Soil Salinity and Stomatal Conductance on Chaparral Plants

In our experiment we evaluated the soil salinity and corresponding stomatal conductance rates of Malosma laurina and Rhus integrifolia located near the coast and farther inland. Our prediction was that stomatal conductance would vary with the change in location of each species. Stomatal conductance was measured using a simple diffusion porometer and soil salinity was measured using a refractometer. We concluded that soil salinity caused a decline in stomatal conductance in both chaparral species. M. laurina was also found to be more sensitive to an increase in soil salinity, as its stomatal conductance rates declined more than that of R. integrifolia

A Data-Driven Regional Model of Stomatal Conductance for Kruger National Park

Stomata are the gateway between the lithosphere, the biosphere, and the atmosphere. Because of photosynthesis, plants inevitably lose water through their stomata. The rate at which water moves through stomata is stomatal conductance. As stomatal conductance increases, the rate of CO2 assimilation increases, therefore, plants must reach a balance between acquiring CO2 and losing H2O. Plants achieve this balance by adjusting stomatal aperture. Therefore, modeling stomatal conductance is important to global circulation models and land surface models, as well as for predicting how changing climate conditions affect water use efficiency and plant productivity, and has implications for agriculture and natural resource management. Here a large dataset of field measurements was used to describe stomatal conductance for Kruger National Park, South Africa and develop statistical models of landscape-level stomatal conductance. Then models were used to estimate stomatal conductance across the region over several growing seasons. Over 8,000 measurements of stomatal conductance were made in four sites that represented a range of precipitation regimes and soil types within Kruger National Park from 2007-2012. Known environmental drivers of stomatal conductance, such as soil moisture, temperature, and shortwave radiation, were also measured during this period. Observed mean daytime stomatal conductance for the park was 75 ± 1 and 155 ± 2 mmol m-2 sec1 for grasses and woody plants, respectively. When statistical models were used to produce three years of continuous estimates of gs from environmental data, average daytime stomatal conductance was estimated as 67 and 158 mmol m-2 sec-1 for grasses and woody plants, respectively. The Random Forest statistical models that were used to produce continuous estimates of gs indicated that soil moisture, particularly at shallow depths, and plant species identity are primary drivers of landscape-scale stomatal conductance for Kruger National Park. However, results indicate that there is still a large amount of landscape-scale variability in stomatal conductance that the environmental drivers investigated here were unable to explain. Results provide a rare example of landscape-level estimates of stomatal conductance based on direct measurements. The models give insight into the relative importance of environmental drivers and the nature of their effect on stomatal conductance in savanna ecosystems. Because the measurements were collected over a range of species and soil conditions, the models should provide inference for many deciduous, sub-tropical savannas of southern Africa

The role of abscisic acid and water relations in drought responses of subterranean clover

The role of water relations and abscisic acid (ABA) in the responses to drought were studied in a mediterranean forage crop, Trifolium subterraneum L. under field conditions. soil and plant water status, leaf gas exchange parameters, and xylem sap ABA content were determined at different times during a long-term soil drying episode in irrigated and droughted plants. The diurnal time-courses of these parameters were also measured at the end of a drought period. In response to soil drying stomatal conductance (g) was reduced early to 50% that of irrigated plants before any substantial change in water potential was detected. A close logarithmic regression between photosynthesis rate (A) and g was present. For the first weeks of drought the decline in A was less pronounced than in g, thus increasing water use efficiency. Stomatal conductance during diurnal time-courses showed no consistent relationships with respect to either ABA or leaf water potential. throughout the experimental period dependence of g on leaf water status was evident from the tight correlation (r(2) = 0.88, P < 0.01) achieved between stomatal conductance and midday water potential, but the correlation was also high when comparing g with respect to ABA content in xylem sap (r(2) = 0.83, P < 0.001). However, the stomata from drought acclimated plants were apparently more sensitive to xylem ABA content. For similar xylem ABA concentrations stomatal conductance was significantly higher in irrigated than in water-stressed plants.info:eu-repo/semantics/publishedVersio

Simulation of long-term stem diameter variation of Ficus benjamina based on simulated transpiration

Greenhouse microclimate (light, temperature, relative humidity and CO2) and irrigation are important factors for plant growth, development and quality in ornamental horticulture. To optimize plant growth, actual stem diameter growth can be measured and compared with a desired growth pattern. Using the deviation between measured and simulated stem diameter growth, growers can decide whether and in which way the microclimate or irrigation needs to be adjusted. Together with this decision, costs associated with climate control and irrigation must also be taken into account. This will help growers to find a proper balance between cultivation costs and plant growth. In this study, Ficus benjamina was grown from cutting to mature plant in a controlled greenhouse environment. Growing conditions, microclimate as well as plant spacing, closely resembled the ones used in commercial greenhouses. Microclimate, soil water content, leaf temperature, sap flow, stem diameter variation and leaf thickness were continuously measured on three plants. In addition, discrete measurements of leaf area, projected crown surface area, stem water potential, photosynthesis, transpiration and stomatal conductance were performed. These measurements were used to further extend a mechanistic plant model, which allows simulation of long-term stem diameter variation

