Do plants adaptively respond to future competition?

Abstract

Plants can detect the presence of competitors through the change the spectral quality of light induced by potentially competing plants. This change in spectral quality can induce shade avoidance plasticity to maximise light acquisition. We examined how simulated competition as seedlings impact performance when plants are exposed to real competition later in life. We predicted that individuals experiencing simulated competition as seedlings will perform better under competition later in life. We grew seedlings of six short-lived herbaceous species under simulated competition and no competition treatments early in life and real competition and no competition later in life. Seedlings in the real competition treatment were grown in pots with grass competitors. Competitors were prevented from interacting with seedlings early in the experiment using above ground by pinning back competitor plants, and below ground through root exclusion pots. We ended the simulated competition treatment and started the real competition treatment (by removing the barriers) when seedlings reached a threshold size. We found that plants in the simulated competition treatment did not express shade-avoidance plasticity. No species performed better under competition when exposed to simulated competition as seedlings. Three of the six species performed significantly worse under competition when exposed to simulated competition as seedlings. Plants are often capable of detecting and responding to their enemies. However, none of the species in our study demonstrated either the capacity to detect the presence of competitors, or increased performance under competition when exposed to the cues for future competition early in life. In some instances, plants respond passively to competitors and adaptive responses to the presence of enemies can be limited.