Marginal Water Use Research Articles

Marginal water use efficiencies of different plant functional types along an elevation gradient in subalpine regions

Marginal water use efficiencies of different plant functional types along an elevation gradient in subalpine regions

Pre-germination treatments of melon seeds for the production of seedlings irrigated with biosaline water.

Melon production in the Brazilian semi-arid region is subject to the use of marginal waters with high salinity. However, the use of regulators and bioactivators in seed treatment can mitigate the harmful effects of salts in irrigation water. In this context, the objective was to evaluate the effect of pre-germination treatments with plant regulators and bioactivator in melon seeds for the production of seedlings irrigated with biosaline water from fish farming effluent. For this, two trials with the Goldex and Grand Prix hybrids were carried out separately. A completely randomized design was used in a 4 × 3 factorial scheme (pre-germination treatments × water dilutions). In addition to the control, the seeds were treated with salicylic and gibberellic acids and thiamethoxam. The waters used for irrigation were local-supply water, fish farming effluent (biosaline water) and these diluted to 50%. Physiological and biochemical analyses were performed for fourteen days. Biosaline water (5.0 dS m-1) did not affect the emergence of Goldex melon seedlings, but compromised the establishment of the Grand Prix cultivar. Seed pre-treatments with salicylic and gibberellic acids attenuate the effects of water salinity and promote growth modulations, resulting in more vigorous melon seedlings.

Effective stakeholder engagement in environmental problem-solving though group model building: An Oklahoma case study

Stakeholder engagement is a vital, yet under-accessed and under-studied, resource for tackling wicked environmental problems. This paper examines mental models – cognitive representations of “real” systems – refined through group model building (GMB) with stakeholders concerned with environmental issues in the US state of Oklahoma. During GMB, a diverse group of high-level decision makers met with a variety of physical and social scientists to collaborate on mental models concerning three environmental focus areas in Oklahoma: encroachment of eastern red cedar, grid and infrastructure resilience, and marginal water use and re-use. We ask: how do individuals from diverse stakeholder groups describe causes and consequences of key environmental problems in Oklahoma? Results from this analysis advance efforts toward developing socially sustainable solutions for environmental problems in Oklahoma and beyond.

Seasonal trends in leaf-level photosynthetic capacity and water use efficiency in a North American Eastern deciduous forest and their impact on canopy-scale gas exchange.

Vegetative transpiration (E) and photosynthetic carbon assimilation (A) are known to be seasonally dynamic, with changes in their ratio determining the marginal water use efficiency (WUE). Despite an understanding that stomata play a mechanistic role in regulating WUE, it is still unclear how stomatal and nonstomatal processes influence change in WUE over the course of the growing season. As a result, limited understanding of the primary physiological drivers of seasonal dynamics of canopy WUE remains one of the largest uncertainties in earth system model projections of carbon and water exchange in temperate deciduous forest ecosystems. We investigated seasonal patterns in leaf-level physiological, hydraulic, and anatomical properties, including the seasonal progress of the stomatal slope parameter (g1 ; inversely proportional to WUE) and the maximum carboxylation rate (Vcmax ). Vcmax and g1 were seasonally variable; however, their patterns were not temporally synchronized. g1 generally showed an increasing trend until late in the season, while Vcmax peaked during the midsummer months. Seasonal progression of Vcmax was primarily driven by changes in leaf structural, and anatomical characteristics, while seasonal changes in g1 were most strongly related to changes in Vcmax and leaf hydraulics. Using a seasonally variable Vcmax and g1 to parameterize a canopy-scale gas exchange model increased seasonally aggregated A and E by 3% and 16%, respectively.

