Plant Water Sources Research Articles

Water use sources and its influencing factors of Pinus massoniana and Quercus acutissima community in hilly region of Southern China.

The process of plant water use is complex and changeable, which is affected by various factors. Exploring the sources and influencing factors of plant water use can provide reference for clarifying the mechanisms of forest water adaptation under climate change. We chosen the typical forest communities in the hilly region of Sou-thern China, Pinus massoniana and Quercus acutissima mixed forest as the research object. By analyzing water sources of plants in different seasons, the factors affecting the changes of water sources were explored in combination with soil water, precipitation, and plant roots. The results showed that water use characteristics of P. massoniana and Q. acutissima were similar and both mainly utilized 0-40 cm soil water during the dry season, with proportions of 60.0% and 66.6%. During the rainy season, as soil water content of deep layers increased, the main water sources of both gradually shifted towards deep soil. The similarity proportion indices of P. massoniana and Q. acutissima were above 60%, indicating that there was an obvious water competition between them. Root system of Q. acutissima had plasticity in water absorption, and played a dominant role in absorbing shallow water during the dry season. Water was the main driving factor for water source transformation of Q. acutissima and P. massoniana during the rainy season. Compared with P. massoniana, Q. acutissima was more sensitive to the changes of water sources. Under the background of future warming and drying, the competition between the two species for shallow water sources might be intensified. Those two species should be sparsely planted or thinned to optimize forest structure to cope with water stress.

The different effects of regional and local winds on dew formation in the Negev desert

Abstract With dew serving as an important water source for various small organisms and plants in deserts, knowledge regarding the spatial distribution of dew (which constitutes an important fraction of the non-rainfall water, NRW) is of prime importance. This is also the case for the Negev dew desert. According to the classical model, local nocturnal katabatic winds that descend down the slopes during the night to the wadi beds are responsible for the accumulation of cold air, subsequently triggering dew formation in the wadis. Nevertheless, NRW measurements that were conducted in a one-order drainage basin in the Negev during the dewy season (late summer and fall) yielded half the amount in the wadi bed in comparison to the hilltop, attributed to the sheltered position of the wadi from the cooling effect of the regional (sea-breeze) winds, which are not considered by the classical model. Hypothesizing that the classical model may however take place at wide wadi where the sea breeze winds are not sheltered, measurements of dew and temperatures were periodically carried out at the beds of a 5 m-wide narrow (NW) and a 200 m-wide (WW) wadi beds and at the hilltop (HT). The findings did not fully support our hypothesis. In comparison to the hilltop, and despite the mutual effect of the katabatic and the sea breeze winds on the wide wadi bed, also the wide wadi exhibited lower amounts of dew than that of the hilltop, with NRW following the pattern HT > WW > NW. The overwhelming effect of the sea-breeze winds was also supported indirectly by periodic NRW and temperature measurements during the winter during which the sea breeze does not commonly take place. Evidence suggests that whereas the classical model takes place during the winter during which the katabatic winds may play a central role in dew formation, the occurrence of the sea breeze (regional wind) during the late summer and fall overshadows the effect of the local katabatic winds. Our findings point to the possibility that the classical model may not adequately predict dew formation in regions subjected to sea-breeze winds.

Uncorrected soil water isotopes through cryogenic vacuum distillation may lead to a false estimation on plant water sources

