Plant Water Relations Research Articles

Organic Hydromulches in Young Olive Trees in Pots: Effects on Soil and Plant Parameters

Organic hydromulches (liquid spray-on mulches) have been used traditionally in land rehabilitation, mainly to mitigate post-fire runoff and erosion. However, in recent years, a new application of these materials as an eco-friendly alternative to the widely used polyethylene mulch, both in vegetable and woody crops, has been studyied. This work analyzes the effects of six hydromulches, based on organic by-products, on different soil parameters (water content, temperature, and CO2 flux), plant–water relations (stem water potential, leaf gas exchange, and leaf temperature), and the growth (trunk diameter) of young olive trees planted in large pots in the open field over a 2-year trial. The hydromulches tested were: rice husk (RH), rice husk with linen oil (RHL), mushroom substrate (MS), wheat straw (WS), pistachio (PW), and vineyard (VW) pruning wood chips, mixed with different additives (gypsum, recycled paper paste, and Kraft fiber). A non-mulched manual weeding control (NM) was included. The results indicated that hydromulches, in comparison with NM, resulted in increased volumetric soil water content (on average, 22.9% in hydromulches and 19.5% in NM), reduced soil temperature fluctuations (4.97 °C in hydromulches and 6.13 °C in NM), and increased soil CO2 fluxes (0.80 and 0.49 g CO2 m−2 h−1, respectively). Although the differences in the soil water content did not have an obvious effect on the plant–water status, crop growth was reduced in NM (≈23% lower than PW, MS, RHL, and WS), suggesting that vegetative growth, especially in young olive trees, is extremely sensitive to water deficit. The overall study leads to considering hydromulches as a good alternative to mulching in large pots, especially PW, which would be useful for nursery crops before their final establishment in the field.

Symbiotic N nutrition, carbon accumulation, and water-use efficiency in species of the genus Aspalathus native to the Cape fynbos, South Africa

Low soil moisture and N in the fynbos are a major constraint to plant growth and N2 fixation in legumes, including Aspalathus species. The 15N and 13C natural abundance techniques were used to study N nutrition and plant water relations in different Aspalathus species sampled from 13 study sites in the fynbos. The results showed that A. acuminata shoots recorded lower δ15N values at Kalbaskraal, Worcester Langerug and Roundebosch, resulting in higher %Ndfa at those sites relative to Elim, which registered greater δ15N values. However, A. hispida shoots showed the lowest δ15N at Elim and Dutoitskloof than Yzerfontein, and Silwerstroomstrand, resulting in high %Ndfa at Elim. Of A. cordata, A. astroites, A. hispida, and A. wildenowiana collected from Dutoitskloof differed in δ15N and %Ndfa. A. cordata and A. astroites shoots showed lower δ15N, leading to higher %Ndfa than A. wildenowiana, which exhibited greater shoot δ15N. Of four Aspalathus species (A. cordata, A. carnosa, A. capensis and A. juniperina) sampled from Silvermine, A. cordata revealed the lowest δ15N and hence the highest %Ndfa. Conversely, A. carnosa recorded the highest shoot δ15N and the lowest %Ndfa. At Kokrivier, shoot δ15N was much greater in A. zeyheri and lowest in A. incurvifolia, resulting in higher %Ndfa in the latter than the former. The Aspalathus species differed in water-use efficiency or shoot δ13C values, which ranged from −30.35‰ to −26.93‰. Rainfall, soil moisture deficit and altitude were the major determinants of shoot δ13C values, but how these factors influence shoot δ13C of plants remains to be determined.

