Soil Water Potential Research Articles

Hydraulic architecture of seedlings and adults of Rhizophora mangle L. in fringe and scrub mangrove

Background: Mangrove plant species have distinctive anatomical and physiological responses to cope with a wide range of salinities and inundations. These strategies pertain a safe and efficient water use and transport, essential for survival.
 Questions: How are the anatomical and physiological attributes of the hydraulic architecture of seedlings and adults of Rhizophora mangle ? what are the changes in hydraulic architecture of seedlings and adults of R. mangle in contrasting microenvironments?
 Studied species: Rhizophora mangle L. (Rhizophoraceae).
 Study site and dates: Scrub and fringe mangroves in Ria Celestún Biosphere Reserve, during the rainy season of 2013 (July to October).
 Methods: Hydraulic conductivity and leaf water potential, as well as xylem vessel density, length, transversal and radial diameter, and area were measured for seedlings and adults from both sites. The prevailing environmental conditions (soil water potential, salinity, photon flux density, air temperature and relative humidity) were also characterized.
 Results: A safer hydraulic conduction system, with narrow and more grouped vessels, was observed in seedlings than in adults of R. mangle in both sites. Adult individuals from the scrub mangrove, in the hyper saline microenvironment, had a safer hydraulic conduction system than adults in the fringe mangrove.
 Conclusions: The seedling stage of R. mangle showed a safer hydraulic system than adults in both types of mangroves. However, over time this hydraulic conduction system could become more efficient or remain safe depending on the microenvironment in which individuals are growing.

Study on the immobile water of saturated compacted clay-rich materials by oil seepage

Immobile water is defined as a firmly bound thin film of water surrounding clay particles that somehow resembles solid features. The characteristics and amount of immobile water depend on pore water chemistry, the type of clay, and the contact area of water with particles. Seepage can occur only when the hydraulic gradient increases sufficiently. To date, no accurate method is available to determine the immobile water content. Therefore, an approach is proposed for direct measurement of the immobile water content, which applies vegetable oil to displace water in saturated compacted clay-rich materials. Under a high hydraulic gradient, the vegetable oil completely displaces the free porewater in the clay-rich materials, and the remaining residual water is assumed to be immobile water. By using carbon tetrachloride (CCl4) as an extracting agent, the oil in the permeated sample was subjected to extraction and distillation, and the total liquid content was determined by the oven-drying method. As a final step, the immobile water content in the sample was calculated. A high-speed centrifugation method was used to determine the immobile water content from the corresponding soil water potential, which accounted for approximately 634.3 kPa. It was found that the immobile water of the clay-rich materials was essentially equal to the bound water. The effective porosity of clay was obtained based on the immobile water content. By comparing the relationship between porosity, effective porosity and hydraulic conductivity, the effective porosity revealed an improved linear relationship with log (k). The test results show the oil seepage method to be useful and reliable for the quantification of the immobile water content of saturated compacted clay-rich materials.

The sensitivity of C and N mineralization to soil water potential varies with soil characteristics: Experimental evidences to fine-tune models

The sensitivity of C and N mineralization in soil to water potential is mostly described in simulation models as a linear function independent of the pedoclimatic conditions. We hypothesized that water sensitivity could be site-specific and dependent of climate or soil properties. In this study, we characterized the responses of C and N mineralization to water stress in ten soils representing a range of French arable cropping systems and evaluated whether the responses differ between soils and pedoclimatic contexts. C and N mineralization kinetics were quantified in laboratory incubations at four soil water potentials (pF) ranging from pF = 2.0 (∼field capacity) to 4.2 (∼permanent wilting point). The C and N mineralization rates, calculated by curve fitting, were linearly correlated with pF or relative water content (RWC). The slope of the linear regression, representing the sensitivity to water potential, differed significantly between sites, ranging from 0.12 to 0.35 pF-1 for C mineralization and 0.20 to 0.44 pF-1 for N mineralization. The sensitivity of C or N mineralization rate to pF or RWC could be well predicted by a couple of two soil properties: either microbial quotient (ratio of microbial biomass-C to total organic C) and soil pH or soil organic C:N ratio and soil pH. The sensitivity of soil to water stress was more accurately predicted by these site-specific variables than a model common to all pedoclimatic conditions. These results open the possibility of improving soil and soil-crop models for a more accurate prediction of water stress on C and N mineralization particularly in the context of climate change.

