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Extreme weather events are expected to occur more frequently in the future, which may influence water distribution and uptake patterns in rocky mountainous areas of North China. To examine how plants respond and adapt to the extreme environment, we investigated water sources of the broadleaved tree species Quercus variabilis under a precipitation gradient (A: no natural precipitation, B: half of natural precipitation, C: natural precipitation, and D: twice the natural precipitation) using the stable isotope approach in the Beijing mountainous area. The results indicated that Q. variabilis exhibited considerable plasticity in the depth of water uptake and showed a strong dependence on deeper soil layers under the precipitation gradient. Q. variabilis mainly absorbed water from the 0–20 cm (20.02–28.61%) and 60–80 cm (22.81–29.44%) soil layers, and also used groundwater (26.32–30.54%) under the low soil water conditions of the A treatment. In the B treatment, Q. variabilis absorbed water from the groundwater (29.60–33.53%) and 60–80 cm (26.05–29.44%) soil layers and a small amount of water from 0 to 20 cm (10.67–12.25%). In the C and D treatments, the soil water content was greater than that of the B treatment; Q. variabilis still predominantly absorbed water from the 60–80 cm (26.88% and 27.35%, respectively) soil layer and groundwater (33.52% and 46.17%, respectively), and took minimal water from the 0–20 cm and 20–40 cm soil layers. We found that Q. variabilis showed no obvious responses to precipitation under the precipitation gradient, and its dimorphic root system allowed it to uptake different water sources under drought and humid environmental conditions and thus maintain its transpiration. Therefore, we can infer that Q. variabilis is well adapted to extreme precipitation events and has a strong adaptability to both extreme drought and flood conditions. [ABSTRACT FROM AUTHOR]

Water stress is regarded as a global challenge to forests. Unlike other water-limited areas, the water use strategies of rocky mountainous forests, which play an important ecohydrological role, have not received sufficient attention. To prove our hypothesis that species adopt different water use strategies to avoid competition of limited water resources, we used site abiotic monitoring, sap flow and stable isotope method to study the biophysiological responses and water use preferences of two commonly distributed forest species, Pinus tabuliformis (Pt) and Quercus variabilis (Qv). The results showed that Pt transpired higher than Qv. Pt was also prone to adopt isohydric water use strategy as it demonstrated sensitive stomatal control over water loss through transpiration. Qv developed cavitation which was reflected by the dropping Ec in response to high vapor pressure deficit, concentrated peak sap flux density ( Js), and enlarged hysteresis loop. Considering the average soil depth of 52.8 cm on the site, a common strategy shared by both species was the ability to tap water from deep soil layers (below 40 cm) when soil water was limited, and this contributed to the whole growing season transpiration. The contribution of surface layer water to plant water use increased and became the main water source for transpiration after rainfall. Qv was more efficient at using water from surface layer than Pt due to the developed surface root system when soil water content was not stressed. Our study proves that different water-using strategies of co-occurring species may be conducive to avoid competition of limited water resources to guarantee their survival. Knowledge of water stress-coping strategies of trees has implications for the understanding and prediction of vegetation composition in similar areas and can facilitate forest management criteria for plantations. [ABSTRACT FROM AUTHOR]

Trees growing in the Beijing mountain area are often located on rocky outcrops. As water sources for these trees are poorly understood, we investigated seasonal water sources of four typical tree species ( Platycladus orientalis , Pinus tabuliformis , Robinia pseudoacacia and Quercus variabilis ) using stable hydrogen and oxygen isotope methods in this area. Results indicate that P. orientalis predominantly utilized water from natural springs (57.8%) during the dry season and uptake water from shallow layer (0– 20 cm, 78.4%) during the wet season. P. tabuliformis predominantly utilized shallow (46.8% and 37.7%, respectively) and deep (60– 100 cm, 24.9% and 27.6%, respectively) soil water in the dry and wet seasons. R. pseudoacacia mainly absorbed shallow soil layers water (54.3%) during the dry season and switched its water source to all of the soil layers (19.2– 30.9%) during the wet season. Q. variabilis predominantly extracted water from the shallow (29.8%) and middle (20– 60 cm, 38.6%) soil layers during the dry season; and it primarily relied on middle layer soil water (25.9%) and natural springs (40.5%) in the wet season. These four tree species showed a strong adaptation to drought periods and our findings provide valuable information which can be used when selecting tree species and planning long-term ecological management of afforestation around the Beijing mountain area. [ABSTRACT FROM AUTHOR]

The determination of water use patterns of plants in a coastal ecosystem is critical to our understanding of local eco-hydrological processes and predicting trends in ecological succession under the background of global climate change. The water use patterns ofZiziphus jujuba, the dominant species on the Chenier Island in the Yellow River Delta, were examined following summer rainfall events. Stable oxygen isotope analysis was employed to analyze the effects of rainfall on the stable isotopic composition in potential water sources inZ. jujuba. The IsoSource model was used to estimate the contributions of potential water sources for xylem water inZ. jujuba. The results showed heavy rainfall could recharge both soil and groundwater but contributed little to the δ18O values in deep soil water (60–100 cm) and groundwater. Light rainfall had an effect only on surface soil water (0–40 cm).Z. jujubamainly absorbed deep soil water on non-rainy days. Rainwater became the predominant water source forZ. jujubaduring and immediately after heavy rainfall. Switching the plant’s main water source between deep soil water and rainwater providedZ. jujubawith a competitive advantage and improved the water use efficiency ofZ. jujubain this coastal ecosystem. [ABSTRACT FROM PUBLISHER]

