Effect of different forage species on the nitrogen uptake in Hulunbeir

Abstract

Knowledge of determining factors for nitrogen uptake preferences and how they are modified in changing environments are critical to understand ecosystem nitrogen cycling and to predict plant responses to future environmental changes. However, it remains unclear in this aspect for the main managed grassland (Medicago sativa, Bromus inermis, Leymus chinensis) and crop (Brassica campestris) under field condition in Hulunbeir area of Inner Mongolia of China. Two 15N tracer experiments utilizing a unique differential labelled nitrogen source were employed in both managed grassland (M. sativa, B. inermis and L. chinensis) and crop (B. campestris) in Hulunbeir area of Inner Mongolia of China. Tracing both labels in the above-and below ground plant biomass, soil NH4+ -N or NO3− -N and NH4+ -N or NO3- -N uptake by plants. There were differences between soil NO3−-N concentration and NH4+-N concentration, and NO3−-N concentration was higher than NH4+-N concentration. NO3−-N concentration was led by different grass species. The NH4+-N concentration in August were higher than in July on the whole, the highest value for B. campestris and the lowest for B. inermis. The plant N concentration in B. inermis, L. chinensis and B. campestris showed decreasing trend, its mean value decreased by 20.1, 47.9 and 26.7%, respectively, and M. sativa increased by 13.7%. Among the four species, the individuals exhibited a preference for 15NO3-, indicated by higher 15N signatures in 15NO3-treatment than in 15NH4+ treatment.