Glutamine synthetase activity and free amino acid pools of eelgrass (Zostera marina L.) roots

Shoot density, shoot, root, and rhizome tissue biomass and N content, and N assimilation by leaf and root tissues of the 2 CO-occurring seagrasses Cymodocea nodosa and Zostera noltii were measured over the course of a year at a central Mediterranean site. Concentrations of dissolved inor- nodosa and Z. noltii appeared to contribute to the replenishment of the sediment DIN reservoir as growth declined and senescence ensued in the fall; the peak in plant-based N preceded the peak of sediment DIN by 1 to 2 mo. C. nodosa had a June peak in glutamine synthetase (GS) activity in leaf tissue, and showed greater variation over the course of the study than &d 2. noltii, for which there was a February peak in shoot GS activity. The leaves, rhizomes, and roots within each species exhibited different patterns of tissue N content over the course of the year, indicating different strategies of N storage and subsequent use. Within a species, assimilated N was first allocated to leaves, then rhizomes and roots. Leaves, in addition to rhizomes, appear to have a N storage function. C. nodosa maintained high tissue N levels for longer periods than &d 2. noltii, suggesting that clonal modules of C. nodosa were more physiologically integrated than modules of Z. noltii. The average potential for N assirmlation through Z. noltii tissues was estimated to be roughly 43% of the total for C. nodosa and 2. noltii.

Section: Methodsmentioning

confidence: 99%

Nitrogen acquisition, storage, and use by the co-occurring Mediterranean seagrasses Cymodocea nodosa and Zostera noltii

Kraemer¹,

Mazzella²

1999

“…From each mesocosm 6 plants were harvested, cleaned, and transported to the laboratory, and NRase was assayed using the technique of Roth & Pregnall (1988). The activity of a key enzyme involved in Ni assimilation, glutamine synthetase (GS), was also assayed from Z. manna after 3 and 14 wk in late summer-fall, following the procedure of Pregnall et al (1987).…”

Section: Methodsmentioning

confidence: 99%

Comparative effects of water-column nitrate enrichment on eelgrass Zostera marina, shoalgrass Halo-dule wrightii, and widgeongrass Ruppia maritime

Burkholder¹,

Glasgow²,

Glasgow³

1994

121

ABSTRACT. In an experimental mesocosm system during late summer-fall, we examined shoot production by eelgrass Zostera marina without nitrate additions (generally with ambient water-column concentrations c 2 pM N03--N) versus production by eelgrass that previously had been exposed to low nitrate enrichment (pulsed additions of 5 pM NO,--N d-' to the water for 12 wk during an unusually cool spring season). During late summer-fall, the previously enriched plants were subjected to higher nitrate loading (10 pM NO<-N d-' for 14 wk), while control plants were maintained without nitrate additions as in spring. We also compared shoot production in fall by recent field transplants of Z. manna, Halodule wrightii, and Ruppia rnarit~rna with and without additions of 10 pM water-column NO3--N d-'. Low water exchange (10% d-l) was used to s~mulate conditions in sheltered embayments or lagoons, and light reduct~on from high tide was simulated by covering the mesocosnls with neutraldensity screens that reduced incident light by 30 % for 3 h d.' on a rotating schedule. Shoot production by both enriched and unenriched Z. marina was comparable dunng the spring low-level NO3--N exposure. However, eelgrass enriched with nitrate in both spring and fall attained significantly lower shoot production than control plants without enrichment. This decrease, unrelated to light reduction from algal growth, suggests a direct adverse effect of long-term water-column nitrate exposure on Z. marina. The more recent transplants of eelgrass without prior enrichment history also showed a trend for decreased lateral growth under moderately elevated nitrate. In contrast, H. wrightii was slightly stimulated and R. rnaritima was highly stimulated by water-column nitrate relative to growth of controls. By the end of the fall experiment, Z. marina (f NO3--N), H. wrightii (k NO3--N), and unenriched R. maritima had increased shoot densities by <50%, whereas nitrate-enriched R. maritima increased shoot production by >300%. The data indicate that H. wrightii or R. maritima could be established successfully by transplanting efforts as a management strategy in nitrate-enriched waters where eelgrass meadows have disappeared. Unlike 2. marina, these species apparently have developed physiological mechanisms to more effectively control nitrate uptake and metabolism.

“…Nitrogen content of new tissue was set to 1.00 % dry wt. for leaves and 0.75 % for root/rhizome (Short & McRoy 1984, Pregnall et al 1987, Short 1987). Growth was not permitted if the internal nitrogen quota (Q) fell below 0.95 '10 dry wt for the whole plant (root and shoot combined).…”

Section: The Modelmentioning

confidence: 99%

“…Although in general photosynthetic rates are well defined for Zostera marina, our understanding of the dynamics of nutrient O Inter-Research/Printed in F. R. Germany utilization is much less complete. Evidence of nutrient limitation has been reported for some eelgrass beds (Orth 1977, Harlin & Thorne-Miller 1981, Short 1983a, 1983b, 1987, yet the generality of nutrient limitation cannot always be demonstrated (Dennison et al 1987, Pregnall et al 1987. Furthermore, a general predictive model of nutrient-limited growth has not been developed, despite the fact that studies of nitrogen limitation have been conducted in eelgrass beds with ammonium concentrations in the sediments ranging from 50 to 500 pM (Iizumi et al 1980, Short 1983a, 198313, Dennison et al 1987.…”

Section: Introductionmentioning

confidence: 99%

“…Lack of photosynthesis at night forces roots to undergo fermentation for prolonged periods, during which time they are unable to assimilate nitrogen available in the sediments (Moms 1984, Monis & Dacey 1984, PregnaU et al 1987. While mass-balance calculations based on experiments and field observations have been used to estimate nitrogen demand under specific conditions , Dennison et al 1987, Pregnall et al 1987, generalization of these results to a wide variety of environmental conditions is difficult. To evaluate dynamics of nitrogen utilization by Zostera marina in a more general context, we developed a mathematical model to examine the effects of light and nitrogen availability on the dynamics of nitrogen uptake and growth.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Is growth of eelgrass nitrogen limited? A numerical simulation of the effects of light and nitrogen on the growth dynamics of Zostera marina

Zimmerman¹,

Smith²,

Alberte³

1987

104

A numerical model of nitrogen uptake and growth was developed for the temperate seagrass Zostera marina L. Goals were to evaluate the relative effects of light and nitrogen availability on nitrogen uptake and partitioning between leaf and root tissue. and to estimate nitrogen concentrations in the s e d m e n t and water column required to saturate growth. Steady-state predichons are quite robust with respect to a range of parameter values justified by available data The calculations indicated that roots are probably more important in overall nitrogen acquisition in most light and nitrogen environments encountered in situ, but may contribute less than 50 '/o of the total uptake in low light. The model also predcted amnlonium to be a much more important source of nitrogen than nitrate Nitrogen concentrahons required to saturate growth (even for nitrate) were estimated to be at least 50 % below concentrations commonly reported in situ, an indicat~on that nitrogen limitation of 2. marina is probably very rare in nature.