Soil Water Deficit Conditions Research Articles

Selection of forage grasses for cultivation under water-limited conditions using Manhattan distance and TOPSIS.

Extreme weather events, such as severe droughts, pose a threat to the sustainability of beef cattle by limiting the growth and development of forage plants and reducing the available pasture for animals. Thus, the search for forage species that are more tolerant and adapted to soil water deficit conditions is an important strategy to improve food supply. In this study, we propose utilizing the mathematical concept of the Manhattan distance to assess the variations in the morphological variables of tropical forage grasses under water-limited conditions. This study aimed to select genotypes of tropical forage grasses under different water stress levels (moderate or severe) at this distance and the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS). Nine varieties from five species were examined. Forage grasses were grown in 12-L pots under three soil irrigation regimes [100% pot capacity-PC (well-irrigated control), 60% PC (moderate drought stress), and 25% PC (severe drought stress)] with four replicates. Drought stress treatments were applied for 25 days during the forage grass tillering and stalk elongation phases. After exposure to drought stress, the growth and morphological traits of forage plants were evaluated. The results show that the use of the Manhattan distance combined with TOPSIS helps in the genotypic selection of more stable tropical forage grass varieties when comparing plants exposed to moderate and severe drought conditions in relation to the nonstressful environment (control). The 'ADR 300', 'Pojuca', 'Marandu', and 'Xaraés' varieties show greater stability when grown in a greenhouse and subjected to water stress environments. The selected forage varieties can be used as parents in plant breeding programs, allowing us to obtain new drought-resistant genotypes.

Response of dew and hydraulic redistribution to soil water in a rainfed dryland jujube plantation in China’s Hilly Loess Region

Soil desiccation occurs widely across China’s Loess Plateau due to long-term water demand in excess of water supply. Hydraulic redistribution (HR) - the movement of water from wet to dry soil via roots - and canopy dew (CD) are crucial to water replenishment in dryland ecosystems. However, much is still not known about the response of CD and HR to soil water deficits (including no deficit, slight deficit, moderate deficit, and severe deficit water conditions) in dryland jujube (Ziziphus jujuba Mill.) plantations in China’s Hilly Loess Region. To this end, the duration and intensity of dew were monitored using dielectric leaf wetness sensors to better understand the effects of soil water status on dew. Also, soil water content, sap flow, and meteorological variables were measured during the jujube growing seasons in 2017–2019. The results showed that the time of occurrence of CD under the no deficit condition came earlier than the time of occurrence of CD under slight, moderate, and severe soil water deficit conditions. Peak CD appeared at 5:00–6:30 am and ended at 6:30–9:00 am local time under the four soil water conditions. The amount, duration, and frequency of CD decreased with increasing soil water deficit. The amount and duration of CD under the no deficit condition were significantly higher than under the slight, moderate, and severe soil water deficit conditions (p < 0.05). The amount and frequency of HR (in the 20–60 cm soil layer) increased with increasing soil water deficit. Under the no deficit condition, HR was significantly lower than under the slight, moderate, and severe soil water deficit conditions (p < 0.05). While HR was influenced by CD, CD enhanced HR under the no deficit condition, but inhibited HR under slight, moderate, and severe soil water deficit conditions. For the growing season, the contribution of CD to total actual evapotranspiration (ETc act, CD/ ETc act ratio) was highest under the no deficit condition (maximum CD/ ETc act ratio of 0.21). The contribution of HR to ETc act (HR/ ETc act ratio) was higher under slight, moderate, and severe soil water deficit conditions (maximum of 0.11). The mutual effects of CD and HR lessened soil water deficit, making them important ecohydrological processes affecting the response of dryland jujube plantations to soil desiccation.

