USING CCI VALUES TO RESEARCH NITROGEN RESORPTION EFFICIENCY IN URBAN PLANTS

We sought to explore a simple and convenient method for determining nitrogen resorption efficiency (NRE) and the uptake and utilization strategy of city garden plants. The Chlorophyll Content Index (CCI) values of mature leaves and fresh litter of Populus tomentosa and Euonymus japonicas in contaminated and residential areas were measured. CCI values of both mature leaves and fresh litter from two species in the contaminated area were higher than values in the residential area, and there were high correlation coefficients between leaf nitrogen content and CCI values (R-2 = 0.887; R-2 = 0.819), demonstrating the validity of CCI values as indicators of leaf nitrogen content. The NRE of Euonymus japonicas was much greater than that of Populus tomentosa. The CCI values and NRE of mature leaves were significantly positively correlated with leaf water content, and significantly negatively correlated with leaf area, indicating that increased water supply promoted NRE, while increased leaf area may increase the cost of N transport as well as the time required for senescent leaf transfer, ultimately leading to decreased NRE. There was no significant difference in NRE between contaminated and residential areas for Euonymus japonicas, which may result from the higher NO absorptive and tolerance capacity of evergreen plants.