Trees planted in paved lands suffer hot and drought stresses in urban environment because pavement could increase land surface temperature and alter soil moisture condition. However it is not clear what are the responses of tree physiology and growth to land pavement. In our study, three species (pine, Pinus tabulaeformis, ash, Fraxinus chinensis and maple, Acer truncatum) of trees commonly planted in north China were grown in perviously, imperviously paved and not paved lands. Leaf light and CO2 response curves of the net photosynthetic rate were constructed based on in situ measurements in the 4th year after planting, and additional photosynthetic parameters were obtained. The height, basal diameter and biomass were measured and assessed.
Results/Conclusions
The maximum net photosynthetic rates of both ash and maple significantly decreased on impervious pavement. Significant decreases in the light saturation point (Isat), photosynthetic capacity (Amax) and maximum carboxylation rate (Vcmax) of maple and in the saturated intercellular CO2 concentration (Cisat) of ash under impervious pavement conditions indicated that both the capacities of leaf photosynthesis and utilization of high light and CO2 concentrations were significantly reduced by land pavement. Although the responses of the photosynthetic parameters to land pavement were different between tree species and across measurement times, ash showed better adaptability. The results also showed that there was less impact from pervious pavement than impervious pavement on the photosynthetic parameters of ash and maple.
Land pavement suppressed tree height and base diameter growth. Tree base diameter was decreased more under perviously paved land than imperviously paved land, suggesting pervious pavement could not always mitigate the impact of pavement on tree growth. This might be caused by more warming surface of pervious paved land than impervious paved land.
Tree biomass also reduced by land pavement and the reductions differ with tree species and spacing.