Estimation of soil water deficit in an irrigated cotton field with infrared thermography

Plant growth and soil water deficit can vary spatially and temporally in crop fields due to variation in soil properties and/or irrigation and crop management factors. We conducted field experiments with cotton (Gossypium hirsutum L.) over two seasons during 2007-2009 to test if infrared thermography can distinguish systematic variation in deficit irrigation applied to various parts of the field over time. Soil water content was measured with a neutron probe and thermal images of crop plants were taken with a thermal infrared camera. Leaf water potential and stomatal conductance were also measured on selected occasions. All measurements were made at fixed locations within three replicate plots of an irrigation experiment consisting of four soil-water deficit treatments. Canopy temperature related as well with soil water within the root zone of cotton as the stomatal conductance index derived from canopy temperature, but it neglected the effect of local and seasonal variation in environmental conditions. Similarities in the pattern of spatial variation in canopy temperature and soil water over the experimental field indicates that thermography can be used with stomatal conductance index to assess soil water deficit in cotton fields for scheduling of irrigation and to apply water in areas within the field where it is most needed to reduce water deficit stress to the crop. Further confidence with application of infrared thermography can be gained by testing our measurement approach and analysis with irrigation scheduling of other crops

Riparian plant water relations along the north fork of the Kings River, California

Plant water relations of five obligate ripar-ian species were studied along California\u27s North Fork Kings River. Diurnal stomatal conductance, transpi-ration, and xylem pressure potentials were measured throughout the 1986 growing season and in mid-season in 1987. Patterns were similar for all species although absolute values varied considerably. Maximum stomatal conductance occurred early in the day and season during favorable environmental conditions and decreased as air temperature and the vapor pressure difference between the leaf and air increased. Maximum transpiration rates occurred in mid-morning and mid-summer resulting in estimated daily water losses per unit sunlit leaf area of 163-328 mol H2O m-2. Predawn xylem pressure poten-tials remained high in 1986 when streamflows averaged 1.41 m3/s (50 cfs), however they were notably lower in 1987 at 0.7 m3/s (25 cfs)

Water-stress induced physiological changes in leaves of four container-grown grapevine cultivars (Vitis vinifera L.)

Predawn leaf water potential, night respiration, stomatal conductance, transpiration, and photosynthesis of 4 grapevine cultivars were assessed under irrigated and non-irrigated conditions in July, August and September 1994. Predawn leaf water potential was not significantly related to either stomatal conductance or photosynthesis. Water stress induced distinct stomatal closure in all cultivars at 11 a.m. For a given stomatal conductance rate, photosynthesis of stressed vines was lower than that of nonstressed vines. At similar stomatal conductance rate, photosynthesis was lower in cv. Chardonnay than in any other cultivar. Photosynthesis was the physiological parameter mostly affected by water stress. Dry matter production was linearly related to stomatal conductance, photosynthesis, and the night respiration to photosynthesis ratio for all vines pooled together. In contrast, under stress conditions dry matter production was not related to any physiological parameter.

Stomatal behavior of cowpea genotypes grown under varying moisture levels

Drought is a major limitation to crop productivity worldwide. Plants lose most of their water through stomata, thus making stomata an important organ in the control of transpiration and photosynthesis. This study assessed the stomatal behavior of four cowpea genotypes grown under four moisture levels under hot semi-arid conditions. Stomatal conductance (gs) was measured at 47, 54, 70 and 77 days after planting (DAP). Biomass and carbon isotope composition (C-13) were also determined at flowering. Genotype and moisture level significantly influenced gs. Genotypes varied in gs at vegetative stages (47 and 54 DAP) only. TVu4607 had higher gs under severe drought conditions at both 47 and 54 DAP. On the other hand, moisture level influenced gs at 54 and 70 DAP only. Stomatal conductance was severely restricted in cowpea under both moderate and severe drought conditions as gs was mostly below the threshold 0.10 mol m(-2) s(-1). Relationships between: biomass and gs, and C-13 and gs were positive under severe drought only. The findings revealed that cowpea genotypes vary in gs under dry conditions and that the variation is more prominent at vegetative stage, suggesting that cowpea productivity in dry areas could be improved through selection of genotypes that maintain higher gs under dry conditions