Photosynthetic Water Use Efficiency Research Articles

Carbon budget at the individual-tree scale: dominant Eucalyptus trees partition less carbon belowground.

Large trees in plantations generally produce more wood per unit of resource use than small trees. Two processes may account for this pattern: greater photosynthetic resource use efficiency or greater partitioning of carbon to wood production. We estimated gross primary production (GPP) at the individual scale by combining transpiration with photosynthetic water-use efficiency of Eucalyptus trees. Aboveground production fluxes were estimated using allometric equations and modeled respiration; total belowground carbon fluxes (TBCF) were estimated by subtracting aboveground fluxes from GPP. Partitioning was estimated by dividing component fluxes by GPP. Dominant trees produced almost three times as much wood as suppressed trees. They used 25 ± 10% (mean ± SD) of their photosynthates for wood production, whereas suppressed trees only used 12 ± 2%. By contrast, dominant trees used 27 ± 19% of their photosynthate belowground, whereas suppressed trees used 58 ± 5%. Intermediate trees lay between these extremes. Photosynthetic water-use efficiency of dominant trees was c. 13% greater than the efficiency of suppressed trees. Suppressed trees used more than twice as much of their photosynthate belowground and less than half as much aboveground compared with dominant trees. Differences in carbon partitioning were much greater than differences in GPP or photosynthetic water-use efficiency.

Jasmonates Improve Drought Tolerance of Hordeum vulgare L. After Biochar Treatment

AbstractTo investigate how and in what amounts biochar and methyl jasmonate can improve drought tolerance of barley. A two-year experimental study was conducted in a factorial randomized complete block design (n = 5) in the research greenhouse of Zanjan University, Iran, to investigate the possible effects of biochar and methyl jasmonate on some traits of winter barley under drought conditions. Two irrigation regimes, D0 (full irrigation in soil field capacity as control) and D1 (withholding irrigation immediately after flowering stage), three methyl jasmonate spray densities [0 (M0), 50 (M50), and 100 (M100) μM] and four levels of biochar in soil [0% (B0), 0.25% (B0.25), 0.5% (B0.5), 1% (B1) per soil weight] were used in this experiment. In this study, drought reduced two-year average leaf area (LA) by 96%, stomatal conductance (gs) by 84%, and photosynthetic water use efficiency (PWUE) by 64%. In addition, drought reduced chlorophyll-b by 1.5% and 81% and transpiration rate (Tr) by 2.5% and 78% in the first and second years, respectively. However, the application of biochar and methyl jasmonate improved all the traits studied in both D0 and D1 drought-treated plants. For most of the parameters studied, the optimal combination of biochar and methyl jasmonate that optimized water use efficiency and alleviated drought was 0.25% and 50 μM, respectively. The synergistic action of biochar and jasmonates improved the tolerance of barley to water stress.

Pollinator and habitat-mediated selection as potential contributors to ecological speciation in two closely related species.

In ecological speciation, incipient species diverge due to natural selection that is ecologically based. In flowering plants, different pollinators could mediate that selection (pollinator-mediated divergent selection) or other features of the environment that differ between habitats of 2 species could do so (environment-mediated divergent selection). Although these mechanisms are well understood, they have received little rigorous testing, as few studies of divergent selection across sites of closely related species include both floral traits that influence pollination and vegetative traits that influence survival. This study employed common gardens in sites of the 2 parental species and a hybrid site, each containing advanced generation hybrids along with the parental species, to test these forms of ecological speciation in plants of the genus Ipomopsis. A total of 3 vegetative traits (specific leaf area, leaf trichomes, and photosynthetic water-use efficiency) and 5 floral traits (corolla length and width, anther insertion, petal color, and nectar production) were analyzed for impacts on fitness components (survival to flowering and seeds per flower, respectively). These traits exhibited strong clines across the elevational gradient in the hybrid zone, with narrower clines in theory reflecting stronger selection or higher genetic variance. Plants with long corollas and inserted anthers had higher seeds per flower at the Ipomopsis tenuituba site, whereas selection favored the reverse condition at the Ipomopsis aggregata site, a signature of divergent selection. In contrast, no divergent selection due to variation in survival was detected on any vegetative trait. Selection within the hybrid zone most closely resembled selection within the I. aggregata site. Across traits, the strength of divergent selection was not significantly correlated with width of the cline, which was better predicted by evolvability (standardized genetic variance). These results support the role of pollinator-mediated divergent selection in ecological speciation and illustrate the importance of genetic variance in determining divergence across hybrid zones.

