Effect of Water-Table Depth on Shoot Growth, Root Growth, and Nodulation of Myrica Gale Seedlings

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Abstract
Seedlings of M. gale, an actinorhizal dinitrogen-fixing shrub, were grown in 2 boxes with a gradient of water-table depth from 3-79 cm. The boxes were outdoors but sheltered from rain by translucent roofs. One box was filled with sand and the other with peat. The seedlings were harvested in autumn shortly before leaf-fall. The plants produced maximum biomass at water-table depths between 10 cm and 35 cm on both substrata but the total amounts produced were substantially greater on peat than on sand. Shoot-root quotients decreased with increasing water-table depth on both substrata but were much larger on sand. The roots did not penetrate below the water table and the orientation of the major lateral roots changed from primarily horizontal to semi-vertical with increasing water-table depth. Nodules formed 6-7% of the total seedling biomass in the wettest soils and decreased to 1% in the driest. Nodule roots showed maximum development in the wettest soils where they were relatively long and thick, and emerged through the surface into the air above. This is consistent with a functional role in enhancing nodule O2 uptake under O2 limiting conditions. The considerable phenotypic plasticity in response to moisture and aeration exhibited by M. gale appears to be a valuable adaptation in its natural habitat where the water level often fluctuates.

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