Soil Water Potential Research Articles

Do Cover Crops Influence In Situ Soil Water Potential After Termination?

Soil water movement is energy-dependent and is influenced by various management practices. It can be understood by measuring the soil water potential (SWP); however, the influence of cover crops (CCs) on SWP is not currently well understood. The objective of this study was to assess the effects of CCs on SWP before and after termination in order to understand their effects on soil water availability for the subsequent cash crop. The experimental design was a completely randomized design with two levels of CCs (CCs vs. no cover crop [NC]) with three replicates. The SWP sensors were buried at 0–10, 10–20, and 20–30 cm depths before CCs were planted. Additionally, soil samples were collected at the aforementioned depths just before CC termination for soil organic carbon (SOC), bulk density (BD), and saturated hydraulic conductivity (Ksat) analysis. Results showed that CCs increased SOC and Ksat, and significantly lowered BD compared with NC management. Before termination, CC plots had significantly lower SWP values compared with NC management, suggesting that the transpirational needs of the CCs can lead to lower water content. After termination, CC management also resulted in lower SWP, suggesting that CCs can increase water-use efficiency by improving soil health parameters. However, effective planning is required for CC implementation, especially in semiarid and arid regions.

Responses of Soil Water Potential and Plant Physiological Status to Pulsed Rainfall Events in Arid Northwestern China: Implications for Disclosing the Water‐Use Strategies of Desert Plants

ABSTRACTSoil water potential (SWP) strongly influences plant productivity and ecosystem functioning, particularly in arid regions characterized by sporadic and pulsed rainfall. This work aims to improve understanding of the response of SWP to varied rainfall pulses, and of the water‐use strategies of a widespread C4 shrub (Haloxylon ammodendron, HA) in arid northwestern China. Rainfall manipulation experiments and field measurements on HA were undertaken to explore the response features of SWP and plant physiological status to pulsed rainfall events of varied magnitudes and durations. The physiological state of HA was evaluated by quantifying critical metrics indicative of plant water‐use strategies, including leaf water potential, photosynthetic rate and transpiration rate. The response value of SWP increased with rainfall magnitude and was most affected by three vital factors (antecedent SWP, total rainfall and rainfall intensity). Low antecedent SWP amplifies SWP's sensitivity to subsequent events, accelerating its response to smaller rainfalls (<5 mm) compared with larger ones (>15 mm). Small rainfall can increase SWP by 0.5–2 MPa in the 20‐cm layer, sustaining plant physiological activities under high antecedent SWP conditions (>−3.5 MPa), with a maximum average rise in photosynthetic rate of 9.20 ± 0.45 μmol CO2 m−2 s−1, enhancing HA's water use efficiency to 1.79 ± 0.22 μmol CO2 mmol−1 H2O. Therefore, small events play a vital role in maintaining SWP and promoting water use of desert plants. Given the nature of plants' utilization of small rainfall events, re‐examining ecologically valid SWP thresholds of HA and other similar desert plants is critical.

Temperature‐driven convergence and divergence of ecohydrological dynamics in the ecosystems of a sky island mountain range

AbstractForest and woodland decline is predicted to be increasingly influenced by meteorological variation and climate change in the future. By determining how meteorological variation leads to similar versus differing ecohydrological dynamics of forest and woodland ecosystems, we can gain insight on how future climate‐driven declines may be realized. We characterized 23 mixed conifer forest (MC), ponderosa pine forest (PP) and piñon pine–juniper woodland (PJ) sites with different canopy covers in southern Nevada, USA. We compared meteorological variation between these sites and employed water balance modelling and information theory to estimate similarity in the density distributions of soil temperature (Ts), soil water potential (SWP) and transpiration partitioning into total evapotranspiration (T/ET) within and across ecosystems in wetter and drier seasons and in cooler and warmer decades. From 1941 to 2020, this location experienced declines in meteorological water deficit due to higher precipitation, although temperatures increased over more recent time periods (1981–2020). From 1981 to 2020, we generally found greater similarity in SWP and T/ET distributions within MC sites and PP sites in the cool season and in the warm season generally found greater similarity in Ts and T/ET distributions within and between PP and PJ sites (excepting T/ET between PJ sites and higher canopy cover PP sites). Recent warm decades promoted convergence in warm and cool season Ts dynamics, such that Ts dynamics generally became more similar between higher elevation MC sites and lower elevation PP–PJ sites. At the same time, warmer decades initiated divergence of SWP and T/ET dynamics within groups of MC–PP and PP–PJ sites that were formerly more similar to each other (excepting SWP in wet seasons). Although their dynamics will remain strongly coupled to precipitation, warming temperatures have the potential to promote divergence in the ecohydrological dynamics of ecosystems at lower and higher elevations in this sky island system and may also promote novel within‐ecosystem divergence associated with variation in vegetation structural attributes.

