Abstract
To test the predicted relationship between growth rate and biomass allocation in relation to nutrient availability, seedlings of 34 woody species from the tropical deciduous forest in Mexico were grown under two contrasting nutrient conditions. Dry biomass, relative growth rate (RGR), root/shoot ratio (R/S), specific leaf area (SLA), leaf area ratio (LAR), leaf weight ratio (LWR), root weight ratio (RWR), net assimilation rate (NAR) and the nitrogen and carbon leaf percentage were determined following an initial and final harvest. In all the parameters evaluated, the trend followed by the species under low nutrient conditions was similar to the trend attained in high nutrient conditions but with different magnitude. The species with the largest seed biomass was Thevetia ovata (3808.6 mg). Lagrezia monosperma had the smallest seeds (0.13 mg) and the highest RGR in the high nutrient treatment. However, the relationship between RGR and seed biomass among the 34 species studied was weak (r = -0.50 in low and -0.62 in high nutrients). Higher biomass allocation to roots was shown under low nutrient condition but the relationship between RGR and root/shoot ratio was non-significant. Species variation in RGR to both the nutrient treatments employed is followed by species variations in LAR (r = 0.50) more than changes in NAR (r = 0.20). Changes in LAR are explained by LWR (r = 0.62) and SLA (r = 0.70). Under low and high nutrients, the RGR was highly correlated with SLA (r = 0.67 and 0.60), suggesting the importance of both the total leaf area produced and the leaf morphological characteristics in determining the RGR. A general characteristic of the distribution of the species' responses in RGR to both nutrient treatments was the existence of a continuum, for all of the parameters studied. This suggests differences in the species' resource utilization and tolerance, which are reflected in different plastic capacities.
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