Abstract Successful use of stable isotopes (δ2H and δ18O) in ecohydrological studies relies on the accurate extraction of unfractionated water from different types of soil samples. Cryogenic vacuum distillation (CVD) is a common laboratory‐based technique used for soil water extraction; however, the reliability of this technique in reflecting soil water δ2H and δ18O is still of concern. This study examines the reliability of a newly developed automatic cryogenic vacuum distillation (ACVD) system. We further assessed the impacts of extraction parameters (i.e. extraction time, temperature and vacuum) and soil properties on the recovery of soil water δ2H and δ18O for the ACVD and traditional cryogenic vacuum distillation (TCVD) systems. Finally, we investigated the potential influence of CVD (ACVD and TCVD) technique on the prediction of plant water uptake through a sensitivity analysis. Both ACVD and TCVD similarly extracted water from the rewetted soils, but none of the CVD systems successfully recovered the isotopic signatures of doped water from soil materials. Mean δ2H offsets of extracted soil water were −2.6 ± 1.3‰ and −2.4 ± 1.7‰ for ACVD and TCVD, respectively, while mean δ18O offsets were −0.16 ± 0.14‰ and −0.39 ± 0.37‰. The isotopic offsets of CVD systems were positively correlated with soil clay content, and negatively correlated with soil water content. Using corrected soil data (with CVD offsets) could improve the prediction of plant water uptake based on its high correlation with the environmental factors. This study identifies the isotopic offsets of CVD systems (i.e. ACVD and TCVD) and provides possible solutions for better predicting plant water sources. Even though, the wide use of CVD techniques probably induce noticeable uncertainties in the prediction of plants water uptake depths. The dataset of soil water extraction in this study will have implications for the technological development of CVD techniques.

Leaf water δ18O, δ2H and d‐excess isoscapes for Australia using region‐specific plant parameters and non‐equilibrium vapour

AbstractOxygen (δ18O) and hydrogen (δ2H) isotope ratios, and their relationship to one another (d‐excess) are altered as water travels from the atmosphere to the land surface, into soils and plants and back to the atmosphere. Plants return water to the atmosphere through transpiration (evaporation through the stomata), which causes isotopic fractionation concentrating the heavier isotopes (18O and 2H) in the water that remains behind in the leaves. The degree of isotopic fractionation during transpiration is controlled largely by climate, and as a result can be predicted using process‐based models and climate data. The modelled transpirational isotopic fractionation can be applied to plant source water isotopic values to predict leaf water isotope ratios and generate maps of isotopic composition, or isoscapes. This approach of mechanistic modelling has been well demonstrated in the first generation of global leaf water isoscapes (PLoS One, 3(6), e2447, 2008). However, use of leaf water isoscapes in fields such as hydrology, ecology, and forensics requires a new generation of updated region‐specific isoscapes. Here, we generate leaf water isoscapes of δ18O, δ2H and d‐excess for Australia, the driest vegetated continent on Earth, where leaf water represents a critical water resource for ecosystems. These isoscapes represent an improvement over previous global isoscapes due to their higher resolution, region‐specific, empirically derived plant parameters, and non‐equilibrium corrections for water vapour isotopic composition. The new isoscapes for leaf water are evaluated relative to observed isotope ratios of leaf cellulose and cherry juice. The model predictions for annual average leaf water isotope ratios showed strong correlations with these plant tissues that integrate over time. Moreover, inclusion of region‐specific leaf temperature estimates and non‐equilibirum vapour corrections improved prediction accuracy. Regionally based isoscapes provide improved characterisations of average leaf water isotope ratios needed to support research in hydrology, plant ecophysiology, atmospheric science, ecology, and geographic provenancing of biological materials.

Integration of Sensing Framework with a Decision Support System for Monitoring Water Quality in Agriculture

Water is an essential element for every plant to survive, absorb nutrients, and perform photosynthesis and respiration. If water is polluted, plant growth can be truncated. The aim of this research is to develop a water quality monitoring system for agriculture purposes based on integration of sensing framework with a smart decision support method. This research consists of three stages: (1) the first stage: developing sensing framework which has four different water quality parameter sensors such as potential hydrogen (pH), electrical conductivity (EC), temperature, and oxidation-reduction potential (ORP), (2) the second stage: developing a hardware platform that uses an Arduino for sensor array of data processing and acquisition, and finally (3) the third stage: developing soft computing framework for decision support which uses python applications and fuzzy logic. The system was tested using water from many sources such as rivers, lakes, tap water, and filtered machine. Filtered water shows the highest value of pH as the filtered machine produces alkaline water, whereas tap water shows the highest value of temperature because the water is trapped in a polyvinyl chloride (PVC) pipe. Lake water depicts the highest value of EC due to the highest amount of total suspended solids (TSS) in the water, whereas river water shows the highest value of ORP due to the highest amount of dissolved oxygen. The system can display three ranges of water quality: not acceptable (NA), adequate (ADE) and highly acceptable (HACC) ranges from 0 to 9. Filtered water is in HACC condition (ranges 7–9) because all water quality parameters are in highly acceptable ranges. Tap water shows ADE condition (ranges 4–7) because one of the water quality parameters is in adequate ranges. River and lake water depict NA conditions (ranges 0–4) as one of the water quality parameters is in not acceptable ranges. The research outcome shows that filtered water is the most reliable water source for plants due to the absence of dissolved solids and contaminants in the water. Filtered water can improve pH and reduce the risk of plant disease. This research can help farmers to monitor the quality of irrigated water which eventually prevents crop disease, enhances crop growth, and increases crop yield.