Increased significance of chickpea (Cicer arietinum L.) senescence trait under water-deficit environment

Characterizing stress–inducing trait(s) and deploying their genetic diversity are crucial for developing stress–tolerant cultivar(s). The study aimed to investigate the genotypic variations in chickpea senescence traits and their significance in yield sustainability under water–deficit stress conditions. Therefore, a panel of eighty–eight chickpea that differ in maturity duration [early–maturing (≤ 100 days) and late–maturing (> 110 days)], were grown under soil water deficit conditions. The parameters viz. days to onset of senescence (DTSI), senescence duration (SD), days to flowering (DF), reproductive period (RP), and days to maturity (DM) were recorded for each genotype and their relations with grain yield were evaluated. The parameter DTSI defines the earliness or delay in the onset of senescence; while SD represents the pace of senescence. Temporal dynamics of senescence were visually scored following a 0–10 scale. The trait senescence duration (SD) exhibited negative correlation with yield, being higher in the late maturing genotypes over the early maturing genotypes. The senescence index [SD/RP], which exhibited a higher genotypic variability over the parameter SD, was found to have a significant negative association with yield. While the index [DTSI/DM] exhibited a strong positive correlation with yield (p < 0.01) in both early and late maturing groups (p < 0.01). Multivariate regression analysis demonstrated that SD and cumulative degree–days of senescence period had a strong negative influence on chickpea yield under water–deficit conditions. Hence, the study suggested that delayed and faster senescence could serve as the selection criterion for drought tolerance in chickpea. The findings suggested that the indices [SD/RP] and [DTSI/DM] could be more realistic indicators when characterizing senescence of chickpea under water–deficit environments.

Mycorrhizal Colonization Enhanced Sorghum bicolor Tolerance under Soil Water Deficit Conditions by Coordination of Proline and Reduced Glutathione (GSH).

Drought stress is an important limiting factor in crop production. Arbuscular mycorrhizal fungi (AMF) enhance plant drought tolerance through antioxidant activities. However, the coordination of nonenzymatic antioxidants against drought remains unclear. Here, we investigated the AMF symbiosis in drought tolerance of Sorghum bicolor by increasing proline and reducing glutathione (GSH). Glomus mosseae inoculation increased grain yield, biochemical content, and bioactivities of millets. Under drought conditions, seedlings inoculated with G.mosseae had higher SOD, POD, CAT, PPO, proline, and GSH activities compared to noninoculated controls. Meanwhile, a lower accumulation of MDA and H2O2 was observed in the G.mosseae seedlings. Furthermore, genes attributed to nonenzymatic antioxidants, such as GST29, P5CS2, FD3, GST, and GAD, were significantly up-regulated by G.mosseae under drought conditions. In conclusion, G.mosseae inoculation enhanced the drought tolerance of S.bicolor by improving reactive oxygen species (ROS) scavengers, including proline and GSH, that regulate ROS production and prevent oxidative damage.

Características morfológicas, fisiológicas e agronômicas de cruzamentos de cafeeiro 'Icatu' x 'Catimor' submetidos a deficit hídrico

Abstract The objective of this work was to select genotypes of Coffea arabica with good yield and potential tolerance to water deficit, as well as to try to understand the physiological and anatomical mechanisms involved in the adaptability of these genotypes to water stress. The physiological, anatomical, and agronomic traits of 19 genotypes of C. arabica were evaluated under the two following water conditions: regular irrigation and no irrigation (soil water deficit). The 'IPR 100', 2, 5, and 7 genotypes showed agronomic, physiological, and anatomical traits that contributed to a better water status maintenance in the initial development of coffee plants. Based on these results, these genotypes are potentially tolerant to water deficit. The 4, 10, 11, 14, 15, and 'Bourbon Amarelo IAC J10' genotypes show a lower adaptability of the anatomical structures under soil-water deficit conditions. The coffee tree genotypes display leaf plasticity, such as the thickness of palisade and spongy parenchyma, and the number, position, dimensions, and mobility of stomata under water deficit conditions.

