Deposition of sediments during a flood event on seasonally flooded forests of the lower Orinoco River and two of its black-water tributaries, Venezuela

Deposition of suspended sediments andtheir associated nutrients were estimated during theflood event of 1995 in the seasonally flooded forestsof the Mapire and Caura Rivers, two black-watertributaries of lower Orinoco, and on two islands ofthis white-water river. The deposition spanned a widerange from 0.07 kg m^–2 in the depositional barforests of the Mapire River to 73.60 kg m^–2 onthe flooded forests of the Orinoco Island site calledJarizo. This variation is associated with the dynamicnature of sediment mobilization, transport anddeposition, as well as with the different geomorphicenvironments and erosion processes upstream from thestudy sites. The deposited sediment in all the studyareas was highly quartzitic with a relatively highcontent of kaolinite and goethite. Only in thesediment of the Orinoco Islands was mica (illite)identified in a relatively high proportion. Thesemineralogical results reflect the intense weatheringprocesses in the catchment areas of the study rivers.The chemical composition of the deposited sedimentsshowed a great variability among the different studyareas, which is in part related to the mineralcomposition of the sediments and their particle sizedistribution. The highest concentrations of K, Caand Mg were found on the clay sediments of the Orinocoagricultural island. The total amount of depositednutrients varied over a wide range, which isinfluenced by the amount of deposited sediments. Inthe Jarizo Island site of lower Orinoco were depositedthe largest amount of nutrients. In the floodedforests of the Mapire River, the nutrient contributionby the deposited sediments to the nutrient cycling isrelatively low in the depositional-bar forests andpractically nonexistent in the forests sites onterraces.     

Mass loss and nutrient release during the decomposition of sixteen types of plant litter with contrasting quality under three precipitation regimes

Mass loss and nutrient release during litter decomposition drive biogeochemical cycling in terrestrial ecosystems. However, the relationship between the litter decomposition process and the decomposition stage, precipitation, and litter quality has rarely been addressed, precluding our understanding of how litter decomposition regulates nutrient cycling in various ecosystems and their responses to climate change. In this study, we measured mass loss as well as carbon and nutrient releases during the decomposition of 16 types of leaf litter under three precipitation treatments over 12 months in a common garden experiment (i.e., using standardized soil and climatic conditions). Sixteen types of leaves were divided into three functional groups (evergreen, deciduous, and herbaceous). The objectives were to understand the effects of decomposition stages and precipitation regimes on litter decomposition and to examine the relationship between this effect and chemical properties. The mass loss and release of nitrogen and potassium were significantly higher in the 6‐ to 12‐month stage of decomposition (high temperature and humidity) than in the 0‐ to 6‐month stage. Phosphorus was relatively enriched in evergreen leaves after 6 months of decomposition. The rates of mass loss and nutrient release were significantly greater in herbaceous than in deciduous and evergreen leaves. Increasing precipitation from 400 to 800 mm accelerated mass loss and potassium release but decreased phosphorus release in the 0‐ to 6‐month stage of decomposition. These results highlighted the contribution to and complexity of litter chemical properties in litter decomposition.     

桂西北喀斯特区原生林与次生林凋落叶降解和养分释放

凋落叶降解及养分释放研究对喀斯特生态脆弱区森林生态系统的恢复与重建具有重要指导意义。本文选取桂西北喀斯特区3种原生林与3种次生林进行比较,研究其凋落叶降解与降解过程中的营养元素释放规律以及降解速率的影响因子。结果表明,原生林凋落叶的降解速率略大于次生林。C、N、K元素在前180天释放速率较快,随后趋于稳定。次生林凋落叶总P含量在降解初始阶段呈净积累,随后净释放,而原生林的凋落叶在降解360天后仍呈现P素净积累。相关分析表明,凋落叶降解速率与凋落叶初始总N、木质素含量及木质素:N比值呈负相关,与C:N比呈正相关。综合比较发现,次生林圆叶乌桕(Sapium rotundifolium Hemsl)凋落叶的降解速率与养分释放速率较快,是喀斯特退化土地及植被恢复过程中潜在的优势种和建群种。     

