Mineral nutrient status of tree species in relation to environmental factors in the subtropical rain forest of Taiwan

Abstract

Until now, the mineral nutrition of rain forest trees is still poorly understood. Very few data are available on the nutrient characteristics of rain forest tree species and the influence of environmental factors especially for subtropical climates. This study evaluated the mineral nutrient status of the dominant tree species and its relation to environmental factors such as elevation, slope, landscape position, and soil nutrient status in a subtropical rain forest of southern Taiwan. Leaf, stem, and wood samples were collected for nutrient analysis from a total of 639 trees belonging to 20 dominant species from 27 contiguous 20 m × 20 m quadrants along an altitudinal transect ranging from 300 to 480 m. Composite soil samples were likewise collected from the 0–5 and 5–15 cm depths in the A horizon in each quadrant for chemical analysis. Soils in the study site ranged from well-developed, acidic with clayey subsoil Typic Paleudult in summit positions, to poorly developed and acidic Typic Dystrudept in backslope positions. Results revealed that leaf nutrient concentration was better correlated with the environmental factors than stem and wood nutrient concentrations. In addition, data showed generally wide concentration ranges for most mineral nutrients except P and Cu and most tree species were clustered at the lower end of the concentration ranges indicating they have low nutrient status. Among the macronutrients, P had the lowest and narrowest foliar concentration (0.25–2.8 g kg −1; mean = 0.8) while for the micronutrients, this was shown by Cu (3.88–17 mg kg −1; mean = 5.8). A few tree species were observed to accumulate (called “accumulator species”) some mineral nutrients like N, P, K, Ca, Mg, Cu and Zn indicating high absorption capacity for these nutrients. Foliar mineral nutrient concentration of the trees was generally correlated with the environmental factors such as elevation, topographic position, slope, vegetation type, and soil nutrient status. However, the effects were interrelated and difficult to isolate from each other although topographic position, vegetation type, and soil nutrient status appeared to be more related to the mineral nutrient concentration of the trees than the other environmental factors. In particular, plants on the footslope had generally higher concentration of N, P and K than those at the higher elevation of the upper backslope and summit. This suggests that the distribution of tree species in the study site is reflected by their foliar nutrient concentration. P appears to be the most limiting nutrient in the rain forest ecosystem studied although fertilization experiment is needed to verify the apparent P limitation.