ABSTRACT
Understanding short-term microbial responses to N fertilizer granule dissolution is essential for elucidating how C substrates are transformed within localized fertilizer–soil microsites, hereafter the fertosphere. We conducted a 20-d laboratory incubation to evaluate the mineralization and apparent microbial C use efficiency (aCUE) of four 14C-labeled substrates — glucosamine, glucose, glycine, and malic acid — added to a tropical clayey soil treated with six granular N fertilizers: ammonium nitrate, ammonium sulfate, diammonium phosphate (DAP), potassium nitrate, struvite, and urea. Apparent microbial C use efficiency was operationally defined as the fraction of substrate label allocated to the slower-turnover pool of a double first-order exponential model, representing a kinetic proxy rather than a direct measure of biosynthetic efficiency. Nitrogen fertilizers stimulated 14C mineralization of labile substrates, particularly urea, which induced the highest 14CO2 emission and the lowest aCUE, concurrent with a pronounced alkalinization (pH up to 8.9) driven by urea hydrolysis. In contrast, DAP and struvite increased glycine half-life and aCUE relative to the unfertilized control, consistent with relief of P limitation in this low-P Ferralsol. Glucose and malic acid were predominantly allocated to the slower (anabolic) pool, whereas glucosamine and glycine were primarily respired. The aCUE reduction was greater for N-containing than for C-only substrates. Overall, granular N fertilizers did not promote short-term retention of low-molecular-weight C substrates in the fertosphere and may instead accelerate their mineralization. These findings underscore that microsite-scale variations in aCUE can transiently modulate soil C turnover in fertilized tropical systems.
Technical info
Description of the data and file structure
Experimental data used for the statistical analyses in the article are provided in a single Microsoft Excel file (dataset.xlsx) containing three worksheets (Sheet1, Sheet2, and Sheet3). Throughout the file, the seven N treatments are denoted by the variable "Fert": Control (unfertilized); Ammonium nitrate; Ammonium sulfate; Diammonium phosphate (DAP); Potassium nitrate; Struvite; and Urea. All 14C variables are expressed relative to the total 14C-labeled substrate added to each experimental unit. Missing observations are coded as a period (.). The column descriptions for each worksheet are as follows:
Sheet1
Cumulative amount of substrate-derived 14C remaining in soil over time, used to fit the double first-order exponential decay model (Eq. 1; Fig. 2).
Fert: granular N fertilizer treatment (see list above).
Day: time after 14C-substrate addition (d).
CREMglucose: glucose-derived 14C remaining in soil (% of the total 14C added).
CREMglycine: glycine-derived 14C remaining in soil (% of the total 14C added).
CREMglucosamine: glucosamine-derived 14C remaining in soil (% of the total 14C added).
CREMmalicacid: malic acid-derived 14C remaining in soil (% of the total 14C added).
Sheet2
Summary, by fertilizer treatment and replicate, of the derived response variables for each 14C-labeled substrate (Figs. 3 and 4; Supplementary Fig. S2).
Fert: granular N fertilizer treatment (see list above).
HLglucose: total substrate half-life (t½,total) of glucose (d).
HLglycine: total substrate half-life (t½,total) of glycine (d).
HLglucosamine: total substrate half-life (t½,total) of glucosamine (d).
HLmalicacid: total substrate half-life (t½,total) of malic acid (d).
CUEglucose: apparent microbial C use efficiency (aCUE) for glucose (dimensionless, 0–1).
CUEglycine: apparent microbial C use efficiency (aCUE) for glycine (dimensionless, 0–1).
CUEglucosamine: apparent microbial C use efficiency (aCUE) for glucosamine (dimensionless, 0–1).
CUEmalicacid: apparent microbial C use efficiency (aCUE) for malic acid (dimensionless, 0–1).
K2SO4glucose: glucose-derived 14C recovered in the 0.5 M K2SO4 extract at the end of the incubation (% of the total 14C added).
K2SO4glycine: glycine-derived 14C recovered in the 0.5 M K2SO4 extract at the end of the incubation (% of the total 14C added).
K2SO4glucosamine: glucosamine-derived 14C recovered in the 0.5 M K2SO4 extract at the end of the incubation (% of the total 14C added).
K2SO4malicacid: malic acid-derived 14C recovered in the 0.5 M K2SO4 extract at the end of the incubation (% of the total 14C added).
Sheet3
Long-format dataset combining each fertilizer treatment with each 14C-labeled substrate, including the fitted model parameters and end-of-incubation soil measurements (Supplementary Table S1; Figs. 5 and 6; statistical analyses).
Fert: granular N fertilizer treatment (see list above).
Sub: 14C-labeled substrate (Glucose; Glycine; Glucosamine; and Malic acid).
Crem: substrate-derived 14C remaining in soil at the end of the 20-d incubation (% of the total 14C added).
Hl: total substrate half-life (t½,total) (d).
CUE: apparent microbial C use efficiency (aCUE) (dimensionless, 0–1).
K2SO4: substrate-derived 14C recovered in the 0.5 M K2SO4 extract at the end of the incubation (% of the total 14C added).
pH: soil pH measured at the end of the incubation in a 1:2.5 (w/v) soil:water suspension.
Nit: soil nitrate-N content (mg/kg).
Ammo: soil ammonium-N content (mg/kg).
a1: fraction of applied 14C partitioned to the fast-turnover (catabolic) pool (Ccatab) (% of the total 14C added).
k1: first-order rate constant of the fast (catabolic) pool (kcatab) (1/d).
a2: fraction of applied 14C partitioned to the slow-turnover (anabolic) pool (Canab) (% of the total 14C added).
k2: first-order rate constant of the slow (anabolic) pool (kanab) (1/d).
R code
Attached is the R script used in the statistical analysis of the experimental data.
Publication Date: 2026-06-14