Submitted to: Journal Of Plant Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 27, 2008
Publication Date: July 1, 2008
Citation: James, J.J., Mangold, J.M., Sheley, R.L., Svejcar, A.J. 2008. Root Plasticity of Native and Invasive Great Basin Species in Response to Soil Nitrogen Heterogeneity. Journal Of Plant Ecology. 202:211-220. Interpretive Summary: Soil nutrients are heterogeneously distributed in rangeland systems. We quantified root growth and physiological responses of native and invasive rangeland plants to soil nutrient heterogeneity. Invasive species had higher growth rates, larger root systems and had greater root nutrient uptake rates in nutrient-rich patches compared to native plants. This positive relationship between traits is one mechanism allowing invasive species to be more competitive in rangeland systems.
Technical Abstract: Soil nutrients are heterogeneously distributed in natural systems. While many species respond to this heterogeneity through root system plasticity, little is known about how the magnitude of these responses may vary between native and invasive species. We quantified root morphological and physiological plasticity of co-occurring native and invasive Great Basin species in response to soil nitrogen heterogeneity and determined if trade-offs exist between these foraging responses and species relative growth rate or root system scale. The nine study species included three perennial bunchgrasses, three perennial forbs and three invasive perennial forbs. The plants were grown in large pots outdoors. Once a week for four weeks equal amounts of 15NH415NO3 were injected in the soil either homogenously, in four patches, or in two patches. All species acquired more N as N heterogeneity increased. None of the species increased root length density in enriched patches compared to control patches but all species increased root N uptake rate in enriched patches. There was a positive relationship between N uptake rate, relative growth rate, and root system size. Path analysis indicated that these positive interrelationships among traits could provide one explanation of how invasive forbs were able to capture 2 and 15-fold more N from enriched patches compared to the native grasses and forbs, respectively. These results support an emerging view that plant traits related to nutrient capture in heterogeneous soil environments may be positively correlated which could potentially promote size-asymmetric competition belowground and facilitate the spread of invasive species.