Effects Of Salinity And Waterlogging To Growth And Physiology Of Laguncularia Racemosa

Laguncularia racemosa seeds were set indoor under 10 salinity gradients,0,5, 10,15,20,25,30,35,40,45,to investigate the seed germination.Radicle outshooting pericarp 5 mm would be treated as germinated.The experiment lasted 15 days. Germination percentage,germinating viability,germination index,average germinating time and vigor index have been choosed as germination indices.L.racemosa seedlings were cultivated out of doors and treated with different levels of salinity and inundation respectively to discuss the ecological and physiological effect on L.racemosa.Inundation experiment set four level waterlogging time:6h,12h,18h,24h,and lasted 180 days.Systemic study on L. racemosa were carried on growth,biomass allocation,chlorophyll,proline and MDA content,photosynthetic properties and the activity of SOD,POD.Salinity experiment set five level salinity gradients:0,10,20,30,40,and lasted 300 days.Growth, biomass allocation,chlorophyll,proline and MDA content,photosynthetic properties and the activity of SOD,POD have also been considered,as well as Na,K,Ca,Mg, Cl,N,P,C content and interrelation.The results showed:1.The germination percentage of L.racemosa seeds was nearly to 100%when the salinity below 25,but decreased with the increased of salinity,when the salinity comes to 45 the germination percentage fell to 4%.Germinating viability came to the maximum in 10,then dropped down with the salinity,got to 0 when the salinity more than 30.With the study of germination percentage,germinating viability,germination index,average germinating time and vigor index showed that L.racemosa's optimum germination salinity was 5～25.Although the germination percentage was inhibited when the salinity above 30,germination rate was still high(73±9%).The germination rate was close to zero under the 45 seawater,but they could normorlly germinate palacing low-salinity(＜25) seawter after 15 days treatment.It indicated that there was no poisoning effect on L.racemosa seed under extreme high salinity seawater. 2.L.racemosa's height increased with the waterlogging time,but there was no significant difference leaf numbers between inundation treatments.In order to increase the effective area of photosynthesis and carbon assimilation rates,L. racemosa increased its leaf area to suit for long inundation time.Root mass,stem mass,leaf mass and seedling mass raised up to maximum on 12h treatment and then decreased with inundation.Root/crown ratio changed as "N" type,18h treatment root/crown ratio decreased maybe due to adapt nutritional deficiencies of root to promote growth of shoot.Long inundation time leads to growth of pneumatophores of 24h treatment so that enhanced the proportion of root.3.Net photosynthetic rate of L.racemosa reached to the highest on 12h treatment and 24h's was less than half of 12's.Intercellular CO₂ concentration had the similar trend of net photosynthetic rate under different waterlogging time. Chlorophyll content and Chla/b ratio were increased with the waterlogging time,this may be because the plant increases the pigment content to improve the efficiency of plant photosynthesis.4.Under different waterlogging time,L.racemosa's root and leaf SOD activity, POD activity,MDA and proline content increased with increasing inundation time, what indicated that although L.racemosa has enough free radical scavenging enzymes to protect the integrity of membrane system.Soluble protein and sugar had the same changing trend of SOD and POD,what showed that L.racemosa would accumulate different osmotic adjustment sub-stances to balance the osmotic pressure under drought stress.5.Salinity's effect on L.racemosa's growth was not significant,but the trend was decreasing with the increasing of salinity.The increment of stem height was largest in salinity 0,and the salinity10,20,30,40 was 94.6%,88.2%,73.1%,35.5% of salinity 0's.Study on the leaf area,leaf numbers and increment indicated that low salinity promotes growth and high salinity inhibits:on salinity 10,the index reached the maximums;on salinity 40,the growth was inhibited extraordinary.In order to reduce moisture loss and increase nutrient absorption area of root,L.racemosa enhanced mass allocation of root.The water content of root,stem,and leaf was the largest of all on salinity 40 so as to storage excessive water to resist physiological drought and dilute the ion concentration to ensure the normal osmotic pressure.6.Leaf chlorophyll and cotyledons content followed by an increased period with the salinity increasing,which arrived at minimize but increased sharply gradually on salinity 40.Net photosynthetic rate went up to the peak and then decreased gradually. Leaf water use efficiency of L.racemosa reflected it can adjust its metabolism and increase water use efficiency to adapt to high salinity(30),but the higher salinity(40) inhibited its water use efficiency.7.Leaf POD activity was about to descend on the salinity 40 and SOD activity reached peak on salinity 20:1200 U·g^-1FW,what showed that L.racemosa has a strong resistance to high salinity.MDA and proline content was ascending gradually with the salinity,on the contrary the soluble protein and soluble sugar turned to decline on the salinity 30.8.Under different salinity treatment,Na,K,Ca,Mg,Cl element content showed significant different.Na and Cl content increases with the salinity,while K,Ca,Mg content decreased with the salinity.Correlation between Na and K,Ca,Mg element indicated that they have obvious antagonistic effect.This paper deemed that there was no significant difference on C,N,P content,but C:N ratio,which was 73.04 on salinity 0,86.84 on salinity 20 - the maximum,and 61.71 on salinity 40.