Chemical composition and nutrient loading by precipitation in the Trachypogon savannas of the Orinoco llanos, Venezuela

Samples of bulk precipitation were collected in the Trachypogon savanna, Calabozo, Venezuela, during three consecutive years. In the first year, rain samples were taken daily; in the following years the samples were grouped on a monthly basis. In addition, samples of dry deposition were collected during the dry seasons. All samples were analyzed for the following water soluble cations and anions: P0₄-P, S0₄-S, N0₃-N, NH₄-N, Ca⁺², Mg⁺², K⁺, Na⁺ and H⁺. The mean annual input rate of chemical constituents (Kg ha^-1 year^-1) was: PO₄-P (0.42); SO₄-S (2.62); NO₃-N (0.21); NH₄-N (2.03); Ca₊₂ (3.50); Mg⁺² (11.31); K⁺ (3.60); Na⁺ (5.93) and H⁺ (0.03). The total mean input of particulate material to the savanna during the dry season was 2.06 Kg ha^-1 year^-1, with a soluble fraction of 30%. Possible sources of nutrients input were analyzed.     

热带森林植物幼叶抗虫食防卫方式研究的现状及进展

综述了热带森林植物幼叶抗虫食的研究概况 ,包括 ( 1)幼叶抗虫食的多元防卫方式 ,主要有生长发育防卫、化学防卫、生物防卫和物候防卫等 ;( 2 )多元防卫方式的成本收益 ;( 3)各种防卫方式之间的生理和生态调节 ,并对当前的研究状况提出了简要评述。     

鼎湖山南亚热带常绿阔叶林植物和土壤微量元素含量

报道了鼎湖山南亚热带常绿阔叶林各层次植物和表层土壤(0～20 cm)四个微量元素(Cu、Fe、Mn和 Zn)的含量和分配格局。结果表明:(1)土壤有效Cu、Fe、Mn和Zn含量(mg／kg)平均值依次为0．72、140．85、 1．42和1．92;(2)所有植物叶片Cu、Fe、Mn和Zn元素含量(mg／kg)分别介于6．1～100．6、6．5～1027．5、46．3 ～1196．7和27．0～338．6,其中乔木层植物叶片微量元素含量(mg／kg)平均值表现为Mn(305．3)>Fe (259．3)>Zn(109．9)>Cu(19．3),而其它植物表现为Fe(586．4)>Mn(336．9)>Zn(141．4)>Cu(36．6);(3) 植物微量元素在各器官的分配格局随元素和植物所在的层次不同而异:乔木层植物Cu含量高低排序为干> 根>枝>叶>皮,Fe为根>皮>叶>枝>干;Mn为叶>皮>枝>根>干;Zn为叶>根>枝>皮>干;(4)在 群落垂直结构上,Fe元素含量表现为自上而下递增的趋势,而Cu、Mn和Zn含量规律不明显;(5)植物和土壤 的微量元素与微量元素间相关性均较差;(6)与亚热带其它森林相比,鼎湖山季风常绿阔叶林土壤Cu、Mn和 Zn含量较低,但乔木层植物因具有很强的吸收或富集能力而含量较高。     