Biomass yield and polyphenol compounds profile in globe artichoke as affected by irrigation frequency and drying temperature

Globe artichoke [Cynara cardunculus var. scolymus (L.) Fiori] is a proven source of nutraceutical compounds with high bioavailability. However, different pre- and post-harvest variables may affect plant secondary metabolism. In this view, the present study investigated the influence of irrigation frequency and drying temperature on the yield of dry leaf biomass and its pharmacological value in terms of polyphenol content. The field treatments included three irrigation frequencies (7, 14 and 21-day intervals) with a single dose of 10 mm water, and control (not irrigated). Artichoke biomass leaves were collected from 120-day plants and dehydrated using different air temperatures (30 °C, 40 °C, and 50 °C). The samples were analyzed for polyphenolic compounds by HPLC method. Antioxidant activity was also studied by ABTS, DPPH, and FRAP assays. Irrigation frequency significantly influenced the yield of dry leaf biomass with a greater increase in the case of irrigation frequency every 7 and 14 days than every 21 days. The content of caffeoylquinic acids (TCQA) was higher under soil water deficit conditions than in the raw material obtained from plants irrigated with different frequencies. The drought stress caused by the lack of additional irrigation increased the content of chlorogenic and ferulic acids in the biomass leaves. Higher drying temperatures (40 and 50 °C) increased the content of cynarine by 100% and 132% and ferulic acid by 100% and 172%, respectively, compared to biomass leaves dried at 30 °C. Irrigation frequency influenced the content of flavonoids, and frequency every 7 and 14 days than 21 days reduced apigenin and increased luteolin content. A high correlation between the content of TCQA and the frequency of irrigation and drying temperature was reported.

A Carica papaya L. genotype with low leaf chlorophyll concentration copes successfully with soil water stress in the field

In the context of increasing drought frequencies, water sensitive plant species need to have defined irrigation thresholds. One such species is papaya (Carica papaya L.), with a current demand for the selection of drought tolerance genotypes. The aim of this study was to evaluate the growth, leaf gas exchanges, sap flow and chlorophyll (Chl) fluorescence in two papaya genotypes (pale-green leaf ‘Golden’ - G and dark-green leaf ‘Aliança’ – AL) under soil water deficit (Ψsoil) conditions. The experiments were carried out in the field, in an unconsolidated alluvial sediment soil type. The two papaya genotypes, contrasting in their leaf Chl contents, were grown under irrigated (I, Ψsoil of -12 kPa), and non-irrigated (NI, Ψsoil gradually diminished from - 23 to -311 kPa) conditions for 41 days. Leaf gas exchanges, xylem sap-flow, green intensity (SPAD index), plant height, trunk diameter and leaf area were measured five times, following Ψsoil decreases. At the lowest Ψsoil (-311 kPa), the Chl photochemistry and fruit number measurements were performed. Intrinsic water use efficiency was higher in the GNI than in the ALNI genotype. Leaf temperature and photochemical efficiency was not affected by soil water restrictions in GNI and ALNI. The water deficit effect on growth traits was linked to whole canopy assimilation, due to the higher leaf area in ALI than GI, or in ALNI than in GNI, once the leaf assimilation rate was similar between those treatments. The ψsoil of ca. -30 kPa can be considered as a threshold for papaya irrigation for the soil type studied here. Soil water stress did not affect the number of fruits in GNI, whilst this was reduced by 83% in ALNI compared to irrigated plants, indicating that pale-green leaf papaya genotypes are an alternative to cope with water stress.

MdHB-7 Regulates Water Use Efficiency in Transgenic Apple (Malus domestica) Under Long-Term Moderate Water Deficit.

Improved water use efficiency (WUE) promotes plant survival and crop yield under water deficit conditions. Although the plant-specific HD-Zip I transcription factors have important roles in plant adaptation to various abiotic stresses, including water deficit, their functions in regulating WUE of apple (Malus domestica) are poorly understood. We characterized the role of MdHB-7 in WUE regulation by subjecting MdHB-7 transgenic plants to long-term moderate soil water deficit. The long-term WUE (WUEL) of transgenic apple plants with MdHB-7 overexpression or MdHB-7 RNA interference (RNAi) differed significantly from that of control plants. Upregulation of MdHB-7 caused reduced stomatal density, whereas the suppression of MdHB-7 increased stomatal density under both normal and long-term moderate soil water deficit conditions. Moderate reduction in stomatal density helped to improve the WUE of MdHB-7 overexpression transgenic plants, especially under water deficit conditions. MdHB-7 overexpression plants maintained high rates of photosynthesis that were conducive to the accumulation of biomass and the improvement of WUEL. MdHB-7 overexpression also alleviated the inhibition of root growth caused by long-term moderate soil water deficit and improved root vitality and hydraulic conductivity, which were essential for improving plant WUEL. By contrast, MdHB-7 RNA interference reduced the WUEL of transgenic plants by inhibiting these factors under normal and long-term moderate soil water deficit conditions. Taken together, our results provide solid evidence for a crucial role of MdHB-7 in the regulation of apple WUEL and provide new insights for improving the WUE of apple plants under moderate soil water deficit.