Xylem water cryogenic vacuum extraction: Testing correction methods with CaviTron-based apple twig sampling

Cryogenic vacuum extraction (CVE), the most popular method for obtaining xylem water for isotopic analysis of ecosystems, is known to cause δ2H offset and may lead to biased inference on transpiration. While δ2H offset correction methods have been proposed recently, their accuracy in identifying plant water sources remains uncertain. In this study, capitalizing on the latest CaviTron centrifuge technique (CACT), we evaluated the accuracy of three current δ2H offset correction methods—CVE-bulk xylem water after the 8.1 ‰ correction method (8.1 ‰ Mean-Correc), CVE-bulk xylem water after the soil water isotope line correction method (Line-Correc), and CVE-bulk xylem water after the rehydration correction method (REHYDR)—for plant water source identification. We tested the three correction approaches on five apple (Malus pumila Mill) orchards. Our results revealed that although δ18O values of the CVE-bulk xylem water and the CACT-sap water matched, the δ2H values differed (P < 0.05), with a mean difference of −10.23‰ ± 3.75‰. By applying the available correction methods to the CVE-bulk xylem water, the δ2H offset was reduced to 2.13±3.75‰ (8.1 ‰ Mean-Correc), 4.43±4.48‰ (Line-Correc), and −0.44 ± 3.69‰ (REHYDR). The corrections also improved the Z-score. However, substantial δ2H offset variations remained after the corrections. Moreover, when applying the corrected xylem water isotopic compositions in plant water apportioning analysis, the Line-Correc method resulted in significant differences (P < 0.05) in 1 out of 80 cases, while the 8.1‰ Mean-Correc (0/80) and REHYDR (0/80) methods did not. Our results suggest that for the available correction methods for cryogenic extraction to reduce δ2H offsets, the REHYDR and 8.1‰ Mean-Correc methods outperformed the Line-Correc method in plant water source identification. Thus, we recommended that the REHYDR method and 8.1‰ Mean-Correc method be used to identify plant water sources of CVE-extracted bulk xylem water.

Seasonal water source patterns in a northern Arizona pine forest

The relationships among stand density and seasonal plant water source patterns in ponderosa pine (Pinus ponderosa) forests are important for informed management decisions in a bimodal climate with increasing variability in winter and monsoon precipitation inputs. Winter precipitation recharges soil moisture, yet it has declined over the past 20 years in the southwestern United States, and monsoon precipitation is becoming more variable in both magnitude and timing. Near Flagstaff, Arizona in August 2013 (monsoon), October 2013 (post-monsoon), and May 2014 (post winter snow melt), we measured soil moisture, soil water δD at five depths, and xylem water δD in Muhlenbergia montana (a perennial C4 grass), Festuca arizonica (a perennial C3 grass), and P. ponderosa seedlings (&amp;lt; 2 years old), saplings (2–5 cm basal diameter), and mature trees (&amp;gt; 60 cm diameter at breast height) in treated (thinned and burned) and untreated (no thinning, no burning) stands. We found that soil moisture was higher at all soil depths in treated stands in May, after snow melt, and this pattern persisted through August in the deepest soil (60 cm). We also found that, in all sampling months, δD in xylem water of grasses and pine seedlings indicated use of shallower soil water than for pine saplings and mature trees, presumably due to differences in rooting depths. Additionally, in August, δD in xylem water of pine saplings and mature trees indicated greater reliance on a deeper water source in untreated stands than in treated stands, likely due to greater competition for shallow water in untreated stands. Our isotopic data indicate that grasses and seedlings used predominantly monsoon water in August and October, while pine saplings and mature trees used predominantly winter water during all sampling months. Importantly, our data indicate that regenerating trees (seedlings and saplings) used both winter and monsoon seasonal water sources, suggesting an increasingly important role for monsoon precipitation if winter precipitation inputs continue to decline. Collectively, these findings demonstrate that management actions can benefit forests via increased soil moisture, that overstory trees rely predominantly on winter precipitation, and that monsoon precipitation is important for herbaceous species and younger, regenerating overstory trees.

