Trichomes as a defense mechanism against climbing plants

Non-glandular trichomes are essential in plant defence against herbivores and water loss. However, evolutionary pressures often favor the development of multifunctional traits, suggesting that trichomes may serve multiple ecological roles. I hypothesized that the stem trichomes of <i>Anchusa officinalis</i> may reduce the likelihood of climbing plants attaching to them, thereby limiting competition for pollinators, light, water, and nutrients. Field observations showed that the majority (96%) of <i>Convolvulus arvensis</i>, a common climbing weed that co-occurs with <i>A. officinalis</i>, did not coil its stems. Pot experiments supported these findings: <i>C. arvensis</i> coiled around <i>A. officinalis</i> less frequently, more slowly (measured as time to first coil), and less intensely (measured by the number of coils) compared to plants with artificial soft trichomes (wire rods with soft plastic bristles), wooden sticks, or <i>A. officinalis</i> with trichomes removed. In contrast, <i>C. arvensis</i> coiled around hard artificial trichomes at similarly low rates as it did around the <i>A. officinalis</i> treatment. While biochemical factors could potentially explain the reduced interaction, it seems less likely, given that the main function of non-glandular trichomes in this species is water conservation. This role typically does not involve the secretion of specific chemicals. I suggest that mechanical stress caused by trichomes may trigger internal signaling in <i>C. arvensis</i>, altering its climbing behavior through thigmotropic responses.