不同林龄第2代杉木林枝叶凋落前的养分转移特征

利用会同杉木林25年的定位测定的基础数据,探讨了不同林龄杉木(Cunninghamia lanceolata(lamb) Hook)枝叶凋落前的养分转移特征,为人工林经营管理提供科学依据。结果表明:杉木枝叶凋落前年均养分转移量为3.22—31.89 kg hm~(-2) a~(-1),其中,叶占71.31%—94.41%,枝占5.59%—28.69%。枝的养分转移量随林龄增加而增加。林分20年生以前,叶的养分转移量呈上升趋势,20年生以后,呈下降趋势。枝的养分转移率为20.97%—22.59%,叶是22.98%—26.06%,枝和叶的养分转移率都随林龄增加而增大。各林龄段的枝的养分转移率差异不显著(P0.05),叶的养分转移率除1—7年生与其他林龄段的差异显著(P0.05),其余各林龄段之间差异不显著(P0.05)。转移的元素量中,N和K占83.75%—84.25%,P、Ca、Mg占15.75%—16.25%。N、P、K、Ca、Mg的转移率分别为24.59%—34.53%,36.36%—46.64%,42.86%—51.27%,3.68%—7.35%,3.67%—9.56%。养分转移率主要受枝叶凋落前、后的养分浓度差值与枝叶凋落前的养分浓度控制,与凋落物量无关。养分的转移量不仅受枝叶凋落前、后的养分浓度差值的影响外,更多地取决于凋落物量,而且与杉木生长发育特征有很大的关联。     

Host species,and not environment,predicts variation in blood parasite prevalence,distribution, and diversity along a humidity gradient in northern South America

Environmental factors strongly influence the ecology and evolution of vector‐borne infectious diseases. However, our understanding of the influence of climatic variation on host–parasite interactions in tropical systems is rudimentary. We studied five species of birds and their haemosporidian parasites (Plasmodium and Haemoproteus) at 16 sampling sites to understand how environmental heterogeneity influences patterns of parasite prevalence, distribution, and diversity across a marked gradient in water availability in northern South America. We used molecular methods to screen for parasite infections and to identify parasite lineages. To characterize spatial heterogeneity in water availability, we used weather‐station and remotely sensed climate data. We estimated parasite prevalence while accounting for spatial autocorrelation, and used a model selection approach to determine the effect of variables related to water availability and host species on prevalence. The prevalence, distribution, and lineage diversity of haemosporidian parasites varied among localities and host species, but we found no support for the hypothesis that the prevalence and diversity of parasites increase with increasing water availability. Host species and host × climate interactions had stronger effects on infection prevalence, and parasite lineages were strongly associated with particular host species. Because climatic variables had little effect on the overall prevalence and lineage diversity of haemosporidian parasites across study sites, our results suggest that independent host–parasite dynamics may influence patterns in parasitism in environmentally heterogeneous landscapes.     

Biomass,production and nutrient distribution of a natural oak forest in central Korea

Biomass, production, and nutrient distribution of a pure Quercus variabilis Bl. stand (stand 1) and two mixed Q. variabilis–Q. mongolica Fisch. stands (stand 2 and 3) were investigated in central Korea. Stand 1 naturally occurred on a site with a southern aspect while stand 2 and stand 3 occurred on sites with a northern aspect. Total (overstory+understory vegetation) biomass (tha^-1) and annual production (tha^–1year^–1) were 137.8 and 11.1 for stand 1, 216.2 and 16.6 for stand 2, and 253.3 and 19.7 for stand 3. Nutrient contents (kgha^–1) in the vegetation were distributed as follows: K, 478–860; N, 471–839; Ca, 428–791; Mg, 72–125; Na, 77–141; and P, 37–71, and were greatest in stand 3 followed by stand 2, and stand 1. Stand density influenced the differences in biomass, annual production and nutrient contents in the vegetation. Forest floor dry mass and N content (kgha^–1) were 13400 and 169 for stand 1, 10400 and 133 for stand 2, and 11200 and 127 for stand 3. Total amounts of N, P and Na in the ecosystem were greatest in the upper 40cm of mineral soil followed by the vegetation and forest floor. However, the vegetation contained a greater amount of K than the mineral soil. It appeared that microenvironments, such as, aspect influenced the distribution of natural oak species within a relatively small area and resulted in differences in biomass, production and nutrient distribution among the stands.     

