The biogeochemistry of basic cations in two forest catchments with contrasting lithology in the Czech Republic

The biogeochemistry of Ca, Mg, K, and Nawere investigated in two forested catchments in theCzech Republic, one underlain by leucogranite, theother by serpentinite. High weathering rates at theserpentinite site at Pluhv Bor resultedin Mg²⁺ as the dominant cation on the soilexchange complex and in drainage water. Other basiccations (Ca²⁺, K⁺, Na⁺) showedrelatively low concentrations and outflow instreamwater. The catchment exhibited high basesaturation in mineral soils (>70%), and nearneutral soil and stream pH, despite elevated inputsof acidic deposition. Slow growth of Norway spruceat Pluhv Bor may be caused by K deficiency, Mgoversupply and/or Ni toxicity. In contrast, thegranitic site at Lysina showed low concentrations ofbasic cations on the soil exchange complex and instreamwater. Soil and drainage water at Lysina werehighly impacted by acidic deposition. Soil pH wasextremely acidic (<4.5) throughout the soilprofile, and the base saturation of the mineral soilwas very low (<5%). Supplies of basic cationsfrom atmospheric deposition and soil processes wereless than inputs of SO^2- ₄ on anequivalence basis, resulting in low pH and highconcentrations of total Al in drainage water. Needle yellowing in Norway spruce was possibly theresult of Mg deficiency at Lysina. Because of theirextremely different lithologies, these catchmentsserve as valuable end-members of ecosystemsensitivity to elevated levels of acidicdeposition.     

Factors controlling long-term changes in soil pools of exchangeable basic cations and stream acid neutralizing capacity in a northern hardwood forest ecosystem

Understanding the factors regulating the concentrations of basic cations in soils and surface waters is critical if rates of recovery are to be predicted in response to decreases in acidic deposition. Using a dynamic simulation model (PnET-BGC), we evaluated the extent to which atmospheric deposition of strong acids and associated leaching by strong anions, atmospheric deposition of basic cations through changes in emissions of particulate matter, and historical forest cutting have influenced soil pools of exchangeable basic cations and the acid-base status of stream water at the Hubbard Brook Experimental Forest (HBEF) in New Hampshire. Historical deposition of basic cations was reconstructed from regression relationships with particulate matter emissions. Simulation results indicate that the combination of these factors has resulted in changes in the percent soil base saturation, and stream pH and acid neutralizing capacity (ANC) from pre-industrial estimates of 20%, 6.3 and 45 eq L^–1, respectively, to current values of 10%, 5.0 and –5 eq L^–1, respectively. These current values fall within the critical thresholds at which forest vegetation and aquatic biotic are at risk from soil and surface water acidification due to acidic deposition. While the deposition of strong acid anions had the largest impact on the acid-base status of soil and stream water, the reduction in deposition of basic cations associated with reductions in particulate emissions was estimated to have contributed about 27% of the depletion in soil Ca²⁺ exchange pool and 15% of the decreases in stream water concentrations of basic cations. Decline in stream water concentrations of basic cation occurred under both increasing and decreasing exchangeable pools, depending on the process controlling the acid base status of the ecosystem. Model calculations suggest that historical forest cutting has resulted in only slight decreases in soil pools of exchangeable basic cations, and has had a limited effect on stream ANC over the long-term.     

Soil bacterial changes upon snowmelt: laboratory studies of the effects of early and late meltwater fractions

The effects of polluted and leached snowmelt waters on an upland soil bacterial community were determined in laboratory soil cores using simulated solutions. 24 isolate characters were determined before, and after, 32 days of solution application.The soil bacterial community exposed to polluted meltwaters (pH 2.3) showed a significant increase in its ability to metabolise the carbohydrates tested, and a significant decrease in the number of Gran-positive coccal forms. The percentage of Micrococcus isolates declined from 27% of the community to 2%, whilst Pseudomonas and Enterobacteriaceae isolates increased in number.The soil bacterial community exposed to leached snowmelt waters (pH 5.4) showed a significant increase in biochemical potential, but the ability to metabolise carbohydrates showed no change.     

