Dust reduces plant female fitness by absorbing secretions and occupying surfaces of the stigma

As a major component of air pollution in urban environments, dust particles are similar in size to pollen grains. When deposited on the stigma, dust may occupy the space for pollen deposition and reduce the adhesion of pollen, potentially leading to a decrease in plant female fitness. Unfortunately, to date, the relevant evidence remains scarce. A dust simulation experiment was conducted on 29 plant species at the Yan'an Botanical Garden. The effects of dust deposition on the stigmatic surfaces were examined using microscopy, and female fitness was compared between experimental (dust) and control (non-dust) groups. We demonstrated that dust significantly occupied stigma surfaces and absorbed stigma secretions. The dust simulation treatment significantly decreased the fruit and seed set but did not influence the fruit length or weight. Moreover, plants with wet or more exposed stigmas showed greater susceptibility to dust, evidenced by relatively lower fruit and seed set in both the non-dust and dust treatments. Dust significantly reduces the reproduction of plants by altering the microenvironment of the flower stigma, including absorbed stigma secretions and occupied stigma surfaces, and its principal effect is observed during the critical pre-fertilization phase. Although our study significantly advances the understanding of the harmful effects of pollutants on plant reproduction, much remains to be learned and the underlying mechanisms need to be investigated in the future.