Relations between stomatal closure, leaf turgor and xylem vulnerability in eight tropical dry forest trees

This study examined the linkage between xylem vulnerability, stomatal response to leaf water potential (Ψ_L), and loss of leaf turgor in eight species of seasonally dry tropical forest trees. In order to maximize the potential variation in these traits species that exhibit a range of leaf habits and phenologies were selected. It was found that in all species stomatal conductance was responsive to Ψ_L over a narrow range of water potentials, and that Ψ_L inducing 50% stomatal closure was correlated with both the Ψ_L inducing a 20% loss of xylem hydraulic conductivity and leaf water potential at turgor loss in all species. In contrast, there was no correlation between the water potential causing a 50% loss of conductivity in the stem xylem, and the water potential at stomatal closure (Ψ_SC) amongst species. It was concluded that although both leaf and xylem characters are correlated with the response of stomata to Ψ_L, there is considerable flexibility in this linkage. The range of responses is discussed in terms of the differing leaf‐loss strategies exhibited by these species.     

Fractal analysis of plant spatial patterns: a monitoring tool for vegetation transition shifts

Spatial heterogeneity, like species diversity, is an important ecosystem property. We examine the effects of land use on the diversity and spatial distribution of plants in five semi-arid communities of eastern Spain using non-linear methods to assess the spatialtemporal dynamics of plant populations. Specifically, we are interested in detecting long-term structural changes or drift in an ecosystem before it is too late to prevent irreversible degradation. Fractal analysis is used to characterize the complexity of plant spatial patterns and Information Theory indices are used to measure change in information flow with land use changes and soil substrate. We found that grazing favored diversity and heterogeneity of species distribution on the impoverished gypsum and saline substrate community, as opposed to the detrimental effect of grazing in the Alpha steppe community. Indeed, old-field succession after 30 years of abandonment showed a recovery of species diversity but not the spatial structure of the vegetation. Further, Information Fractal Dimension, representing the unpredictability of plant spatial patterns in the landscape, increased as we moved from a highly diverse to a less diverse community, revealing the change to a more scattered and homogeneous spatial plant distribution. The Information Fractal Dimension is a good estimator of ecosystem disturbance, independent of scale, and thus can be used to monitor ecosystem dynamics.     

Dynamics of leaf area and nitrogen in the canopy of an annual herb, <Emphasis Type="Italic">Xanthium canadense</Emphasis>

We studied leaf area and nitrogen dynamics in the canopy of stands of an annual herb Xanthium canadense, grown at a high (HN)- and a low-nitorgen (LN) availability. Standing leaf area increased continuously through the vegetative growth period in the LN stand, or leveled off in the later stage in the HN stand. When scaled against standing leaf area, both production and loss rates of leaf area increased but with different patterns: the production rate was retarded, while the loss rate was accelerated, implying an upper limit of standing leaf area of the canopy. The rate of leaf-area production was higher in the HN than in the LN stand, which was caused by the higher rate of leaf production per standing leaf area as well as the greater standing leaf area in the HN stand. Although the rate of leaf-area loss was higher in the HN than in the LN stand, it was not significantly different between the two stands when compared at a common standing leaf area, suggesting involvement of light climate in determination of the leaf-loss rate. On the other hand, the rate of leaf-area loss was positively correlated with nitrogen demand for leaf area development across the two stands, suggesting that leaf loss was caused by retranslocation of nitrogen for construction of new leaves. A simple simulation model of leaf and nitrogen dynamics in the canopy showed that, at steady state, where the rate of leaf-area loss becomes equal to the production rate, the standing leaf area was still greater in the HN than in the LN stand. Similarly, when the uptake and loss of nitrogen are equilibrated, the standing nitrogen was greater in the HN than in the LN stand. These results suggest that leaf-area production is strongly controlled by nitrogen availability, while both nitrogen and light climate determine leaf-loss rates in the canopy.     

Topography and Nanomechanics of Live Neuronal Growth Cones Analyzed by Atomic Force Microscopy

Neuronal growth cones are motile structures located at the end of axons that translate extracellular guidance information into directional movements. Despite the important role of growth cones in neuronal development and regeneration, relatively little is known about the topography and mechanical properties of distinct subcellular growth cone regions under live conditions. In this study, we used the AFM to study the P domain, T zone, and C domain of live Aplysia growth cones. The average height of these regions was calculated from contact mode AFM images to be 183 ± 33, 690 ± 274, and 1322 ± 164 nm, respectively. These findings are consistent with data derived from dynamic mode images of live and contact mode images of fixed growth cones. Nano-indentation measurements indicate that the elastic moduli of the C domain and T zone ruffling region ranged between 3-7 and 7-23 kPa, respectively. The range of the measured elastic modulus of the P domain was 10-40 kPa. High resolution images of the P domain suggest its relatively high elastic modulus results from a dense meshwork of actin filaments in lamellipodia and from actin bundles in the filopodia. The increased mechanical stiffness of the P and T domains is likely important to support and transduce tension that develops during growth cone steering.     