关帝山华北落叶松林凋落物分解过程及其养分动态

采用野外凋落物收集器法和埋置凋落物分解袋法,对关帝山林区华北落叶松林凋落物的数量和组成、年凋落过程、不同埋置层凋落叶分解速率和营养元素动态进行了分析.结果表明:华北落叶松林年凋落物总量为19.15 t · hm-2 · a-1,其中树叶占35.7%,树枝占54.4%,花果占6.7%,树皮和杂物占3.1%.凋落物逐月动态变化为单峰型,10月为年凋落量高峰期,但各成分的凋落进程不同.华北落叶松林凋落物残留量均值为9.803t/hm2,凋落物分解常数为1.95;凋落叶在不同埋置层的分解失重率有明显差异,凋落叶的周年平均失重率29.82%,分解半衰期1.5～2a,分解95%需7～9a;凋落叶分解过程中,氮磷钾元素含量表现出不同的动态过程,其中氮素的年动态变化总体上属于富集过程,到后期开始出现下降,磷素的年动态变化表现为7月份前下降,之后出现快速富集,到生长季末期富集过程变缓,钾素的年动态变化表现为持续下降过程,不出现富集过程.     

Inter-annual,seasonal and spatial variability in nutrient limitation of phytoplankton production in a river impoundment

We characterize seasonal and spatial patterns in phytoplankton abundance, production and nutrient limitation in a mesotrophic river impoundment located in the southeastern United States to assess variation arising from inter-annual differences in watershed inputs. Short-term (48 h) in situ nutrient addition experiments were conducted between May and October at three sites located along the longitudinal axis of the lake. Nutrient limitation was detected in 12 of the 18 experiments conducted over 2 years. Phytoplankton responded to additions of phosphorus alone although highest chlorophyll concentrations were observed in enclosures receiving combined (P and N) additions. Growth responses were greatest at downstream sites and in late summer suggesting that those populations experience more severe nutrient limitation. Interannual variation in nutrient limitation and primary production corresponded to differences in the timing of hydrologic inputs. Above average rainfall and discharge in late-summer (July–October) of 1996 coincided with higher in-lake nutrient concentrations, increased production, and minimal nutrient limitation. During the same period in 1995, discharge was lower, nutrient concentrations were lower, and nutrient limitation of phytoplankton production was more pronounced. Our results suggest that nutrient limitation is common in this river impoundment but that modest inter-annual variability in the timing of hydrologic inputs can substantially influence seasonal and spatial patterns.     

Decomposition and nutrient release patterns of mistletoe litters in a semi‐arid savanna,southwest Zimbabwe

Nutrient loss from litter plays an essential role in carbon and nutrient cycling in nutrient‐constrained environments. However, the decomposition and nutrient dynamics of nutrient‐rich mistletoe litter remains unknown in semi‐arid savanna where productivity is nutrient limited. We studied the decomposition and nutrient dynamics (nitrogen: N, phosphorous; P, carbon: C) of litter of three mistletoe species, Erianthemum ngamicum, Plicosepalus kalachariensis, and Viscum verrucosum and N‐fixing Acacia karroo using the litter‐bag method in a semi‐arid savanna, southwest Zimbabwe. The temporal dynamics of the soil moisture content, microbial populations, and termite activity during decomposition were also assessed. Decay rates were slower for A. karroo litter (k = 0.63), but faster for the high quality mistletoe litters (mean k‐value = 0.79), which supports the premise that mistletoes can substantially influence nutrient availability to other plants. Nitrogen loss was between 1.3 and 3 times greater in E. ngamicum litter than in the other species. The litter of the mistletoes also lost C and P faster than A. karroo litter. However, soil moisture content and bacterial and fungal colony numbers changed in an opposite direction to changes in the decomposition rate. Additionally, there was little evidence of termite activity during the decay of all the species litters. This suggests that other factors such as photodegradation could be important in litter decomposition in semi‐arid savanna. In conclusion, the higher rate of decay and nutrient release of mistletoe than A. karroo litter indicate that mistletoes play an important role in carbon and nutrient fluxes in semi‐arid savanna.     