Differences between stem and branch xylem water isotope composition in four tropical tree species

AbstractStable isotope studies (δ2H and δ18O) of water within plants are providing new information on water sources, competitive interactions and water use patterns under natural conditions. This is based on the assumption that there is no fractionation at the time of water uptake or during its transport within trees. However, previous studies have found fractionation does occur in water taken up through the roots in halophytic and xerophytic plants. It is unclear how widespread such fractionation is in other species. In this study, we tested this fractionation by comparing stem and branch xylem water isotopes over the period of one day (from 8 am to 5 pm) in four wet tropical rainforest tree species (Dendrocnide photinophylla,Aphananthe philippinensis,Daphnandra repandulaandMallotus polyadenos). We found branch water isotope ratios (δ2H and δ18O) were enriched compared with stem xylem water isotopes.D. photinophyllahad a significantly different branch δ18O ratio thanA. philippinensis,D. repandulaandM. polyadenos. In contrast, there were no significant differences in stem xylem δ18O among the four observed tree species. We found clear differences in the stable isotope ratios of δ18O for stem and branch xylem water forD. photinophyllaandD. repandulaof upto −0.85% and 0.50%, respectively. Remarkable δ2H differences were also found between stem and branch xylem water isotope ratios forA. philippinensis,D. repandulaandM. polyadenos, being upto −12.14%, −16.17% and −9.65%, respectively. A dual isotope (δ2H–δ18O) plot showed branch water values were more enriched than stem xylem water values forD. photinophyllaandD. repandula, indicating a clear difference between stem and branch xylem water. This study suggests that δ2H and δ18O fractionation could be a species‐specific phenomenon in tropical trees, which has important implications for plant water source identification and evapotranspiration partitioning.

Water Age Dynamics in Plant Transpiration: The Effects of Climate Patterns and Rooting Depth

AbstractWater ages in plant transpiration reveal important processes of water dynamics in soil‐plant‐atmosphere continuum, which is regulated by water variability and availability in both precipitation inputs and root zone. However, the impacts of climate patterns and rooting depth on water age dynamics in transpiration are inadequately investigated. In this study, variations in root‐zone water replenishment are estimated based on stable isotope compositions of precipitation and plant xylem water, and a piecewise linear mixing water age model is employed to quantify water ages in plant transpiration under five different climates. The results show that water ages in transpiration are very dynamic in all climates with a range between 1 and 229 days. Water replenishments in the root‐zone reveal whether and how much precipitation enters the root zone. Climate patterns control median (mean) water age in plant transpiration but modified by rooting depth. In wet climates, plants mainly rely on water source that originates from precipitation in the current month (accounting for about 60% on average of their water sources), while plants in dry climates largely rely on water source that originates from precipitation fallen on previous months/seasons. These indicate that climate has profound impacts on plant water source by regulating precipitation inputs, root zone water storage and residence time, and evapotranspiration. Despite the limitations of this study, our study provides an alternative way to reveal the precipitation partitioning in root‐zone and seasonal changes in plant water use of precipitation, which highlights different vegetation responses to water variability between climate types.

Performance valuation of onion (Allium cepa L.) genotypes under different levels of salinity for the development of cultivars suitable for saline regions.