Effect of betamethasone phosphate loaded polymeric nanoparticles on a murine asthma model

Although inhaled steroids are the treatment of first choice to control asthma, administration of systemic steroids is required for treatment of asthmatic exacerbation and intractable asthma. To improve efficacy and reduce side effects, we examine the effects of betamethasone disodium phosphate (BP) encapsulated in biocompatible, biodegradable blended nanoparticles (stealth nanosteroids) on a murine model of asthma. These stealth nanosteroids were found to accumulate at the site of airway inflammation and exhibit anti-inflammatory activity. Significant decreases in BALF eosinophil number were maintained for 7 days with a single injection of nanosteroids containing 40 μg BP. Airway responsiveness was also attenuated by the injection of stealth nanosteroids. A single injection of 40 μg of free BP and 8 μg of free BP once daily for 5 days did not show any significant effects. We conclude that stealth nanosteroids achieve prolonged and higher benefits at the site of airway inflammation compared to free steroids.     

白洋淀轮虫多样性及群落结构的初步研究

于2006年12月、2007年3～5月调查了白洋淀9个采样点的轮虫种类组成、数量及优势种,并对轮虫群落的多样性指数和群落相似性系数进行了测算,综合评价了白洋淀水质及富营养化状况.本次共发现轮虫41种,平均丰度为607～5024 ind./L,优势种为蒲达臂尾轮虫Brachionus budapesllensis、长肢多肢轮虫Polyarthra doli-choptera、角突臂尾轮虫B.angularis、矩形龟甲轮虫Keratella quadrata等,均为耐污性种类,各样点轮虫群落具较高相似性.从轮虫群落Margalef多样性指数看,白洋淀水质属中度污染和严重污染状况.     

Nucleotide pocket thermodynamics measured by EPR reveal how energy partitioning relates myosin speed to efficiency

We have used spin-labeled ADP to investigate the dynamics of the nucleotide-binding pocket in a series of myosins, which have a range of velocities. Electron paramagnetic resonance spectroscopy reveals that the pocket is in equilibrium between open and closed conformations. In the absence of actin, the closed conformation is favored. When myosin binds actin, the open conformation becomes more favored, facilitating nucleotide release. We found that faster myosins favor a more closed pocket in the actomyosin•ADP state, with smaller values of ΔH⁰ and ΔS⁰, even though these myosins release ADP at a faster rate. A model involving a partitioning of free energy between work-generating steps prior to rate-limiting ADP release explains both the unexpected correlation between velocity and opening of the pocket and the observation that fast myosins are less efficient than slow myosins.     

秸秆还田条件下灌水模式对冬小麦产量和水肥利用效率的影响

于2008-2010年,在山西省临汾市尧都区半干旱、半湿润季风气候区,通过大田试验研究了玉米秸秆连续还田条件下灌水模式对冬小麦籽粒产量、干物质转移及水肥利用效率的影响.结果表明:浇越冬水可促进小麦分蘖;浇拔节水可提高分蘖成穗率,增加成穗数;浇孕穗水可促进穗部干物质积累,提高千粒重.浇2水时,推迟第2次浇水时期使叶片干物质转移量和穗粒数增加;浇2水比浇l水的肥料表观利用率高,可促进穗部干物质积累.越冬水灌水量和总灌水量对分蘖、穗部干物质积累的影响较小;拔节期或孕穗期增加灌水量则更有利于养分吸收及干物质积累与转移,提高籽粒水分利用效率,产量构成因素协调,增产效果明显.因此,确保越冬水可实现稳产,在越冬水基础上,拔节期增量灌水(900 m3·hm-2)可满足冬小麦中后期生长发育的需要,提高籽粒水分利用效率,实现节水高产栽培.     

Algal epilithon and water quality of a stream receiving oil refinery effluent

Changes in epilithic algal communities colonizing introduced substrata were determined in a stream polluted with oil refinery effluent at Digboi (Assam, India). The number of algal taxa was reduced but the growth of blue-green algae, particularly two species ofOscillatoria, was encouraged. Epilithic biomass (as chlorophylla) also declined at polluted stations. The algal community of the upstream station was markedly different from the community occurring just after the confluence of effluent; however, the differences were gradually reduced downstream, indicating improvement in water quality. Of the various criteria tested for possible relationships with the level of pollutants, species richness, Shannon diversity and biomass showed significant relationships. The study demonstrates the usefulness of algal criteria for monitoring oil pollution in running waters.