title: Effect of orchard age on soil nitrogen transformation in subtropical China and implications.
abstract: A better understanding of nitrogen transformation in soils could reveal the capacity for biological inorganic N supply and improve the efficiency of N fertilizers. In this study, a (15)N tracing study was carried out to investigate the effects of converting woodland to orchard, and orchard age on the gross rates of N transformation occurring simultaneously in subtropical soils in Eastern China. The results showed that inorganic N supply rate was remained constant with soil organic C and N contents increased after converting woodland into citrus orchard and with increasing orchard age. This phenomenon was most probably due to the increase in the turnover time of recalcitrant organic-N, which increased with decreasing soil pH along with increasing orchard age significantly. The amoA gene copy numbers of both archaeal and bacterial were stimulated by orchard planting and increased with increasing orchard age. The nitrification capacity (defined as the ratio of gross rate of nitrification to total gross rate of mineralization) increased following the Michaelis-Menten equation, sharply in the first 10 years after woodland conversion to orchard, and increased continuously but much more slowly till 30 years. Due to the increase in nitrification capacity and unchanged NO3(-) consumption, the dominance of ammonium in inorganic N in woodland soil was shifted to nitrate dominance in orchard soils. These results indicated that the risk of NO3(-) loss was expected to increase and the amount of N needed from fertilizers for fruit growth did not change although soil organic N accumulated with orchard age.
authors.affiliation: School of Geography Sciences, Nanjing Normal University, Nanjing 210023, China; Institute of Soil and Fertilizer, Fujian Academy of Agricultural Sciences, Fuzhou 350013, China; Jiangsu Provincial Key Laboratory of Materials Cycling and Pollution Control, Nanjing 210023, China. Electronic address: zys3505@126.com.
authors.forename: Yushu
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: School of Geography Sciences, Nanjing Normal University, Nanjing 210023, China; Jiangsu Provincial Key Laboratory of Materials Cycling and Pollution Control, Nanjing 210023, China; Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application, Nanjing 210023, China; Key Laboratory of Virtual Geographical Environment, Ministry of Education, Nanjing Normal University, Nanjing 210023, China.
authors.forename: Jinbo
authors.initials: J
authors.lastname: Zhang
authors.affiliation: School of Geography Sciences, Nanjing Normal University, Nanjing 210023, China; Jiangsu Provincial Key Laboratory of Materials Cycling and Pollution Control, Nanjing 210023, China.
authors.forename: Tongbin
authors.initials: T
authors.lastname: Zhu
authors.affiliation: Department of Plant Ecology, Justus-Liebig University Giessen, 35392 Giessen, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Müller
authors.affiliation: School of Geography Sciences, Nanjing Normal University, Nanjing 210023, China; Jiangsu Provincial Key Laboratory of Materials Cycling and Pollution Control, Nanjing 210023, China; Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application, Nanjing 210023, China; Key Laboratory of Virtual Geographical Environment, Ministry of Education, Nanjing Normal University, Nanjing 210023, China. Electronic address: zccai@njnu.edu.cn.
authors.forename: Zucong
authors.initials: Z
authors.lastname: Cai
mesh_terms: D000383:Agriculture; D002681:China; D002957:Citrus / Q000254:growth & development; D004777:Environment; D004784:Environmental Monitoring; D005308:Fertilizers / Q000032:analysis*; D065928:Forests; D058465:Nitrification; D009584:Nitrogen / Q000378:metabolism*; D009587:Nitrogen Isotopes / Q000032:analysis; D012987:Soil / Q000737:chemistry*
chemical_list: D005308:Fertilizers; D009587:Nitrogen Isotopes; D012987:Soil; D009584:Nitrogen
keywords: (15)N tracing technique; Gross rates of nitrogen transformation; Subtropical orchard soil