Write on photoinhibition.
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The inhibition of photosynthesis at high light intensities must be taken into account in ecological studies, since the intensities typically experienced in the surface layer of natural waters in sunny weather are in the range that can produce photoinhibition. Indeed if the depth profile of phytoplankton photosynthetic activity is measured by the suspended bottle method in inland or marine waters, a noticeable diminution in the specific photosynthetic rate or the rate per unit volume is commonly, although not invariably, observed near the surface. Figure l0.4 shows examples of this surface inhibition of photosynthesis in a coastal and an inland water. With increasing depth and diminishing light intensity, photoinhibition lessens and the maximum, light-saturated but not inhibited, photosynthetic rate is achieved. With further increase in depth, irradiance falls to the point at which light intensity becomes limiting and from here on the photosynthetic rate diminishes roughly exponentially with depth approximately in parallel with irradiance.
Many, but not all, macrophyte species also show inhibition of photosynthesis when exposed to light intensities in the range of full sunlight, fldtE of phoiflivn Uliesia (rug C m"* h"L> 0 20 40 60 BO 10O 120
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