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Mrad, A., Domec, J.C., Huang, C.-W., Lens, F., Katul, G., 2018 – A network model links wood anatomy to xylem tissue hydraulic behavior and vulnerability to cavitation

Plant Hydraulics

While the term “plant hydraulics” refers to the study of how plants use water, our project aims at better understanding how plants lose their ability to use water efficiently.

Flowering plants rely on ducts, called vessels, to transport water from the roots to the leaves (shown in the figure below). The process through which water transport happens is fascinating: the plant can lift water tens of meters against gravity without an organ similar to the heart in humans. The method used by the plant, as described by the Cohesion-Tension theory, comes with the risk of air bubbles filling the vessels and blocking water movement. This happens after prolonged droughts.

Hardwood Pore Image
Cross-sectional view of Oak vessels (Attribution: McKDandy at English Wikipedia)

Our research is focused on discerning what anatomical features, on the micro- and nano-meter scales, affect how plants lose their efficient water use abilities. Doing so helps:

  • bridging a gap between the endeavors of anatomists and those of ecologists,
  • identifying advantageous anatomical features for different climate conditions, and
  • understanding how microscopic phenomena, like water movement in vessels and air bubble formation, upscale to affect whole-plant health and vice-versa.

Our work has both a numerical and analytical approach.

Photosynthetic response to drought

Culminating my third year as a PhD candidate is a study on the effects of water scarcity in the soil on plant photosynthesis. The inspiration for this work comes from the well-known argument that plant optimize the amount of carbon gained per unit loss of water. Since the inception of this method in the 1970s, there has been a lot of work on ridding this approach of all its initial assumptions. Some of these assumptions were that the soil is well watered and that the plant optimizes its activity over the span of 24 hours only. The accuracy of this method has been demonstrated under these conditions.

Even with the more recent work on this topic, the scientific community is still oblivious regarding the implication of this approach under water scarcity especially when competition among plants exists. To cast some light on this unknown, the team re-derived the optimality argument from first principles but with a twist. Back in 2013, a former postdoc at our lab relaxed the assumption that the optimum was achieved only within the span of 24 hours and more accurately extended it to the period between rainfall occurrences. Moreover, the lab members in 2013 introduced the concept of long-term gains to the mix. In short, it could be beneficial for the plant to conserve water in the soil for use in later dry period and this was now captured.

Our new paper, now in press, adds the following to the argument of photosynthetic optimality:

  • It resolves the photosynthetic activity at a half-hour timescale
  • It includes the effects of plant competition for water
  • It provides the necessary means for the addition of extra constraints in new plant ecosystems
  • It shows how the additions agree with data from a controlled experiment published elsewhere