Morpho-physiological mechanisms of two different quinoa ecotypes to resist salt stress

BackgroundQuinoa (Chenopodium quinoa Willd.) is a facultative halophyte showing various mechanisms of salt resistance among different ecotype cultivars. This study aimed to determine salt resistance limits for a Peruvian sea level ecotype “Hualhuas” and a Bolivian salar ecotype “Real” and elucidate individual mechanisms conferring differences in salt resistance between these cultivars. The plants were grown in sandy soil and irrigated with various saline solutions concentrations (0, 100, 200, 300, 400, and 500 mM NaCl) under controlled conditions.ResultsHigh salinity treatment (500 mM NaCl) reduced the plant growth by 80% and 87% in Hualhuas and Real cultivars, respectively. EC50 (water salinity which reduces the maximum yield by 50%) was at a salinity of 300 mM NaCl for Hualhuas and between 100 and 200 mM NaCl for Real plants. Both cultivars were able to lower the osmotic potential of all organs due to substantial Na+ accumulation. However, Hualhuas plants exhibited distinctly lower Na+ contents and consequently a higher K+/Na+ ratio compared to Real plants, suggesting a more efficient control mechanism for Na+ loading and better K+ retention in Hualhuas plants. Net CO2 assimilation rates (Anet) were reduced, being only 22.4% and 36.2% of the control values in Hualhuas and Real, respectively, at the highest salt concentration. At this salinity level, Hualhuas plants showed lower stomatal conductance (gs) and transpiration rates (E), but higher photosynthetic water use efficiency (PWUE), indicative of an efficient control mechanism over the whole gas-exchange machinery.ConclusionThese results reveal that Hualhuas is a promising candidate in terms of salt resistance and biomass production compared to Real.

Altered cell wall hydroxycinnamate composition impacts leaf- and canopy-level CO2 uptake and water use in rice.

Cell wall properties play a major role in determining photosynthetic carbon uptake and water use through their impact on mesophyll conductance (CO2 diffusion from substomatal cavities into photosynthetic mesophyll cells) and leaf hydraulic conductance (water movement from xylem, through leaf tissue, to stomata). Consequently, modification of cell wall (CW) properties might help improve photosynthesis and crop water use efficiency (WUE). We tested this using 2 independent transgenic rice (Oryza sativa) lines overexpressing the rice OsAT10 gene (encoding a "BAHD" CoA acyltransferase), which alters CW hydroxycinnamic acid content (more para-coumaric acid and less ferulic acid). Plants were grown under high and low water levels, and traits related to leaf anatomy, CW composition, gas exchange, hydraulics, plant biomass, and canopy-level water use were measured. Alteration of hydroxycinnamic acid content led to statistically significant decreases in mesophyll CW thickness (-14%) and increased mesophyll conductance (+120%) and photosynthesis (+22%). However, concomitant increases in stomatal conductance negated the increased photosynthesis, resulting in no change in intrinsic WUE (ratio of photosynthesis to stomatal conductance). Leaf hydraulic conductance was also unchanged; however, transgenic plants showed small but statistically significant increases in aboveground biomass (AGB) (+12.5%) and canopy-level WUE (+8.8%; ratio of AGB to water used) and performed better under low water levels than wild-type plants. Our results demonstrate that changes in CW composition, specifically hydroxycinnamic acid content, can increase mesophyll conductance and photosynthesis in C3 cereal crops such as rice. However, attempts to improve photosynthetic WUE will need to enhance mesophyll conductance and photosynthesis while maintaining or decreasing stomatal conductance.

