Inorganic nitrogen acquisition in the seagrass Thalassia testudinum: Development of a whole‐plant nitrogen budget

摘要: Whole-plant nitrogen (N) uptake experiments were used to quantify the N budget of Thalassia testudinumgrowing under different sediment nutrient regimes at two locations in western Gulf Mexico. At both sites, Corpus Christi Bay (CCB) and lower Laguna Madre (LLM), Texas, concurrent measurements plant biomass levels dissolved inorganic (DIN) water column sediments made over a 12-month period (October 1996‐October 1997). Water-column NH NO 1 concentrations not significantly 12 2 43 between study sites (ca. 1.2 mM [NH ] 0.7 [NO sites), but 4 CCB (87 mM) higher than LLM (26mM). The correlated with leaf CCB, there was no difference root sites. Leaf showed clear seasonal variation: Vmax highest summer fall, Km winter. did change season, decreased increasing incubation temperature. 3 There differences rates although affinity that . Root variable season saturate 21 34 experimental either site (0‐300 mM). Based on these measurements, acquisition during fall lowest winter spring. Roots leaves contributed nearly equally total (root 5 52%; 38%; 10%) Annual 11 44 double (97.03 53.49 g m 22 yr , respectively), .50% incorporated into site. DIN turnover time ranged from 0.21 0.91 d 0.95 1.75 pore water, indicating importance regeneration processes for supporting seagrass production. similarity relative tissue contributions plants despite significant pool sizes, results fraction allocated below1 ground tissues living low-sediment conditions (LLM). In N-sufficient sediments, overall productivity is greater as T. testudinum able allocate proportion its photosynthetic aboveground tissues.