Effects Of Flooding And Plant Density On The Growth,interspecific Competition And Physiological Characteristics Of Cynodon Dactylon And Hemarthria Altissima

To restore the degraded grass vegetation and reveal the best ratio of grass species mixture for artificial restoration of the riparian zone of the Three Gorges Reservoir area,the two local dominant species,Hemarthria altissima(H)and Cynodon dactylon(C)were used to investigate the growth,intraspecific and interspecific competition and physiological characteristics under different water conditions.On April 29,2016,a pot experiment was conducted using a replacement series design in which H.altissima and C.dactylon were planted at seven ratios(H0C12,H2C10,H4C8,H6C6,H8C4,H10C2,and H12C0)under three water treatments,including normal growth water condition(CK),flooding at 10 cm above the soil surface(SF)and flooding at 2 m above the soil surface(TF).Results showed that:(1)Regardless of the planting being a monoculture or a combination of the two species,biomass production of both species decreased under water stress.However H.altissima was more sensitive to water stress than C.dactylon.There was a density-dependent effect on the growth of both species but this effect was stronger on C.dactylon.Under all three water treatments,the relative yield total(RYT)was greater than 1 when both species were planted together.Under CK,the two species showed a competitive relationship,whereas under SF and TF,they were facilitated by each other.(2)The flooding and density had significant(P<0.05)effects on net photosynthetic rate(P_n)of H.altissima and C.dactylon.The P_n of H.altissima on the ratio of H2C10 was greater than the single planting while the P_n of C.dactylon significantly decreased in the mixed intercropping pots compared with the planting being a monoculture under the CK(P<0.05).The P_n of H.altissima on the ratio of H8C4 was greater than the other planting densities irrespective of the P_n of C.dactylon with a single planting which was lower than the mixed intercropping pots under the SF(P<0.05).Compared with the CK,the P_n of H.altissima significantly decreased under the TF(P<0.05).(3)As compared with those in CK,the overground carbohydrate contents of H.altissima and C.dactylon were higher under SF,whereas under TF,the overground carbohydrate contents of H.altissima and C.dactylon were lower;The density had significant(P<0.05)effects on root carbohydrate contents of C.dactylon.Under all three water treatments,the root carbohydrate contents of C.dactylon decreased when both species were planted;The density had significant(P<0.05)effects on carbohydrate contents of H.altissima,but had no effect on stem sugar.These results indicated that the stored non-structural carbohydrate contents in tissues of C.dactylon and H.altissima can be transferred to adapt to the flooding environments(SF and TF)and plant density.These results provide a reference for vegetation restoration and reconstruction in the riparian zone of the Three Gorges Reservoir area,and also provide a guidance to manage established artificial grass vegetation in similar areas.