Water Productivity Indices of Onion (Allium cepa) under Drip Irrigation and Mulching in a Semi-Arid Tropical Region of Colombia

Efficient water management is crucial for sustainable agriculture and water resource conservation, particularly in water-scarce regions. This study investigated the effect of different irrigation depths on onion (Allium cepa L.) yield and water use patterns in a semi-arid tropical region of Colombia, using a completely randomized design with five treatments. The treatments ranged from 0–100% of total available water (TAW), T1 (100% of TAW), T2 (80% of TAW), T3 (60% of TAW), T4 (40% of TAW), and T5 (20% of TAW). The experiment was conducted in a greenhouse during one growing season (2022–2023). The normalized water productivity (WP *), irrigation water productivity (IWP), consumptive water productivity, blue water footprint (WFblue), marginal water use efficiency (MWUE), and elasticity of water productivity (EWP), as well as some parameters of quality onion, were determined. The soil in the experimental field was classified as sandy loam; the results show that the WP * of onion is 17.42 g m−2, the water production function shows the maximum production will be achieved at a water application depth of approximately 943 mm, and beyond that, the biomass yield will decrease with additional water application, IWP values for onion ranged from 2.18 to 3.42 kg m−3, the highest Wfblue was in T5 (34.10 m3 t−1), and low Wfblue was T1 (20.95 m3 t−1). In terms of quality, treatment T1 had the most favorable effects on bulb weight, polar diameter, and equatorial diameter, while treatment T5 had the least favorable effects. The study highlights the importance of efficient irrigation on sandy loam soils to maximize yield and water use efficiency. It provides valuable data for evaluating the potential yield benefits of precision irrigation in the study area. Optimizing irrigation depth can significantly improve onion yield and water use efficiency in semi-arid regions.

Framework for the Integrated Sustainability Assessment of Irrigation with Marginal Water

The use of marginal water, such as reclaimed wastewater or effluent, for irrigation can reduce the pressure on existing freshwater resources. However, this can cause contaminants to accumulate in compartments such as the soil, crop, air, surface- and groundwater, which may harm the public health and the environment. Environmental quality standards for these compartments are generally considered separately. However, the compartments are related to each other by the fluxes between them, and the concept of sustainability should hold for all compartments simultaneously. An integrated approach is therefore required for the sustainability assessment of irrigation with marginal water. Since such an approach has not been provided yet, we develop an integrated framework in this study. We provide sustainability indicators by comparing the long-term contaminant concentration and fluxes with quality standards for each environmental compartment. These indicators give comprehensible information on which contaminants will cause problems, which environmental compartments are threatened, and on what timescale this will occur. This allows for the prioritization of mitigation and preventive measures for better sustainability management. We illustrate the use of the framework by means of a case study.

Circadian Regulation Does Not Optimize Stomatal Behaviour.

The circadian clock is a molecular timer of metabolism that affects the diurnal pattern of stomatal conductance (gs), amongst other processes, in a broad array of plant species. The function of circadian gs regulation remains unknown and here, we test whether circadian regulation helps to optimize diurnal variations in stomatal conductance. We subjected bean (Phaseolus vulgaris) and cotton (Gossypium hirsutum) canopies to fixed, continuous environmental conditions of photosynthetically active radiation, temperature, and vapour pressure deficit (free-running conditions) over 48 h. We modelled gs variations in free-running conditions to test for two possible optimizations of stomatal behaviour under circadian regulation: (i) that stomata operate to maintain constant marginal water use efficiency; or (ii) that stomata maximize C net gain minus the costs or risks of hydraulic damage. We observed that both optimization models predicted gs poorly under free-running conditions, indicating that circadian regulation does not directly lead to stomatal optimization. We also demonstrate that failure to account for circadian variation in gs could potentially lead to biased parameter estimates during calibrations of stomatal models. More broadly, our results add to the emerging field of plant circadian ecology, where circadian controls may partially explain leaf-level patterns observed in the field.

Competition and Drought Alter Optimal Stomatal Strategy in Tree Seedlings.