Effect of Water Regime, Nitrogen Level, and Biostimulant Application on the Water and Nitrogen Use Efficiency of Wild Rocket [Diplotaxis tenuifolia (L.) DC

The use of biostimulants in agriculture is an emerging technique that can contribute to improved production and resource use efficiency. This research was carried out in southern Italy to evaluate the biostimulating effects of seaweed extract (SW) and azoxystrobin (AZ) on wild rocket subjected to two water regimes (WRs) and three nitrogen levels (NLs), and grown in pots under unheated greenhouse conditions. The following treatments were compared: (i) two WRs: restoration of 100% (WR100) and 50% (WR50) of crop evapotranspiration; (ii) three NLs: 0 (N0), 75 (N75), or 150 (N150) kg ha−1 of N; and (iii) three biostimulants (BSs): an untreated control (C), and the application of AZ or SW. This paper reports the effects on N uptake (Nup), N use efficiency (NUE), and water use efficiency (WUE). The following indicators of NUE were assessed: apparent recovery efficiency (RE), internal utilization efficiency (IE), partial productivity factor (PFPn) of N supplied, agronomic efficiency (AE), and physiological efficiency (PE). The following indicators of WUE were assessed: photosynthetic WUE (p_WUE), yield WUE (Y_WUE), biomass WUE (B_WUE), and irrigation yield WUE (IY_WUE). The indicators of NUE were affected differently by treatments. RE was 20% higher with SW. IE was higher with AZ. PFPn increased by 10.4 and 8.1% with AZ and SW, respectively. AE increased by 10.9 and 19.9% after applying AZ and SW, respectively. PE rose by 6.7 and 9.3% after applying AZ and SW. AZ and SW improved p_WUE, mainly under water deficit (interaction of WR × BS). With AZ application, Y_WUE, B_WUE, and IY_WUE were higher by 17.8, 13.8, and 19.3%, respectively, while the application of SW resulted in a smaller increase (9.5–7.7 and 9.9%). SW and AZ were shown to be effective through the moderate improvement of wild rocket’s nitrogen and water use efficiency. The two biostimulants were more effective at improving p_WUE in water deficit conditions, proving to be particularly useful for farmers operating with water scarcity. Therefore, they can provide valuable support to farmers by improving the sustainability of resource use.

Evolution of stomatal closure to optimize water-use efficiency in response to dehydration in ferns and seed plants.

Plants control water-use efficiency (WUE) by regulating water loss and CO2 diffusion through stomata. Variation in stomatal control has been reported among lineages of vascular plants, thus giving rise to the possibility that different lineages may show distinct WUE dynamics in response to water stress. Here, we compared the response of gas exchange to decreasing leaf water potential among four ferns and nine seed plant species exposed to a gradually intensifying water deficit. The data collected were combined with those from 339 phylogenetically diverse species obtained from previous studies. In well-watered angiosperms, the maximum stomatal conductance was high and greater than that required for maximum WUE, but drought stress caused a rapid reduction in stomatal conductance and an increase in WUE in response to elevated concentrations of abscisic acid. However, in ferns, stomata did not open beyond the optimum point corresponding to maximum WUE and actually exhibited a steady WUE in response to dehydration. Thus, seed plants showed improved photosynthetic WUE under water stress. The ability of seed plants to increase WUE could provide them with an advantage over ferns under drought conditions, thereby presumably increasing their fitness under selection pressure by drought.

Effects of water-nitrogen coupling on photosynthetic characteristics, yield, water and nitrogen use efficiency for mountain apple trees under surge-root irrigation in Northern Shaanxi area of China.

Taking 7-year-old apple trees (Hanfu) as the test material, an experiment with three irrigation levels including high water (W1, 85%-100%θf, θf was the field water holding capacity), medium water (W2, 70%-85%θf) and low water (W3, 55%-70%θf), and three nitrogen application levels, high (N1, 600 kg·hm-2), medium (N2, 400 kg·hm-2) and low (N3, 200 kg·hm-2), was conducted to investigate the effects of water and nitrogen coupling on photosynthetic characteristics, yield and water and nitrogen utilization of apple trees in mountainous areas under surge-root irrigation (SRI). The results showed that the net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (gs), intercellular CO2 concentration (Ci), leaf instantaneous water use efficiency (WUEi) of apple trees leaves decreased with decreasing nitrogen application rates under the same irrigation amount, but Ci increased. Under the same nitrogen application rate, foliar Pn, Tr, gs and WUEi decreased with decreasing irrigation amount, but Ci increased. The daily average values of Pn and Tr under W1N1 treatment were the largest, while W2N2 treatment had the largest WUEi. Apple yield, irrigation water use efficiency (IWUE) and nitrogen partial productivity (NPFP) were significantly affected by irrigation and nitrogen application. The W2N2 treatment had the highest yield (26761 kg·hm-2). IWUE increased significantly with the decreasing irrigation and the increasing nitrogen application, while NPFP increased significantly with the increases of irrigation and the decreases of nitrogen application. Results of the regression analysis showed that the combination of irrigation and nitrogen application was closest to W2N2 treatment when yield and IWUE got the optimal solution. Therefore, W2N2 treatment was the best combination mode of water and nitrogen application for apple under SRI in Northern Shaanxi mountain area.

