Composition Of Soil Water Research Articles

Stable isotopes of water reveal differences in plant – soil water relationships across northern environments

AbstractWe compared stable isotopes of water in plant stem (xylem) water and soil collected over a complete growing season from five well‐known long‐term study sites in northern/cold regions. These spanned a decreasing temperature gradient from Bruntland Burn (Scotland), Dorset (Canadian Shield), Dry Creek (USA), Krycklan (Sweden), to Wolf Creek (northern Canada). Xylem water was isotopically depleted compared to soil waters, most notably for deuterium. The degree to which potential soil water sources could explain the isotopic composition of xylem water was assessed quantitatively using overlapping polygons to enclose respective data sets when plotted in dual isotope space. At most sites isotopes in xylem water from angiosperms showed a strong overlap with soil water; this was not the case for gymnosperms. In most cases, xylem water composition on a given sampling day could be better explained if soil water composition was considered over longer antecedent periods spanning many months. Xylem water at most sites was usually most dissimilar to soil water in drier summer months, although sites differed in the sequence of change. Open questions remain on why a significant proportion of isotopically depleted water in plant xylem cannot be explained by soil water sources, particularly for gymnosperms. It is recommended that future research focuses on the potential for fractionation to affect water uptake at the soil‐root interface, both through effects of exchange between the vapour and liquid phases of soil water and the effects of mycorrhizal interactions. Additionally, in cold regions, evaporation and diffusion of xylem water in winter may be an important process.

Using Soil Water Stable Isotopes to Investigate Soil Water Movement in a Water Conservation Forest in Hani Terrace

Water conservation forests significantly contribute to the stability of mountain agricultural ecosystems in Hani Terrace. In this study, we analyzed the relationship between the stable isotopic composition of soil water and precipitation to determine the mechanisms of soil water movement in the small watershed of Quanfuzhuang. We observed significant seasonal variations in soil water sources: antecedent precipitation was the dominant supply during the dry season, and current precipitation dominated during the rainy season. The recharge ratio of precipitation to soil water in the grassland was significantly higher than that in the arbor land and shrubland. The influence of water infiltration, old and new soil water mixing, and soil evaporation on the soil water stable isotopes gradually decreased from the surface (0–20 cm) to the deep (60–80 cm) soil. We observed significant seasonal variability in average soil water δ18O in the upper 0–60 cm and lower variability at 60–100 cm. The average soil water δ18O was generally higher in the dry season than in the rainy season. The mixing of old and new water is a continuous and cumulative process that is impacted by soil structure, soil texture, and precipitation events. We therefore identified a significant time delay in soil water supply with increasing soil depth. Moreover, the piston flow of soil water co-occurred with preferential flow, and the latter was the dominant supply during the rainy season.

Water isotopic constraints on the enhancement of the mid-Holocene West African monsoon

During the early to mid-Holocene, changes in orbital precession led to considerable increases in West African monsoon (WAM) rainfall compared to today and shifted its reach further north. However, climate proxies and paleoclimate model simulations disagree over fundamental aspects of the mid-Holocene (MH; 6 ka BP) enhancement of the WAM. Here, we use a water isotope-enabled Earth system model (iCESM1) to, for the first time, directly compare simulated northern African hydroclimatic change between the mid-Holocene and pre-industrial era (PI) with the hydroclimate signal inferred from leaf wax n-alkanes in order to study the WAM's past spatial change. iCESM1 simulates a northernmost WAM extent of ∼24°N, which broadly agrees with the extent inferred from pollen and dust records (23–28°N) but falls short of that from leaf wax n-alkanes (27–31°N). While the isotopic composition of rainfall (δDP) inferred from leaf wax n-alkanes is lower during the MH than the PI, simulated MH δDP is higher in northwestern Africa, especially in boreal fall. This discrepancy can be reconciled by interpreting the inferred signal of leaf wax n-alkanes as being reflective of the isotopic composition of soil water (δDS) and its subsequent influence by soil evaporation. We postulate that leaf wax n-alkanes may overestimate inferred mean annual precipitation rates in the MH by not incorporating the enrichment of precipitation shown by iCESM1. Our results have broad implications for reconstruction of past hydrologic change in northern Africa and lend further support to the northernmost WAM extents inferred from pollen and dust records.

