Response of plant functional traits and leaf economics spectrum to urban thermal environment

ObjectiveExploring variations of plant functional traits and leaf economics spectrum along urban thermal environment provides a chemical basis for examining species strategies as shaped by their local habitat.

MethodIn this study, we quantified the land surface temperature, soil moisture content and leaf functional traits of Sophora japonica, Koelreuteria paniculate and Fraxinus pennsylvanica, which were grown in urban thermal environment in Beijing.

Result(1) The urban thermal environment significantly increased the land surface temperature (P < 0.05), and showed high temperature region(HTR)>low temperature region(CTR); the soil moisture content was CTR>HTR, but the difference was not significant(P>0.05). (2) There were some differences in the effects of urban thermal environment on different tree species. The effects of urban thermal environment on Sophora japonica and Koelreuteria paniculate were mainly originated from high temperature stress, and its effects on Fraxinus pennsylvanica were mainly originated from drought stress, especially in high temperature environments. (3) The relationships between leaf traits under the urban thermal environment were similar to those on the global scale. Specific leaf area (SLA) presented significant negative correlation with chlorophyll content (CHL), leaf dry matter content (LDMC) and leaf tissue density(LTD) (P < 0.01). CHL presented significant positive correlation with LDMC and LTD (P < 0.01), and there was a positive correlation between LDMC and LTD (P < 0.05). Stomatal density(SD) showed a negative correlation with stomatal size(SS), stomatal aperture(SA) and SLA, but they did not reach a significant level (P>0.05). (4) RDA results showed that SLA was mainly affected by land surface temperature (R²=0.97, P < 0.05), but soil moisture content had negative effects on plant functional traits (R²=0.75, P < 0.05). Land surface temperature had positive effects on LDMC, LTD, and CHL, but soil moisture content had negative effects on them.

ConclusionThe results of this study indicated that a leaf economics spectrum also existed in plant species in the urban thermal environment with a quick investment-return on the leaf economics spectrum. The species in HTR had lower SLA, SS and SA, higher CHL, LDMC, LTD and SD, which may be involved in the adaptation of plants to high-temperature and arid conditions. Therefore, when planting plants in urban areas, heat-resistant and drought-tolerant tree species should be selected in HTR. At the same time, the effects of high temperature should be reduced by increasing cooling and irrigation in the growing season.