Forecasting changes in water quality in rivers associated with growing biofuels in the Arkansas-White-Red river drainage,USA

Excess nutrients from agriculture in the Mississippi River drainage, USA have degraded water quality in freshwaters and contributed to anoxic conditions in downstream estuaries. Consequently, water quality is a significant concern associated with conversion of lands to bioenergy production. This study focused on the Arkansas-White-Red river basin (AWR), one of five major river basins draining to the Mississippi River. The AWR has a strong precipitation gradient from east to west, and advanced cellulosic feedstocks are projected to become economically feasible within normal-to-wet areas of the region. In this study, we used large-scale watershed modeling to identify areas along this precipitation gradient with potential for improving water quality. We compared simulated water quality in rivers draining projected future landscapes with and without cellulosic bioenergy for two future years, 2022 and 2030 with an assumed farmgate price of $50 per dry ton. Changes in simulated water quantity and quality under future bioenergy scenarios varied among subbasins and years. Median water yield, nutrient loadings, and sediment yield decreased by 2030. Median concentrations of nutrients also decreased, but suspended sediment, which is influenced by decreased flow and in-stream processes, increased. Spatially, decreased loadings prevailed in the transitional ecotone between 97° and 100° longitude, where switchgrass, Panicum virgatum L., is projected to compete against alternative crops and land uses at $50 per dry ton. We conclude that this region contains areas that hold promise for sustainable bioenergy production in terms of both economic feasibility and water quality protection.     

Long-term changes in chemical features of waters of seven Ethiopian rift-valley lakes

Chemical and chlorophyll a concentrations of seven Ethiopian rift-valley lakes were studied during 1990–2000. Results were compared with studies made between 1960 and 1990 in an attempt to detect long-term changes. Three different trends are apparent in the salinities (and the correlates conductivity, alkalinity, sodium concentration) of these lakes over the last 40 years: three lakes (lakes Zwai, Shalla and Abaya) have maintained their salinity levels from the 1960s, two lakes (lakes Langano and Awassa) have become more dilute, and the salinity levels of Lake Chamo and the soda lake Abijata have increased. Concentrations of silicate decreased in almost all the lakes whereas soluble reactive phosphorus (SRP) increased in most lakes. Chlorophyll a concentrations were higher in the recent samples from all lakes except two, which in conjunction with results from SRP and silicate analyses suggest eutrophication in four out of the seven lakes studied. The study relates salinization in lakes with closed drainage to increased human activities in their catchments, intensified by changes in climate during the last three decades in sub-Saharan Africa.     

Factors controlling soil water and stream water aluminum concentrations after a clearcut in a forested watershed with calcium-poor soils

The 24 ha Dry Creek watershed in the Catskill Mountains of southeastern New York State USA was clearcut during the winter of 1996–1997. The interactions among acidity, nitrate (NO₃⁻), aluminum (Al), and calcium (Ca²⁺) in streamwater, soil water, and groundwater were evaluated to determine how they affected the speciation, solubility, and concentrations of Al after the harvest. Watershed soils were characterized by low base saturation, high exchangeable Al concentrations, and low exchangeable base cation concentrations prior to the harvest. Mean streamwater NO₃⁻ concentration was about 20 μmol l⁻¹ for the 3 years before the harvest, increased sharply after the harvest, and peaked at 1,309 μmol l⁻¹ about 5 months after the harvest. Nitrate and inorganic monomeric aluminum (Al_im) export increased by 4−fold during the first year after the harvest. Al_im mobilization is of concern because it is toxic to some fish species and can inhibit the uptake of Ca²⁺ by tree roots. Organic complexation appeared to control Al solubility in the O horizon while ion exchange and possibly equilibrium with imogolite appeared to control Al solubility in the B horizon. Al_im and NO₃⁻ concentrations were strongly correlated in B-horizon soil water after the clearcut (r ² = 0.96), especially at NO₃⁻ concentrations greater than 100 μmol l⁻¹. Groundwater entering the stream from perennial springs contained high concentrations of base cations and low concentrations of NO₃⁻ which mixed with acidic, high Al_im soil water and decreased the concentration of Al_im in streamwater after the harvest. Five years after the harvest soil water NO₃⁻ concentrations had dropped below preharvest levels as the demand for nitrogen by regenerating vegetation increased, but groundwater NO₃⁻ concentrations remained elevated because groundwater has a longer residence time. As a result streamwater NO₃⁻ concentrations had not fallen below preharvest levels, even during the growing season, 5 years after the harvest because of the contribution of groundwater to the stream. Streamwater NO₃⁻ and Al_im concentrations increased more than reported in previous forest harvesting studies and the recovery was slower likely because the watershed has experienced several decades of acid deposition that has depleted initially base-poor soils of exchangeable base cations and caused long-term acidification of the soil.     