Selenium improved antioxidant response and photosynthesis in fragrant rice (Oryza sativa L.) seedlings during drought stress.

Drought stress substantially influences the growth and development of many crops. The present study was conducted to investigate the effects of exogenous selenium on the growth, photosynthesis and antioxidant response of fragrant rice seedlings under drought stress. In a pot experiment, fragrant rice seedlings were subjected to drought stress (soil water potential was controlled at - 0.025 ± 5MPa) and foliar application of selenium (Se) at 0, 10, 30, and 50μmol L-1. Rice seedlings not exposed to drought stress and Se were used as control. Exposure of fragrant rice seedlings to drought stress resulted in significant (P < 0.05) decrease in fresh weight, dry weight, plant height and stem diameter relative to the control. Total chlorophyll, chlorophyll a, chlorophyll b and carotenoid were 20.54-27.24%, 20.82-26.83%, 19.45-29.07% and 21.49-29.17% lower with drought stress treatment compared to CK. Drought stress also significantly (P < 0.05) decreased net photosynthetic rate and soluble protein content. However, Se treatments (30 and 50μmol L-1) substantially improved fresh weight and dry weight of fragrant rice seedlings under drought stress. Net photosynthetic rate, activities of antioxidant enzymes (GPX, SOD and CAT) and soluble protein content in rice seedlings under drought stress improved due to Se treatment. Higher transcript levels of antioxidant-related genes (GPX1, GPX4, CATA and CATC) were also observed with Se treatment.

Validating the Generality of a Closed-Form Equation for Soil Water Isotherm

Total soil water potential ψt is conventionally defined as the sum of matric potential ψm and osmotic potential ψo, i.e., ψt=ψm+ψo, when gravitational potential is ignored. Soil water isotherm (SWI) is the constitutive relationship between ψt and soil water content w, i.e., ψt(w)=ψm(w)+ψo, where ψm(w) is called soil water retention curve (SWRC) or soil water characteristic curve. SWI and SWRC are arguably the two most important soil constitutive relationships because they govern virtually all phenomena in soil such as flow, stress and deformation, and biological activities. A closed-form SWI, recast from a generalized SWRC equation for adsorption and capillarity, is experimentally validated for its generality in representing SWI. Adsorption isotherms of 49 soils, covering all spectrum of soil types with plasticity index up to 185% and specific surface area up to 600 m2/g, are used to validate the SWI equation. It is shown that the SWI equation can nearly perfectly represent the isotherms of these soils with almost all of the coefficients of determination R2≥0.99, validating the generality of the SWI equation. Comparative analysis is also conducted by using two existing SWI equations, namely, the Brunauer–Emmett–Teller (BET) equation and the augmented BET (A-BET) equation. It is demonstrated that the SWI equation is superior to the BET and A-BET equations in representing soil–water interactions by adsorption and capillarity, and in the full relative humidity range.

A hierarchical approach to understanding physiological associations with climate

AbstractAimOur understanding of species’ responses to climate depends on choosing the scale for the analysis. Processes driving physiological adaptation that occur at the small spatial scales most relevant to animals may be masked in correlations between organismal traits and broad‐scale climatologies, but the extent to which this undermines our understanding of the macroevolution of physiological traits is unknown.LocationGlobal.Time periodCurrent.Major taxa studiedLizards.MethodsWe investigated relationships between physiological traits (water loss rate, standard and field metabolic rates, thermal preferences and critical thermal limits) and environmental conditions in 369 lizard species across sets of environmental predictors representing different processes across hierarchically nested spatial scales: macroclimate, microclimate and biophysical.ResultsWe found that microclimatic and biophysical predictors had greater explanatory power than macroclimatic predictors for all traits except standard and field metabolic rates. Across spatial scales, standard metabolic rate was negatively related to maximum temperatures whereas field metabolic rate was positively related to minimum temperatures. Thermal preference and critical limits showed expected relationships with environmental temperature, but preferred temperature and critical thermal maxima were most strongly associated with soil water potential, as was evaporative water loss.Main conclusionsThe use of proximal environmental predictors, via the principles of microclimatic and biophysical modelling, can be more informative in comparative physiological analyses than the more traditional application of macroclimatic data. In our study it led us to new, testable hypotheses about the role of habitat structure mediated by soil moisture. New datasets and computational methods mean that proximal environmental predictors can be readily computed for any kind of organism and their application to comparative studies should improve our understanding of physiological evolution.

