Effect of endophytic fungi inoculation on the growth of Casuarina equisetifolia seedlings under salt stress
The aim of this study was to investigate the effects of adding two salt-tolerant endophytic fungi and their mixtures on root morphology,root activity of nutrient elements,seedling height,ground diameter,and biomass of Casuarina seedlings under soil stress with different salinities.Casuarina equisetifolia seedlings were planted in soils with different salinities(mass fractions:0‰,3‰,6‰,and 9‰).Botryosphaeria Z1(Z1),Hypoxylon Y6(Y6),and their mixture(Z1+Y6)were used as treatments,and the carrier(CK)was used as the control.We found that root activity,total root length(TRL),total root surface area(TRSA),total root volume(TRV),total root diameter(TRD),root length density(RLD),and root surface area density(SAD)of Casuarina seedlings decreased under soil salt stress,but root tissue density(RTD)increased.Fungal inoculation markedly improved root activity and biomass in seedlings subjected to salt stress.The morphology and nutrient content of seedling roots under the same strain treatment were profoundly affected by changes in soil salinity.Compared with CK,the inoculation treatment significantly increased TRD,as well as root vigor,total phosphorus(TP)content at 3‰ and 6‰ salinity and TRV,TRSA and RSD at 9‰ salinity.At 3‰ salinity,TRL,RLD,root total nitrogen(TN)content of Z1 treatment was significantly higher than that of CK,and carbon to phosphorus(C/P)ratio was significantly lower than that of CK.The Z1+Y6 treatment also significantly increased TRSA,TRV,SAD,and root carbon to phosphorus(C/P)ratio at 3‰ and 6‰ salinity.At 9‰ salinity,the TP content and root vigor of Z1 and Z1+Y6 treatments were also significantly higher than those of CK.Based on the stepwise regression analysis,RLD was the main factor affecting seedling height,whereas root activity and TC content were the main factors affecting ground diameter.Path analysis showed that root tissue density,total root volume,total phosphorus content,and total root diameter were the main factors affecting biomass and that the direct effect of total root volume had the most positive contribution.In conclusion,strain treatment affected seedling root morphology,nutrient uptake,and biomass accumulation under salt stress,proving that the salt-tolerant strain improved salt tolerance by inducing the growth and development of the host root system.The effect of the mixed strain was evident and more conducive to alleviating salt damage.
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