Greater Water Use Efficiency Research Articles

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

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

Identifying physiological traits related with drought tolerance and water‐use efficiency in floral hemp (Cannabis sativa L.)

AbstractHemp (Cannabis sativa L.) is a reemerging crop that was once deeply rooted in many global civilizations. Due to climate change and the increasing risk of water‐deficit situations, it is important to use water judiciously. Hemp production has interested many producers; however, due to its past illegal status, there is a lack of research‐based knowledge about the physiological parameters that are affected by drought and which parameters could be responsible for drought tolerance. Therefore, our objective was to study and understand the effects of different drought intensities and timings on physiological parameters such as water‐use efficiency (WUE), photosynthesis, stomatal conductance, and fluorescence parameters and determine if cultivar variation exists as this could mean the possibility of selection for drought‐tolerant cultivars. In addition, we tested if carbon isotope discrimination can be used to predict whole plant WUE as this technique is quick and allows moderate throughput for selection. Hemp cultivars BaOx and Cherry Mom were grown in a greenhouse from July to October during 2021 and 2022 under different water stress intensities and timings. During the water stress period, WUE was determined by the gravimetric method and photosynthetic traits were measured using two portable gas analyzers (LI‐6800). Moderate water stress (30%–50% field capacity) was found to have the least effect on physiological parameters studied, while intense water stresses significantly reduced many physiological parameters such as photosynthesis, stomatal conductance (gs), and electron transport rate (ETR). It was found that the cultivar BaOx had a greater WUE than Cherry Mom. This was confirmed with carbon isotope discrimination measurements, which were demonstrated to estimate WUE accurately, and therefore, this technique could be used for germplasm screening. Drought first decreased gs, which caused the reduction in photosynthesis, although cultivar variation in these traits was not observed. Twenty days after drought, negative effects on fluoresce parameters such as ETR were observed with the cultivar Cherry Mon being more affected. This study states that hemp is negatively affected by different timings and intensities of drought; however, there is physiological variation in the response between cultivars. More research is needed to investigate the sources of genotypic variation in physiological parameters to find the sources of drought tolerance.

Enhanced pearl millet yield stability, water use efficiency and soil microbial activity using superabsorbent polymers and crop residue recycling across diverse ecologies

Under changing climate scenarios, developing sustainable adaptation strategies in agriculture will be obligatory. To understand the effect of carbohydrate-based superabsorbent polymer (SAP) and crop-residue mulch (CRM) on pearl millet productivity and water-use efficiency (WUE), field experiments were undertaken for three consecutive years at 11 different locations (representing ⁓30 % of the global pearl millet growing area). Eight treatments, namely, Control; CRM 5.0 t/ha; SAP 2.5 kg/ha; SAP 5.0 kg/ha; SAP 7.5 kg/ha; SAP 2.5 kg/ha + CRM 5.0 t/ha; SAP 5.0 kg/ha + CRM 5.0 t/ha and SAP 7.5 kg/ha + CRM 5.0 t/ha were evaluated. Co-application of CRM and SAP increased pearl millet grain and stover yield by up to ⁓45 % and ⁓36 %, respectively. Pearl millet responded significantly up to 2.5 kg/ha SAP application (with or without CRM) only. Further, soil microbial biomass carbon improved significantly with CRM (20 %) and SAP (10.9–12.1 %) individually and with simultaneous application of CRM and SAP (⁓30 %). Likewise, dehydrogenase, alkaline phosphatase, acid phosphatase, and urease activities also improved significantly due to the co-use of CRM and SAP. Positive effects of CRM, SAP, and their co-application were also witnessed on soil microbial (bacterial, fungal, actinobacteria) populations and water-use efficiency (WUE) across environments. Among the locations, New Delhi and Aurangabad were the most desirable and stable ecologies, whereas Bikaner and Vijayapur remained the least consistent. Hence, to tackle the moisture-stress problem under pearl millet production systems and to achieve stable productivity, greater WUE and better soil microbial activity, CRM 5 t/ha in conjunction with SAP 2.5 kg/ha may be recommended across diverse ecologies.

