Plant size, environmental factors and functional traits jointly shape the stem radius growth rate in an evergreen coniferous species across ontogenetic stages

Abstract

Abstract Aims Plant size, environmental conditions and functional traits are important for plant growth; however, it is less clear which combination of these factors is the most effective for predicting tree growth across ontogenetic stages. Methods We selected 65 individuals of an evergreen coniferous species, Pinus koraiensis, with diameters at breast height (DBH) from 0.3 to 100 cm in Northeast China. For each individual, we measured the stem radius growth rate (SRGR, µm/year) for the current year, environmental factors (light, soil nutrient and soil water) and functional traits (leaf, branch and root traits). Important Findings SRGR increased with DBH when the DBH was lower than 58 cm, whereas it decreased with DBH when the DBH was larger than 58 cm. Structural equation modeling analysis suggested that, when the DBH was 0–15 cm, plant size had a direct negative influence on SRGR and an indirect positive influence on SRGR due to the light intensity above the plant. Plant size had direct positive and negative effects when the DBH was 16–58 cm and 59–100 cm, respectively. When the DBH was larger than 15 cm, soil parameters were more important than light intensity for SRGR. The functional traits selected for use in the best model were changed from the specific leaf area and wood density to the root nitrogen concentration with increasing tree size. In summary, plant size, environmental factors and functional traits jointly shaped tree growth, and their relative influence varied with size, suggesting that the resources limiting tree growth may change from light to soil nutrient with increasing tree size.