Foliar Application of Salicylic Acid Improves Water Stress Tolerance in Conocarpus erectus L. and Populus deltoides L. Saplings: Evidence from Morphological, Physiological, and Biochemical Changes.

Reforestation efforts are being challenged as water stress is hampering the sapling growth and survival in arid to semiarid regions. A controlled experiment was conducted to evaluate the effect of foliar application of salicylic acid (SA) on water stress tolerance of Conocarpus erectus and Populus deltoides. Saplings were watered at 90%, 60%, and 30% of field capacity (FC), and half of the saplings under 60% and 30% FC were sprayed with 1.0 mM SA. Results indicated that dry weight production decreased significantly in Populus deltoides under both water deficit conditions, and leaf gas exchange parameters decreased significantly in both the species under both soil water deficit conditions. Foliar application of SA resulted in a significant increase in leaf gas exchange parameters, and compatible solutes, thereby increasing the dry weight production in both of the species under soil water deficit. Oxidative stress (hydrogen peroxide and superoxide anions) increased under soil water deficit and decreased after the foliar application of SA and was parallel to the increased antioxidant enzymes activity (superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase). Therefore, it can be concluded that foliar application of 1.0 mM SA can significantly improve the water stress tolerance in both species, however, positive impacts of SA application were higher in Conocarpus erectus due to improved photosynthetic capacity and increased antioxidant enzyme activity.

Mycorrhizal mixtures affect the growth, nutrition, and physiological responses of soybean to water deficit

Drought stress has a negative impact on crop growth and productivity worldwide. Plant symbionts such as arbuscular mycorrhizal fungi (AMF) can enhance plant growth and improve plant resistance to drought stress. AMF mixture inocula and plant responses to drought still require further study. The objective of this study was to investigate the effects of non-inoculation (NM) or inoculation with three commercial AMF inocula containing a single or mixtures comprising different numbers of AMF species: M1 (Rhizophagus intraradices), M2 (Rhizophagus clarus, R. intraradices, Septoglomus deserticola, Funneliformis mosseae), and M3 (Rhizophagus intraradices, R. aggregatum, Funneliformis mosseae, Olaroideoglomus etunicatum) on growth, nutritional, and physiological responses of soybean (Glycine max L. cv. Hutcheson) grown in a greenhouse under different water stress levels [WW = well watered (90% FC), MS = medium (60% FC) and SS = severe stressed (30% FC)]. The AMF-inoculated plants had significantly higher plant biomass, chlorophyll content, stomatal conductance, leaf water relations, and mineral contents in comparison to NM plants. Applied mycorrhizal inocula differed in their response to water-deficit conditions. M2 inoculant generally supported greater plant biomass, stomatal conductance, leaf water content, and leaf N, P, K, S, Mn, and Cu contents than M1 and M3 inocula, especially under MS and SS treatments. These results indicated that all mycorrhizal inocula supported plant growth both generally and with soil water deficit; however, M2-inoculated plants performed better than M1 and M3 under drought stress. Therefore, mycorrhizal inocula are effective for supporting soybean growth and offsetting the effects of drought and AMF technology that can support sustainable crop cultivation under soil water-deficit conditions. Different types of inocula have different effects, however, and thus require testing for individual crops.