Fine mapping of QTL for water use efficiency‐related traits on chromosome 9 of Solanum habrochaites in the field

AbstractFresh water is increasingly limited due to climate change. One way to reduce fresh water use by irrigated agriculture is to breed plants that can produce adequate yields with less water. A wild tomato, Solanum habrochaites, is more water stress tolerant than cultivated tomato, S. lycopersicum L. Our study aimed to fine map quantitative trait loci (QTL) for maturity, yield, and water use efficiency (WUE)‐related traits (shoot dry weight and carbon isotope discrimination, ∆13C) on chromosome 9 in S. habrochaites using a set of 21 sub‐near isogenic lines (sub‐NILs). These sub‐NILs and controls were evaluated in field experiments grown under full and reduced irrigation treatments across 2 yr. Genotype × environment interactions were significant, so the data was separated into subsets of environments for further analyses. Significant QTL were detected for 20 trait–environment combinations. All QTL were partially or completely coincident. The presence of the S. habrochaites allele at QTL was associated with later maturity, lower yields, and greater WUE. However, yield and ∆13C exhibited no or low correlations with each other, suggesting these traits could be selected for improvement independently during breeding. Two of 21 sub‐NILs showed superior performance for WUE and yield compared to controls. These two genotypes may prove useful in breeding programs to improve the WUE of tomato cultivars without negative effects on yield.

The effects of heat and drought stress on the ecophysiological responses and growth of Afrocarpus falcatus and Podocarpus henkelii seedlings

Drought and heat are major abiotic stresses that affect recruitment and growth which in turn affects the distribution of species. Plant distribution and forest composition may be determined by species abilities to tolerate and/or avoid drought and heat stress, particularly at the vulnerable seedling stage. Here we investigate the physiological and morphological responses of Afrocarpus falcatus (needle-like leaf) and Podocarpus henkelii (broadleaf) to heat and drought stress. To measure these responses, A. falcatus and P. henkelii seedlings were exposed to heat (ambient, heat wave and heat stress) and drought stress (well-watered and water-stressed) over a 4-week period. Both species showed a significant reduction in maximum quantum yield efficiency of photosystem II (PSII) and chlorophyll content under stressful conditions. Under both stresses P. henkelii was able to maintain minimal fluorescence yield, and maximum activity of PSII. Water use efficiency (WUE) of A. falcatus was significantly reduced under drought stress, while P. henkelii seedlings exposed to drought stress had greater WUE than well-watered seedlings across all heat treatments. Morphologically, leaf senescence and loss were accelerated by the drought and heat treatments in both podocarps. However, the drought and heat treatments did not have a significant effect on biomass allocation pattern, root:shoot ratio and leaf relative water content of A. falcatus and P. henkelii, except for leaf mass fraction in A. falcatus which was significantly reduced by drought and heat stress combined. Overall, the morphological and physiological responses of A. falcatus and P. henkelii to drought and heat stress are indicative of a heat and drought avoidance strategy, allowing both podocarps to persist during heat stress and under limited water availability. This research informs us of the responses of podocarp species to environmental stress, and how this may influence the distribution and potential persistence of these species under current and future environmental conditions.

Lack of coordination between stomatal and vein traits provides functional benefits to the dioecious tropical tree Myrsine coriacea.

Climate change will affect the distribution of many tropical plant species. However, the understanding of how dioecious tropical species cope with different environmental conditions is still limited. To address this issue, we investigated how secondary trait attributes in populations of the dioecious tropical tree Myrsine coriacea change along an altitudinal gradient. Eighty individual plants (40 male and 40 female) were selected among seven natural populations. Leaf variation in morphological and stomatal traits, and carbon and nitrogen isotopic compositions were analyzed. Female plants had greater isotopic leaf carbon composition (δ13 C) and nitrogen content than male plants, increasing their carboxylation capacity. Plants of both sexes had smaller stomata, greater water-use efficiency (greater δ13 C), and greater nitrogen isotopic composition (δ15 N) at higher altitudes. They also showed lower δ15 N and had greater carbon: nitrogen ratios at lower altitudes. There was a lack of coordination between stomatal and vein traits, which was compensated for by variation in specific leaf areas. This mechanism was essential for increasing plant performance under the limiting conditions found by the species at higher altitudes.

