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2 Polish Journal of Ecology

2 2009

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Isometric scaling relationship between leaf number and size within current-year shoots of woody species across contrasting habitats

Li T., Deng J., Wang G., Cheng D., Yu Z.

Polish Journal of Ecology

2009

Vol. 57, nr 4

659-667

The scaling relationship between the number and size of plant.s components has been observed traditionally as reflective of a trade-off in resource allocation over ontogeny. The recent finding of a negative isometric leaf size/number trade-off across 24 deciduous woody species extends knowledge of such trade-offs to current-year shoots. Before generally accepted, this isometry has to be consistent across more datasets that represent diverse habitats. We tested this scaling relationship using 12 deciduous shrub species from the western Gobi Desert and 56 woody species from the northeastern temperate zone of China. Our results showed that leaf number per stem mass of current-year shoots scaled approximately isometrically with individual leaf mass within and across habitats, which, combined with the independence of total leaf mass and individual leaf mass, supports isometric scaling for shoot-scale leaf deployment. However, the intercepts of these relationships decreased significantly along the environmental gradients, suggesting that habitats could place a constraint on the total leaf number that can be supported by a given size shoot. Convergence towards higher leaf number and smaller leaf size for some desert species suggests important adaptive implications for photosynthetic carbon gain and reproductive growth.

Invariant allometric relationship between aboveand below-ground biomass along a moisture gradient in North-West China

Cheng D., Wang G., Tang Q., Li T., Zhong Q.

Polish Journal of Ecology

2009

Vol. 57, nr 4

669-675

Biomass allocation pattern is an important plant characteristic which influences how plants respond to abiotic and biotic heterogeneity. Prior studies indicate that above-ground biomass scales nearly isometrically with respect to below-ground biomass regardless of environment or phyletic affinity. However, such rule has been mostly tested with data on trees and usually without drought stress. Given the importance of this predicted relationship, it should be evaluated for a wider range of species and environmental conditions. Variations of the above- and belowground biomass (M[A] and M[R], respectively) were determined from five sites in north-west China, which compose a natural moisture gradient (aridity index ranging from 0.95 to 1.98). Model Type II regression protocols were used to compare the numerical values of M[A] vs M[R] scaling exponents (i.e. slopes of log-log linear relationships). The resulting five scaling exponents were indistinguishable and had a similar, nearly isometric slope (i.e. M[A] [is proportional to] M[R] [is approximately equal to] 1.0). Significant variation was observed in the Y-intercepts of the five regression curves, because of the absolute differences in M[A] or M[R]. These results support prior allometric theory, which reveals an isometric relationship between above- and below-ground biomass, and may provide a suitable method to estimate the regional below-ground biomass based on the direct aboveground measurements.