广东白盆珠水库水源林土壤水源涵养能力研究

通过对广东省白盆珠水库水源林土壤类型调查及土壤水分物理性质的测定,结果表明:库区水源林水平地带性土壤属赤红壤,山地土壤垂直带谱明显,分布有赤红壤、山地红壤、山地黄壤和山顶灌丛草甸土4个类型。土壤容重约为1.338g·cm^-3,随海拔升高土壤砂粒含量增加。土壤总孔隙度在45%～50%,非毛管孔隙度在5%～9%之间,毛管孔隙度35%～50%。不同森林类型土壤的最大持水量在30%～50%,即50～60mm,变化不大;蓄水容量有较大区别,范围在500～850t·hm^-2,灌丛草甸土最大,针阔混交林次之,沟谷阔叶林最小;排水能力约在130～180t·hm^-2,并以灌丛草甸土为最大,次生阔叶林为最小。该库区水源林土壤的排水和蓄水容量分别为62.69万t、316.29万t,消洪补枯能力明显。但水源林土壤非毛管孔隙度较小,蓄水量小于广东各种有林地森林类型平均蓄水量,所以该库区的水源林还需加强保育,以提升土壤的水源涵养能力。     

The biogeochemistry of two forested catchments in the Black Forest and the eastern Ore Mountains (Germany)

The biogeochemical input-output fluxes of two forested catchments with contrasting levels of atmospheric deposition were investigated in Germany. This paper focuses on the effects of recent changes in atmospheric inputs on the chemical composition in the soil solution and stream. The catchment 'Schluchsee' (Black Forest; SW Germany) is characterized by relatively low atmospheric inputs whereas 'Rotherdbach' (Ore Mountains; E Germany) received significant amounts of acid deposition (mainly originating from SO₂ emissions) until recent years. Both sites reveal decreases in H⁺ and S deposition during the 1990s. This pattern is typical when compared to trends in Europe. In response to the reduced S deposition, soil solution and streamwater SO₄ ^2– concentrations decreased significantly. A net release of SO₄ ^2– (output > input) was observed at both sites due to the release of S previously stored in the soil. The level of N deposition was more or less constant at both sites. At Schluchsee, NO₃ ^– concentration in streamwater remained more or less unchanged, whereas a decrease at Rotherdbach was observed. A recovery from acidification was found in seepage water as indicated by increasing acid neutralizing capacity (ANC). Streamwater ANC increased only in the permanently acidified Rotherdbach. No change of ANC was observed in the Schluchsee stream, which was characterized by episodic acidification during high-flow conditions. Nevertheless, the key factor controlling the recovery from surface water acidification was the type, amount and distribution of stored S pools in the ecosystem. Thus, time series analysis of long-term data of input-output chemistry can be a valuable instrument in order to improve the understanding of linked terrestrial-aquatic systems and give useful clues for modeling efforts.     

Changes in the character of DOC in streams during storms in two Midwestern watersheds with contrasting land uses

Dissolved organic carbon (DOC) dynamics in streams is important, yet few studies focus on DOC dynamics in Midwestern streams during storms. In this study, stream DOC dynamics during storms in two Midwestern watersheds with contrasting land uses, the change in character of stream DOC during storms, and the usability of DOC as a hydrologic tracer in artificially drained landscapes of the Midwest are investigated. Major cation/DOC concentrations, and DOC specific UV absorbance (SUVA) and fluorescence index (FI) were monitored at 2–4 h intervals during three spring storms. Although DOC is less aromatic in the mixed land use watershed than in the agricultural watershed, land use has little impact on stream DOC concentration during storms. For both watersheds, DOC concentration follows discharge, and SUVA and FI values indicate an increase in stream DOC aromaticity and lignin content during storms. The comparison of DOC/major cation flushing dynamics indicates that DOC is mainly exported via overland flow/macropore flow. In both watersheds, the increase in DOC concentration in the streams during storms corresponds to a shift in the source of DOC from DOC originating from mineral soil layers of the soil profile at baseflow, to DOC originating from surficial soil layers richer in aromatic substances and lignin during storms. Results also suggest that DOC, SUVA and FI could be used as hydrologic tracers in artificially drained landscapes of the Midwest. These results underscore the importance of sampling streams for DOC during high flow periods in order to understand the fate of DOC in streams.     

