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 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 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 activity 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.KEY WORDS: Nitrogen metabolism · Spartina · Salt marsh · Glutamine synthetase · Phragmites australis · Native Phragmites · Invasive plants · Enzyme partitioning Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 414: [57][58][59][60][61][62][63][64] 2010 of growth (Colmer et al. 1996, Hester et al. 2001, requiring a high nitrogen use efficiency (NUE) to balance stress tolerance and growth (Stewart & Rhodes 1978). Spartina alterniflora is more stress tolerant than S. patens (Maricle et al. 2007), but stress increases its N requirement (Bradley & Morris 1992). To tolerate the low marsh environment, S. alterniflora has a higher Nuptake rate, NUE and biomass accumulation than S. patens (Drake et al. 2008). S. alterniflora is likewise more salt tolerant than introduced Phragmites australis (Vasquez et al. 2006); however, once established, P. australis can outcompete S. alterniflora under field salinities and has greater N-uptake rates, tissue N concentration (Farnsworth & Meyerson 2003), shoot biomass, root biomass (under controlled conditions: introduced P. australis > native P. australis > S. alterniflora), a higher affinity for N at low and high concentrations and more readily uses dissolved organic N .We compared Spartina patens and S. alterniflora and the 2 subspecies of Phragmites australis to investigate how the location of glutamine synthetase (GS) relates to growth in salt marsh plants. GS is the rate-limiting enzyme in amino acid biosynthesis (Lam et al. 1996, Kichey et al. 2006. As part of the GS-(GOGAT) cycle, GS assimilates inorganic N (NH 4 + ) by catalyzing the ammination of glutamate to glutamine (Miflin & Lea 1977). Multiple isoforms of GS fall into 3 general categories: cytosolic GS I , chloroplastic GS II and root-specific GS (GS R ) (Lam et al. 1996). Leaf GS is critical to a...

Clonal growth: Invasion or stability? A comparative study of clonal architecture and diversity in native and introduced lineages of Phragmites australis (Poaceae)

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Maximal stomatal conductance to water and plasticity in stomatal traits differ between native and invasive introduced lineages of Phragmites australis in North America

“…Nonetheless, native P. australis does demonstrate considerable plasticity, which may underpin observations of long-term resistance to invasion, resilience and site consolidation. For example, the native lineage is well adapted to both low nutrient environments and exploitation of increasing nitrogen (sensu Hazelton et al . 2010 ).…”

Biotic resistance, disturbance, and mode of colonization impact the invasion of a widespread, introduced wetland grass

“…Seeds for the second part of the experiment (objective 2) were stratified and initially germinated in a growth chamber following the methods of Kettenring and Whigham (2009). Seedlings were then transplanted into seedling flats with potting soil and maintained on a modified 20% Hoagland's solution (following Hazelton et al [2010]) in a glasshouse under ambient light. Temperatures in the glasshouse varied with external temperatures (night temperatures .608F, day temperatures occasionally .908F) until planting in the field in June 2010.…”