Whole-tree mesophyll conductance reconciles isotopic and gas-exchange estimates of water-use efficiency.

Photosynthetic water-use efficiency (WUE) describes the link between terrestrial carbon (C) and water cycles. Estimates of intrinsic WUE (iWUE) from gas exchange and C isotopic composition (δ13 C) differ due to an internal conductance in the leaf mesophyll (gm ) that is variable and seldom computed. We present the first direct estimates of whole-tree gm , together with iWUE from whole-tree gas exchange and δ13 C of the phloem (δ13 Cph ). We measured gas exchange, online 13 C-discrimination, and δ13 Cph monthly throughout spring, summer, and autumn in Eucalyptus tereticornis grown in large whole-tree chambers. Six trees were grown at ambient temperatures and six at a 3°C warmer air temperature; a late-summer drought was also imposed. Drought reduced whole-tree gm . Warming had few direct effects, but amplified drought-induced reductions in whole-tree gm . Whole-tree gm was similar to leaf gm for these same trees. iWUE estimates from δ13 Cph agreed with iWUE from gas exchange, but only after incorporating gm . δ13 Cph was also correlated with whole-tree 13 C-discrimination, but offset by -2.5±0.7‰, presumably due to post-photosynthetic fractionations. We conclude that δ13 Cph is a good proxy for whole-tree iWUE, with the caveats that post-photosynthetic fractionations and intrinsic variability of gm should be incorporated to provide reliable estimates of this trait in response to abiotic stress.

Partial Root-Zone Drying and Deficit Irrigation Effect on Growth, Yield, Water Use and Quality of Greenhouse Grown Grafted Tomato

The tomato is an important horticultural crop, the cultivation of which is often under influence of abiotic and biotic stressors. Grafting is a technique used to alleviate these problems. Shortage of water has stimulated the introduction of new irrigation methods: deficit irrigation (DI) and partial root-zone drying (PRD). This study was conducted in two spring–summer season experiments to evaluate the effects of three irrigation regimes: full irrigation (FI), PRD and DI on vegetative growth, leaf gas-exchange parameters, yield, water-use efficiency (WUE), nutrients profile and fruit quality of grafted tomatoes. In both years, the commercial rootstocks Emperador and Maxifort were used. In the first year, the scion cultivar Clarabella was grown on one stem and in the second year the cultivar Attiya was grown on two stems. Self-grafted cultivars were grown as a control. In both experiments, higher vegetative traits (leaf area and number, height, shoot biomass) were recorded in tthe plants grafted on commercial rootstocks. The stomatal conductance and transpiration rate were higher under FI. Under DI, transpiration was lowest and photosynthetic WUE was highest. Photosynthetic rate changed between irrigation treatments depending on plant type. In both years, the total yield was highest in grafted plants as result of more and bigger fruits per plant. In the 2nd year, grafted plants under FI had higher yield compared to PRD, but not to DI, while self-grafted plants did not differ between irrigation treatments. WUE was highest in DI and PRD treatments and in grafted plants. Leaf N, P, K and Ca was highest in tthe plants grafted on Emperador and Maxifort, while more Mg was measured in self-grafted plants. More Ca and Mg were recorded in tthe plants under DI and PRD. Fruit mineral concentrations were higher in tthe plants grafted on commercial rootstocks. Total soluble solids differed between irrigation regarding plant types, while fruit total acidity was higher in Emperador and Maxifort. In conclusion, our study showed that grafted plants could be grown under DI with minor yield reduction with 30–40% less water used for irrigation. Moderate DI could be used before PRD for cultivation of grafted tomato and double stemmed plants did not show negative effect on tomato yield so it can be used as standard under reduced irrigation.