A better understanding of plant stomatal strategies holds strong promise for improving predictions of vegetation responses to drought because stomata are the primary mechanism through which plants mitigate water stress. It has been assumed that plants regulate stomata to maintain a constant marginal water use efficiency and forego carbon gain when water is scarce. However, recent hypotheses pose that plants maximize carbon assimilation while also accounting for the risk of hydraulic damage via cavitation and hydraulic failure. This “gain-risk” framework incorporates competition in stomatal regulation because it takes into account that neighboring plants can “steal” unused water. This study utilizes stomatal models representing both the water use efficiency and carbon-maximization frameworks, and empirical data from three species in a potted growth chamber experiment, to investigate the effects of drought and competition on seedling stomatal strategy. We found that drought and competition responses in the empirical data were best explained by the carbon-maximization hypothesis and that both drought and competition affected stomatal strategy. Interestingly, stomatal responses differed substantially by species, with seedlings employing a riskier strategy when planted with a high water use competitor, and seedlings employing a more conservative strategy when planted with a low water use competitor. Lower water users in general had less stomatal sensitivity to decreasing ΨL compared to moderate to high water users. Repeated water stress also resulted in legacy effects on plant stomatal behavior, increasing stomatal sensitivity (i.e., conservative behavior) even when the seedling was returned to well-watered conditions. These results indicate that stomatal strategies are dynamic and change with climate and competition stressors. Therefore, incorporating mechanisms that allow for stomatal behavioral changes in response to water limitation may be an important step to improving carbon cycle projections in coupled climate-Earth system models.

Maximizing leaf carbon gain in varying saline conditions: An optimization model with dynamic mesophyll conductance

While the adverse effects of elevated salinity levels on leaf gas exchange in many crops are not in dispute, representing such effects on leaf photosynthetic rates (A) continues to draw research attention. Here, an optimization model for stomatal conductance (gc ) that maximizes A while accounting for mesophyll conductance (gm ) was used to interpret new leaf gas exchange measurements collected for five irrigation water salinity levels. A function between chloroplastic CO2 concentration (cc ) and intercellular CO2 concentration (ci ) modified by salinity stress to estimate gm was proposed. Results showed that with increased salinity, the estimated gm and maximum photosynthetic capacity were both reduced, whereas the marginal water use efficiency λ increased linearly. Adjustments of gm , λ and photosynthetic capacity were shown to be consistent with a large corpus of drought-stress experiments. The inferred model parameters were then used to evaluate the combined effects of elevated salinity and atmospheric CO2 concentration (ca ) on leaf gas exchange. For a given salinity level, increasing ca increased A linearly, but these increases were accompanied by mild reductions in gc and transpiration. The ca level needed to ameliorate A reductions due to increased salinity is also discussed using the aforementioned model calculations.

A stomatal optimization approach improves the estimation of carbon assimilation from sap flow measurements

Modeling the carbon uptake process by plants provides the foundation for global vegetation models. We modified the Canopy Conductance Constrained Carbon Assimilation (4C-A) model, a multi-level assimilation model that utilizes sap-flux measurements, based on the stomatal optimization theory. A novel method of calculating optimal stomatal conductance and carbon assimilation (Anet), which considers the co-limitation of Rubisco activity and RuBP regeneration, has now been incorporated into the modified 4C-A model. Results show that the calculated daily average Anet by the modified 4C-A model was lower than that from the original 4C-A and a big-leaf model but agreed well with that from leaf gas exchange measurement. When the marginal water use efficiency (λ) was high, the calculated daily average Anet became lower than that derived from lower λ. Differences in Anet between the modified and original model were larger when the canopy exhibited higher stomatal conductance or VPD was lower. Hence, a more accurate Anet was estimated by the modified model at dawn and dusk or during humid days when low VPD occurred. In addition, the modified 4C-A model performed better on a diurnal timescale for Anet and stomatal conductance estimation compared to the original one. This modified 4C-A model provides a more realistic estimation of Anet on half hourly to daily timescales, and, thus, can be applied to elucidate the coupling between carbon and water cycles and test the responses of carbon assimilation to environmental change.

Transport in a coordinated soil-root-xylem-phloem leaf system

Abstract Links between the carbon and water economies of plants are coupled by combining the biochemical demand for atmospheric CO2 with gas transfer through stomates, liquid water transport in the soil-xylem hydraulic system and sucrose export in the phloem. We formulated a model to predict stomatal conductance (gs), consistent with the maximum energy circulation concept of Lotka and Odum, by maximizing the sucrose flux out of photosynthesizing leaves. The proposed modeling approach recovers all prior results derived from stomatal optimization theories and profit-maximization arguments for the xylem hydraulic system aimed at predicting gs. The novel features of this approach are its ability to 1) predict the price of losing water in carbon units using xylem and phloem properties (i.e., the marginal water use efficiency) and 2) explain why water molecules become more expensive to exchange for CO2 molecules when soil moisture becomes limiting or when plants acclimate to new elevated atmospheric CO2 concentration. On short time-scales (sub-daily), predicted gs under many environmental stimuli were consistent with measurements reported in the literature, including a general sensitivity of gs to vapor pressure deficit and leaf water potential. During progressive droughts, differences in the coordination among the leaf, xylem, and phloem functioning determine the isohydric-to-anisohydric behavior among plants.

