NUTRIENT AVAILABILITY AND GROWTH-RATE OF 34 WOODY SPECIES FROM A TROPICAL DECIDUOUS FOREST IN MEXICO

1. 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. 2. Dry biomass, relative growth rate (RGR), root/shoot ratio (R/S), specific leaf area (SLA), leaf are a ratio (LAR), leaf weight ratio (LWR), root weight ratio (RWR), net a ssimilation rate (NAR) and the nitrogen and carbon leaf percentage wer e determined following an initial and final harvest. In all the parame ters evaluated, the trend followed by the species under low nutrient c onditions was similar to the trend attained in high nutrient condition s but with different magnitude. 3. The species with the largest seed b iomass was Thevetia ovata (3808.6mg). Lagrezia monosperma had the smal lest seeds (0.13 mg) and the highest RGR in the high nutrient treatmen t. 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) . 4. Higher biomass allocation to roots Was shown under low nutrient c ondition but the relationship between RGR and root/shoot ratio was non -significant. 5. Species variation in RGR to both the nutrient treatme nts employed is followed by species variations in LAR (r=0.50) more th an changes in NAR (r=0.20). Changes in LAR are explained by LWR (r=0.6 2) 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 bo th the total leaf area produced and the leaf morphological characteris tics in determining the RGR. 6. A general characteristic of the distri bution of the species' responses in RGR to both nutrient treatments wa s the existence of a continuum, for all of the parameters studied. Thi s suggests differences in the species' resource utilization and tolera nce, which are reflected in different plastic capacities.