木榄和秋茄对水渍的生长与生理反应的比较研究

Studies on differences in growth and physiological responses to waterlogging between Bruguiera gymnorrhiza and Kandelia candel

研究了不同水渍时间对两种红树植物木榄 (Bruguiera gymnorrhiza (L.) Lam )和秋茄 (Kandelia candel (L.)Druce)的生长与生理的影响。随着淹水时间的增加 ,木榄的相对生长率明显减小 :排水处理的木榄相对生长率最大而淹水时间最长 (1 2周 )的植物具有最低的生长率。相反 ,淹水与排水处理对秋茄的相对生长率的影响并无显著差异。在生物量的分配即茎根比 (S/ R值 )上 ,这两种植物亦表现出对水渍的不同反应。较长淹水时间 (8周或 1 2周 )处理组的秋茄具有较高的 S/ R值 ,但各处理间木榄 S/ R值无显著变化。由此看出 ,随着淹水时间的延长 ,秋茄生物量分配从根部向地上部转移 ,而木榄却无这种变化。 1 2周淹水处理的秋茄具有比排水处理组更高的根系活力 ,而所有淹水处理组的木榄的根系活力均低于排水处理的值。这些差异表明 ,木榄比秋茄对水渍更敏感。淹水处理中秋茄基本上比木榄具有更高的硝酸盐还原酶、过氧化物酶及超氧化物歧化酶活性 ,这进一步说明秋茄比木榄对水渍有更强的耐受力。但在叶片叶绿素和胡萝卜素含量上 ,两种植物对水渍有类似的反应 :淹水处理比排水处理有更高的光合色素含量。

Effects of different waterlogged time on growth and physiological responses of two mangrove species, Bruguiera gymnorrhiza and Kandelia candel,were investigated.Mature propagules of K.candel and B.gymnorrhiza were collected at Mai Po Mangrove Nature Reserve in Hong Kong in March and April 1997,respectively.Four propagules were planted in a plastic pot containing 4 kg soils collected from the same mangrove forest.On 14 October 1998,4 B.gymnorrhiza pots and 4 K.candel pots were selected as materials for the waterlogged experiment.For each species,4 treatments were set up to examine the growth and physiological responses to 4 waterlogged times,that is,drained for 12 weeks(D),drained for 8 weeks +waterlogged for 4 weeks(W4),drained for 4 weeks+waterlogged for 8 weeks(W8),and waterlogged for 12 weeks(W12).During drained periods,each pot was put onto a shallow tray(3 cm deep) and irrigated with 400 ml artificial seawater(salinity of 15)every two days,in the same way as previously described.For waterlogged treatments,each pot was placed inside a plasic container full of artificial seawater to ensure that the pot was waterlogged and the soil surface was inundated with 5 cm seawater. At the beginning of the experiment,all pots had similar redox potentials as the soils were drained before.The soil redox potentials of B.gymnorrhiza pots and K.candel pots were-14 and -8mv,respectively.At the end of the experiment,soil redox potentials decreased significantly with waterlogged time,in the descending order of D>W4>W8>W12 for both B.gymnorrhiza and K.candel pots.This indicates that continuous waterlogging resulted in oxygen-deficiency in mangrove soils.The redox potentials of K.candel pots were less negative than those in B.gymnorrhiza pots,suggesting that K.candel plants may transport more oxygen through aerial parts to roots then to soil than B.gymnorrhiza plants.From this,it seems that K.candel may have more tolerance to waterlogging than B.gymnorrhiza,which will be further tested by their different responses to waterlogging on growth and physiology as follows. Growth responses,in terms of biomass partitioning and relative growth rath,to waterlogging were different between the two species.Generally K.candel had lower shoot/root biomass ratio(S/R) than B.gymnorrhiza.For B.gymnorrhiza,no significant differences were found in S/R among the four treatments.For K.candel, S/R was low in drained (D) plants when compared to plants subjected to 8-weeks(W8) or 12-weeks(W12) waterlogged treatments,suggesting that more biomass were allocated to shoots than roots under prolonged waterlogging in K.candel. The relative growth rate(RGR)was not significantly different among four treatments in K.candel but the RGR dropped significantly with waterlogged time in B.grmnorrhiza.The RGR of B.gymnorrhiza was higher than that of K.candel if the plants were drained or were waterlogged for less than 8 weeks.However,in the 12-weeks waterlogged treatment (W12),there was no significant difference in RGR between K.candel and B.gymnorrhiza.According to two-way ANOVA,a very significant interaction was found between species and treatment,implying that these two species responded differently to waterlogging in growth. The interaction between species and treatment in terms of root activity measurement was significant,indicating the two species had different responses to waterlogging.Root activity of B.gymnorrhiza subjected to 12-weeks waterlogging(W12)declined significantly when compared to the drained(D),W4 and W8 plants.On the contrary,the highest root activity was found in K.candel plants with prolonged waterlogging,the activity in W12 treated plants were significantly higher than the drained plants which had similar activity as the plants subjected to 4 or 8 weeks waterlogged treatments. The concentrations of chlorophyll a,chlorophyll b and total carotenoids in W8 and/or W12 treated B.gymnorrhiza and K.candel were significantly higher than the respective drained (D) or W4 plants.This suggests that mangrove plants had an increase in photosynthesis under prolo