Rhizosphere water content drives hydraulic redistribution: Implications of pore-scale heterogeneity to modeling diurnal transpiration in water-limited ecosystems

Trees typically survive prolonged droughts by absorbing water from deeper layers. Where soils are shallow, roots may be extract water from the underlying fractured bedrocks. In dry seasons, surface-soil moisture dynamics reflect hydraulic redistribution (HR). HR is usually estimated based on the gradient of mean, or bulk, soil water potential among layers in the rooting zone (HRB). This approach neglects the potential effect of spatial heterogeneity of water content at the millimeter scale between the rhizosphere and bulk soil. We proposed to account for the rhizosphere water balance, estimating HR to the rhizosphere (HRR) of the dry surface soil from the underlying fractured rock. The model was evaluated using a 15-year dataset collected in Sardinia. When the typical approach, based on moisture gradients among bulk soil layers, was used for estimating HRB, tree transpiration was underpredicted in all seasons, especially in spring and summer. Forcing the model with measured tree transpiration, HRB decreased during spring and summer, while the contribution of the underlying rock layer to tree transpiration was threefold that estimated using HRR-based model. The average water content of the bulk surface soil layer was very low, reaching 0.06 in the driest summers while showing little diurnal dynamics; however, concentrating water in roughly estimated rhizosphere volume, produced rhizosphere water content appreciably higher (≈0.16), and much more dynamic. Predicted HRR dominated evapotranspiration (60% - 65%) in dry springs and summers reaching 80% of tree transpiration. Most importantly, the proposed rhizosphere-HR model correctly predicts the diurnal dynamics of tree transpiration year-round, and the grass transpiration in its active spring period. Eco-hydrological models operating at sub-daily scale should consider partitioning the soil to rhizosphere volume, thus allowing both diagnostic and prognostic estimates of diurnal biosphere-atmosphere mass and energy exchanges.

Response of Primed Rice (Oryza sativa L.) Seeds towards Reproductive Stage Drought Stress

Seed priming could be promoted as a potential alternative in alleviating drought stress challenges in rice cultivation. The present study was conducted as an attempt to verify potential performance of seed priming in improving seedling growth and harvestable grain yield of rice under reproductive stage drought stress (RS). Seed treatments involved were non-primed seeds as control (T1), hydro-primed (T2) and osmo-primed at -1.0 mPa with polyethylene glycol (PEG6000) (T3). Reproductive stage drought stress (RS) was imposed at soil water potential lower than -60 kPa. The well-watered plants served as control of the experiment. In general, seedling growth of T3 was better than T2 and T1 for all growth parameters in both planting seasons. Yield components were significantly lower in RS as compared to well-watered treatment (WW). The agronomic performance of primed seeds in T2 and T3 were not significantly different with T1 under both RS and WW for both planting seasons. As a conclusion, seed priming treatments used in this study was ineffective in improving agronomic performance of rice under RS. Therefore, other alternatives such as development of drought tolerant rice should be highly emphasized in order to minimize the impact of drought on growth and yield of rice plant.

Water use efficiency of castor bean under semi-arid conditions of Brazil

Castor bean is one of the main and promising agricultural crops for the production of biodiesel, castor oil and castor bean cake, which have high added value, especially the castor oil. The objective of the present study was to evaluate the water use efficiency (WUE) of castor bean cultivars by assessing the soil water balance components (storage and water storage variation; internal drainage; capillary rise; irrigation depth; rainfall and actual evapotranspiration), according to the phenological stages. The experimental design was in randomized blocks, in 8 × 6 factorial scheme (eight cultivars: BRS Paraguaçu; EBDA MPA11; EBDA MPB01; IAC 2028; IAC 226; BRS Nordestina; IAC Guarani, AG IMA 110–204 and BRS Energia and six periods of evaluation), with three repetitions and 15 plants in each experimental plot. Daily monitoring of soil water content was performed with a capacitance probe (Frequency Domain Reflectometry - FDR, PR2/6 model), at depths of 0.1, 0.2, 0.3, 0.4 and 0.6 m, with 0.6 m being the lower limit of the soil control volume for castor bean. The total soil water potential gradient was determined with tensiometers installed at depths of 0.5 and 0.7 m, and the flux densities were estimated using the Darcy-Buckingham equation. Supplemental irrigation was efficient in maintaining water availability during the crop cycle. Soil water storage was lower for the most productive castor bean cultivar (EBDA MPA 11), with an inverse relationship between yield and water storage, due to its water requirement. The highest and lowest values of internal drainage and capillary rise were found for BRS Nordestina and IAC 226, respectively. EBDA MPA 11 had the best water use efficiency among the castor bean cultivars, differing only from IAC Guarani and EBDA MPB 01.