Long-term follow-up of cognitive dysfunction in patients with aluminum hydroxide-induced macrophagic myofasciitis (MMF)

Macrophagic myofasciitis (MMF) is characterized by specific muscle lesions assessing long-term persistence of aluminum hydroxide within macrophages at the site of previous immunization. Affected patients are middle-aged adults, mainly presenting with diffuse arthromyalgias, chronic fatigue, and cognitive dysfunction. Representative features of MMF-associated cognitive dysfunction (MACD) include (i) dysexecutive syndrome; (i) visual memory; (iii) left ear extinction at dichotic listening test. In present study we retrospectively evaluated the progression of MACD in 30 MMF patients. Most patients fulfilled criteria for non-amnestic/dysexecutive mild cognitive impairment, even if some cognitive deficits seemed unusually severe. MACD remained stable over time, although dysexecutive syndrome tended to worsen. Long-term follow-up of a subset of patients with 3 or 4 consecutive neuropsychological evaluations confirmed the stability of MACD with time, despite marked fluctuations.     

Long-term changes in spatial patterns of emergent vegetation in a Mediterranean floodplain: natural versus anthropogenic constraints

This study describes the long-term changes of spatial patterns of cut-sedge (Cladium mariscus) and common reed (Phragmites australis) in the Spanish floodplain wetland Las Tablas de Daimiel. Using seven sets of aerial photographs, we determined changes in their spatial patterns (size of patches) between 1945 and 2001 that resulted from combinations of natural change and anthropogenic stress (irrigated agriculture, waste water discharge, fire, ploughing). Our approach consisted in using 1 ha cells as units of spatial resolution in principal coordinates of neighbour matrices and spatial correlograms to assess the spatial scale of interest and spatial patterns at (1) the whole wetland and (2) two areas of the wetland with locally contrasting biophysical settings and anthropogenic stress history. Results showed that vegetation spatial patterns were influenced by natural variability until the 1970s. Thereafter, anthropogenic perturbation became the main driver of vegetation change, especially in the lower part of the wetland where local impacts were stronger. Natural variability did not fragment cut-sedge patches, and the effects of biological traits were less important for its spatial pattern. By contrast, man-made change resulted in a marked cut-sedge cover decrease and patch fragmentation, and the importance of its biological traits on spatial patterns increased. The trends of reed spatial patterns were generally opposite to, but not as clear as those for, cut-sedge. The trends of spatial patterns were especially evident at very broad (3,500–10,000 m) and broad (1,000–3,400 m) spatial scales. Competition for space and abiotic factors (water quality and water depth) were not strong predictors of cover variability at the 1-ha scale, particularly in the lower area of the wetland. This suggests that other environmental variables need to be considered in spatially explicit modelling of vegetation spatial patterns in wetlands. Consideration of spatial hierarchies and species-specific ecological traits is paramount to the conservation of degraded wetlands.     

Long-term changes in the phosphorus loading to and trophic state of the Salton Sea,California

The Salton Sea (Sea) is a eutrophic to hypereutrophic lake characterized by high nutrient concentrations, low water clarity, and high biological productivity. Based on dissolved phosphorus (P) and nitrogen (N) concentrations and N:P ratios, P is typically the limiting nutrient in the Sea and, therefore, should be the primary nutrient of concern when considering management efforts. Flows in the major tributaries to the Sea have been measured since 1965, whereas total P (TP) concentrations were only measured intermittently by various agencies since 1968. These data were used to estimate annual P loading from 1965 to 2002. Annual loads have increased steadily from ∼940,000 kg around 1968 to ∼1,450,000 kg in 2002 (∼55% increase), primarily a result of increased TP concentrations and loads in the New River. Although the eutrophic condition of the Salton Sea is of great concern, only limited nutrient data are available for the Sea. It is difficult to determine whether the eutrophic state of the Sea has degraded or possibly even improved slightly in response to the change in P loading because of variability in the data and changes in the sampling and analytical methodologies. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Guest editor: S. H. Hurlbert The Salton Sea Centennial Symposium. Proceedings of a Symposium Celebrating a Century of Symbiosis Among Agriculture, Wildlife and People, 1905–2005, held in San Diego, California, USA, March 2005     

Relationships of bio-climatic zones and lithology with various characteristics of forest soils in Greece

