Phenological changes in Amaranthaceae pollen in south-eastern Spain (Mediterranean region)

The Amaranthaceae family comprises approximately 173 genera and more than 2100 species, many of which are important from an ornamental, agronomic and clinical point of view due to the high prevalence of allergic sensitisation associated with their pollen. It has been suggested that species in this family could maintain or even increase their presence under changing climate scenarios, given their high tolerance to poor soils and prolonged arid conditions.This study analyses aerobiological and phenological variables of Amaranthaceae pollen in three cities in south-eastern Spain (Cartagena, Murcia and Lorca; Region of Murcia) during the period 2010–2021. Data from the Aerobiological Network of the Region of Murcia (REAREMUR) were used, obtained using Hirst-type volumetric traps (VPPS 2000) and analysed following standardised methodologies (EN 16868:2019).The results show two main pollen release seasons (MPS 1 and MPS 2), defined using the Nilsson and Persson (1981) method: a first peak in spring (April-June) and a second peak in summer (July-September). During MPS 1, the highest concentrations were recorded in Lorca, followed by Murcia and Cartagena, while in MPS 2 this pattern was reversed, with peaks in Cartagena. However, since 2017, a pronounced and sustained decline in concentrations during MPS 2 has been observed in Cartagena, a behaviour also described in other coastal cities in south-eastern Spain, such as Alicante and Almería.Trend analysis using linear regression showed a significant increase in Seasonal Pollen Integral (SPIn) in Cartagena during MPS 1. In MPS 2, a significant advance in the start of the season, a delay in the end, and an increase in its duration were detected, along with a significant decrease in both the peak day concentration and the SPIn. In Lorca, MPS 1 showed an earlier start and longer duration, while in MPS 2, a prolongation of the period was also observed, associated with a delay in the end date. No statistically significant trends were identified in Murcia. These trends were re-evaluated using the non-parametric Mann-Kendall test and the Theil-Sen slope estimate, which confirmed these results, except in the case of the increase in SPIn in MPS 1 in Cartagena, which did not reach statistical significance. During MPS 1 in Lorca, no significant trends were found with this test either, although the results were replicated in MPS 2.Overall, the results point to a phenological change in Amaranthaceae pollen in south-eastern Spain, with a significant decrease in the amount of pollen in the bioaerosol in MPS 2, raising concerns about a possible impact on plant biodiversity that should be addressed.The result of this work is part of grant PID2024-157581OB-I00, funded by MICIU/AEI/10.13039/501100011033 and by the FSE+.