Water Use Efficiency Index Research Articles

Inter- and intra-annual carbon isotope fluctuations in Pinus sylvestris L. tree rings whole wood and cellulose in north-eastern Lithuania

In temperate regions trees typically exhibit growth sensitivity to climatic conditions during the growth season. Annual tree ring growth increments correlate with a variety of environmental factors. As an index of water use efficiency, δ13C is a preferred proxy to allow accurate interpretation of environmental factors critical for the tree growth, including changes in climate patterns, variation in the ambient temperature and precipitation. We assumed that isotopic differences within individual tree rings are likely to produce seasonal isotope fluctuations in the chronology that might be interpreted as response to environmental impacts. To verify the assumption, we measured δ13C in annual tree rings of Pinus Sylvestris L. split into 13 intra-annual segments each and checked δ13C correlations with temperature, precipitation, the number of sunshine hours and relative air humidity. For the investigation, we chose a site in north-eastern Lithuania, Zarasai, located in boreal latitude and remote from industrial pollution sources. The methodology of the research was based on high coherence of δ13C chronologies measured in the whole wood and α-cellulose extracted by means of two different methods. The experiment produced strong δ13C correlations with hydrometeorological parameters, especially in the earlywood formed in June

Genome size variation in Cape schoenoid sedges (Schoeneae) and its ecophysiological consequences.

Increases in genome size in plants-often associated with larger, low-density stomata and greater water-use efficiency (WUE)-could affect plant ecophysiological and hydraulic function. Variation in plant genome size is often due to polyploidy, having occurred repeatedly in the austral sedge genus Schoenus in the Cape Floristic Region (CFR), while species in the other major schoenoid genus in the region, Tetraria, have smaller genomes. Comparing these genera is useful as they co-occur at the landscape level, under broadly similar bioclimatic conditions. We hypothesized that CFR Schoenus have greater WUE, with lower maximum stomatal conductance (gwmax) imposed by larger, less-dense stomata. We investigated relationships between genome size and stomatal parameters in a phylogenetic context, reconstructing a phylogeny of CFR-occurring Schoeneae (Cyperaceae). Species' stomatal and functional traits were measured from field-collected and herbarium specimens. Carbon stable isotopes were used as an index of WUE. Genome size was derived from flow-cytometric measurements of leafy shoots. Evolutionary regressions demonstrated that stomatal size and density covary with genome size, positively and negatively, respectively, with genome size explaining 72-75% of the variation in stomatal size. Larger-genomed species had lower gwmax and C:N ratios, particularly in culms. We interpret differences in vegetative physiology between the genera as evidence of more-conservative strategies in CFR Schoenus compared to the more-acquisitive Tetraria. Because Schoenus have smaller, reduced leaves, they likely rely more on culm photosynthesis than Tetraria. Across the CFR Schoeneae, ecophysiology correlates with genome size, but confounding sources of trait variation limit inferences about causal relationships between traits.

Rising water-use efficiency in European grasslands is driven by increased primary production

Water-use efficiency is the amount of carbon assimilated per water used by an ecosystem and a key indicator of ecosystem functioning, but its variability in response to climate change and droughts is not thoroughly understood. Here, we investigated trends, drought response and drivers of three water-use efficiency indices from 1995–2018 in Europe with remote sensing data that considered long-term environmental effects. We show that inherent water-use efficiency decreased by −4.2% in Central Europe, exhibiting threatened ecosystem functioning. In European grasslands it increased by +24.2%, by regulated transpiration and increased carbon assimilation. Further, we highlight modulation of water-use efficiency drought response by hydro-climate and the importance of adaptive canopy conductance on ecosystem function. Our results imply that decoupling carbon assimilation from canopy conductance and efficient water management strategies could make the difference between threatened and well-coping ecosystems with ongoing climate change, and provide important insights for land surface model development.

Half-sibling loblolly pine clones exhibited intraspecific variation, a G × E interaction, and differences in stable isotope composition in response to soil moisture availability

We examined the response of three loblolly pine half-sibling clones (hereafter referred to as Clone 1, 2, and 3) to soil moisture availability in a greenhouse study. Three soil moisture treatments were imposed. Two were constant soil moisture treatments at either high (−0.3MPa) or low (−1.5MPa) soil water potential. The third was an alternating wet-dry treatment that alternated between one week at high (−0.3MPa) and three weeks at low (−1.5MPa) soil water potential, which simulated several natural wetting-drying cycles. At intervals throughout the experiment we measured biomass accumulation (via sequential harvesting), change in height, pre-dawn needle water potential, afternoon needle water potential, dark respiration, and morning and afternoon gas exchange (photosynthesis, stomatal conductance, intercellular CO2, and transpiration). Carbon allocation to root and shoot biomass, stomatal density, and carbon isotope composition were measured at the end of the experiment.All clones accumulated more biomass in the high soil moisture treatment than in the low soil moisture treatment, but there was a genetic by environment (G×E) interaction: Clone 1 accumulated more biomass than the other clones in the low soil moisture treatment and less than the others in the high soil moisture treatment. Stable carbon isotope composition, which we interpreted as a time-integrated index of water use efficiency, was significantly higher (indicating greater water use efficiency) in Clone 2, compared to Clones 1 and 3 across all soil moisture treatments except in the wet-dry treatment, where Clone 1 and 3 were not significantly different. A strong negative correlation was found between stable carbon isotope composition and biomass accumulation. Gas exchange parameters and needle water potential were higher in the high soil moisture treatment compared to the other treatments across all clones. Morning measurements of gas exchange were higher in Clones 2 and 3 than in Clone 1 across all treatments. Stomatal density varied significantly among clones but not among treatments. These results demonstrated that closely related clones differed in their growth and physiological responses to moisture availability, suggesting that clonal variation could be used to breed for increased drought resistance or to identify drought resistant genotypes for selective deployment.

