Photosynthesis, water relations, and foliar nitrogen of Piceamariana and Larixlaricina from drained and undrained peatlands

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Abstract
Rates of net assimilation and related ecophysiological parameters were measured three times during the 1988 growing season on a total of 80 black spruce (Piceamariana (Mill.) B.S.P.) and 80 tamarack (Larixlaricina (Du Roi) K. Koch) trees from two peatland locations, each with paired drained and undrained plots. Ditching for drainage was completed in March 1984. There was no evidence of improved water relations in trees on the drained plots. The initial effect of drainage was the improvement of nitrogen relations. This, in turn, was associated with higher rates of net assimilation. In general, trees in the drained plots were characterized by higher rates of net assimilation, water-use efficiency, mesophyll conductance to CO2, a lower ratio of intercellular to ambient partial pressure of CO2, and higher foliar nitrogen content. For tamarack, the drainage effect was only significant at one location, which was described as the poorer site. For both species, measures of net assimilation and foliar nitrogen were positively correlated with leader growth.

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