Physiological quality of maize seeds produced under soil water deficit conditions

ABSTRACT Crop strategies focused on the rational use of water are required in semiarid regions. Thus, the objective of this work was to evaluate the physiological quality of maize seeds produced under soil water deficit conditions. Five irrigation water depth were established, based on the field capacity (100, 85, 70, 55 and 40%), to control the available water for two maize hybrids (2B-587 and DKB-390). A randomized block design was used, with a split-plot arrangement and four repetitions. The plots consisted of irrigation water depths, and the subplots consisted of maize hybrids. The seed water concentration, germination, and vigor were determined after the harvest, using data from first germination counting, seedling emergence, germination speed index, seedling length, and accelerated aging, electrical conductivity, and modified cold tests. The maize hybrid DKB-390 showed better physiological potential under the soil water deficit conditions evaluated. The irrigation water depths lower than 70% of field capacity resulted in decreases in soil water contents and affected negatively the physiological quality of the maize seeds produced.

Soil organic matter dynamics and microbial metabolism along an altitudinal gradient in Highland tropical forests

The highland forests of tropical regions are highly vulnerable to climate change because changes in soil organic quality due to the increased soil water deficit conditions through rising temperatures. Several authors have reported that labile molecules dominate soil organic matter at higher elevations, and it is therefore more vulnerable to the rising temperatures associated with climate change. The objective of the present study was to analyze the effect of interaction between the chemical composition of organic matter derived from the dominant plant species and the metabolism of microbial community along an elevational gradient in a highland forest in Central Mexico. The study compared three vegetation-soil systems that represent three different elevational levels: Alnus-system (3100 m.a.s.l.), Abies-system (3500 m.a.s.l.) and Pinus-system (3700 m.a.s.l.). The SOM produced in the lowest site is more recalcitrant (i.e., higher Alkyl:O-Alkyl ratio) as a result of the lower water availability than in the highest site. The results of Threshold Elemental RatioC:N (TERC:N) and TERC:P for the organic layer were lower than their C:N and C:P ratios in the organic layer, supporting that the microbial community of the organic layer in the site of lowest elevation must be limited by the carbon source, rather than by N and P. However, these results were not found in the mineral soil, suggesting that the drivers of organic matter decomposition differ between the organic layer and the mineral soil. As a conclusion, our results suggest that the chemical recalcitrance of organic matter (at the lowest site) and temperature (at the highest site) reduce the microbial metabolic activity in the forest floor. Integrated study of plant-derived organic material and the microbial metabolism of the forest floor is therefore required to achieve a full understanding of the vulnerability of tropical mountain ecosystems to climate change.

Effects of Growth Medium and Water Stress on Soybean [Glycine max (L.) Merr.] Growth, Soil Water Extraction and Rooting Profiles by Depth in 1-m Rooting Columns.

The pattern of soil water availability in frequently watered small pots is different from field environments. In small pots, volumetric soil water content (VSWC) is relatively high throughout the rooting zone due to a lack of suction to remove water from large and midsize capillaries. This necessitates the use of growing media with large pore space to avoid anaerobic conditions and so prohibits the use of field soil (FS) in small pots. We hypothesized that in 1-m rooting columns, the 0.01-MPa gravitational potential difference between top and bottom may permit the use of lightly-amended FS as a growing medium and provide for realistic VSWC and rooting profiles by depth. This study aimed to investigate the effects of amending a typical sand-based potting mix with different proportions of FS on soybean growth [dry matter (DM) accumulation], water use, VSWC and rooting profiles by depth under control and water stress conditions, in 1-m rooting columns (polyvinyl chloride tubes having an inside diameter of 10 cm and length of 1 m). We tested three growth media (0, 50, and 67% FS mixes), watered daily to either 100% of the maximum soil water holding capacity (SWHC; control) or 75% SWHC (stress). VSWC was calculated from time-domain reflectometry measurements. Compared to all growth media, the 67% FS mix resulted in the highest DM accumulation, water use, water use efficiency (WUE), and also produced realistic VSWC and rooting profiles by depth similar to those reported in the literature under field conditions. Compared to the control, the water stress treatment reduced shoot DM by 24%, root DM by 13%, whole-plant DM by 22%, and water use by 25%, but increased root-to-shoot DM ratio by 18% and WUE by 6%. Of the three growth media tested, the 67% FS mix was the most suitable growth medium for controlled environment phenotyping studies of root functional traits affecting drought tolerance in soybean. This study provides novel phenotyping tools to select for root function and yield formation traits that could increase soybean yield under soil water deficit conditions.

