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Nitrogen (N) limitation is common in most terrestrialPlants and microorganisms compete for the same soil resources, but they are mutually dependent on each other 1 . Soil microorganisms need labile organic substances from plants in the form of litter and root exudates 2-4 to mineralize nutrients from organic to inorganic forms. Plants rely on nutrient supplies mediated by soil microorganisms 4-6 . Plant productivity and soil microbial activities are often tightly coupled, especially in nutrient-poor ecosystems 2,6 . Understanding how plants and microorganisms acquire limited nutrients from soils is essential for understanding carbon (C) and nitrogen (N) cycles.Nitrogen is a fundamental nutrient for plant growth and metabolism but limited in most terrestrial ecosystems 7 , causing strong competition for available N between roots and soil microorganisms 8,9 . Studies have explored plant-microbial competition for N to understand the mechanisms responsible for plant productivity 6 , species coexistence 10,11 , and ecological consequences of this competition in various terrestrial ecosystems. The consequences of competition often lead to: i) limitation on plant growth, ii) reduced microbial mineralization, and iii) increased competition for N between coexisting plant species.The old paradigm for terrestrial N cycling assumed that plants were only capable of using inorganic N (i.e., NH 4 + and NO 3 − ), mineralized by microorganisms from organic N forms. Many studies had investigated competition for inorganic N between plants and microorganisms 12-14 . However, some studies 15,16 also showed that plants could utilize organic N, such as free amino acids and peptides, found in the soil 17,18 . To understand

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