| The growth and distribution of mangroves are influenced by many abiotic factors and biological factors.Among these abiotic factors,tidal flooding has the most significant effect on mangrove plants.In addition,the insect herbivory of mangrove have become more seriously,which has become an important biological factor affecting the growth of mangrove.This study conducted ’marsh organ’to manipulate the elevation tidal gradient(set the lower limit of natural vegetation distribution as 0 cm,range from-50 cm to 225 cm)to monitor the growth and the degree of herbivory by different feeding guilds of Kandelia obovata seedlings along tidal gradient.By obtaining the pattern of growth and insect herbivory of K.obovata,we analyzed the structural and functional characteristics of leaves for exploring the etffects of environmental gradient on plant growth and plant-insect interaction and its ecological effects in combination with plant palatability.The results are as follows:1.With the elevation rising from-50 cm to 150 cm,the flooding time decreases linearly,while it decreases slowly after 150 cm elevation,ranging from 0.01 h/d to 15.10 h/d;the soil water content decreases linearly with the elevation rising from-50 cm to 225 cm,ranging from 52.58%to 4.50%.There is no significant difference in the of soil porewater salinity between-50 cm and 150 cm,which vaires from 17.62 to 32.94 PSU,while from 175 cm to 225 cm,it increases sharply and ranging from 67.08 to 181.02 PSU.2.With the increase of elevation,the height of K.obovata seedlings decreased linearly,ranging from 17.25 to 105.50 cm,while the basal diameter,branch number,total leaf number and biomass showed a hump-shaped pattern,which performed the best at mid-tide elevation,but grew poorly at low and high elevations.The basal diameter ranged from 5.93 to 14.70 mm,the nulmber of branches ranged from 2.29 to 8.33 per plant,and the branches ranged from 2.29 to 8.33 per plant.The range of the leaf number change ranged from 13.88 to 68.83 per plant,and biomass change ranged from 13.05 to 77.46 g per plant.3.Leaf traits of K.obovata seedlings change with elevation.With the elevation increasing,the leaf thickness of K.obovata decreased at first and then increased,the water content and SLA decreased linearly,while leaf area slowly decreased and then decreased linearly when the elevation higher than 125 cm.While C content increased at first and then decreased,N content decreased at first and then increased in contrary to C content,so that C/N showed a hump-shaped pattern.The total phenol content in leaves increased at first and then decreased with elevation,which was positively correlated with C/N,and suppoted the Carbon Nutrient Bala,nce I lypothesis.4.The chewer and buds-borer guilds presented the same hump-shaped patterns at different elevations,with the highest degree of feeding on leaves at mid-tidal elevation.The damaged leaves for chewer ranged from 23.94%～99.07%,leaf area consumed ranged from 1.18%～32.95%,while the buds-borer ranged from 0～83.70%.But for sucker,the damaged ranged slightly from 0 to 15.15%without obvious trends.5.In the early stage of seedling growth,the plant has more vigor(plant height increases),the higher the degree of insect herbivory,which supported Plant Vigor Hypothesis.The main carbon-containing substance in plants is the energy source of herbivorous activities,which affects the growth,development and reproduction of herbivores.Therefore,the degree of insect herbivory increased with the increasing of leaf Cmass.In addition,although the leaves of the seedlings at lower elevation have higher specific leaf area,higher water content and lower total phenol content,the degree of insect herbivory is relatively slight,which may result in lower insect viability due to the high frequency of flooding in this elevation.The above results showed that tidal elevation could significantly afect the growth of K.obovata seedlings,and then affect the herbivory of K.obovata.The growth indexes and biomass of the seedlings at mid-tidal elevation were the best,but the growth of seedlings was poor due to long flooding at low tidal elevation and drought and high salinity at high tidal elevation.In addition,the leaves at high tidal elevation had poor palatability,while the insect hardly survived due to the high frequency of flooding in low tide elevation,which leaded to low herbivory of seedlings at high and low tidal elevations.The seedlings of K.obovata had more vigor at mid-tidal elevation and better palatability,so they were affected by insect herbivory seriously.From field observation,it was found that the degree of mangrove seedlings fed by different guilds was different.In view of the seedling of mangrove,this study systematically and comprehensively studied the differences of feeding on mangrove seedlings by different guilds,which is of scientific significance for regeneration and herbivory prevention in the process of mangrove restoration and afforestation in China. |
