Document: TER-3-38-2

Plant competition intensity along a soil depth gradient in an old field.

KEOGH, T.M* ¹ and P.AKEDDY ^1,2

University of Ottawa, Ottawa, ON, Canada. ¹
Southeastern Lousiana University, Hammond, LA, USA. ²

Abstract:
A fundamental question in plant ecology is whether and how the intensity of competition changes with productivity. This question has been the source of considerable discussion during the last few decades. Often artificial productivity gradients have been created in order to address this question. Fewer studies have measured competition intensity (CI) along natural gradients, with only a subset of these distinguishing between the above and belowground components of competition. We examined the intensity of total, above and belowground competition along a natural soil depth gradient in an old field where flat clay plain overlay undulating gneiss bedrock. Four distinct plant communities could be discerned, rocky outcrops, grass dominated areas, areas dominated by Asters and Solidagos and areas dominated by Lythrum salicaria, which flood in the spring. Two test species or phytometers (Lythrum salicaria and Liatris spicata) were grown along the gradient in four treatments: without neighbours, with neighbour's roots only, with neighbours' roots and shoots and with a cage to reduce herbivory while growing with both neighbour's roots and shoots. The final biomass of each phytometer in each treatment (after one growing season) was then measured. Overall, the intensities of total competition and belowground competition were significantly greater than zero (p<0.05), whereas that of aboveground competition was not. This was true for both phytometers. Apparently, competition in that system is primarily belowground. Rock outcrops had the greatest competition intensity, with CI then decreasing with increasing soil depth and biomass. Herbivory, however, did not change along the gradient for either phytometer. Therefore, herbivory does not change with competition intensity.

Keywords: competition intensity, above and belowground competition, herbivory, soil depth gradient, old field, Lythrum salicaria, Liatris spicata

This abstract is being presented at: 10:15 AM in session:
Oral Session #72: Plant Competition.