Submitted to: Invasive Plant Science and Management
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/1/2010
Publication Date: 4/1/2010
Publication URL: bioone.org/doi/abs/10.1614/IPSM-D-09-00033.1?journalCode=ipsm
Citation: James, J.J., Ziegenhagen, L.L., Aanderud, Z. 2010. Exploitation of Nutrient-Rich Soil Patches by Invasive Annual and Native Perennial Grasses. Journal of Invasive Plant Science and Management. 3(2):169-177 Interpretive Summary: We examined if differences in ability to place roots in nutrient rich soil microsites could be one mechanism contributing to the success of invasive annual grasses in perennial dominated systems. By growing plants in even uniform or patchy soil nutrient environments, we found that invasive annual grasses had greater precision in root placement than slow-growing native perennials. However, the non-invasive annual rye grass showed root growth responses comparable to the invasive annuals. While this suggests annuals have a greater ability to place roots in nutrient-rich microsites, it also suggests these traits are not unique to invaders. This study is a positive step towards simplifying annual grass management strategies because it indicates managers can focus on easier to manage traits such as abundant seed production and early germination and emergence, rather than these complex, difficult to manage, root traits examined here.
Technical Abstract: Invasion of nutrient-poor habitats may be related to the ability of a species to exploit nutrient-rich microsites. Recent research suggests fast-growing species may have a greater ability to allocate root biomass to nutrient-rich microsites (root foraging precision) than slow growing species. The broad objective of this research was to examine if differences in relative growth rate (RGR) between invasive and native species were related to differences in foraging precision. We hypothesized: 1) fast-growing invasive species would have greater foraging precision than slow-growing native species but 2) greater foraging precision would come at a cost in terms of root nutrient uptake capacity. We evaluated foraging precision of four annual and four perennial grasses grown in soils with uniform or patchy nutrient distribution in a common garden experiment. Plants were harvested at a common time and a common developmental stage to separate indirect effects of RGR on species root foraging ability. Nutrient uptake capacity was examined by exposing species to a one-time low or high nitrogen (N) pulse. Annuals foraged more precisely than perennials but had lower N uptake capacity than perennials. While these results support the idea of a positive relationship between RGR and foraging precision, there was substantial variation in these traits among species within a group. Moreover, biomass production in heterogeneous soils showed no relationship to root proliferation. Instead, species with a greater initial leaf surface area and RGR produced more biomass across all harvests and treatments and had higher root length density, allowing greater nutrient capture in heterogeneous soils. While these results do not exclude a role for proliferation in influencing invasion of heterogeneous, nutrient-poor habitat, or the potential for heterogeneity to influence population or community processes, these results suggest other traits may have an overriding importance in determining invader success in these systems.