[Critical tidal level for forestation with hypocotyls of Rhizophora stylosa Griff along Guangxi coast of China].

From August 2004 to August 2005, three replicated experimental platforms were constructed in a section of tidal flat in Yingluo Bay of Guangxi to study the growth and physiological responses of Rhizophora stylosa Griff seedlings to the waterlogging stress of tide in diurnal tide zone. A total of eight tidal flat elevation (TFE) treatments, i. e., 320 cm, 330 cm, 340 cm, 350 cm, 360 cm, 370 cm, 380 cm and 390 cm above Yellow Sea Datum (YSD), were created on each platform. The results showed that lower TFEs (320-330 cm YSD) slightly increased the stem height of 1-year old seedlings, while higher TFFs ( > 340 cm YSD) increased the seedlings growth significantly. Moderate TFEs (350-370 cm YSD) favored the development of knots. Leaf number, leaf conservation rate, and leaf area per seedling all decreased dramatically with decreasing TFE. Lower TFEs had a larger damage to Chl a, but Chl b was less affected. The Chl a/b ratio decreased with decreasing TFE. Prolonged waterlogging induced a higher SOD activity in root, while moderate TFE inhibited the SOD activity in leaf. The POD activity in root and leaf increased with decreasing TFE. Waterlogging stress decreased the biomass of individual organs and whole seedling. With increasing waterlogging, the biomass partitioning in 1-year old seedlings increased from leaf to stem. The survival rate decreased sharply from 88.9% to 40.0% as TFE decreased, while more than 80% of the seedlings could survive at the TFE being 370 cm YSD and above. It was proposed that the local mean sea level could be adopted as the critical tidal level for the forestation with hypocotyls of R. stylosa along the Guangxi coast.