PARENT SESSION
Thursday, August 10, 1:30-5:00 pm
COS 92 - Nitrogen cycling II
Sultana, Mezzanine Level, Cook Convention Center
Presiders: J Ely and S Baer
The effects of light, soil nutrients, and herbivory on the growth and survivorship of symbiotic, nitrogen-fixing clovers in temperate old fields.
Rodgers, Vikki*,1, Finzi, Adrien1, 1 Boston University, Boston, MA
ABSTRACT- In N limited ecosystems, theoretical models suggest that plants capable of symbiotic N fixation should be at a competitive advantage over species that cannot fix N. However N fixing plants rarely dominate communities, even in demonstrably N limited ecosystems. Although several studies have suggested that some combination of light, soil nutrient availability, and herbivory limit the abundance of N fixing plants, there have been few experiments testing all three factors. We designed a factorial experiment in two old fields of northwestern Connecticut to determine whether these three factors alone, or in combination, affect the growth rate and survivorship of Trifolium pratense and T. agrarium. Light availability was reduced by 75% using shade tents, soil nutrient availability was increased by adding 100 kg P ha-1yr-1, 8 kg Fe ha-1yr-1, and 5 kg Mo ha-1yr-1, and herbivory was reduced using mammal exclosures and insecticide spray. All plants were tagged and measured in 2003 and treatments were imposed in April 2004. Shading significantly decreased the survivorship of T. pratense and T. agrarium. In unshaded plots, fertilizing with P, Fe, and Mo significantly increased the growth rate of both species. The reduction in herbivory had no significant effect. We are currently performing a greenhouse experiment to test the effects of soil P, Fe, and Mo availability, alone and in combination. Our results suggest that light availability is the main factor limiting the distribution of N-fixing plants, whereas soil P, Fe, and Mo availability are largely responsible for constraining the growth rate of N-fixing plants in temperate old fields.
Key words: symbiotic nitrogen fixation, old fields, Trifolium