Levels Of Soil Water Availability Research Articles

The differential expression of the P5CR and αTPS6 genes in cowpea plants increases tolerance to water-deficit and high temperatures

Plants exposed to adverse environmental conditions develop molecular mechanisms of adaptation and/or defense, the osmoprotectors, which function as compatible solutes and contribute to tolerance via prevention systems and protection against cellular damage caused by these abiotic stresses. This study aimed to identify and characterize the osmoprotectors proline and trehalose in cowpea plants cv. Carijó under controlled conditions of water-deficit and heat stress based on the IPCC scenario of 4.8 °C increase in temperature, evaluating their structure and function through computational methods, as well as gene expression by RT-qPCR. The experimental assays were carried out in growth chambers under controlled conditions with different levels of soil water availability, phenological phases and temperature regimes. From the in silico analyses, ten TPS genes and one P5CR gene were identified in Vigna unguiculata, and these were named according to their chromosomal location. The VuP5CR and VuTPS genes play roles in hormone pathway signaling and in the response to light and biotic and abiotic stresses. The genes P5CR (proline) and αTPS6 (trehalose) were induced with increased temperature and lower water availability in the vegetative phase of cowpeas. In addition, P5CR also showed induction with 50% water availability at high temperatures. In the pod filling phase, the P5CR and αTPS6 genes were repressed with water availability of 75%, while only the P5CR gene was induced when water availability was reduced to 25% under heat stress. P5CR and TPS6 genes were induced in cowpea cv. Carijó in response to associated abiotic stresses (water-deficit and high temperatures), which suggests their participation in the mechanisms of adaptation of the species in adverse environmental conditions.

Water productivity in pineapple (Ananas comosus) cultivation using plastic film to reduce evaporation and percolation

Irrigated agriculture needs significant amounts of water for increasing irrigated areas to meet the increase food demand. New alternatives with high water use efficiency are needed to increase crop productivity. This work evaluates the use of plastic film mulch either as groundcover or as a percolation barrier to increase yields and water use efficiency of pineapple (Ananas comosus L.). An experiment was carried out with pineapple on a loamy sand-soil. The treatments were: (i) soil tillage with plastic film as groundcover combined with plastic film as a percolation barrier installed at 0.40 m below the soil surface; (ii) soil tillage with no groundcover combined with a percolation barrier; (iii) soil tillage with plastic film as groundcover only; (iv) soil tillage without groundcover and percolation barrier. The use of plastic mulch maintained the levels of soil water availability at least 80% during the crop cycle, while without it soil water values ranged from 15% to 70%. Groundcover with plastic mulch contributed significantly to decrease evapotranspiration and the medium crop coefficient. The plastic groundcover combined with or without the plastic percolation barrier yielded the better results of productivity, irrigation water productivity, and water footprint. The mean irrigation water productivity and water footprint were 667.12 kg mm−1 ha−1 and 109.0 L kg−1, respectively, for the use of a plastic groundcover combined with a plastic percolation barrier. The percolation barrier was more effective for saving water than for increasing yield. The use of percolation barrier with plastic contributed for saving 92–103 L kg−1 ha−1 when combined with or without ground cover.

Silicon uptake and utilization on Panicum maximum grass modifies C:N:P stoichiometry under warming and soil water deficit

Future increases in air temperature are expected to increase the growth of Panicum maximum, but with climate change it will be common for the binomial increase in temperature and drought to occur. In this condition, plants may use strategies to adapt to this new scenario by favoring the uptake of beneficial elements such as Si and modifying plants nutritional status, but this needs to be tested. Thus, this research was conducted with the objective of evaluating the effect of warming and water restriction on Si uptake, accumulation, Si use efficiency, the C:Si, N:Si and P:Si stoichiometric ratios and their effects on growth of Panicum maximum plants grown under field conditions. The experiment was carried out in a 2 × 2 factorial scheme, with two temperature conditions (T): ambient temperature (aT), and high temperature (eT - increase of 2 °C above ambient temperature) combined with two levels of soil water availability (W), with water stress - non-irrigated (wS) and irrigated (sW), arranged in randomized blocks. Si concentration and accumulation are affected by temperature variations and soil water availability in different ways. Soil water restriction reduces leaf Si concentration, accumulation and increases the C, N and P stoichiometric ratios. Biomass production always improved for all growth cycles under warming and irrigated conditions, while, leaf C: Si, N: Si, and P: Si ratios decreased under non-irrigated and elevated temperature. It was revealed for the first time that the tolerance of Panicum maximum to warming and soil water restriction can be associated with Si uptake and changes in plant C:N:P stoichiometry.