Abiotic stress, especially salt stress, is one of the major barriers to crop production worldwide. Crops like onion that belong to the glycophytic group are more sensitive to salinity stress. A huge study regarding the influence of salinity stress on the growth and development of crops has already been done and is still ongoing. One of the major targets of the research is to develop genotypes that have enhanced performance under stress environments. The world needs more of these types of genotypes to combat the ever-growing salt-stressed soils. Therefore, a number of germplasm were studied during the 2019-2020 and 2020-2021 seasons under different salt concentrations to identify tolerant genotypes as well as to study the plants' responses at different growth stages against elevated salinity levels. A 2-year study was conducted where germination potential was evaluated in the first year and carried out in petri dish culture of seeds, followed by plastic pot culture for plant establishment and bulb development evaluation during the second year. Four different saline water solutions having different salt concentrations (0, 8, 10, and 12 dS m-1) were applied to the petri dishes and pots as the source of water for plants in both seasons. Results indicated that a significant reduction in plants' performance occurs under higher salinity levels. Salt concentration had an adverse impact on germination, leaf development and growth, the height of plants, bulb size and shape, and the bulb weight of onion. All the growth phases of onion are sensitive to elevated concentrations. Variable performances were observed in the genotypes under stress conditions, and a few genotypes (Ac Bog 409, Ac Bog 414, Ac Bog 424, Ac Bog 430, Ac Bog 417, Ac Bog 419, Ac Bog 420, Ac Bog 422, and Ac Bog 425) having some sort of tolerance to salt stress were identified, which might be recommended for mass production. Tolerance indices could successfully be applied in selecting the salt-tolerant genotypes. Thus, the present findings and the identified genotypes could be further utilized in salt stress improvement research on onion.

Ecohydrological niche segregation among desert shrubs in a gypsum-calcareous formation, north-western Iran

ABSTRACT Background Xerophilic subshrubs exhibit multiple functional types and frequently show hydrological niche segregation. In the poorly studied Irano-Turanian gypsum deserts, knowledge of the ecohydrological strategies of different plant species is essential to understand community complexity in these vulnerable ecosystems. Aim We studied the ecohydrological strategies of five co-existing subshrub members of Caryophyllales, ascertaining if their rooting architecture, gypsum affinity or photosynthetic pathway determined their water uptake, and if gypsum crystallisation water could be a relevant water source for plants in different seasons. Methods We conducted soil and xylem sampling for isotope analyses in spring and summer and extracted water by cryogenic vacuum distillation. Oxygen and hydrogen isotope compositions were determined and compared with visual representation and Bayesian Mixing Models to determine species ecohydrological strategies. Results Species – season interactions were related to differences in xylem sap isotopic composition. Three basic strategies relying on contrasting the use of free topsoil moisture and deep soil water could be detected and were in part explained by rooting architecture. Plant gypsum affinity and photosynthetic pathways did not have a significant effect on the water sources used by the plants. Conclusions Ecohydrological niche segregation was explained partly by rooting architecture and species-specific traits. Gypsum crystallisation water was not used in summer by the studied species.

Three Bayesian Tracer Models: Which Is Better for Determining Sources of Root Water Uptake Based on Stable Isotopes under Various Soil Water Conditions?

Stable hydrogen and oxygen isotopes provide a powerful technique for quantifying the proportion of root water uptake (RWU) from different potential water sources. Although many models coupled with stable isotopes have been developed to estimate plant water source apportionment, inter-comparisons of different methods are still limited, especially their performance under different soil water content (SWC) conditions. In this study, three Bayesian tracer mixing models, which included MixSIAR, MixSIR and SIAR, were tested to evaluate their performances in determining the RWU of winter wheat under various SWC conditions (normal, dry and wet) in the North China Plain (NCP). The proportions of RWU in different soil layers showed significant differences (p &lt; 0.05) among the three Bayesian models, for example, the proportion of 0–20 cm soil layer calculated by MixSIR, MixSIAR and SIAR was 69.7%, 50.1% and 48.3% for the third sampling under the dry condition (p &lt; 0.05), respectively. Furthermore, the average proportion of the 0–20 cm layer under the dry condition was lower than that under normal and wet conditions, being 45.7%, 58.3% and 59.5%, respectively. No significant difference (p &gt; 0.05) was found in the main RWU depth (i.e., 0–20 cm) among the three models, except for individual sampling periods. The performance of three models in determining plant water source allocation varied with SWC conditions: the performance indicators such as coefficient of determination (R2) and Nash-Sutcliffe efficiency coefficient (NS) in MixSIAR were higher than that in MixSIR and SIAR, showing that MixSIAR performed well under normal and wet conditions. The rank of performance under the dry condition was MixSIR, MixSIAR, and then SIAR. Overall, MixSIAR performed relatively better than other models in predicting RWU under the three different soil moisture conditions.