Seleção precoce de genótipos de Coffea arabica tolerantes à seca em estágio de mudas utilizando-se divergência funcional

ABSTRACT The development of more drought-tolerant cultivars is essential for the maintenance of global agricultural production. This study aimed to perform an early selection of drought-tolerant Coffea arabica genotypes by evaluating their functional divergence using morphological, anatomical and physiological analyses. Seedlings of 14 genotypes were subjected to the drought stress imposed by irrigation for 18 days. Growth and anatomical parameters, leaf water potential and gas exchanges were measured. Under irrigated conditions and prolonged drought (18 days), the divergence among the genotypes was determined mainly by morphological traits, such as leaf area, stem diameter and, consequently, shoot dry mass. Under moderate drought (14 days), parameters such as water potential, cuticle thickness, stomatal density, number of xylem vessels and water-use efficiency were important for the divergence of the group with the highest ability to maintain its water status. The genotypes 1, 2, 4, 11 and 12 have characteristics that contributed to the maintenance of water status, such as greater cuticle thickness, stomatal density, smaller number of xylem vessels and phloem thickness, bigger root length and greater water-use efficiency. The functional divergence combining morphological, anatomical and physiological analyses in response to the moderate drought indicated the early selection of the genotypes 1, 2,4, 11 and 12 as more drought tolerant during the seedling stage.

Globally important plant functional traits for coping with climate change

The last decade has seen a proliferation of studies that use plant functional traits to assess how plants respond to climate change. However, it remains unclear whether there is a global set of traits that can predict plants’ ability to cope or even thrive when exposed to varying manifestations of climate change. We conducted a systematic global review which identified 148 studies to assess whether there is a set of common traits across biomes that best predict positive plant responses to multiple climate changes and associated environmental changes.  Eight key traits appear to best predict positive plant responses to multiple climate/environmental changes across biomes: lower or higher specific leaf area (SLA), lower or higher plant height, greater water-use efficiency (WUE), greater resprouting ability, lower relative growth rate, greater clonality/bud banks/below-ground storage, higher wood density, and greater rooting depth. Trait attributes associated with positive responses appear relatively consistent within biomes and climate/environmental changes, except for SLA and plant height, where both lower and higher trait attributes are associated with a positive response depending on the biome and climate/environmental change considered.  Overall, our findings illustrate important and general trait-climate responses within and between biomes that help us understand which plant phenotypes may cope with or thrive under current and future climate change.

Effect of nitrogen supply on stay-green sorghum in differing post-flowering water regimes.

The expression of stay-green (SG) characteristic in sorghum under water stress was related to N supply. SG genotype performed better than a non-stay-green (NSG) genotype at medium and high N levels. The differences in physiological parameters between SG and NSG genotypes were not significant at low N level and severe water stress. Grain sorghum [Sorghum bicolor (L.) Moench] with stay-green (SG) trait has the potential to produce more biomass and use soil water and nitrogen (N) more efficiently under post-flowering water stress. Previous studies were mostly conducted without N deficiency and more information is needed for interactions among soil N availability, SG genotype, and post-flowering water stress. In this study, the differences in leaf growth and senescence, shoot and root biomass, evapotranspiration (ET), water use efficiency (WUE), leaf photosynthetic responses, and nitrogen use efficiency (NUE) between a SG genotype (BTx642) and a non-stay-green (NSG) genotype (Tx7000) were examined. The two genotypes were grown at three N levels (Low, LN; Medium, MN; High, HN) and under three post-flowering water regimes (No water deficit, ND; Moderate water deficit, MD; Severe water deficit, SD). The genotypic difference was generally significant while it frequently interacted with N levels and water regimes. At medium and high N levels, SG genotype consistently had greater green leaf area, slower senescence rate, more shoot biomass and root biomass, and greater WUE and NUE than the NSG genotype under post-flowering drought. However, differences in several variables (e.g., leaf senescence, ET, WUE and NUE) between genotypes were not significant under SD at LN. At HN and MN, photosynthetic function of SG genotype was better maintained under drought. At LN, SG genotype maintained greater green leaf area but had lower photosynthetic activity than the NSG genotype. Nonetheless, adequate N supply is important for SG genotype under drought and greater root biomass may contribute to greater NUE in SG genotype.

PdGNC confers drought tolerance by mediating stomatal closure resulting from NO and H2 O2 production via the direct regulation of PdHXK1 expression in Populus.

