Effects of arbuscular mycorrhiza on absorption of nitrogen and phosphorus of Spartina alterniflora and Phragmites australis
丛枝真菌对互花米草和芦苇氮磷吸收的影响

Extensive competitions has been found between two species: the native plant, Phragmites australis, and the invasive plant, Spartina alterniflora, in the large areas of coastal China. Although their different influence on various species has been recognized, the impact of arbuscular mycorrhiza fungi (AMF) on the inter\|specific relationship between S. alterniflora and P. australis, especially their role in the invasion of S. alterniflora, still remain an open important topic. In this paper, a three\|factor experiment is designed to clear the impact. Two plant species are grown both separately and together in soil under mycorrhizal inoculation or un\|inoculation conditions, while fresh water or artificial seawater with two levels of concentrations are supplied, respectively. Experimental results indicated that the mycorrhizal colonization declined significantly as the salinity ascended in the mono\|cultured P. australis and mix\|cultured S. alterniflora, while was not affected by the salinity factor in the mix\|cultured P. australis and mono\|cultured S. alterniflora. In mix\|cultured cases, an inter\|reaction of the colonization rates of AMF between two species existed, which correlated with the salinity. Specifically, compared with mono\|cultured cases, the colonization rate on P. australis declined significantly with 40.5% and 24.7%, in fresh water and low salinity seawater respectively; the colonization rate on S. alterniflora increased dramatically with 86.9% in fresh water, in spite of a negligible change in low salinity seawater. In mix\|cultured case with high salinity seawater, however, the colonization rate on P. australis was unaffected, while that on S. alterniflora declined significantly with 78.7%. The N and P concentration of two plants were promoted by mycorrhizal inoculation with fresh water. However, the N and P concentration of P. australis were significantly affected by salinity, with a positive correlation. The effect of mycorrhizal inoculation on N and P concentration was overwhelmed and suppressed by the salinity in this case, implying the N and P concentrations of S. alterniflora were immune to the salinity. Thus, we conclude that, the AMF inoculation has different levels of promotion effects on the absorption of N and P of the two species, the effect is correlated with the infection degree, which is influenced by salinity and planting patterns.