Differences In Water Use Efficiency Research Articles

Measures of leaf-level water-use efficiency in drought stressed endophyte infected and non-infected tall fescue grasses

Neotyphodium coenophialum [Morgan-Jones and Gams], grows in the above-ground parts of tall fescue [ Lolium arundinaceum (Schreb.) Darbysh.]. It is an asexual fungus that is transmitted through seed of its host plant. This grass/endophyte association is enhanced by the protection of the host from herbivory and improved drought stress. We investigated how a decline in leaf-level stomatal conductance impacts the instantaneous water-use efficiency (WUE), in endophyte-infected (E+) versus non-infected (E−) Kentucky-31 tall fescue grasses grown in a controlled environmental chamber over a 10-week period. Grasses were cut at 6 weeks after germination and allowed to regrow under high and low soil moisture availability. One week after cutting, soil moisture was allowed to decline in the low water treatment for 2 weeks until severe stress was demonstrated through a decline in stomatal conductance to less than 100 mmol m −2 s −1. We found no differences in WUE between E+ and E− plants when water was not limiting while higher WUE was exhibited in E+ plants relative to E− plants under severe drought stress. The E− plants showed an 18-fold reduction in mean WUE and a 70-fold reduction in photosynthesis under drought stress, while there was no change in WUE and only a fourfold decline in photosynthesis between well-watered and drought stressed E+ plants at 21 days. While there were no differences in the rates of transpiration between E+ and E− plants under severe drought stress, differences in WUE can be attributed mainly to higher photosynthetic rates of E+ than E− plants. The difference in photosynthetic rates between E+ and E− plants under drought conditions could not be explained by differences in stomatal conductance and Rubisco (EC 4.1.1.39) activities.

Photosynthetic performance along a light gradient as related to leaf characteristics of a naturally occurring Cypripedium flavum

Photosynthesis, leaf structure, nitrogen content and nitrogen allocation in photosynthetic functions of Cypripedium flavum were studied in a naturally varying light regime. Light-saturated leaf net photosynthetic rate (A max) was strongly correlated with leaf dry mass per area (LMA), mesophyll conductance (g (m)) and area-based leaf nitrogen content (N area), with all variables increasing with increasing irradiance. Such coordinate variation of all these parameters illustrates the plastic response of leaf structure to high light (HL). Leaf N area was greater under HL than in low light (LL). The fractions of leaf nitrogen partitioning in carboxylation (P (R)) and bioenergetics (P (B)) were positively related to LMA. In contrast, P (R) and P (B) decreased with increasing mass-based leaf nitrogen content (N mass). However, no correlation was found between leaf nitrogen investment in light harvesting (P (L)) and either LMA or N mass. Like maximum rate of carboxylation (V cmax) and electron transport (J max), the J max/V cmax ratio, which was strongly correlated to LMA, also increased significantly with irradiance. Under HL, leaf maximum photosynthetic nitrogen efficiency (ANUE) and intrinsic water use efficiency (WUE) were greater than in LL conditions, despite a small difference in WUE. This suggests that a functional balance in the photosynthetic machinery favors leaf photosynthetic plasticity of C. flavum in response to different light conditions. Given an ample soil nitrogen supply, C. flavum may offset its susceptibility to HL by efficient nitrogen use and higher stomatal and mesophyll conductance against photoinhibition so as to keep leaf photosynthesis positive.

Land Equivalent Ratios, Light Interception, and Water Use in Annual Intercrops in the Presence or Absence of In‐Crop Herbicides

Increased crop production (overyielding) often observed in intercrops compared to sole crops has been attributed to enhanced resource use. The objective of this study was to investigate intercropping complementarity of wheat (Triticum aestivum L.), canola (Brassica napus L.), and field pea (Pisum arvense L.) for light and water use. Sole crop and intercrop combinations were evaluated for effects on land equivalent ratios (LERs), canopy light interception, soil moisture, water use (WU), and water use efficiency (WUE), with or without in‐crop herbicides at two field sites in Manitoba, Canada. The mean LER was 1.1, but LERs varied greatly between site‐years and herbicide treatments, and were significantly greater than one in 22% of the site‐year‐treatment combinations. The wheat‐canola‐pea and canola‐pea intercrops showed the greatest frequency of overyielding for dry matter (50%) and grain yield (38%), respectively. Peak light interception tended to occur earlier with canola than with field pea, thus increasing the potential for light use complementarity between these crops. There was a positive correlation between LER and light interception in half of the site‐years with applied herbicides and a negative correlation between LER and weed biomass at most site‐years without herbicides. Although crop treatments used water differently within the soil profile, there were no differences in WU, but some differences in WUE, between crop treatments; however, WUE generally was not greater in intercrops compared to sole crops. In this study, overyielding in intercrops was inconsistent, and seemed to be related more to light interception than to water utilization.