Leaf Area Duration and Crop Radiation Use Efficiency Determine Biomass Yield of Lignocellulosic Perennial Grasses under Different Soil Water Content

The aim of the present work was to assess the leaf area duration (LAD) and the radiation use efficiency (RUE) of six warm-season perennial biomass grasses (PBGs) in a two-year field trial in the semiarid Mediterranean climate under different soil water availability. Two ecotypes of giant reed (Arundo donax L., ARCT and ARMO), one ecotype of African fodder cane (Saccharum spontaneum L. subsp. aegyptiacum (Willd.) Hack., SAC) and three hybrids of Miscanthus (the commercial M. × giganteus J.M. Greef, Deuter ex Hodk., Renvoize, M × G, and two new seed-based hybrids, GNT9 and GNT10) were compared under three levels of soil water availability: rainfed, 50% and 100% of maximum crop evapotranspiration (ETm) restoration. The determination of RUE of perennial plants is controversial and has led to contrasting results in past studies. In the present work, LAD and RUE differed among crops and irrigation regimes, being positively affected by supplemental water inputs. SAC, ARCT and ARMO showed both high LAD and RUE, which determined the high biomass yield than both the commercial M × G and the improved Miscanthus hybrids GNT9 and GNT10. RUE was particularly high and less affected by soil water availability during the mid-season, while the effect of irrigation and the differences among the genotypes were larger during the late season. Adequate biomass yield can be achieved by sub-optimal soil water availability, thus reducing the water footprint and increasing the sustainability of these biomass perennial grasses selected for the Mediterranean climate.

Physiological and morphological responses of industrial hemp (Cannabis sativa L.) to water deficit

With drought projected to increase in severity and frequency in the future, selection of emerging drought-tolerant species that exhibit improved water use efficiency will be key to maintaining cropping productivity. Industrial hemp ( Cannabis sativa ) shows potential for cropping in water-limited environments, but studies into its water use and drought tolerance are conflicting. We evaluated the morphological, physiological and biochemical responses of the industrial hemp cultivar ‘Black Label’ to extreme and moderate water deficit in an 85-day greenhouse experiment. Under water deficit, hemp reduced biomass production and total seed yield, but maintained filled seeds for effective reproduction. Water use efficiency, measured using δ 13 C isotope analysis, increased under water deficit due to reductions in stomatal opening and transpiration . Water deficit increased proline accumulation, likely to allow osmotic adjustment. While extreme water deficit initiated water stress responses in hemp, plants were able to survive and maintain seed production. We report that hemp can survive at exceptionally low levels of soil water availability, which could have far-reaching consequences as agricultural industries pursue innovative, sustainable and water-efficient crops for the future. • Water deficit induces reductions in biomass, seed yield and water potential in hemp. • Seeds remained filled under extreme water deficit for effective reproduction. • Hemp increases water use efficiency under water deficit by closing stomata. • Water deficit increased proline accumulation, likely to allow osmotic adjustment. • Hemp can survive under very low water supply for 85 days in greenhouse conditions.

Effect of water regimes and harvest times on yield and phytochemical accumulation of two ginger species

In South Africa, both Commercial ginger (Zingiber officinale Roscoe) and African ginger (Siphonochilus aethiopicus (Schweinf.) BL Burtt) are significant medicinal plants. This study aimed to determine the effect of water regimes on the two-ginger species' phenolic content, antioxidant properties and yield at various harvest times. During the 2015/2016 and 2016/2017 crop seasons, a field experiment was conducted. The experiment used a randomised complete block design (RCBD) and included two ginger species, four irrigation regimes, and three replicate blocks. Four different levels of soil water availability (20-25%, 40-45%, 60-65%, and 80-85% maximum allowable depletion, MAD) were used. The severely stressed treatment (80-85% MAD) significantly increased total flavonoid and phenolic content and total antioxidant activity in both species, but the biomass yield was lower than the other treatments. The well-watered control (20-25% MAD) resulted in a significant increase in rhizome yield at different harvesting times but resulted in lower total flavonoid and phenolic content and total antioxidant activity for both species. However, the moderately stressed treatment (40-45% MAD) obtained a higher WUE, flavonoid, phenolic and antioxidant content without reducing yield significantly in both species. The results indicated a similar trend in phytochemical constituents for leaves and rhizomes. The species can be harvested seven to eight months after planting under open field conditions. The accumulation of phytochemicals is dependent on water regime, harvesting time, and plant part; growers should consider 40-45% MAD and harvest seven to eight months after planting when growing ginger species to save the scarce resource (water), high phytochemical content and rhizome yield.

