The transformation and renewal of soil amino acids induced by the availability of extraneous C and N----Institute of Applied Ecology, Chinese Academy of Sciences

Research

The transformation and renewal of soil amino acids induced by the availability of extraneous C and N

Release Time：2016-11-16 【Big】【Small】【 Print】【Close】

Amino-acids are important component of soil organic matter. They regulate the cycling of soil organic matter. Understanding the kinetics of amino acid transformation and renewal is helpful to deepen our knowledge on the stabilization and decomposition of soil organic matter and provide new idea in the research on soil C, N cycling. Soil amino acids exist mainly in the aggregated form (in protein), but also in free form. Research indicated that the availability of substrate for soil microbes controls the synthesis and decomposition of amino-acids. Compared to our knowledge in the turnover of free amino acids, the effect of C,N availability on the accumulation and turnover of amino acids aggregated in proteins is still not clear.

Dr HE Hongbo and coworkers in IAE investigated the effects of extraneous C and N on synthesis and transformation dynamics of 13 species of ¹⁵N labeled NH₄⁺-N and NO₃^-N amino-acids in an incubation experiment. N¹⁵ isotope based high performance liquid chromatography/mass spectrometric technique was used in N¹⁵ measurement. The results show that after extraneous substrate adding, N was rapidly immobilized as metabolic constituents. During the process of microbial proliferation, the soil amino-acid dynamics and maintenance is dependent on the changes in substrate availability but not static stoichiometry. The amount of NH₄⁺-N that microbes use to synthesize amino-acids is higher than that of NO₃^-N. This confirms microbes prefere to utilize reduced N in NH₄⁺-N rather than oxidized form N in NO₃^-N becsause assimilation of NH₄⁺-N consumes less C source and energy. In latre stage of incubation, the indiginous amino acids in soil were decomposed indicating a part of amino acids may mineralized to fufill the need of microbes for C sourse and energy, but the extent of decomposition is affected by the forms of added N source. Giving NH₄⁺ as N source can maintain higher extraneous N immobilization and induce the net accumulation of amino acids. If take NO₃^- as N source in the substrate, will let the newly synthesized amino acids were offset by the decomposition. The results implicate that the energy requirement regulates the use of different N forms by microbes and turnover of functional Protein in soil. The finding is of important significance to soil N cycling management and regulation.

Further investigation found that the chemical properties of various amino acid such as C and N content, synthesis pathway have little influnces on the turover of amino acid that incoperrated into proteins. Various amino acid monomer as protein constituent co-regulate the renewal and accumulation of amino acids. This Is different from free amino acids. The latter’ s transformation is controlled by their own property and synthesis pathway. This finding provides important inspiration to the research in turnover of soil organic matter and deepens the knowledge in Bio-geo chemical cycling of Carbon.

The results were published entitled as The transformation and renewal of soil amino acids induced by the availability of extraneous C and N in Soil Biology and Chemistry 96 (2016) 86-96.

The work was supported by key project (41130524) and general project (41271251) of NNSFC and Strategic Pillot project of CAS (No. XDB15010303).

Full text URL: http://www.sciencedirect.com/science/article/pii/S0038071716000341

Abstract: Developing an understanding of the transformation kinetics of amino acids in soil is of fundamental importance to probe into the stabilization and decomposition processes central to soil organic matter (SOM) cycling. Considering the transitional function of amino acids in SOM turnover, substrate availability controls the formation and decomposition of soil amino acids critically. However, compared to broad knowledge on free amino acid turnover, how the changing bio-availability of carbon (C) and nitrogen (N) influences the accumulation and turnover of proteinaceous amino acids in soil is not well understood. Therefore, a laboratory experiment was conducted in which soil samples were incubated and supplemented weekly with glucose and ¹⁵N-labeled inorganic N as either ammonium (NH₄⁺ ) or nitrate (NO₃^-). The concentrations of soil amino acids, differentiated into the newly synthesized (¹⁵N-labeled) and endogenous (unlabeled) portion, were temporally quantified by an isotope-based high-performance liquid chromatography/mass spectrometric technique.

During the incubation, extraneous substrates were rapidly immobilized into soil amino acids as important metabolic constituents. However, the dynamics and maintenance of soil amino acids were determined by changing C and N availability during microbial proliferation rather than static stoichiometry of available substrates. The significantly greater amount of de-novo synthesized amino acids in treatments with NH₄⁺ addition than NO₃^- addition confirmed that microorganisms preferred the reduced N than the oxidized form due to significantly lower energy and C requirements. The decomposition of endogenous amino acids during the later stages of the incubation indicated that amino acids could partly meet microbial C and energy demand, but the capacity to get decomposed was independent on N species. Therefore, higher rate of extraneous N immobilization in glucose plus NH₄⁺ treatment was closely associated with the net accumulation of amino acids; whereas the formation of new proteinaceous amino acids after weekly additions of glucose plus NO₃^- was eventually offset by the loss of the endogenous portion, resulting in apparently unchanged amounts of amino acids in the microcosms.

Under the two incubation conditions with available C and N addition, both the intrinsic C percentage in molecules and the biosynthetic pathways have minor influence on the turnover pattern of HCl hydrolyzed amino acids. However, the transformation of individual amino acids was significantly correlated throughout the entire incubation. These findings suggested that the turnover of soil amino acids in proteinaceous form was critically interrelated instead of being controlled by the transformation pathways of different free amino acids. Compared to the NH₄⁺ supply, the addition of NO₃^- enhanced the decomposition of glycogenic amino acid while reduced the degradation of most of ketogenic amino acids, possibly suggesting the important regulating strategy of energy yield on microbial speciation of the N forms.

Publication Name: Hu Guoqing, He Hongbo, Zhang Wei, Zhao Jinsong, Cui Jiehua, Li Bo, Zhang Xudong.

Email: hehongbo@iae.ac.cn.