Variability in Stomatal Adaptation to Drought among Grapevine Cultivars: Genotype-Dependent Responses

Leaf stomata are the primary determinants of the plant water relations. Physiological adaptations of stomata in response to water stress have been extensively reported for grapevine. On the contrary, little is known about how the plasticity in stomatal anatomical features may affect their adaptability to drought conditions. In this study, we investigated, at the molecular and anatomical level, the effect of water stress on the stomatal anatomical features of four grapevine varieties extensively cultivated in the north of Italy. Potted plants of Garganega, Glera, Moscato giallo, and Merlot varieties were subjected to a 12–13 day period of water restriction during two consecutive seasons. Stomatal density and size were investigated in newly developed young leaves, 7 days after tip separation, following the occurrence of a water stress event. Furthermore, the gene expression of three key stomagenesis genes (VvEPFL9, VvEPF1, and VvEPF2) was analysed. The response of stomatal anatomical features to drought varied among the studied varieties. Moscato and Glera showed an increase in stomatal density and a decrease in stomatal size. On the contrary, Merlot displayed a reduction in stomatal number, while Garganega remained unchanged in terms of these values. Transcript levels of VvEPFL9 were overall in agreement with stomatal densities measured in the four varieties, showing an up-regulation when drought induced an increase in stomatal density or a down-regulation when the stomatal number decreased. The wide variability in stomatal response observed in the four varieties under study suggests that anatomical changes in stomatal characteristics are genotype dependent. These variations contribute to the intra-specific variability in grapevine’s response to water stress.

Yield loss of inferior crop species and its physiological mechanism in a semiarid cereal-legume intercropping system

Reducing the yield loss of inferior crop species is crucial for improving the production of intercropping systems, particularly in drought-prone regions. Yet, the physiological mechanism of yield loss caused by interspecific competition in response to soil water availability is unclear. A two-year (2018–2019) field experiment was conducted to explore the impacts of interspecific competition on yield formation of the inferior crop in the maize-faba bean intercropping system with and without plastic film mulching in a semiarid rainfed region. The plant-water relation, and yield formation in association with nitrogen (N) remobilization were determined and compared. Results indicated that the land equivalent ratio of the intercropping system was greater than 1, regardless of whether treated with plastic mulching. However, the net effect of the intercropping system was significantly greater than 0 only under plastic mulching. Intercropping with faba beans prolonged the anthesis-silking interval of maize by 93.7% (p < 0.05) and the bald tip length by 56.2% (p < 0.05). This trend resulted in insufficient pollination of tassels and an increased kernel abortion rate in maize (p < 0.05). Moreover, the amount of dry matter and N transfer to grain in vegetative organs decreased by 34.0% and 23.2% (p < 0.05), respectively. Physiologically, this brought about yield loss in the intercropped maize. Water competition from faba bean significantly reduced the soil water availability in the intercropped maize strips, regardless of whether treated with plastic mulching. However, plastic mulching alleviated the competition for water between faba bean and maize, and thus kernel abortion in maize was significantly reduced. Our findings reveal the physiological mechanism of yield loss in intercropped inferior species, by connecting kernel formation and remobilization function, in the semi-arid and rainfed intercropping systems. Specific water or nutrient management strategies might be needed for inferior crops to further improve the total productivity of cereal-legume intercropping system in drought-prone environments.

Response of strawberry (Fragaria ananassa L.) to chilling and potassium supply from inorganic and amino acid-complexed sources

There is growing evidence that plants need higher potassium (K) when subjected to environmental stresses i.e., chilling in order to tolerate oxidative damages provided by stress. In this work, influence of potassium (K) foliar spray from different fertilizer sources including K2SO4 and lysine (Lys)- and methionine (Met)-complexed K on physiological and antioxidative responses of strawberry (Fragaria ananassa ‘Gavieta’) to chilling (6 h d−1 at 4 °C for 3 consecutive days) was investigated. Chilling of control, Lys, and K-Lys-strawberry plants to 4 °C increased ion leakage and malondialdehyde (MDA) concentration. In contrast, chilling was ineffective on the amount of ion leakage and MDA in the plants supplied by K2SO4, K-Met, and only Met. The leaf chlorophyll concentration was found to reduce by chilling in both control (free of K and amino acid) and Lys-treatments, however, the chill-treatment leaf chlorophyll concentration remained unchanged in the plants supplied with K-Met, K2SO4, and only Met. The chilling at 4 °C resulted in between 0.58 % to 5.2-fold rise in strawberry leaf CAT, APX, and SOD activities, the largest increase was found at K-Met-treatment. Chilling substantially increased leaf proline concentration (on average 99.5 %), the largest increase was found at the K-Met-treatment. Chilling caused significant reduction in water potential (ΨL) and relative water content (RWC) of control and only Lys-and Met-strawberry plants but it had no effect on these water relations of K-fed plants. According to the results, foliar fertilization of K particularly from K-Met-complex was effective in alleviating the destructive effect of chilling on cell membrane of plant leaves. The protective effect of K and Met-fertilization against chilling-induced injuries was in part related to a substantial rise in leaf activity of CAT, APX, and SOD and leaf proline concentration.

