ISHS Acta Horticulturae 751: IV International Symposium on Rose Research and Cultivation
METHODS FOR MEASUREMENT OF THE XYLEM CONDUIT LENGTH DISTRIBUTION AND HYDRAULIC CONDUCTIVITY |
| Authors: | J. Nijsse, H.M.C. Put |
| Keywords: | xylem conduit, xylem length, mathematical description, hydraulic conductivity |
| Abstract:
A mathematical description has been developed of xylem conduit length distribution, as a function of plant stem height. Nijsse et al. (2001) preferred to describe the anatomical relations as exponential functions, even in cases where linear functions gave as good a fit. 1st: exponential functions can represent first order stochastic underlying processes. 2nd: exponential functions are independent upon starting value (e.g., where you choose the h = 0 point). 3rd: simple exponential functions do not generate negative values as results (e.g., negative conduit lengths). Later, the author has shown that the theoretically most simple regulation mechanism for vessel lengths in plants indeed result in exponential vessel length distributions (Nijsse, 2004). Assuming that conduits are randomly located in the longitudinal direction, the length distribution of the entire conduits can be calculated using the half-length value. The increase of the inter-conduit resistivity can be explained by the finding that higher in the stem the conduits are shorter. Thus, higher in the stem the water flux has to cross more inter-conduit passages per unit of stem length. The dimensions of bordered pit pairs can also vary within one plant resulting in different resistances. Studies of cross-sectional areas of xylem vessels shows further how a simple and accurate description of hydraulic anatomical properties of plant stems can be achieved. The approach used allows the comparison of conduit lumen characteristics and hydraulic properties at different locations in one plant or between cultivars or between different species. Three-dimensional imaging techniques will be needed to explore the detailed shape of individual conduits (diameter and roundness fluctuations) and the conduit connection patterns. | |
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