In karst regions, forests often grow on bedrock outcrops, however the water sources used by the forest vegetation are not known. This study aimed at investigating whether there were seasonal shifts (dry/wet season) of water sources for plants growing on the continuous dolostone outcrops, and comparing their differences with those growing on nearby thin soils in karst areas of southwest China. Rainwater, soil water within 0-30 cm depths, spring water (as a reflection of local deep water sources) and plant xylem water were sampled in March (late dry season) and July (mid rainy season) 2009, respectively. A direct inference approach and the IsoSource mixing model were used to estimate the contributions of different sources to the plant xylem water. On the outcrops, the deciduous tree species Radermachera sinica mainly used deep water sources during the dry season and a mixture of rainwater and deep water sources during the wet season. By contrast, the deciduous small shrub Alchornea trewioides largely relied on recent rainwater during both dry and wet seasons. Three non-deciduous species ( Sterculia euosma, Schefflera octophylla and Ficus orthoneura) appear to rely on deep water sources during the wet seasons. In nearby thin soils, R. sinica mainly utilized deep water in the dry season and a mixture of soil water and deep water in the wet season. A. trewioides relied on the same water sources (rainwater-derived soil water) in the different seasons. The above results indicate that inter-specific differences in rooting patterns and leaf phenologies may lead to the differences in the sources of water used by coexisting plant species in karst regions. [ABSTRACT FROM AUTHOR]

South Africa is a water-stressed country and the efficient management of the demand for and frugal use of water is a topic that can no longer be avoided. Community-based natural resource management is an alternative approach to government steward- ship of natural resources, and in the instance of water management it is a particularly relevant and logical avenue to consider. The Constitution of the Republic of South Africa enshrines the right of the citizens of the country to a healthy environment and to a supply of safe water. These rights are attained through relevant legislation and government action. In this study, the residents of two rural villages in the Steelpoort River basin, South Africa, were interviewed and observed in relation to their water consumption needs and water use practices. The analysis of the research findings resulted in the design of a framework to guide the development of community-based educational programmes related to the management of water demand and water conservation in the Mangabane and Makgemeng communities in the Steelpoort River basin. [ABSTRACT FROM AUTHOR]

• Water use pattern was investigated for Caragana korshinskii on sunny and shady slopes. • Caragana korshinskii seasonally switched its water sources from different soil layers. • Caragana korshinskii on sunny slope used shallower soil water than that on shady slope. • Root distribution and soil moisture affect water use pattern of Caragana korshinskii. Flexible water use patterns are of great importance for the survival of vegetation in dryland regions. Our study aimed to investigate the influences of season and slope aspect on the water use patterns of Caragana korshinskii on typical shady and sunny slopes on the Loess Plateau in China. We collected xylem water, soil water from the 0–200 cm soil layers, and precipitation in May, July, September and November 2018 and measured their hydrogen (δD) and oxygen (δ18O) isotope compositions. The root distribution of C. korshinskii in the 0–200 cm soil layer on both slopes was also investigated. The 0–20, 20–80, and 80–200 cm soil layers were identified as three potential water sources for C. korshinskii , and their proportional contributions to the plant water supply were calculated using a linear mixed model. The results showed that C. korshinskii on the sunny slope absorbed 89.3% of their water from the 0–20 cm soil layer in May but mainly utilized water from the 0–20 and 20–80 cm soil layers in both July and September, and the total contribution percentages of these layers were 84.5% and 89.2%, respectively. However, C. korshinskii on the shady slope extracted water evenly from all three soil layers in May. Thereafter, the plants absorbed water from the 20–80 and 80–200 cm soil layers in both July and September, and the total contribution percentages of these layers were 96.0% and 91.8%, respectively. In November, C. korshinskii absorbed 84.8% and 78.0% of their water from the 80–200 cm soil layer on the shady and sunny slopes, respectively. The generally shallower soil water use of C. korshinskii on the sunny slope than on the shady slope may be due to the larger fine-root (d < 2 mm) length density in the 0–80 cm soil layer on the sunny slope (1.12 ± 0.28 mm/cm3) than on the shady slope (0.57 ± 0.16 mm/mm3) (P < 0.05). This study indicates that C. korshinskii on both shady and sunny slopes seasonally switched their water sources from different soil water layers during the growing season. However, due to their reliance on soil water at the 0–20 cm depth, which is supplied by unstable rainfall, C. korshinskii on sunny slopes may be more vulnerable to future climatic warming and drying on the Loess Plateau. Our findings provide valuable information related to optimal water management in the afforested shrublands in this region. [ABSTRACT FROM AUTHOR]

Canola has a high nitrogen requirement and optimal nitrogen (N) management in environments with variable rainfall is a challenge. This study investigated the impact of timing of N as a single or split application at different growth stages on seed yield, N uptake and water-use efficiency in canola. Nitrogen rates of 100 and 200 kg ha−1 were applied after sowing when two leaves were unfolded or equally split between the rosette, green bud and first flower stages. The experiments were conducted at two sites with contrasting rainfall and a supplementary irrigation treatment at the low rainfall site, generating a third environment. Nitrogen application increased seed yield by up to 20% at a high rainfall site and by up to 77% at a medium rainfall site, but the timing of N did not significantly affect the yield response to N. Seed yield was closely associated with total dry matter production and seed m−2. N-use efficiency was influenced more by N recovery and uptake efficiency, rather than physiological efficiency, which highlights the importance of soil moisture availability and the ability of the crop to exploit soil water and N reserves. The results suggest that better use of subsoil moisture by overcoming some of the subsoil constraints may be an avenue for further improvements in yield and nitrogen-use efficiency (NUE) of canola in this environment. [ABSTRACT FROM AUTHOR]