Effects of simulated sea level rise on the mangrove Kandelia candel
- 海洋环境－已发表论文 
研究了壤质沙土 (粗质土 )和粘土 (细质土 )条件下红树植物秋茄 (K andelia candel)对水位上升和淹水时间延长的反应。模拟海平面上升 30 cm导致红树林土壤的酸化 ,且细质土的酸化比粗质土严重 ;秋茄繁殖体的萌苗速度明显加快 ;促进秋茄的早期生长 ,尤其是导致最初 2个月茎高生长的增加 ,然而 ,后 2个月秋茄的相对生长率并不因水位的升高而增加 ;地下部 /地上部生物量比减小 ,在粗质土中尤为如此 ;幼苗粗根比例明显增加 ;叶片叶绿素 a/ b比值下降。在微型盆栽试验条件下 ,无论是高水位还是低水位 ,所有的秋茄繁殖体均成功萌发且幼苗在整个试验期间均成活。在野外条件下 ,秋茄幼苗成活率在高水位和低水位条件下均高达 90 %以上。野外条件下 ,无论是经胚轴萌发还是幼苗移栽的幼苗 ,最初 4个月的茎高生长均为低潮区高于高潮区 ,与微型试验结果相同。微型盆栽试验和野外种植试验均表明 ,海平面上升 30 cm对秋茄的萌发和早期生长具有促进作用Due to their special habitats, intertidal zones along tropical and subtropical coastlines, mangroves may be influenced by decreased intertidal elevation and prolonged tidal inundation from sea level rise. Kandelia candel is a major viviparous mangrove species of the east group and dominative along South China coastlines. The present study aims to investigate propagule establishment, seedling growth and physiological responses of Kandelia candel to simulated sea level rise of 30cm under different soil types. Mesocosm experiment was set up as follows. Mature viviparous propagules of K. candel were planted in pots containing soils from Mai Po and Sai Kung mangrove forests in Hong Kong with loamy-sandy (coarse) and silty (fine) textures. Four tanks were used in this experiment, one for high water level with coarse soil (Treatment HC), one for high water level with fine soil (Treatment HF), one for low water level with coarse soil (Treatment LC), one for low water level with fine soil (Treatment LF). Artificial seawater with salinity of 15 was pumped into and out of the tanks at regular intervals so that the systems formed simulated semidiurnal tidal conditions with two “flooding tide” periods and two “ebbing tide” periods everyday. Daily inundation time of high and low water treatments was 16 h and 4 h, respectively. Water level of HC and HF was 30 cm above soil surface, higher than those of LC and LF (0 cm). Each treatment had 3 replicate pots, i.e., there were three pots in each tank. Under both high and low water levels, all propagules successfully established and the seedlings survived throughout the mesocosm experiment. Acidity due to simulated sea level rise was more serious in fine soil than that in coarse soil. Propagules had more rapid establishments under high water level and prolonged inundation. Water level rise of 30cm and prolonged inundation stimulated early growth especially in stem height increments during the first two months. However, relative growth rates (RGRs) during the second two months did not significantly change with water level rise. The root/shoot biomass ratio in seedlings treated with high water level was significantly lower than that treated with low water level, especially in coarse soil. Biomass percentages of coarse roots significantly increased with water level rise. Water level rise led to decreases in chlorophyll a/b ratios in leaves. Contents of N and P in roots tended to increase with water level rise and prolonged inundation. To test the results from mesocosm experiment, field trials were set up in two intertidal zones, lower intertidal (LI) and upper intertidal (UI) zones, in seaward open flat of a natural mangrove forest at Sai Kung of Hong Kong. The annual mean seawater salinity at Sai Kung was about 15, similar to that in mesocosm experiment. LI was about 20m farther from the forest than UI and the latter was near the forest seaward fringe. The two zones had similar soil physio-chemical characteristics to those in treatments HC and LC of mesocosm experiment, with loamy-sandy (coarse) texture. Daily duration of tidal inundation of the LI zone was about 4h longer than that of the UI zone, and the elevation of the former was about 30cm lower than the latter. For the field trials, K. candel seedlings had similar high survival rates of over 90%. Survived seedlings from both propagule plantation and seedling transplantation also showed higher stem increments during the first four months in lower intertidal zones with higher water level and prolonged inundation than those in upper zones.