Physiological Responses to Different Substrate Water Contents: Screening for High Water-use Efficiency in Bedding Plants

Efficient use of irrigation water is increasingly important in the production of bedding plants. Two approaches to efficient water use include reducing irrigation water wastage during production by growing plants at the optimal substrate water content (θ) and growing species with high water-use efficiency (WUE). However, there is little information on the effects of different θ levels on leaf physiology of bedding plants and variation in WUE among different species of bedding plants. The objectives of this study were to determine the effects of θ on leaf water relations, gas exchange, chlorophyll fluorescence, and WUE of bedding plants and to identify the physiological basis for differences in WUE between two bedding plant species. We grew salvia ‘Bonfire Red’ (Salvia splendens Sellow ex Roemer & J.A. Schultes), vinca ‘Cooler Peppermint’ [Catharanthus roseus (L.) G. Don.], petunia ‘Lavender White’ (Petunia × hybrida Hort ex. Vilm.), and impatiens ‘Cherry’ (Impatiens walleriana Hook F.) at four constant levels of θ (0.09, 0.15, 0.22, and 0.32 m3·m−3) using an automated irrigation controller. Regardless of species, leaf water potential (Ψw) and leaf photosynthesis (A) of all four species were lower at a θ of 0.09 m3·m−3 and were not different among the other θ levels, but stomatal conductance to H2O (g S) was lower at 0.09 than at 0.15 and 0.22 m3·m−3 and highest at 0.32 m3·m−3. WUE of bedding plants at different θ levels depended on species. The WUE of petunia was unaffected by θ, whereas for the other three species, WUE was higher at a θ of 0.09 m3·m−3 than at 0.32 m3·m−3. Differences in WUE between petunia and salvia were partly from differences in photosynthetic capacity between the two species. Based on the response of A to leaf internal CO2 concentration (Ci), mesophyll conductance to CO2 [gm (a measure of photosynthetic capacity)] was higher in petunia than salvia, whereas gas phase conductance to CO2 (gCO2 ) was similar for these two species, which resulted in higher WUE in petunia than salvia.

Testing a hypothesis of the relationship between productivity and water use efficiency in Patagonian forests with native and exotic species

The resource use efficiency, the relationship between productivity and the amount of used resources, have been proposed to increase as forests increase their productivity and rate of resource use (Binkley, D., Stape, J.L., Ryan, M.G., 2004. Thinking about efficiency of resource use in forests. For. Ecol. Manage. 1–2, 5–16). To test the generality of this hypothesis, we estimated annual productivity and water use efficiency (WUE) of an exotic Douglas-fir ( Pseudotsuga menziesii (Mirb) Franco) plantation and a multi-species native forest in N.W. Patagonia, both growing on the same site. We hypothetized that, within a site, the more productive system ( a priori the Douglas-fir plantation) has a higher WUE than the less productive system (the native forest), and that within the native forest, the more productive species have higher WUE than the less productive ones. Five taxa were the most conspicuous woody species in the native forest, which was codominated by Nothofagus antarctica and Lomatia hirsuta. Both studied systems had reached their maximum leaf area index (approximately, 5 and 11 for the native and exotic forests, respectively). Annual productivity was 2.3 times higher in the Douglas-fir plantation than in the native forest, however two native species showed similar values of biomass productivity than the exotic species. The amount of water used by the native system was lower than that used by the Douglas-fir plantation, but not as low as the observed differences in productivity, thus resulting in a higher WUE in the Douglas-fir plantation than in the native forest (1.8 times higher). In addition, WUE was also different among the native species. The lower WUE at the stand level in the case of the native forest probably is due to the presence of retamos and lauras. We concluded that: (1) the more productive system (the Douglas-fir plantation) had a higher WUE than the less productive system (the native mixed forest); (2) within the native mixed forest, the most productive species ( L. hirsuta and N. antarctica) had the highest WUE of all native species. Future research is needed to explain the physiological causes (daily patterns of transpiration and carbon fixation and allocation) of the observed differences in WUE between species and whole systems.

