Abstract: Hyphae of arbuscular mycorrhizal fungi (AMF) in soil often form complex mycorrhizal networks among roots of same or different plant species for transfer of nutrients from one plant to another. However, the effect of soil nitrogen (N) availability on nutrient transfer between different plant species via common mycorrhizal networks (CMNs) has not been experimentally examined. In order to quantify CMN-mediated nutrient transfer between Leymus chinensis (LC) and Cleistogene squarrosa (CS), two systems, i.e. the CS-LC system (CS and LC were donor and recipient, respectively) and the LC-CS system (LC and CS were donor and recipient, respectively) were established. Stable isotopic ¹⁵N was applied to track N transfer between heterospecific seedlings connected by CMNs under three levels of soil N additions: no N addition control (N0), N addition with 7 mg/kg (N1) and N addition with 14 mg/kg (N2). In the CS-LC system, the highest rate of AMF colonization and hyphal length density (HLD) were found at N1. In contrast, maximum AMF colonization rate and HLD were recorded at N2 in LC-CS system. Consequently, plant biomass was significantly higher under N1 and N2 levels in CS-LC and LC-CS systems, respectively. Moreover, in CS-LC system, ¹⁵N transfer rate ranged from 16% to 61%, with maximum transfer rate at N1. For LC-CS system, ¹⁵N transfer rate was much lower, with the maximum occurring at N0. These findings suggest that CMNs could potentially regulate N transfer from a donor to recipient plant depending upon the strength of individual plant carbon sink.

Key words: CMNs, ¹⁵N transfer, differential response, Cleistogene squarrosa, Leymus chinensis, typical steppe