,每月进行1次该处理的试验,分别使用(NH₄)₂SO₄和(NH₄)₂HPO₄作为氮源和磷源配置成不同质量浓度的液体肥,施肥量设置低剂量(L,N、P添加量均为5 g/m²)、中剂量(M,N添加量为15 g/m²,P添加量为10 g/m²)、高剂量(H,...     

深水管道弃置回收非线性受力分析及其形态控制

采用弹性地基板理论和非线性梁理论分别建立弃置回收作业中深水管道触底段和悬跨段几何大变形管道模型。以悬链线理论对管道进行初始构形,将DnV规范与土样调查数据相结合处理触底段管道和海床地基的边界条件,得到垂向、侧向、轴向3个方向的土壤反力公式。以某深水气田管道为研究对象,采用有限元软件ABAQUS进行初选管道提升角的有限元分析,得到管道的应力分布。结果表明:提升角增大,管线提升端的轴向拉力减小、最大应力位置从提升点向触地点转移。当提升角处于合理范围时,管道应力水平较低,提升端轴向力相对于AR绞车能力比较合理。顺流时轴向拉力最大,AR绞车负载较大;逆流时管道轴向拉力最小。管线等效应力主要取决于弯曲应力。来流方向对管道触地点等效应力的影响非常大,应避免逆流环境作业。     

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。     

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.     

北亚热带毛竹林林冠截留特征的研究

对长江三角洲森林生态定位站的北亚热带毛竹林林冠截留作用进行了观测研究,结果表明：研究区毛竹林的林冠全年截留总量为171.7 mm,场均截留率为29.4%,有着较好的生态水文作用。不同雨量级、雨强级下,毛竹林林冠截留效果差异显著,在小雨量级、雨强级下,毛竹林林冠截留效果较好。毛竹林林冠截留量(率)与降雨量、降雨强度、降雨历时、叶面积指数、枝叶雨前干燥度存在不同程度的相关性,降雨历时对林冠截留量起重要作用,降雨强度对林冠截留率起重要作用。在已有的林冠截留模型基础上,引入叶面积指数变化动态加以改进,改进后的模型有更好的适用性。     

微量元素在林木中的应用研究进展

微量元素对林木生长发育至关重要,它们参与林木呼吸作用、光合作用、营养吸收及激素信号传导等多种生理生化过程。目前与林木生长有关的微量元素共有8种。微量元素与树体营养元素浓度、林木生长量及产量密切相关,是林木施肥与营养诊断的理论基础。笔者对微量元素在林木中的功能、微量元素与林木生长发育、林分类型、土壤和病虫害的关系及林木微量元素吸收转运分子机制、营养诊断等方面的研究现状进行综述,总结了现阶段存在的问题并对未来研究提出建议,认为我国林木可用的微肥品种和产量较少,与国外相关情况相比还有一定差距,且尚未组织微肥生产和制定质量标准,产品未达到多样化、定型化等;不同微量元素之间存在协同或拮抗作用。虽然在生产中尚未完全掌握土壤微量元素分布规律,导致林木施肥存在一定的盲目性,但我国生态农林业的发展已经起步。从我国林木的营养诊断技术、微肥研究利用、高效养分管理和速生丰产林的培育等方面开展深入研究,建议在林木施肥中应用微生物肥,以减缓土地营养衰退趋势,同时要进行树种选优、改良土壤、加强管理来提高林木经营总体效益。     

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.     

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.