Responses of water use efficiency of 9 plant species to light and CO 2 and their modeling

Photosynthesis coupled with transpiration determines water use efficiency ( WUE) at leaf level, and the responses of WUE controlled by gas exchanges through stomata to environment are the basis of carbon and water cycles in the ecosystem. In this paper, by using Li-6400 Portable Photosynthesis System (LI-COR), WUE at leaf level was analyzed under controlled photosynthetic photons flux density ( PPFD) and CO 2 concentration conditions across 9 plant species including maize ( Zea mays), sorghum ( Sorghum vulgare), millet ( Setaria italica), soybean ( Glycine max), peanut ( Arachis phyogaea), sweet potato ( Ipomoea batatas), rice ( Oryza sativa), Masson pine ( Pinus massoniana) and Schima superba. We had developed a new model to estimate the water use efficiency in response to the combined effects of light and CO 2 concentration. Our measured data validated that this model could simulate the changes of water use efficiency very well under combined effect of light and CO 2 concentration. It could be used to estimate contribution of photosynthesis increase and transpiration decline on water use efficiency with the rising of CO 2 concentration. Great differences in water use efficiency occurred in these different plant species under various CO 2 concentration levels. Based on water use efficiency at regional scale, we concluded that plants should be separated into C 3 plants and C 4 plants, and furthermore, C 3 plants should be separated into herbaceous plants and woody plants. Our separation criteria would do a great favor in modeling the evapotranspiration of terrestrial ecosystem with carbon and water balance.

Leaf traits and tree rings suggest different water-use and carbon assimilation strategies by two co-occurring Quercus species in a Mediterranean mixed-forest stand in Tuscany, Italy

We compared the water-use characteristics of co-occurring mature Quercus cerris L. and Quercus pubescens Willd. trees growing in resource-limited (mainly water) hilly habitats in Tuscany, Italy. The species differed in their distribution along soil water gradients and in their access to, and use of, water, even though the study year was wetter than average, though with a summer drought. Compared with Q. cerris, Q. pubescens had greater access to soil water (less negative predawn water potentials) and a more conservative water-use strategy based on its relatively low stomatal conductance, high instantaneous water-use efficiency, less negative midday water potential and high soil-to-leaf hydraulic conductance. Quercus cerris had less conservative water-use characteristics than Q. pubescens, exhibiting relatively high stomatal conductance, low instantaneous water-use efficiency, more negative midday water potentials and low soil-to-leaf hydraulic conductance; however, Q. cerris had higher photosynthetic rates than Q. pubescens. Photosynthesis and stomatal conductance were positively correlated in both species. Although a strong correlation between ring widths and precipitation patterns was not found, some dry periods influenced ring-width growth. Quercus pubescens has always grown faster than Q. cerris, probably because of more efficient water use, although stand dynamics (driven by exogenous disturbance factors, including coppicing, browsing and competition) cannot be excluded. Ring-width variability, as well as tree-ring growth in dry years, which should be unaffected by stand dynamics, were higher in Q. pubescens than in Q. cerris. Moreover, Q. pubescens recovered completely after the drought in the seventies, even showing higher tree-ring growth than in the recent past, whereas Q. cerris showed a minor growth decline followed by a recovery to values comparable with those observed before the 1970s drought. Beginning in the early eighties, tree-ring growth decreased in both species, though Q. pubescens showed consistently higher values than Q. cerris. These differences can be explained by differences in water-use efficiency. Despite differences between the species in water use and water status, the results are consistent with the interpretation that both are drought tolerant, but that Q. pubescens is at an advantage on xeric ridges because of its greater ability to access soil water and use it more conservatively compared with Q. cerris.

