Litterfall Mass,Chemistry, and Nutrient Retranslocation in a Monodominant Forest on Maracá Island,Roraima, Brazil1

Maracá Island is on the boundary of the Amazon rain forest and the Rio Branco-Rupunini savanna. The annual rainfall is ca. 1800 mm, with a dry season from October-March and a wet season from April-September. A forest type dominated by Peltogyne gracilipes (Caesalpiniaceae) occurs on parts of the island and the adjacent mainland, the least species-rich (for trees > 10 cm DBH) of any recorded in Brazilian Amazonia. The goal of this study was to test the hypothesis that the dominance by Peltogyne is associated with an unusual litterfall mass, nutrient concentrations, or retranslocation. Three plots (50 × 50 m) were set up in each of three forest types: (1) Peltogyne-rich forest (PRFa), dominated by Peltogyne gracilipes; (2) Peltogyne-poor forest (PPF), with a sparse occurrence of Peltogyne; and (3) forest without Peltogyne (FWPa). Litterfall was collected for 360 d at ca 15-d intervals in 11 randomly positioned traps (0.32 m²) per plot. Mature Peltogyne leaves were collected at random from three randomly selected understory Peltogyne trees in each of the three PRFa plots during the early dry and early wet season. Additionally, young Peltogyne leaves were collected during the early wet season. Chemical analyses were made on bulked (on a 2-mo basis) litterfall samples and young and mature Peltogyne leaves. The estimated annual litterfall was similar among PRFa (7.9 t/ha), PPF (9.1 t/ha) and FWPa (8.6 t/ha); however, PRFa was distinguished by its litterfall seasonality, because of the deciduous Peltogyne, and its higher concentrations of Ca (9.3 compared to 6.5 mg/g in FWPa) and Mg (3.2 compared to 1.9mg/g in FWPa). About 40–50 percent of N and P, 25–41 percenr of K, and 2–13 percent of Mg were rerranslocated from Peltogyne leaves.     

Habitat Use of Juvenile Fish in the Lower Danube and the Danube Delta: Implications for Ecotone Connectivity

Functional processes in freshwater ecosystems are highly influenced by acidic conditions. Foodwebs are affected and macroinvertebrate species diversity is decreased. This study aims to investigate leaf decomposition at very low pH in the acidic Banyupahit–Banyuputih river originating from the acidic crater lake Kawah Ijen in Indonesia. Leaf decomposition experiments were carried out for 200 days in the acidic river at pHs of approximately 0.7, 2.3 and 3.0 and in the neutral Kali Sengon river, using leaves from teak, Tectona grandis, and bamboo, Bambusa sp. Two different types of leaf packs were used: fine mesh size packs were used to exclude macroinvertebrates and coarse mesh size packs allowed macroinvertebrate colonization. Clear differences in decomposition rate were observed between the neutral Kali Sengon and the acidic Banyupahit–Banyuputih river with decomposition in the Kali Sengon river proceeding significantly faster for both leaf types. In the Kali Sengon k values (d⁻¹) over 46 days were 0.0202 for fine teak, 0.0236 for coarse teak, 0.0114 for fine bamboo and 0.0151 for coarse bamboo. No significant differences were observed between the three sites in the acidic Banyupahit–Banyuputih river with k values of 0.0034–0.0066 for fine teak, 0.0002–0.0057 for coarse teak, 0.0029–0.0054 for fine bamboo and 0.0000–0.0068 for coarse bamboo. Moreover, no clear adaptation of macroinvertebrates or microbes to low pH conditions could be detected. The coarse mesh leaf packs in the neutral Kali Sengon river revealed that macroinvertebrates are important in the breakdown process. Fine mesh packs revealed that microbial activity is depressed under acidic conditions. Based on this evidence, we conclude that the toxicity at low pH conditions, and probably also the precipitation of metals on the leaf material, seriously affects leaf decomposition.     

