Residue-Derived Amino Sugar Formation and Its Carbon Use Efficiency

Abstract

A 21-day lab incubation experiment was carried out with arable soil and uniform ¹³C-labeled wheat residues. Residue-derived amino sugars (AS_R) accumulated exponentially and were fitted with a first-order model C _t = C_Max(1 − e^−kt) well. Their maxima were 88–381 nmol g⁻¹ for glucosamine (GluN_R), 52–105 nmol g⁻¹ for galactosamine (GalN_R), and 107–137 nmol g⁻¹ for muramic acid (MurN_R), respectively. Their half-lives (T _1/2) separately varied between 1.2 and 3.3 days for GluN_R, 1.6 and 4.7 days for GalN_R, and less than 0.3 day for MurN_R. A close relationship was observed between carbon mineralization and AS_R (P < 0.05), and carbon use efficiency of cumulative AS_R was calculated and compared.

Introduction

Though amino sugars (AS) have widely been used to investigate microbial residues and correlated organic compounds sequestration, little is known about their formation dynamics in soil (Zhang and Amelung 1996; He et al. 2011). Difficulties are probably ascribed to the definition and differentiation of varied ASs pools, substrate availability, and time scale of the study. With ¹³C-labeled residues’ incubation, LC-c-IRMS was utilized to investigate AS formation kinetics and its carbon use efficiency for the first time in this study.

Materials and Methods

0–10-cm top soil from conventional till (CT) and no till (NT) was amended with ¹³C-labeled wheat grain (G), leaf (L), and root (R) at 6-mg substrate Cg⁻¹ for a 21-day incubation, including six treatments: NG (NT + G), NL (NT + L), NR (NT + R), CG (CT + G), CL (CT + L), and CR (CT + R). Concentrations and δ ¹³C of AS were determined by LC-c-IRMS. Residue-derived AS (AS_R) formation was described in AS_R,t  = AS_R,Max ∙ (1 − e^−kt), where AS_R,Max is potentially accumulative AS_R,t , and k is AS_R,t the formation rate constant, and t is the incubation time.

Results and Discussion

This study showed that T _1/2 of AS_R formation increased as MurN (≤0.3 day) < GluN (1.2–3.3 days) < GalN (1.6–4.7days); their maxima were 88–381 nmol g⁻¹ for GluN, 52–105 nmol g⁻¹ for GalN, and 107–137 nmol g⁻¹ for MurN; and AS_R,Max/AS_SOM,0h were separately 14.9–17.8% for MurN, 5.5–13.0% for GluN, and 2.7–6.3% for GalN (AS_SOM data not shown) (Fig. 1, Table 1), which agrees with previous studies (Glaser and Gross 2005). MurN is exclusively originated from bacteria, and its faster formation suggested the important role of bacteria at the early stage of mineralization of wheat residues.

Fig. 1

Modeled and measured residue-derived amino sugar concentration (AS_R,t ) as a function of time

Table 1 Parameters description of AS_R formation

The cumulative GluN_R or GalN_R was significantly correlated to the mineralized carbon (C_M) across all treatments throughout the whole incubation, which strongly suggests that a certain proportion of C_M is allocated into newly formed AS_R (except for MurN_R, Fig. 2). The intercepts and slopes of linear functions between GluN_R and C_M were evidently different from their counterparts between GalN_R and C_M, which clearly signifies a much higher carbon use efficiency of accumulative GluN_R than GalN_R. The stoichiometric relationship between C_M and AS_R could be calculated: an increase of 0.1 μmol GluN_R needed 0.38 μmol C_M, which was 13.61 lower than GalN_R, while after 1 μmol C_M, 0.16 μmol GluN_R would be synthesized, which was nearly 16 times the GalN_R.

Fig. 2

Correlation between C mineralization and AS_R