Breeding phenology of a terrestrial‐breeding frog is associated with soil water potential: Implications for conservation in a changing climate

AbstractAmphibian breeding is often linked to environmental cues. Given accelerating global climate change and habitat alteration, it is important to understand how environmental changes may affect male calling activity, the necessary precursor to mating. Here, we investigate the calling phenology and activity of Geocrinia alba, a critically endangered terrestrial‐breeding frog with a highly restricted distribution in southwestern Australia – a region undergoing significant warming and drying. We investigated whether calling periods differed across eight sites during a single breeding season, and the environmental conditions associated with calling activity at the start, peak and end of the calling period. We found consistent and prolonged calling activity over several months of the austral spring, but the length of the calling period varied two‐fold across sites, ranging from 3 to 6 months. Initiation of calling by G. alba was relatively similar across sites and was associated with warmer temperatures and higher soil water potential. However, the end of the calling period varied from October to January and was significantly associated with decreasing soil water potential. Calling only occurred when soils were close to saturation point, between −8 to −11 kPa, and therefore, breeding opportunities were likely also constrained by the length of time that soils were close to saturation. Changes in the regional climate, such as declining winter rainfall, could result in shorter breeding periods and consequently reduced breeding opportunities. More broadly, our study highlights the sensitivity of amphibians, particularly terrestrial‐breeding species, to changes in soil water potential and temperature, and the importance of maintaining suitable hydrological conditions during the breeding period.

Photosynthetic physiological response of water-saving and drought-resistant rice to severe drought under wetting-drying alternation irrigation.

Water-saving and drought-resistant rice (WDR) is widely grown in central China in recent years. However, studies have not explored the interaction effect of WDR and irrigation regimes on drought-resistance capacities under severe drought at sensitive growth periods. A pot experiment was conducted using a WDR cultivar Hanyou73 (HY73) and traditional high-yielding and drought-sensitive cultivar Huiliangyou 898 (HLY898). Three irrigation regimes, including flooding irrigation (W1), mild wetting-drying alternation irrigation (W2), and severe wetting-drying alternation irrigation (W3), were applied before heading. At heading, severe drought with -50 KPa soil water potential was established for all treatments and cultivars. The findings showed that cultivar HY73 under W2 treatment had the highest yield, 1000-grain yield, filled grain, relative water content, and photosynthesis potential compared with the other combinations. The higher net photosynthetic rate (Pn ) was attributed to larger mesophyll conductance (gm ) in drought for cultivar HY73 under W2 treatment compared with that for cultivar HLY898 and the other water treatments. Enhanced photo-respiration rate may be an important photoprotection mechanism for achieving high Pn for cultivar HY73 coupled with W2 treatment than for other combinations in drought. The relative expression level of OsPIP1;1 gene was significantly down-regulated during drought in all cultivars and water regimes. But OsPIP1;2, OsPIP2;3, OsTIP2;2, and OsTIP3;1 genes were upregulated to alleviate the significant decrease in gs and gm under drought. These results suggest that WDR and mild wetting-drying alternation irrigation (W2) have significant interaction effects in improving photosynthetic production potential by maintaining higher gm under severe drought.

Arbuscular Mycorrhiza Symbiosis Enhances Water Status and Soil-Plant Hydraulic Conductance Under Drought.

