Abstract The conversion of primary forest (PF) to other types of land cover, such as pasture and agriculture, in Amazonia, affects regional carbon and water balances, significantly contributing to increased carbon emissions and reduced evapotranspiration. However, secondary forest (SF) growth, resulting from the abandonment of low-productivity pasture areas, offers a potential alternative to counterbalance the effects of deforestation on carbon release to the atmosphere and evapotranspiration reduction. In this work, we present four years of eddy flux measurements of a SF that is approximately 20 years old, located in Central Amazonia, and we compare these measurements with those of a PF in the same region, analyzing daily and seasonal variations in evapotranspiration, gross primary productivity of carbon and water use efficiency. On average, evapotranspiration is 20% higher in the SF (3.6 mm day−1) than in the PF (3.1 mm day−1), while gross primary productivity is only 5% higher in the SF (8.1 gC m−2 day−1) than in the PF (7.8 gC m−2 day−1). Despite robust evidence of higher evapotranspiration and gross primary productivity in SF, the estimated uncertainty range of WUE is large to reach definite conclusions about the differences on carbon gain per water loss between the sites. Nonetheless, the significantly higher evapotranspiration and gross primary productivity of SF may counterbalance both water and C losses from deforestation and has important implications for regional budgets.

中文翻译：

---

涡度协方差推断亚马逊流域次生植被的蒸散量和总初级生产力

摘要 亚马逊河流域的原始森林 (PF) 向其他类型的土地覆盖（如牧场和农业）转变，会影响区域碳和水平衡，显着导致碳排放增加和蒸发蒸腾减少。然而，由于放弃低生产力牧场而导致次生林 (SF) 的生长，提供了一种潜在的替代方法来抵消森林砍伐对大气中碳排放和蒸发蒸腾减少的影响。在这项工作中，我们展示了位于亚马逊中部大约 20 年的 SF 的四年涡流测量值，并将这些测量值与同一地区的 PF 的测量值进行比较，分析蒸散的每日和季节性变化，碳和水利用效率的总初级生产力。一般，SF (3.6 mm day-1) 的蒸散量比 PF (3.1 mm day-1) 高 20%，而 SF (8.1 gC m-2 day-1) 的总初级生产力仅高 5%在 PF 中（7.8 gC m−2 day−1）。尽管有确凿的证据表明 SF 的蒸散量和总初级生产力较高，但 WUE 的估计不确定性范围很大，无法得出关于站点之间单位水损失的碳增益差异的明确结论。尽管如此，SF 显着更高的蒸散量和总初级生产力可能会抵消森林砍伐造成的水和碳损失，并对区域预算产生重要影响。尽管有确凿的证据表明 SF 的蒸散量和总初级生产力较高，但 WUE 的估计不确定性范围很大，无法得出关于站点之间单位水损失的碳增益差异的明确结论。尽管如此，SF 显着更高的蒸散量和总初级生产力可能会抵消森林砍伐造成的水和碳损失，并对区域预算产生重要影响。尽管有确凿的证据表明 SF 的蒸发蒸腾量和总初级生产力较高，但 WUE 的估计不确定性范围很大，无法得出关于站点之间单位水损失的碳增益差异的明确结论。尽管如此，SF 显着更高的蒸散量和总初级生产力可能会抵消森林砍伐造成的水和碳损失，并对区域预算产生重要影响。