Glutamine synthetase partitioning in native and introduced salt marsh grasses

Abstract

Plants with higher glutamine synthetase (GS) activity in photosynthetic tissues than below-ground structures (high leaf:root (L:R) GS activity) show growth advantages over plants with a low L:R GS activity ratio. The benefits of a high L:R GS activity ratio are well documented in agri- cultural systems, but little is known about the ecology of GS partitioning in natural systems. To deter- mine the ecological significance of GS partitioning, we measured above- and below-ground GS activity in Spartina grasses field-collected from a Maine salt marsh and others raised in a growth chamber from seed. The more stress-tolerant, faster growing S. alterniflora had a higher L:R GS activ- ity than S. patens in chamber- and marsh-grown plants throughout the growing season. Additionally, we compared GS partitioning in native and introduced subspecies of Phragmites australis. While we did not find a significant difference between the subspecies, the L:R GS activity in both native and introduced reeds was among the highest reported. Our results indicate that high L:R GS activity corresponds with observed stress tolerance, growth and competitive ability in both natural and agricultural systems.