Evaluation of wild Solanum species for drought resistance : 1. Solanum gandarillasii Cardenas

Since drought is a major factor limiting global potato production, identification of Solanum germplasm with drought resistance features is essential. The current study compared responses of Solanum tuberosum L. ‘Kennebec’ to those of the wild tuber bearing species, Solanum gandarillasii Cardenas, with respect to drought and heat stress. The cultivar Kennebec exhibited more leaf water loss as well as increased osmotic adjustment compared to S. gandarillasii during the imposition of progressively severe drought. In Kennebec, this stress led to severe leaf wilting and eventual canopy loss. However, S. gandarillasii was less sensitive to prolonged drought in terms of reduced loss of above ground biomass. The conservative “water saving” responses of S. gandarillasii included drought sensitive stomata resulting in low transpiration rates. Coupled with this apparent loss of an effective cooling mechanism, S. gandarillasii demonstrated superior thermal tolerance. Decreased intrinsic water use efficiency (WUE) at the leaf level was evident in Kennebec compared to S. gandarillasii when exposed to increasing levels of soil moisture stress and regardless of radiation level. This difference in WUE could be attributed to differences in transpiration rate and not to photosynthetic rate. S. gandarillasii may be appropriate for growth areas exhibiting drought conditions where reduced desiccation and thermal damage to leaf tissues are assets. Kennebec, however, was a ‘water spender’ that would be more appropriately grown under temperate growing conditions with an adequate water supply.

Relationship between water use efficiency (WUE) and production of different wheat genotypes at soil water deficit

Through 2-year field experiments, 7 wheat genotypes were better in their field yield. These 7 wheat genotypes and other 3 wheat species, which are being popularized on a large scale in different locations of China, were selected as experimental materials for the sake of measuring their difference in WUE and production and comparing their relationship at soil water deficits, future more, providing better drought resistance lines and theoretical guide for wheat production and practices and exploring anti-drought physiological mechanisms of different wheat genotypes. Under the condition of 3 soil–water–stress treatments (75% field capacity (FC), 55% FC, 45% FC, named level 1, level 2 and level 3, respectively), pot experiments for them were conducted and the related data were collected from their life circle. The main results were as followed: (1) according to the selected soil stress levels, water use efficiency (WUE) of 10 different wheat genotypes was divided into two groups (A and B); group A included genotypes 2, 3, 4, 5, 6, 7, 8, whose WUE decreased basically from level 1 to level 3 and reached individual peak of WUE at level 1; Group 2 included genotypes 1, 9, 10, whose WUE reached their individual peak at level 2; (2) based on total water consumption through all life circle, genotypes 1, 4, 8, 9 had lower water consumption (TWC) at level 1, genotypes 2, 3, 5, 6, 7 lower TWC at level 2, genotype 10 lower TWC at level 3; (3) at level 1, genotypes 2, 3, 4, 5, 6, 7, 8 had higher grain weight of single spike (GWSS), genotypes 1, 9, 10 better GWSS at level 2, which was in good line with individual WUE of different wheat genotypes; (4) by analyzing the indexes related to examining cultivars, it was found that genotypes 1, 2, 3, 4, 5, 6, 9, 10 had longer plant length (PL), spike length (SL), bigger grain number (GN) except genotypes 7 and 8 at level 1, RL was in better line with genotypes 1, 2, 3, 8, 9, 10, but not in the other genotypes at level 1.

Irrigation Requirements and Drought Response of Two Ornamental Grass Species

Water use is the most important environmental issue facing the horticulture industry. As a result, many water management districts are recommending native plants for their putative low-water requirements. Numerous textbooks and trade journals claim native plants use less water than non-natives; however, previous research found no difference in water use efficiency in the field between native and non-native species. Furthermore, recommendations of ornamental grasses for use as low-maintenance and low-water-requiring landscape plants have recently escalated. This study evaluated non-native Miscanthus sinensis `Adagio' and the native Eragrostis spectabilis for irrigation requirements and drought response in a landscape setting. To simulate maximum stress, both species were planted into field plots in an open-sided, clear polyethylene covered shelter. Each species was irrigated on alternating days at 0, 0.25, 0.5, or 0.75 L for a 90-day period. Growth index and height were recorded at biweekly intervals, and final shoot and root dry masses were taken at completion of the study. Significant treatment and species effects were found for height, growth index, shoot dry weight, and biomass. Plants receiving 0.75 L of irrigation had the greatest growth, and non-irrigated plants grew significantly less. Comparisons between species found growth was greatest among Eragrostis spectabilis plants for all parameters.