Performance Assessment of Chlorophyll Meter to Determine When to Irrigate Wheat under Different Soil Moisture Deficit Conditions: An Initial Study

ABSTRACTProper irrigation timing can minimize the negative impacts that reduce crop yields. Therefore, in an initial pot experimental study, we assessed the SPAD (Soil–Plant Analysis Development)-chlorophyll meter as a tool to determine proper irrigation timing of wheat under different soil water deficit conditions in a controlled-environment greenhouse. The treatments were controlled irrigation at 100% (T1), 70% (T2), 50% (T3) and 30% (T4) of soil water content at field capacity; and the growth stages were development, mid-season and late-season. SPAD readings were measured pre-irrigation events. The results indicated that the T3 and T2 achieved maximum grain yield per accumulated crop evapotranspiration, i.e. water productivity (0.82 and 0.76 kg m−3), and were at par with T1. Moreover, the SPAD readings had a high Pearson’s correlation coefficient with crop evapotranspiration (r = 0.95; P ≤ 0.001) and wheat grain yield (r = 0.90; P ≤ 0.001), indicating that SPAD reading could be used to reliably estimate when to irrigate wheat. Therefore, T3 and T2 SPAD readings were averaged to estimate a target limit at which irrigation should be applied. Accordingly, the target limit was defined as >44.76 for the development stage, >50.72 for the mid-season stage, and >37.64 for the late-season stage; readings below this target limit indicate that it is time to irrigate.

A method to assess the impact of soil available water capacity uncertainty on crop models with a tipping‐bucket approach

AbstractMost agronomic crop models use a reservoir tipping‐bucket approach to model the water budget in the soil. Soil available water capacity (AWC) is the main soil property considered in this approach. Because AWC is difficult to measure, uncertainty in AWC may be high. We developed a method using a specific kriging technique to determine the effects of uncertainty in AWC on crop model predictions. The AqYield crop model was used as an example to assess the effects of uncertainty in AWC on two agronomic output variables (grain yield and drainage). The factors considered were the climatic region, crop type and soil depth. We assessed the results using the coefficient of variation (CV) and sets of critical values for which CV exceeded 5, 10 and 15%. The experiment provided insight into the criticality of AWC uncertainty over a wide range of agropedoclimatic situations according to crop, model and output of interest. The method revealed the greater effect of AWC uncertainty on both outputs for the spring crop than for the winter crop and identified cases where AWC uncertainty was critical. There was a stronger effect of AWC uncertainty on yield for shallow soil and climatic water deficit conditions. For each situation, the AWC uncertainty levels were determined above or below which the impact becomes significant on a given output because the sensitivity was very dependent on climate–crop–soil combinations. It was also observed that uncertainty in AWC had little effect in AqYield for a wide range of situations. The method developed uses a small number of model simulations to produce accurate results to better understand the impact of this major soil input data according to the target model and specific objectives. It could help to determine the level of accuracy needed in AWC measurement, depending on the objectives.Highlights The method quantifies the effects of AWC uncertainty on crop models with a tipping‐bucket approach. This method can assess the impact of uncertainty with only a few runs using a kriging approach. The method identifies critical situations for a wide range of agropedoclimatic conditions. Critical region graphs give critical thresholds for accuracy needed in AWC.

Physiological, biochemical and molecular responses to drought conditions in field-grown grafted and ungrafted citrus plants