Nutrient transport in mycorrhizas: structure,physiology and consequences for efficiency of the symbiosis

Nutrient transport in mycorrhizas occurs across specialized interfaces which are the result of corrdinated development of the organisms. The structural modifications give rise to large areas of either inter- or intra-cellular interface in which wall synthesis is frequently modified and in which altered distribution of membrane bound ATPases is important, particularly with respect to mechanisms that may be involved in bidirectional transfer of nutrients. Except in orchid mycorrhizas, net movement of organic carbon from plant to fungus occurs, complemented by mineral nutrient movement in the opposite direction. The general consensus is that sustained transfer at rates that will maintain the growth and development of the organisms requires increases in the rates at which nutrients are lost from the organisms; possible mechanisms for this are discussed. The transfer processes are essential in determining both plant and fungal productivity and an approach to calculating the efficiency of the symbiosis in terms of the expenditure of carbon (or of phosphorus) is discussed.     

Poachers and Forest Fragmentation Alter Seed Dispersal,Seed Survival,and Seedling Recruitment in the Palm Attalea butyraceae,with Implications for Tropical Tree Diversity1

We examined the interaction between a palm and two bruchid beetles along with several mammal species to explore how poachers and habitat fragmentation may indirectly alter the spatial pattern of seed dispersal, seed predation, and seedling recruitment in central Panama. The large, stony endocarps of Attalea butyraceae decay slowly and bear distinctive scars when opened by rodents or beetles. We determined the final distance between endocarps and reproductive trees (which we call an ecologically effective dispersal distance), the predation status of each endocarp, and the distance between seedlings and reproductive trees. The 68 focal trees were divided among 14 sites and four levels of anthropogenic disturbance. Levels of disturbance included full protection from poachers, light and heavy pressure from poachers, and small island habitat fragments. Ecologically effective seed dispersal distances were greatest for protected sites, intermediate for lightly poached sites, and shortest for heavily poached sites and habitat fragments. Seed predation by rodents increased with distance to the nearest reproductive Attalea and was greatest for fully protected sites, intermediate for lightly poached sites, and least for heavily poached sites and habitat fragments. Seed predation by beetles reversed the patterns described for seed predation by rodents. Total seed predation by beetles and rodents combined was independent of distance, greatest for fully protected sites, and lower for poached sites and habitat fragments. Seedling densities were always greatest close to reproductive trees; however, the increase in seedling densities close to reproductive trees was minimal for fully protected sites, clearly evident for poached sites, and pronounced for habitat fragments. Increased seedling recruitment near conspecific trees may in time reduce tree diversity where humans disrupt mammal communities.     

香港草地,芒萁和灌木群落的养分利用效率

香港草地、芒萁和灌木群落的养分利用效率管东生（中山大学环境科学系广州５１０２７５）ＮｕｔｒｉｅｎｔＵｔｉｌｉｚａｔｉｏｎＥｆｆｉｃｉｅｎｃｙｏｆＧｒａｓｓｌａｎｄ,ＦｅｒｎｌａｎｄａｎｄＳｈｒｕｂｌａｎｄｉｎＨｏｎｇＫｏｎｇ．￥ＧｕａｎＤｏｎｇｓｈｅ...     

Ecosystem Nutrient Use Efficiency, Productivity, and Nutrient Accrual in Model Tropical Communities

Ecosystem nutrient use efficiency–the ratio of net primary productivity to soil nutrient supply–is an integrative measure of ecosystem functioning. High productivity and nutrient retention in natural systems are frequently attributed to high species diversity, even though some single-species systems can be highly productive and effective at resource capture. We investigated the effects of both individual species and life-form diversity on ecosystem nutrient use efficiency using model tropical ecosystems comprised of monocultures of three tree species and polycultures in which each of the tree species was coplanted with species of two additional life forms. Tree species significantly influenced nutrient use efficiency by whole ecosystems in monocultures; however, in polycultures, the additional life forms interacted with the influence exerted by the dominant tree. Furthermore, the presence of the additional life forms significantly increased nutrient uptake and uptake efficiency, but in only two of the three systems and 2 of the 4 years of the study period. These results indicate that the effect of life-form diversity on ecosystem functioning is not constant and that there may be temporal shifts in the influence exerted by different components of the community. Furthermore, although species (and life forms) exerted considerable influence on ecosystem nutrient use efficiency, this efficiency was most closely related to soil nutrient availability. These findings demonstrate that ecosystem nutrient use efficiency is an outcome not only of the characteristics of the species or life forms that comprise the system but also of factors that affect soil nutrient supply. The results argue against the simple upward scaling of nutrient use efficiency from leaves and plants to ecosystems. Received 29 March 2000; accepted 27 April 2001.     