Comparison of ecosystem water‐use efficiency among Douglas‐fir forest, aspen forest and grassland using eddy covariance and carbon isotope techniques

AbstractComparisons were made among Douglas‐fir forest, aspen (broad leaf deciduous) forest and wheatgrass (C3) grassland for ecosystem‐level water‐use efficiency (WUE). WUE was defined as the ratio of photosynthetic CO2 assimilation rate and evapotranspiration (ET) rate. The ET data measured by eddy covariance were screened so that they overwhelmingly represented transpiration. The three sites used in this comparison spanned a range of vegetation (plant functional) types and environmental conditions within western Canada. When compared in the relative order Douglas‐fir (located on Vancouver Island, BC), aspen (northern Saskatchewan), grassland (southern Alberta), the sites demonstrated a progressive decline in precipitation and a general increase in maximum air temperature and atmospheric saturation deficit (Dmax) during the mid‐summer. The average (±SD) WUE at the grassland site was 2.6±0.7 mmol mol−1, which was much lower than the average values observed for the two other sites (aspen: 5.4±2.3, Douglas‐fir: 8.1±2.4). The differences in WUE among sites were primarily because of variation in ET. The highest maximum ET rates were approximately 5, 3.2 and 2.7 mm day−1 for the grassland, aspen and Douglas‐fir sites, respectively. There was a strong negative correlation between WUE and Dmax for all sites. We also made seasonal measurements of the carbon isotope ratio of ecosystem respired CO2 (δR) in order to test for the expected correlation between shifts in environmental conditions and changes to the ecosystem‐integrated ratio of leaf intercellular to ambient CO2 concentration (ci/ca). There was a consistent increase in δR values in the grassland, aspen forest and Douglas‐fir forest associated with a seasonal reduction in soil moisture. Comparisons were made between WUE measured using eddy covariance with that calculated based on D and δR measurements. There was excellent agreement between WUE values calculated using the two techniques. Our δR measurements indicated that ci/ca values were quite similar among the Douglas‐fir, aspen and grassland sites, despite large variation in environmental conditions among sites. This implied that the shorter‐lived grass species had relatively high ci/ca values for the D of their habitat. By contrast, the longer‐lived Douglas‐fir trees were more conservative in water‐use with lower ci/ca values relative to their habitat D. This illustrates the interaction between biological and environmental characteristics influencing ecosystem‐level WUE. The strong correlation we observed between the two independent measurements of WUE, indicates that the stable isotope composition of respired CO2 is a useful ecosystem‐scale tool to help study constraints to photosynthesis and acclimation of ecosystems to environmental stress.

Herbage production, persistence, nutritive characteristics and water use of perennial forages grown over 6 years on a Wakanui silt loam

Herbage production, persistence, nutritive characteristics and utilisation of chicory, lucerne, and red clover swards grown under irrigated and dryland conditions were compared over a 6‐year period on a Wakanui silt loam soil in Canterbury, New Zealand. Under irrigated conditions, annual yields of lucerne (16–28 t DM/ha) were 30% greater than chicory or red clover. Lucerne yielded 17.5–21 t DM/ha under dryland conditions, which was also 30–50% greater than chicory or red clover. The yield advantage of irrigated lucerne came from greater cool season growth, with 15 kg DM/ha per day higher growth rates in September and 10–30 kg DM/ha per day higher growth rates from March to May. The yield advantage of dryland lucerne was due to higher growth rates during September (non‐limiting soil moisture) and during periods of high soil water deficit in summer. Lucerne also had superior persistence, being 94% (dryland) and 55% (irrigated) of the botanical composition of swards in the sixth year, compared with 61% (dryland) and 55% (irrigated) for chicory and 0% for red clover. All three forages had similar metabolisable energy (ME) content in utilised herbage (10.9–11.6 MJ/kg), but red clover and lucerne had higher crude protein (CP) content (25–29%) than chicory (18%). The combination of herbage nutritive characteristics with production and utilisation data showed that grazing stock consumed 30% more CP and ME annually from Lucerne than either chicory or red clover swards. Water use (WU) was measured to investigate the production differences in dryland swards. Chicory and red clover extracted water to a maximum depth of 1.9 m whereas lucerne extracted at least 50 mm per annum of water between 1.9 and 2.3 m depth (maximum depth measured), and evidence is presented to show it also extracted water below this. Comparisons of WU showed no differences in water use efficiency but revealed greater dryland production from lucerne due solely to greater soil water extraction.