Using High-Frequency Water Vapor Isotopic Measurements as a Novel Method to Partition Daily Evapotranspiration in an Oak Woodland

Partitioning evapotranspiration (ET) into its constituent fluxes (transpiration (T) and evaporation (E)) is important for understanding water use efficiency in forests and other ecosystems. Recent advancements in cavity ringdown spectrometers (CRDS) have made collecting high-resolution water isotope data possible in remote locations, but this technology has rarely been utilized for partitioning ET in forests and other natural systems. To understand how the CRDS can be integrated with more traditional techniques, we combined stable isotope, eddy covariance, and sap flux techniques to partition ET in an oak woodland using continuous water vapor CRDS measurements and monthly soil and twig samples processed using isotope ratio mass spectrometry (IRMS). Furthermore, we wanted to compare the efficacy of δ2H versus δ18O within the stable isotope method for partitioning ET. We determined that average daytime vapor pressure deficit and soil moisture could successfully predict the relative isotopic compositions of soil (δe) and xylem (δt) water, respectively. Contrary to past studies, δ2H and δ18O performed similarly, indicating CRDS can increase the utility of δ18O in stable isotope studies. However, we found a 41–49% overestimation of the contribution of T to ET (fT) when utilizing the stable isotope technique compared to traditional techniques (reduced to 4–12% when corrected for bias), suggesting there may be a systematic bias to the Craig-Gordon Model in natural systems.

Plant genetic variation drives geographic differences in atmosphere-plant-ecosystem feedbacks.

The objective of this study was to understand how genetic variation in a riparian species, Populus angustifolia, affects mass and energy exchange between the land and atmosphere across ~1,700km of latitude of the western United States. To examine the potential for large-scale land-atmosphere feedbacks in hydrologic processes driven by geographic differences in plant population traits, we use a physical hydrology model, paired field, and greenhouse observations of plant traits, and stable isotope compositions of soil, stem, and leaf water of P. angustifolia populations. Populations show patterns of local adaptation in traits related to landscape hydrologic functioning-a 47% difference in stomatal density in greenhouse conditions and a 74% difference in stomatal ratio in the field. Trait and stable isotope differences reveal that populations use water differently which is related to historical landscape hydrologic functioning (evapotranspiration and streamflow). Overall, results suggest that populations from landscapes with different hydrologic histories will differ in their ability to maintain favorable water balance with changing atmospheric demands for water, with ecosystem consequences.

Water sources of major plant species along a strong climatic gradient in the inland Heihe River Basin

Knowledge on vegetation water sources is crucial to understand the ecohydrological processes and ecological management of arid and semi-arid ecosystems. The identification and quantification of plant water uptake from precipitation, soil and groundwater remain challenging along large climatic gradient. Stable oxygen isotope compositions of xylem water, soil water and groundwater were analyzed to assess seasonal and spatial patterns of water uptake of 11 major plant species along the Heihe River Basin. In the upper reaches, soil water recharged by precipitation was the main plant water source, and plants extracted water from the shallow soil water in wet season while used more deep soil water in dry season. In the middle reaches of desert-oasis ecotone, the water sources of shrubs shifted between soil moisture and groundwater depending on variations of precipitation and groundwater level, while shrubs at Gobi relied on deep soil water and shallow soil water after rainfall. In the lower reaches, the driest part of the region, groundwater and deep soil water were main water sources for the riparian plants. Groundwater was stable water source for shrubs growing on the planted shrubland, and soil water was stable water sources for shrubs growing at Gobi. Our results also revealed that water use strategies of the same species were plastic under different groundwater level and precipitation. This study identified water use patterns of different plant species along a climatic gradient and provided scientific implication for water management of different ecosystems of the arid and semi-arid ecosystems.

Air moisture and soil texture are crucial for the water dynamics of riparian bamboo in a subtropical region

This study investigated the influence of soil properties and plant age on the water use pattern of Bambusa rigida at different distances from a river during the dry season. The oxygen and hydrogen isotope compositions (δ18O and δ2H) of soil water and culm water in B. rigida forests from sites located at different distances from a river (site A: beside the river with high air moisture; site B: 200 m from the river with high clay content; site C: 400 m from the river with low clay content) were measured. Water uptake was not affected by plant age during early summer. Bambusa rigida at site A were able to use water from the soil organic horizon and moist air contributed 26% and 16% of soil water in this layer during winter and early summer. Bambusa rigida mainly took up water from soil layers with a high clay content at a depth < 50 cm due to the high water storage of these layers, although a high clay concentration weakened water uptake of bamboo roots at greater depths. This study is the first to identify the importance of air moisture for water dynamics of riparian bamboo and offers new insights into water use strategies of riparian B. rigida.

