Effects of cropland and cultivars on phyllosphere bacterial communities in forage crops in Southwest China

Rotation between rice (Oryza sativa) or corn (Zea mays) (summer) and forage crop (winter) is common in Southwest China. However, the impact of different ecological environments on phyllosphere bacterial communities and the factors influencing the survival and distribution of undesirable bacteria remain unclear. Therefore, we aimed to investigate the effects of cropland and cultivars on the abundance and diversity of phyllosphere bacteria in forage crops. Field experiments were conducted on croplands (dryland, DL; paddy field, PF) and three cultivars (forage pea, FP [Lathyrus sativus]; Italian ryegrass, IR [Lolium multiflorum]; smooth vetch, SV [Vicia villosa]). The results revealed 87 shared operational taxonomic units (OTUs) between the PF and DL bacterial communities, while FP, IR and SV shared 58 OTUs. Pantoea, Plesiomonas and Bryobacter were the three most abundant genera between the two cropland types. The relative abundances levels of Rahnella1, Aeromonas, Cetobacterium, Flavobacterium and Vibrio were significantly different among the three cultivars (p < 0.05). The physico-biochemical properties and microorganism numbers in SV and FP exhibited a high degree of overlap; however, they were distinct from those of IR (95% confidence interval). Physiological properties did not directly contribute to bacterial abundance but rather explained the differences in bacterial abundance among samples, likely by indirectly shaping the phyllosphere microenvironment. In summary, compared with PF, DL indirectly influenced microbial numbers indirectly by regulating leaf physiological properties, while both exhibited similar effects on bacterial diversity. Among the different forage crops, IR suppressed phyllosphere moisture and nutrient exchange owing to its lower stomatal density, resulting in a lower bacterial relative abundance than those of FP and SV. This finding elucidates bacterial community dynamics, particularly during the initial establishment phase of crop rotation systems, providing a valuable perspective for optimizing forage crop rotation strategies.