An enhanced understanding of plant water uptake is critical for making better-informed management decisions involving vegetative manipulation practices aimed to improve site productivity. This is particularly true in arid and semiarid locations where water is a scarce, yet precious commodity. In this project, we evaluated the interannual and seasonal variability of soil moisture and transpiration in sapling, juvenile, and mature western juniper (Juniperus occidentalis) trees in a semiarid rangeland ecosystem of central Oregon, USA. Transpiration levels were greatest in mature juniper trees in an untreated juniper watershed (Jensen WS), while the lowest transpiration levels were observed in juniper saplings in a treated watershed (Mays WS) where most mature juniper trees were removed in 2005. Significant differences (p ≤ 0.05) in leaf water potential levels observed between predawn and midday readings for all juniper growth stages indicated water is lost over the course of the day. Results showed seasonal precipitation was highly variable over the course of the study (2017 through 2019) and this was reflected in soil water available for tree uptake. This resulted in considerable intra- and inter-annual variation in transpiration. In years with greater winter precipitation amounts (2017 and 2019), juniper transpiration rates were highest during the summer, followed by spring, autumn, and winter. On average, transpiration rates during the summer in the wettest (329 mm) year 2017 were 115 and 2.76 L day−1 for mature and sapling trees, respectively. No data were collected for juvenile trees in 2017. In the drier (245 mm) year 2018, higher transpiration rates were observed in the spring. On average, spring transpiration rates were 72.7, 1.61, and 1.00 L day−1 for mature, juvenile, and sapling trees, respectively. Study results highlight the sensitivity of western juniper woodlands to variations in seasonal precipitation and soil moisture availability.

中文翻译：

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西部杜松不同生长阶段水分利用与土壤水分关系

加深对植物吸水量的了解对于做出更明智的管理决策至关重要，这些决策涉及旨在提高现场生产力的植物操纵实践。在干旱和半干旱地区尤其如此，在这些地区，水是一种稀缺而宝贵的商品。在该项目中，我们评估了美国俄勒冈州中部半干旱牧场生态系统中幼树、幼年和成熟的西部杜松 (Juniperus occidentalis) 树的土壤水分和蒸腾的年际和季节变化。在未经处理的杜松流域 (Jensen WS) 中，成熟杜松树的蒸腾水平最高，而在处理过的流域 (Mays WS) 中的杜松树苗中观察到的蒸腾水平最低，其中大多数成熟的杜松树在 2005 年被移除。显着差异 (p ≤ 0。05）在所有杜松生长阶段的黎明前和中午读数之间观察到的叶水势水平表明水分在一天中流失。结果表明，在研究过程中（2017 年至 2019 年），季节性降水变化很大，这反映在可供树木吸收的土壤水分中。这导致了蒸腾作用的相当大的年内和年际变化。在冬季降水量较大的年份（2017 年和 2019 年），杜松的蒸腾速率在夏季最高，其次是春季、秋季和冬季。平均而言，2017 年最潮湿（329 毫米）年份夏季的蒸腾速率分别为成熟和幼树的 115 和 2.76 L day-1。没有收集 2017 年幼树的数据。在 2018 年较干燥（245 毫米）的年份，在春季观察到较高的蒸腾率。平均而言，成熟、幼年和幼树的春季蒸腾速率分别为 72.7、1.61 和 1.00 L day-1。研究结果强调了西部杜松林地对季节性降水和土壤水分可用性变化的敏感性。