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Slope position and water use by trees in a headwater catchment dominated by Japanese cypress: Implications for catchment‐scale transpiration estimates
Ecohydrology ( IF 2.6 ) Pub Date : 2020-08-25 , DOI: 10.1002/eco.2245
Kenji Tsuruta 1 , Hiroyuki Yamamoto 2 , Yoshiko Kosugi 2 , Naoki Makita 3 , Masanori Katsuyama 4 , Ken'ichirou Kosugi 2 , Makoto Tani 5
Affiliation  

We assessed tree transpiration at three slope positions with different soil water conditions in a small Japanese cypress‐dominated catchment under a humid climate using the sap flow technique. Differences in canopy transpiration (EC) were explained by total sapwood area (AS_tree) of the stand rather than by sap flux density at the three slope positions. Although soil water storage nearly reached the lower limit of plant available water during the growing season at mid‐slope and ridge positions with shallow soils, we observed no clear reductions in EC. EC was maintained by canopy stomatal conductance (GC) in addition to large ratios of fine root to total root biomass in trees growing at mid‐slope and ridge positions. Conversely, in a riparian area characterized by high soil moisture throughout the growing season, EC was maintained by variations in GC and a lower ratio of fine root to total root biomass. Our results suggest that Japanese cypress trees adapted to variations in soil water conditions associated with different slope positions under a humid region, by short‐term stomatal regulation as well as long‐term morphological changes in traits such as AS_tree and fine root biomass. Because AS_tree was highly correlated with diameter at breast height (DBH), whole‐tree transpiration was also correlated with DBH across the three slope positions. Our results suggest that the distribution of DBH size classes in a catchment could be a useful parameter for estimating catchment‐scale transpiration irrespective of topographic gradients and associated variations in soil water conditions.

中文翻译:

日本柏树主导的上游水源地的斜坡位置和树木的用水:对流域规模蒸腾量估算的影响

我们使用树汁流动技术,在潮湿的气候下,在一个以日本柏树为主的小流域,在不同土壤水分条件下的三个斜坡位置评估了树木的蒸腾作用。林分蒸腾量(E C)的差异是由林分的总边木面积(A S_tree)来解释的,而不是由三个斜坡位置的树汁通量密度来解释的。尽管在生长季中,在土壤较浅的中坡和山脊处土壤蓄水几乎达到了植物可用水的下限,但我们并未观察到E C的明显减少。È Ç保持由天篷气孔导度(G ^ C ^)以及在中坡和山脊位置生长的树木中细根与总根生物量的比例很大。相反,在整个生长期土壤湿度高的河岸地区,由于G C的变化和细根与根总生物量的比率较低,维持了E C。我们的研究结果表明,日本柏树通过短期气孔调节以及长期性状(例如A S_tree和细根生物量)的形态变化,适应了与潮湿地区不同坡位相关的土壤水分条件的变化。因为一个S_tree与胸高(DBH)的直径高度相关,整棵树的蒸腾也与三个坡度位置的DBH相关。我们的结果表明,不论地形梯度和土壤水分状况的相关变化如何,流域中DBH大小类别的分布可能是估算流域规模蒸腾作用的有用参数。
更新日期:2020-08-25
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