•Ψstem acted as better water stress indicator than Ψfruit in sweet cherry.•Ψᴫfruit explained changes in Ψfruit better than Ψρfruit.•SSC increased and Ψᴫfruit strongly decreased in stage III of fruit ...development.•Postharvest deficit irrigation did not harm fruit quality or yield.•Deficit irrigation led to lower pedicel browning after cold storage.
The performance of 'Prime Giant' sweet cherry trees under three different irrigation regimes was examined during two consecutive seasons, 2015–2016 and 2016–2017. The irrigation treatments evaluated were: (i) a control treatment (CTL) irrigated at 110% of crop evapotranspiration (ETcd) to maintain non-limiting soil water conditions, (ii) RDM a regulated deficit irrigation treatment which applied a mild water stress during preharvest (90% of ETcd.) and a medium stress during postharvest (65% of ETcd) and (iii) RDS a regulated deficit irrigation treatment which applied a severe water stress (55% of ETcd.) during postharvest.
There were significant differences during postharvest in soil and plant water indicators such as soil matric potential, midday stem water potential and maximum daily branch shrinkage between CTL and regulated deficit irrigation treatments (RD). However, only midday stem water potential was able to distinguish between RDM and CTL during preharvest. Fruit quality parameters such as fruit size, color, soluble solids concentration (SSC) were periodically measured during fruit developing as well as fruit water potential and osmotic fruit water potential. In 2016, there were no differences in any parameter between treatments. However in 2017 both deficit treatments led to fruits with a higher SSC and darker color than CTL. There were no differences in fruit yield or number of fruits per tree among treatments in either year of the study. When fruit quality was assessed in 2016, the color of the pedicels of fruits from the deficit irrigation treatments were greener than those from CTL after 20 days of cold storage at 2 °C and 90% relative humidity (RH) but and after 5 days of shelf-life simulation (15 °C and 65% RH) the differences between treatments disappeared.
Soil drying is a limiting factor for crop production worldwide. Yet, it is not clear how soil drying impacts water uptake across different soils, species, and root phenotypes. Here we ask (1) what ...root phenotypes improve the water use from drying soils? and (2) what root hydraulic properties impact water flow across the soil–plant continuum? The main objective is to propose a hydraulic framework to investigate the interplay between soil and root hydraulic properties on water uptake. We collected highly resolved data on transpiration, leaf and soil water potential across 11 crops and 10 contrasting soil textures. In drying soils, the drop in water potential at the soil–root interface resulted in a rapid decrease in soil hydraulic conductance, especially at higher transpiration rates. The analysis reveals that water uptake was limited by soil within a wide range of soil water potential (−6 to −1000 kPa), depending on both soil textures and root hydraulic phenotypes. We propose that a root phenotype with low root hydraulic conductance, long roots and/or long and dense root hairs postpones soil limitation in drying soils. The consequence of these root phenotypes on crop water use is discussed.
Summary statement
During soil drying, the drop in soil–plant hydraulic conductance causes a decline in root water uptake, which is impacted by soil and root hydraulic phenotypes. Lower root conductance, longer root length and longer root hairs would allow plants to maintain water uptake at lower soil matric potential.
The fundamental question as to what triggers stomatal closure during soil drying remains contentious. Thus, we urgently need to improve our understanding of stomatal response to water deficits in ...soil and atmosphere. Here, we investigated the role of soil–plant hydraulic conductance (Ksp) on transpiration (E) and stomatal regulation. We used a root pressure chamber to measure the relation between E, leaf xylem water potential (ψleaf‐x) and soil water potential (ψsoil) in tomato. Additional measurements of ψleaf‐x were performed with unpressurized plants. A soil–plant hydraulic model was used to simulate E(ψleaf‐x) for decreasing ψsoil. In wet soils, E(ψleaf‐x) had a constant slope, while in dry soils, the slope decreased, with ψleaf‐x rapidly and nonlinearly decreasing for moderate increases in E. The ψleaf‐x measured in pressurized and unpressurized plants matched well, which indicates that the shoot hydraulic conductance did not decrease during soil drying and that the decrease in Ksp is caused by a decrease in soil–root conductance. The decrease of E matched well the onset of hydraulic nonlinearity. Our findings demonstrate that stomatal closure prevents the drop in ψleaf‐x caused by a decrease in Ksp and elucidate a strong correlation between stomatal regulation and belowground hydraulic limitation.
