Plant hydraulics - Zwieniecki lab
Typical crossection of the leaf (click to enlarge.)
Go to the Zwieniecki lab website.
Plants are complicated micro-fluidic systems consisting of a self-assembled network of conduits made from specialized cells. My research addresses how the structure, surface chemistry and mechanical properties of this network influence its ability to distribute water, solutes and energy over long distances, as well as how the terminal exchange surfaces (roots and leaves) interface with the environment. The goal is to use this fundamental knowledge to better understand limitations and environmental drivers that shape woody plant diversification in three major areas.
Leaves—the major sites of gas exchange
It is generally assumed that stomata are the major control mechanisms in the soil-plant-atmosphere continuum. However, despite decades of effort we still can not answer the basic question of how water availability—the most important of the many signals that are known to influence stomatal aperture—controls transpiration rates. My approach to this problem combines micro-experimental measurements of the xylem-to-stomata connections, with mathematical models of the underlying hydraulic properties that give rise to the observed stomatal dynamics. This work provides a mechanistic understanding of the link between liquid and vapor phase transport, and thus has the potential to substantially expand our ability to model controls on water flux from plant canopies.
Stems—secure systems of material transport
Stepping down from leaves to stems, I study a second level of flux control that exists in plants. My work has demonstrated that xylem vessels, despite being dead at maturity, possess the ability to autonomously change their hydraulic properties in response to the concentration of dissolved cations. The response time (seconds) is an order of magnitude faster than most human-made hydrogel-based systems, providing these rigid organisms (no moving parts) with a mechanism to actively change the distribution of water among thousands of branches, thus tailoring their supply network to short term (minutes to hours) changes in local water demand. My work on the internal control of xylem hydraulic resistance transforms the old paradigm of a passive redistribution system into one that is both active and responsive to internal and external conditions.
Roots—resource acquisition
Roots have to be understood by analogy to the hydraulics of porous pipes. Combining experimental measurements of water flow through roots with mathematical models of both flow rates and pressure dissipation around and within growing root tips, I have quantified the tradeoff between water uptake and root length utilization. This work helps to explain why root maturation leads to a loss of permeability, as well as provides a context for addressing how profiles of water uptake along the root influence spatial and temporal patterns of solute uptake. I am also interested in the potential role of roots in controlling water flux across the plant and am exploring the role that hydrogels in cell walls may play in variable root resistance. My analysis of root hydraulic properties is a continuation of my long term interest in the role of roots in shaping the soil environment.
More information on Maciej Zwieniecki's work is available on his lab's website: http://zatoichi.huh.harvard.edu/~zwieniecki/