ABSTRACT

URBAN VEGETATION IN MACAO SAR IS EXPOSED TO PARTICULATE MATTER FROM TRAFFIC AND OTHER URBAN ACTIVITIES, WHICH MAY AFFECT LEAF SURFACE CONDITIONS AND PHYSIOLOGICAL PERFORMANCE. THIS STUDY MEASURED LEAF-DEPOSITED PARTICULATE MATTER (LDPM), CHLOROPHYLL CONTENT, AND CHLOROPHYLL FLUORESCENCE IN SELECTED URBAN PLANT SPECIES UNDER DIFFERENT ENVIRONMENTAL EXPOSURE CONDITIONS. THREE MAIN SAMPLING SITES WERE SELECTED: DR. SUN YAT SEN MUNICIPAL PARK (SYS), OUR LADY OF SORROWS CHAPEL IN KA HO (KH), AND LONG CHAO KOK COASTAL TRAIL (LCK). THE UNIVERSITY OF SAINT JOSEPH (USJ) WAS USED AS AN ALTERNATIVE LOWER-EXPOSURE SAMPLING LOCATION FOR HIBISCUS ROSA-SINENSIS BECAUSE THIS SPECIES WAS ABSENT AT LCK. FOUR COMMON URBAN PLANT SPECIES WERE STUDIED: MACARANGA TANARIUS, FICUS MICROCARPA, MURRAYA EXOTICA, AND HIBISCUS ROSA-SINENSIS. SHORT-TERM PM₂.₅ MEASUREMENTS WERE RECORDED DURING FIELD SAMPLING AS SUPPORTING ENVIRONMENTAL CONTEXT. LEAF-DEPOSITED PARTICULATE MATTER (LDPM) WAS DETERMINED USING A LEAF WASHING AND GRAVIMETRIC METHOD. CHLOROPHYLL CONTENT WAS MEASURED USING 80% ETHANOL EXTRACTION AND SPECTROPHOTOMETRIC ANALYSIS, AND CHLOROPHYLL FLUORESCENCE WAS MEASURED USING FV/FM, THE MAXIMUM QUANTUM EFFICIENCY OF PHOTOSYSTEM II (PSII), AS THE MAIN FLUORESCENCE INDICATOR. LDPM DIFFERED SIGNIFICANTLY AMONG SAMPLING SITES (P < 0.001), WITH THE HIGHEST MEAN VALUE AT KH AND THE LOWEST AT LCK. SPECIES-LEVEL DIFFERENCES IN LDPM WERE NOT STATISTICALLY SIGNIFICANT. TOTAL CHLOROPHYLL CONTENT ALSO DIFFERED SIGNIFICANTLY AMONG SITES (P < 0.001) AND PLANT SPECIES (P < 0.05). THE HIGHEST MEAN TOTAL CHLOROPHYLL CONTENT WAS OBSERVED AT SYS, WHILE THE LOWEST WAS OBSERVED AT LCK. HOWEVER, CHLOROPHYLL CONTENT DID NOT SHOW A SIMPLE DECREASING PATTERN UNDER RELATIVELY HIGHER EXPOSURE CONDITIONS. FV/FM VALUES WERE RELATIVELY SIMILAR AMONG THE AVAILABLE SAMPLES, SUGGESTING THAT STRONG PSII IMPAIRMENT WAS NOT CLEARLY DETECTED BY THIS PARAMETER ALONE. WHEN ALL SAMPLES WERE POOLED, THE CORRELATION BETWEEN LDPM AND TOTAL CHLOROPHYLL CONTENT WAS WEAK AND NOT STATISTICALLY SIGNIFICANT (R = 0.207, P = 0.080). WEAK AND NON-SIGNIFICANT CORRELATIONS WERE ALSO OBSERVED WITHIN INDIVIDUAL ENVIRONMENTAL EXPOSURE CONDITIONS, SUGGESTING THAT CHLOROPHYLL CONTENT WAS NOT CLOSELY RELATED TO LDPM ALONE. LDPM SHOWED THE CLEAREST SITE-LEVEL DIFFERENCE IN PARTICULATE ACCUMULATION, WHEREAS CHLOROPHYLL CONTENT AND FV/FM CAPTURED ADDITIONAL PHYSIOLOGICAL CONTEXT. THE FIELD RESPONSES OF URBAN PLANTS WERE THEREFORE INTERPRETED USING THESE THREE INDICATORS TOGETHER RATHER THAN RELYING ON A SINGLE MEASUREMENT.