Does the invader Hieracium lepidulum have a comparative growth advantage over co-occurring plants? High leaf area and low metabolic costs as invasive traits

Abstract

High leaf area has been associated statistically with plant invasiveness, but few studies have quantified metabolic costs of this trait. We have little information on whether high leaf area provides a universal growth advantage or an advantage only under limited conditions. We ask, do invasive Hieracium lepidulum and co-occurring aliens in New Zealand have higher leaf area and lower metabolic tissue costs than co-occurring native species? Invasive and co-occurring plants were grown under standard conditions across a resource availability gradient and leaf area ratio (LAR) estimated. To quantify metabolic costs of above- and below-ground plant tissues, construction costs based on heat of combustion (Wg), plant ash, and nitrogen content (Vg) were measured. Leaf longevity was measured as an index of nutrient use and metabolic efficiency. Hieracium lepidulum and invaders overall did have higher LAR than cooccurring native plant species. Tissue construction costs overlapped among invaders and native species; however, unlike in native species, tissue construction costs in both invaders were reduced at lower nutrient resource levels. This suggests that there would not be a universal growth advantage for invaders, rather there would be more pronounced growth advantage at lower nutrient resource levels. This is discussed in terms of the ecological context within which H. lepidulum and its co-occurring species are found.