## 3 Results and Discussion
### Meteorological Conditions
This is confirmed by the negative values of NEE measured by the EC system, since they indicate that the CO\({}_{2}\) capture balance was greater than the emission balance in the plots monitored. [PERSON] et al. [85] found, in an old-growth forest, a maximum monthly GPP of 179.5 g C m\({}^{-2}\) in August [85]. The maximum monthly GPP in our study was 263.7 g C m\({}^{-2}\) in 5-year-old almond trees in May 2021. This result is promising in terms of potential carbon capture in almond orchards. In addition, similar daily and monthly cumulative GPP values have been found in a boreal Scots pine forest [86], with the authors reporting monthly GPP values of between 150 and 200 g C m\({}^{-2}\) month\({}^{-1}\) in summer months over 10 consecutive years and maximum values of ca. 250 g C m\({}^{-2}\) month\({}^{-1}\)[86]. Moreover, maximum daily values in this boreal Scots  
Figure 3: Monthly sum of daily values of Net Ecosystem Exchange (NEE) Gross Primary Productivity (GPP) and mean daily values of ecosystem water use efficiency (eWUE) between May and October during the 6-season experiment in Las Tiesas (2017–2019) and Tarazona (2020–2022). pine forest of ca 10 g C m\({}^{-2}\) day\({}^{-1}\) are also consistent with the results obtained in this study (Figure 4A). However, as previously mentioned, natural forests or ecosystems cannot be fairly compared with a well-fertilized and irrigated almond orchard. In fact, for a complete carbon assessment, crop management practices that might release CO\({}_{2}\) (such as fertilization, pruning, etc.) need to be incorporated into the carbon balance. In other crops, the different management practices [17; 20; 91], age of the plants [18] species studied [92; 93] and short-term climatic conditions [19; 21; 23; 25] were found to greatly influence the carbon uptake and fixation. For example, [17] reported significant differences in NEE in olive trees managed under different weeding practices, with lower annual cumulative NEE under weed cover compared with weed free soil management. In our study, monthly cumulative NEE values between May and October were lower (more negative) (Figure 3) than those reported by [PERSON] et al. [17] under both treatments, indicating higher CO\({}_{2}\) capture capacity in our almond orchard. In an 11-year apple orchard, [PERSON] et al. [24] obtained GPP values between 0 and 10 g C m\({}^{-2}\) d\({}^{-1}\), reporting similar yearly GPP to that of a temperate-humid deciduous forest (with 1375 \(\pm\) 12 and 1263 \(\pm\) 189 g C m\({}^{-2}\) yr\({}^{-1}\) in the forest and apple orchard, respectively). In our study, average daily GPP ranged between 1.5 and 9 g C m\({}^{-2}\) d\({}^{-1}\) (Figure 5C,D), closely coinciding with the former work. The maximum daily GPP results for our young almonds are slightly below those reported for olive trees (1-15 g C m\({}^{-2}\) d\({}^{-1}\)) [47] and those reported in maize (0-18 g C m\({}^{-2}\) d\({}^{-1}\)) [93] to those observed for citrus (2-10 g C m\({}^{-2}\) d\({}^{-1}\)) [23] and for grassland (0-9 g C m\({}^{-2}\) d\({}^{-1}\)) [93]. All these results highlight the potential carbon-fixing capacity of almond orchards. Figure 4: Mean daily values of GPP and NEE (**A**) and eWUE and ET (**B**) for the six-year experiment. The values depicted are those obtained after filtering and gap filling. As in the aforementioned studies, the seasonal and interannual variability of both NEE and GPP was observed in the present work. The factors month, year and location were found to be significant for NEE and GPP (\(p<0.001\)). At both study sites, Las Tiesas (3-5 years old in 2017-2019) and Tarazona (4-6 years old in 2020-2022), there is a general trend of increasing CO\({}_{2}\) sequestration (more negative NEE values) and plant carbon fixation (GPP) as the almond trees grew across the growing seasons at each of the locations. This  
Figure 5: Monthly average daily values of NEE (**A,B**); GPP (**C,D**) and eWUE (**E,F**) for the six-year experiments, between April and October.