The soil type is a key factor influencing N(nitrogen)cycling in soil;however,gross N transformations and N_(2)O emission sources are still poorly understood.In this study,a laboratory 15N tracing experiment was carrie...The soil type is a key factor influencing N(nitrogen)cycling in soil;however,gross N transformations and N_(2)O emission sources are still poorly understood.In this study,a laboratory 15N tracing experiment was carried out at 60%WHC(water holding capacity)and 25℃to evaluate the gross N transformation rates and N_(2)O emission pathways in sandy loam and silt loam soils in a semi-arid region of Heilongjiang Province,China.The results showed that the gross rates of N mineralization,immobilization,and nitrification were 3.60,1.90,and 5.63 mg N/(kg·d)in silt loam soil,respectively,which were 3.62,4.26,and 3.13 times those in sandy loam soil,respectively.The ratios of the gross nitrification rate to the ammonium immobilization rate(n/ia)in sandy loam soil and silt loam soil were all higher than 1.00,whereas the n/ia in sandy loam soil(4.36)was significantly higher than that in silt loam soil(3.08).This result indicated that the ability of sandy loam soil to release and conserve the available N was relatively poor in comparison with silt loam soil,and the relatively strong nitrification rate compared to the immobilization rate may lead to N loss through NO_(3)–leaching.Under aerobic conditions,both nitrification and denitrification made contributions to N_(2)O emissions.Nitrification was the dominant pathway leading to N_(2)O production in soils and was responsible for 82.0%of the total emitted N_(2)O in sandy loam soil,which was significantly higher than that in silt loam soil(71.7%).However,the average contribution of denitrification to total N_(2)O production in sandy loam soil was 17.9%,which was significantly lower than that in silt loam soil(28.3%).These results are valuable for developing reasonable fertilization management and proposing effective greenhouse gas mitigation strategies in different soil types in semiarid regions.展开更多
Although to date individual gross N transformations could be quantified by 15N tracing method and models, studies are still limited in paddy soil. An incubation experiment was conducted using topsoil （0-20 cm） and s...Although to date individual gross N transformations could be quantified by 15N tracing method and models, studies are still limited in paddy soil. An incubation experiment was conducted using topsoil （0-20 cm） and subsoil （20-60 cm） of two paddy soils, alkaline and clay （AC） soil and neutral and silt loam （NSL） soil, to investigate gross N transformation rates. Soil samples were labeled with either 15NHaNO3 or NH4SN03, and then incubated at 25 ℃for 168 h at 60% water-holding capacity. The gross N mineralization （recalcitrant and labile organic N mineralization） rates in AC soil were 1.6 to 3.3 times higher than that in NSL soil, and the gross N nitrification （autotrophic and heterotrophic nitrification） rates in AC soil were 2.4 to 4.4 times higher than those in NSL soil. Although gross NO3 consumption （i.e., NO3 immobilization and dissimilatory NO3 reduction to NH＋） rates increased with increasing gross nitrification rates, the measured net nitrification rate in AC soil was approximately 2.0 to 5.1 times higher than that in NSL soil. These showed that high NO3 production capacity of alkaline paddy soil should be a cause for concern because an accumulation of NO3 can increase the risk of NO3 loss through leaching and denitrification.展开更多
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, a15 N tracing study was carried out to...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, a15 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 p H along with increasing orchard age significantly. The amo A 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.展开更多
基金financed by the National Natural Science Foundation of China(41301345,41101284)。
文摘The soil type is a key factor influencing N(nitrogen)cycling in soil;however,gross N transformations and N_(2)O emission sources are still poorly understood.In this study,a laboratory 15N tracing experiment was carried out at 60%WHC(water holding capacity)and 25℃to evaluate the gross N transformation rates and N_(2)O emission pathways in sandy loam and silt loam soils in a semi-arid region of Heilongjiang Province,China.The results showed that the gross rates of N mineralization,immobilization,and nitrification were 3.60,1.90,and 5.63 mg N/(kg·d)in silt loam soil,respectively,which were 3.62,4.26,and 3.13 times those in sandy loam soil,respectively.The ratios of the gross nitrification rate to the ammonium immobilization rate(n/ia)in sandy loam soil and silt loam soil were all higher than 1.00,whereas the n/ia in sandy loam soil(4.36)was significantly higher than that in silt loam soil(3.08).This result indicated that the ability of sandy loam soil to release and conserve the available N was relatively poor in comparison with silt loam soil,and the relatively strong nitrification rate compared to the immobilization rate may lead to N loss through NO_(3)–leaching.Under aerobic conditions,both nitrification and denitrification made contributions to N_(2)O emissions.Nitrification was the dominant pathway leading to N_(2)O production in soils and was responsible for 82.0%of the total emitted N_(2)O in sandy loam soil,which was significantly higher than that in silt loam soil(71.7%).However,the average contribution of denitrification to total N_(2)O production in sandy loam soil was 17.9%,which was significantly lower than that in silt loam soil(28.3%).These results are valuable for developing reasonable fertilization management and proposing effective greenhouse gas mitigation strategies in different soil types in semiarid regions.
基金supported by the Ministry of Science and Technology of China(No.2007DFA30850)the German Ministry of Education and Research(No.0330800C)a German DAAD-PPP Project(No.50751522)joint with the China Scholarship Council(No.2011016097)
文摘Although to date individual gross N transformations could be quantified by 15N tracing method and models, studies are still limited in paddy soil. An incubation experiment was conducted using topsoil （0-20 cm） and subsoil （20-60 cm） of two paddy soils, alkaline and clay （AC） soil and neutral and silt loam （NSL） soil, to investigate gross N transformation rates. Soil samples were labeled with either 15NHaNO3 or NH4SN03, and then incubated at 25 ℃for 168 h at 60% water-holding capacity. The gross N mineralization （recalcitrant and labile organic N mineralization） rates in AC soil were 1.6 to 3.3 times higher than that in NSL soil, and the gross N nitrification （autotrophic and heterotrophic nitrification） rates in AC soil were 2.4 to 4.4 times higher than those in NSL soil. Although gross NO3 consumption （i.e., NO3 immobilization and dissimilatory NO3 reduction to NH＋） rates increased with increasing gross nitrification rates, the measured net nitrification rate in AC soil was approximately 2.0 to 5.1 times higher than that in NSL soil. These showed that high NO3 production capacity of alkaline paddy soil should be a cause for concern because an accumulation of NO3 can increase the risk of NO3 loss through leaching and denitrification.
基金supported by the National Natural Science Foundation of China (Nos.41401339, 41330744)the Natural Science Foundation of Jiangsu Province (No.BK20140062)and Fujian Province (No.2014J01145)
文摘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, a15 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 p H along with increasing orchard age significantly. The amo A 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.
