Changes In Interactions Between Plant Species Along A Salinity Gradient

The nature and strength of plant-plant interactions are often affected by environmental stress gradient (salt, water deficit, adverse temperature, etc.). The mechanisms explaining plant interactions have been focused on aboveground interactions and abiotic stress, while belowground interactions and biotic interactions are less well known. To investigate the responses of plant interactions to salt stress gradient, and to test the effects of canopy and root system on these responses, I conducted two controlled experiments by using Medicago sativa. L as target plant and Tamarix chinensis Lour as nurse plant. I designed the salinity gradient as0.05%,0.2%and0.5%. The relative interaction index (Rll) was used to indicate the nature of interaction. The results are as follows:(1) The interspecific plant interactions along salinity gradientAlong increasing gradient of salt, the biomass of M. sativa decreased significantly, while there was no significant difference of the biomasses in T. chinensis. The Rll values were all negative under all salty treatments, suggesting that the net neighbor effects of the two species under all salty treatments were competition. The most negative Rll occurred under moderate salt level, indicating highest competition between the two species.(2) Effects of canopy and root on interspecific interactions along salinity gradientBoth the canopy and root significantly influenced plant interaction. Under moderate salt level, the canopy effects were mutually beneficial, while the root effects were characterized by competition. Under the high salt level, however, the canopy effects were negative, while root effects were positive.(3) The effects of mycorrhiza on interspecific plant interactions along salinity gradientSalt levels affected the mycorrhizal effect on plant interactions between plant species in this study. Mycorrhizae enhanced competition between M. sativa and T. chinensis under all salt levels. Soil solution had no effect on plant-plant interactions under all salt levels. These results suggested that mycorrhizal effect was the main components of root system effects in affecting interactions between M. sativa and T. chinensis along the salt gradient.