Institute of Botany, Department of Integrative Biology and Biodiversity Research, BOKU, Gregor-Mendel-Straße 33, Vienna, 1190, Austria.
University of Trieste, Dept. of Life Sciences, Via L. Giorgieri 10, 34127 Trieste, Italy.
Sci Total Environ. 2019 Nov 20;692:669-675. doi: 10.1016/j.scitotenv.2019.07.096. Epub 2019 Jul 8.
Environmental sustainability of viticulture is negatively affected by prolonged droughts. In limestone dominated regions, there is limited knowledge on grapevine water status and on methods for accurate evaluation of actual water demand, necessary to appropriately manage irrigation. During a dry vintage, we monitored plant and soil water relations in old and young vines of Istrian Malvasia on Karst red soil. The vineyard with young vines was additionally subdivided into two areas, based on their soil type, 1) karst silty-clay loam, and 2) mixture of crushed rocks and karst silty-clay loam (stony soil). Seasonal changes in exploited water resources were estimated via analysis of oxygen isotope composition (δO) of rainfall, deep soil water, and xylem sap. We hypothesized that plants are able to thrive during drought thanks to the water stored in deep soil layers, while they rely less on superficial soil horizons. Our results show that vines growing on karstic substrates have deep roots securing the use of stable water sources during summer, with consequent favourable plant water status. In fact, both young and mature vines approached the threshold of severe water stress, but never surpassed it, as midday leaf water potentials were >-1.3MPa in all study sites. Vines roots showed flexible water uptake, i.e. the ability to absorb water from deep or shallow soil horizons during drought and after late-summer thunderstorms, which was particularly evident in vines growing on the stony soil. In fact, precipitations of 20mm were enough for plant water status recovery, due to fast infiltration. On the other hand, at least 50mm of rainfall were necessary to induce water status recovery in more compact soil (karst silty-clay loam). Our findings provide new knowledge on the rooting depth and water needs of vines growing on shallow soils overlying fractured limestone bedrock.
葡萄栽培的环境可持续性受到长时间干旱的负面影响。在以石灰岩为主的地区，对于葡萄树的水分状况以及准确评估实际需水量的方法知之甚少，而这些是适当管理灌溉的必要条件。在一个干旱的年份，我们监测了在喀斯特红壤上老藤和幼藤的伊斯特拉马尔瓦西亚葡萄的植株和土壤水分关系。有幼藤的葡萄园还根据其土壤类型进一步分为两个区域，1）喀斯特粉砂壤土和 2）碎岩石和喀斯特粉砂壤土的混合物（多石土壤）。通过分析降雨、深层土壤水和木质部汁液的氧同位素组成（δO）来估计季节性耗水情况。我们假设，由于深层土壤层中储存的水分，植物能够在干旱期间茁壮成长，而对浅层土壤的依赖较少。我们的结果表明，生长在喀斯特基质上的葡萄树具有深根，可确保在夏季使用稳定的水源，从而使植物具有良好的水分状况。事实上，幼藤和成熟藤都接近严重水分胁迫的阈值，但从未超过该阈值，因为所有研究地点的中午叶片水势都>-1.3MPa。葡萄树根系具有灵活的吸水能力，即在干旱期间以及夏末雷暴后，从深层或浅层土壤吸收水分的能力，这在多石土壤上生长的葡萄树中尤为明显。事实上，由于快速渗透，20mm 的降雨量就足以使植物的水分状况恢复。另一方面，至少需要 50mm 的降雨才能使水分状况在更紧实的土壤（喀斯特粉砂壤土）中恢复。我们的研究结果为覆盖在断裂石灰岩基岩上的浅层土壤中生长的葡萄树的根系深度和需水量提供了新的认识。
