from reference 1
Plants don’t have hearts to pump fluids throughout their systems, so how do they generate the pressure to move water against the force of gravity from their roots to their shoots (leaves)? Capillary action (the tendency of a fluid to move through small spaces due to it’s molecular constituents cohesive properties or surface tension) can explain the movement of water over small distances, but it cannot account for the large scale movement of water from the bases to the tips of tall trees like the Giant Sequoia of Redwood Forest.
Instead, it has long been thought that evaporation of water at the leaves draws water up in a long continuous column from the root, a process known as transpiration. This hypothesis was recently verified in the form of an artificial model1. Abraham Stroock and his graduate student at Cornell University built a small (10 cm) proof-of-concept tree model with artificial membranes representing roots and leaves and small “microfluidic” channels connecting them. Though small, this device demonstrates the functional capacity of the evaporation/water-column idea, and might eventually be used to test failures of this model (such as when air-bubbles intervene in the column) and to draw small amounts of water out of hard to reach places.
1. Wheeler TD, Stroock AD. The transpiration of water at negative pressures in a synthetic tree. Nature, 455(7210): 208-212, 2008.
How do plants converse with each other? As human beings, we posses probably the most sophisticated communication abilities of any species on the planet. This makes it very easy for us to forget that every form of life has some ability to transmit information between individuals. This is true even at a microscopic level where bacterial cell-to-cell signaling is a popular research topic (ref 1).
Having been around for a very long time and being unable to move much, it is no surprise that plants have developed many sophisticated adaptations for the purpose of communication. Plants can communcate in a host of ways, see (ref. 2) for a brief overview. One of the most fascinating of these is the use of “smoke signals.”
Ten years ago, researchers interested in plant biology and forest fires discovered that exposing seeds to smoke or certain nitrogenous compounds in smoke will induce germination (ref. 3). The evolutionary advantage of this behavior is presumed to be that forest fires leave an area rife for new growth.
The greater significance of this ability is our ongoing opportunity to learn from biological organisms. Although we use our intelligence to guide us in solving problems, we still use trial and error extensively. The greatest expert on trial and error is evolution. The process of evolving progressively more sophisticated life forms has relied on the use of trial and error for the last 3.7 billion years, and we would do well to realize that when it comes to the challenges of existing on earth, we’ve got a teacher who’s got a valuable store of experience.
1. Melissa B. Miller & Bonnie L. Bassler Quorum Sensing in Bacteria Annual Review of Microbiology 55: 165-199 [doi:10.1146/annurev.micro.55.1.165]
2. Ragan M. Callaway & Bruce E. Mahall Plant ecology: Family roots Nature 448, 145-147 [DOI: 10.1038/448145a]
3. Jon E. Keeley & C. J. Fotheringham Trace Gas Emissions and Smoke-Induced Seed Germination Science 276: 1248-1250 [DOI: 10.1126/science.276.5316.1248]