Does sea level rise influence propagule establishment, early growth and physiology of Kandelia candel and Bruguiera gymnorrhiza?

摘要

Responses of Kandelia candel and Bruguiera gymnorrhiza in loamy-sandy (coarse) and silty (fine) soils to water level rise, and prolonged inundation were investigated under mesocosm and field conditions. Acidity due to simulated sea level rise of 30 cm was more serious in fine soil than that in coarse soil. Propagules of K. candel had more rapid establishments under high water level and prolonged inundation, but establishments of B. gymnorrhiza were not significantly influenced by tide condition. Water level rise of 30 cm and prolonged inundation stimulated early growth especially in stem height increments during the first 2 months for K. candel and B. gymnorrhiza. However, relative growth rates (RGRs) during the second 2 months did not significantly change for K. candel and even decreased for B. gymnorrhiza with water level rise. The root/shoot biomass ratio in both K. candel and B. gymnorrhiza treated with high water level was significantly lower than that treated with low water level, especially in coarse soil. Biomass percentages of coarse roots of K. candel and B. gymnorrhiza seedlings significantly increased with water level rise. Water level rise led to decreases in Chl. alb ratios in leaves of K. candel seedlings, but the ratios did not significantly change with water level for B. gymnorrhiza. Decreases in RGRs of B. gymnorrhiza were due to decreases in total leaf area resulting from increases in stomatal density. Contents of N and P in roots tended to increase with water level rise and prolonged inundation. Under both high and low water levels, all propagules of K. candel and B. gymnorrhiza successfully established and the seedlings survived throughout the mesocosm experiment. For the field trial, K. candel seedlings had similar high survival rates of over 90%, while B. gymnorrhiza seedlings had much less survival in lower intertidal zones than in upper intertidal zones. These differences were ascribed to stronger tidal action and more sedimentation in the field than under mesocosm conditions. Survived seedlings of K. candel and B. gymnorrhiza from both propagule plantation and seedling transplantation in field trial also showed higher stem increments during the first 4 months in lower intertidal zones.