Harvard Forest Research

How trees control the onset of leaf senescence?

Principal Investigator: N. Michele Holbrook
Harvard College (Harvard University): May 15 2009 - Oct 15 2009:

Abstract:
A central and unsolved question in forest ecology is what controls the timing of leaf senescence. The marked changes in gene expression that accompany the onset of senescence indicate that this is a highly regulated developmental transition. As the nexus between carbon, nitrogen and water balance in plants, the leaf vascular system is well positioned to integrate the variety of environmental and endogenous signals known to trigger leaf senescence. My hypothesis is that the hydraulic conductance of the leaf lamina (Kleaf) controls the onset of leaf senescence through its effect on the delivery of xylem transported compounds such as nitrogen and cytokinins. To test this hypothesis I will: (1) document temporal patterns of Kleaf, and associated changes in photosynthesis (A), transpiration (E), nitrogen (N), cytokinins, and chlorophyll as a function of leaf age in tree species at Harvard Forest; (2) experimentally manipulate both E and A using humidity chambers and shading treatments to examine the role of xylem transport versus stomatal limitations on CO2 uptake in controlling leaf senescence; and (3) determine how interactions between environmental and endogenous signals influence Kleaf as leaves age.: