ecophyslab research
Plant vascular function, dysfunction, and failure.
Vascular plants are defined by the presence of conducting tissue. Vascular tissue is composed of xylem, phloem, and their shared progenitor—the vascular cambium. Vascular tissue is responsible for the bulk flow of water and nutrients in plants, aids in structural support, and plays important parts in many physiological and signaling processes in plants. Describing the function, dysfunction, and eventual failure of plant vascular systems is a key aim of Dr. Hammond’s work. During environmental stresses, especially drought and heat, the plant vascular system is faced with challenges to maintaining levels of function essential for plant growth, reproduction, and even survival. Employing the tools and techniques of plant ecophysiology and hyperspectral imaging, we are determining the limits of function, dysfunction, and failure for plant vascular systems of diverse plant systems, from agriculturally important annual crop species to perennial woody trees. This research aims to understand boundary conditions for plant vascular function (e.g., how hot is too hot? how dry is too dry?) on our warming planet.
(figure from Hammond, Johnson, and Meinzer, 2021, doi: 10.1111/pce.14033)
Plant tipping points: from xylem to ecosystems.
Environmental stress often leads to declines in plant physiological performance, but at certain thresholds (such as when plant vascular systems fail during drought), critical transitions occur (so-called ‘tipping points’) to alternative states—including lasting dysfunction or death of individuals, with ecosystem-level consequences as individual-level failures aggregate in populations and communities. Identifying and quantifying these legacies of dysfunction in the xylem of plants is urgently needed, as evidence of tipping-point behavior in the xylem of individual plants, and in populations of plants, has been recently reported by Dr. Hammond. Read more in Dr. Hammond’s recently published perspective: “A matter of life and death: alternative stable states in trees, from xylem to ecosystems”.
(figure from Hammond, 2020. doi: 10.3389/ffgc.2020.560409)
Global forest mortality
Earth’s forests have experienced widespread heat- and drought-induced pulses of tree die-off in recent decades. Dr. Hammond is leading an effort to precisely locate these events, and when they begin. This work is part of a larger mission of the international tree mortality network (ITMN) where Dr. Hammond is the network’s database manager. Additional information can be found on the ITMN website.
(Figure from Hammond et al., in revision)
The global vulnerability of plant xylem
Xylem is the tissue through plants transport water from the soil to Earth’s atmosphere. Understanding the conditions for function, dysfunction, and failure of xylem is critical in predicting plant performance and mortality in a warming world. Dr. Hammond is presently leading an international collaboration to synthesize a global database describing the global vulnerability of plant xylem—often reported as a plant hydraulic ‘vulnerability curve’. Preliminary findings and future updates can be found at https://xylemfunctionaltraits.org. A manuscript presenting the database, and initial analyses, is in preparation.
(Figure from Hammond et al., in prep)