Recent studies have identified soil drying as a dominant driver of transpiration reduction at the global scale. Although Arbuscular Mycorrhiza Fungi (AMF) are assumed to play a pivotal role in plant response to soil drying, studies investigating the impact of AMF on plant water status and soil-plant hydraulic conductance are lacking. Thus, the main objective of this study was to investigate the influence of AMF on soil-plant conductance and plant water status of tomato under drought. We hypothesized that AMF limit the drop in matric potential across the rhizosphere, especially in drying soil. The underlying mechanism is that AMF extend the effective root radius and hence reduce the water fluxes at the root-soil interface. The follow-up hypothesis is that AMF enhance soil-plant hydraulic conductance and plant water status during soil drying. To test these hypotheses, we measured the relation between transpiration rate, soil and leaf water potential of tomato with reduced mycorrhiza colonization (RMC) and the corresponding wild type (WT). We inoculated the soil of the WT with Rhizophagus irregularis spores to potentially upsurge symbiosis initiation. During soil drying, leaf water potential of the WT did not drop below −0.8MPa during the first 6days after withholding irrigation, while leaf water potential of RMC dropped below −1MPa already after 4days. Furthermore, AMF enhanced the soil-plant hydraulic conductance of the WT during soil drying. In contrast, soil-plant hydraulic conductance of the RMC declined more abruptly as soil dried. We conclude that AMF maintained the hydraulic continuity between root and soil in drying soils, hereby reducing the drop in matric potential at the root-soil interface and enhancing soil-plant hydraulic conductance of tomato under edaphic stress. Future studies will investigate the role of AMF on soil-plant hydraulic conductance and plant water status among diverse plant species growing in contrasting soil textures.

Isohydricity of Two Different Citrus Species under Deficit Irrigation and Reclaimed Water Conditions.

Citrus species are frequently subjected to water and saline stresses worldwide. We evaluated the effects of diurnal changes in the evaporative demands and soil water contents on the plant physiology of grapefruit and mandarin crops under saline reclaimed (RW) and transfer (TW) water conditions, combined with two irrigation strategies, fully irrigated (fI) and non-irrigated (nI). The physiological responses were different depending on the species. Grapefruit showed an isohydric pattern, which restricted the use of the leaf water potential (Ψl) as a plant water status indicator. Its water status was affected by salinity (RW) and water stress (nI), mainly as the combination of both stresses (RW-nI); however, mandarin turned out to be relatively more tolerant to salinity and more sensitive to water stress, mainly because of its low hydraulic conductance (K) levels, showing a critical drop in Ψl that led to severe losses of root–stem (Kroot–stem) and canopy (Kcanopy) hydraulic conductance in TW-nI. This behavior was not observed in RW-nI because a reduction in canopy volume as an adaptive characteristic was observed; thus, mandarin exhibited more anisohydric behavior compared to grapefruit, but isohydrodynamic since its hydrodynamic water potential gradient from roots to shoots (ΔΨplant) was relatively constant across variations in stomatal conductance (gs) and soil water potential. The gs was considered a good plant water status indicator for irrigation scheduling purposes in both species, and its responses to diurnal VPD rise and soil drought were strongly correlated with Kroot–stem. ABA did not show any effect on stomatal regulation, highlighting the fundamental role of plant hydraulics in driving stomatal closure.

Contrasted effects of climate change on low-altitude relict Pinus uncinata stands in the Northern French Alps

This paper reports on climate-induced growth changes in relict, low-altitude mountain pines (Pinus uncinata Mill. ex. Mirb.) from two refugia with cold microclimates located in the Northern French Alps. The P. uncinata stands analyzed grow at the lower bound of their ecological limit and are thus thought to be sensitive indicators of ongoing climate change. Using dendroecological approaches, we compare tree-ring growth at two closely spaced low-altitude stands in the Chartreuse massif (French Alps): La Plagne and Cirque de Bresson. La Plagne is a N-NW-exposed, ventilated slope with cold air circulating in the scree during summer, and the presence of sporadic permafrost as well as ground overcooling, whereas Cirque de Bresson is located on a small, S-exposed fan with sporadic avalanche activity. At both sites, growth responses of P. uncinata to changes in twentieth and twenty-first centuries temperature and precipitation conditions were investigated by means of moving correlation analyses. At Cirque de Bresson, a significant and rapid decline in tree-ring widths has been observed since the early 1990s. We attribute this decline to (i) increasing air temperatures at the beginning of the growing season (May–June) as well as to (ii) a decrease in soil water potential. At La Plagne, we do not detect any significant trend between the higher summer temperatures and tree growth, presumably as a result of the circulation of cold air in the scree slope, which is thought to maintain fresh and humid soil conditions and therefore favor tree growth. These forest stands provide prime examples on how dendroecology can contribute to the study of the dynamics and local variability of tree growth and climate change in relict forest populations with high ecological and conservation values.