Drought alters the physiological quality of runner-type peanut seeds during seed formation

Sub-optimal water supply during crop development, especially during peak flowering and pod filling, affects the quality of the produced seeds, generally resulting in poor seed quality. The goals of this study were to identify the acquisition pattern of physiological components in peanut seeds as well as to assess the impact of drought during peanut seed development on its physiological quality. The research was conducted at the USDA-ARS National Peanut Research Laboratory in Dawson, GA for three consecutive years (2019, 2020, and 2021) using field conditions under two water regimes, well-watered control and drought stress. Rainout shelters were used to prevent rain in the drought-stressed block for 30 d, starting 80 d after planting. The well-watered block received supplemental irrigation when soil water potential reached -40 kPa. Peanut pods from the cultivar Georgia-06G were harvested at 2500 growing degree days, and the peanut maturity profile board was used to classify the pods into different maturity classes. Germination, vigor, desiccation tolerance (DT), and longevity tests were performed on seeds from each maturity class and both water regimes. The acquisition pattern for the physiological components of seed quality was developed for seeds grown under well-watered and drought conditions. Maximum germination occurred in ‘brown 1’ and ‘brown 2’ under drought and well-watered conditions, respectively. Both water regimes reached maximum vigor in the 'brown 1'; however, under well-watered conditions, vigor had a rapid decline after ‘brown 1’ while under drought stress, the decline in vigor was slower. Maximum DT was achieved between ‘orange’ and ‘brown 1’ under drought conditions, whereas under well-watered conditions, maximum DT was achieved between ‘brown 2’ and ‘black 1’. Seeds from immature classes had lower capacity to be stored compared with mature seeds. Overall, drought stress promoted greater physiological quality in the peanut seeds than the well-watered treatment. Maximum physiological quality was achieved in the transition from ‘orange’ into ‘brown 1' under drought conditions, and in the transition from ‘brown 2’ to ‘black 1’ class under well-watered conditions. Also, drought stress preserved seed quality for a longer period.

Diversity in stomatal and hydraulic responses to post-flowering drought in common (Phaseolus vulgaris) and tepary (P. acutifolius) beans.

Plants differ widely in how soil drying affects stomatal conductance (gs) and leaf water potential (ψleaf), and in the underlying physiological controls. Efforts to breed crops for drought resilience would benefit from a better understanding of these mechanisms and their diversity. We grew 12 diverse genotypes of common bean (Phaseolus vulgaris L.) and four of tepary bean (P. acutifolius; a highly drought resilient species) in the field under irrigation and post-flowering drought, and quantified responses of gs and ψleaf, and their controls (soil water potential [ψsoil], evaporative demand [Δw] and plant hydraulic conductance [K]). We hypothesised that (i) common beans would be more "isohydric" (i.e., exhibit strong stomatal closure in drought, minimising ψleaf decline) than tepary beans, and that genotypes with larger ψleaf decline (more "anisohydric") would exhibit (ii) smaller increases in Δw, due to less suppression of evaporative cooling by stomatal closure and hence less canopy warming, but (iii) larger K declines due to ψleaf decline. Contrary to our hypotheses, we found that half of the common bean genotypes were similarly anisohydric to most tepary beans; canopy temperature was cooler in isohydric genotypes leading to smaller increases in Δw in drought; and that stomatal closure and K decline were similar in isohydric and anisohydric genotypes. gs and ψleaf were virtually insensitive to drought in one tepary genotype (G40068). Our results highlight the potential importance of non-stomatal mechanisms for leaf cooling, and the variability in drought resilience traits among closely related crop legumes.

