Effects Of Arbuscular Mycorrhizal (AM) Fungi And Fertilization On Plant Productivity And Species Diversity In The Meadow Steppe Of Northeast China

Background and aimsBecause of interest in understanding the relative importance of processes that contribute to the conservation and restoration of plant diversity, many researches are increasing the knowledge of the effects of Arbuscular Mycorrhizal (AM) fungi and fertilizers on the plant community structure and thereby ecosystem functions. However, the combined effects of both AM fungi and fertilization on plant productivity and species diversity in natural grassland are still unclear. The current study aimed to investigate the responses of plant community to fertilization and suppression of AM fungi in a meadow steppe by focusing on the changes in the aboveground and belowground net productivity, plant species diversity and plant nutrients on the context of two plant communities characterized initially by a low and high plant diversity (4vs.20plant species) in two experimental years.MethodsAt both plant communities, six replicate plots were established in order to compare the effects of six treatments (control, benomyl, nitrogen, benomyl plus nitrogen, phosphorus, and benomyl plus phosphorus) on plant productivity and species diversity. AM fungi were suppressed with benomyl application every two weeks and fertilizers were supplied at the beginning of each growth season. Quadrat sampling was carried out at the peak of aboveground biomass in each growth season and chemical analysis was performed to evaluate the changes in aboveground and belowground nutrient contents.ResultsSuppression of AM fungi by the applications of benomyl fungicide during two years enhanced significantly the aboveground biomass production and abundance of dominant plant species in both plant communities (P<0.05). Moreover, suppression of AM fungi induced a shift in plant community structure by decreasing plant diversity (P=0.03) and evenness (P=0.02) in high plant diversity community, but no effects in low plant diversity community were observed (P>0.05).Nitrogen fertilization enhanced biomass production of dominant plant species in both plant communities by more than20%while phosphorus fertilization decreased the abundance of grass functional group in the low plant diversity community by190units/m2in the second experimental year.In general, nutrient contents of dominant plant species were enhanced when AM fungi were suppressed, whereas the presence of AM fungi combined with nitrogen fertilization increased the N content of aboveground part of grass by1.35g N/m2and belowground part of all plants by8.12g N/m2in the high plant diversity community.Conclusions and implicationsThe results in this study indicate AM fungi and fertilizers have opposite effects on plant community productivity by shifting plant competition especially the competitive ability of dominant plant species. AM fungi generated a negative feedback restraining the growth of dominant species and enhanced the plant species diversity in the high plant diversity community. This suggests that the negative feedback occurring between plants and AM fungi contributes to plant coexistence by suppressing the growth of dominant species.Hence, future studies investigating the factors and mechanisms linking to the negative feedback of AM fungi should be conducted for further understanding of the importance of AM fungi functions in grassland ecosystem.