Robusta coffee transpiration rate in smallholder coffee plantations on Inceptisols of Malang, East Java

Climate change and the erratic and uneven rainfall distribution are the causes of reduced water available in the soil for plant needs to the transpiration process. This study aimed to determine coffee transpiration rate on dry land with rain harvesting techniques during the dry season, transition season, and rainy season and the factors that influence it. This study used field observation and laboratory analysis with two treatments, i.e. a bench terrace as a control (P1) and an L-shaped silt pit (P2). The variables observed were soil moisture content, transpiration rate, soil water potential, leaf water potential, and microclimate, especially temperature and sunlight intensity. The results showed that the transpiration rate of coffee plants was significantly different in the two treatments. The highest transpiration rate was found in P2 as much as 13.17 mm week-1 or equivalent to 1.88 mm day-1 during the dry season. Application of the L-shaped silt pit (P2) increased soil moisture content compared to the control (P1). This increase was followed by an increase in soil water potential and leaf water potential, which could reach the highest values of 0.18 bar and 0.49 bar, respectively. The transpiration decreases with the change of seasons from the dry season to the transitional season and the rainy season. This decrease is caused by changes in the microclimate, especially the temperature and sunlight intensity. Both are the most variables that affect the rate of transpiration.

Improved understanding of natural weathering on the seismic-to-acoustic coupling ratio over buried containers

The long term effects of natural weathering on the acoustic-to-seismic coupling ratio over buried containers is being investigated at a test site near the campus of the University of Mississippi. The weathering experiment has been carried out over five years. Two containers were buried at a 30 cm depth in 2014 and the coupling ratio monitored during 2014 and 2017. During this time period the soil matrix was not disturbed. Four different containers, buried at 15 cm in 2021, are exposed to the natural weather and the coupling ratio is being monitored. The soil water potential or pressure is measured continuously over the measurement periods. This talk will present the long-term effects of natural weathering on the ratio of normal velocity component of a surface geophone normalized by a surface microphone in response to normally incident airborne sound. As the soil matrix dries it becomes more consolidated increasing the soil acoustic stiffness, the S/A ratio becomes less sensitive to the hydraulic capillary pore pressure. During the rainy season, the soil consolidation relaxes resulting in an increased coupling ratio. The phenomenon is cyclical with the local annual soil wetting and drying cycles.

From hydraulic root architecture models to macroscopic representations of root hydraulics in soil water flow and land surface models

Abstract. Root water uptake is an important process in the terrestrial water cycle. How this process depends on soil water content, root distributions, and root properties is a soil–root hydraulic problem. We compare different approaches to implement root hydraulics in macroscopic soil water flow and land surface models. By upscaling a three-dimensional hydraulic root architecture model, we derived an exact macroscopic root hydraulic model. The macroscopic model uses the following three characteristics: the root system conductance, Krs, the standard uptake fraction, SUF, which represents the uptake from a soil profile with a uniform hydraulic head, and a compensatory matrix that describes the redistribution of water uptake in a non-uniform hydraulic head profile. The two characteristics, Krs and SUF, are sufficient to describe the total uptake as a function of the collar and soil water potential, and water uptake redistribution does not depend on the total uptake or collar water potential. We compared the exact model with two hydraulic root models that make a priori simplifications of the hydraulic root architecture, i.e., the parallel and big root model. The parallel root model uses only two characteristics, Krs and SUF, which can be calculated directly following a bottom-up approach from the 3D hydraulic root architecture. The big root model uses more parameters than the parallel root model, but these parameters cannot be obtained straightforwardly with a bottom-up approach. The big root model was parameterized using a top-down approach, i.e., directly from root segment hydraulic properties, assuming a priori a single big root architecture. This simplification of the hydraulic root architecture led to less accurate descriptions of root water uptake than by the parallel root model. To compute root water uptake in macroscopic soil water flow and land surface models, we recommend the use of the parallel root model with Krs and SUF computed in a bottom-up approach from a known 3D root hydraulic architecture.

The physiological and ecological traits of strip management with straw and plastic film to increase grain yield of intercropping wheat and maize in arid conditions

