Environmental Productivity and Biodiversity Effects on Invertebrate Community Invasibility

Productivity influences the availability of resources for colonizing species. Biodiversity may also influence invasibility of communities because of more complete use of resource types with increasing species richness. We hypothesized that communities with higher environmental productivity and lower species richness should be more invasible by a competitor than those where productivity is low or where richness is high. We experimentally examined the invasion resistance of herbivorous meiofauna of Jamaican rock pools by a competitor crustacean (Ostracoda: Potamocypris sp. (Brady)) by contrasting three levels of nutrient input and four levels of species richness. Although relative abundance (dominance) of the invasive was largely unaffected by resource availability, increasing resources did increase the success rate of establishment. Effects of species richness on dominance were more pronounced with a trend towards the lowest species richness treatment of 2 resident species being more invasible than those with 4, 6, or 7 species. These results can be attributed to a ‘sampling effect associated with the introduction of Alona davidii (Richard) into the higher biodiversity treatments. Alona dominated the communities where it established and precluded dominance by the introduced ostracod. Our experimental study supports the idea that niche availability and community interactions define community invasibility and does not support the application of a neutral community model for local food web management where predictions of exotic species impacts are needed.     

Plant Performance in a Warmer World: General Responses of Plants from Cold, Northern Biomes and the Importance of Winter and Spring Events

During the past three decades the Earth has warmed with a rate unprecedented during the past 1000 years. There is already ample evidence that this fast climate warming has affected a broad range of organisms, including plants. Plants from high-latitude and high-altitude sites (‘cold biomes’) are especially sensitive to climate warming. In this paper we (1) review the response in the phenology of plants, changes in their range and distribution, soil nutrient availability, and the effects on the structure and dynamics of plant communities for cold, northern biomes; and (2) we show, by using data from an ongoing snow and temperature manipulation experiment in northern Sweden, that also winter and spring events have a profound influence on plant performance. Both long-term phenological data sets, experimental warming studies (performed in summer or year-round), natural gradient studies and satellite images show that key phenological events are responsive to temperature increases and that recent climate warming does indeed lead to changes in plant phenology. However, data from a warming and snow manipulation study that we are conducting in northern Sweden show that plants respond differently to the various climatic scenarios that we had imposed on these species and that especially winter and spring events have a profound impact. This indicates that it is necessary to include several scenarios of both summer and winter climate change in experimental climate change studies, and that we need detailed projections of future climate at a regional scale to be able to assess their impacts on natural ecosystems. There is also ample evidence that the range shift of herbs and shrubs to more northern regions is for the vast majority of species mainly caused by changes in the climate. This is in line with the observed ‘up-greening’ of northern tundra sites. These rapid northern shifts in distribution of plants as a result of climate warming may have substantial consequences for the structure and dynamics of high-latitude ecosystems. An analysis of warming studies at 9 tundra sites shows that heating during at least 3 years increased net N-mineralization from 0.32±0.31 (SE) g N m⁻² yr⁻¹ in the controls to 0.53±0.31 (SE) g N m⁻² yr⁻¹ in the heated plots (p<0.05), an increase of about 70%. Thus, warming leads to higher N availability in high-latitude northern tundra sites, but the variability is substantial. Higher nutrient availability affects in turn the species composition of high-latitude sites, which has important consequences for the carbon and water balance of these systems.     

Left- and right-handed LHC II macroaggregates revealed by circularly polarized chlorophyll luminescence

Circularly polarized chlorophyll luminescence (CPL) may serve as a measure of chiral macroaggregates of the light-harvesting chlorophyll-protein complexes (LHC II) in both isolated chloroplasts and intact leaves (Gussakovsky et al (2000) Photosynth Res 65: 83–92). In the present work, we applied the CPL approach to study the effect of fast (1–2 min) thermal impacts on LHC II macroaggregates. The results revealed unexpected temperature-response kinetics, composed of initial bell-shaped changes in the CPL signal, followed by degradation down to a steady state (equilibrium). The bell-shape effect was dependent upon illumination, and vanished in the dark. A mathematical analysis of the temperature-response kinetics uniquely indicated that LHC II chiral macroaggregates may persist in both left- and right-handed forms. These forms differ in their response to high temperatures. Both forms are more thermostable in leaves than in isolated chloroplasts. The cooperative degradation of LHC II macroaggregates, which is induced by the thermal impact, is irreversible. It is therefore suggested that the native LHC II macroaggregates are stable, stationary, non-equilibrium, spatially heterogeneous (dissipative) structures. The dissipative properties probably allow the interconversion between left- and right-handed forms under perturbation by certain factors. Illumination probably serves as one such perturbation factor, initiating the interconversion of dark-adapted, left-handed to light-dependent, right-handed LHC II macroaggregates. The chiral heterogeneity of the LHC II macroaggregates is a newly revealed aspect which needs to be taken into consideration in future circular dichroism or CPL studies.     