In Winter Wheat (Triticum Aestivum L.), No-Till Improves Photosynthetic Nitrogen and Water-Use Efficiency

To evaluate the combined effect of different agricultural practices on photosynthetic nitrogen and water-use efficiency, winter wheat was grown in the field under tillage and no-till conditions, with and without cover crops under low and high nitrogen fertilization inputs. Leaf physiological traits, such as the rate of photosynthesis, stomatal conductance, the rate of transpiration, the chlorophyll content index, the leaf area ratio, and specific leaf area were used as indicators representative of nitrogen and water-use efficiency. Six years after conversion to no-till, in the presence and in the absence of cover crops, significant increases in photosynthetic water-use efficiency and soil water content were observed both under low and high nitrogen fertilization input. Moreover, we observed that photosynthetic nitrogen-use efficiency, the rate of photosynthesis and specific leaf area were higher in the absence of tilling than in the presence of tilling. Thus, agronomic practices based on continuous no-till appear to be promising for increasing both photosynthetic nitrogen- and water-use efficiency in winter wheat.

Irrigation increases forage production of newly established lucerne but enhances net ecosystem carbon losses

In New Zealand, dairy farming faces increasing scrutiny for its environmental impacts, including those on soil carbon (C) stocks; hence, alternative management practices are required. One such practice is usage of deep-rooting forage, such as lucerne (Medicago sativa L.). We measured the C and water exchange of two neighbouring lucerne fields on stony, well-drained soil for 3 years, following conversion from grassland. One field received irrigation and effluent; the other received neither. Net CO2 exchange and evaporation were measured by eddy covariance, drainage and leaching with lysimeters, and water inputs with rain gauges. Biomass removal from harvesting and grazing was recorded by direct sampling. In the conversion year, irrigated lucerne was C-neutral despite two harvests and losses from the conversion process. In the 2nd and 3rd years combined, the biomass-C removal exceeded net CO2 uptake, causing net losses of 450 g C m−2 and 210 g C m−2 for irrigated and non-irrigated lucerne, respectively. Leaching losses accounted for 1 to 9 % of annual net C uptake from the atmosphere. The ratio of ecosystem respiration to gross photosynthetic productivity (GPP) increased from <0.7 in spring to ≈ 1 in autumn. Consequently, the net C balance for both lucerne crops showed gains in the first two growth periods of each year and losses in the subsequent two to four growth periods. Irrigation made no difference to the photosynthetic water-use efficiency at field scale (GPP/evaporation), but enhanced production water-use efficiency (biomass/water input). Irrigation increased both the absolute amount of drainage and the fraction of water inputs lost by drainage. In one year, significant summer drainage occurred for the irrigated lucerne. To prevent that, soil-water content should be kept well below field capacity but above the crop's water-stress level. Such practice would likely also help retain soil carbon.

Diurnal variation in mesophyll conductance and its influence on modelled water-use efficiency in a mature boreal Pinus sylvestris stand

Mesophyll conductance (gm) is a critical variable for the use of stable carbon isotopes to infer photosynthetic water-use efficiency (WUE). Although gm is similar in magnitude to stomatal conductance (gs), it has been measured less often, especially under field conditions and at high temporal resolution. We mounted an isotopic CO2 analyser on a field photosynthetic gas exchange system to make continuous online measurements of gas exchange and photosynthetic 13C discrimination (Δ13C) on mature Pinus sylvestris trees. This allowed the calculation of gm, gs, net photosynthesis (Anet), and WUE. These measurements highlighted the asynchronous diurnal behaviour of gm and gs. While gs declined from around 10:00, Anet declined first after 12:00, and gm remained near its maximum until 16:00. We suggest that high gm played a role in supporting an extended Anet peak despite stomatal closure. Comparing three models to estimate WUE from ∆13C, we found that a simple model, assuming constant net fractionation during carboxylation (27‰), predicted WUE well, but only for about 75% of the day. A more comprehensive model, accounting explicitly for gm and the effects of daytime respiration and photorespiration, gave reliable estimates of WUE, even in the early morning hours when WUE was more variable. Considering constant, finite gm or gm/gs yielded similar WUE estimates on the diurnal scale, while assuming infinite gm led to overestimation of WUE. These results highlight the potential of high-resolution gm measurements to improve modelling of Anet and WUE and demonstrate that such gm data can be acquired, even under field conditions.

