Growth, photosynthesis and carbohydrate utilization in submerged Scirpus maritimus L. during spring growth

Abstract

summaryThe importance of underwater photosynthesis and the use of reserve‐carbohydrates were assessed in submerged Scirpus maritimus L. during spring growth. Submerged plants were grown in outdoor ponds (90 cm deep) using different initial tuber sizes (mean 8.9 and 16.2 g f. wt) and different light treatments (0, 40, 70 and 100% of full daylight). After shoot emergence the recovery from shading and darkness was studied.The period of submerged growth lasted 9 wk. During this period the mean relative growth rate (RGR) was independently affected by shading and tuber size. At the end of this period dry weight of plants grown in darkness was only 50% of that of plants grown in full daylight or shade (70 or 40% of full daylight), whereas that of plants from small tubers was only 67% of that from large ones. As a result plants grown from small tubers in darkness had only 33% of the dry weight of those grown from large tubers in full daylight or shade.Despite these large differences in total dry weight at the end of the submerged period, shoot length remained unaffected by shading and tuber size. Shoots grown in darkness were strongly etiolated, with a slower rate of leaf appearance, but with longer leaves, than those grown in full daylight or shade. Only after emergence was shoot length as well as dry matter production greater in plants grown previously in full daylight or shade than in darkness, and greater in plants grown from large than from small tubers.During the submerged period, the relative depletion rate of reserve‐carbohydrates increased with time, but remained unaffected by shading and tuber size. The reserve‐carbohydrates were replenished after plants emergedIt was concluded that both underwater photosynthesis and tuber size had a large impact on total dry matter production in S. maritimus. They did not, however, affect the ability of S. maritimus to emerge from 90 cm deep water.