Synthesis and import of GDP-l-fucose into the Golgi affect plant-water relations.

Land plants evolved multiple adaptations to restrict transpiration. However, the underlying molecular mechanisms are not sufficiently understood. We used an ozone-sensitivity forward genetics approach to identify Arabidopsis thaliana mutants impaired in gas exchange regulation. High water loss from detached leaves and impaired decrease of leaf conductance in response to multiple stomata-closing stimuli were identified in a mutant of MURUS1 (MUR1), an enzyme required for GDP-l-fucose biosynthesis. High water loss observed in mur1 was independent from stomatal movements and instead could be linked to metabolic defects. Plants defective in import of GDP-l-Fuc into the Golgi apparatus phenocopied the high water loss of mur1 mutants, linking this phenotype to Golgi-localized fucosylation events. However, impaired fucosylation of xyloglucan, N-linked glycans, and arabinogalactan proteins did not explain the aberrant water loss of mur1 mutants. Partial reversion of mur1 water loss phenotype by borate supplementation and high water loss observed in boron uptake mutants link mur1 gas exchange phenotypes to pleiotropic consequences of l-fucose and boron deficiency, which in turn affect mechanical and morphological properties of stomatal complexes and whole-plant physiology. Our work emphasizes the impact of fucose metabolism and boron uptake on plant-water relations.

Combined application of biochar and partial root-zone drying irrigation improves water relations and water use efficiency of cotton plants under salt stress

Reduced irrigation in combination with biochar application can improve stomatal anatomy, water relations and intrinsic water use efficiency (WUEi), thus having a positive effect on the alleviation of salinity and drought stresses. A split-root pot experiment was executed to explore the effects of two biochar applications (WSP: wheat straw biochar; SWP: soft wood biochar) in combination with three irrigation strategies (FI: full irrigation; DI: deficit irrigation, PRD: partial root-zone drying irrigation) on stomatal anatomy, water relations and WUEi of cotton plants under normal soil (S0, EC=0.36 dS m-1) and saline soil (S1, EC=16.55 dS m-1). The results revealed that both salinity and drought stresses negatively affected plant water relations and reduced stomatal conductance, carbon isotope discrimination (Δ13C), stomatal size (SS) and hydraulic conductance (Kl) while increased leaf abscisic acid (ABA) concentration ([ABA]leaf). However, biochar amendment under salt stress significantly decreased [ABA]leaf while improved leaf water relations, increased Kl, stomatal density (SD), SS, Δ13C and maximum stomatal conductance (gsmax). Meanwhile, compared with FI and DI, PRD plants had greater SD, gsmax, and WUEi but lowered stomatal conductance (gs). Among all treatments, the combined application of WSP and PRD significantly increased SD and gsmax, improved leaf water relations, Kl and [ABA]leaf and WUEi. It is concluded that the altered stomatal features caused by the biochar and irrigation treatments are associated with changes in [ABA]leaf and Kl, and have a major role in affecting plant hydraulic integrity and water use efficiency of cotton exposed to salinity stress.

