Morphological and physiological responses of the invasive weed <i>Isatis tinctoria</i> to contrasting light, soil‐nitrogen and water

Abstract

Summary We evaluated the morphological and physiological responses to contrasting above‐ and below‐ground resources for the invasive weed, Isatis tinctoria L. (dyer's woad). Plants were grown under low and high levels of light [shade (50% of ambient) and full sun], soil water (50 and 100 mL day −1 ), and soil nitrogen (N) (0 and 20 mg N kg −1 soil) in 8 L pots in 63 day glasshouse experiments conducted during winter and spring. Soil‐N enrichment did not increase any of the growth variables (shoot and root dry mass, shoot:root ratio, leaf area, and specific leaf area) or physiological variables (stomatal conductance and 13 C discrimination) in either experiment. The absence of plasticity in response to changes in soil‐N supply suggests that I. tinctoria may survive and persist in nutrient‐poor conditions by having low‐N requirements, low‐N productivity, or both. In contrast, plants compensated for shaded conditions by altering leaf area, specific leaf area, and shoot:root ratio to improve light capture. We discuss the potential mechanisms whereby response to these variable resources may be associated with a series of adaptations that favour the ability to tolerate and colonize harsh, nutrient‐poor conditions, as well as invade shaded and undisturbed sites.