苔藓植物蓝光/紫外光-A 信号传导的研究

种子植物含有5个已分离的光受体和至少1个未鉴定的蓝光/紫外光-A受体。隐花色素(CRY1、CRY2和CRY3) 调节植物的生长发育,而向光蛋白(PHOT1和PHOT2) 调节植物对光的营养反应。黄素可以吸收蓝光和紫外光-A,是生色团。对这些光受体的结构和作用模式已了解很多。苔藓植物小立碗藓中含有2个已分离的隐花色素(CRY1a和CRY1b),负责调节侧枝形成和生长素代谢;有4个向光蛋白(PHOTA1,PHOTA2,PHOTB1,PHOTB2) 调节叶绿体的运动。苔藓细胞内蓝光/紫外光-A刺激引发的信号转导有Ca2+参与。     

A dynamic analysis of the shade-induced plasticity in Arabidopsis thaliana rosette leaf development reveals new components of the shade-adaptative response

BACKGROUND AND AIMS: It is well known that plant aerial development is affected by light intensity in terms of the date of flowering, the length of stems and petioles, and the final individual leaf area. The aim of the work presented here was to analyse how shade-induced changes in leaf development occur on a dynamic basis from the whole rosette level to that of the cells. METHODS: Care was taken to ensure that light intensity was the only source of micro-meteorological variation in the study. The dynamics of leaf production, rosette expansion, individual leaf area expansion and epidermal cell expansion were analysed in Arabidopsis thaliana plants grown under two light intensities in three independent experiments. KEY RESULTS: The total area of rosette leaves was reduced by the shading treatment. Both the number of leaves produced and their individual leaf areas were reduced. The reduction in leaf number was associated with a reduction in leaf initiation rate and the duration of the phase of leaf production. The reduction in individual leaf area was associated with a reduction in leaf expansion rate and an increase in the duration of leaf expansion. The changes in leaf expansion dynamics were accompanied by a decrease in epidermal cell number which was partly compensated for by an increase in epidermal cell area. Overall, the whole rosette leaf expansion rate was reduced by shading, whereas the total duration of rosette leaf expansion was unaffected. This was mainly due to the accumulation of the increases in the durations of expansion of each individual leaf which was associated with an increase in cell expansion. CONCLUSIONS: The dynamic analysis presented here reveals a new shade-adaptative response mediated via the control of area expansion at the cell, organ and whole plant levels.     

Branch development controls leaf area dynamics in grapevine (Vitis vinifera) growing in drying soil

BACKGROUND AND AIMS: Soil water deficit is a major abiotic stress with severe consequences for the development, productivity and quality of crops. However, it is considered a positive factor in grapevine management (Vitis vinifera), as it has been shown to increase grape quality. The effects of soil water deficit on organogenesis, morphogenesis and gas exchange in the shoot were investigated. METHODS: Shoot organogenesis was analysed by distinguishing between the various steps in the development of the main axis and branches. Several experiments were carried out in pots, placed in a greenhouse or outside, in southern France. Soil water deficits of various intensities were imposed during vegetative development of the shoots of two cultivars ('Syrah' and 'Grenache N'). KEY RESULTS: All developmental processes were inhibited by soil water deficit, in an intensity-dependent manner, and sensitivity to water stress was process-dependent. Quantitative relationships with soil water were established for all processes. No difference was observed between the two cultivars for any criterion. The number of leaves on branches was particularly sensitive to soil water deficit, which rapidly and strongly reduced the rate of leaf appearance on developing branches. This response was not related to carbon availability, photosynthetic activity or the soluble sugar content of young expanding leaves. The potential number of branches was not a limiting factor for shoot development. CONCLUSIONS: The particularly high sensitivity to soil water deficit of leaf appearance on branches indicates that this process is a major determinant of the adaptation of plant leaf area to soil water deficit. The origin of this particular developmental response to soil water deficit is unclear, but it seems to be related to constitutive characteristics of branches rather than to competition for assimilates between axes differing in sink strength.     

