木榄胚轴萌发及幼苗生长与生理对水渍和底质条件的响应

采用模拟半日潮系统研究了水渍和底质条件对红树植物木榄(Bruguieragymnorrhiza)的影响。水位上升和淹水时间延长导致红树林底质的酸化,且壤质底质的酸化比沙质底质严重;对木榄的萌苗速度无显著影响;促进木榄的早期生长,尤其是导致最初2个月茎高生长的增加,但后2个月木榄的相对生长率受抑制;地下部/地上部生物量比值下降,沙质底质中尤为如此;粗根比例明显增加;叶绿素含量增加,叶绿素a/b比值无显著影响;叶面积减少;壤质底质上生长植株的叶片气孔密度增加,沙质底质无显著变化;根N含量无显著变化,P含量显著增加。

PROPAGULE DEVELOPMENT OF BRUGUIERA GYMNORRHIZA UNDER DIFFERENT TIDAL AND SEDIMENTAL CONDITIONS

Due to their special habitats in intertidal zones along tropical and subtropical coastlines, mangroves are influenced by the conditions of water depth, duration and sediment types.To investigate responses in early development of Bruguiera gymnorrhiza including propagule establishment and seedling growth to tidal and sedimentary conditions of simulated semi-diurnal tidal systems, a 4-month experiment was set up.Mature propagules of B.gymnorrhiza were planted respectively in pots containing silty and loamy-sandy soils collected from Mai Po and Sai Kung mangrove forests in Hong Kong.Four plastic tanks(85 cm in length, 64 cm in width and 50 cm in height) were used in this experiment mimicking 4 combinational conditions, i.e.high water level with coarse soil(HC), high water level with fine soil(HF), low water level with coarse soil(LC), and low water level with fine soil(LF).Artificial seawater in salinity of 15 was pumped into and out of the tanks in designed intervals to simulate daily semidiurnal tidal phases including two floods and two ebbs.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, and 0 cm for LC and LF.Each treatment was triplicate. Under both high and low water levels, all propagules established and grew well in the experiment.As water level and inundation time increased, the acidity increased, which is higher in fine sediment than that in coarse ones.High acidity would not favor the plant growth.The establishment of B.gymnorrhiza propagules was not significantly influenced by the condition change.Early growth especially the stem height increments was stimulated by the increases in water level and inundation time in the first two months then relative growth rates slowed down in the second two months.In addition, as water level and inundation time increased, the ratio in biomass below-ground/above-ground significantly decreased, especially in coarse sediment and the percentages of coarse roots, P contents in roots and chlorophyll contents in leaves tended to increase.Other physiological parameters such as carotene and stoma density were also analyzed, along with detail discussions on the relationship of water depth, inundation length and sediment type to the plant development.