Integrated understanding of the Critical Zone processes in a subtropical karst watershed (Qingmuguan, Southwestern China): Hydrochemical and isotopic constraints

Improving the management and protection of karst groundwater resources and addressing karst-related environmental and ecological problems still face challenges raised from the limited knowledge on the entire karstic Critical Zone (K-CZ), including soil, epikarst, the vadose and saturated zones. Particularly, there is still a lack of integrated understanding of K-CZ properties and major CZ processes across space and time. In this study, we measured and analyzed the hydrochemical and multiple stable isotopic compositions of soil water, surface- and groundwaters from various compartments of the K-CZ in a typical subtropical karst watershed - Qingmuguan (QKW), Southwestern China, in order to explore the source and spatiotemporal variations of water and solutes (C, N, S) within the K-CZ; thereby elucidating the hydrological and biogeochemical processes and their affecting factors. The results show that (i) the K-CZ of QKW is characterized by high heterogeneity and permeability, with fast and strong hydrologic variations in response to rainfall variability; (ii) water-CO2‑carbonate interactions (i.e. carbonate weathering) are remarkably active in different zones and are significantly modulated by hydrologic dynamics and seasonal change in biological activities; (iii) efficient migration of nitrate and sulfate occurs across the surface toward the saturated aquifer zone, which is affected by the source availability, elemental transformation and flow transport processes; (iv) human activities have clearly influenced groundwater quality and the natural K-CZ processes, for example, exogenic acids of anthropogenic origin (e.g. acid precipitation and nitrogenous fertilizers from crop lands) have been proven to be involved in the carbonate weathering, with a contribution of ~20%–30%. Our study highlights the strong coupling of hydrological and various biogeochemical processes and the interactive connection among various layers of K-CZ. Thus, systematical monitoring along the CZ profile and a process-based dynamic approach to elucidating climatic and anthropogenic forcing are necessary to better understand the K-CZ properties and functions.

Do stream water solute concentrations reflect when connectivity occurs in a small, pre-Alpine headwater catchment?

Abstract. Expansion of the hydrologically connected area during rainfall events causes previously disconnected areas to contribute to streamflow. If these newly contributing areas have a different hydrochemical composition compared to the previously connected contributing areas, this may cause a change in stream water chemistry that cannot be explained by simple mixing of rainfall and baseflow. Changes in stormflow composition are, therefore, sometimes used to identify when transiently connected areas (or water sources) contribute to stormflow. We identified the dominant sources of streamflow for a steep 20 ha pre-Alpine headwater catchment in Switzerland and investigated the temporal changes in connectivity for four rainfall events based on stream water concentrations and groundwater level data. First, we compared the isotopic and chemical composition of stormflow at the catchment outlet to the composition of rainfall, groundwater and soil water. Three-component end-member mixing analyses indicated that groundwater dominated stormflow during all events, and that soil water fractions were minimal for three of the four events. However, the large variability in soil and groundwater composition compared to the temporal changes in stormflow composition inhibited the determination of the contributions from the different groundwater sources. Second, we estimated the concentrations of different solutes in stormflow based on the mixing fractions derived from two-component hydrograph separation using a conservative tracer (δ2H) and the measured concentrations of the solutes in baseflow and rainfall. The estimated concentrations differed from the measured stormflow concentrations for many solutes and samples. The deviations increased gradually with increasing streamflow for some solutes (e.g. iron and copper), suggesting increased contributions from riparian and hillslope groundwater with higher concentrations of these solutes and thus increased hydrological connectivity. The findings of this study show that solute concentrations partly reflect the gradual changes in hydrologic connectivity, and that it is important to quantify the variability in the composition of different source areas.