Low concentrations of NaHSO3 increase photosynthesis, biomass, and attenuate photoinhibition in Satsuma mandarin (Citrus unshiu Marc.) plants

Spraying low concentrated (0.5–5.0 mM) solutions of NaHSO₃ on Satsuma mandarin (Citrus unshiu Marc.) leaves resulted in enhancement (maximal about 15 % at 1 mM NaHSO₃) of net photosynthetic rate (P _N) for 6 d. The potential photochemical efficiency of photosystem 2 (PS2, F_v/F_m) and the quantum yield of PS2 electron transport (Φ_PS2) were increased under strong photon flux density (PFD). The slow phase of millisecond delayed light emission (ms-DLE) was increased, showing that the transmembrane proton motive force related to photophosphorylation was enhanced. We also observed that low concentrations of NaHSO₃ promoted the production of ATP in irradiated leaves. We suggest that the increase in P _N in Satsuma mandarin leaves caused by low concentrations of NaHSO₃ solution may have been due to the stimulation of photophosphorylation and, hence, the increase in photochemical efficiency through speeding-up of PS2 electron transport. Photoinhibition of photosynthesis in leaves was modified by NaHSO₃ treatment under high PFD. Hence the increase in leaf dry mass seems to be associated with the mitigation of photoinhibition caused by strong PFD.     

Dissociation and unfolding of inducible nitric oxide synthase oxygenase domain identifies structural role of tetrahydrobiopterin in modulating the heme environment

The oxygenase domain of the inducible nitric oxide synthase, Δ65 iNOSox is a dimer that binds heme, L-Arginine (L-Arg), and tetrahydrobiopterin (H₄B) and is the site for NO synthesis. The role of H₄B in iNOS structure-function is complex and its exact structural role is presently unknown. The present paper provides a simple mechanistic account of interaction of the cofactor tetrahydrobiopterin (H₄B) with the bacterially expressed Δ65 iNOSox protein. Transverse urea gradient gel electrophoresis studies indicated the presence of different conformers in the cofactor-incubated and cofactor-free Δ65 iNOSox protein. Dynamic Light Scattering (DLS) studies of cofactor-incubated and cofactor-free Δ65 iNOSox protein also showed two distinct populations of two different diameter ranges. Cofactor tetrahydrobiopterin (H₄B) shifted one population, with higher diameter, to the lower diameter ranges indicating conformational changes. The additional role played by the cofactor is to elevate the heme retaining capacity even in presence of denaturing stress. Together, these findings confirm that the H₄B is essential in modulating the iNOS heme environment and the protein environment in the dimeric iNOS oxygenase domain. (Mol Cell Boichem xxx: 1–10, 2005) Supported by Calcutta University Research Grants.     

Potential of cadmium sulphide nanorods as an optical microscopic probe to the folding state of cytochrome C

The folding behavior of cytochrome C (Cyt-C) conjugated with CdS nanorods (CdSnr) is amenable to monitoring by bright field microscopy, the porosity and percolating behavior of such protein conjugated nanoclusters depending on the folding history prior to the conjugation. The method has been used to predict the thermal melting behavior as well as guanidine hydrochloride induced unfolding of Cyt-C. Dynamic light scattering studies indicate that the size distribution of the nanoforms widens in presence of the protein. Furthermore, there is emergence of clusters with higher conductivity and altered zeta potential. Increase of second virial coefficient of CdS nanoforms in the presence of Cyt-C (obtained from static light scattering experiments) implies presence of protein coat over the hydrophobic nanosurface. The results are supported by morphological changes observed through scanning electron microscopy (SEM). Accordingly, the X-ray diffraction pattern shows a change of crystallographic orientations of CdSnr in presence of Cyt-C.     

Leaf lifespan and lifetime carbon balance of individual leaves in a stand of an annual herb, Xanthium canadense

Leaf lifespan in response to resource availability has been documented in many studies, but it still remains uncertain what determines the timing of leaf shedding. Here, we evaluate the lifetime carbon (C) balance of a leaf in a canopy as influenced by nitrogen (N) availability. Stands of Xanthium canadense were established with high-nitrogen (HN) and low-nitrogen (LN) treatments and temporal changes of C gain of individual leaves were investigated with a canopy photosynthesis model. Daily C gain of a leaf was maximal early in its development and subsequently declined. Daily C gain at shedding was nearly zero in HN, while it was still positive in LN. Sensitivity analyses showed that the decline in the daily C gain resulted primarily from the reduction in light level in HN and by the reduction in leaf N in LN. Smaller leaf size in LN than in HN led to higher light levels in the canopy, which helped leaves of the LN stand maintain for a longer period. These results suggest that the mechanism by which leaf lifespan is determined changes depending on the availability of the resource that is most limiting to plant growth.