What triggers stomatal closure during soil drying?
We investigated this fundamental question in tomato and demonstrated that, as the soil dried, the relation between leaf xylem water potential and transpiration rate became markedly nonlinear, indicating a drop in soil–plant hydraulic conductance. The loss of soil–plant hydraulic conductance, which was concomitant with stomatal closure, was primarily explained by a decrease in soil–root conductance.
Drought‐induced mortality and regional dieback of woody vegetation are reported from numerous locations around the world. Yet within any one site, predicting which species are most likely to survive ...global change‐type drought is a challenge. We studied the diversity of drought survival traits of a community of 15 woody plant species in a desert‐chaparral ecotone. The vegetation was a mix of chaparral and desert shrubs, as well as endemic species that only occur along this margin. This vegetation boundary has large potential for drought‐induced mortality because nearly all species are at the edge of their range. Drought survival traits studied were vulnerability to drought‐induced xylem cavitation, sapwood capacitance, deciduousness, photosynthetic stems, deep roots, photosynthetic responses to leaf water potential and hydraulic architecture. Drought survival strategies were evaluated as combinations of traits that could be effective in dealing with drought. The large variation in seasonal predawn water potential of leaves and stem xylem ranged from −6·82 to −0·29 MPa and −6·92 to −0·27 MPa, respectively. The water potential at which photosynthesis ceases ranged from −9·42 to −3·44 MPa. Architecture was a determinant of hydraulic traits, with species supporting large leaf area per sapwood area exhibiting high rates of water transport, but also xylem that is vulnerable to drought‐induced cavitation. Species with more negative midday leaf water potential during the growing season also showed access to deeper water sources based on hydrogen isotope analysis. Drought survival mechanisms comprised of drought deciduousness, photosynthetic stems, tolerance of low minimum seasonal tissue water potential and vulnerability to drought‐induced xylem cavitation thus varied orthogonally among species, and promote a diverse array of drought survival strategies in an arid ecosystem of considerable floristic complexity.
Summary
Some plants exhibit dynamic hydraulic regulation, in which the strictness of hydraulic regulation (i.e. iso/anisohydry) changes in response to environmental conditions. However, the ...environmental controls over iso/anisohydry and the implications of flexible hydraulic regulation for plant productivity remain unknown.
In Juniperus osteosperma, a drought‐resistant dryland conifer, we collected a 5‐month growing season time series of in situ, high temporal‐resolution plant water potential (Ψ) and stand gross primary productivity (GPP). We quantified the stringency of hydraulic regulation associated with environmental covariates and evaluated how predawn water potential contributes to empirically predicting carbon uptake.
Juniperus osteosperma showed less stringent hydraulic regulation (more anisohydric) after monsoon precipitation pulses, when soil moisture and atmospheric demand were high, and corresponded with GPP pulses. Predawn water potential matched the timing of GPP fluxes and improved estimates of GPP more strongly than soil and/or atmospheric moisture, notably resolving GPP underestimation before vegetation green‐up.
Flexible hydraulic regulation appears to allow J. osteosperma to prolong soil water extraction and, therefore, the period of high carbon uptake following monsoon precipitation pulses. Water potential and its dynamic regulation may account for why process‐based and empirical models commonly underestimate the magnitude and temporal variability of dryland GPP.
Macro to micro Konings, Alexandra G.; Rao, Krishna; Steele-Dunne, Susan C.
The New phytologist,
August 2019, Letnik:
223, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Although primarily valued for their suitability for oceanographic applications and soil moisture estimation, microwave remote sensing observations are also sensitive to plant water content (M
w). ...Since M
w depends on both plant water status and biomass, these observations have the potential to be useful for a range of plant drought response studies. In this paper, we introduce the principles behind microwave remote sensing observations to illustrate how they are sensitive to plant water content and discuss the relationship between landscape-scale M
w and common stand-scale metrics, including plant-scale relative water content, live fuel moisture content and leaf water potential. Lastly, we discuss how various sensor types can be leveraged for specific applications depending on the spatio-temporal resolution needed.