Exogenous application of glycine betaine improved water use efficiency in winter wheat (Triticum aestivum L.) via modulating photosynthetic efficiency and antioxidative capacity under conventional and limited irrigation conditions

Improving water use efficiency (WUE) is an important subject in agricultural irrigation for alleviating the scarcity of water resources in semiarid regions of the North China Plain. Moreover, glycine betaine (GB) is one of the most effective compatible solutes synthesized naturally in plants for enhancing stress tolerance under abiotic stress, but little information is available on the involvement of GB in regulating crop WUE under field conditions. This study was conducted to explore the role of exogenously applied GB in improving WUE and plant physiological and biochemical responses in winter wheat subjected to conventional or limited irrigation during the 2015–2016 and 2016–2017 growing seasons. Exogenous application of GB significantly enhanced antioxidant enzyme activities and reduced the accumulation of malondialdehyde and hydrogen peroxide under limited irrigation conditions. Furthermore, GB-treated plants maintained higher leaf relative water content and membrane stability, which led to higher chlorophyll content and gas exchange attributes for better intrinsic and instantaneous water use efficiencies compared to control plants under limited irrigation conditions. GB-treated plants had higher indole-acetic acid and zeatin riboside levels but lower ABA levels compared to control plants under conventional and limited irrigation conditions. Additionally, GB enhanced the grain filling rate and duration, grain number per spike, and final grain weight, which resulted in higher grain yield compared to the control. Interestingly, GB significantly improved the integrative and photosynthetic WUE under conventional and limited irrigation conditions, although GB treatment did not markedly affect total water consumption. These results suggest the involvement of GB in improving WUEs in winter wheat by modulating hormonal balance, membrane stability, photosynthetic performance and antioxidant systems to maintain higher grain yield under conventional and limited irrigation conditions.

Gas exchange and water‐use efficiency in plant canopies

In this review, I first address the basics of gas exchange, water-use efficiency and carbon isotope discrimination in C3 plant canopies. I then present a case study of water-use efficiency in northern Australian tree species. In general, C3 plants face a trade-off whereby increasing stomatal conductance for a given set of conditions will result in a higher CO2 assimilation rate, but a lower photosynthetic water-use efficiency. A common garden experiment suggested that tree species which are able to establish and grow in drier parts of northern Australia have a capacity to use water rapidly when it is available through high stomatal conductance, but that they do so at the expense of low water-use efficiency. This may explain why community-level carbon isotope discrimination does not decrease as steeply with decreasing rainfall on the North Australian Tropical Transect as has been observed on some other precipitation gradients. Next, I discuss changes in water-use efficiency that take place during leaf expansion in C3 plant leaves. Leaf phenology has recently been recognised as a significant driver of canopy gas exchange in evergreen forest canopies, and leaf expansion involves changes in both photosynthetic capacity and water-use efficiency. Following this, I discuss the role of woody tissue respiration in canopy gas exchange and how photosynthetic refixation of respired CO2 can increase whole-plant water-use efficiency. Finally, I discuss the role of water-use efficiency in driving terrestrial plant responses to global change, especially the rising concentration of atmospheric CO2 . In coming decades, increases in plant water-use efficiency caused by rising CO2 are likely to partially mitigate impacts on plants of drought stress caused by global warming.

