Rapid microbial uptake and mineralization of 14C-labelled cysteine and methionine along a grassland productivity gradient. (May 2023)

• Record Type: Journal Article
• Authors: Wang, Deying; Chadwick, David R.; Hill, Paul W.; Ge, Tida; Jones, Davey L.
• Is Part Of: Soil biology and biochemistry. Volume 180(2023)
• Publication Date: 2023-05
• Subjects: Cysteine -- Methionine -- Microbial uptake -- Mineralization -- Grassland productivity gradient -- 14C tracer; Soil biochemistry -- Periodicals; Soil biology -- Periodicals; Sols -- Biochimie -- Périodiques; Sols -- Biologie -- Périodiques; Sols -- Microbiologie -- Périodiques; Bodembiologie; Biochemie; 631.46
• DOI: 10.1016/j.soilbio.2023.109022
• Languages: English
• ISSNs: 0038-0717

Abstract

Abstract: Cysteine (Cys) and methionine (Met) are central to terrestrial S cycling because they are sources of carbon (C), nitrogen (N), and sulphur (S) for plant nutrition and microbial growth. However, soil microorganisms are expected to compete for the C, N and S in these S-amino acids. We hypothesized that microbial competition would be greater in soils with low plant productivity due to lower C inputs from plants. Here we added 14 C-labelled Cys and Met to 5 soils collected from an altitude-driven primary grassland productivity gradient, we then measured microbial uptake with a centrifugal drainage procedure over 60 min, and the subsequent mineralization with NaOH traps over 48 h. Our results revealed that both Cys and Met were rapidly assimilated by soil microbes, with half-lives ranging from 0.34 to 2.14 min, which is an order of magnitude (or more) faster than when determined from measurement of 14 CO2 evolution. This considerable delay between microbial 14 C removal from soil solution and subsequent 14 CO2 evolution indicates that the degradation of Cys and Met in grassland soils occurred mainly through biological processes. Soil microbial uptake of Cys and Met was dominated by a high-affinity transport system (0.01–0.1 mM), while a lower affinity transport system became more important at higher substrate concentrations (1–100 mM). In addition, microbial uptake and mineralization rates of Cys and Met declined in less productive, higher elevation sites, suggesting that the turnover of organic N and S, and subsequent availability for plant uptake is likely to be controlled by soil fertility. We conclude that although Cys and Met may represent a minor component of DON and DOS pools in soil, their importance for soil microbes and plant nutrition may have been underestimated due to their fast turnover and replenishment rates in grassland soils. Highlights: Cystine and methionine turned over faster in soils from low altitude sites. Methionine showed a lower mineralization rate than cysteine. < 20% of amino acid- 14 C was retained in soil solution within 10 min. Degradation of cysteine or methionine occurred mainly through biological processes.