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The evaluation of Murray's law in Psilotum nudum (Psilotaceae), an analogue of ancestral vascular plants
Author(s) -
McCulloh Katherine A.,
Sperry John S.
Publication year - 2005
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.3732/ajb.92.6.985
Subject(s) - xylem , biology , stele , botany , electrical conduit , transpiration , law , mechanical engineering , photosynthesis , political science , engineering
Previous work has shown that the xylem of seed plants follows Murray's law when conduits do not provide structural support to the plant. Here, compliance with Murray's law was tested in the stem photosynthesizer Psilotum nudum , a seedless vascular plant. Psilotum nudum was chosen because the central stele does not provide structural support, which means that Murray's law is applicable, and because its simple shoot structure resembles the earliest vascular plants. Murray's law predicts that the sum of the conduit radii cubed (Σ r 3 ) should decrease in direct proportion with the volume flow rate ( Q ) to maximize the hydraulic conductance per unit vascular investment. Agreement with Murray's law was assessed by estimating the transpiration rate distal to a cross‐section, which should determine Q under steady state conditions, and comparing that with the Σ r 3 of that cross‐section. As predicted, regressions between the Σ r 3 of the cross‐section and Q resulted in a linear relationship with a y ‐intercept that was not different from zero. Two more rigorous statistical tests were also unable to reject Murray's law. Psilotum nudum plants also increased their conductance per investment by having more conduits distally than proximally, which is more efficient hydraulically than equal or declining conduit numbers distally.