Photosynthetic characteristics explain the high growth rate for Eucalyptus camaldulensis: Implications for breeding strategy

Eucalypt wood is a valuable raw material for pulping worldwide. Because of its high growth rate, Eucalyptus camaldulensis has been introduced for plantation production in many tropical and subtropical areas in China. However, photosynthetic mechanisms underlying the rapid growth rate of E. camaldulensis are not well known. Furthermore, little is known about the relative photosynthetic limitations that complicate breeding strategies for this species. In the present study, we examined the photosynthetic characteristics for leaves of E. camaldulensis and observed stomata on both adaxial and abaxial surfaces, with their density being higher on the latter. Regardless of which surface was exposed to sunlight, the actual whole-leaf photosynthesis of E. camaldulensis reached 42.00 μmol CO2 m−2 s−1, which is much higher than that reported for other C3 plants. Although both surfaces showed high photosynthetic rates, photosynthesis and intrinsic water-use efficiency were always greater on the abaxial surface, mainly because of differences in mesophyll conductance (gm). Analysis of quantitative limitations revealed that gm was the most constraining factor for photosynthesis while stomatal conductance was much less important. Taken together, our results imply that gm is a potential target for simultaneous improvement of photosynthesis and photosynthetic water-use efficiency in E. camaldulensis, and we propose that increased gm is an important trait for breeding of that species.

Water- and Nitrogen-Use Efficiencies of Hemp (Cannabis sativa L.) Based on Whole-Canopy Measurements and Modeling.

Interest in hemp (Cannabis sativa L.) as a crop for the biobased economy is growing worldwide because hemp produces a high and valuable biomass while requiring low inputs. To understand the physiological basis of hemp's resource-use efficiency, canopy gas exchange was assessed using a chamber technique on canopies exposed to a range of nitrogen (N) and water levels. Since canopy transpiration and carbon assimilation were very sensitive to variations in microclimate among canopy chambers, observations were adjusted for microclimatic differences using a physiological canopy model, with leaf-level parameters estimated for hemp from our previous study. Canopy photosynthetic water-use efficiency (PWUEc), defined as the ratio of gross canopy photosynthesis to canopy transpiration, ranged from 4.0 mmol CO2 (mol H2O)−1 to 7.5 mmol CO2 (mol H2O)−1. Canopy photosynthetic nitrogen-use efficiency (PNUEc), the ratio of the gross canopy photosynthesis to canopy leaf-N content, ranged from 0.3 mol CO2 d−1 (g N)−1 to 0.7 mol CO2 d−1 (g N)−1. The effect of N-input levels on PWUEc and PNUEc was largely determined by the N effect on canopy size or leaf area index (LAI), whereas the effect of water-input levels differed between short- and long-term stresses. The effect of short-term water stress was reflected by stomatal regulation. The long-term stress increased leaf senescence, decreased LAI but retained total canopy N content; however, the increased average leaf-N could not compensate for the lost LAI, leading to a decreased PNUEc. Although hemp is known as a resource-use efficient crop, its final biomass yield and nitrogen use efficiency may be restricted by water limitation during growth. Our results also suggest that crop models should take stress-induced senescence into account in addition to stomatal effects if crops experience a prolonged water stress during growth.

Acclimation to higher VPD and temperature minimized negative effects on assimilation and grain yield of wheat

Adapting to climate change and minimizing its negative impact on crop production requires detailed understanding of the direct and indirect effects of different climate variables (i.e. temperature, VPD). We investigated the direct (via heat stress) and indirect effects (through increased VPD) of high temperature on growth, physiology and yield of two wheat cultivars (Taifun and Vinjett) at two watering levels; well-watered: WW (100% evapotranspiration (ET)) and drought stress: DS (50% of WW ET). Three climate treatments were applied for five days, starting at one week after anthesis. Treatments included hot humid (HH: 36°C; 1.96kPa VPD), hot dry (HD: 36°C; 3.92kPa VPD) and normal (NC: 24°C; 1.49kPa VPD). Difference between HH and HD was considered as the indirect effect of temperature through increased VPD. HD increased transpiration by 2–22% and decreased photosynthetic water-use efficiency (WUEp) by 24–64% over HH during stress but whole-plant WUE at final harvest was not affected. HD reduced grainfilling duration (3days), resulted in relatively lower green leaf area (GLA) after the stress and showed a tendency of lower net assimilation rate during the stress compared to HH. However, yield and yield components were not affected under WW conditions due to two reasons (i) acclimation of the photosynthesis, stomatal conductance and rubisco carboxylation efficiency to high temperature and VPD and (ii) translocation of assimilates from stem/leaf to grains after the stress episode. Five days of high temperature stress alone (HH) reduced GLA, grainfilling duration (5days) and thousand-grain weight (17%), which ultimately reduced grain yield by 17%. DS mainly affected GLA, grainfilling duration and reduced grain yield by 7% vis-à-vis WW. Two cultivars differed only for GLA (lower for Vinjett under HH) and WUEp (higher for Vinjett under DS). This indicates that the temperature induced increase in VPD has little effect on growth and yield, if sufficient soil moisture is available, because acclimation and tolerance mechanisms tend to alleviate stress effects. These compensatory mechanisms should also be considered when modelling climate effects on crops. However, heat waves and drought events during sensitive crop developmental stages (i.e. anthesis, grainfilling) are important climate variables that need to be considered for adaption to climate change.

