ABSTRACT

THIS STUDY USED KANDELIA OBOVATA SEEDLINGS AS THE RESEARCH MATERIAL AND ADOPTED AN OUTDOOR CONTROLLED CULTURE EXPERIMENT WITH SIX TREATMENT GROUPS (INCLUDING THE CONTROL GROUP) TO EXPLORE THE EFFECTS OF PLASTICS WITH DIFFERENT TYPES AND EXPOSURE MODES ON THE GROWTH, PHOTOSYNTHETIC PHYSIOLOGY, AND SUBSTRATE POROSITY OF KANDELIA OBOVATA SEEDLINGS. THE TREATMENTS INCLUDED: A CONTROL GROUP (CK) WITH NO PLASTIC ADDITION; TWO POLYETHYLENE MICROPLASTIC TREATMENTS, NAMELY THE SM GROUP (13 ΜM PARTICLE SIZE, 5% W/W CONCENTRATION) AND THE MM GROUP (150 ΜM PARTICLE SIZE, 10% W/W CONCENTRATION); THREE MACROPLASTIC TREATMENTS, NAMELY THE LPA GROUP WITH 100% COVERAGE, THE LPB GROUP WITH EMBEDDED PLASTIC FRAGMENTS LARGER THAN 5 MM, AND THE LPC GROUP WITH 50% SAND SURFACE COVERAGE. THE EXPERIMENT WAS CONDUCTED FROM NOVEMBER 2025 TO APRIL 2026. GROWTH INDICATORS (PLANT HEIGHT, BIOMASS, LEAF NUMBER), PHOTOSYNTHETIC PIGMENTS (CHLOROPHYLL A, CHLOROPHYLL B, CAROTENOIDS), CHLOROPHYLL FLUORESCENCE PARAMETERS (Y(II), ETR, NPQ, FV/FM) UNDER LIGHT AND DARK ADAPTATION, AND SUBSTRATE POROSITY WERE MEASURED. THE RESULTS SHOWED THAT SHORT-TERM PLASTIC EXPOSURE HAD NO SIGNIFICANT INHIBITORY EFFECT ON SEEDLING BIOMASS, LEAF NUMBER, AND PHOTOSYNTHETIC PIGMENTS. CHLOROPHYLL FLUORESCENCE PARAMETERS WERE MAINLY DOMINATED BY NATURAL TEMPORAL CHANGES, WITH NO SIGNIFICANT DIFFERENCES AMONG TREATMENTS. PLANT HEIGHT SHOWED A DOWNWARD TREND, AND THE INHIBITORY EFFECT WAS MORE OBVIOUS IN THE SMALL-SIZE MICROPLASTIC GROUP. SUBSTRATE POROSITY DECREASED MARGINALLY SIGNIFICANTLY, AND PLASTIC PARTICLES CHANGED THE PHYSICAL STRUCTURE OF THE SUBSTRATE BY FILLING PORES. KANDELIA OBOVATA SEEDLINGS SHOWED STRONG PHYSIOLOGICAL BUFFERING CAPACITY AND TOLERANCE TO PLASTIC POLLUTION. THEIR RESPONSE PRESENTED A HIERARCHICAL PATTERN: PLASTICS FIRST DISTURBED THE PHYSICAL STRUCTURE OF THE SUBSTRATE, THEN AFFECTED SENSITIVE GROWTH INDICATORS SUCH AS PLANT HEIGHT, WHILE BIOMASS AND THE PHOTOSYNTHETIC SYSTEM REMAINED RELATIVELY STABLE.