Effect of galls induced by Endocronartium harknessii on stem hydraulic conductivity and growth of lodgepole pine

摘要

P>To test the hypothesis that galls resulting from infection by western gall rust [Endocronartium harknessii (J. P. Moore) Y. Hiratsuka] on lodgepole pine [Pinus contorta Dougl. ex Loud.] create hydraulic constrictions that reduce tree growth, the hydraulic conductivity (K-Sigma; m2 s-1 Pa-1), leaf area (A(L)) and sapwood area (A(S)) were measured on 6- to 15-year-old trees having galls encircling 0-100% of the stem. Increases in gall encirclement were accompanied by decreases in K-Sigma, foliar nitrogen concentration, A(L) and A(S), although the A(L):A(S) ratio remained constant. Dye flow patterns through galled stem sections indicated that water moved primarily through the non-galled portions of the stem. In a second field study, xylem and phloem wounds were applied to 13-year-old galled and non-galled trees on either the galled or non-galled side of the tree. Although both galls and xylem wounds reduced K-Sigma, radial and height growth were unaffected. In aggregate the two experiments showed that although trees are quite tolerant to small galls and short term reductions in K-Sigma, the disruption of water movement by larger galls may be sufficient to initiate a chain of events leading to tree death, especially in very dense stands with high levels of intraspecific competition.