Linkage of root morphology to anatomy with increasing nitrogen availability in six temperate tree species

Aims Fine root morphological traits are generally changed under soil nitrogen (N) enrichment, however, the underlying mechanism and functional significance are still not well understood. Our aims were to investigate the linkage of root morphology to anatomy, and its implication for root function at elevated soil N availability. Methods Ingrowth cores were used to sample root tips (0-20 cm soil depth) from six temperate tree species growing in monoculture plantations at a common site in northeastern China. Root morphological and anatomical traits were concurrently measured, and their relationships were determined within and among species in both control and N fertilization (10 g N m(-2)y(-1)) plots. Results Root diameter generally increased in all six species (non-significant for Phellodendron amurense) following N fertilization, which was caused by the increased root stele radius rather than cortical thickness. Congruently, N fertilization significantly decreased the ratio of cortical thickness to stele radius, but increased the ratio of total cross-sectional area of conduits to stele area in root tips across all species. Conclusions The observed anatomical changes of root tips contributed to the alternations of morphological root traits following N fertilization, with potentially important impacts on root physiological functions, like increased water and nutrient transport.