Seasonal variations in photosynthetic parameters and leaf area index in an urban park

Parks account for a large proportion of green spaces in urban regions, but most previous studies have focused on the values of recreational services in urban parks-carbon uptake by plants in urban parks has been studied less extensively. Urban parks typically form complex landscapes in space and time by integrating multiple species with open canopies. Thus, to better understand canopy photosynthesis in urban park, measuring spatial and temporal variations in photosynthetic parameters and canopy structural variables is essential. Here, we report seasonal and spatial variations in two key photosynthetic parameters (Vcmax and Jmax which are the maximum rates of carboxylation and electron transport, respectively) and leaf area index (LAI) in Seoul Forest Park. During the peak growing season, we found an eightfold difference (20 to 149 μmol m−2 s−1) and fourfold difference (38 to 141 μmol m−2 s−1) in Vcmax and Jmax, respectively, across 10 species. Over the seasons, two woody species (Zelkova serrata (Thunb.) Makino and Prunus yedoensis Matsum), respectively showed three- to fivefold differences in Vcmax and two- to fivefold differences in Jmax. We evaluated whether leaf nitrogen contents could predict Vcmax and Jmax, and found significant correlations among the three variables during the peak growing season across 10 species, but no significant correlations among them over the seasons in the two woody species. LAI computed using in- situ observations and satellite remote-sensing imagery showed a high spatial heterogeneity during the growing season. These results highlight the considerable spatial and temporal variability in photosynthetic parameters and LAI, which implies that individual tree-based three-dimensional canopy modeling will be essential for accurate estimation of canopy photosynthesis in urban parks.