Facilitation in the Dry Season: Species Interactions Between a Limestone-Endemic Plant and Moss Altered by Precipitation Dynamics

Plant-to-plant interactions are essential for structuring plant communities and supporting adaptation in nutrient-poor, seasonally dry environments. This study examined the interactions between moss <i>Leucobryum aduncum</i> Dozy & Molk and <i>Oreocharis hainanensis</i> by analyzing microbial communities and physicochemical parameters across various sample types. These included soil [bare (B), <i>O. hainanensis</i> (O), moss (M), and moss + <i>O. hainanensis</i> (MO)], rhizosphere soil [<i>O. hainanensis</i> (ORS), moss (MRS), and moss + <i>O. hainanensis</i> (MORS)], and root [<i>O. hainanensis</i> (OHR), moss (MR), and moss + <i>O. hainanensis</i> (MOR)] using metagenomics sequencing across dry and wet seasons in limestone habitats on Hainan Island. During the dry season, combined plant samples MOR, MO, and MORS showed higher nutrients, supported by microbes that enhance nutrient turnover, which may indicate facilitation. Conversely, during the wet season, increased moisture leads to decreased nutrient levels and microbial communities shift, associated with slower nutrient turnover in combined plant samples, which may reflect competition. According to KEGG analysis, an increase in oxidative phosphorylation and ABC transporters in the dry season supported the facilitative interaction, while quorum sensing and two-component systems supported the competitive interaction in the wet season. These findings show how shifts between facilitation and competition arise from seasonal conditions and microbes in the limestone ecosystem.