Hydrological and pedological effects of combining Italian alder and blackberries in an agroforestry windbreak system in South Africa

Abstract. The Western Cape in South Africa is a water-scarce region which will likely receive less rainfall and higher air temperatures under projected climate change scenarios. The integration of trees within agricultural systems provides an effective measure for improving water retention on agricultural land. Studying an established and irrigated agroforestry system (AFS) combining alder (Alnus cordata (Loisel.) Duby) as a linear windbreak with a blackberry (Rubus fructicosus L.) crop, we explore the water use dynamics of the intercrop as influenced by the windbreak element by combining methods from hydrology, soil science and forestry disciplines. Our objective is to explore whether the AFS positively impacts the water balance by combining measurement campaigns to characterise the spatial variability of various key system properties with continuous monitoring. The campaigns encompassed extensive soil sampling to determine soil characteristics (nutrient concentrations, hydraulic conductivity, texture, water retention) in the laboratory as well as terrestrial laser scans of the field site, especially of the windbreaks. The continuous measurements covered meteorological, soil water content and soil water potential observations over a 6-month period (in summer). These were applied to understand soil water dynamics during rainstorms and dry spells, including root water uptake as well as soil water storage. We recorded a total of 13 rainfall events delivering 2.5–117.6 mm of rainfall with maximum intensities of 4.1 to 82.6 mm h−1. Further analyses showed that infiltration is likely dominated by preferential flow, with root water uptake potentially occurring in two depth zones corresponding to different plant communities. While soil water content varied by depth and was influenced by physical and environmental factors, it was generally higher in the intercrop zone than within the windbreak-influenced zone. During dry spells, soil water content did not drop below the water content of the permanent wilting point (<-1500 kPa). Values corresponding to soil water tensions above 1000 kPa were recorded on several occasions; these were mitigated by irrigation and, thus, did not result in water stress. Nutrient distribution and soil physical properties differed near the windbreak in comparison to the blackberry crop, and the carbon sequestration potential is great in comparison to monoculture farming. We could demonstrate positive effects of the windbreak on the water balance and dynamics in the blackberry field site, even though questions remain as to the extent of these benefits and how they compared to disadvantageous aspects brought about by the presence of the trees (e.g. increased water usage). Irrigation did, in fact, shift the AFS from a water-limited regime to an energy-limited one.

Moderate alternate wetting and drying irrigation enhances drought-resistance abilities by improving structural mesophyll conductance of water-saving and drought-resistant rice under severe drought.

Water-saving and drought-resistant rice (WDR) coupled with alternate wetting and drying irrigation (AWDI) possesses a high photosynthetic potential due to higher mesophyll conductance (gm) under drought conditions. However, the physiological and structural contributions to the gm of leaves and their mechanisms in WDR under AWDI are still unclear. In this study, WDR (Hanyou 73) and drought-sensitive rice (Huiliangyou 898) were selected as materials. Three irrigation patterns were established from transplanting to the heading stage, including conventional flooding irrigation (W1), moderate AWDI (W2), and severe AWDI (W3). A severe drought with a soil water potential of -50 kPa was applied for a week at the heading stage across all treatments and cultivars. The results revealed that severe drought reduced gas exchange parameters and gm but enhanced antioxidant enzyme activities and malondialdehyde content in the three treatments and both cultivars. The maximal photosynthetic rate (Amax) of HY73 in the W2 treatment was greater than that in the other combinations of cultivars and irrigation patterns. The contribution of leaf structure (54%) to gm (gm-S, structural gm) was higher than that of leaf physiology (46%) to gm (gm-P, physiological gm) in the W2 treatment of Hanyou 73. Additionally, gm-S was significantly and linearly positively correlated with gm under severe drought. Moreover, both the initial and apparent quantum efficiencies were significantly and positively with gm in rice plants (p < 0.05). These results suggest that the improvements in photosynthesis and yield in the WDR combined with moderate AWDI can mainly be attributed to the enhancement of gm-S under severe drought conditions. Quantum efficiency may be a potential factor in regulating photosynthesis by cooperating with the gm of rice plants under severe drought conditions.