Summary Soils derived from a number of different parent materials (lithologies) and developed along a climatic gradient, manifested by the altitudinal succession of natural vegetation zones (Mediterranean, sub-Mediterranean, Mountainous and Pseudoalpine), were sampled throughout mainland Greece.In soils derived from siliceous parent materials low in clay, acidity increase and percent base saturation decreases from the Mediterranean to the Pseudoalpine vegetation zones. Clay illuviation is found mainly in soils developed in the Mediterranean and the sub-Mediterranean zones. No such changes are apparent in clayey soils rich in bases.Organic matter content of the mineral portion of the soil profile increases by a factor of 2 with a decrease in mean annual air temperature of about 10°C. The pattern of change in clay and soil organic matter content with climate is in relatively good agreement with soil development trends in the area, when soil profiles are named according to the FAO-Unesco soil map of the world.Concentrations of Ca and Mg decrease and those of total N, total and extractable P, K, Fe, Mn and Zn increase from the Mediterranean to the Mountainous zone. Within the same zone, however, concentrations of N, Ca, K, Fe, Mn and Zn decrease, but those of Mg, total and extractable P increase with soil depth. The concentrations of most macro- and micronutrients in the humic horizon are several times higher than those in the mineral portion of the soil profile due to biological enrichment.     

Sexual interference in two Chamerion species with contrasting modes of movement herkogamy

Evolution of herkogamy has been ascribed to preventing autonomous selfing within flowers, but this argument has received challenges due to the negative effects of sexual interference on reproductive success of plant species. We examined the effects of the two contrasting modes of herkogamy, detailed by the different patterns of style movement, on the foraging time of pollinators on flowers, pollen removal, and deposition in two Chamerion species. Our results suggested that the duration of foraging time of bumblebees was generally higher in C. angustifolium (L.) Holub than in C. conspersum (Hausskn.) Holub during the male-phase of flowers, but the reverse during the female-phase of flowers. As a result, stigma interfered with pollen removal more in C. conspersum than in C. angustifolium, based on examinations of pollen removal after one visit by a pollinator. However, this negative effect on total pollen removal was covered by the high pollinator diversity and the possible high visitation rate in the study sites. In contrast, we found that almost no difference existed in pollen deposition rate after one visit of a pollinator between the two Chamerion species, and emasculation did not increase the total pollen deposition in either species, indicating that anthers did not interfere with pollen deposition in the two Chamerion species. Our results suggested that, compared with C. conspersum, the derived mode of herkogamy in C. angustifolium reduced interference of stigmas in pollen removal. This might contribute to the wide distribution of C. angustifolium, to some degree, in environments of pollinator scarcity and low activity in newly colonized habitats.     

Long-term records of strontium isotopic composition in tree rings suggest changes in forest calcium sources in the early 20th century

Many studies made in Europe and North America have shown an increasing depletion of exchangeable base cations that may cause tree nutritional deficiencies in sensitive soils. We use radial variation of strontium isotope in tree-rings (⁸⁷Sr/⁸⁶Sr ratio) to monitor possible changes in Ca sources for tree nutrition (Sr is used as an analog to Ca). The two main sources of Ca in forest stands are mineral weathering release and atmospheric inputs. Measurements in several forest stands in temperate regions show a steep decrease from pith to outer wood of the Sr isotope ratio from∼1870 to∼1920 except for stands developed on soils with a higher Ca status. This suggests a decrease of the weathering contribution (high ⁸⁷Sr/⁸⁶Sr ratio) when cations are displaced from the soil exchange complex by acid deposition at a rate faster than the replenishment of the cation pool by mineral weathering. This displacement enhances the atmospheric contribution, which is characterized by a low ⁸⁷Sr/⁸⁶Sr ratio. Tree-ring chronologies are an exceptional historic-timing record of chemical changes in the soil environment induced by atmospheric pollution. The reliability of the tree-ring recorder has been verified with a well-controlled nutritional perturbation in the context of a limed forest stand (with a known liming Sr isotopic signature). Our data suggest that forest ecosystems were affected by atmospheric inputs of strong acids earlier than previously thought.     

