摘要
Plants show different growth responses to N sources supplied with either NH4^＋ or NO3^-. The uptake of different N sources also affects the rhizosphere pH and therefore the bioavallability of soil phosphorus, particularly in alkaline soils. The plant growth, P uptake, and P availability in the rhizosphere of oat （Arena nuda L.） grown in hydroponics and in soil culture were investigated under supply with sole NH4^＋-N, sole NO3-N, or a combination. Sole NO^- -fed oat plants accumulated more biomass than sole NH4^＋ -fed ones. The highest biomass accumulation was observed when N was supplied with both NH^＋ -N and NO3^- -N. Growth of the plant root increased with the proportion of NO3^- in the cultural medium. Better root growth and higher root/shoot ratio were consistently observed in NO3^- fed plants. However, root vigor was the highest when N was supplied with NO3^- ＋NH4^＋. NH4^＋ supply reduced the rhizosphere pH but did not affect P uptake by plants grown in soils with CaHPO4 added as P source. No P deficiency was observed, and plant P concentrations were generally above 2 g kg^-1. P uptake was increased when N was supplied partly or solely as NO3^--N, similarly as biomass accumulation. The results suggested that oat was an NO3-preferring plant, and NO3^- -N was essential for plant growth and the maintenance of root absorption capacity. N supply with NH4^＋ -N did not improve P nutrition, which was most likely due to the absence of P deficiency.
Plants show different growth responses to N sources supplied with either NH4+ or NO-3 . The uptake of different N sources also affects the rhizosphere pH and therefore the bioavailability of soil phosphorus, particularly in alkaline soils. The plant growth, P uptake, and P availability in the rhizosphere of oat (Avena nuda L.) grown in hydroponics and in soil culture were investigated under supply with sole NH4+ -N, sole NO3- -N, or a combination. Sole NO3- -fed oat plants accumulated more biomass than sole NH+4 -fed ones. The highest biomass accumulation was observed when N was suppliedw ith both NH4+ -N and NO3- -N. Growth of the plant root increased with the proportion of NO3- in the cultural medium. Better root growth and higher root/shoot ratio were consistently observed in NO3- -fed plants. However, root vigor was the highest when N was supplied with NO3- +NH4+ . NH4+ supply reduced the rhizosphere pH but did not affect P uptake by plants grown in soils with CaHPO4 added as P source. No P deficiency was observed, and plant P concentrations were generally above 2 g kg-1. P uptake was increased when N was supplied partly or solely as NO3- -N, similarly as biomass accumulation. The results suggested that oat was an NO3- -preferring plant, and NO-3 -N was essential for plant growth and the maintenance of root absorption capacity. N supply with NH+4 -N did not improve P nutrition, which was most likely due to the absence of P deficiency.
基金
Project supported by the National Natural Science Foundation Council of China (No.30660086)
the Natural Science Foundation of Inner Mongolia of China (No.200607010302)
Hong Kong Research Grants Council (No.2465/05M)
Hong Kong University Grants Committee (No.AOE/B-07/99)
Hong Kong Baptist University Matching Research Fund.