Strip intercropping is a feasible cropping pattern to improve crop productivity via enhancing the stability of farmland ecosystem. Straw returning and plastic film mulch are effective and valuable measures to boost crop productivity in arid or semi-arid regions. It is unknown whether the yield advantage of strip intercropping can be further enhanced by improving photosynthetic characteristics when applied synchronously with straw returning and plastic film mulch measures. A field experiment on wheat-maize intercropping system was conducted at strip management with straw and plastic film, and photosynthetic characteristics, leaf and soil water potential, and grain yield were determined. The results showed that the SPAD value of wheat and maize leaves with NTSM/NTP (no-tillage with wheat straw mulch in wheat strips and previous residual plastic film mulch in maize strips) was decreased at the vegetative growth period, a higher SPAD value was maintained at the reproductive growth period, compared to CT/CTP (conventional tillage with no straw returning in wheat strips and annual new plastic film mulch in maize strips), it indicated that NTSM/NTP treatment can maintain high physiological activity of intercropped wheat and maize at their reproductive growth period. NTSM/NTP treatment raised net photosynthetic rate (Pn) and leaf water use efficiency (WUEL) of wheat by 9.0–15.8 % and 4.9–8.8 % from filling (Feekes 11.0) to doughing (Feekes 11.2) stage, and raised both indexes of maize by 11.5–25.5 % and 4.7–14.8 % from milking (R3) to doughing (R4) stage, with little effect on transpiration rate (Tr), in comparison to CT/CTP, respectively. NTSM/NTP treatment kept relatively high leaf and soil water potential of intercropped strips, and favorably created a suitable soil moisture environment for enhancing the drought resistance on intercrops. In addition, the value of difference between leaf and soil water potential of wheat and maize in NTSM/NTP treatment was lower than that in CT/CTP treatment at given determining stages, it indicated that NTSM/NTP treatment was beneficial to maintaining the stability of crop water demand and soil water supply for growth of two intercrops. Thus, NTSM/NTP treatment obtained high grain yields, increased by 8.6–11.1 % for intercropped wheat, increased by 16.0–20.2 % for intercropped maize, and increased by 13.8–17.1 % for intercropped wheat plus maize, in comparison to CT/CTP treatment. The improved photosynthetic capacity, optimized leaf and soil water potential, and increased grain yields for intercropped wheat and maize in NTSM/NTP treatment. Therefore, strip intercropping integrated of no tillage with wheat straw and previous residual plastic film mulch can be recommended as the excellent technique to coordinate the contradiction between water shortage and high grain yield in arid irrigated regions.

Thermodynamic Concept of Water Retention and Physical Quality of the Soil

The physical quality of the soil is determined by its interfacial interactions in conditions of variable water content. In this regard, water retention characteristics in the form of functions of water content and its thermodynamic potentials are used as indicators of physical quality and its dynamics in the soil. The combination of centrifugation and thermodesorption methods allowed for the first time the assessment of soil water potentials in the entire range of variation from 0 to 106 J/kg for a representative database (more than 400 samples) of the main genetic types of Eurasian soils, grouped into 5 FAO/USDA soil texture classes. The main fundamental achievement of the research is a physically based diagnosis of the critical values of water content and its thermodynamic potentials that separate the areas of dominance of various forms of soil water, physical forces, and mechanisms of interfacial interactions on the WRC-diagrams of the physical quality of the soil. Theoretical and experimental results of the study are of practical interest of sustainable agronomy for determining the optimal ranges of water content in the soil during plant cultivation, water saving, and salt protection in irrigation, mechanical tillage, and other technological operations.

Stomatal regulation and water potential variation in European beech: challenging the iso/anisohydry concept.

The iso/anisohydric continuum has been used to classify tree species' drought response strategies. The range over which stomata are regulating leaf water potential (ψl) before turgor loss occurs can be described with metrics such as the dependence of ψl on soil water potential (ψsoil) and the size of 'hydroscape area' (HA), but corresponding field data from adult trees are scarce. We examined the stomatal conductance (gs)-ψl relationship in its temporal (diurnal vs seasonal and interannual) and spatial (within-crown vs between-site) variation in European beech, using extensive ψl and gs measurements in the canopy of four beech stands across a precipitation gradient, and complemented the data set by published ψl and gs measurements in further Central European beech stands (including the extreme 2018 drought) in order to cover the full water potential operation space of the species. Both metrics characterize beech as a strictly anisohydric species with δψl/δψsoil>>1 and HA=4MPa2. However, stomates close sensitively in response to increasing vapor pressure deficit, disproving the widely assumed dependence of large ψl variation on looser stomatal control. Characterizing the water status regulation mechanisms of trees requires separating diurnal from day-to-day variation in ψl and gs. The large diurnal and seasonal ψl variation in beech leaves is partly caused by a low leaf tissue elasticity, suggesting that a whole-plant perspective with consideration of osmotic and elastic tissue properties and stem and root hydraulics is needed for fully understanding ψl regulation and the drought tolerance strategy of trees.