The physiological, biochemical and molecular alterations developed by plants under soil water restriction, especially rootstock, is important to elucidate the mechanisms associated to drought tolerance. In order to verify the influence of rootstock and grafting on drought tolerance of citrus plants, we examined water status, photosynthesis, oxidative stress and gene expression in grafted and ungrafted citrus plants subjected to different soil water regimes (well-watered, moderate and severe drought and rehydrated) under field conditions. Analysis were performed in roots and leaves of six plant combinations: ungrafted ‘Rangpur Santa Cruz’ lime (RL) and ‘Sunki Maravilha’ mandarin (SM), RL and SM grafted onto themselves (RL/RL and SM/SM) and ‘Valencia’ sweet orange (VO) grafted onto RL or SM (VO/RL and VO/SM). Drought stress reduced chloroplastid pigment contents and limited the photosynthetic rate, mainly in RL/RL plants. In contrast, the lowest leaf osmotic potential, the best osmotic adjustment and the greater phenotypic plasticity were observed in SM, SM/SMand VO/SM plants. Phenotypic plasticity and the main components of multivariate analysis showed that the physiological variables, such as Fv/F0, F0/Fm and Fv/Fm, were more responsive to soil water deficit. An increase in the superoxide dismutase (SOD) activity and transcript abundance of mitochondrial SOD [Mn-Fe], especially in the scion onto RL, and chloroplastidic SOD [Cu -Zn], inthe scion onto SM, was also observed under water deficit. Besides, an induction of transcription of genes coding for catalase (CAT X2) and ascorbate peroxidase (APX) was also observed, respectively, in leaves and roots of plants subjected to water deficit. However, such transcription increment did not affect the activity of these enzymes, especially in RL/RL plants. RL plants were more effective in soil water extraction than SM plants, evidenced mainly by the maintenance of leaf gas exchange and increase in the leaf relative water content after rehydration. The grafted plants showed alterations in their responses to the stress factor, expressed by a reduction of photosynthetic rates, changes in pigment contents, activity of antioxidant enzymes and expression of genes associated to the antioxidant metabolism, mainly in RL/RL plants. Plants with ‘Valencia’ scion, regardless of the rootstock studied, showed similar physiological, biochemical and molecular responses when exposed to soil water deficit. Multivariate analysis showed that Fv/F0, F0/Fm and Fv/Fm were the most important physiological variables for discriminating citrus plants subjected to control and soil water deficit conditions.

Combining Electrical Resistivity Tomography and Satellite Images for Improving Evapotranspiration Estimates of Citrus Orchards

An adjusted satellite-based model was proposed with the aim of improving spatially distributed evapotranspiration (ET) estimates under plant water stress conditions. Remote sensing data and near surface geophysics information, using electrical resistivity tomography (ERT), were used in a revised version of the original dual crop coefficient (Kc) FAO-56 approach. Sentinel 2-A imagery were used to compute vegetation indices (VIs) required for spatially estimating ET. The potentiality of the ERT technique was exploited for tracking the soil wetting distribution patterns during and after irrigation phases. The ERT-derived information helped to accurately estimate the wet exposed fraction (few) and therefore the water evaporated from the soil surface into the dual Kc FAO-56 approach. Results, validated by site-specific ET measurements (ETEC) obtained using the eddy covariance (EC) technique, showed that ERT-adjusted ET estimates (ETERT) were considerably reduced (15%) when compared with the original dual Kc FAO-56 approach (ETFAO), soil evaporation overestimation being the main reason for these discrepancies. Nevertheless, ETFAO and ETERT showed overestimations of 64% and 40% compared to ETEC. This is because both approaches determine ET under standard conditions without water limitation, whereas EC is able to determine ET even under soil water deficit conditions. From the comparison between ETEC and ETERT, the water stress coefficient was experimentally derived, reaching a mean value for the irrigation season of 0.74. The obtained results highlight how new technologies for soil water status monitoring can be incorporated for improving ET estimations, particularly under drip irrigation conditions.

Effect of the water stress on gross primary production modeling of a Mediterranean oak savanna ecosystem

Abstract. Dehesa ecosystem consists of widely-spaced oak trees combined with crops, pasture and Mediterranean shrubs. It is located in the southwest of the Iberian Peninsula, where water scarcity is recurrent, severely affecting the multiple productions and services of the ecosystem. Upscaling in situ Gross Primary Production (GPP) estimates in these areas is challenging for regional and global studies, given the significant spatial variability of plant functional types and the vegetation stresses usually present. The estimation of GPP is often addressed using light use efficiency models (LUE-models). Under soil water deficit conditions, biomass production is reduced below its potential rate. This work investigates the effect of different parameterizations to account for water stress on GPP estimates and their agreement with observations. Ground measurements of GPP are obtained using an Eddy Covariance (EC) system installed over an experimental site located in Córdoba, Spain. GPP is estimated with a LUE-model in the footprint of the EC tower using several approaches: a fixed value taken from previous literature; a fixed value modified by daily weather conditions; and both formulations modified by an additional coefficient to explicitly consider the vegetation water stress. The preliminary results obtained during two hydrological years (2015/2016 and 2016/2017) are compared, focusing on specific wet and dry periods.