Water Use Efficiency, Carbon Isotope Discrimination and Biomass Production of Two Sugar Beet Varieties Under Well‐Watered and Dry Conditions

AbstractTwo sugar beet (Beta vulgaris sp.) varieties, which were supposed to differ in drought tolerance, were exposed to drought stress in a growth chamber and a container experiment in field. The aim was to test for (i) differences between the varieties in water use efficiency (WUE), biomass production and distribution and (ii) the relationship between WUE and carbon isotope discrimination (Δ), and between biomass production and Δ. Significant differences in WUE were detected between plants of well‐watered and drought treatments in both experiments, but not between the varieties. Production losses due to drought were large for both varieties in both experiments. Losses in the growth chamber were up to 50 % of plant dry weight and the corresponding value in the field was 24 %, when plants were given 60 and 30 %, respectively, of the full‐watered treatments. Significant negative correlations between WUE and Δ were found, but not between biomass production and Δ, when both varieties were included. Negative correlations between WUE and Δ were also found for each variety separately. The results suggest that Δ estimates from leaf tissue of sugar beet may provide a useful tool for genetic selection of drought‐tolerant sugar beet varieties.

Photosynthesis, root respiration, and grain yield of spring wheat in response to surface soil drying

The aims of this research were to test the influence of surface soil drying on photosynthesis, root respiration and grain yield of spring wheat (Triticum aestivum), and to evaluate the relationship between root respiration and grain yield. Wheat plants were grown in PVC tubes 120 cm in length and 10 cm in diameter. Three water regimes were employed: (a) all soil layers were irrigated close to field water capacity (CK); (b) upper soil layers (0–40 cm from top) drying (UD); (c) lower soil layer (80–120 cm from top) wet (LW). The results showed that although upper drying treatment maintained the highest root biomass, root respiration and photosynthesis rates at anthesis, the root respiration of the former was significantly (P < 0.05) lower than the latter at the jointing stage. There were no differences in water use efficiency or harvest index between plants from the upper drying and well-watered treatment. However, the grain weight for plants in the upper drying treatment was significantly (P< 0.05) higher than that of in well-watered control. The results suggest that reduced root respiration rate and the amount of photosynthates utilized by root respiration in early season growth may also have contributed to improve crop production under soil drying. Reduced root activity and root respiration rate, in the early growth stage, not only increased the photosynthate use efficiency (root respiration rate: photosynthesis ratio), but also grain yield. Rooting into a deeper wet soil profile before grain filling was crucial for spring wheat to achieve a successful seedling establishment and high grain yield.

Water?yield relationships and optimal water management for winter wheat in the Loess Plateau of China

High evaporative demand and limited precipitation restrict the yield of winter wheat (Triticum aestivum L.) grown in the Loess Plateau of China under semiarid climatic conditions. Grain yield can be improved by effective water management practices. A 13-year field experiment was conducted at the CERN Changwu Agro-ecological Experimental Station of the Loess Plateau to determine optimal irrigation strategies under limited water supply and to develop relationships among grain yield (Y), seasonal evapotranspiration (SET) and water-use efficiency (WUE). The experiment consisted of five irrigation treatments and three blocks. Measurements included grain yield, soil water content at various depth intervals in the 0–3,000 mm layer, irrigation amount, and precipitation. Results showed that winter wheat grown in this area experienced serious water stress during critical growth stages for the no-irrigation treatment. The amount and timing of irrigation had an important effect on grain yield, but significant differences in yield were not observed between the three-irrigation and the four-irrigation treatments. Grain yield was linearly related (R2=0.66) to SET, but differences in WUE were not significant for any of the treatments. The relationship between WUE and Y was best represented by a second order polynomial (R2=0.65) consisting of a nearly linear portion between 1.5 and 5.0 Mg ha−1. Optimum water management of winter wheat in the Loess Plateau should consist of three 87.5 mm irrigations applied at stem elongation, booting, and anthesis.