Мониторинг состава атмосферных и почвенных вод в лесных экосистемах: достижения и перспективы

Мониторинг состава атмосферных и почвенных вод в лесных экосистемах: достижения и перспективы

Variation of the stable isotopes of water in the soil-plant-atmosphere continuum of a Cinnamomum camphora woodland in the East Asian monsoon region

The hydrogen and oxygen stable isotopic (2H and 18O) tracer method has become an important means of studying water transfer between the atmosphere, rivers and lakes, soils, plants, and aquifers. We conducted a study on the variations of the stable isotopes of water, and the seasonal variations in water use of Cinnamomum camphora, in the soil-plant-atmosphere continuum in a C. camphora woodland in Changsha, central-southern China, which lies within the monsoon region of East Asia. Stable isotopes were monitored in precipitation, soil water (0–130-cm depth), groundwater, twig xylem water of C. camphora, and at the same time relevant environmental variables (soil water content, and meteorological variables) were measured, from March 2017 to August 2019. The monitoring data were collated and analyzed to determine the variations of stable isotopes in different water pools and mutual exchanges. The results indicate that daily precipitation (P) greater than 3.7 mm (regarded as effective precipitation) contributed to soil water replenishment. Isotopic composition of soil water and twig xylem water fell below the LMWLP>3.7 (the local meteoric water line eliminated rainfall events with P ≤ 3.7 mm). Isotopic composition of shallow soil water (0–60 cm) and twig xylem water was positively correlated with that of cumulative antecedent precipitation within two months. These patterns of precipitation isotopic signal propagation delineate a clear pathway of water transfer in this soil and plant continuum. The slope of the soil water line in the study area was higher than that of the LMWLP>3.7 because of the situation that precipitation in warm season with a larger evaporative demand is more depleted with heavy isotopes (i.e., more negative delta values) than that in cold season when the evaporative demand is low. Therefore, it was not feasible to determine the strength of isotopic fractionation based on the isotopic water line method. According to the MixSIR model, C. camphora water uptake mainly sourced from shallow soil water during the observation period. However, in July-September when soil was dry, deep soil water (60–130 cm) contributed to C. camphora water uptake for ~50%. These findings improve our understanding of the water cycle of the soil-plant-atmosphere continuum in the East Asian monsoon region.

Investigation of soil water hydrological process in the permafrost active layer using stable isotopes

AbstractHere, we studied the isotope characteristics and source contributions of soil water in the permafrost active layer by collecting soil samples in July 2018 in Yangtze River basin. Soil moisture and temperature showed decreasing trends from 0–80 cm, and an increasing trend from 80–100 cm. The value of δ18O and δD first increased and then decreased in the soil profile of 0–100 cm; however, d‐excess increased from 0–100 cm. δ18O values became gradually positive from the southwest to northeast of the study area, while d‐excess gradually increased from southeast to northwest. The evaporation water line (EL) was δD = 7.56 δ18O + 1.50 (R2 = 0.90, p &lt; 0.01, n = 96). Due to intense solar radiation and evaporation on the Tibetan Plateau, the elevation did not impact the surface soil. The altitude effect of the soil depths of 0–20 cm was not obvious, but the other soil layers had a significant altitude effect. Soil moisture and temperature were closely related to the stable isotopic composition of soil water. The contribution of precipitation to soil water on the sunny slope was 86%, while the contribution of the shady slope was 84%. However, the contribution of ground ice to soil water on sunny slope was 14% and the shady slope was 16%. The contribution of ground ice to soil water increased with increasing altitude on the sunny slope, but the contribution of ground ice to soil water had no obvious trend on the shady slope.

Coffee and shade trees show complementary use of soil water in a traditional agroforestry ecosystem

Abstract. Globally, coffee has become one of the most sensitive commercial crops, being affected by climate change. Arabica coffee (Coffea arabica) grows in traditionally shaded agroforestry systems in tropical regions and accounts for ∼70 % of coffee production worldwide. Nevertheless, the interaction between plant and soil water sources in these coffee plantations remains poorly understood. To investigate the functional response of dominant shade tree species and coffee (C. arabica var. typica) plants to different soil water availability conditions, we conducted a study during near-normal and more pronounced dry seasons (2014 and 2017, respectively) and a wet season (2017) in a traditional coffee plantation in central Veracruz, Mexico. For the different periods, we specifically investigated the variations in water sources and root water uptake via MixSIAR mixing models that use δ18O and δ2H stable isotope composition of rainfall, plant xylem and soil water. To further increase our mechanistic understanding of root activity, the distribution of below-ground biomass and soil macronutrients was also examined and considered in the model as prior information. Results showed that, over the course of the two investigated dry seasons, all shade tree species (Lonchocarpus guatemalensis, Inga vera and Trema micrantha) relied, on average, on water sources from intermediate (&gt;15 to 30 cm depth: 58± 18 % SD) and deep soil layers (&gt;30 to 120 cm depth: 34±21 %), while coffee plants used much shallower water sources (&lt;5 cm depth: 42±37 % and 5–15 cm depth: 52±35 %). In addition, in these same periods, coffee water uptake was influenced by antecedent precipitation, whereas trees showed little sensitiveness to antecedent wetness. Our findings also showed that during the wet season coffee plants substantially increased the use of near-surface water (+56 % from &lt;5 cm depth), while shade trees extended the water acquisition to much shallower soil layers (+19 % from &lt;15 cm depth) in comparison to drier periods. Despite the plasticity in root water uptake observed between canopy trees and coffee plants, a complementary use of soil water prevailed during the dry and wet seasons investigated. However, more variability in plant water sources was observed among species in the rainy season when higher soil moisture conditions were present and water stress was largely absent.