Responses of yield, fruit quality and water relations of sweet pepper in Mediterranean greenhouses to increasing salinity

Increasing salinization of groundwater used for irrigation is a current and growing problem for vegetable production in greenhouses in the Mediterranean Basin. Vegetable growers in this system require clear information of crop response to salinity, particularly of threshold values. For sweet pepper in Mediterranean greenhouses, this work (i) evaluated the effect of increasing salinity on various parameters of crop yield, fruit quality and plant water relations, and (ii) determined threshold and slope values for the Maas and Hoffman (M&H) model. Sweet pepper was grown with nutrient solutions (ns) with electrical conductivities (EC) of 2.5 (T1), 3.5 (T2), 4.5 (T3), 5.5 (T4), 6.5 (T5) and 7.5 (T6) dS m−1. There were substantial and statistically significant reductions in total and marketable yield, dry matter production (DMP) and average fruit weight, with increasing salinity. In treatment T4 (ns of 5.5 dS m−1), the respective reductions for these parameters, compared to T1 (ns of 2.5 dS m−1), were 37%, 37%, 47%, 52% and 30%. Applying the M&H model, soil solution EC threshold (ECsst) values for total and marketable yield were 4.8 and 5.0 dS m−1. The respective slope values were − 8.0 and − 12.0%/dS m−1. The more rapid decline in marketable yield was influenced by a large increase in the incidence of blossom end rot (BER) with increasing salinity. In treatment T1, 25% of discarded fruit had BER which increased to 70% in T6. Average fruit size was affected by salinity, but fruit number was not. Most fruit quality parameters were unaffected by increasing salinity. However, fruits were more red and more yellow. Leaf water potential (ΨW), leaf osmotic potential (ΨO), stomatal conductance (gS) and leaf turgor potential (ΨP) followed the Maas and Hoffman model, with ΨW, ΨO and gS declining and ΨP increasing after the EC threshold value. The ECsst value for ΨW was 5.0 dS m−1, and for ΨO, gS and ΨP was 5.6–5.8 dS m−1. Considering all data, an ECsst value of 5.0 dS m−1 is suggested for sweet pepper grown in Mediterranean greenhouses.

Perfluoroalkyl substances exposure alters stomatal opening and xylem hydraulics in willow plants

Climate change and pollution are increasingly important stress factors for life on Earth. Dispersal of poly- and perfluoroalkyl substances (PFAS) are causing worldwide contamination of soils and water tables. PFAS are partially hydrophobic and can easily bioaccumulate in living organisms, causing metabolic alterations. Different plant species can uptake large amounts of PFAS, but little is known about its consequences for the plant water relation and other physiological processes, especially in woody plants. In this study, we investigated the fractionation of PFAS bioaccumulation from roots to leaves and its effects on the conductive elements of willow plants. Additionally, we focused on the stomal opening and the phytohormonal content. For this purpose, willow cuttings were exposed to a mixture of 11 PFAS compounds and the uptake was evaluated by LC-MS/MS. Stomatal conductance was measured and the xylem vulnerability to air embolism was tested and further, the abscisic acid and salicylic acid contents were quantified using LC-MS/MS. PFAS accumulated from roots to leaves based on their chemical structure. PFAS-exposed plants showed reduced stomatal conductance, while no differences were observed in abscisic acid and salicylic acid contents. Interestingly, PFAS exposure caused a higher vulnerability to drought-induced xylem embolism in treated plants. Our study provides novel information about the PFAS effects on the xylem hydraulics, suggesting that the plant water balance may be affected by PFAS exposure. In this perspective, drought events may be more stressful for PFAS-exposed plants, thus reducing their potential for phytoremediation.