Photosynthetic pathway alters xylem structure and hydraulic function in herbaceous plants

ABSTRACTPlants using the C4 photosynthetic pathway have greater water use efficiency (WUE) than C3 plants of similar ecological function. Consequently, for equivalent rates of photosynthesis in identical climates, C4 plants do not need to acquire and transport as much water as C3 species. Because the structure of xylem tissue reflects hydraulic demand by the leaf canopy, a reduction in water transport requirements due to C4 photosynthesis should affect the evolution of xylem characteristics in C4 plants. In a comparison of stem hydraulic conductivity and vascular anatomy between eight C3 and eight C4 herbaceous species, C4 plants had lower hydraulic conductivity per unit leaf area (KL) than C3 species of similar life form. When averages from all the species were pooled together, the mean KL for the C4 species was 1.60 × 10−4 kg m−1 s−1 MPa−1, which was only one‐third of the mean KL of 4.65 × 10−4 kg m−1 s−1 MPa−1 determined for the C3 species. The differences in KL between C3 and C4 species corresponded to the two‐ to three‐fold differences in WUE observed between C3 and C4 plants. In the C4 species from arid regions, the difference in KL was associated with a lower hydraulic conductivity per xylem area, smaller and shorter vessels, and less vulnerable xylem to cavitation, indicating the C4 species had evolved safer xylem than the C3 species. In the plants from resource‐rich areas, such as the C4 weed Amaranthus retroflexus, hydraulic conductivity per xylem area and xylem anatomy were similar to that of the C3 species, but the C4 plants had greater leaf area per xylem area. The results indicate the WUE advantage of C4 photosynthesis allows for greater flexibility in hydraulic design and potential fitness. In resource‐rich environments in which competition is high, an existing hydraulic design can support greater leaf area, allowing for higher carbon gain, growth and competitive potential. In arid regions, C4 plants evolved safer xylem, which can increase survival and performance during drought events.

Canopy scale measurements of CO2 and water vapor exchange along a precipitation gradient in southern Africa

AbstractShort‐term measurements of carbon dioxide, water, and energy fluxes were collected at four locations along a mean annual precipitation gradient in southern Africa during the wet (growing) season with the purpose of determining how the observed vegetation–atmosphere exchange properties are functionally related to the long‐term climatic conditions. This research was conducted along the Kalahari Transect (KT), one in the global set of International Geosphere‐Biosphere Program transects, which covers a north–south aridity gradient, all on a homogenous sand formation. Eddy covariance instruments were deployed on a permanent tower in Mongu, Zambia (879 mm of rainfall per year), as well as on a portable tower in Maun (460 mm yr−1), Okwa River Crossing (407 mm yr−1), and Tshane (365 mm yr−1), Botswana for several days at each site. The relationships between CO2 flux, Fc, and photosynthetically active radiation were described well by a hyperbolic fit to the data at all locations except for Mongu, the wettest site. Here, there appeared to be an air temperature effect on Fc. While daytime values of Fc routinely approached or exceeded −20 μmol m−2 s−1 at Mongu, the magnitude of Fc remained less than −10 μmol m−2 s−1 when the air temperature was above 27°C. Canopy resistances to water vapor transfer, rc, displayed an overall decline from the wetter sites to the more arid sites, but the differences in rc could be almost exclusively accounted for by the decrease in leaf area index (LAI) from north to south along the KT. Ecosystem water use efficiency (WUE), defined as the ratio of net carbon flux to evapotranspiration, showed a general decrease with increasing vapor pressure deficit, D, for all of the sites. The magnitudes of WUE at a given D, however, were dissimilar for the individual sites and were found to be stratified according to the position of the sites along the long‐term aridity gradient. For example, Mongu, which has the wettest climate, has a much lower WUE for like levels of D than Tshane, which historically has the most arid climate. Given the similar inferred stomatal resistances between the sites, the disparate carbon uptake behavior for the grass vs. woody vegetation is the likely cause for the observed differences in WUE along the aridity gradient. The short‐term flux measurements provide a framework for evaluating the vegetation's functional adaptation to the long‐term climate and provide information that may be useful for predicting the dynamic response of the vegetation to future climate change.

