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

Abstract

Background and aims: 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.

Methods: We performed a pot study with Carex thunbergii that were either colonized by AMF or not colonized and also subjected to different water conditions. We used 15N labelling to track plant N uptake.

Key results: Colonization by AMF 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-colonized plants in conditions of low soil water. A decreased NO3- uptake rate in AMF-colonized plants reduced the N:P ratio of the plants. Although 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.

Conclusions: These results emphasize the importance of AMF colonization in controlling the N uptake strategies of plants and can improve predictions of N budget under the changing water table conditions in this subtropical wetland ecosystem.

Keywords: arbuscular mycorrhizal fungi; nitrogen uptake; plant functional traits; soil water content; stable isotope labelling; subtropical wetland ecosystem.