by Carl Strang
This week’s bit of scientific literature is a study of leaf size and vein pattern (C. Scoffoni, M. Rawls, A. McKown, H. Cochard, L. Sack. Decline of Leaf Hydraulic Conductance with Dehydration: Relationship to Leaf Size and Venation Architecture. Plant Physiology, 2011; 156 (2): 832 DOI: 10.1104/pp.111.173856). The paper was described in an article in ScienceDaily, the best website for scientific research news I have seen on the web.
Scoffoni and company did a broad review of how leaf sizes change in different plant environments. Leaves get smaller as the habitat gets drier, and they found that the complexity of vein networks increases as leaves get smaller. The importance of this appears to be that leaves need carbon dioxide to build plant structure and store energy, but in order to get that gas the leaves need to open up their interiors. That exposes them to drying. Transpiration occurs mainly to replace this lost water, as leaf interiors must stay humid to function. Anything which interferes with the water flow is harmful, and in this case the problem with drought is that it can introduce air bubbles into leaf veins, blocking water flow. Having complex vein systems provides multiple alternative ways for transpired fluid to bypass such embolisms.