The effects of light shading on chlorophyll and nitrogen dynamics in the submerged macrophyte, Ruppia maritima (draft)

Zubricki, Brendhan; Roman, Charles

FIELD WORK: June 1991. 'Field plots were established in Ruppia maritima L. (wigeongrass) meadows of the Bass Harbor Marsh estuary (Maine, USA) in summer 1991 to evaluate leaf chlorophyll, leaf nitrogen and root/rhizome nitrogen responses to experimentally induced shading. Shading, expected to simulate a sympton of estuarine eutrophication, was experimentally established in 2m2 plots (n=3) reducing light energy in the water column by 53% (high shade treatment) when compared to the control (no experimental shading), and 28% for the intermediate treatment. By day five of the 27 day experiment, chlorophyll a+b levels in the high shade plots were significantly elevated compared to the other treatments. Leaf nitrogen levels revealed a decreasing trend, most pronounced in the control. It is suggested that increased leaf nitrogen levels related to chlorophyll production were masked by translocation of leaf nitrogen to support reproductive shoots. There also appeared to be a significant allocation of below ground nitrogen to reproductive shoots. It is postulated that under reduced light regimes, as expected under scenarios of coastal eutrophication, the enhanced utilization of nitrogen for chlorophyll production could result in decreased allocation of nitrogen to reproductive shoots, thus impacting the reproductive success of Ruppia.' /STUDY LOCATIONS:/ /MOUNT DESERT ISLAND/Bass Harbor Marsh/