Generalizing plant–water relations to landscapes

Aims Changing climate and land use patterns make it increasingly important that the hydrology of catchments and ecosystems can be reliably characterized.The aim of this paper is to identify the biophysical factors that determine the rates of water vapor loss from different types of vegetation,and to seek,from an array of currently available satelliteborne sensors,those that might be used to initialize and drive landscape-level hydrologic models.Important Findings Spatial variation in the mean heights,crowd widths,and leaf area indices(LAI)of plant communities are important structural variables that affect the hydrology of landscapes.Canopy stomatal conductance(G)imposes physiological limitation on transpiration by vegetation.The maximum value of G(Gmax)is closely linked to canopy photosynthetic capacity,which can be estimated via remote sensing of foliar chlorophyll or nitrogen contents.Gcan be modeled as a nonlinear multipliable function of:(i)leaf–air vapor pressure deficit,(ii)water potential gradient between soil and leaves,(iii)photosynthetically active radiation absorbed by the canopy,(iv)plant nutrition,(v)temperature and(vi)the CO_(2) concentration of the air.Periodic surveys with Light Detection and Ranging(LiDAR)and interferometric RADAR,along with high-resolution spectral coverage in the visible,near-infrared,and thermal infrared bands,provide,along with meteorological data gathered from weather satellites,the kind of information required to model seasonal and interannual variation in transpiration and evaporation from landscapes with diverse and dynamic vegetation.

Responses of Dobera glabra and Eight Co-Occurring Species to Drought and Salinity Stress at a Savanna-Scrub Ecotone:Implications in the Face of Climate Change

To quantify the resistance of different co-occurring species to drought and osmotic stress (salinity stress), plant water (Ψ) and osmotic (Ψp) potentials were measured during the dry season. We applied a pressure chamber and cryoscopy to measure Ψ and Ψp, respectively. The species revealed a wide range of responses to water stress (-0.83 to -5.8 MPa) and osmotic stress (-1.3 to -3.2 MPa) and not all plants fit closely into one or the other category. Evergreen species tended to have lower Ψ than deciduous species. Notably, Dobera glabra, well known as drought indicator tree in the region, showed the lowest Ψ (up to -5.8 MPa) and Ψp (-3.2 MPa). This indicates its outstanding drought and osmotic stress tolerance and explains its ability to thrive in drought prone areas and years. The recent expansion of A. oerfota and A. mellifera in the study area could be related to their tolerance of osmotic stress, which may imply a trend of soil salinization. The division of plant responses into categories or strategies can be valuable aid to understanding long-term plant survival and distribution, monitor site condition and predict the direction of future changes.

Potential Effects of Global Change to Urban Vegetation： Vulnerability and Adaptations

An urban area is a space with high population density which develops new, major and complex structures in comparison to the areas surrounding it. In order to develop these structures and maintain population and its activity, the metabolism of urban areas needs a lot of external sources of energy and nutrients （water, food, materials...）, which produces heat waste, garbage, sewage and pollution which are some of the major problems for urban sites, and the related areas from it. This metabolism promotes major environmental changes in the urban areas, which promote stress on vegetation used in gardening. The main environmental factors that affect vegetation in urban areas are the same that have been defined in literature from long time ago, but now they are acting as the sum of complementary and synergic effects of these classical stresses at the same moment, in the same place, which happen due to the incredibly amount of energy that we place in the systems. This is called global change. Ecophysiological studies can provide objective information to be used as a tool to improve the vegetation management in urban areas from design to process, and consequently avoiding the potential vulnerabilities associated with global change. Present paper tries to show several examples about the plant response, measurement tools and vulnerabilities and adaptations to global change under urban conditions. It can be concluded that the large availability of vegetal material and the great technical development can be highlighted as strong points of gardening and urban landscaping while, as weak points, it could be mentioned the changing taste of consumers, which can force the introduction of new vegetal material with no time for adaptation, Urban gardening and landscaping can be considered to be exposed to global change, but in our opinion it is necessary to carry out more studies to determine the real degree of vulnerability of this activity to this complex kind of stress.

Regulation Mechanisms of Stomatal Oscillation

Stomata function as the gates between the plant and the atmospheric environment. Stomatal movement, including stomatal opening and closing, controls CO2 absorption as the raw material for photosynthesis and water loss through transpiration. How to reduce water loss and maintain enough CO2 absorption has been an interesting research topic for some time. Simple stomatal opening may elevate CO2 absorption, but, in the meantime, promote the water loss, whereas simple closing of stomatal pores may reduce both water loss and CO2 absorption, resulting in impairment of plant photosynthesis. Both processes are not economical to the plant. As a special rhythmic stomatal movement that usually occurs at smaller stomatal apertures, stomatal oscillation can keep CO2 absorption at a sufficient level and reduce water loss at the same time, suggesting a potential improvement in water use efficiency. Stomatal oscillation is usually found after a sudden change in one environmental factor in relatively constant environments. Many environmental stimuli can induce stomatal oscillation. It appears that, at the physiological level, feedback controls are involved in stomatal oscillation. At the cellular level, possibly two different patterns exist： （i） a quicker responsive pattern; and （ii） a slower response. Both involve water potential changes and water channel regulation, but the mechanisms of regulation of the two patterns are different. Some evidence suggests that the regulation of water channels may play a vital and primary role in stomatal oscillation. The present review summarizes studies on stomatal oscillation and concludes with some discussion regarding the mechanisms of regulation of stomatal oscillation.