Drought is one of the primary abiotic stresses, seriously implicating plant growth and productivity. Stomata play a crucial role in regulating drought tolerance. However, the molecular mechanism on stomatal movement-mediated drought tolerance remains unclear. Using genetic, molecular and biochemical techniques, we identified that the PdGNC directly activating the promoter of PdHXK1 by binding the GATC element, a hexokinase (HXK) synthesis key gene. Here, PdGNC, a member of the GATA transcription factor family, was greatly induced by abscisic acid and dehydration. Overexpressing PdGNC in poplar (Populus clone 717) resulted in reduced stomatal aperture with greater water-use efficiency and increased water deficit tolerance. By contrast, CRISPR/Cas9-mediated poplar mutant gnc exhibited increased stomatal aperture and water loss with reducing drought resistance. PdGNC activates PdHXK1 (a hexokinase synthesis key gene), resulting in a remarkable increase in hexokinase activity in poplars subjected to water deficit. Furthermore, hexokinase promoted nitric oxide (NO) and hydrogen peroxide (H2 O2 ) production in guard cells, which ultimately reduced stomatal aperture and increased drought resistance. Together, PdGNC confers drought stress tolerance by reducing stomatal aperture caused by NO and H2 O2 production via the direct regulation of PdHXK1 expression in poplars.

Identification of physiological and morphological traits governing high water use efficiency in alfalfa

AbstractTo sustain high production of alfalfa (Medicago sativa) with limited water resource in many areas, cultivars with improved water use efficiency (WUE) are urgently needed. We recently conducted greenhouse experiments and identified an alfalfa collection, River side (RS) that is naturized to the environment in the Grand River National Grassland in South Dakota, with a greater water use efficiency (WUE) under drought than other ten alfalfa accessions. To understand the mechanisms that may contribute to the higher WUE in RS, we examined physiological and morphological traits in comparison with Alfagraze (AF), a commercial variety with lower WUE under drought under greenhouse conditions. RS showed a greater reduction of water loss through transpiration despite more stomata per unit area under drought. Both RS and AF showed a reduction of stomatal aperture under drought compared to respective well‐watered plants but stomatal aperture in RS was smaller compared to AF regardless of irrigation status. Leaves of RS showed a more rapid accumulation of abscisic acid (ABA), at 14 days versus at 28 days in AF under drought. RS also closed stomata more rapidly when treated with 10 µM ABA. In addition, leaves of RS showed denser but shorter leaf hairs under drought. A correlation analysis points to a greater stomatal sensitivity to ABA in RS as a key factor contributing to its greater WUE under drought.

Effects of irrigation and nitrogen fertilization rates on yield, agronomic efficiency and morphophysiology in Tithonia diversifolia

Tithonia diversifolia (Tithonia) is performed as an invasive species with a high adaptive potential that can be used for several purposes, including an alternative source of forage for different animal categories. The use of Tithonia is growing rapidly as farmers recognize its high accumulation of biomass, good nutritional value and adaptation to tropical environments. However, the effects of irrigation and nitrogen on the characteristics of Tithonia have been poorly studied. In this context, the objective of this study was to identify changes in the productive characteristics and morphophysiology of Tithonia under different irrigation simulations and nitrogen fertilization rates, seeking to understand its adaptive potential in different water and nutritional scenarios, improvements in the efficiency of the use of water and nitrogen and its potential for use in a global context. Field trials was a split-plot design with three replicates. Whole plots were irrigation rate (0%, 25%, 50%, 75% and 100% of crop evapotranspiration - ETc) and the subplots were the nitrogen fertilizer rate (0, 50, 100 and 150 kg ha−1). There were significant effects of irrigation, nitrogen, and their interaction on dry biomass accumulation, nitrogen- and water-use efficiency, plant height, chlorophyll index, and photosynthetic rate. Irrigation and nitrogen rates increased the dry biomass accumulation. The highest dry biomass accumulation was 7.32Mgha−1 in cycle I and 10.4Mgha−1 in cycle II. The greatest nitrogen-use efficiency was observed at a rate of 100 kg of nitrogenha−1, and the greatest water-use efficiency was observed at irrigation 75% ETc. Irrigation and nitrogen also increased plant height, chlorophyll index, and photosynthetic rate. Tithonia proved to be a plant adapted to the humid temperate climate and sandy-loam texture soil, presenting great dry biomass accumulation potential even without irrigation and nitrogen fertilization. However, the greatest dry biomass accumulation was obtained with water replacement of 100% of ETc, the crop evapotranspiration, and nitrogen fertilization of 150 kg ha−1.

