Mycorrhizal colonization had little effect on growth of Carex thunbergii but inhibited its nitrogen uptake under deficit water supply.

Abstract

Plant nitrogen (N) acquisition via arbuscular mycorrhizal fungi (AMF) serves as a dominant pathway in the N nutrition of many plants, but the functional impact of AMF in acquisition of N by wetland plants has not been well quantified. Subtropical lake-wetland ecosystems are characterized by seasonal changes in the water table and low N availability in soil. Yet, it is unclear whether and how AMF alters the N acquisition pattern of plants for various forms of N and how this process is influenced by soil water conditions. We performed a pot study with Carex thunbergii that were either colonized by AMF or un-colonized and also subjected to different water conditions. We used 15N labelling to track plant N uptake. AMF colonization had little effect on the biomass components of C. thunbergii but did significantly affect the plant functional traits and N acquisition in ways that were dependent on the soil water conditions. The N uptake rate of AMF-colonized plants was significantly lower than that of the non-colonize plants under low soil water conditions. Decreased NO3 - uptake rate in AMF-colonized plants reduced the plants' N/P ratio. Even though C. thunbergii predominantly took up N in the form of NO3 -, higher water availability increased the proportion of N taken up as NH4 +, irrespective of the inoculation status. These results emphasize the importance of AMF colonization in controlling the plant's N uptake strategies and can improve predictions of N budget under the changing water table conditions in this subtropical wetland ecosystem.