A Small Amount of Nitrogen Transfer from White Clover to Citrus Seedling via Common Arbuscular Mycorrhizal Networks

Few studies have examined if perennial leguminous cover crops are able to transfer nitrogen (N) via common mycorrhizal networks (CMNs) to neighboring fruit trees; the gradient of such N transfer could affect the N nutrition of both plants. Using separated three-column chambers to grow plants in a greenhouse, 99 atom% N-15 as ((NH4)-N-15)(2)SO4 was applied to leaves of white clover (Trifolium repens L.) and N-15 was then traced in neighboring citrus (Citrus sinensis (L.) Osbeck) seedlings interconnected by an arbuscular mycorrhizal fungus (AMF, Rhizophagus intraradices). A range of 66.85-68.74% mycorrhizal colonization in white clover (mycorrhizal and/or Rhizobium trifolii inoculated) and 19.29-23.41% in citrus (non-mycorrhizal inoculated) was observed after 12 months of AMF inoculation in the white clover, indicating a successful CMN linkage was established between these two plant species. This CMN establishment resulted in significant increases in biomass, N accumulation, and N-15 content of citrus when accompanied with nodulated and mycorrhizal fungus colonized white clover. N transfer from white clover to citrus was significantly greater under nodulation plus mycorrhization (46.23 mg N per pot, 1.71% of N transferred) than under non-inoculated control (4.36 mg N per pot, 0.21% of N transferred), and higher than sole mycorrhization (36.34 mg N per pot, 1.42% of N transferred). The percentage of N in citrus derived from white clover under nodulated/mycorrhization was 1.83-1.93%, and was highest in leaves (3.31%), moderate in stems (2.47%), and lowest in roots (0.41%) of citrus. In summary, results from this experiment demonstrated that nearly 2.0% of N transferred from white clover to citrus via CMN. Further studies are needed to quantify N transfer between white clover and citrus by other routes, including soil or root exudation pathways.

Automated summary

This study found that white clover successfully transferred nitrogen to citrus via common mycorrhizal networks, accounting for approximately 2% of total nitrogen content. A successful connection was established between white clover and citrus through the mycorrhizal fungi network, leading to increased biomass, nitrogen accumulation, and nitrogen content in citrus.