Young plants of Rhizophora mucronata Lam. were tested for oxidative stress, photosynthetic capacity and dry matter accumulation under two abiotic stress conditions; prolonged submergence and soil water stress. The experiment of prolonged submergence was performed in field conditions with two treatment levels; 50% inundation (control) and 100% inundation levels. The experiment of soil water stress was conducted in a plant-house with four treatment levels, 100% water holding capacity (WHC) (control), 50% WHC, 25% WHC and high salinity (> 35 psu). The experimentation period was 18 months. According to the results, antioxidant activity was increased in the 100% inundation level in field conditions and in the 25% WHC, 50% WHC and high salinity levels in plant-house conditions. However, decreased radical scavenging capacity reflected by low 2,2-diphenyl-1-picrylhydrazyl (DPPH) and high IC50 values were only observed in the 25% and 50% WHCs. Plant cell membranes were highly damaged in the 25%, 50% WHCs and high salinity level and a significant decrease in photosynthetic capacity (~ 90% reduction) and in dry matter content of Rhizophora plants were also observed in the same treatment levels. It was recorded that a higher proportion of dry matter is allocated to the root system under the 100% inundation level and it may be an adaptation to keep up the standing stability. Although, the antioxidant and scavenging capacities of young Rhizophora plants have increased under abiotic stress conditions, oxidative stress and its associated impacts on leaf photosynthetic capacity and dry weight contents were unavoidable under persistence of the stress. |
