Image_3_Photoacclimation and Light Thresholds for Cold Temperate Seagrasses.JPEG

• Main Authors: Romy Léger-Daigle, Fanny Noisette, Simon Bélanger, Mathieu Cusson, Christian Nozais
• Format: Still Image
• Language: unknown
• Published: 2022
• Subjects: Botany; Plant Biology; Plant Systematics and Taxonomy; Plant Cell and Molecular Biology; Plant Developmental and Reproductive Biology; Plant Pathology; Plant Physiology; Plant Biology not elsewhere classified; photophysiology; PAM fluorometry; Zostera marina; subarctic; light attenuation and limitation; photosynthesis; eelgrass; Canada; Subarctic
• Online Access: https://doi.org/10.3389/fpls.2022.805065.s003; https://figshare.com/articles/figure/Image_3_Photoacclimation_and_Light_Thresholds_for_Cold_Temperate_Seagrasses_JPEG/19150541

Water quality deterioration is expected to worsen the light conditions in shallow coastal waters with increasing human activities. Temperate seagrasses are known to tolerate a highly fluctuating light environment. However, depending on their ability to adjust to some decline in light conditions, decreases in daily light quantity and quality could affect seagrass physiology, productivity, and, eventually, survival if the Minimum Quantum Requirements (MQR) are not reached. To better understand if, how, and to what extent photosynthetic adjustments contribute to light acclimation, eelgrass (Zostera marina L.) shoots from the cold temperate St. Lawrence marine estuary (Rimouski, QC, Canada) were exposed to seven light intensity treatments (6, 36, 74, 133, 355, 503, and 860 μmol photons m –2 s –1 , 14:10 light:dark photoperiod). Photosynthetic capacity and efficiency were quantified after five and 25 days of light exposure by Pulse Amplitude Modulated (PAM) fluorometry to assess the rapid response of the photosynthetic apparatus and its acclimation potential. Photoacclimation was also studied through physiological responses of leaves and shoots (gross and net primary production, pigment content, and light absorption). Shoots showed proof of photosynthetic adjustments at irradiances below 200 μmol photons m –2 s –1 , which was identified as the threshold between limiting and saturating irradiances. Rapid Light Curves (RLC) and net primary production (NPP) rates revealed sustained maximal photosynthetic rates from the highest light treatments down to 74 μmol photons m –2 s –1 , while a compensation point (NPP = 0) of 13.7 μmol photons m –2 s –1 was identified. In addition, an important package effect was observed, since an almost three-fold increase in chlorophyll content in the lowest compared to the highest light treatment did not change the leaves’ light absorption. These results shed new light on photosynthetic and physiological processes, triggering light acclimation in cold temperate eelgrass. Our study documents ...