Correction to: Water relations in plants treated with growth promoting rhizosphere bacteria

Correction to: Water relations in plants treated with growth promoting rhizosphere bacteria

The critical role of nitrogen in plants facing the salinity stress: Review and future prospective

Salinity stress is a serious abiotic stress that negatively affect the crop growth and development. Mineral nutrient supplementation is considered as an effective strategy to mitigate the adverse effects of salinity. Nitrogen (N) is an important nutrient needed for plants and its application also an effective strategy to mitigate adverse impacts of salinity. Salinity stress disturbs plant physiological, and biochemical functions, antioxidant activities, cellular membranes, antioxidant activities and nutrient uptake thereby cause significant reduction in plant growth and development. The application of N maintains membrane stability, plant water relations, leaf gas exchange characteristics, and protect the plants from oxidative damages which induce the salt tolerance in plants. Besides, this N also improves nutrient uptake and it also induce cellular signaling that mitigate the adverse impacts of salinity. Therefore, it is interesting to understand the role of N in inducing salt tolerance in plants. In present review the mechanisms of N uptake and assimilation in plants under saline conditions are discussed. The present review provides information on how N mitigates ionic toxicity, and oxidative damages and maintains nutrient balance to counter the toxic effects of salinity stress in plants. This review will help the readers to learning more about the role of N in inducing salt tolerance in plants.

Water relations in plants treated with growth promoting rhizosphere bacteria

Water relations in plants treated with growth promoting rhizosphere bacteria

Responses of salicylic acid encapsulation on growth, photosynthetic attributes and ROS scavenging system in Lactuca sativa exposed to polycyclic aromatic hydrocarbon pollution

Salicylic acid (SA) is a phytohormone that plays a key role in the regulation of the defense response against environmental variables in plants, and it provides increased yield and stress tolerance when exogenously applied to plants as a growth regulator. The role of SA-mediated signals in abiotic stress tolerance varies according to the species, stressor, application method, and dose. This study investigated the effects of salicylic acid (SA, 0.1 mg ml−1) or β-cyclodextrin encapsulated salicylic acid (e-SA, 0.1 mg ml−1) treatments on growth parameters, gas exchange, photosynthesis efficiency, and antioxidant capacity in lettuce seedlings exposed to polycyclic aromatic hydrocarbon pollution. Fluorene (FLN, 100 mg L−1) contamination resulted in a 27% growth rate and a 14% water content reduction in lettuce leaves. Significant suppressions of stomatal conductance, carbon assimilation, and PSII photochemistry were detected in plants under stress. FLN + SA and FLN + e-SA treatments regulated plant-water relations by stimulating proline accumulation and relieving stomatal limitations. As indicated by the high Fv/Fm ratio, photosynthesis efficiency was recovered in FLN + SA and FLN + e-SA group plants. FLN stress caused high oxidative stress in lettuce leaves and increased lipid peroxidation level by 40%. However, especially e-SA application to plants under stress, increased SOD activity by 3-fold and CAT activity by 80% and was successful in preventing H2O2 accumulation and lipid peroxidation. Both SA and e-SA treatments partially activated the AsA-GSH cycle. As a result, direct SA application was effective in mitigating stress-induced physiological limitations with high SA accumulation in the tissues, while encapsulated SA treatment was more effective in regulating photosynthetic and biochemical reactions, alleviating oxidative damage by activating the antioxidant defense, and promoting growth under stress with moderate SA accumulation.

How Does Zinc Improve Salinity Tolerance? Mechanisms and Future Prospects.

Salinity stress (SS) is a serious abiotic stress and a major constraint to agricultural productivity across the globe. High SS negatively affects plant growth and yield by altering soil physio-chemical properties and plant physiological, biochemical, and molecular processes. The application of micronutrients is considered an important practice to mitigate the adverse effects of SS. Zinc (Zn) is an important nutrient that plays an imperative role in plant growth, and it could also help alleviate the effects of salt stress. Zn application improves seed germination, seedling growth, water uptake, plant water relations, nutrient uptake, and nutrient homeostasis, therefore improving plant performance and saline conditions. Zn application also protects the photosynthetic apparatus from salinity-induced oxidative stress and improves stomata movement, chlorophyll synthesis, carbon fixation, and osmolytes and hormone accumulation. Moreover, Zn application also increases the synthesis of secondary metabolites and the expression of stress responsive genes and stimulates antioxidant activities to counter the toxic effects of salt stress. Therefore, to better understand the role of Zn in plants under SS, we have discussed the various mechanisms by which Zn induces salinity tolerance in plants. We have also identified diverse research gaps that must be filled in future research programs. The present review article will fill the knowledge gaps on the role of Zn in mitigating salinity stress. This review will also help readers to learn more about the role of Zn and will provide new suggestions on how this knowledge can be used to develop salt tolerance in plants by using Zn.