THE EFFECTS OF ANITRANSPIRANT DI-1-P-MENTHENE ON SOME PHYSIOLOGICAL TRAITS OF STRAWBERRY

Strawberry is a species sensitive to water shortages, especially during fruit growth and ripening. One method of limiting water loss in plant production involves the use of antitranspirants, which reduce plant transpiration. One method of limiting water loss in plant production involves the use of antitranspirants, which reduce plant transpiration. One of substances used for this purpose is, amongst others, natural terpene polymer di-1-p-menthene (pinolene). Research on the influence of a pinolene-containing antitranspirant (with the commercial name of Vapor Gard) on gas exchange parameters (intensity of net CO2 assimilation, intensity of transpiration, stomatal conductance for water, substomatal CO2 concentration), the water balance and the content of assimilation pigments (chlorophyll “a”, “b”, total chlorophyll, carotenoids) in the leaves of the cv. ‘Salsa’ strawberry was conducted in the years 2009–2010. The antitranspirant was used once at a concentration of 0.75% before flowering. The measurements were performed four times: before flowering (1st measurement date), when the plants were in full flowering (2nd measurement date), in the middle of the harvest season (3rd measurement date) and after the end of the harvest season (4th measurement date). Foliar application of the Vapor Gard antitranspirant decreases the intensity of strawberry transpiration without changing the CO2 assimilation activity. Plants sprayed with the tested preparation were characterised by a higher relative water content (RWC) in leaves and a higher value of the photosynthetic index of water use efficiency (WUE). The antitranspirant did not influence the content of assimilation pigments in strawberry leaves. The values of the determined physiological features depended on the measurement date (developmental stage) of the tested strawberry cultivar.

Correlated variation of floral and leaf traits along a moisture availability gradient

Variation in flower size is an important aspect of a plant's life history, yet few studies have shown how flower size varies with environmental conditions and to what extent foliar responses to the environment are correlated with flower size. The objectives of this study were to (1) develop a theoretical framework for linking flower size and leaf size to their costs and benefits, as assessed using foliar stable carbon isotope ratio (delta(13)C) under varying degrees of water limitation, and then (2) examine how variation in flower size within and among species growing along a naturally occurring moisture availability gradient correlates with variation in delta(13)C and leaf size. Five plant species were examined at three sites in Oregon. Intra- and inter-specific patterns of flower size in relation to moisture availability were the same: the ratios of the area of flower display to total leaf area and of individual flower area to leaf area were greater at sites with more soil moisture compared to those sites with less soil moisture. The increase in flower area per unit increase in leaf area was greater at sites with more soil moisture than at sites where water deficit can occur. Values of delta(13)C, an index of water-use efficiency, were greater for plants with larger floral size. The patterns we observed generalize across species, irrespective of overall plant morphology or pollination system. These correlations between flower size, moisture availability, and delta(13)C suggest that water loss from flowers can influence leaf responses to the environment, which in turn may indirectly mediate an effect on flower size.

USING CROP YIELD AND EVAPOTRANSPIRATION RELATIONS FOR REGIONAL WATER REQUIREMENT ESTIMATION1

ABSTRACT: Values of dry biomass of corn, sugarcane, sorghum, rice, taro, millet, cotton, cowpeas, soybeans, and velvet beans as related to the evapotranspiration (ET) were studied. The linear regression model was sufficiently accurate to establish the crop dry biomass and ET relations. A water‐use efficiency index (WUE), which is defined as the additional crop dry biomass per unit ET, is used in this study. The WUE were grouped into high, medium, and low categories. The WUE varied from greater than 35 kg ha‐1/mm for the high category, between 15 and 35 kg ha‐1/mm for the medium category, and less than 15 kg ha‐1/mm for the low category. Application of the established model to the Everglades Agricultural Area, Florida, showed that the regional El can be predicted from the known regional crop yields. The crop yield and ET relations could be used as a potential tool to improve water resources planning and management practices for crop production.

Microclimate-plant architectural interactions: Influence of leaf width on the mass and energy exchange of a soybean canopy

Two isolines of soybean ( Glycine max L. Merrill, cv. Clark) differing only in leaf width were studied to ascertain the effects of leaf width on the canopy microclimate and mass and energy exchanges. The study was performed during the 1981 growing season at Mead, Nebraska. Mass and energy exchanges were determined by means of micrometeorological techniques. Turbulent mixing was affected in a complex manner. Before full cover was achieved, turbulent mixing (expressed in terms of friction velocity, u ∗ ) was slightly greater over the isoline with narrower leaves (denoted CLN). After full-cover was achieved, turbulent mixing was greater over the isoline with normal leaves (CN). Analysis of data indicated that greater u ∗ values in the CN canopy were due to greater canopy density which caused greater bluff-body effects. Differences in leaf width did not affect the above-canopy radiation balance, but did affect the within-canopy profile of net radiation ( Rn). Rn was greater deep inside the CLN isoline since this isoline established a canopy with less leaf area. This difference in the vertical profile of Rn affected the canopy microclimate and the partitioning of this radiation. Higher air temperatures, lower vapor pressures, lower latent heat exchange and greater sensible and soil heat flux were observed in the CLN canopy. Greater CO 2 concentrations were also measured within the CLN canopy because warmer soil temperatures caused greater soil efflux of CO 2. Also, less leaf area of that canopy prevented a stronger drawdown in [CO 2]. Canopy CO 2 exchange was greater over the CLN isoline when expressed on a leaf area basis, whereas no differences in CO 2 exchange were observed between fluxes expressed on a ground area basis. The CO 2—water flux ratio, an index of water use efficiency, was improved in the CLN crop because of its lower evapotranspiration rates.