The nitrogen content of plants and the self-thinning rule of plant ecology: a test of the core-skin hypothesis
1987
Hardwick, R.C.
The ‘core-skin’ hypothesis postulates that secondarily thickened plants behave energetically as an inert ‘core’ covered by an active ‘skin’, the ‘skin’ being two-imensional, the ‘core’ three-dimensional. This would explain the ‘self-thinning ‘or‘ −3/2’ rule of plant ecology, that is, the tendency for log (dry weight per plant) and log (number of plants per unit area) to progress along a straight line relationship, with slope = − 3/2’. The hypothesis was tested as follows. Plant nitrogen content was used as an estimate of the mass of ‘skin’ per plant, and dry weight as an estimate of the mass of the ‘core’. As plants mature the slope of the relationship between y = log (mass of nitrogen per plant) and x = log (mass of dry matter per plant) is expected to decline from an initial value of 1.0 towards a final value of 0.66. The intercept of the relationship is expected to reflect the intrinsic content of ‘skin’ per unit of ‘core’. Genotypic variation in this parameter should cause genotypic differences in the maximum attainable yield of biomass per unit area. The expectations were investigated by fitting the function y = p+qx+r exp − x to 30 sets of data on plant nitrogen content, plant weight and time in 18 different vegetables. Simple linear regressions of y on x were fitted to more limited sets of data on weights and nitrogen contents of mature trees. The expectations were, with some minor exceptions, confirmed.
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