Benefits of symbiotic ectomycorrhizal fungi to plant water relations depend on plant genotype in pinyon pine

Rhizosphere microbes, such as root-associated fungi, can improve plant access to soil resources, affecting plant health, productivity, and stress tolerance. While mycorrhizal associations are ubiquitous, plant–microbe interactions can be species specific. Here we show that the specificity of the effects of microbial symbionts on plant function can go beyond species level: colonization of roots by ectomycorrhizal fungi (EMF) of the genus Geopora has opposite effects on water uptake, and stomatal control of desiccation in drought tolerant and intolerant genotypes of pinyon pine (Pinus edulis Engelm.). These results demonstrate, for the first time, that microorganisms can have significant and opposite effects on important plant functional traits like stomatal control of desiccation that are associated with differential mortality and growth in nature. They also highlight that appropriate pairing of plant genotypes and microbial associates will be important for mitigating climate change impacts on vegetation.

Measuring tissue water potential in marine macroalgae via an updated Chardakov method.

Regulation of tissue water potential is a key mechanism in macroalgal osmotic responses to changing external osmotic conditions, which are common in tidally influenced estuarine and intertidal systems. Nevertheless, significant knowledge gaps exist in our understanding of osmotic responses in macroalgae because few methods measure osmotic potential within macroalgal tissues. Leaf psychrometers have furthered understanding of osmotic potentials in terrestrial plant water relations, yet these have not been developed to measure the range of highly negative potential values found in marine macroalgae. To address these gaps, we present an effective, updated version of the Chardakov method to measure tissue water potential in macroalgae. Here, we present a case study examining macroalgal response in tissue water potential by two morphologically and evolutionarily distinct species, Ulva lactuca (Chlorophyta) and Hypnea musciformis (Rhodophyta) to four paired salinity and nutrient treatments at two temperatures. These treatments simulate a gradient from full coastal ocean conditions to brackish submarine groundwater discharge, an ecosystem type found on basaltic shorelines. Both algae demonstrated plasticity in osmotic response to submarine groundwater discharge with significant positive correlations between tissue water potential and proportion of submarine groundwater discharge in the treatment. These results are the first to describe macroalgal response in tissue water potential, a first step to understanding algal physiological ecology in such complex coastal environments. This revised Chardakov method is a valuable tool to better understand species-specific osmotic responses to ecologically relevant conditions, and can augment the study of other tidal systems and ontogenetic stages.

Role of ABA in the adaptive response of Arabidopsis plants to long-term boron toxicity treatment

Boron (B) toxicity causes impairments in several plant metabolic and physiological processes. Under conditions of excessive B availability, this micronutrient is passively transported through the transpiration stream and accumulates in leaves, causing the development of necrotic regions in leaf tips. Some plants have developed adaptive mechanisms to minimize the toxic effects of excessive B accumulation in their tissues. Thus, for instance, in Arabidopsis it has been described an ABA-dependent decrease in the transpiration rate that would restrict B accumulation in aerial plant tissues in response to short-term B toxicity, this effect being mediated by AtNCED3 (which encodes a key enzyme for ABA biosynthesis). The present work aimed to study the possible involvement of ABA in the adjustment of plant water balance and B homeostasis during the adaptive response of Arabidopsis to prolonged B toxicity. For this purpose, Arabidopsis wild-type and the ABA-deficient nced3-2 mutant plants were subjected to B toxicity for 7 days. We show that ABA-dependent stomatal closure is determinant for the adjustment of plant water relations under conditions of prolonged B toxicity. Results suggest that, in addition to the AtNCED3 gene, the AtNCED5 gene could also be involved in this ABA-dependent stomatal closure. Finally, our results also indicate the possible role of endogenous root ABA content in the mechanism of active efflux of B via BOR4 (efflux-type B transporter) from the root to the external environment under excess B conditions.

