Pathogen shapes effects of host plant diversity on community productivity

Pathogens can regulate plant community productivity and its relationship with plant biodiversity. However, there remains a significant gap in understanding how pathogen specialization and transmission among host plants affect plant diversity–productivity relationships, as experimental methods often fall short in examining these factors. Therefore, we developed an epidemic model to fill this gap. Our models indicate specialist pathogens lead to positive biodiversity effects, while generalist pathogens result in negative effects, aligning with dilution effects and amplification effects, respectively. Moreover, these biodiversity effects are strengthened as pathogen transmissibility increases. We also found when both specialist and generalist pathogens are present, the patterns in plant diversity–productivity relationships vary greatly, depending on the relative transmissibility of specialist versus generalist pathogens. Our study significantly contributes to understanding the mechanisms underlying plant diversity–productivity relationships, and highlights the dual role of pathogens, which enhance or reduce biodiversity effects based on their specialization and spread.