Tolerance to water stress and shade in the invasive Impatiens parviflora.
Premise of research. Invasive plants usually have growth and reproductive abilities that allow them to cope with new habitats and environments. The small balsam, Impatiens parviflora, is one of the most widespread annual invasive species in Europe. As no precise physiological assessment for this species has been performed, we compared physiological traits linked to growth performance in contrasting environments. Methodology. Plants were cultivated in growth chambers under four different treatments varying by light and water conditions. We assessed the impact of water stress and low light levels on traits related to plant growth, leaf physiology, photosynthesis, and water status. Pivotal results. Tolerance of low light level was reflected by several morphological and physiological characteristics. The number of leaves initiated was not affected by light condition, whereas specific leaf area increased for plants grown under low light. In addition, the chlorophyll fluorescence parameters revealed that low light did not affect the light-dependent reactions of photosynthesis. Although the net rate of photosynthesis was reduced, plant growth was not markedly affected. Our results thus suggest that I. parviflora generally copes well with shady conditions. The traits involved in efficiency of water use and water conservation indicated that I. parviflora is also highly tolerant to water stress. Although a reduction in plant growth and abscission of old leaves were observed after 4 wk of stress, I. parviflora demonstrated several mechanisms to maintain the light-dependent reactions of photosynthesis under water-stress conditions. Water use efficiency strongly increased in response to water stress, and plants adjusted their water potential to maintain their water supply. Conclusions. Impatiens parviflora shows physiological traits that allow plant growth under contrasting and stressful environments. These physiological traits may contribute to its invasive ability.