Woody plants optimise stomatal behaviour relative to hydraulic risk.

Stomatal response to environmental conditions forms the backbone of all ecosystem and carbon cycle models, but is largely based on empirical relationships. Evolutionary theories of stomatal behaviour are critical for guarding against prediction errors of empirical models under future climates. Longstanding theory holds that stomata maximise fitness by acting to maintain constant marginal water use efficiency over a given time horizon, but a recent evolutionary theory proposes that stomata instead maximise carbon gain minus carbon costs/risk of hydraulic damage. Using data from 34 species that span global forest biomes, we find that the recent carbon-maximisation optimisation theory is widely supported, revealing that the evolution of stomatal regulation has not been primarily driven by attainment of constant marginal water use efficiency. Optimal control of stomata to manage hydraulic risk is likely to have significant consequences for ecosystem fluxes during drought, which is critical given projected intensification of the global hydrological cycle.

Balancing water scarcity and quality for sustainable irrigated agriculture

AbstractThe challenge of meeting the projected doubling of global demand for food by 2050 is monumental. It is further exacerbated by the limited prospects for land expansion and rapidly dwindling water resources. A promising strategy for increasing crop yields per unit land requires the expansion of irrigated agriculture and the harnessing of water sources previously considered “marginal” (saline, treated effluent, and desalinated water). Such an expansion, however, must carefully consider potential long‐term risks on soil hydroecological functioning. The study provides critical analyses of use of marginal water and management approaches to map out potential risks. Long‐term application of treated effluent (TE) for irrigation has shown adverse impacts on soil transport properties, and introduces certain health risks due to the persistent exposure of soil biota to anthropogenic compounds (e.g., promoting antibiotic resistance). The availability of desalinated water (DS) for irrigation expands management options and improves yields while reducing irrigation amounts and salt loading into the soil. Quantitative models are used to delineate trends associated with long‐term use of TE and DS considering agricultural, hydrological, and environmental aspects. The primary challenges to the sustainability of agroecosystems lies with the hazards of saline and sodic conditions, and the unintended consequences on soil hydroecological functioning. Multidisciplinary approaches that combine new scientific knowhow with legislative, economic, and societal tools are required to ensure safe and sustainable use of water resources of different qualities. The new scientific knowhow should provide quantitative models for integrating key biophysical processes with ecological interactions at appropriate spatial and temporal scales.

Increasing water use efficiency along the C3 to C4 evolutionary pathway: a stomatal optimization perspective.

C4 photosynthesis evolved independently numerous times, probably in response to declining atmospheric CO2 concentrations, but also to high temperatures and aridity, which enhance water losses through transpiration. Here, the environmental factors controlling stomatal behaviour of leaf-level carbon and water exchange were examined across the evolutionary continuum from C3 to C4 photosynthesis at current (400 μmol mol(-1)) and low (280 μmol mol(-1)) atmospheric CO2 conditions. To this aim, a stomatal optimization model was further developed to describe the evolutionary continuum from C3 to C4 species within a unified framework. Data on C3, three categories of C3-C4 intermediates, and C4 Flaveria species were used to parameterize the stomatal model, including parameters for the marginal water use efficiency and the efficiency of the CO2-concentrating mechanism (or C4 pump); these two parameters are interpreted as traits reflecting the stomatal and photosynthetic adjustments during the C3 to C4 transformation. Neither the marginal water use efficiency nor the C4 pump strength changed significantly from C3 to early C3-C4 intermediate stages, but both traits significantly increased between early C3-C4 intermediates and the C4-like intermediates with an operational C4 cycle. At low CO2, net photosynthetic rates showed continuous increases from a C3 state, across the intermediates and towards C4 photosynthesis, but only C4-like intermediates and C4 species (with an operational C4 cycle) had higher water use efficiencies than C3 Flaveria. The results demonstrate that both the marginal water use efficiency and the C4 pump strength increase in C4 Flaveria to improve their photosynthesis and water use efficiency compared with C3 species. These findings emphasize that the advantage of the early intermediate stages is predominantly carbon based, not water related.