Salinity effect on crop development and yield, analysis of salt tolerance according to several classification methods

The publication is a synthesis of previous publications on the results of a long-term lysimeter experiment. From 1989 to 1998, the experimental variables were soil salinity and soil type, from 1999 onwards, soil salinity and crop variety. The plant was studied during the whole growing period by measuring the saline stress and analyzing its effect on leaf area and dry matter development and on crop yield. Salinity affected the pre-dawn leaf water potential, stomatal conductance, evapotranspiration, leaf area and yield. The following criteria were used for crop salt tolerance classification: soil salinity, evapotranspiration deficit, water stress day index. The classification according to soil salinity distinguished the salt tolerant group of sugar beet and wheat, the moderately salt sensitive group comprising broadbean, maize, potato, soybean, sunflower and tomato, and the salt sensitive group of chickpea and lentil. The results for the salt tolerant and the moderately salt sensitive groups correspond with the classification of Maas and Hoffman, excepted for soybean. The evapotranspiration deficit criterion was used, because for certain crops the relation between yield and evapotranspiration remains the same in case of drought and salinity. This criterion, however, did not appear useful for salt tolerance classification. The water stress day index, based on the pre-dawn leaf water potential, distinguished a tolerant group, comprising sugar beet, wheat, maize, sunflower and potato, and a sensitive group, comprising tomato, soybean, broadbean, chickpea and lentil. The classification corresponds with a difference in water use efficiency. The tolerant crops show a more or less constant water use efficiency. The sensitive crops show a decrease of the water use efficiency with increasing salinity, as their yield decreases stronger than the evapotranspiration. No correlation could be found between osmotic adjustment, leaf area and yield reduction. As the flowering period is a sensitive period for grain and fruit formation and the sensitive crops are all of indeterminate flowering, their longer flowering period could be a cause of their greater sensitivity. The tolerant group according to water stress day index can be divided according to soil salinity in a salt tolerant group of sugar beet and wheat and a moderately sensitive group, comprising maize, sunflower and potato. The difference in classification can be attributed to the difference in evaporative demand during the growing period. The sensitive group according to water stress day index can be divided according to soil salinity in a moderately sensitive group, comprising tomato, soybean and broadbean, and a salt sensitive group of chickpea and lentil. The difference in classification can be attributed to the greater salt sensitivity of the symbiosis between rhizobia and grain legume in the case of chickpea and lentil.

The effect of internal Co2 conductance on leaf carbon isotope ratio

We estimated internal CO2 conductance (gi ) for C3 plant species of different life forms (annual herbs, deciduous trees and evergreen trees) grown in a variety of environments to examine the effect of g i on their leaf carbon isotope ratio (i13C). The purpose of this study was to test the validity of using i13C as an index of photosynthetic water use efficiency (WUE). When comparing deciduous tree species grown in contrasting light environments, there was a strong positive relationship between i13C and WUE. Similarly, i13C was positively correlated to WUE when comparing the different species of evergreen trees. However, the difference in WUE between evergreen and deciduous tree species did not relate to that in leaf i13C. In addition, WUE was similar between highland and lowland herbaceous plants, although the former had a much higher i13C. The positive relationship between i13C and WUE did not hold across different life forms and different altitudes when differences in gi did not relate to those in stomatal conductance, resulting in independence of chloroplast CO2 partial pressure from intercellular CO2 partial pressure.

Sexual dimorphism in reproductive allocation and water use efficiency in Maireana pyramidata (Chenopodiaceae), a dioecious, semi-arid shrub

Sexual dimorphism in dioecious plant species is widely attributed to the differential impacts of reproduction on male v. female plants. We investigated sexual dimorphism in reproductive, morphological and physiological traits of Maireana pyramidata (Benth.) Paul G.Wilson (Chenopodiaceae), a dioecious, semi-arid shrub endemic to Australia. We estimated reproductive allocation for each sex by calculating the relative biomass allocated to flowers and fruits per gram of leaf tissue, based on one branch per sample plant. Morphological measurements included leaf mass, stem mass, specific leaf area, plant height and plant leaf area index. We also measured leaf nitrogen and chlorophyll, gas exchange and Δ13C. Reproductive allocation was nine times greater in females than in males. No significant difference between the sexes in photosynthetic rate or transpiration could be detected but instantaneous water use efficiency (photosynthesis/transpiration) was significantly lower in females than in males during the fruiting period. Δ13C did not differ between the sexes. The results indicate that greater reproductive allocation in females has an immediate impact on their capacity for conservative water use but does not lead to long-term differences in water use efficiency.