Nitrogen transfer between N₂-fixing plant and non-N₂-fixing plant

Abstract

The transfer mechanisms, calculating methods and ecological significance of nitrogen transfer between legumes and non-legumes are briefly reviewed. There are three pathways of nitrogen transfer from legumes to neighboring non-legumes: (1) the nitrogen pass in soluble form from the donor legume root into the soil solution, move by diffusion or/and mass flow to the receiver root and be taken up by the latter; (2) nitrogen pass into the soil solution as before, be taken up and transported by mycorrhizal hyphae attached to the receiver roots; (3) if mycorrhizal hyphae form connections (bridges) between the two root systems, the nitrogen could pass into the fungus within the donor root and be transported into the receiver root without ever being in the soil solution. The mechanisms of nitrogen transfer between N₂-fixing plants and non-N₂-fixing plants are reviewed in terms of indirect and direct pathways. The indirect N-transfer process is related to the release of nitrogen from legumes (donor plants), the possible interaction of this nitrogen with soil, the decomposition and mineralization of legumes and turnover of nitrogen, the nitrogen absorbing and competing abilities of the legume and the non-legume (receiver plant). The direct nitrogen transfer process is generally considered to be related to the nitrogen gradient and physiological imbalance between legumes and non-legumes, and when the donor legume lies in stressful stage (i.e. removal of shoots or attacked by insects), the nitrogen transfer can be improved significantly. The methods of determining nitrogen transfer (indirect¹⁵N-isotope dilution method and direct¹⁵N determination method) are evaluated, and their advantages and shortcomings are shown in this review.

Keywords

Nitrogen transfer / N₂-fixing plant / Non-N₂-fixing plant / S714.6 / S158.3 / A