Effects of Fairy Rings on Carbon and Water Fluxes in Hulunbuir Meadow Steppe

This study aimed to investigate the spatial heterogeneity of vegetation and soil in the grassland fairy ring and its influence on the ecosystem carbon and water exchange characteristics.

Using a measurement system consisting of Licor-6400 and static bright/dark boxes, the different components of plant community carbon and water fluxes were determined, including net ecosystem carbon exchange (NEE), ecosystem respiration (ER), and evapotranspiration (ET), and estimated grassland ecosystem gross primary productivity (GPP), carbon utilization efficiency (CUE), and water utilization efficiency (WUE).

Plants on the fairy ring (green grass ring) were mainly dominated by Gramineae, Cyperaceae and Asteraceae, and the number of species and diversity index on the ring were significantly smaller than those inside and outside the ring (P<0.05). The above-ground biomass on the ring (324.72 g·m^-2) was significantly higher than those inside (184.66 g·m^-2) and outside (194.86 g·m^-2); while the below-ground biomass on the ring (340.55 g·m^-2) was smaller than those inside (508.29 g·m^-2) and outside (394.77 g·m^-2), and the root shoot ratio of the ring was significantly lower than that outside of the ring (P<0.05), which might be related to the cumulative effect of soil available nutrient on the fairy ring. The average contents of soil total nitrogen (STN), soil organic carbon (SOC), soil available potassium (SAK), soil available phosphorus (SAP), soil ammonium nitrogen (SAN) and soil nitrate nitrogen (SNN) were higher than those in and out of the ring to different degrees. GPP and NEE were significantly greater on the grassland fairy ring than in and out of the ring (P<0.05), and ER, ET, CUE and WUE were higher on the ring than in and out of the ring too, but the differences were not significant (P>0.05). Carbohydrate flux components GPP, NEE, ER and ET were positively correlated with above-ground biomass to different degrees; CUE and WUE were positively correlated with soil nutrients to different degrees.

The developmental process of fairy ring fungi changed the structural characteristics of grassland communities and the spatial pattern of soil nutrients, and the soil “fertilization effect” driven by fairy ring fungi was the fundamental reason for the spatial heterogeneity of carbon and water flux fractions and carbon and water use efficiencies in different layers of the fairy ring.