Effects of Leaf Hydrophilicity and Stomatal Regulation on Foliar Water Uptake Capacity of Desert Plants

Foliar water uptake (FWU) is one of the primary water sources for desert plants. Desert plants’ water uptake capacity is essential in maintaining the balance of carbon and water. However, there are few studies on FWU capacity in desert plants and the physiological and ecological characteristics that lead to differences in FWU capacity. In order to clarify FWU strategies and the influencing factors of plants in desert ecosystems, this study measured the contact angle, FWU parameters, and hydraulic parameters to explore six desert plants’ FWU capacity and the effects of leaf wettability and hydraulic parameters on FWU capacity. The results showed that all six plants had FWU capacity, among which the leaves of Nitraria sibirica Pall. and Halimodendron halodendron (Pall.) Voss had a high foliar water uptake rate (k) and high foliar water uptake accumulation (FWU storage), and the leaves of Glycyrrhiza uralensis Fisch. had a high k and low FWU storage. The leaves of Populus euphratica Oliv., Apocynum hendersonii Hook. f., and Alhagi sparsifolia Shap. had a low k and low FWU storage. Additionally, FWU capacity was mainly affected by stomatal regulation compared with leaf wettability and leaf structure. The results of this study will help to improve the understanding of the physiological and ecological adaptability of desert plants.

Patterns and drivers of seasonal water sources for artificial sand-fixing plants in the northeastern Mu Us sandy land, Northwest China

Understanding plant water-use patterns is important for improving water-use efficiency and for sustainable vegetation restoration in arid and semi-arid regions. However, seasonal variations in water sources and their control by different sand-fixing plants in water-limited desert ecosystems remain poorly understood. In this study, stable isotopic ratios of hydrogen (δ2H) and oxygen (δ18O) in precipitation, soil water, groundwater, and xylem water were determined to document seasonal changes in water uptake by three representative plant species (Pinus sylvestris var. mongolica Litv., Amygdalus pedunculata Pall., and Salix psammophila) in the northeastern Mu Us sandy land, Northwest China. Based on the depth distribution and temporal variation of measured gravimetric soil water content (SWC), the soil water profile of the three species stands was divided into active (0.01 g g-1 < SWC < 0.08 g g-1, 20% < coefficient of variation (CV) < 45%), stable (0.02 g g-1 < SWC < 0.05 g g-1, CV < 20%), and moist (0.08 g g-1 < SWC < 0.20 g g-1, CV > 45%) layers. Annually, P. sylvestris, A. pedunculata, and S. psammophila obtained most water from deep (59.2% ± 9.7%, moist layer and groundwater), intermediate (57.4% ± 9.8%, stable and moist layers), and shallow (54.4% ± 10.5%, active and stable layers) sources, respectively. Seasonally, the three plant species absorbed more than 60% of their total water uptake from the moist layer and groundwater in the early (June) dry season; then, they switched to the active and stable layers in the rainy season (July–September) for water resources (50.1%–62.5%). In the late (October–November) dry season, P. sylvestris (54.5%–66.2%) and A. pedunculata (52.9%–63.6%) mainly used water from stable and moist layers, whereas S. psammophila (52.6%–70.7%) still extracted water predominantly from active and stable layers. Variations in the soil water profile induced by seasonal fluctuations in precipitation and groundwater levels and discrepancies in plant phenology, root distribution, and water demand are the main factors affecting the seasonal water-use patterns of artificial sand-fixing plants. Our study addresses the issue of plant water uptake with knowledge of proportional source-water use and reveals important implications for future vegetation restoration and water management in the Mu Us sandy land and similar desert regions around the world.