Soil water repellency and its importance for the climate-smart sustainable management of fen peatland soils in Central Poland

The paper aims to assess potential soil water repellency (SWR) in the surface layers of long-term agricultural fen soils. Furthermore, we attempt to enhance our understanding of the links between selected soil properties (e.g., secondary transformation, total organic carbon (TOC) content) and SWR in differently used (grasslands and arable lands) fen soils in the temperate climate zone. The study was conducted in the Grójec Valley, Central Poland. The soil samples for laboratory analyses were collected in June 2022 from 64 sampling points – 56 grassland and 8 arable sites. We found that secondary soil transformation (mursh forming process) was significantly positively correlated with SWR – determined by MED (molarity of ethanol droplet) and WDPT (water drop penetration time) methods (r = 0.42 and r = 0.40, p < 0.05) only in the organic samples (i.e., mursh). The significant positive correlation between SWR and TOC content (r = 0.73 (MED) and r = 0.74 (WDPT), p < 0.05) indicates that, as well as organic matter depletion, there was a decrease in the water repellency of the studied soils. Our results indicate that study fen sites should be rewetted, and that the implementation of the paludiculture must take place in the near future. At a minimum, further arable cultivation of organic soils should be avoided, as they are the most vulnerable to secondary transformation and exhibit high SWR values. Furthermore, in the case of crop production on post-organic soils, it is recommended that the conservation tillage method is applied to prevent further depletion of soil organic matter content.

PSInet: a new global water potential network.

Given the pressing challenges posed by climate change, it is crucial to develop a deeper understanding of the impacts of escalating drought and heat stress on terrestrial ecosystems and the vital services they offer. Soil and plant water potential play a pivotal role in governing the dynamics of water within ecosystems and exert direct control over plant function and mortality risk during periods of ecological stress. However, existing observations of water potential suffer from significant limitations, including their sporadic and discontinuous nature, inconsistent representation of relevant spatio-temporal scales and numerous methodological challenges. These limitations hinder the comprehensive and synthetic research needed to enhance our conceptual understanding and predictive models of plant function and survival under limited moisture availability. In this article, we present PSInet (PSI-for the Greek letter Ψ used to denote water potential), a novel collaborative network of researchers and data, designed to bridge the current critical information gap in water potential data. The primary objectives of PSInet are as follows. (i) Establishing the first openly accessible global database for time series of plant and soil water potential measurements, while providing important linkages with other relevant observation networks. (ii) Fostering an inclusive and diverse collaborative environment for all scientists studying water potential in various stages of their careers. (iii) Standardizing methodologies, processing and interpretation of water potential data through the engagement of a global community of scientists, facilitated by the dissemination of standardized protocols, best practices and early career training opportunities. (iv) Facilitating the use of the PSInet database for synthesizing knowledge and addressing prominent gaps in our understanding of plants' physiological responses to various environmental stressors. The PSInet initiative is integral to meeting the fundamental research challenge of discerning which plant species will thrive and which will be vulnerable in a world undergoing rapid warming and increasing aridification.

Resin acid δ13C and δ18O as indicators of intra-seasonal physiological and environmental variability.

Understanding the dynamics of δ13C and δ18O in modern resin is crucial for interpreting (sub)fossilized resin records and resin production dynamics. We measured the δ13C and δ18O offsets between resin acids and their precursor molecules in the top-canopy twigs and breast-height stems of mature Pinus sylvestris trees. We also investigated the physiological and environmental signals imprinted in resin δ13C and δ18O at an intra-seasonal scale. Resin δ13C was c. 2‰ lower than sucrose δ13C, in both twigs and stems, likely due to the loss of 13C-enriched C-1 atoms of pyruvate during isoprene formation and kinetic isotope effects during diterpene synthesis. Resin δ18O was c. 20‰ higher than xylem water δ18O and c. 20‰ lower than δ18O of water-soluble carbohydrates, possibly caused by discrimination against 18O during O2-based diterpene oxidation and 35%-50% oxygen atom exchange with water. Resin δ13C and δ18O recorded a strong signal of soil water potential; however, their overall capacity to infer intraseasonal environmental changes was limited by their temporal, within-tree and among-tree variations. Future studies should validate the potential isotope fractionation mechanisms associated with resin synthesis and explore the use of resin δ13C and δ18O as a long-term proxy for physiological and environmental changes.

