Photosynthetic capacity of common tree species under conditions of soil metal induced stress within an urban brownfield

Background/Question/Methods: As global demographic transition tends to favor urbanization, the role of urban forests is becoming increasingly significant. This study examines temporal resilience in an urban forest using a bivariate analysis where temperature and soil metal load are treated as dependent variables impacting net productivity of dominate urban tree species. By comparing net photosynthetic assimilation and respiration rates throughout the spring and summer season, the compensation points at which respiration exceeds photosynthesis are clearly defined.

 Specific sites were chosen to represent varying levels of soil metal induced stress.  The dominant tree species of the site, Betula populifolia, Populus deltoids and Populus tremuloides were examined. Both light response and assimilation to internal CO₂ concentration (A/C_i) curves were developed throughout the spring and summer.  Preliminary results indicate that compensation points differ significantly between Betla and Populus but not between the two Populus species. In addition, there were significant differences between the sites examined.

Results/Conclusions: These data, suggest that differences in in resource allocation between growth and maintenance within the heterogeneous edaphic conditions of the urban context results in differing compensation points and hence carbon sequestration rates.   Such data helps to define the value of urban forest and the point at which mitigation is necessary.