Source Water Apportionment Using Stable Isotopes for Typical Riparian Plants along the Manas River in Xinjiang, Northwest China

Clarifying the water uptake patterns and competition among riparian plants under different ecological water conveyance conditions is crucial for the stability of the riparian ecosystem in arid areas. Here, we have utilized the Bayesian isotope mixing model to quantify the plant water sources for two typical riparian plants (Tamarix ramosissima and Phragmites australis) along the Manas River in Xinjiang, Northwest China. The water competition relationship between these two typical riparian plants is evaluated using the proportional similarity index (PSI). Our findings demonstrated the following: (1) The climate in the study area is dry and strongly evaporative, and the slope and intercept of the local meteoric water line are smaller than the global meteoric water line. The interconversion between surface water and groundwater occurred mainly in the upper reaches of the river. (2) At the sample site with the long-term ecological water conveyance, the water uptake pattern for typical riparian plants is predominantly shallow soil water or the uniform use of potential water sources. Among them, the utilization rate of shallow soil water reached 30.7 ± 12.6%. At sample sites with intermittent ecological water conveyance and the non-ecological water conveyance sample site, the growth of T. ramosissima and P. australis primarily uses deep soil water and groundwater, with mean values of 34.5 ± 5.1% and 32.2 ± 1.9%, respectively. (3) The water competition between plants at the intermittent ecological water conveyance and non-ecological water conveyance sample sites was more intense. However, the long-term ecological water conveyance effectively reduced water competition among plants. Our results will provide basic theoretical support for maintaining the stability of the Manas River riparian ecosystem and determining environmental flows.

Water competition among the coexisting Platycladus orientalis, Prunus davidiana and Medicago sativa in a semi-arid agroforestry system

Agroforestry has been widely used for the ecological restoration construction of semi-arid regions of the Chinese Loess Plateau. Investigating plant water sources is crucial for understanding the key ecohydrological processes of plant root water uptake and the water relations between coexisting plants. Clarifying the plant water use strategies can help to assess the sustainability of the vegetation restoration in agroforestry systems and provide references for the vegetation management. Thus, we investigated the water use characteristics of plants in an agroforestry system consisting of Platycladus orientalis, Prunus davidiana and Medicago sativa. The δD and δ18O of plant stem water and soil water in the 0–300 cm layer were measured. The MixSIAR model and proportional similarity (PS) were used to quantify the proportion of soil water absorbed by the plants in each layer and the hydrological niche overlap of plants. The results showed that the combined effects of rainfall recharge and evapotranspiration (ET) loss resulted in a decrease in soil water content (SWC) for the agroforestry system with increasing soil depth, and the SWC of the deep layer (80–300 cm) had minor variability (6.1–7.1%) throughout the study period. During the study period, due to the deep soil desiccation, P. orientalis, P. davidiana and M. sativa mainly utilized water from shallow (0–80 cm) soil layers, with a contribution rate of 65.4 ± 8.3%, 64.9 ± 7.7% and 73.0 ± 0.2%, respectively. The three coexisting plants relied on the unstable shallow soil water (recharged by rainfall) while the water use proportion of the deep soil layer was consistently low. This implies that the three plants were less resistant to drought stress, thus posing a threat to the stability and sustainability of the agroforestry system. Moreover, even in July and September with the high SWC in agroforestry, the partitioning of soil water among the three coexisting plants did not increase with increased ET loss. The three coexisting plants showed strong competition for soil water use, as indicated by the high values (0.69–0.97) of PS. Overall, the hydrological niche overlap of the coexisting plants in the agroforestry system resulted in low ecosystem stability. Density reduction or selection of suitable species is required to achieve sustainable vegetation restoration.

