Vegetative Phenology and Growth of a Facultatively Deciduous Bamboo in a Monsoonal Climate1

Canopy closure, leaf flush, and ramet recruitment in Bambusa arnhemica, a semelparous, clumping bamboo from the Australian monsoonal tropics, were monitored monthly for 2.5 years at three sites along a flood gradient. Bambusa arnhemica was facultatively deciduous, remaining evergreen at a downslope riparian site but suffering total loss of canopy on a hillside for up to 4 mo during the dry season. Leaf flush was flexible, occurring after as little as 25 mm of rain at the onset of wet season, in response to unusual dry season storms, and apparently also in response to fire independent of rainfall. New culms emerged soon after leaf flush early in the wet season. Culm growth took place during the middle and late wet season, with peak elongation rates of 15–30 cm/day. Some growth continued into the dry season, mostly on branches and leaves of new culms at riparian sites. Not all culms completed elongation before the onset of the dry season, and those that did not were permanently stunted. The demands of culm elongation may limit the occurrence of bamboo in wet‐dry climates to areas with predictable and sustained wet season rainfall, but the flexibility of branching and leaf processes facilitates coping with, and permits exploitation of less predictable pre‐ and postmonsoonal rains. The bamboo growth form and phenological patterns differ markedly from those of dicotyledonous trees and shrubs.     

岷江上游干旱河谷灌丛群落种-面积曲线的拟合及最小面积确定

研究采用3种饱和曲线方程拟合出的群落种-面积曲线,对岷江上游干旱河谷灌丛群落的最小面积进行研究,取比例因子P分别为0．6、0．7、0．8、0．9,求得灌丛群落的最小面积或临界取样面积。研究结果表明：当ρ取0．6、0．7、0．8时,阴、阳坡各海拔梯度样地群落最小面积均小于或略大于100m^2,样方可设置为10m×10m,即样地面积为100m^2,可以满足精度60％～80％的研究要求。当ρ取0．9时,阴、阳坡各海拔梯度样地群落最小面积均小于200m^2,样方可设置为10m×20m,即样地面积为200m^2,可以满足精度90％的研究要求;群落最小面积呈现出随海拔梯度的升高而逐渐增大的趋势,且最小面积所含物种数也随之增加;在相对应的海拔高度上,海拔2000m以下群落最小面积及所含物种数阴坡明显大于阳坡,而在2200m左右的高海拔则是阴坡与阳坡相接近;对于岷江上游干旱河谷灌丛群落类型而言,由方程（1）、（2）拟合所得的种一面积曲线较好于由方程（3）拟合所得的种．面积曲线。     

岷江上游干旱河谷区域空间变化的定量判定

采用遥感和地理信息系统技术,准确界定了岷江上游干旱河谷的范围,在此基础上分析了岷江上游干旱河谷的面积变化及其边界分布海拔的最高上限在垂直方向上的抬升距离。结果表明,干旱河谷面积在不断扩大,由1974年的93140hm2扩大到2000的123078hm2,其中1995～2000年间年变化率较1974～1995年有所降低;岷江上游干旱河谷的边界沿山体向上攀升非常迅速,1974岷江上游干旱河谷边界的最高上限海拔为3128m,1995年为3167m,较1974年抬升了39m;2000年为3181m,与1995年相比沿垂直方向向上抬升了14m。1974到2000年间岷江上游干旱河谷边界最高上限沿垂直方向抬升了53m,大约平均每年抬升2m。为了遏制干旱河谷进一步扩大的趋势,必须加大植被恢复和生态建设力度。     

