In nutrient-limited alpine meadows,nitrogen(N) mineralization is prior to soil microbial immobilization;therefore,increased mineral N supply would be most likely immobilized by soil microbes due to nutrient shortage i...In nutrient-limited alpine meadows,nitrogen(N) mineralization is prior to soil microbial immobilization;therefore,increased mineral N supply would be most likely immobilized by soil microbes due to nutrient shortage in alpine soils.In addition,low temperature in alpine meadows might be one of the primary factors limiting soil organic matter decomposition and thus N mineralization.A laboratory incubation experiment was performed using an alpine meadow soil from the Tibetan Plateau.Two levels of NH4NO3(N) or glucose(C) were added,with a blank without addition of C or N as the control,before incubation at 5,15,or 25 ℃ for 28 d.CO2 efflux was measured during the 28-d incubation,and the mineral N was measured at the beginning and end of the incubation,in order to test two hypotheses:1) net N mineralization is negatively correlated with CO2 efflux for the control and 2) the external labile N or C supply will shift the negative correlation to positive.The results showed a negative correlation between CO2 efflux and net N immobilization in the control.External inorganic N supply did not change the negative correlation.The external labile C supply shifted the linear correlation from negative to positive under the low C addition level.However,under the high C level,no correlation was found.These suggested that the correlation of CO2 efflux to net N mineralization strongly depend on soil labile C and C:N ratio regardless of temperatures.Further research should focus on the effects of the types and the amount of litter components on interactions of C and N during soil organic matter decomposition.展开更多
The effects of carbon （C） and nitrogen （N） sources on N utilization and biosynthesis of amino acids were examined in the germinating spores of the arbuscular mycorrhizal （AM） fungus Glomus intraradices Schenck ...The effects of carbon （C） and nitrogen （N） sources on N utilization and biosynthesis of amino acids were examined in the germinating spores of the arbuscular mycorrhizal （AM） fungus Glomus intraradices Schenck ＆ Smith after exposure to various N substrates, CO2, glucose, and/or root exudates. The N uptake and de novo biosynthesis of amino acids were analyzed using stable isotopic labeling with mass spectrometric detection. High-performance liquid chromatography-based analysis was used to measure amino acid levels. In the absence of exogenous N sources and in the presence of 25 mL L^-1 CO2, the germinating AM fungal spores utilized internal N storage as well as C skeletons derived from the degradation of storage lipids to biosynthesize the free amino acids, in which serine and glycine were produced predominantly. The concentrations of internal amino acids increased gradually as the germination time increased from 0 to 1 or 2 weeks. However, asparagine and glutamine declined to the low levels; both degraded to provide the biosynthesis of other amino acids with C and N donors. The availability of exogenous inorganic N （ammonium and nitrate） and organic N （urea, arginine, and glutamine） to the AM fungal spores using only CO2 for germination generated more than 5 times more internal free amino acids than those in the absence of exogenous N. A supply of exogenous nitrate to the AM fungal spores with only CO2 gave rise to more than 10 times more asparagine than that without exogenous N. In contrast, the extra supply of exogenous glucose to the AM fungal spores generated a significant enhancement in the uptake of exogenous N sources, with more than 3 times more free amino acids being produced than those supplied with only exogenous CO2. Meanwhile, arginine was the most abundant free amino acid produced and it was incorporated into the proteins of AM funsal spores to serve as an N storage compound.展开更多
基金Supported by the National Basic Research Program (973 Program) of China (Nos.2010CB951704 and 2010CB833502)the National Natural Science Foundation for Young Scientists of China (No.30600070)the West Light Joint Scholarship of the Chinese Academy of Sciences
文摘In nutrient-limited alpine meadows,nitrogen(N) mineralization is prior to soil microbial immobilization;therefore,increased mineral N supply would be most likely immobilized by soil microbes due to nutrient shortage in alpine soils.In addition,low temperature in alpine meadows might be one of the primary factors limiting soil organic matter decomposition and thus N mineralization.A laboratory incubation experiment was performed using an alpine meadow soil from the Tibetan Plateau.Two levels of NH4NO3(N) or glucose(C) were added,with a blank without addition of C or N as the control,before incubation at 5,15,or 25 ℃ for 28 d.CO2 efflux was measured during the 28-d incubation,and the mineral N was measured at the beginning and end of the incubation,in order to test two hypotheses:1) net N mineralization is negatively correlated with CO2 efflux for the control and 2) the external labile N or C supply will shift the negative correlation to positive.The results showed a negative correlation between CO2 efflux and net N immobilization in the control.External inorganic N supply did not change the negative correlation.The external labile C supply shifted the linear correlation from negative to positive under the low C addition level.However,under the high C level,no correlation was found.These suggested that the correlation of CO2 efflux to net N mineralization strongly depend on soil labile C and C:N ratio regardless of temperatures.Further research should focus on the effects of the types and the amount of litter components on interactions of C and N during soil organic matter decomposition.
基金Supported by the National Natural Science Foundation of China (No. 30970101)
文摘The effects of carbon （C） and nitrogen （N） sources on N utilization and biosynthesis of amino acids were examined in the germinating spores of the arbuscular mycorrhizal （AM） fungus Glomus intraradices Schenck ＆ Smith after exposure to various N substrates, CO2, glucose, and/or root exudates. The N uptake and de novo biosynthesis of amino acids were analyzed using stable isotopic labeling with mass spectrometric detection. High-performance liquid chromatography-based analysis was used to measure amino acid levels. In the absence of exogenous N sources and in the presence of 25 mL L^-1 CO2, the germinating AM fungal spores utilized internal N storage as well as C skeletons derived from the degradation of storage lipids to biosynthesize the free amino acids, in which serine and glycine were produced predominantly. The concentrations of internal amino acids increased gradually as the germination time increased from 0 to 1 or 2 weeks. However, asparagine and glutamine declined to the low levels; both degraded to provide the biosynthesis of other amino acids with C and N donors. The availability of exogenous inorganic N （ammonium and nitrate） and organic N （urea, arginine, and glutamine） to the AM fungal spores using only CO2 for germination generated more than 5 times more internal free amino acids than those in the absence of exogenous N. A supply of exogenous nitrate to the AM fungal spores with only CO2 gave rise to more than 10 times more asparagine than that without exogenous N. In contrast, the extra supply of exogenous glucose to the AM fungal spores generated a significant enhancement in the uptake of exogenous N sources, with more than 3 times more free amino acids being produced than those supplied with only exogenous CO2. Meanwhile, arginine was the most abundant free amino acid produced and it was incorporated into the proteins of AM funsal spores to serve as an N storage compound.