Optimization of stomatal conductance for maximum carbon gain under dynamic soil moisture

Optimization theories explain a variety of forms and functions in plants. At the leaf scale, it is often hypothesized that carbon gain is maximized, thus providing a quantifiable objective for a mathematical definition of optimality conditions. Eco-physiological trade-offs and limited resource availability introduce natural bounds to this optimization process. In particular, carbon uptake from the atmosphere is inherently linked to water losses from the soil as water is taken up by roots and evaporated. Hence, water availability in soils constrains the amount of carbon that can be taken up and assimilated into new biomass. The problem of maximizing photosynthesis at a given water availability by modifying stomatal conductance, the plant-controlled variable to be optimized, has been traditionally formulated for short time intervals over which soil moisture changes can be neglected. This simplification led to a mathematically open solution, where the undefined Lagrange multiplier of the optimization (equivalent to the marginal water use efficiency, λ) is then heuristically determined via data fitting. Here, a set of models based on different assumptions that account for soil moisture dynamics over an individual dry-down are proposed so as to provide closed analytical expressions for the carbon gain maximization problem. These novel solutions link the observed variability in λ over time, across soil moisture changes, and at different atmospheric CO2 concentrations to water use strategies ranging from intensive, in which all soil water is consumed by the end of the dry-down period, to more conservative, in which water stress is avoided by reducing transpiration.

A perspective on optimal leaf stomatal conductance under CO2 and light co-limitations

To describe stomatal response to micro-environmental variations, optimization theories for canopy gas exchange are often used as alternatives to empirical or mechanistic but complex models of stomatal function. Solutions for optimal stomatal conductance have been proposed assuming leaf photosynthesis is limited by either Rubisco activity (and hence by CO2 at the photosynthetic site) or ribulose-1,5-biphosphate (RuBP) regeneration rate (and hence light availability). These contrasting assumptions result in different relations between the marginal water use efficiency λ (the key optimization parameter) and atmospheric CO2 concentration (ca). Contrasting predictions of stomatal responses to elevated ca ensue, begging the question as to which approach is most suitable. Here, it is proposed that stomatal aperture is optimized for shifting limitations, motivating the development of a framework where Rubisco activity and electron transport co-limit photosynthesis. This approach attempts to reconcile the two previously proposed optimality solutions. Based on a minimalist model of photosynthesis that accounts for both limitations, optimal stomatal conductance is derived as a function of photosynthetic parameters, λ, and leaf micro-environmental conditions. The optimal stomatal conductances resulting from the different formulations of photosynthesis and functional dependencies of λ on ca are compared for varying environmental conditions, with reference to often observed patterns and scaling relationships. The results suggest that short-term (e.g., sub-daily) fluctuations in ca trigger small adjustments in stomatal aperture at a constant λ, while long-term (e.g., growing season or longer) elevated ca may elicit acclimation mechanisms, potentially resulting in changes in λ.

How should we model plant responses to drought? An analysis of stomatal and non-stomatal responses to water stress

Models disagree on how to represent effects of drought stress on plant gas exchange. Some models assume drought stress affects the marginal water use efficiency of plants (marginal WUE=∂A/∂E; i.e. the change in photosynthesis per unit of change in transpiration) whereas others assume drought stress acts directly on photosynthetic capacity. We investigated drought stress in an analysis of results from 22 experimental data sets where photosynthesis, stomatal conductance and predawn leaf water potential were measured at increasing levels of water stress.Our analysis was framed by a recently developed stomatal model that reconciles the empirical and optimal approaches to predicting stomatal conductance. The model has single parameter g1, a decreasing function of marginal WUE. Species differed greatly in their estimated g1 values under moist conditions, and in the rate at which g1 declined with water stress. In some species, particularly the sclerophyll trees, g1 remained nearly constant or even increased.Photosynthesis was found almost universally to decrease more than could be explained by the reduction in g1, implying a decline in apparent carboxylation capacity (Vcmax). Species differed in the predawn water potential at which apparent Vcmax declined most steeply, and in the steepness of this decline. Principal components analysis revealed a gradient in water relation strategies from trees to herbs. Herbs had higher apparent Vcmax under moist conditions but trees tended to maintain more open stomata and higher apparent Vcmax under dry conditions. There was also a gradient from malacophylls to sclerophylls, with sclerophylls having lower g1 values under well-watered conditions and a lower sensitivity of apparent Vcmax to drought.Despite the limited amount of data available for this analysis, it is possible to draw some firm conclusions for modeling: (1) stomatal and non-stomatal limitations to photosynthesis must both be considered for the short-term response to drought and (2) plants adapted to arid climate respond very differently from others.