Direct and correlated responses to artificial selection for growth and water-use efficiency in a Mediterranean pine.

Persistence of tree populations in the face of global change relies on their capacity to respond to biotic and abiotic stressors through plastic or adaptive changes. Genetic adaptation will depend on the additive genetic variation within populations and the heritability of traits related to stress tolerance. Because traits can be genetically linked, selective pressure acting on one trait may lead to correlated responses in other traits. To test direct and correlated responses to selection for growth and drought tolerance in Pinus halepensis, we selected trees in a parental population for higher growth and greater water-use efficiency (WUE) and compared their offspring with the offspring of random trees from the parental population in two contrasting common gardens. We estimated direct responses to selection for growth and WUE and correlated responses for growth and tolerance to abiotic and biotic stressors. We found a strong response to selection and high realized heritability for WUE, but no response to selection for growth. Correlated responses to selection in other life-history traits were not significant, except for concentration of some chemical defenses, which was greater in the offspring of mother trees selected for growth than in the offspring of unselected control trees. The empirical evidence of direct responses to selection for high WUE suggests that P. halepensis has the potential to evolve in response to increasing drought stress. Contrary to expectations, the results are not conclusive of a potential negative impact of WUE and growth selection on other key life-history traits.

Physiological responses and forage accumulation of Marandu palisadegrass and Mombaça guineagrass to nitrogen fertilizer in the Brazilian forage‐based systems

AbstractIn Brazil, the livestock systems are mainly forage‐based, and nitrogen inputs are an uncommon practice, despite its great benefits. The objective was to evaluate the effect of nitrogen input on the physiological responses of Marandu palisadegrass (Urochloa brizantha [Hochst. ex A. Rich.] R. D. Webster) and Mombaça guineagrass (Megathyrsus maximus [Jacq.] B. K. Simon & S. W. L. Jacobs), and its impacts on the forage accumulation rate (FAR). The experiment was carried out in Sinop, MT, Brazil, in a randomized block design with a 2 × 2 × 5 factorial arrangement (two cultivars: Mombaça and Marandu; unfertilized and fertilized [50 kg N ha−1 cycle−1]; and five seasons: autumn 2015, winter 2015, spring 2015, summer 2015 and autumn 2016) with three replicates. The experimental period was from March 2015 to June 2016, when plots were harvested to mimic intermittent stocking. Fertilized Mombaça presented greater FAR pastures (74.0 kg DM ha−1 day−1) than unfertilized (26.6 kg DM ha−1 day−1) and Marandu fertilized (52.5 kg DM ha−1 day−1), with the greatest values during the summer (147.6 kg DM ha−1 day−1). The greatest leaf (A) and canopy photosynthesis (CP) rates occurred on fertilized pastures during the summer 2015 and autumn 2015. Marandu presented 19% greater A than Mombaça. During the winter, under water stress, Marandu had greater water use efficiency (WUE). However, during the summer 2015 and autumn 16, Mombaça had the greatest WUE (12.76 μmol CO2/mol H2O). In all seasons, Marandu presented the greatest chlorophyll index, which may support the greatest photosynthetic rates. It was concluded that Mombaça was highly responsive to nitrogen input during the rainy season with accumulation over 140 kg DM ha−1 day−1 and is recommended to intensified systems. Marandu had the greatest WUE in the lower precipitation seasons and is an alternative to a year‐round strategy in forage‐based systems.

Differences in Biomass Production and Water Use Efficiency among Seven Different Cover Crops in the Wet Winter Seasons of 2016/17 and 2018 in South Carolina

Cover crops can protect soil health and increase climate resilience of crop production systems. Agronomic crop producers in the southern USA often demand information on the best cover crops for their locality and cropping system and on the potential impacts of cover crops on stored soil water. The present research evaluated biomass production and water use efficiency (WUE) of single species and multispecies winter cover crops in South Carolina. Overall, a five-species mixture of Austrian winter pea, rye, crimson clover, hairy vetch, and oats and a single species of rye had the greatest biomass production (4600–6480 kg ha−1) at the end of the season (19 April 2017 in season-1 and 10 May 2018 in season-2). The five-species mixture also had the greatest WUE (2184–2232 g m−3). None of the cover crops depleted soil water (in 60 cm depth) greater than a weed-free fallow maintained through herbicide application and a weedy fallow (no herbicide application). Since both the seasons, in which the present study was conducted, received greater than normal rainfall, further studies should verify the applicability of the results in dry years.

