The importance of maintenance respiration by living cells in the sapwood of subalpine conifers

Graduation date: 1989Xylem conducting tissue or sapwood is an important storage organ\ud for water, carbohydrates, and nutrients, and this storage helps trees\ud accommodate environmental change. However, the living ray parenchyma\ud cells in sapwood, which store the carbohydrates and nutrients,\ud require energy for maintenance. I examined how sapwood maintenance\ud costs vary among species, and how these costs change with tree growth\ud and stand development.\ud First, I explored how sapwood volume and leaf area, indices of\ud maintenance costs and net assimilation, varied with tree size among\ud three subalpine conifers (Engelmann spruce, subalpine fir, and\ud lodgepole pine). As trees grew in size and leaf area, sapwood volume\ud increased exponentially. The ratio of sapwood volume to leaf area\ud increased with tree size, indicating that maintenance costs were\ud greater in large trees, relative to leaf area. Lodgepole pine showed the most rapid increase in sapwood volume with increasing leaf area,\ud suggesting storage capacity and sapwood maintenance are important\ud processes for this species.\ud Next, I measured stem growth and maintenance respiration for\ud Engelmann spruce and lodgepole pine. Stem maintenance respiration\ud was linearly related to sapwood volume for lodgepole pine from 4 to\ud 40 cm dbh and for Engelmann spruce from 0 to 20 cm dbh. Maintenance\ud respiration was not correlated with annual stemwood production or\ud phloem volume for either species, but stem respiration during the\ud growing season, corrected for maintenance, correlated well with\ud annual stemwood growth. Annual stem maintenance respiration for\ud trees and stands can be estimated using sapwood volume, sapwood\ud temperature and knowledge of respiratory behavior.\ud Finally, I examined a chronosequence of subalpine lodgepole pine\ud stands to test the hypothesis that the balance between photosynthetic\ud and respiring tissue changes with stand development. I predicted\ud that woody tissue respiration (particularly stem sapwood) would\ud increase with stand development and account for the majority of\ud observed decreases in stem growth. Leaf area and nutrient\ud availability indicated that carbon assimilation was similar for the\ud chronosequence, but stem growth decreased from 0.14 to 0.04 kg C ha⁻¹\ud y⁻¹. However, maintenance respiration of woody tissues in stems, branches and coarse roots accounted for less than 40% of the decrease\ud in stem growth