Studys On Relation Between Two Seagrasses And Soil, Caloric Value And Element Content In Seagrass Leaves At The Different Development Stages

Biomass and Seagrass community of main seagrass meadows in Beihai,Guangxi(Guchengling seagrass meadow,Zhulin seagrass meadow,Ronggenshan seagrass meadow and Beimu salt field seagrass meadow)were studied.This study also discussed the rules and diversities about the biomass and community structure of dominant seagrass species in Guangxi(Zostera japonica Aschers.et Graebn.and Halophila ovalis(R.Br.)Hook.).The results showed that(1)About Z. japonica,underground biomass(UB),ratio between aboveground biomass and UB and biomass were indistinctive in the different seagrass meadow,but aboveground height(AH)was very significantly distinctive in the different seagrass meadow.(2)About H.ovalis,AB and AH were indistinctive in the different seagrass meadow;but UB and biomass were significantly distinctive,and ratio between AB and UB was very significantly distinctive.(3)Ratio between AB and UB of Z.japonica was significantly less than that of H.ovalis,but AB,UB and species biomass were significantly more than those of H.ovalis.(4)Total seagras biomasses were indistinctive in the seagrass meadows where dominant seagrass species was Z.japonica,but total seagras biomasses in the seagrass meadows where dominant seagrass species were significantly more than that in Beimu salt field seagrass meadow which dominant seagrass species was H.ovalis.(5)Total seagrass biomass are very significantly correlate with UH.The rules of elemental content in the soil of main seagrass meadows in Beihai,Guangxi and the relation between seagrass biomass,AH and elemental content in the soil were studied.The results showed that(1) The diversities of Cd,Cr and N:P were not significant in the soil of different seagrass meadow,but the diversity of oraganic carbon,TP, Fe:Mn was remarkably significant;the diversities of organic carbon,TN, Ca,Mg,Fe,Mn,As,Cu,Pb,Zn and C:N:P were distinct according to seagrass meadow.(2)Oragan carbon,TP,Mg,Fe,Mn and Fe:Mn in the soil were remarkably correlate to dominant seagrass species,but Cd,Cr and N:P were independent of dominant seagrass species.(3)About Z. japonica,AB,species biomass and AH were remarkably correlate to elemental contents in the soil,but UB was independent of elemental contents in the soil.About H.ovalis,species biomass and its allocation were remarkably correlate to elemental contents in the soil,but UH was independent of elemental contents in the soil. Elemental contents in every organ of Z.japonica and their dynamics at the different growth stages of seagrass leafs were studied.The results showed that(1)About macroelements in the different organ:Ca＞Mg＞TN＞TP＞Fe and Mn,and about microelements in the different organ:Zn＞Cu＞Cr＞As＞Pb and Cd.(2)Elemental contents of Z.japonica were independent of those in the soil.(3)Z.japonica strongly accumulated P, and weakly accumulated Ca,Mg,Cu and Zn,and weakly uptook N,As, Cr,Fe,Pb,Cd and Mn.(4)With the growrh of leafs(young leaf-ripe leaf -senile leaf),the contents of N:P,Ca,Mg,Fe,Mn,As and Cd rose,but the contents of TN,TP,Zn and Cu dropped;the content of Cr firstly rose and then dropped.(5)During the senescence of seagrass leaf,elemental resorptions of N,P,Cu and Zn were positive,but elemental resorptions of Ca,Mg,Fe,Mn,As,Pb,Cr and Cd were negative;elemental contents in the soil and in the green leaf weakly influence the nutriment resorption.Caloric values,ash contents in the rhizome and leaves at the different growth stages of Z.japonica and the correlation between Caloric values,ash contents and elemental compositions were studied.The results were as follows:(1)ash contents(AC)increased with the growth of leaves,but gross caloric values(GCV)and ash free caloric values (AFCV)decreased with the growth of leaves.However these tendencies were not significant.(2)The ash content and AFCV of the rhizome were more than those of leaves,but these diversities were not significant;there was no diversity between GCV of the rhizome and that of leaves.(3)GCV of senile leaves and Z.japonica(leaves and the rhizome)were remarkably negatively correlated with ash contents,and GCV of leaves was very remarkably negatively correlated with ash contents,but GCV of young leaves,ripe leaves and the rhizome were independent of ash contents.(4)The correlations of AC,GCV,AFCV and elemental compositions of Z.japonica were different because of leave development and different apparatus.