Eficiência no uso de água e qualidade de cebola em cenários climáticos futuros

ABSTRACT Considering that changes in climatic parameters directly interfere in crop yields, this study aimed to evaluate the impact of changes in carbon dioxide concentrations, temperature and soil water availability on production, water-use efficiency and onion (Allium cepa L. cv. IPA 11) quality. Four levels of soil water availability (40, 60, 80 and 100 %) and two concentrations of atmospheric CO2 (770 and 390 ppm) were evaluated in three experiments with different temperature regimes (18-24-30, 22-28-34 and 26-32-38 ºC), in Phytotron growth chambers. The water-use efficiency, bulb diameter and weight, shoot dry weight, pulp frmness, soluble solids content, pH and titratable acidity were also evaluated. The increase in temperature reduces the production, and a higher soil water availability increases the production of IPA 11 onion bulbs. The temperature regime of 18-24-30 ºC and the water availability of 76.72 % provide the best water-use efficiency for the onion crop.

Biomass allocation of Vincetoxicum rossicum and V. nigrum in contrasting competitive environments.

Understanding how drought and biomass allocation patterns influence competitive ability can help identify traits related to invasiveness and guide management. Vincetoxicum nigrum and V. rossicum are increasingly problematic herbaceous perennial vines in the northeastern United States and southeastern Canada. Using a greenhouse experiment, we investigated how biomass allocation and competition intensity of Vincetoxicum spp. responded to four competitive regimes at two levels of soil water availability in the presence of conspecific or congeneric neighbors. Soil moisture was the most important influence on growth and biomass allocation. Vincetoxicum nigrum had a greater capacity for growth and reproduction than V. rossicum, especially under drought. Drought reduced the probability of reproduction for V. rossicum. Vincetoxicum rossicum had a higher root-to-shoot ratio than V. nigrum under adequate soil moisture. This difference more than doubled under drought. Under interspecific competition, V. nigrum maximized its biomass, while V. rossicum limited aboveground growth and reproduction. Root-only competition increased shoot and root biomass relative to shoot-only competition. The effects of root and shoot competition were additive under interspecific competition, but interacted under intraspecific competition (negative interaction under drought and positive interaction under sufficient soil moisture). Management strategies targeting mixed populations of V. rossicum and V. nigrum are most important under ample water availability. Under drought conditions, strategies focused on V. nigrum should effectively limit Vincetoxicum growth and seed reproduction. Phenotypic plasticity and the positive competition intensity associated with drought in monocultures may contribute to drought resistance in these invasive species.

Differential Changes in D1 Protein Content and Quantum Yield of Wild and Cultivated Barley Genotypes Caused by Moderate and Severe Drought Stress in Relation to Oxidative Stress

The aim of this study was to investigate the effects of drought stress on oxidative damage and efficiency of PSII photochemistry in barley and compare the varietal response of different genotypes including Yusof (tolerant), Moroc9-75 (sensitive), and wild barley (HS) to drought. Plants were subjected to different levels of soil water availability including control, moderate, and severe drought stress. Exposure to drought stress led to decrease in leaf water potential, biomass production, and stomatal conductance (gs) in all genotypes. Drought induced an increase in H2O2 content followed by increase in malondialdehyde (MDA) as a final result of lipid peroxidation. Drought stress also resulted in reduction of D1 protein content in all genotypes and decreased the maximal quantum yield of PSII photochemistry (FV/FM). These parameters were more affected in Moroc9-75 cultivar by drought stress compare to Yusof and HS genotype. Based on our results, drought-induced reactive oxygen species may decrease PSII photochemistry either through peroxidation of thylakoid membranes or interfering with D1 protein synthesis, necessary for proper function of PSII.