格氏栲天然林与人工林凋落物数量、养分归还及凋落叶分解(英文

通过对中亚热带格氏栲天然林(natural forest of Castanopsis kawakamii。约150年生)、格氏挎和杉木人工林(monoculture plantations of C．kawakamii and Cunninghamia lanceolata,33年生)凋落物数量与季节动态、养分归还及凋落叶分解与其质量的关系为期3a的研究表明。林分年均凋落量及叶所占比例分别为：格氏栲天然林11．01t／hm^1。59．70t／hm^2;格氏栲人工林9．54％。71．98％;杉木人工林5．47t／hm^2。58．29％。格氏栲天然林与人工林凋落量每年只出现1次峰值(4月份)。而杉木林的则出现3次(4或5月份、8月份和11月份)。除杉木林的Ca和格氏栲人工林的Mg年归还量最大外。N、P、K及养分总归还量均以格氏栲天然林的为最大。杉木人工林的最小。分解la后格氏栲天然林中格氏栲叶的干重损失最大(98．16％)。杉木叶的最小(60．78％)。C／N及木质素／N比值与凋落叶分解速率呈显著负相关。而N、水溶性化合物初始浓度与分解速率呈显著正相关。与针叶树人工林相比,天然林的凋落物数量大、养分归还量高、分解快。具有良好自我培肥地力的能力。因此。保护和扩大常绿阔叶林资源已成为南方林区实现森林可持续经营的重要措施之一。     

咸淡交替灌溉对克隆植物大米草生长繁殖和生物量分配的影响

通过温室模拟控制实验,研究了咸淡交替灌溉处理对外来克隆植物大米草(Spartina anglica)形态性状、克隆生长、生物量积累及分配格局的影响。实验共设6种浇灌处理:单一淡水灌溉(D)、单一咸水浇灌(X)、淡咸交替灌溉(DX)、咸淡交替灌溉(XD)、淡咸淡交替灌溉(DXD)和咸淡咸交替灌溉(XDX)。结果表明:DX处理条件下,大米草株高、叶片数及根长均达到最高;克隆数最多,且显著高于X、DXD和XDX处理;芽数及根状茎总长均显著大于XDX处理;在DX和D处理下,地上生物量、根系生物量、地下生物量和总生物量均显著高于其它处理。这表明作为滨海盐沼植物,大米草种群比较适应淡咸水交替环境,单一的咸水,以及过度的咸淡转换均不利于大米草的生长繁殖与生物量积累,而淡咸水交替过程的失序可能是引起我国大米草种群衰退的重要原因。     

Relationships among net primary productivity, nutrients and climate in tropical rain forest: a pan-tropical analysis

Tropical rain forests play a dominant role in global biosphere-atmosphere CO(2) exchange. Although climate and nutrient availability regulate net primary production (NPP) and decomposition in all terrestrial ecosystems, the nature and extent of such controls in tropical forests remain poorly resolved. We conducted a meta-analysis of carbon-nutrient-climate relationships in 113 sites across the tropical forest biome. Our analyses showed that mean annual temperature was the strongest predictor of aboveground NPP (ANPP) across all tropical forests, but this relationship was driven by distinct temperature differences between upland and lowland forests. Within lowland forests (相似文献   