Expressing the yeast HAL1 gene in tomato increases fruit yield and enhances K+/Na+ selectivity under salt stress

The yeast HAL1 gene facilitates K⁺/Na⁺ selectivity and salt tolerance of cells. Ectopic expression of HAL1 in transgenic tomato (Lycopersicon esculentum Mill.) plants minimized the reduction in fruit production caused by salt stress. Maintenance of fruit production by transgenic plants was correlated with enhanced growth under salt stress of calli derived from the plants. The HAL1 transgene enhanced water and K⁺ contents in both leaf calli and leaves in the presence of salt, which indicates that HAL1 functions in plants using a similar mechanism to that in yeast, namely by facilitating K⁺/Na⁺ selectivity under salt stress.     

Correlated traits for migration in the Gerridae (Hemiptera, Heteroptera): a field test

Abstract. 1. The hypothesis that the migratory tendency of macropters is correlated with proportion macropterous in wing-polymorphic insects is tested by comparing the migration of macropters of three species of waterstriders (Heteroptera, Gerridae) under natural conditions.
2. Migration of marked individuals among four permanent and seventeen ephemeral water bodies was recorded between 1 April 1986 and 2 June 1987, within an area of approximately 2 km2.
3. The proportion of macropters migrating was significantly lower for G.buenoi Kirkaldy than for L.dissortis Drake and Harris and G.comatus Drake and Hottes. Similar results were obtained in. comparisons of proportions captured on ephemeral sites.
4. Distances measured in this study appear to be small relative to the migratory capacity of all of the species, and migration distance did not differ significantly among species. All species migrated primarily in early spring, and differences among species were most apparent at this time.
5. The observed differences among species combined with the results of a similar study of macropters from the primarily apterous species, G.remigis Say, support the initial hypothesis. The implications of this for our understanding of the evolution and maintenance of wing polymorphisms are discussed.     

Age of A2 Horizon Charcoal and Forest Structure near Porto Trombetas,Pará, Brazil1

To study the structure and composition of old‐growth forest in the Saracá‐Taquera National Forest near Porto Trombetas, Brazil, we established 36 0.25 ha plots and described the vegetation. We collected charcoal from the A2 soil horizon of each plot for radiocarbon dating. Although fires have been very rare in this forest during historic times, the presence of charcoal in these soils indicates fire at some earlier period. The ages (conventional radiocarbon age adjusted to 1997) of the charcoal ranged from 177 to 1547 years. These ages, however, did not correlate significantly with any of several measures of biodiversity or stand characteristics. The relative uniformity of the current old‐growth forest indicates that either the prehistoric fires were of such low intensity that they had little long‐term effect on the vegetation or that the present stands have progressed to near steady state.     