Water stress and warming impact nutrient use efficiency of Mombasa grass (Megathyrsus maximus) in tropical conditions

AbstractTemperature and other abiotic factors, such water and nutrient availability, play an important role for plants in response to the changing environments. At this regard, both warming and drought might affect the nutrient use efficiency (NUE) and growth of Megathyrsus maximus a C4 forage grass of high interest for cattle feeding. However, the nutrient requirements of this species under climate change are unknown. Therefore, we aimed to evaluate the individual and combined effects of two levels of temperature: ambient and elevated temperature (2°C above ambient temperature), and two levels of soil water availability: irrigated plants and non‐irrigated plants on accumulation of leaf nutrients, NUE and biomass production of M. maximus. Temperature control was performed by a temperature free‐air‐controlled enhancement (T‐FACE) system under field conditions. In general, we observed that warming under well‐irrigated conditions increased the leaf accumulation of most nutrients, improving the NUE of N, P, K, Ca, Mg, Cu, Mn and Zn. Plant growth was also enhanced under warming effects, with higher leaf dry mass accumulation and root development. Meanwhile, drought decreased NUE of K, Ca, B and leaf dry biomass, while root growth was stimulated. The combined effects of warming and drought on nutrient accumulation, NUE and plant growth tended to be greater than the individual effects expected from a single factor; thus, warming mitigated the negative impacts of individual drought. In summary, our findings suggest that warming and drought, both as individual and combined factors, will change the nutrient requirements of M. maximus in tropical ecosystems.

Competitive dominance mediates the effects of topography on plant richness in a mountain grassland

Small-scale landforms influence plant species richness, but their mechanisms and effects in semi-natural dry grasslands have been poorly investigated. In this study we compared vascular plant richness, species composition, plant traits, soil properties and biomass nutrient content of convex (hillocks) and concave (hollows) karst landforms in a mountain pasture of the Central Apennines (Italy), at a small spatial scale (1 m2 plots). We found hillocks had significantly higher species richness than hollows. On hillocks, smaller Specific Leaf Area and Lateral Width, together with greater allocation of resources to Below-Ground Organs, indicated lower water availability, whereas hollows had deeper (thus moister), more acidic and more fertile soils, with aboveground plant biomass displaying higher nutrient levels. Partial correlation and regression tree models suggested that fine-scale richness patterns were not directly determined by abiotic properties, but were rather the result of competition levels associated with the cover of Agrostis capillaris (=A. tenuis) – a calcifuge and drought-sensitive grass able to achieve dominance only in hollows. The higher functional convergence exhibited by hollows suggests that A. capillaris is a strong competitor both above- and below-ground, mediating the effects of topography by imposing a biotic filter. On hillocks, competition is released by lower levels of available soil water in summer and higher soil pH, resulting in higher species richness and a more functionally divergent assemblage.

Expression pattern and physiological roles of Plastid Terminal Oxidase (PTOX) in wild and cultivated barley genotypes under drought stress

Plastid terminal oxidase (PTOX) is a plastid-localized protein that acts as plastoquinol oxidase. The objective of this study was to determine the role of plastid terminal oxidase in response to drought stress and examine the differential response of PTOX pathway in both cultivated (Yousef and Morocco) and tolerant wild barley (spantaneum; HS) genotypes. Plants were subjected to different levels of soil water availability including control, mild and severe drought stress. Decrease in leaf relative water content as a result of progressive drought stressed led to decrease in stomatal conductance and increased enzymatic antioxidant machinery in all genotypes. Drought stress did not affect the PTOX transcript and protein level in cultivated genotypes Yousef and Morocco. However, PTOX gene expression and protein content significantly increased in HS genotype under severe drought. Assessment of PTOX activity via fast fluorescence induction curve in presence of PTOX specific inhibitor revealed that PTOX could efficiently oxidize plastoquinon pool and acts as alternative electron pathway in HS genotype. Results indicated that the role of PTOX in stress response was more significant in the wild barley than the cultivated barley varieties, where the emphasis has been on the desirable agronomic traits.