Winter cover crop production and water use in Southern Great Plains cotton

AbstractCover crops can provide several ecosystem services in agricultural cropping systems. Benefits may be enhanced with increasing cover crop biomass production. In water‐limited environments, feasibility of cover crop germination and production is not always certain. This study was conducted to determine differences in biomass production, water use, and water use efficiency (WUE) between monoculture cover crops and a mixture at Chillicothe, TX, in the Southern Great Plains under rainfed conditions in a continuous cotton (Gossypium hirsutum L.) cropping system over a 6‐yr period. Evaluated cover crops included Austrian winter pea (Pisum sativum L.), crimson clover (Trifolium incarnatum L.), hairy vetch (Vicia villosa L.), hard red winter wheat (Triticum aestivum L.), and a grass/broadleaf mixture. Although cover crops were planted after optimum planting dates and under varying climatic conditions, biomass production was 2863, 2480, and 2301 kg ha−1 for the mixture, pea, and vetch, respectively. Peas and the mixture were the most consistent, producing significantly greater biomass than wheat and clover but not more than vetch. The mixture resulted in greater WUE than wheat. Clover resulted in reduced biomass production and WUE than vetch, pea, and the mixture over the study period. A cover crop mixture did not produce significantly greater biomass or significantly increase water use efficiency compared with vetch and pea. Under dryland conditions, peas, vetch, and a mixture were shown to be viable cover crop options in Southern Great Plains cotton systems, performing as well as a wheat cover crop.

Comparative effects of soil resource availability on physiology and growth of Scotch broom (Cytisus scoparius) and Douglas-fir (Pseudotsuga menziesii) seedlings

Scotch broom (Cytisus scoparius (L.) Link) is an invasive, N-fixing shrub in recently harvested Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) forests in the Pacific Northwest. The ability of Scotch broom to dominate a site and displace Douglas-fir in this region may be mediated by site quality and site resource supply. Individual seedlings of Scotch broom (n = 46) and Douglas-fir (n = 46) were planted in a controlled nursery setting and monitored over two years to test the effects of irrigation and fertilization treatments on the physiology and growth of these oft-conflicting species. Overall, Scotch broom remained largely unaffected by resource availability relative to Douglas-fir, which was more sensitive to water and nutrient availability. Scotch broom consistently showed greater assimilation and transpiration rates and plant water potentials than Douglas-fir under all treatments – indicating an elevated ability to acquire soil water resources. The conservative ecology of Douglas-fir resulted in greater water-use efficiency than Scotch broom throughout the experiment, however. Similarly, Douglas-fir crown and height growth started later in the growing season and ended earlier than that of Scotch broom, indicating a longer growing season for Scotch broom but also the importance of resource availability early in the growing season for Douglas-fir given its determinate growth. While Douglas-fir growth reflected the additive effects of increased resource availability, it did not surpass the growth of Scotch broom, which maintained steady growth and biomass accrual under all treatment conditions. The height of Douglas-fir growing under optimized conditions was approximately 40 cm less than that of Scotch broom regardless of treatment regime by the end of the two-year study. This demonstrates how critical early intervention is for land managers in order to control this invasive to avoid Scotch broom overtopping Douglas-fir seedlings during stand establishment.

