Photosynthetic and Growth Responses of Silver Maple (Acer saccharinum L.) Seedlings to Flooding

Abstract

Flooding affected several growth parameters of silver maple (Acer saccharinum L.) seedlings. Root biomass and leaf area were sharply reduced. Photosynthetic rates of recently germinated seedlings decreased significantly after 21 days of root-flooding and after only 3 days of submersion. In some treatments, reduced net photosynthesis/transpiration ratios after flooding indicated a decline in water use efficiency. Seedlings submersed in water containing suspended sediments had lower rates of photosynthesis than plants submersed in clear water. The timing of flooding treatments (spring vs. late summer) had no apparent effect on the pattern of decline in net photosynthesis. Two-year-old seedlings had a greater capacity for net photosynthesis after flooding than recently germinated seedlings, suggesting that recovery of normal physiological function after flooding is an important survival feature of older silver maple seedlings. Light conditions had minimal effect on seedling growth and photosynthesis. Seedlings had relatively high rates of photosynthesis over a broad range of photosynthetically active photon flux density and developed a shade leaf' morphology when grown at low light intensity. Duration of flooding is the most important characteristic of the flood cycle affecting the survival and establishment of silver maple seedlings in floodplain habitats. INTRODUCTION Silver maple (Acer saccharinum L.) is widely distributed throughout the eastern United States. It occurs chiefly on floodplains and on the moist sites of creek bottoms, and is the dominant species in many floodplain communities in the Midwest (Bell, 1974; Franz and Bazzaz, 1977). Silver maple develops best in well-drained, moist soils (Fowells, 1965), and is extremely tolerant of flooding (Hosner, 1960; Teskey and Hinckley, 1977b). Seedlings experience periodic flooding which normally occurs during spring or summer in the Midwest. Furthermore, floodwaters vary considerably in their sediment and nutrient loads, especially in watersheds that drain agricultural fields (Peterson and Rolfe, 1982b). It is critical that silver maple and other bottomland species have the ability to withstand periodic flooding. Excess water in flooded soils displaces air from the pore space, and the resulting poor aeration increases root resistance to water uptake (Kramer and Kozlowski, 1979). An early physiological response to flooding is stomatal closure (Regehr et al., 1975; Pereira and Kozlowski, 1977), which prevents loss of leaf turgor in the absence of water uptake. Some species develop adventitious roots and hypertrophied lenticels in response to prolonged flooding (Keeley, 1979), and stomata reopen as water uptake is initiated (Kozlowski and Pallardy, 1979). Additional environmental factors, such as night temperature, have been shown to affect stomatal resistance and net photosynthesis in some bottomland tree species (Drew and Bazzaz, 1979). The present study was initiated to determine growth and physiological responses of silver maple seedlings to flooding. Patterns of net photosynthesis and transpiration were measured for seedlings subjected to root-flooding and total submersion. Both 1 Present address: U.S. Forest Service, Riverside Fire Laboratory, 4955 Canyon Crest Drive, Riverside, California 92507.