Estimation of long-term variation in nutrient loads from the Hii River by comparing the change in observed and calculated loads in the catchments

To study the long-term change in nutrient loads from the Hii River to Lake Shinji, water samples were taken repeatedly over a year in 1983/1984 and again in 2001/2002. Annual total nitrogen (TN) loads, estimated from observations of water quality and river flow, increased from 860 to 920 t with a corresponding increase in NO₃–N concentration during the cool season. In contrast, total phosphorus (TP) loads decreased from 96 to 62 t. Annual TN and TP loads, calculated using emission factors and annual statistics for the catchments, showed a tendency to decline from 1986 to 2002. No source could be identified which would result in the increase in TN in the catchments, therefore, the increase in observed TN loads was considered to originate in other areas. Atmospheric nitrogen deposition transported from long distances has elevated the sum of NH₄–N and NO₃–N concentration in rainwater in the cool season. Therefore, it was considered that this resulted in the increase in TN loads in the Hii River.     

Review of Campylobacter spp. in drinking and environmental waters

Consumption of contaminated drinking water is a significant cause of Campylobacter infections. Drinking water contamination is known to result from septic seepage and wastewater intrusion into non-disinfected sources of groundwater and occasionally from cross-connection into drinking water distribution systems. Wastewater effluents, farm animals and wild birds are the primary sources contributing human-infectious Campylobacters in environmental waters, impacting on recreational activities and drinking water sources. Culturing of Campylobacter entails time-consuming steps that often provide qualitative or semi-quantitative results. Viable but non-culturable forms due to environmental stress are not detected, and thus may result in false-negative assessments of Campylobacter risks from drinking and environmental waters. Molecular methods, especially quantitative PCR applications, are therefore important to use in the detection of environmental Campylobacter spp. Processing large volumes of water may be required to reach the desired sensitivity for either culture or molecular detection methods. In the future, applications of novel molecular techniques such as isothermal amplification and high-throughput sequencing applications are awaited to develop and become more affordable and practical in environmental Campylobacter research. The new technologies may change the knowledge on the prevalence and pathogenicity of the different Campylobacter species in the water environment.     

Influences of forested watershed conditions on fluctuations in stream water temperature with special reference to watershed area and forest type

In order to gain insight into the effect of watershed conditions on fluctuations in stream water temperature, we statistically analyzed water temperature data for 1 year, using root mean square (Rms) and harmonic (A Amplitude, φ delay time) methods. The average values of delay time (days) between air and water temperatures (T _a and T _w) of small (< 0.5 ha), medium (0.5–100 ha) and large (> 100 ha) watersheds were 4.53 ± 0.82 days, 11.83 ± 3.88 days and 4.45 ± 1.52 days, respectively. Fluctuations in stream water temperature expressed by Rms (Rms T _w/Rms T _a) and harmonic methods (A −T _w/A −T _a) in the medium-sized watersheds with moderate slope gradients were 0.37 ± 0.09 and 0.56 ± 0.14, respectively. These values increased in the larger watersheds with low slope gradients, including five large rivers covered by various landscapes, with their averages of 0.53 ± 0.09 and 0.78 ± 0.09, respectively, indicating the influences of solar radiation and heat transfer processes. In the smaller watersheds with high slope gradients, these values were 0.73 ± 0.02 and 0.87 ± 0.03, respectively, suggesting that shorter passage time affected water temperatures. With respect to forest type, these values at badly managed hinoki forest watersheds (0.45 ± 0.04 and 0.73 ± 0.07) were larger than those at broadleaf forest (0.34 ± 0.04 and 0.51 ± 0.12) and well-managed hinoki forest (0.33 ± 0.04 and 0.51 ± 0.07) watersheds, indicating different proportions of flow paths.     

Sugar accumulation in roots of two grape varieties with contrasting response to water stress

Root sugar accumulation was studied in two grapevine varieties contrasting in tolerance to water stress. During a 10‐day water withholding treatment, the drought‐tolerant variety, Grenache, sustained less negative predawn and midday leaf water potentials as well as root water potential compared with the sensitive variety, Semillon. Grenache vines also maintained lower stomatal conductance and transpiration than Semillon vines throughout the drying period. In both varieties there was accumulation of sucrose in the roots and concentrations were inversely correlated to leaf and root water status. In both Grenache and Semillon, elevated root osmolality was associated with decreased soil moisture indicating that sugar accumulation may play a role in osmotic protection. Petiole xylem sap abscisic acid (ABA) concentrations increased with water deficit in both varieties and were highest for vines with the most negative root and predawn leaf water potentials. Furthermore, root sucrose concentrations were positively correlated with leaf xylem sap ABA concentrations, indicative of integration between carbohydrate metabolism and the ABA signalling system. Similar root sugar accumulation patterns between the two varieties, however, demonstrate that other factors are likely influencing the ability of the drought‐tolerant variety to remain hydrated.