Nutrient limitation of tree seedling growth in three soil types found in Sabah

Variation in soil nutrient may contribute to species–habitat associations and landscape-scale plant diversity in tropical forests. A nutrient bioassay experiment was used to test the hypotheses that (a) plant growth rate would be greater in more nutrient-rich alluvial soil than in soils taken from low mudstone and sandstone hills in the Sepilok Forest Reserve, Sabah and that (b) p would be the main limiting nutrient for plant growth in all three soil types. Seedlings of the pioneer tree Neolamarckia cadamba were grown for 45 to 52 days in pots of soil taken from alluvial, mudstone hill and sandstone hill habitats. The experiment comprised six macronutrient addition treatments and a control, with 10 replicates for each treatment. The growth rate of N. cadamba seedlings increased in response to P addition in sandstone hill soil and in response to K in alluvial soil. Relative growth rates were highest in alluvial soil, which had the highest concentrations of available nutrients. We conclude that alluvial, mudstone hill and sandstone hill soils provide contrasting soil chemical environments that are sufficient to induce differential growth rates for N. cadamba seedlings in pots. Phosphorus availability was non-limiting for N. cadamba seedlings in the alluvial forest soil, which unmasked limitation by K.