Effects Of Sulfur On Photosynthesis And Growth Of Spartina Alterniflora

The invasion of Spartina alterniflora has caused significant influence on structure and functioning of coastal saltmarshes.Besides human interactions,such invasion events are also related to the adaptation ability of S.alterniflora towards saltmarsh environments.Some recent studies showed that S.alterniflora had advantages of adaptation to sulfur stress in addition to the total salinity.The Spartina marsh had been found to contain relatively higher sulfur content than the adjacent native Phragmites marsh,and the antioxidant system of S.alterniflora was stronger than P.australis under sulfur stress.Focused on photosynthesis and seedling growth,this research is aimed to investigate if the sulfur helps with the invasion of S.alterniflora in coastal saltmarshes.In this series of experiments,we chose seeds,clonal ramets collected from China's Yancheng Natural Reserve.By adding different concentrations of NaCl,Na2SO4,Na2S to the cultural medium,we conducted the following experiments:1)the seedlings growth index with photosynthetic pigment content under different concentrations of salt stress;2)light response curves of S.alterniflora clonal seedlings under different concentrations of salt stress obtained by measuring gas exchange with varying light levels,as well as photosynthesis II(PSII)light induction curves measured by chlorophyll fluorescence analysis in the spring;3)in the summer,photosynthetic parameters and chlorophyll fluorescence parameters of seedlings of S.alterniflora and P.australis under different salt treatment were also measured and compared.The main findings are as follows:1)Compared with clonal ramets in the spring and summer,seed and seedling was more sensitive to salt stress,especially in response to Na2S treatment.According to height and root length data,seedling shoot growth was earlier and more quickly than root growth.Besides,compared to the above-ground part,roots were more vulnerable to high sulfur.The seedlings growth of the control group was better than all the other of salt treated group.The inhibition effect of Na2SO4 to seedling root length was less than that of NaCl,which was much less than that of Na2S.2)Photosynthesis of S.alterniflora in spring and summer were positively stimulated by Na2S,with the data in spring being more significant.Similar but less promotion effects-were found with NaCl.However,Na2SO4 improved the photosynthetic ability of S.alterniflora in spring,and had no significant influence on which in summer.The results indicate that Na2S,compared to Na2SO4 and NaCl,may exert the strongest effect on the growth of S.alterniflora.3)In the summer,the comparative experiments of S.alterniflora and P.australis showed that 50 mmol·L-1 Na2S treatment significantly increased net photosynthetic rate(Pn)of S.alterniflora,and had negative effect on P.australis.NaCl could also promote the net photosynthetic rate of S.alterniflora slightly,but decreased that of P.australis.However,Na2SO4 had no significant effect on photosynthetic efficiency of the two plants.Our results suggest that S.alterniflora has great tolerance to sulfuric environments.Therefore,sulfuric compounds and especially sulfide in saltmarsh environments may benefit the competition of S.alterniflora over native plants during the invasion to coastal saltmarshes,which could contribute to the formation of the mono-specific vegetation of the invasive S.alterniflora.