马尾松人工林林窗大小对四种凋落叶质量损失和养分释放的影响

马尾松人工林乔木层植物凋落物的分解对林地养分平衡和系统物质循环具有重要意义,并可能受不同大小林窗下微环境差异的影响。采用凋落物袋分解法,以马尾松(Pinus massoniana)人工林人为砍伐形成的7个不同大小林窗(G1:100 m~2、G2:225 m~2、G3:400 m~2、C4:625 m~2、G5:900 m~2、G6:1225m~2、G7:1600 m~2)为研究对象,林下(G0)为对照,研究林窗大小对红椿(Toona ciliata)、桢楠(Phoebe zhennan)、香樟(Cinnamomum camphora)和马尾松4种乡土树种凋落叶质量损失及养分释放的影响。结果显示:1)林窗大小(G0-G7)显著影响林窗中心放置的红椿和桢楠凋落叶N和P释放率、香樟凋落叶失重率和N、P、K释放率以及马尾松凋落叶P和K释放率。相对于林下,中小型林窗(G1-G4)的凋落叶失重率和N、P释放率明显较大,而大型林窗(G6-G7)的凋落叶K释放率明显较大。2)林窗内放置位置显著影响红椿、桢楠和马尾松凋落叶的K释放率及香樟凋落叶的P释放率。红椿和桢楠的凋落叶K释放率从林窗中心到边缘显著减少,而马尾松凋落叶K释放率及香樟P释放率从林窗中心到边缘显著增加。3)4种凋落叶类型中红椿凋落叶分解最快,其分解50%和95%所需时间分别为5.29和23.14个月。上述结果表明,林窗大小和林窗内位置对凋落物质量损失及其养分释放具有显著影响,但影响大小及趋势随物种初始基质质量的差异具有明显变化,研究结果为亚热带低山丘陵区马尾松人工低效林的科学经营及管理提高了一定的科学依据。     

Responses of benthic algae to nutrient enrichment in a shallow lake: Linking community production,biomass, and composition

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Regulation of the abundance and turnover of copepod species by temperature,turbidity and habitat type in a large river basin

Freshwater copepods were sampled in the La Plata River basin to identify the processes that affect beta diversity and to determine the main factors influencing their geographical distribution and patterns of endemism. Beta diversity patterns exhibited strong dissimilarity between locations; the turnover process was predominant and indicated a replacement of species along the basin. Redundancy analysis indicated the presence of two large sets of species separated geographically by a boundary zone, with several associated variables. Northern species were associated with water transparency and temperature, mean air temperature, mean air temperature during winter and minimum air temperature of coldest month, indicating that these species are not tolerant to low temperatures and are abundant in reservoirs that are common in the upper stretch of the Paraná River basin. Southern species were related with amplitude of air temperature, turbidity, total phosphorus and total suspended matter, indicating that these species are polythermic and have adapted to live in river stretches. From 20 environmental variables analyzed in our study, partial least squares analysis indicated four variables with increased retention of effects on copepod abundance: air temperature, minimum temperature of coldest month, turbidity and transparency. Because almost all of the species found in this study occurred across a wide range of habitat types, the cause of the separation between river and reservoir species could be considered to be more anthropogenic than natural, and it primarily affected species abundance. For certain members of the northern group of copepod species, distribution was dependent on high temperatures, whereas the distribution of the southern group indicated that the species were polythermic.     

Impact of defoliation intensities on plant biomass,nutrient uptake and arbuscular mycorrhizal symbiosis in Lotus tenuis growing in a saline‐sodic soil

The impact of different defoliation intensities on the ability of Lotus tenuis plants to regrowth, mobilise nutrients and to associate with native AM fungi and Rhizobium in a saline‐sodic soil was investigated. After 70 days, plants were subjected to 0, 25, 50, 75 and 100% defoliation and shoot regrowth was assessed at the end of subsequent 35 days. Compared to non‐defoliated plants, low or moderate defoliation up to 75% did not affect shoot regrowth. However, 100% treatment affected shoot regrowth and the clipped plants were not able to compensate the growth attained by non‐defoliated plants. Root growth was more affected by defoliation than shoot growth. P and N concentrations in shoots and roots increased with increasing defoliation while Na⁺ concentration in shoots of non‐defoliated and moderately defoliated plants was similar. Non‐defoliated and moderately defoliated plants prevented increases of Na⁺ concentration in shoots through both reducing Na⁺ uptake and Na⁺ transport to shoots by accumulating Na⁺ in roots. At high defoliation, the salinity tolerance mechanism is altered and Na⁺ concentration in shoots was higher than in roots. Reduction in the photosynthetic capacity induced by defoliation neither changed the root length colonised by AM fungi nor arbuscular colonisation but decreased the vesicular colonisation. Spore density did not change, but hyphal density and Rhizobium nodules increased with defoliation. The strategy of the AM symbiont consists in investing most of the C resources to preferentially retain arbuscular colonisation as well as inoculum density in the soil.