Effect of Water Table Depth on Soybean Water Use, Growth, and Yield Parameters

Water table contribution to plant water use is a significant element in improving water use efficiency (WUE) for agricultural water management. In this study, lysimeter experiments were conducted in a controlled greenhouse environment to investigate the response of soybean water uptake and growth parameters under four different water table depths (WTD) (30, 50, 70, and 90 cm). Soybean crop water use, WUE, and root distribution under the different WTD were examined. For 30, 50, 70, and 90 cm of WTD treatments, the average water table contributions were 89, 83, 79, and 72%; the grain yields were 15.1, 10.5, 14.1, and 17.2 g/lys.; and the WUEs were 0.22, 0.18, 0.25, and 0.31 g/lys./cm, respectively. Further analysis of the root mass and proportional distribution among the different soil layers illustrated that the lysimeters with 70 and 90 cm WTD had greater root mass with higher root distribution at 40–75 cm of the soil layer. The results indicated that 70 and 90 cm of constant WTD can yield higher grain yield and biomasses with greater WUE and better root distribution than the irrigated or shallow WTD treatments.

Relationship of Carbon Isotope Discrimination with Biomass and Water Use Efficiency for Alfalfa in Northwestern China

Carbon isotope discrimination (Δ) has been proposed as a method for evaluating transpiration efficiency in C3plants. It is important to study the association of Δ in different parts with the long‐term water use efficiency (WUE). In this paper, plant height, Δ in leaf water soluble carbohydrates (ΔWSC), photosynthetic gas exchange parameters, Δ in aboveground shoot (ΔAGS), stem/leaf weight ratio, aboveground biomass (AGB), evapotranspiration, and WUE were determined in a collection of 10 alfalfa (Medicago sativaL.) genotypes under three water treatments (230 [T1], 460 [T2], and 700 mm irrigation [T3]) in a Ningxia central desert steppe in 2012 and 2013. Significant interactions were found for AGB and WUE among year, treatment, and genotype, whereas significant interactions of year × treatment and year × genotype were only found for ΔAGSbut not for ΔWSC. Generally, more water input increased the values of the traits tested except for WUE and single‐leaf intrinsic WUE (Pn/Gs). More irrigated water input resulted in increase in AGB, ΔAGS, and ΔWSCand decrease inPn/Gs. The greatest WUE was recorded under T2in 2012. Significant and positive correlations were observed between AGB and ΔAGS(r= 0.588, 0.574, and 0.386 under T1, T2, and T3, respectively). Under T2and T3, ΔWSCcorrelated negatively with WUE (r= −0.383 and 0.602, respectively). Ningmu No. 1 was found to have the greatest WUE (18.34 kg ha−1mm−1) and yield (17.71 Mg ha−1) across water treatments and years. The findings suggest that in the semiarid areas applying irrigation of 230 to 700 mm yr−1, Δ in aboveground shoots or in leaf water‐soluble carbohydrates at the flowering stage seems to be a useful indicators reflecting aboveground biomass and integrated WUE for alfalfa.

Physiological characteristics and forage accumulation of grazed Marandu palisade grass (Brachiaria brizantha) growing in monoculture and in silvopasture with Eucalyptus urograndis

Adoption of silvopasture is increasing, but proper design and management of pasture–tree associations is required to sustain pasture productivity. Our objective was to compare agronomic and physiological characteristics of Brachiaria brizantha (Hochst. Ex A.Rich.) Stapf. (palisade grass) cv. Marandu growing in monoculture, or in silvopasture with Eucalyptus urograndis, in the Brazilian Amazon biome. Trees were planted in triple rows (intra-row spacing 3 m, inter-row spacing 3.5 m), referred to as a grove, with three groves per 2-ha silvopasture experimental unit. Space between groves was 30 m, and tree density was 270 ha–1. From October 2015 to September 2016, all experimental units were stocked continuously with cattle by using a variable stocking rate to maintain a Marandu canopy height of 30 cm. In the silvopasture, sampling occurred at 4, 7.5 and 15 m into the non-treed area from the outer tree row in a grove. Photosynthetically active radiation (PAR) reaching the Marandu canopy averaged 21% less for silvopasture than for grass monoculture; however, forage accumulation was not different between systems, nor were Marandu stomatal conductance, water-use efficiency (WUE), transpiration rate, transpiration ratio and leaf temperature. In silvopasture, PAR and forage accumulation were 33% and 29% less, respectively, at the 4-m distance than the 15-m distance from the edge row of trees, associated with lower transpiration rate and transpiration rate and greater WUE. We conclude that Marandu palisade grass can tolerate PAR reduction in silvopasture up to ~20% without reduction in forage accumulation, supporting its potential use in agroforestry systems for cattle production in the Brazilian Amazon Biome.