Biogeochemical Migration of Elements within the Lake Watershed of a Reference Site (Valdai Upland)

This study concerns the distribution of elements in the atmospheric precipitation–throughfall–soil water system of the Gusinoe Lake watershed in the Valdai Upland. The chemical compositions of precipitation, throughfall, and soil water, as well as soils, are determined. Element budgets are calculated in the soil profile studied for the summer–autumn period. Estimates are made of the soil enrichment in elements and the intensity of element migration in soil water.

Variation in the access to deep soil water pools explains tree-to-tree differences in drought-triggered dieback of Mediterranean oaks

Individual differences in the access to deep soil water pools may explain the differential damage among coexisting, conspecific trees as a consequence of drought-induced dieback. We addressed this issue by comparing the responses to a severe drought of three Mediterranean oak species with different drought tolerance, Quercus pubescens L. and Quercus frainetto Ten., mainly thriving at xeric and mesic sites, respectively, and Quercus cerris L., which dominates at intermediate sites. For each species, we compared coexisting declining (D) and non-declining (ND) trees. The stable isotope composition (δ2H, δ18O) of xylem and soil water was used to infer a differential use of soil water sources. We also measured tree size and radial growth to quantify the long-term divergence of wood production between D and ND trees and non-structural carbohydrates (NSCs) in sapwood to evaluate if D trees presented lower NSC values. The ND trees had access to deeper soil water than D trees except in Q. frainetto, as indicated by significantly more depleted xylem water values. However, a strong δ2H offset between soil and xylem water isotopes observed in peak summer could suggest that both tree types were not physiologically active under extreme drought conditions. Alternative processes causing deuterium fractionation, however, could not be ruled out. Tree height and recent (last 15-25years) growth rates in all species studied were lower in D than in ND trees by 22 and 44%, respectively. Lastly, there was not a consistent pattern of NSC sapwood concentration; in Q. pubescens, it was higher in ND trees while in Q. frainetto, the D trees were the ones exhibiting the higher NSC concentration. We conclude that the vulnerability to drought among conspecific Mediterranean oaks depends on the differential access to deep soil water pools, which may be related to differences in rooting depth, tree size and growth rate.

Analysis on Feature of Soil_River_Ground_Plants Water Based on Stable Oxygen Isotope in Poyang Lake Wetland

Poyang Lake is the largest freshwater lake in China, the water level of Poyang Lake was declined continuous, and extreme droughts have frequently occurred in recent years, the structure and function of the wetland ecosystem were destroyed. In this paper, Stable oxygen isotopes was used as a tracer to identify composition of soil water, river water, ground water, and plants water. The focus was on characterize the variation with depth of the stable oxygen isotope composition and identifying the main sources of oxygen in soil water, ground water, river water and plants water, understanding the mechanisms of water movement among them. Soil water sampled at 10 cm intervals over the top 100 cm at two sections in the Poyang Lake wetland, and water samples collected from the plants, river water and ground water, were analysed for stable oxygen isotope composition, exploring the recharge and discharge of relationship between them. The results shown that the values of δ18O at depth of 0∼30cm at section I were declined with increasing soil depth, the value of δ18O at depth of 0∼40cm at section II had rare variation with increasing soil depth. The groundwater supply at section I was mainly influenced by precipitation, at section II was by precipitation and river water. The average value of δ18O in the domain species plants leaves of phalaris arundinacea, crex cinerascens, and phragmites communis was -0.9%º, -4.23%º, -5.25%º respectively.

