Vascular Transport Systems in Plants
Projects:
1) We are investigating the mechanisms underlying dynamic changes, both seasonal and short term, in xylem hydraulic properties of stems and leaves of Harvard Forest trees. Our work examines the role cavitation due to water stress and/or freezing in reducing xylem hydraulic conductivity, as well as the effects of xylem sap ion concentrations and embolism repair on increasing xylem hydraulic conductivity.
2) We are investigating whether infection by the hemlock woolly adelgid results in a loss of xylem hydraulic conductivity. This insect attacks xylem parenchyma, raising the question of whether the loss of these cells diminishes the ability of hemlock to either avoid or repair cavitation of xylem tracheids.
3) We are investigating the hydraulic properties of fern leaves, focusing on five species common at the Harvard Forest. Our goal is to document the leaf-area specific xylem conductivity of these plants, as well as their vulnerability to cavitation. There have been almost no studies of fern hydraulics, and thus a first step will be to see how these basic hydraulic parameters compare with other vascular plants.
4) Previous studies by our group at the Harvard Forest indicate significant seasonal changes in leaf hydraulic conductivity. We now wish to determine the extent to which these changes are coordinated with leaf photosynthetic capacity and nitrogen content.
5) Rachel Spicer, a Ph.D. student in this lab, is studying factors responsible for the sapwood/heartwood transition in Harvard Forest trees. Her work examines patterns of ray cell death, the role of bole gas composition on respiration, and the relation between cell death patterns and sap flow rates.
Further Information: http://www.oeb.harvard.edu/faculty/holbrook/
Selected Publications
Sack, L., C. M. Streeter*, and N. M. Holbrook. 2004. Hydraulic analysis of water flow through leaves of sugar maple and red oak. Plant Physiology 134: 1824.
Sack, L., P. D. Cowan*, N. S. Jaikumar, and N. M. Holbrook. 2004. The 'hydrology' of leaves: coordination of structure and function in temperate woody species. Plant, Cell and Environment (In press).
Orians, C. M., S. D. P. Smith*, and L. Sack. 2004. How are leaves plumbed in a branch? The sectoriality of xylem hydraulics in six temperate tree species. Journal of Experimental Botany (submitted).
Sack, L., P. D. Cowan, and N. M. Holbrook. 2003. The major veins of mesomorphic leaves, revisited: a test of conductive overload in leaves of Acer saccharum (Aceraceae) and Quercus rubra (Fagaceae). American Journal of Botany 90: 32-39
Melcher, P. J., M. A. Zwieniecki, and N. M. Holbrook. 2003. Vulnerability of xylem vessels to cavitation in Acer saccharum (Marsh.): scaling from individual vessels to whole branches. Plant Physiology 131: 1775-1780
Sack, L., P. J. Melcher, M. A. Zwieniecki, and N. M. Holbrook. 2002. The hydraulic conductance of the angiosperm leaf lamina: a comparison of three methods. Journal of Experimental Biology 53: 2177-2184
Holbrook, N. M., M. A. Zwieniecki, and P. J. Melcher. 2002. The dynamics of "dead" wood: maintenance of water transport through plant stems. Integrative and Comparative Biology 42: 492-496
Zwieniecki, M. A., P. J. Melcher, and N. M. Holbrook. 2001. Hydrogel control of xylem hydraulic resistance. Science 291: 1059-1062
Zwieniecki, M. A., P. J. Melcher, and N. M. Holbrook. 2001. Hydraulic properties of individual xylem vessels of Fraxinus americana. Journal of Experimental Botany 52: 257-264
Feild, T. S., D. W. Lee, and N. M. Holbrook. 2001. Why leaves turn red in autumn: the role of anthocyanims in senescing leaves of red-osier dogwood (Cornus stolonifera). Plant Physiology 127: 566-574
Cavender-Bares, J. and N. M. Holbrook. 2001. Hydraulic properties and freezing-induced cavitation in sympatric evergreen and deciduous oaks with contrasting habitats. Plant, Cell and Environment 24: 1243-1256
Zwieniecki, M. A., L*. Hutrya, M. V. Thompson, and N. M. Holbrook. 2000. Dynamic changes in petiole specific conductivity in red maple (Acer rubrum L.), tulip tree (Liriodendron tulipifera L.) and northern fox grape (Vitis labrusca L.). Plant and Cell Environment 23: 407-414
Holbrook, N. M. and M. A. Zwieniecki. 1999. Embolism repair and xylem tension: do we need a miracle? Plant Physiology 120: 7-10
Zwieniecki, M. A. and N. M. Holbrook. 1998. Diurnal variation in xylem hydraulic conductivity in white ash (Fraxinus americana L.), red maple (Acer rubrum L.) and red spruce (Picea rubens Sarg.). Plant, Cell and Environment 21: 1173-1180
Maherali, H., E. H. DeLucia, and T. W. Sipe. 1997. Hydraulic adjustment of maple saplings to canopy gap formation. Oecologia 112: 472-480