Plant water use strategy is one of the key factors to predict drought impact on vegetation and land-atmosphere fluxes. Vegetation optical depth (VOD) based on microwave radiative transfer inversion ...has recently been used to assess plant water use strategy. However, VOD is sensitive to both total aboveground biomass (AGB) and leaf water content, with only the latter being a proxy of leaf water potential whose diurnal variation can be used to characterize vegetation iso/anisohydricity. In this study, by using a network of soil water measurements (used as a proxy for predawn leaf water potential), satellite retrieved normalized difference vegetation index (NDVI, as a proxy for AGB), and two satellite VOD products from the Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E) sensor, we compare three linear models and one machine learning model to investigate to what extent can VOD be used to represent leaf water potential changes during soil moisture dry-down periods. Linear models with both NDVI and leaf water potential, on average, can explain 33% and 51% of VOD variations of each product respectively. Models using only NDVI explain 27% and 46% of the VOD variance, compared to less than 10% by models using leaf water potential only. With the NDVI and leaf water potential (full) model, leaf water potential contributes around 17% of the VOD variance, which is smaller than NDVI (33%). The machine learning model has overall better performance than the linear models, and also highlight the dominant contribution of AGB to VOD signals. After the AGB contribution to VOD is eliminated by normalizing daytime VOD with nighttime VOD, the residuals carry the information of diurnal variations of leaf water potential and calculations from both VOD datasets are consistent with each other (r = 0.42±0.17, P < 0.01 for 88 out of 94 sites). The response of VODdaytimeVODnighttime to soil water potential can also be used as a new metric for ecosystem iso/anisohydricity. Our study demonstrates that a large proportion of variations in VOD are caused by AGB for temperate ecosystems, and higher accuracy VOD products with additional root-zone soil water potential are needed for ecosystem iso/anisohydricity estimations.
•VOD contains information of both AGB and leaf water potential.•AGB can explain more VOD variations than leaf water potential.•VODday/VODnight can be used to assess leaf water potential variations to soil dry down.
Climate change is expected to lead to increases in drought frequency and severity, with deleterious effects on many ecosystems. Stomatal responses to changing environmental conditions form the ...backbone of all ecosystem models, but are based on empirical relationships and are not well-tested during drought conditions. Here, we use a dataset of 34 woody plant species spanning global forest biomes to examine the effect of leaf water potential on stomatal conductance and test the predictive accuracy of three major stomatal models and a recently proposed model. We find that current leaf-level empirical models have consistent biases of over-prediction of stomatal conductance during dry conditions, particularly at low soil water potentials. Furthermore, the recently proposed stomatal conductance model yields increases in predictive capability compared to current models, and with particular improvement during drought conditions. Our results reveal that including stomatal sensitivity to declining water potential and consequent impairment of plant water transport will improve predictions during drought conditions and show that many biomes contain a diversity of plant stomatal strategies that range from risky to conservative stomatal regulation during water stress. Such improvements in stomatal simulation are greatly needed to help unravel and predict the response of ecosystems to future climate extremes.
Many studies report that, under some circumstances, amending soil with biochar can improve field capacity and plant-available water. However, little is known about the mechanisms that control these ...improvements, making it challenging to predict when biochar will improve soil water properties. To develop a conceptual model explaining biochar's effects on soil hydrologic processes, we conducted a series of well constrained laboratory experiments using a sand matrix to test the effects of biochar particle size and porosity on soil water retention curves. We showed that biochar particle size affects soil water storage through changing pore space between particles (interpores) and by adding pores that are part of the biochar (intrapores). We used these experimental results to better understand how biochar intrapores and biochar particle shape control the observed changes in water retention when capillary pressure is the main component of soil water potential. We propose that biochar's intrapores increase water content of biochar-sand mixtures when soils are drier. When biochar-sand mixtures are wetter, biochar particles' elongated shape disrupts the packing of grains in the sandy matrix, increasing the volume between grains (interpores) available for water storage. These results imply that biochars with a high intraporosity and irregular shapes will most effectively increase water storage in coarse soils.
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