Using field measurements and FAO-56 model to assess the eco-physiological response of citrus orchards under regulated deficit irrigation

Micro-irrigation is considered one of the most efficient water distribution systems and allows increasing water use efficiency if coupled with effective water-saving irrigation management strategies as regulated deficit irrigation (RDI) or partial root-zone drying (PRD) techniques. However, application of these strategies makes it crucial the real-time monitoring of soil and crop water status, in order to identify appropriate irrigation scheduling parameters (irrigation timing and doses) and to prevent irreversible damage of plant system and/or crop yield reductions.Even if midday stem water potential (MSWP) is considered one of the most affordable indicator for direct determinations of crop water status, its measurement requires skilled operators, is destructive and time consuming, so that indirect and fast estimations are desirable. In this direction, agro-hydrological models can be considered an easy-to-use tool for indirect evaluations of soil and crop water status aimed to identify irrigation scheduling parameters even when micro-irrigation distribution systems and water saving management strategies are adopted.The paper, after examining the eco-physiological response of citrus orchards to soil water deficit, assessed the potential of FAO-56 agro-hydrological model to identify the crop water stress under different irrigation management strategies.Experiments carried out during three years (2009–2011) allowed identifying the crop water stress response to soil water deficit conditions, also confirming the schematization proposed in FAO-56 paper for citrus orchards. Moreover, after evaluating the similarity between the measured MSWP with the simulated crop water stress coefficient, Ks, it was proved the fairly good performance of FAO-56 agro-hydrological model to predict soil water content (RMSE=0.04m3m−3), from one side, and the crop response to different irrigation management strategies, from the other.The obtained results evidenced that the crop water stress coefficient estimated by the model can be used as a suitable indicator to replace the tedious and time-consuming field measurements of MSWP.

Drought-Induced Leaf Proteome Changes in Switchgrass Seedlings.

Switchgrass (Panicum virgatum) is a perennial crop producing deep roots and thus highly tolerant to soil water deficit conditions. However, seedling establishment in the field is very susceptible to prolonged and periodic drought stress. In this study, a “sandwich” system simulating a gradual water deletion process was developed. Switchgrass seedlings were subjected to a 20-day gradual drought treatment process when soil water tension was increased to 0.05 MPa (moderate drought stress) and leaf physiological properties had expressed significant alteration. Drought-induced changes in leaf proteomes were identified using the isobaric tags for relative and absolute quantitation (iTRAQ) labeling method followed by nano-scale liquid chromatography mass spectrometry (nano-LC-MS/MS) analysis. Additionally, total leaf proteins were processed using a combinatorial library of peptide ligands to enrich for lower abundance proteins. Both total proteins and those enriched samples were analyzed to increase the coverage of the quantitative proteomics analysis. A total of 7006 leaf proteins were identified, and 257 (4% of the leaf proteome) expressed a significant difference (p < 0.05, fold change <0.6 or >1.7) from the non-treated control to drought-treated conditions. These proteins are involved in the regulation of transcription and translation, cell division, cell wall modification, phyto-hormone metabolism and signaling transduction pathways, and metabolic pathways of carbohydrates, amino acids, and fatty acids. A scheme of abscisic acid (ABA)-biosynthesis and ABA responsive signal transduction pathway was reconstructed using these drought-induced significant proteins, showing systemic regulation at protein level to deploy the respective mechanism. Results from this study, in addition to revealing molecular responses to drought stress, provide a large number of proteins (candidate genes) that can be employed to improve switchgrass seedling growth and establishment under soil drought conditions (Data are available via ProteomeXchange with identifier PXD004675).