Predawn leaf water potential of grapevines is not necessarily a good proxy for soil moisture

BackgroundIn plant water relations research, predawn leaf water potential (Ψpd) is often used as a proxy for soil water potential (Ψsoil), without testing the underlying assumptions that nighttime transpiration is negligible and that enough time has passed for a hydrostatic equilibrium to be established. The goal of this research was to test the assumption Ψpd = Ψsoil for field-grown grapevines.ResultsA field trial was conducted with 30 different cultivars of wine grapes grown in a single vineyard in arid southeastern Washington, USA, for two years. The Ψpd and the volumetric soil water content (θv) under each sampled plant were measured multiple times during several dry-down cycles. The results show that in wet soil (Ψsoil > − 0.14 MPa or relative extractable water content, θe > 0.36), Ψpd was significantly lower than Ψsoil for all 30 cultivars. Under dry soil conditions (Ψsoil < − 0.14 MPa or θe < 0.36) Ψpd lined up better with Ψsoil. There were differences between cultivars, but these were not consistent over the years.ConclusionThese results suggest that for wet soils Ψpd of grapevines cannot be used as a proxy for Ψsoil, while the Ψpd = Ψsoil assumption may hold for dry soils.

Thinning effectively mitigates the decline of aging Mongolian pine plantations by alleviating drought stress and enhancing plant carbon balance

Intensifying drought around the globe poses strong challenges to the growth and survival of trees, emphasizing the urgency of understanding the physiological mechanisms of drought-induced tree decline and mortality and the necessity of using silvicultural approaches to mitigate drought effects on tree growth. We experimentally explored whether thinning enhances tree growth vigor and drought resilience in early aging Mongolian pine (Pinus sylvestris var. mongolica Litv.) plantations in a water-limited area of Northeast China using dendrochronological methods. Meanwhile, we compared plant hydraulic traits, water relations, and non-structural carbohydrate concentrations between trees growing in the thinned and un-thinned stands with the aim of unraveling the physiological mechanisms underlying the density effects on tree growth performance. The results showed that basal area increments of Mongolian pine trees in the high-density plantations started to decline continuously at tree cambium age of around 15 years over about a decade, while thinning effectively reversed their growth decline. Trees in thinned stands exhibited significantly higher predawn leaf water potentials, higher stem hydraulic conductivities, and larger carbon reserves than trees in un-thinned stands. Although trees growing in high-density stands maintained as low risks of xylem hydraulic dysfunction as trees growing in low-density stands, that was at the cost of substantially reducing tree crown size through branch mortality that unavoidably undermined their carbon balance at the whole-plant level. Consistently, trees growing in the thinned low-density stands showed significantly higher levels of non-structural carbohydrate reserve in stems and enhanced growth resilience to extreme drought than trees growing in the high-density reference stands. Our results suggest that thinning can effectively enhance xylem hydraulic transport efficiency and reduce the risk of carbon imbalance by increasing soil water availability and hence mitigates the early aging of Mongolian pine plantations in water-limited environments.

Challenges in pea breeding for tolerance to drought: Status and prospects

AbstractDrought is increasingly frequent in the context of climate change and is considered a major constraint for crop yield. Water scarcity can impair growth, disturb plant water relations and reduce water use efficiency. Pea (Pisum sativum) is a temperate grain legume rich in protein, fibre, micronutrients and bioactive compounds that can benefit human health. In reducing pea yield because of drought, the intensity and duration of stress are critical. This review describes several drought resistance mechanisms in pea based on morphology, physiology and biochemical changes during/after the water deficit period. Drought tolerance of pea can be managed by adopting strategies such as screening, breeding and marker‐assisted selection. Therefore, various biotechnological approaches have led to the development of drought‐tolerant pea cultivars. Finally, the main objective of the current research is to point out some useful traits for drought tolerance in peas and also, mention the methods that can be useful for future studies and breeding programmes.