Adult plants nurse their neighboring conspecific seedlings via arbuscular mycorrhizae in a saline soil

Background/Question/Methods

Understanding how adult plants affect their neighboring seedlings is important for the regeneration of plant populations in harsh environments. It is well documented that adult plants can facilitate their neighboring seedlings by canopy shading or micro-climate amelioration or herbivore driving under stressful conditions. Here, we tested the hypothesis that adult plants can help their neighboring seedlings develop symbiosis with arbuscular mycorrhizal fungi (AMF), thereby increasing seedling nutrient uptake and growth in a saline soil.

Using the halophytic shrub Tamarix chinensis as a model plant, we conducted two field experiments in a reclaimed saline tidal flat and a third experiment in greenhouse. Field experiment 1 compared the importance of aboveground vs. belowground effects of neighbor plants. Field experiment 2 used the fungicide benomyl to determine the involvement of AMF in neighbor effects. The greenhouse experiment determined whether neighbor effects were influenced by AMF hyphal connection between adults and seedlings.

Results/Conclusions

Field experiment 1 showed that adult neighbors reduced soil salinity, increased soil organic matter, and provided AMF spores for target seedlings. Adult neighbors increased shoot biomass and AMF colonization of target seedlings via whole plant effects (above- plus belowground) or belowground effects alone. Field experiment 2 showed that shoot biomass and AMF colonization of target seedlings was greater in the “with neighbors, without benomyl” treatment (high AMF) than in the “with neighbors, with benomyl” (low AMF) or no neighbors (with or without benomyl) treatments, i.e., the neighbor effect mediated by AMF was facilitative. In the greenhouse experiment, adult neighbors with AMF hyphal connection increased shoot biomass, AMF colonization, and ¹⁵N content of target seedlings under the high salt level, suggesting that adult neighbors can facilitate offspring under salt stress via AMF symbiosis. Summary, our results show that in a saline soil, T. chinensis adults facilitated the growth of their neighboring offspring, and the facilitation involved AMF. The neighboring adults increased AMF symbiosis of the seedlings and thus enhanced seedling nutrient uptake and growth.