Prolonged hot periods known as heat waves (HW) are likely to increase in frequency and intensity due to climate change. Several studies analyzed the impact of recent heat waves on different un-managed terrestrial ecosystems, while little is known about the change they provoke in the carbon and water fluxes on irrigated agroecosystems. In this study we analyzed observations from 6 years continuous eddy covariance measurements (2013–2018) in an apple orchard located in South Tyrol (Northern Italy), regularly irrigated to prevent any limitations in soil water availability. The aim was to assess the impact of the heatwaves (at least 3 consecutive days of unusually high maximum temperature for the summer period) on the gross primary production (GPP), net ecosystem exchange (NEE), and actual evapotranspiration (ETa) fluxes. Out of the 13 heat waves that emerged from the temperature data analysis, five occurred in 2015, which together with 2013 was the hottest year in the considered period. In these two years, GPP and NEE patterns indicated a small but significant reduction in the assimilation capacity of the orchard with increasing T_max, which was not present in the remaining years. ETa, instead, consistently increased across all the temperature range. During heatwaves, we observed an increase in the available energy, and a further reduction in the sensible heat flux in favour of latent heat, with a consequent increase in ETa. Additionally, during 9 out of the 13 heat waves, ETa values were among the 5% highest ever recorded in summer. Although heatwaves differed in length (max. 8 days) and magnitude (with peaks of 37 °C), ETa generally increased during heat waves by approximately 9% with respect to the week before. No similar consistent patterns were observed for GPP and NEE, which supports the hypothesis of decoupling between carbon and water fluxes during heat waves in an irrigated agroecosystem.

由于气候变化，被称为热浪 (HW) 的长时间高温期可能会增加频率和强度。几项研究分析了近期热浪对不同无人管理的陆地生态系统的影响，但人们对它们在灌溉农业生态系统中引起的碳和水通量的变化知之甚少。在这项研究中，我们分析了位于南蒂罗尔（意大利北部）的苹果园 6 年连续涡流协方差测量（2013-2018 年）的观察结果，该果园定期灌溉以防止土壤水分供应受到任何限制。目的是评估热浪（夏季期间至少连续 3 天异常高的最高温度）对初级生产总值 (GPP)、净生态系统交换 (NEE) 和实际蒸散量 (ETa) 通量的影响。在温度数据分析中出现的 13 次热浪中，有 5 次发生在 2015 年，与 2013 年一起是研究期间最热的一年。在这两年中，GPP 和 NEE 模式表明，随着 T 的增加，果园的同化能力小幅但显着降低_max，其余年份不存在。相反，ETa 在所有温度范围内持续增加。在热浪期间，我们观察到可用能量增加，感热通量进一步减少，有利于潜热，因此 ETa 增加。此外，在 13 次热浪中的 9 次中，ETa 值是夏季有记录以来最高的 5%。尽管热浪的长度（最长 8 天）和幅度（峰值为 37 °C）不同，但热浪期间的 ETa 通常比前一周增加约 9%。GPP 和 NEE 没有观察到类似的一致模式，这支持了灌溉农业生态系统中热浪期间碳和水通量之间脱钩的假设。