| 英文摘要： |
Plant-microbial competition for N in the rhizosphere affects net primary production and N cycling, and depends on plant physiological factors, including photosynthesis and transpiration. Here, we studied the diurnal competition for N between plants and microorganisms and quantified plant C allocation by maize (Zea mays) and wheat (Triticum aestivum) in a nutrient-poor soil. In situ concurrent pulse (NO3-)-N-15 and (CO2)-C-13 labeling was carried out to trace the N uptake from the soil and C allocation to plant-microorganisms-soil system in the first 12 and 24 h after labeling, corresponding to daytime and nighttime. Plants outcompeted microorganisms for NO3- uptake from the rhizosphere during daytime and nighttime. Diurnal dynamics had a low effect on microbial NO3- uptake, which varied between 7 and 15% of added N for maize and between 3 and 6% of added N for wheat after the first 12 and 24 hours. NO3- uptake by maize was not affected by diurnal dynamics, but NO3- uptake by wheat was higher during daytime than that during nighttime. The C-13 allocation to plants and microorganisms was similar between daytime and nighttime. N utilization was closely related to photosynthate partitioning in plant shoots and roots, indicating coupling between C allocation and N utilization. These findings indicate that plants grown in nutrient-poor soils (as used in this study) dominate over microorganisms for N uptake and release newly photosynthesized C for rhizosphere microorganisms. The diurnal dynamics of these plant-microbial interactions are plant species-specific: important for wheat but irrelevant for maize. |
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