PETER MELCHER (Section 09)
Long-distance transport of water, minerals, and nutrients from the roots to the leaf within a plant is pulled through small hollow pipes (30-100 um openings) located within the woody tissue called xylem tracheary elements. The open lumens of these elements allow water to move (in mass) through a plant with minimal resistance. Water movement in plants is powered by evaporation of water from the internal leaf spaces to the dry air. The cohesive and adhesive properties of water allow the water to withstand large negative pressures (allow water to tolerate large pulling stress). The negative pressure results from the resistance to fluid drag and the gravitational potential acting on the long continuous water columns. Interestingly, these conduits are separated at discrete regions by bordered pit membranes (composed of cellulose) which is believed to prevent gas bubbles or embolisms from spreading within the hydraulic system. Because embolisms break the continuity of the liquid water columns it stops water movement though the xylem conduits. In our lab, we are assessing the impact that various solutions have on the integrity of these bordered pit membranes to prevent the spread of embolism within the hydraulic system of plants.
Recent evidence suggests that a xylem-mediated wound response impacts our ability to measure the hydraulic properties of plants. This is important in understanding how plants move water through their bodies and in characterizing plant adaptations to drought.
We have devised a new method to measure the hydraulic resistance of plant tissue that contains multiple years of growth. Measurements of stem hydraulic resistance are used to characterize overall plant hydraulic form. These measurements are used to model the vascular network in plants. These data are important to understand how plants move water from the soil to the leaf while under negative pressure gradients through the pipes within their tissues.
We are investigating the impact that various leaf extracts have on soil microbial activity. Because plants rely on a soil-microbe-fungal food web to enhance nutrients uptake, many plants actually feed these soil organisms by secreting sugars out of their roots into the soil. We are interested in other potential food sources for the soil-microbe community in the soil. One potential food source is the leaf litter from tree. Thus, we are testing the affects of leaf extract on soil-microbe activity and growth.
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