Dynamics of soil water potential as a function of stand types in a temperate forest: Emphasis on flash droughts

In the context of a changing climate and the increasing occurrences of extreme events, including droughts, field evidence, and models suggest that cases of forest decline and migration of tree species to more suitable climates will augment in the 21st century. In northeastern North America, an expansion of American beech at the expense of maples has been observed since the 1970s and has been associated to several causes. Through an analysis of time series leveraging thousands of data collected in a temperate forest in southern Quebec, Canada, dynamics of soil water potential were analyzed in interaction with soil temperature, meteorological variables and forest types, including hardwoods (mostly maple) with a large presence of beech trees (hardwood-beech stands), hardwoods (maple and birch) and mixedwoods (maple and fir). During flash drought events with a net precipitation deficit and water stress, the presence of beech led to a decrease in soil temperature and favored the maintenance of low soil water potential and faster restoration of water reserves compared to mixedwoods. Using machine learning-based approaches, distinct critical soil temperature thresholds in regard to water potential were identified for the various forest types, and the temporality in soil water regime changes was more favorable under hardwood-beech stands. The presence of beech appears to render greater resilience in regard to water stress in this forest. A greater capacity of beech to preserve and restore soil water not only offers an additional explanation for its establishment in hardwoods in the last decades, but greater water conservation in the presence of beech, assuming it remains in the landscape, could also help local plant species adapt to climate change and to the predicted increased water deficits, as well as species migrating northward to find more suitable environmental envelopes.

Abscisic acid increase correlates with the soil water threshold of transpiration decline during drought.

By regulating carbon uptake and water loss by plants, stomata are not only responsible for productivity but also survival during drought. The timing of the onset of stomatal closure is crucial for preventing excessive water loss during drought, but is poorly explained by plant hydraulics alone and what triggers stomatal closure remains disputed. We investigated whether the hormone abscisic acid (ABA) was this trigger in a highly embolism-resistant tree species Umbellularia californica. We tracked leaf ABA levels, determined the leaf water potential and gravimetric soil water content (gSWC) thresholds for stomatal closure and transpiration decline during a progressive drought. We found that U. californica plants have a peaking-type ABA dynamic, where ABA levels rise early in drought and then decline under prolonged drought conditions. The early increase in ABA levels correlated with the closing of stomata and reduced transpiration. Furthermore, we found that transpiration declined before any large decreases in predawn plant water status and could best be explained by transient drops in midday water potentials triggering increased ABA levels. Our results indicate that ABA-mediated stomatal regulation may be an integral mechanism for reducing transpiration during drought before major drops in bulk soil and plant water status.

Measurements of Soil Water Potential and Conductivity based on a Simple Evaporation Experiment using a Hydraulic Property Analyzer.

The measurement of soil hydraulic properties is critical in understanding the physical components of soil health as well as integrated knowledge of soil systems under various management practices. Collecting reliable data is imperative for informing decisions that affect agriculture and the environment. The simple evaporation experiment described here uses instrumentation in a laboratory setting to analyze soil samples collected in the field. The soil water tension of the sample is measured by the instrument, and tension data is modeled by software to return soil hydraulic properties. This method can be utilized to measure soil water retention and hydraulic conductivity and give insight into differences in treatments or environmental dynamics over time. Initial establishment requires a user, but data acquisition is automated with the instrument. Soil hydraulic properties are not easily measured with traditional experiments, and this protocol offers a simple and optimal alternative. Interpretation of results and options for extending the data range are discussed.

Effects of water stress on apoplastic barrier formation in soil grown roots differ from hydroponically grown roots: Histochemical, biochemical and molecular evidence.

In root research, hydroponic plant cultivation is commonly used and soil experiments are rare. We investigated the response of 12-day-old barley roots, cultivated in soil-filled rhizotrons, to different soil water potentials (SWP) comparing a modern cultivar (cv. Scarlett) with a wild accession ICB181243 from Pakistan. Water potentials were quantified in soils with different relative water contents. Root anatomy was studied using histochemistry and microscopy. Suberin and lignin amounts were quantified by analytical chemistry. Transcriptomic changes were observed by RNA-sequencing. Compared with control with decreasing SWP, total root length decreased, the onset of endodermal suberization occurred much closer towards the root tips, amounts of suberin and lignin increased, and corresponding biosynthesis genes were upregulated in response to decreasing SWP. We conclude that decreasing water potentials enhanced root suberization and lignification, like osmotic stress experiments in hydroponic cultivation. However, in soil endodermal cell suberization was initiated very close towards the root tip, and root length as well as suberin amounts were about twofold higher compared with hydroponic cultivation.

