The 18O ecohydrology of a grassland ecosystem – predictions and observations
The 18O ecohydrology of a grassland ecosystem – predictions and observations
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DOI：
10.5194/hess-23-2581-2019
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发表时间：
2019-06
影响因子：
6.3
通讯作者：
R. Hirl;H. Schnyder;U. Ostler;R. Schäufele;Inga Schleip;S. Vetter;K. Auerswald;Juan C. Baca Cabrera-Juan-C.-Baca-Cabr
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作者：
R. Hirl;H. Schnyder;U. Ostler;R. Schäufele;Inga Schleip;S. Vetter;K. Auerswald;Juan C. Baca Cabrera-Juan-C.-Baca-Cabr
抽象的。叶片水的氧同位素组成(δ18O)是生物档案中发现的环境和生理信息的重要决定因素，但关于降雨的δ18O通过土壤和木质部水传播到δ180叶的系统尺度的理解尚未在草原得到证实。在这里，我们报告了一个独特和全面的数据集，每两周对土壤、茎和叶的水分进行一次δ18O观测，这些观测是在一个温带、易干旱、混合物种的草原上进行的，历时七个生长季。利用基于物理的18O土壤-植物-大气迁移模型(MUSICA)的生态水文学部分，我们评估了我们预测土壤水中δ18O的动态、水分吸收深度以及土壤和大气湿度对该生态系统中叶片水分(Δ18O)富集的影响。该模型准确地预测了不同生态系统水池的δ18O动态，表明该模型对土壤水分垂直分布和根系吸水动态有较好的预测效果。观测和模型预测表明，在所有年份的干旱和潮湿时期，水分吸收主要发生在土壤浅层(<；20 cm)，推测(至少部分)是由于高放牧压力对根系周转和位置的影响。Δ18Oaf对土壤和大气水分含量都有反应，最好的描述是未富集水和蒸发富集水的恒定比例(两池模型)。模型预测与观测之间的良好一致性是显着的，因为描述土壤和植被的相关物理特征或功能关系的模型参数保持不变，整个混合物种生态系统只有一个值。
Abstract. The oxygen isotope composition (δ18O) of leaf water (δ18Oleaf) is an important determinant of environmental and physiological information found in biological archives, but the system-scale understanding of the propagation of the δ18O of rain through soil and xylem water to δ18Oleaf has not been verified for grassland. Here we report a unique and comprehensive dataset of fortnightly δ18O observations in soil, stem and leaf waters made over seven growing seasons in a temperate, drought-prone, mixed-species grassland. Using the ecohydrology part of a physically based, 18O-enabled soil–plant–atmosphere transfer model (MuSICA), we evaluated our ability to predict the dynamics of δ18O in soil water, the depth of water uptake, and the effects of soil and atmospheric moisture on 18O enrichment of leaf water (Δ18Oleaf) in this ecosystem. The model accurately predicted the δ18O dynamics of the different ecosystem water pools, suggesting that the model generated realistic predictions of the vertical distribution of soil water and root water uptake dynamics. Observations and model predictions indicated that water uptake occurred predominantly from shallow (<20 cm) soil depths throughout dry and wet periods in all years, presumably due (at least in part) to the effects of high grazing pressure on root system turnover and placement. Δ18Oleaf responded to both soil and atmospheric moisture contents and was best described in terms of constant proportions of unenriched and evaporatively enriched water (two-pool model). The good agreement between model predictions and observations is remarkable as model parameters describing the relevant physical features or functional relationships of soil and vegetation were held constant with one single value for the entire mixed-species ecosystem.