Effects of Drought Stress on the Photosynthesis in Maize

To clarify how the components of the entire photosynthetic electron transport chain in response to drought stress in maize. The activities of photosystem II (PSII), photosystem I (PSI), and the electron transport chain between PSII and PSI of maize were investigated by prompt fluorescence (PF), delayed fluorescence (DF) and 820 nm modulated reflection (MR). Maize (Zea mays L.) plants were subjected to different levels of soil water availability including control, moderate and severe drought stress. A significant decrease in ϕE0, Ψ0 and PIABS was found in maize treated with moderate drought stress. A significant increase in ABS/RC was observed, but there were no significant change in the fast MR phase and the amplitude of DF under moderate drought stress compared to the control. Under severe drought stress, the exchange capacity between QA to QB, reoxidation capacity of plastoquinol, and the oxidation and re-reduction rates of PC and P700 all decreased. These results demonstrated that moderate drought stress reduced the photochemical activity of PSII from QA to PQH2, while the photochemical activity of PSI was unscathed. However, severe drought stress inhibited the entire electron transport chain from the donor side of PSII to PSI-end electron acceptors. In addition, the photochemical activity of PSII is more sensitive to drought stress than PSI.

Effects of drought stress on cold hardiness of non-acclimated viola ( Viola × wittrockiana ‘Iona Gold with Blotch’) in controlled conditions

Abstract Predicted increases in winter temperatures may negatively impact plant survival by preventing maximal cold acclimation prior to cold temperatures. Accordingly, research is needed to identify strategies that may help promote cold hardiness and increase freezing tolerance of cold season ornamental plants. Therefore, the objectives of this research were to study the effects of drought stress on freezing tolerance of Viola × wittrockiana Iona Gold with Blotch during cold season under non-cold acclimating (20 ± 1 °C) conditions and examine the physiological and biochemical changes in plants in response to freezing temperature. After being grown in the greenhouse, plants were first subjected to different levels of soil water availability including control (90%), 70% and 50% field capacity (FC). Then, some traits including proline, carbohydrate and chlorophyll were determined. Finally, plants were transferred to the Thermo Gradient Freezer with six freezing temperatures (0, −3, −6, −9, −12, and −15 °C), as well as 20 °C as the control treatment. Electrolyte leakage (EL) after temperature treatments, plant survival percentage (SU) and some traits related to regrowth after recovery period were determined. Result showed that drought stress increased some factors such as carbohydrate, proline and chlorophyll. Electrolyte leakage significantly increased by lowering temperature and increased by 46% at 15 °C compared to control. Plant survival was significantly affected by treatments so that lowering the temperature to −15 °C caused total mortality in all the plants of irrigation treatments. Plants under 70% FC at 0 °C had the highest increased reproductive component. Number of leaf and leaf area peaked under the moderate water deficit (70% FC) conditions at 0 °C. Plants under 70% FC at 0 °C had the highest increases (87, 134, 90 and 101%, respectively) in dry weights of vegetative, reproductive, root, and total dry weights compared to control. Drought stress can increase freezing tolerance of viola depending on temperature regime.

Herbaceous species diversity and soil attributes along a forest-savanna-grassland continuum in a dry tropical region

Dry tropical vegetation is under major pressure of degradation due to various anthropogenic interferences and is characterized by the patches of forest, savanna and grassland systems. These adjacent systems may represent a gradient of various ecological attributes which can be better understood by studying these in a continuum approach to recognise changes at grassroots level. The herbaceous vegetation, a dynamic layer of an ecosystem, acts as an indicator of the environmental changes. The present study is designed to assess the herbaceous plant diversity and soil attributes along the dry deciduous forest-savanna-grassland continuum. A total of nine sites equally distributed in forest, savanna and grassland systems of Vindhyan region were selected. Soil moisture, water holding capacity, carbon, nitrogen, phosphorus and species richness, evenness, diversity and plant biomass were measured at each site. The results showed significant changes in soil attributes and herbaceous species composition, diversity and biomass along the continuum. Forest exhibited higher soil moisture, carbon and nitrogen contents than the savanna and grassland, while the herbaceous species diversity and biomass were higher in grassland vegetation. Savanna revealed intermediate levels of soil water availability, soil nutrients, community composition and species diversity of the herbs. The results showed that the herbaceous diversity was maximum in the grassland followed by savanna and forest. Moreover, a change in community composition and plant functional attributes was also observed. Evolvulus nummularius-Justicia simplex, Justicia simplex-Evolvulus nummularius and Cynodon dactylon-Cyperus compressus communities characterised the forest, savanna and grassland vegetation, respectively. Fabaceae was the most dominant family having the highest number of species in grassland followed by savanna and forest vegetation. Correlation analysis revealed a significant interaction between soil water and nutrient availability with vegetation parameters. Overall, heterogeneity of soil attributes maintaining the community structure and species diversity are essential components for understanding the ecology of herbaceous vegetation in dry tropical ecosystems. The findings of this study may contribute to the holistic understanding and development of ecological management tools for such a continuum.