Effect of deficit irrigation on early-maturing peach tree performance

The effects of different deficit-irrigation strategies on plant-water status and yield were studied for 5 years in early-maturing peach trees (cv. Flordastar) growing under Mediterranean climatic conditions. The deficit-irrigation (DI) treatments were continuous, regulated (RDI), partial root-zone drying and a soil water content-based treatment. Peach fruit yield was more affected by post-harvest irrigation than by pre-harvest irrigation. Deficit irrigation for this cultivar produced significant water savings but caused a yield penalty, with the RDI treatment showing the clearest manifestation of this. Deficit irrigation in general affected the number of fruits per tree more than fruit size. Average stem water potential threshold values for summer (July–August–September) should be maintained above −0.9 MPa if yields are not to decrease by more than 10 %. The marginal water use efficiency value of 0.07 for the irrigation range studied indicates that the maximum benefit, derived from a linear production function, will always occur at the limit of the water constraint prior to maximum yield values. Decision-makers should apply the minimal amount of irrigation water that allows maximum yields. Since DI treatments decrease yield due to smaller tree sizes, it is advisable that thinning practices be adapted when deficit irrigation is imposed.

Growth, Photosynthesis and Yield of Chickpea as Influenced by Urban Wastewater and Different Levels of Phosphorus

The use of effluents or marginal water in agriculture is an unavoidable practice and its largest source is the urban wastewater. In order to evaluate its effect on agricultural crops, an experiment was conducted to study its impact on Cicer arietinum L. along with different levels of phophorus. Three levels of water used for irrigation included ground water (GW), 50% wastewater (50%WW) and 100% wastewater (100%WW) and the varying levels of phosphorus (P0, P20, P40, P60) were also applied along with the basal application of nitrogen and potassium at the rate of 15 and 20 kg ha -1 respectively. The effect was evaluated on the basis of growth, biochemical attributes, photosynthesis and yield of the crop. From the results it was clear that the wastewaters proved not only effective source of water but the nutrients also and enhanced growth and photo- synthetic capacity and thereby yield of the plants. Moreover the fertilizer (P) requirement of the crop was also reduced. In conclusion the urban wastewater showed no inhibitory effect on the growth of the crop and thus could effectively supplement not only the nutrient requirement of the crop but may also act as the source of water.

Estimating Leaching Requirements for Barley Growth under Saline Irrigation

The utilization of marginal water resources for agriculture is receiving considerable attention. The lands irrigated with saline water are required to reduce salt accumulations through leaching and/or drainage practices. A field experiment was carried out to investigate the effect of saline irrigation and leaching fraction on barley (Hordeum vulgare L.) growth. For this purpose highly saline water was diluted to the salinity levels of 3, 6 and 9 dS m-1 and applied by drip irrigation at 0.0, 0.15, 0.20 and 0.25 leaching fractions (LF). The results of the experiment showed that both quantity and quality of water regulated salts distribution within the soil in the following manner: a) the salts were found higher near or immediate below the soil surface; b) an enhanced LF carried more salts down the soil horizon but there was no significant difference in plant yield between different treatments of leaching fractions. Salinity of water significantly impaired barley growth. The good drainage of sandy soil enhanced the leaching process and minimized the differences between leaching fractions. The increment in saline treatments (3, 6 and 9 dS m-1) added more salts and stressed plant growth. However, the conjunctive use of marginal water at proportional LF could be effective in enhancing the yield potential of crops in water-scarce areas.