Abstract
AbstractUnderstanding root water uptake sources in agricultural systems is becoming increasingly important in the sustainable management of water resources under changing climatic conditions. In this work, a stable isotope approach was adopted to investigate water sources accessed by apple trees in two orchards growing in two different locations in the upper Etsch/Adige valley (Eastern Italian Alps). We tested the general hypothesis that soil water, composed of a mixture of rain and irrigation water, was the main source for tree transpiration in both fields, but trees could also access groundwater according to the different proximity to the groundwater table of the two orchards. Our results revealed that apple trees during the 2015 and 2016 growing seasons relied mostly on soil water present in the upper 20–40 cm of soils, with an apparently negligible contribution of groundwater, irrespective of the field location in the valley bottom. The isotopic composition of xylem water did not reflect irrigation water composition (or that of groundwater) but rather of rainfall and throughfall, and soil water. We related this behaviour to the intense rate of soil evaporation during the growing period that modified the original isotopic signature of irrigation water in the shallower layers, masking its actual contribution. This work contributes to improving the understanding of water uptake strategies in Alpine apple orchards and paves the way for further analysis on the proportion of irrigation and rainwater used by apple trees in mountain agroecosystems.
Highlights
Agriculture is globally characterised by having the highest rates of water consumption (FAO, 2011)
Zheng et al (2018) quantified root water uptake of 5-year-old apple trees using isotope-based mixing models and a numerical model with the aim of improving water use efficiency under limited irrigation conditions. Their analysis revealed contrasting results compared to those of Wang et al (2020, 2018). They showed that the principal depth of root water uptake was in the 0– 60 cm range, with the main contribution being within 0–40 cm, giving an indication towards reducing surface irrigation depth in order to improve water use efficiency (Zheng et al, 2018)
The same research group estimated the soil layer where apple tree roots absorbed most of the soil water: 0–40 cm when trees were irrigated by traditional surface irrigation and 20– 100 cm when the water storage pit irrigation system was deployed (Zheng et al, 2019)
Summary
Agriculture is globally characterised by having the highest rates of water consumption (FAO, 2011). Zheng et al (2018) quantified root water uptake of 5-year-old apple trees using isotope-based mixing models and a numerical model with the aim of improving water use efficiency under limited irrigation conditions Their analysis revealed contrasting results compared to those of Wang et al (2020, 2018). They showed that the layer with a depth of 60–100 cm was the main water source of the apple trees, but that they absorbed water from depths of 40–60 cm in the early stage of the growing period, whereas maize exclusively relied on water extracted from 20 to 60 cm depths, indicating competition for water use at 40–80 cm between apple trees and maize (Liu et al, 2020) From this brief review of previous studies, a knowledge gap is evident as to the water sources exploited by apple trees in regions outside of China's Loess Plateau, where different climatic and soil conditions, rootstocks, and cultivars can lead to different ecohydrological dynamics and water use strategies. Can isotopes support a conceptual model of water uptake strategies and ecohydrological dynamics in Alpine apple orchards?
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