Stem girdling indicates prioritized carbon allocation to the root system at the expense of radial stem growth in Norway spruce under drought conditions

The early culmination of maximum radial growth (RG) in late spring has been found in several coniferous species in a dry inner Alpine environment. We hypothesized that an early decrease in RG is an adaptation to cope with drought stress, which might require an early switch of carbon (C) allocation to belowground organs. To test this hypothesis, we experimentally subjected six-year-old Norway spruce saplings (tree height: 1.35m; n=80 trees) to two levels of soil water availability (watered versus drought conditions) and manipulated tree C status by physically blocking phloem transport at three girdling dates (GD). The influence of C availability and drought on tree growth (radial and shoot growth; root biomass) in response to girdling was analyzed in both treatments. Non-structural carbohydrates (NSCs, soluble sugars and starch) were measured in the stem, root and current leader to evaluate changes in tree C status due to girdling. The main finding was a significant increase in RG of the girdled trees compared to the controls above the girdling zone (UZ). At all girdling dates the RG increase was significantly more intense in the drought-stressed compared with watered trees (c. 3.3 and 1.9-fold higher compared with controls in the drought-stressed and watered trees, respectively), most likely indicating that an early switch of C allocation to belowground occurs as an adaptation to maintain tree water status under drought conditions. Reactivation of the cambium after the cessation of its regular activity was detected in UZ in drought-stressed trees, while below the girdling zone no xylem formation was found and the NSC content was strikingly reduced. Irrespective of water availability, girdling before growth onset significantly reduced the progression of bud break (P<0.05) and the length of the current leader shoot by −47% (P<0.01) indicating a reduction in xylem hydraulic conductance, which was corroborated by significantly reduced xylem sap flow (P<0.001). Based on our findings, we conclude that during the growing season drought stress prioritizes an early switch of C allocation to the root system as an adaptation to maintain adequate tree water status in drought-prone environments.

Direct Penman–Monteith parameterization for estimating stomatal conductance and modeling sap flow

The novel approach for direct parameterization of the Penman–Monteith equation was developed to compute diurnal courses of stand canopy conductance from sap flow. The Penman–Monteith equation of evaporation is often combined with sap flow measurements to describe canopy transpiration and stomatal conductance. The traditional approach involves a two-step calculation. In the first step, stomatal conductance is computed using an inverted form of Penman–Monteith equation. The second step correlates these values with environmental factors. In this work, we present an improved approach for direct parameterization of the Penman–Monteith equation developed to compute diurnal courses of stand canopy conductance (g c) from sap flow. The main advantages of this proposed approach versus using the classical approach are: (1) the calculation process is faster and involves fewer steps, (2) parameterization provides realistic values of canopy conductance, including conditions of low atmospheric vapor pressure deficit (D), whereas the traditional approach tends to yield unrealistic values for low D and (3) the new calculation method does not require enveloping curves to describe dependence of g c on D and thus avoids subjective data selection but it still allows to visualize separable responses of g c to environmental drivers (i.e., global radiation and vapor pressure deficit). The proposed approach was tested to calculate g c and to model the sap flow of a high mountain Pinus canariensis forest. The new calculation method permitted us to describe the stand canopy conductance and stand sap flow in sub-hour resolution for both day and night conditions. Direct parameterization of the Penman–Monteith approach as implemented in this study proved sufficiently sensitive for detecting diurnal variation in g c and for predicting sap flow from environmental variables under various atmospheric evapotranspirative demands and differing levels of soil water availability.

