The dry forests of South America are a key player of the global carbon cycle and the regional water cycle, but they are being intensively deforested. We used eddy covariance measurements to compare the temporal patterns of CO₂ and water vapour fluxes and their relationships with environmental variables in dry forest and pastures sites of central Argentina. Ecosystem fluxes showed clear contrasts in magnitude, timing and response to environmental controls between ecosystems. The dry forest displayed higher daily gross primary productivity (GPP, 10.6 vs. 7.8 g CO₂ m⁻² d⁻¹) and ecosystem respiration (R_eco, 9.1 vs. 7.0 g CO₂ m⁻² d⁻¹) and lower net ecosystem exchange (NEE, −1.5 vs. −0.7 g CO₂ m⁻² d⁻¹) than the pasture. These differences were explained by a lower tolerance of the pasture to cool temperatures and drought. The lowest NEE rates were observed between 26°C and 34°C in the pasture, but below this range, NEE increased sharply, switching to a carbon source with temperatures <20°C. By contrast, the dry forest remained as a strong carbon sink down to 18°C. The pasture also showed a stronger drop of GPP with drought compared with the dry forest, becoming a carbon source with soil wetness <25% of soil available water. Rainfall was strongly coupled with GPP in both ecosystems, but the dry forest responded to longer rainfall integration periods. This study helps to understand how ecosystems can respond to climate change, improve global scale modelling and increase the productivity and resilience of rangelands.

中文翻译：

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阿根廷中部干旱森林和牧场的二氧化碳和水蒸气通量的对比

南美的干旱森林是全球碳循环和区域水循环的关键参与者，但它们正在被严重砍伐。我们使用涡度协方差测量结果来比较阿根廷中部干旱森林和牧场地点的CO ₂和水蒸气通量的时间模式及其与环境变量的关系。生态系统通量在大小，时间和对生态系统之间的环境控制的反应方面显示出明显的对比。干旱森林表现出更高的每日总初级生产力（GPP，10.6与7.8 g CO ₂ m ^-2 d ^-1）和生态系统呼吸（R _eco，9.1与7.0 g CO ₂ m ^-2 d ^-1）。）和较低的净生态系统交换量（NEE，-1.5 vs. -0.7 g CO ₂ m ^-2 d ^-1）比牧场。牧场对低温和干旱的耐受性较低，可以解释这些差异。在牧场中，在26°C至34°C之间观察到最低的NEE速率，但是在此范围以下，NEE急剧增加，转而使用温度<20°C的碳源。相比之下，干旱的森林在18°C时仍然是强大的碳汇。与干旱森林相比，牧草还显示出干旱导致GPP下降幅度更大，成为土壤湿度小于土壤可利用水量25％的碳源。在两个生态系统中，降雨都与GPP密切相关，但是干旱森林对更长的降雨整合期做出了响应。这项研究有助于了解生态系统如何应对气候变化，改善全球规模模型并提高牧场的生产力和复原力。