Integral Assessment of the Soil Cover State in Gas Production Area in the Middle Reaches of the Angara River

Long-term research data have been used to compile a soil map of the most transformed part of the gas-condensate field in the Middle Angara region. The studied area is assigned to the North Baikal mountainous province with podzolic (Podzols), soddy-podzolic (Retisols), peat-podzolic (Histic Podzols), peat-cryozemic (Histic Cryosols), gray-humus (Cambisols), and dark-humus (Phaeozems) soils. The natural diversity of the soil cover and the content of macro- and microelements in soils have been determined. In soils near some gas-condensate field facilities, the contents of oil products, lead, zinc, nickel, and chrome exceed the background values and health and safety standards. The chemical composition of soil water in the area has changed, and chloride soil salinization is recorded. Ecological zoning of the area with respect to its significance for humans and ecosystems and soil susceptibility to anthropogenic loads has been performed. A larger part of the gas field is suitable for the development, except for permafrost taiga areas, valuable virgin landscapes, and vulnerable soils of steep slopes. The zone requiring rehabilitation measures with subsequent extensive use includes the areas with strongly disturbed ground cover and the sod layer.

Investigating the root plasticity response of Centaurea jacea to soil water availability changes from isotopic analysis.

Root water uptake is a key ecohydrological process for which a physically based understanding has been developed in the past decades. However, due to methodological constraints, knowledge gaps remain about the plastic response of whole plant root systems to a rapidly changing environment. We designed a laboratory system for nondestructive monitoring of stable isotopic composition in plant transpiration of a herbaceous species (Centaurea jacea) and of soil water across depths, taking advantage of newly developed in situ methods. Daily root water uptake profiles were obtained using a statistical Bayesian multisource mixing model. Fast shifts in the isotopic composition of both soil and transpiration water could be observed with the setup and translated into dynamic and pronounced shifts of the root water uptake profile, even in well watered conditions. The incorporation of plant physiological and soil physical information into statistical modelling improved the model output. A simple exercise of water balance closure underlined the nonunique relationship between root water uptake profile on the one hand, and water content and root distribution profiles on the other, illustrating the continuous adaption of the plant water uptake as a function of its root hydraulic architecture and soil water availability during the experiment.

Chemical composition of soil waters in oil and gas production areas of north of Western Siberia

This study describes the changes in the chemical composition of soil waters under the influence of natural and anthropogenic factors in the area of development of oil and gas condensate fields in the north of Western Siberia. The concentration of chemical elements (Na, K, Ca, Cu, Zn, Fe, Pb, Cd, Ni, Co, Cr, Ba, Sr, Cd, and Mn) in soils, ground and soil waters was determined. Pollution of soil water and soil is local in nature and it is characteristic of areas located in the immediate vicinity of industrial facilities. A set of indicators is proposed for assessing the transformation of natural complexes under the influence of oil and gas production. The increased pH values, concentrations of petroleum hydrocarbons, nitrates, chlorides, sodium, potassium, calcium, barium, strontium, iron and manganese, as well as zinc, vanadium, cobalt and nickel are observed. In the impact zones in soil waters and soils. Mechanical disturbances of the soil and vegetation cover lead to an increase in defrost, secondary waterlogging and are accompanied by an increase in the migration of chemical elements in the catenary structure of landscapes.

Relationships between grape composition of Tempranillo variety and available soil water and water stress under different weather conditions

The aim of the research was to analyse the relationship between grape composition of the Tempranillo variety, and available soil water along the growing cycle. The study was conducted in the Rioja DOCa (Qualified Designation of Origin (Spain). Grape composition (berry weight, acidity and phenolic composition) was analysed between veraison and maturity in non-irrigated vines and related to available soil water along the growing cycle. The available soil water (ASW) was simulated for the period 2008–2018, taking into account soil properties and the weather conditions recorded at each location. Soil water was simulated for each plot and year analysed, after calibration in one plot and the ASW was evaluated under the different conditions. The results showed that soil properties conditioned available soil water, which influenced berry weight, acidity, anthocyanins and total polyphenol index. Under the rainfed conditions in which the vines were cultivated, vines suffered from moderate to high water stress in some periods along the growing cycle. The results showed the most critical periods regarding water availability for grape composition. An increase in available soil water between one and three weeks after bloom and at the end of the ripening period increased acidity and decreased pH while an increase in available soil water content between two and seven weeks after bloom and at the ripening period increased berry weight and decreased anthocyanins and other phenolic compounds.