Glutamine synthetase partitioning in native and introduced salt marsh grasses

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 agricultural systems, but little is known about the ecology of GS partitioning in natural systems. To determine the ecological significance of GS partitioning, we measured above- and below-ground GS activity inSpartinagrasses field-collected from a Maine salt marsh and others raised in a growth chamber from seed. The more stress-tolerant, faster growingS. alterniflorahad a higher L:R GS activity thanS. patensin chamber- and marsh-grown plants throughout the growing season. Additionally, we compared GS partitioning in native and introduced subspecies ofPhragmites 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.