Soil water effect on crop growth, leaf gas exchange, water and radiation use efficiency of Saccharum spontaneum L. ssp. aegyptiacum (Willd.) Hackel in semi-arid Mediterranean environment

Great effort has been placed to identify the most suited bioenergy crop under different environments and management practices, however, there is still need to find new genetic resources for constrained areas. For instance, South Mediterranean area is strongly affected by prolonged drought, high vapour pressure deficit (VPD) and extremely high temperatures during summertime. In the present work we investigated the soil water effect on crop growth and leaf gas exchange of Saccharum spontaneum L. ssp. aegyptiacum (Willd.) Hackel, a perennial, rhizomatous, herbaceous grass. Furthermore, the net increase of biomass production per unit light intercepted [radiation use efficiency (RUE)] and per unit water transpired [water use efficiency (WUE)] was also studied. To this end a field trial was carried out imposing three levels of soil water availability (I100, I50 and I0, corresponding to 100%, 50% and 0% of ETm restutition) under a semi-arid Mediterranean environment. Leaf area index (LAI), stem height, biomass dry matter yield, CO2 assimilation rate, and transpiration rate resulted significantly affected by measurement time and irrigation treatment, with the highest values in I100 and the lowest in I0. RUE was the highest in I100 followed by I50 and I0; on the other hand, WUE was higher in I0 than I50 and I100. At LAI values greater than 2.0, 85% photosynthetically active radiation was intercepted by the Saccharum stand, irrespective of the irrigation treatment. Saccharum spontaneum spp. aegyptiacum is a potential species for biomass production in environment characterized by drought stress, high temperatures and high VPD, as those of Southern Europe and similar semi-arid areas.

Leaf gas exchange, water status and radiation use efficiency of giant reed (Arundo donax L.) in a changing soil nitrogen fertilization and soil water availability in a semi-arid Mediterranean area

Abstract The aim of the present work was to ascertain, in a two-year field trial, leaf gas exchange, plant water status and radiation use efficiency of giant reed (Arundo donax L.) under different nitrogen fertilization and soil water availability in semi-arid Mediterranean area. Three levels of nitrogen (0, 60 and 120 kg N ha−1) and three levels of soil water availability (rainfed, 50% ETm restitution and 100% ETm restitution) were compared. Throughout the crop growing season significant effects of soil water availability, nitrogen fertilization and time of measurement on net photosynthesis (A), transpiration rate (E), stomatal conductance (gs), canopy temperature (Tc), midday (ψM) and predawn leaf water potential (ψPD) were found. Significant interactions of soil water availability x time of measurement were also observed, while nitrogen x time of measurement was significant only for A, gs, E and ψM. Radiation use efficiency (RUE) was lowest in rainfed and no-nitrogen fertilization (1.40 and 1.26 g MJ−1 in 1998 and in 1999, respectively) and highest in 100% ETm and 120 kg N ha−1 in both years (1.78 and 1.94 g MJ−1 in 1998 and in 1999, respectively). The fraction of intercepted PAR approached the asymptote when leaf area index was greater than 4.0, irrespective of soil water availability and nitrogen fertilization. The extinction coefficient (k) ranged from 0.38 to 0.44. Present results may have practical applications to help maximize physiological performances with improved WUE, optimized resource use efficiency and reduced irrigation demands.

Respuestas fisiológicas de Theobroma cacao L. en etapa de vivero a la disponibilidad de agua en el suelo

En el estudio se evaluó el efecto del déficit de agua en el potencial hídrico foliar y el intercambio de gases de plantas de tres clones de cacao (Theobroma cacao L.) en etapa de vivero. El experimento se estableció en un diseño de parcela dividida con arreglo de bloques aleatorizados y cinco repeticiones. La parcela principal correspondió a cuatro niveles de agua disponible en el suelo y la subparcela a plántulas injerta-das de tres meses de edad. Los resultados mostraron diferencias altamente significativas (P &amp;lt; 0.01) para los contenidos de agua en el suelo, pero no se encontraron diferencias entre los materiales evaluados. La pérdida de agua en el suelo disminuyó el potencial hídrico foliar (Ψf) y ocasionó el cierre de estomas alte-rando el intercambio de gases. El déficit de presión de vapor (DPV) se acentuó principalmente en horas del mediodía cuando aumentó la evapotranspiración. La magnitud del impacto del déficit hídrico depende de las variaciones climáticas a lo largo del día. Las variables climáticas que afectaron el desarrollo de la planta fueron la temperatura y la humedad relativa en forma de DPV. La fotosíntesis neta y el crecimien-to de las plántulas de cacao son variables fisiológicas muy sensibles al exceso y especialmente al déficit de agua.