Evapotranspiration (ET) and its induced perturbations in the surface energy balance have significant impacts on the carbon cycle, water cycle, and regional climate. The partitioning of ET (transpiration (T) and evaporation (E)) has significant implications for agricultural production and water management. Rising tropospheric ozone (O3) concentrations currently alter leaf stomatal conductance, which may affect ET. Paddy fields are characterized by flooding (during most of the growth period), vigorous crop ET, and a high percentage of E in ET. This may cause differences in the effects of elevated O3 on the ET in rice fields relative to previously reported dryland crops. Based on 3 years of in-situ observations, this study investigated energy allocation in a rice ecosystem using the energy balance residual method under two O3 treatments (1.5 times ambient air (AA; E-O3) and AA) at a Free Air O3 Concentration Enrichment facility. E-O3 caused a trend of higher net radiative flux (Rn) and sensible heat flux (H) in rice but only reached statistical significance on some days and at specific growth stages (e.g., jointing or booting) compared with AA. E-O3 attenuated the degree of response in energy allocation owing to the unique land-use patterns of paddy fields and climatic conditions during rice growth. Based on the modified Priestley–Taylor model, T decreased significantly at the grain-filling stage, and E increased during the full reproductive period, causing a significant increase in ET on some days after exposure to elevated O3. In conclusion, rice ecosystems have a weaker capacity to influence the water cycle and regional climate than drylands regarding rising O3 concentrations. However, the effects of E-O3 on E and T adversely affect the carbon cycle and agricultural production, indicating the need to optimize agricultural water management and cropping strategies under high O3 concentration region.

中文翻译：

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臭氧升高对全露天田间条件下水稻生态系统蒸散和能量分配的影响


蒸散发 （ET） 及其对表面能量平衡的诱导扰动对碳循环、水循环和区域气候有重大影响。ET（蒸腾 （T） 和蒸发 （E））的分配对农业生产和水资源管理具有重大影响。目前上升的对流层臭氧 （O3） 浓度会改变叶片气孔导度，这可能会影响 ET。稻田的特点是洪水（在生长期的大部分时间）、作物 ET 旺盛和 ET 中 E 的百分比很高。这可能会导致相对于先前报道的旱地作物，升高的 O3 对稻田 ET 的影响存在差异。基于 3 年的原位观察，本研究在两种 O3 处理（1.5 倍环境空气 （AA;E-O3） 和 AA） 的 BetaS Package。E-O3 导致水稻净辐射通量 （Rn） 和感热通量 （H） 呈升高趋势，但与 AA 相比，仅在某些天数和特定生育阶段（例如，拔节或孕穗）达到统计学意义。由于稻田独特的土地利用模式和水稻生长过程中的气候条件，E-O3 减弱了能源分配的反应程度。基于改良的 Priestley-Taylor 模型，T 在籽粒灌浆期显著降低，E 在整个生殖期增加，导致暴露于升高的 O3 后几天 ET 显著增加。总之，就 O3 浓度上升而言，水稻生态系统影响水循环和区域气候的能力比旱地弱。 然而，E-O3 对 E 和 T 的影响对碳循环和农业生产产生不利影响，表明需要在 O3 高浓度区域优化农业水分管理和种植策略。