In situ photosynthesis in the seagrass Halodule wrightii in a hypersaline subtropical lagoon

Abstract

Photosynthesis versus irradiance ( P vs 1) parameters in the shoalgrass Halodule wrlghtii Ascherson were calculated from measurements of oxygen evolution collected in situ, using entire plants in Laguna Madre, Texas, USA. Eleven expenmental incubations were performed from May 1989 to April 1991 using pulsed oxygen electrodes that collected data continuously under natural daylight conditions For comparison with in situ measurements of photosynthesis, P v s 1 parameters were calculated from laboratory measurements on blade segments incubated In a small volume chamber. For field plants, average saturation 111-adiance (I,) was 319 pm01 m -2 S -' , photosynthetic capacity (P,,,) was 374 pm01 O2 g -l dry wt (dw) h -' , and relative quantum efficiency (a) generally ranged from 0.5 to 1.6 pm01 O2 g-I dw h -l (pm01 photons m -2 S-').'. Whole plant respration was 70 pm01 g ' dw (leaf) h ' , and compensation irradiance (I,,) was ca 85 pm01 m -2 S -' Chlorophyll a concentrations averaged 12.8 mg g -' dw. and the mean chl d:chl b ratio over the 2 yr period was 2 2 For blade segments incubated in the laboratory under similar temperatures to field plants and at corresponding chlorophyll concentrations. P,,, was not significantly different but a was signif~cantly higher, ranging from 3.4 to 5.3 pm01 O2 g -' dw h -' (~.lmol photons n r 2 S-').' The higher a values resulted In significantly lower estimates for 1, (mean of 101 pm01 m -2 S-'). The higher U in laboratory plants was largely related to the perpendicular orientation of leaf tissue to a directed hght field, which is not reflective of natural conditions for H. wrightii. The significant difference in 1, values calculated from incubations performed in the laboratory and field has profound effects on model calculations of H,,,, the duration of irradiancesaturated photosynthesis, and thus predictions of the minimum llght requirements required to sustain growth in H. wrightii. Consequently, the application of laboratory-derived 1, values for H. wrightii would result in overestimates of its maximum depth limlts and rates of area1 primary production

Modeling daily production of aquatic macrophytes from irradiance measurements: a comparative analysis

“…(Onuf 1991, Dennison et al 1993, Dunton & Tomasko 1994. In addition, different mean light requirements have been reported for the same species growing in different habitats (Ostenfeld 1908, Borum 1983, Dennison 1987, Kenworthy et al 1991, and the apparent light requirement of a single species growing within a single estuary appears to increase as the variance in light availability increases (Zimmerman et al 1991).…”

Depth-acclimation of photosynthesis, morphology and demography of Posidonia oceanica and Cymodocea nodosa in the Spanish Mediterranean Sea

“…Photosynthetic characteristics determined with leaf segments in a unidirectional light field cannot, however, be used to predict differences among species in light requirements for growth in natural populations. Photosynthetic rates depend on leaf age (Alcoverro et al 1999) and the carbon budget of whole plants is affected by the belowground biomass, which can significantly increase the minimum light requirement to sustain growth (Fourqurean & Zieman 1991, Dunton & Tomasko 1994.…”

Morphological and physiological differences between two morphotypes of Zostera noltii Hornem. from the south-western Iberian Peninsula

“…The pieces were excised some hours before the measurements to minimize wounding effects (Dunton and Tomasko 1994). Oxygen evolution was recorded with a Hansatech polarographic O 2 electrode at 17°C.…”