Differential Growth and Rooting of Upland and Peatland Black Spruce, Picea mariana, in Drained and Flooded Soils

A reciprocal experiment was analyzed to determine whether 30 open-pollinated families of peatland and upland populations of black spruce [Picea mariana (Mill.) B.S.P.] sampled from a single area in north-central Alberta, Canada, performed consistently when grown in either flooded or well-drained soils (i.e., if there is a family x soil interaction or generally called genotype x environment interaction (GEI)). The data for the analysis consisted of five traits (height, root dry weight, shoot dry weight, root/shoot dry weight ratio and number of braches) describing growth and rooting performance of tree seedlings in flooded and drained soils (root environments) in a greenhouse for 16 weeks. A mixed-model analysis was used to characterize GEI. The analysis revealed an interesting contrast of GEI patterns between the peatland vs. upland populations: GEI was absent (as indicated by a perfect correlation between flooded and drained soils) in peatland population but present in the upland population. Our results from the characterization of GEI are also consistent with the well-known theory about selection in different environments that correlated responses due to indirect selection are in general less than direct responses. The contrasting patterns of GEI in peatland vs. upland populations may be reflective of different strategies of adaptation to the contrasting environmental conditions, with the peatland trees growing slowly but steadily and with the upland populations growing fast and very responsive to environmental changes.