A review of stable hydrogen and oxygen isotopic offset in plant water source research

A review of stable hydrogen and oxygen isotopic offset in plant water source research

Documentary Film Creation “Impact of Kanta River Water Pollution on Conditions Social Economic Citizens Around The Estuary of Drainage”

The Kanta River flows in Pujon District and Ngantang District. This river water is used for irrigation, livestock sanitation, and the main source of water for hydropower plants and tourist water sources of the Selorejo Reservoir. The high role of this river water is apparently not realized so that residents use the Sunga Kanta watershed as a place to dispose of garbage and sewage. The current water condition of the Kanta River is quite poor and the settlement around the Selorejo Reservoir as a drainage estuary is the most affected area. The author responds to this water pollution problem in a film with the title "The Impact of Canta River Water Pollution on the Socioeconomic Conditions of Residents Around the Drainage Estuary". The documentary genre is an option because according to the character of this film, which presents facts according to reality, it is actually considered capable of accommodating the message of the film. The film narrative is prepared based on research data that has been analyzed descriptively and obtained by three data collection methods which include observation, literature study, and interviews. Films are shown publicly so that the message of the film can be widely accepted by citizens. In the end, this documentary is expected to be able to give birth to awareness to jointly maintain the water ecosystem, especially rivers.

Foliar water uptake improves branch water potential and photosynthetic capacity in Calligonum mongolicum

Atmospheric water is among the most important water sources for plants in arid ecosystems and plays an important role in facilitating drought stress survival in plants. However, little is known about the specific physiological benefits of foliar water uptake (FWU) for woody plants inhabiting arid desert areas. The objective of this study was to explore the physiological responses of Calligonum mongolicum to atmospheric water uptake by the assimilating branches, with a special focus on the FWU effect on shoot water status and photosynthesis. To this end, the canopies of natural C. mongolicum plants in a desert region of northwestern China were humidified in a field in-situ misting experiment and a long-term wetting experiment, during which physiological measurements of plant water relations and photosynthetic capacity were performed, alongside the observation of FWU by H218O isotopic tracing. Following the in-situ misting experiment, the water potential of the assimilating branches was significantly higher than that of the secondary branches at midnight, suggesting that FWU resulted in a reverse water potential gradient in C. mongolicum at the branch level. The 18O isotope was markedly enriched in the assimilating branches, secondary branches, and trunk xylem following the foliar uptake of 18O labeled water, indicating that the water uptake from the atmosphere by the assimilating branches could replenish the stem. The relative water content and water potential of the assimilating branches were significantly increased by FWU. The net photosynthetic rate, stomatal conductance, and maximum photochemical efficiency of C. mongolicum plants were markedly increased following the wetting treatment. Our results clearly show that C. mongolicum is capable of FWU, and that the absorbed water could be transported downward through the xylem and improve the branch water status and photosynthetic capacity. These findings provide a new perspective for deepening our understanding of the drought survival mechanism of plants in arid environments.

Tracing plant source water dynamics during drought by continuous transpiration measurements: An in-situ stable isotope approach.

The isotopic composition of xylem water (δX ) is of considerable interest for plant source water studies. In-situ monitored isotopic composition of transpired water (δT ) could provide a nondestructive proxy for δX -values. Using flow-through leaf chambers, we monitored 2-hourly δT -dynamics in two tropical plant species, one canopy-forming tree and one understory herbaceous species. In an enclosed rainforest (Biosphere 2), we observed δT -dynamics in response to an experimental severe drought, followed by a 2 H deep-water pulse applied belowground before starting regular rain. We also sampled branches to obtain δX -values from cryogenic vacuum extraction (CVE). Daily flux-weighted δ18 OT -values were a good proxy for δ18 OX -values under well-watered and drought conditions that matched the rainforest's water source. Transpiration-derived δ18 OX -values were mostly lower than CVE-derived values. Transpiration-derived δ2 HX -values were relatively high compared to source water and consistently higher than CVE-derived values during drought. Tracing the 2 H deep-water pulse in real-time showed distinct water uptake and transport responses: a fast and strong contribution of deep water to canopy tree transpiration contrasting with a slow and limited contribution to understory species transpiration. Thus, the in-situ transpiration method is a promising tool to capture rapid dynamics in plant water uptake and use by both woody and nonwoody species.