硫硒配施对茎瘤芥生长和营养效应的研究

以茎瘤芥品种‘涪杂1号’为材料,通过盆栽实验探讨不同浓度的硫(S)、硒(Se)配施处理对茎瘤芥干物质积累、矿质元素吸收及膨大茎营养品质的影响,为生产中合理施用硫、硒肥提供理论依据.结果表明:与对照(S0Se0,未施硫硒肥)相比,增施硫、硒肥处理均能显著提高茎瘤芥的根、膨大茎、叶片和单株干物质产量,并以S50Se1[S/Se=50(mg/kg)/1(mg/kg)]和S100Se1的处理效果较好,其单株干物质产量分别比对照显著增加32.3%和36.2%;不同硫、硒浓度配施处理对茎瘤芥13种矿质元素积累的影响不同,主要显著促进了茎、叶对氮、磷、钾、硫、硒的吸收积累,而对其它元素的影响不显著,其中茎、叶的硒含量以S50Se3处理最高,硫含量以S100Se1处理最高;各硫硒配施处理对膨大茎营养品质的影响不同,其中S50Se1和S50Se3处理能显著提高膨大茎有机硒、总氨基酸和粗蛋白含量,而对维生素C和可溶性糖含量无显著影响.可见,适宜的硫硒配施可以明显促进其对矿质元素的吸收,提高植株干物质积累,有效改善茎瘤芥膨大茎营养品质,且硫硒配施用量以S 50mg/kg、Se 1mg/kg为宜.     

Fire regime shifts affect bird species distributions

Aim Fire is a major driver of ecosystem structure and process, and shifts in fire regimes are implicated in the decline of many species. Shifting fire regimes have been documented around the world, and fire frequency and extent is predicted to increase in many areas because of changes in both climate and land management. Here, we evaluate how predicted increases in fire frequency are likely to impact on species distributions. Location The tropical savannas of northern Australia. Methods We developed distribution models for 44 bird species using the modelling algorithm Maxent. Our models incorporated bird locality records and environmental variables including climate, total fire frequency and the subset of fire frequency occurring late in the dry season. We investigated the effect of increasing total fire frequency and increasing fire late in the dry season, on species distributions by projecting species model algorithms onto scenarios of incrementally increased total fire frequency. Results The probability of presence for most species was higher when fire frequency late in the dry season was low. Species showed a mixed response to an overall increase in total fire frequency, with one‐third predicted to increase in distribution. However, almost all species (98%) showed a decrease in predicted range with increased late‐dry season fire, and species distribution area was generally negatively correlated with an increase in late‐dry season fire. Main conclusions Our study highlighted the array of responses of species to increasing fire frequency and suggested that increased fire frequency late in the dry season is detrimental to most savanna‐restricted bird species. The understanding of individual species’ preferences for particular fire frequencies is important for informed conservation planning.     

High diversity of arbuscular mycorrhizal fungi in natural and anthropized sites of a Brazilian tropical dry forest (Caatinga)

Arbuscular mycorrhizal fungi (AMF) establish symbiotic associations with higher plants, which support the establishment and maintenance of plant communities across a range of environments, including those adversely affected by anthropogenic activity as well as natural sites. This study aimed at determining the diversity and distribution of AMF in areas of the tropical semi-arid region of Caatinga, Brazil, and compare areas in a naturally preserved state with anthropized sites. We characterized AMF communities in soil samples (n = 108), based on morphological taxonomy, at three sampling occasions and from six areas (typical Caatinga, extremely sandy Caatinga, stony Caatinga, rocky Caatinga, and two typical Caatinga areas that had been modified by human activities), at the National Park of Catimbau, Northeast Brazil. Eighty AMF species were recorded, with Glomus and Acaulospora predominating at all sites. There were significant differences in the composition of AMF communities between natural and anthropized sites, and among sampling occasions. Habitat-types also influenced AMF communities in Caatinga. Extensive tropical dry forest areas, such as the Catimbau National Park possess distinct niches, which maintain diverse AMF communities that are determined by anthropogenic activities, as well as vegetation types and environmental conditions.     

Impact of severe dry season on net ecosystem exchange in the Neotropical rainforest of French Guiana

The lack of information on the ways seasonal drought modifies the CO₂ exchange between Neotropical rainforest ecosystems and the atmosphere and the resulting carbon balance hinders our ability to precisely predict how these ecosystems will respond as global environmental changes force them to face increasingly contrasting conditions in the future. To address this issue, seasonal variations in daily net ecosystem productivity (NEP_d) and two main components of this productivity, daily total ecosystem respiration (R_Ed) and daily gross ecosystem productivity (GEP_d), were estimated over 2 years at a flux tower site in French Guiana, South America (5 °16′54″N, 52 °54′44″W). We compared seasonal variations between wet and dry periods and between dry periods of contrasting levels of intensity (i.e. mild vs. severe) during equivalent 93‐day periods. During the wet periods, the ecosystem was almost in balance with the atmosphere (storage of 9.0 g C m^?2). Seasonal dry periods, regardless of their severity, are associated with higher incident radiation and lower R_Ed combined with reduced soil respiration associated with low soil water availability. During the mild dry period, as is normally the case in this region, the amount of carbon stored in the ecosystem was 32.7 g C m^?2. Severe drought conditions resulted in even lower R_Ed, whereas the photosynthetic activity was only moderately reduced and no change in canopy structure was observed. Thus, the severe dry period was characterized by greater carbon storage (64.6 g C m^?2), emphasizing that environmental conditions, such as during a severe drought, modify the CO₂ exchange between Neotropical rainforest ecosystems and the atmosphere and potentially the resulting carbon balance.     