Physiological and biochemical changes of Picea abies (L.) during acute drought stress and their correlation with susceptibility to Ips typographus (L.) and I. duplicatus (Sahlberg)

IntroductionIn recent years, Norway spruce (Picea abies L.) forests in Central Europe have faced escalating threats from bark beetles, primarily Ips typographus (L.), and other species, such as I. duplicatus (Sahlberg). Outbreaks are partially attributed to weakened tree defense resulting from drought periods induced by climate change. This study examines Norway spruce’s physiological and metabolic reactions to acute drought stress during the growing season and evaluates its susceptibility to I. typographus and I. duplicatus.MethodologyIn order to induce drought stress, mature Norway spruces had their roots covered with a roof in April 2021, depriving them of water. Control trees were left with free access to natural rainwater. Over 5 months of the growing season, soil water potential, bark temperature, tree trunk circumference, and sap flow were monitored. Roofed trees and controls were sampled in July, August, and September and analyzed for non-structural carbohydrates and the two classes of defensive compounds, phenolics and terpenes. Furthermore, two different bioassays in tubes and boxes were performed using adult I. typographus and I. duplicatus beetles to assess host choice and acceptance.ResultsRoofed trees exhibited signs of stress as early as July, resulting in decreased tree trunk and a consequent increase in non-structural carbohydrate content. Defensive metabolites remained largely unaffected except for an increase in diterpenes in September. In bioassays, I. typographus preferred boring into the bark of roofed trees in August in tubes and in September in boxes. This increased tree acceptance correlated with increased levels of soluble carbohydrates in the phloem. I. typographus and I. duplicatus beetles showed higher mobility in boxes in August and September on roofed trees but not in July, even though bark surface temperatures were elevated in roof-covered trees during all three bioassay periods.ConclusionThe study revealed rapid physiological responses of trees to acute drought stress, although not many changes were observed in defense traits. Despite the absence of natural bark beetle attacks, drought trees were more accepted by I. typographus than naturally watered trees. This response may indicate the beetles’ preference for trees with phloem of higher nutritional quality induced by the acute drought stress conditions.

Unseen consequences: tracking soil water potential in forests influenced by coal mining

Abstract Over the past decades, anthropogenic disturbance of geological structures has been significantly documented in Slovakia, mainly driven by the national economy’s demand for mining resources. Among these resources, brown coal, primarily mined in the Upper Nitra coal basin in the Prievidza district (Slovakia), has been essential. Mining activities around town of Handlová, and villages of Koš, Cígeľ and Sebedražie, particularly at the Cígeľ coal mine, have induced several geological defects. These defects, characterised by large cracks and local landslides, disrupt the hydrogeological conditions, significantly impacting the soil water regime stability of the forest ecosystems in these damaged areas. This study investigates the variability and dynamics of the soil water potential in a mining-affected site (Račkov laz) compared to an intact reference area (Čertove chodníky) between 2020 and 2022. Our findings suggest that mining activities could have substantial implications for the soil water regime and, consequently, the ecological stability of forest ecosystems.

Longevity and persistence of arrowleaf sida seeds in soil and emergence modeling using thermal and hydrothermal time models