滇中亚高山森林植物叶-凋落叶-土壤生态化学计量特征

为了深入认识滇中亚高山区域5种典型森林生态系统养分循环规律和系统稳定机质,通过测定植物叶、凋落叶和土壤C、N、P含量,掌握该区域典型森林植物叶-凋落叶-土壤生态化学计量特征。结果显示：（1）5种森林类型C、N、P含量差异显著,其中各林型植物叶和凋落叶C、N、P含量均高于土壤。（2）5种森林类型植物N、P再吸收率均为华山松林 > 云南松林 > 常绿阔叶林 > 高山栎林 > 滇油杉林;5种森林类型的再吸收率均为P（均值为61.20%）高于N（均值为36.48%）,表明了该区域土壤P的相对匮乏。（3）5种森林类型C/N、C/P、N/P均表现为凋落叶 > 植物叶 > 土壤;各林型植物叶N/P范围为10.17-15.31。（4）5种森林类型植物叶与凋落叶C、N、P含量、C/N和C/P均呈极显著或显著正相关;凋落叶与土壤的C、N含量及N/P呈显著正相关;5种森林类型植物叶N与P含量呈显著正相关关系;土壤N与P含量呈显著负相关关系。本文探究养分元素在"植物叶-凋落叶-土壤"之间的化学计量特征,为了解该区域森林生态系统的养分状况和揭示生物地球化学循环过程提供了理论数据。     

Nutrient limitations in wet, drained and rewetted fen meadows: evaluation of methods and results

Restoration of wet grassland communities on peat soils involves management of nutrient supply and hydrology. The concept of nutrient limitation was discussed as well as its interaction with drainage and rewetting of severely drained peat soils. Different methods of assessing nutrient limitation were compared and the type and extent of nutrient limitation were determined for several wet grassland communities. It was concluded that a full-factorial field fertilisation experiment is the most preferable method. Plant tissue analyses and soil chemical analyses were considered less suitable, although they may provide helpful additional information. Fertilisation experiments in the laboratory using sods or using test plants appear to be the proper means to study mechanisms or processes, but have a restricted predictive value for field situations. Generalising the results, it seems that many relativily undisturbed grassland plant communities on peaty soils are characterised by N limitation. Phosphate limitation for vegetation on peat soils is mainly observed in specific circumstances such as extreme calcium richness, high concentrations of Fe or as a result of drainage or long-term hay cropping. The latter two may also cause K limitation. Rewetting is regarded as a prerequisite in restoring wet grassland communities. Further restoration measures to influence nutrient availability depend on aims of the management and the individual site conditions. This revised version was published online in June 2006 with corrections to the Cover Date.     

Forest Succession in Tropical Hardwood Hammocks of the Florida Keys: Effects of Direct Mortality from Hurricane Andrew1

A tree species replacement sequence for dry broadleaved forests (tropical hardwood hammocks) in the upper Florida Keys was inferred from species abundances in stands abandoned from agriculture or other anthropogenic acitivities at different times in the past. Stands were sampled soon after Hurricane Andrew, with live and hurricane‐killed trees recorded separately; thus it was also possible to assess the immediate effect of Hurricane Andrew on stand successional status. We used weighted averaging regression to calculate successional age optima and tolerances for all species, based on the species composition of the pre‐hurricane stands. Then we used weighted averaging calibration to calculate and compare inferred successional ages for stands based on (1) the species composition of the pre‐hurricane stands and (2) the hurricane‐killed species assemblages. Species characteristic of the earliest stages of post‐agricultural stand development remains a significant component of the forest for many years, but are gradually replaced by taxa not present, even as seedlings, during the first few decades. This compositional sequence of a century or more is characterized by the replacement of deciduous by evergreen species, which is hypothesized to be driven by increasing moisture storage capacity in the young organic soils. Mortality from Hurricane Andrew was concentrated among early‐successional species, thus tending to amplify the long‐term trend in species composition.     

Foliar and Litter Nutrients, Nutrient Resorption, and Decomposition in Hawaiian Me t rosideros polymorpha

The native tree Metrosideros polymorpha dominates Hawaiian forests across a very wide range of soil fertility, including both sites where forest production is limited by nitrogen (N) and others where it is limited by phosphorus (P). Five long-term fertilization experiments have further broadened the range of nutrient availabilities experienced by Metrosideros. Adding P to P-limited sites increased foliar P concentrations threefold and litter P concentrations up to 10-fold; lignin concentrations decreased, and the decomposability of leaf litter increased from 32%–35% to 36%–46% mass loss in the first year. Adding N to N-limited sites increased leaf and litter N concentrations by only 15%–20%, with little or no effect on the decomposability of tissue. Received 22 January 1998; accepted 4 May 1998.