Development of cesium phosphotungstate salt and chitosan composite membrane for direct methanol fuel cells

A novel composite membrane has been developed by doping cesium phosphotungstate salt (Cs_xH_3−xPW₁₂O₄₀ (0 ≤ x ≤3), Cs_x-PTA) into chitosan (CTS/Cs_x-PTA) for application in direct methanol fuel cells (DMFCs). Uniform distribution of Cs_x-PTA nanoparticles has been achieved in the chitosan matrix. The proton conductivity of the composite membrane is significantly affected by the Cs_x-PTA content in the composite membrane as well as the Cs substitution in PTA. The highest proton conductivity for the CTS/Cs_x-PTA membranes was obtained with x = 2 and Cs₂-PTA content of 5 wt%. The value is 6 × 10⁻³ S cm⁻¹ and 1.75 × 10⁻² S cm⁻¹ at 298 K and 353 K, respectively. The methanol permeability of CTS/Cs₂-PTA membrane is about 5.6 × 10⁻⁷, 90% lower than that of Nafion-212 membrane. The highest selectivity factor (φ) was obtained on CTS/Cs₂-PTA-5 wt% composite membrane, 1.1 × 10⁴/S cm⁻³ s. The present study indicates the promising potential of CTS/Cs_x-PTA composite membrane as alternative proton exchange membranes in direct methanol fuel cells.     

Commonness,rarity, and oligarchies of woody plants in the tropical dry forests of Mexico

We assessed woody plant communities in two widely separated forests in the tropical dry forest (TDF) biome of Mexico for evidence of similar patterns of species commonness and rarity. We used belt transects laid out along contour lines (i.e., constant elevation) and stratified across elevation gradients at sites in Jalisco and Oaxaca to sample woody plant species diversity, abundance, relative frequency and basal area. We assembled a combined species list and compared species found in both sites (shared) to species found in only one site, assessing whether the most and least common species at a site tended to be shared or unshared. Of the 8242 individuals sampled, 370 species or morpho‐species were identified, with 222 species recorded at the Jalisco site and 270 at the Oaxaca site—122 (33%) species were shared across sites. Abundance, frequency and basal area of shared species were greater on average than for unshared species, and were positively correlated across sites. A subset of 68 shared species (18%) accounted for over half of all individuals encountered at the two sites. Species in the most common quartile were more likely to be shared than expected by chance, while species in the least common quartile were less likely. A genus‐level analysis found similar patterns. Our findings suggest that the TDF of Pacific coast Mexico shows evidence of widespread dominance by a small subset of species. These findings have potentially important implications for predicting species composition, understanding the role of oligarchic species in ecological processes, and conserving rare species.     

Optimal Gait for Bioinspired Climbing Robots Using Dry Adhesion:A Quasi-Static Investigation

Legged robots relying on dry adhesives for vertical climbing are required to preload their feet against the wall to increase contact surface area and consequently maximize adhesion force. Preloading a foot causes a redistribution of forces in the entire robot, including contact forces between the other feet and the wall. An inappropriate redistribution of these forces can cause irreparable detachment of the robot from the vertical surface. This paper investigates an optimal preloading and detaching strategy that minimizes energy consumption, while retaining safety, during locomotion on vertical surfaces. The gait of a six-legged robot is planned using a quasi-static model that takes into account both the structure of the robot and the characteristics of the adhesive material. The latter was modelled from experimental data collected for this paper. A constrained optimization routine is used, and its output is a sequence of optimal posture and motor torque set-points.