Arrowleaf sida (Sida rhombifolia L.) is a weed that has a fibrous stem, aggressive root system and waxy leaves that can hinder herbicide absorption. Based on knowledge of the environmental requirements for germination of this species, it is possible to predict emergence to assist in integrated management. The aim of this investigation was to characterize the air temperature and soil water potential requirements for arrowleaf sida germination, to model the emergence in the field using thermal and hydrothermal time models and to evaluate the longevity of the arrowleaf sida seed bank. Laboratory experiments were conducted to determine the temperature and water potential for seed germination by testing eight temperatures (10, 15, 20, 25, 30, 35, 40, and 45 °C) and 10 water potentials (0, −0.05, −0.1, −0.2, −0.4, −0.6, −0.9, −1.2, −1.5, and −2.0 MPa). Field experiments were conducted between 2014 and 2018 to model the emergence using three sampling times (starting on 10/20, 11/10, and 12/01), during which soybean seeds were sown. To evaluate the longevity and persistence of the seed bank, a factorial experiment was conducted, in which the first factor included three burial depths (0, 3, and 6 cm) and the second factor included five collection times (0, 1, 4, 10, and 16 months) after seed burial. The base, optimal and maximum temperatures for arrowleaf sida germination were 10.0, 24.8, and 42.5 °C, respectively, and the base water potential was −1.20 MPa. It is possible to predict the emergence of arrowleaf sida in the field by hydrothermal and thermal time models under different environmental conditions. In addition, this species has a persistent seed bank, with 30% of seeds being viable after 16 months of burial.

Does no-till cover crop influence in situ measured soil water potential and saturated hydraulic conductivity?

Does no-till cover crop influence in situ measured soil water potential and saturated hydraulic conductivity?

Scheduling irrigation events in corn using three soil water potential strategies

AbstractScheduling irrigation events is important for high corn (Zea mays L.) yield, water use efficiency, economic returns, and water conservation. The use of shallow subsurface drip irrigation (S3DI) is cost effective for small irregular shaped field areas. Currently there are no irrigation scheduling recommendations for S3DI systems for corn production. The objective was to evaluate three water potential value strategies for scheduling irrigation events and the effect on corn yield, test weight, irrigation water use efficiency (IWUE), and value water use efficiency (VWUE). Corn was grown multiple years (2012–2013; 2019–2023) at two locations (Dawson and Shellman, GA) using soil water potential sensors to schedule irrigation events. Sensors were installed at 10 and 20 inches (25 and 50 cm) soil depth. Irrigation events were scheduled when the average water potential was between 40 to 60 cbar (I1), 60 to 80 cbar (I2), 80 to 100 cbar (I3), and compared to a dryland control (I0). There was no difference in corn yield, IWUE, or VWUE between irrigation treatments, but all irrigation treatments had greater yield than I0, except in high rainfall years. At the Shellman location, total water applied for I3 was 46% less than for I1. At Dawson, I2 applied 17% more water than either I1 or I3. Across both sites, I1 and I2 applied 1.5 and 1.3 times more water than I3, respectively. Therefore, irrigation events scheduled at 80 to 100 cbar can be a viable technique for irrigating corn using S3DI without yield reductions while promoting water conservation.

Coordination between degree of isohydricity and depth of root water uptake in temperate tree species

In an increasingly dry environment, it is crucial to understand how tree species use soil water and cope with drought. However, there is still a knowledge gap regarding the relationships between species-specific stomatal behaviour, spatial root distribution, and root water uptake (RWU) dynamics.Our study aimed to investigate above- and below-ground aspects of water use during soil drying periods in four temperate tree species that differ in stomatal behaviour: two isohydric tracheid-bearing conifers, Scots pine and Norway spruce, and two more anisohydric deciduous species, the diffuse-porous European beech, and the ring-porous Downy oak. From 2015 to 2020, soil-tree-atmosphere-continuum parameters were measured for each species in monospecific forests where trees had no access to groundwater. The hourly time series included data on air temperature, vapor pressure deficit, soil water potential, soil hydraulic conductivity, and RWU to a depth of 2 m. Analysis of drought responses included data on stem radius, leaf water potential, estimated osmotically active compounds, and drought damage.Our study reveals an inherent coordination between stomatal regulation, fine root distribution and water uptake. Compared to conifers, the more anisohydric water use of oak and beech was associated with less strict stomatal closure, greater investment in deep roots, four times higher maximum RWU, a shift of RWU to deeper soil layers as the topsoil dried, and a more pronounced soil drying below 1 m depth. Soil hydraulic conductivity started to limit RWU when values fell below 10−3 to 10−5 cm/d, depending on the soil. As drought progressed, oak and beech may also have benefited from their leaf osmoregulatory capacity, but at the cost of xylem embolism with around 50 % loss of hydraulic conductivity when soil water potential dropped below −1.25 MPa.Consideration of species-specific water use is crucial for forest management and vegetation modelling to improve forest resilience to drought.