Comparative studies of the response of larch and birch seedlings from two origins to water deficit

BackgroundEarly developmental stages of plants are expected to be a major bottleneck to recruitment. Information on the response of seedling to anticipated water availability is urgently needed in regions where tree seedlings may experience more frequent water deficits. In this paper, we focused on the influence of water deficit on different species (larch vs. birch) and origins (xeric vs. mesic).MethodsPrince Rupprecht’s larch (Larix gmelinii var. principis-rupprechtii (Mayr) Pilg.) and white birch (Betula platyphylla Sukaczev) from northern China were selected to represent the xeric origin. Eastern larch (Larix laricina (Du Roi) K. Koch) and paper birch (Betula papyrifera Marshall) from eastern Canada were selected to represent the mesic origin. For each species, half of seedlings were assigned to a well-watered treatment (WW, 75% water holding capacity (WHC) and the other half to a low-watered treatment (LW, 35% WHC). After 20 weeks of treatment, we collected data on morphological indexes of shoot height, root collar diameter, total leaf area and total root area; measured photosynthetic rate (Asat), transpiration rate (E), photosynthetic water-use efficiency (WUE) and apparent chlorophyll concentration (Chl); harvested seedlings and measured biomass allocation of leaf, stem and root.ResultsWe found that reduced photosynthetic rate, transpiration rate and increased water-use efficiency were physiological responses of the four species to drought, and the responses varied among the species. All larch seedlings appeared no leaf shedding, survived through the drought treatment and showed a longer duration and high tolerance to drought. In low-watered conditions, survival rate, biomass, shoot height, root collar diameter, total leaf area, total root area and chlorophyll concentration of birch seedlings were significantly decreased. The response of seedlings to water deficits also differed according to the seed origins. Xeric origin of Prince Rupprecht’s larch was more affected than mesic origin of eastern larch, mainly because Prince Rupprecht’s larch originated in a narrower range of mountainous regions, resulting in lower adaptation of this species to water deficits, whereas eastern larch was distributed widely along coastal regions, contributing to higher phenotypic plasticity to variable soil conditions. Similarly, higher plasticity of paper birch may be responsible for its better performance in the low-watered treatment than white birch.ConclusionsLarch seedlings were less sensitive to water deficit than birch seedlings. Larch seedlings were characteristics of a conservative water-use strategy, whereas birch seedlings responded with a profligate water-use strategy. Plasticity or adaptation of seedlings outweighs the seed origins in determining their drought responses.

The relationship between the soil water storage and water-use efficiency of seven energy crops

The aim of this work was to determine two types of photosynthetic water-use efficiency in order to examine their utility as selection criteria for tolerance of energy crops to soil water deficit. Furthermore, effects of crop cultivation on soil water content and storage were investigated. Seven energy crops were examined: miscanthus, prairie cordgrass, willow, thorn-free rose, Virginia mallow, Bohemian knotweed, and topinambour. The highest values of instantaneous (WUE) and intrinsic (WUEi) water-use efficiencies were found for miscanthus and prairie cordgrass. The reduction of WUE and/or WUEi was caused mainly by a rapid rise in the transpiration rate and a greater stomatal conductance, respectively. Principal component analysis showed that neither WUE nor WUEi could be recommended as universal selection criteria for the drought tolerance in different energy crops. The proper localization of soil with a good supply of water is most the important condition for energy crop plantations.