Abstract
The impact of crop straw-derived artificial humic acid (A-HA) on plant growth and its relationship with extraction process parameters remain uncertain. This study involved the preparation of six A-HA samples from rice straw using hydrothermal reactions, KOH extraction solutions at three different concentrations, and two pH endpoints for A-HA precipitation. The effects and physiological mechanism of these A-HAs on maize biomass and nitrogen (N) uptake were investigated via hydroponics experiments. In addition, the relationships between A-HA biological activity and its structure and composition were explored. The findings revealed that A-HA1–1 (one of the six A-HAs), at concentrations of 2.5–10 mg/L, significantly enhanced maize biomass by 13.8 %–24.1 % and N uptake by 13.8 %–25.0 %. This increase was attributed to increased root plasma membrane H + -ATPase activity and enhanced nitrate ion influx into root cells. A-HA biological activity in promoting maize growth decreased with a rise in extraction solution alkali concentration from 1 % to 10 %, primarily due to a reduction in the proportion of low-molecular-weight components in A-HA. Moreover, A-HA precipitated at pH 3 exhibited superior stimulation of maize growth and N uptake compared with that at pH 1, owing to higher contents of O-alkyl-C, O-substituted aromatics-C, carboxylic-C, and amide-C. These findings demonstrate that crop straw could be used to develop plant growth stimulants, which will provide valuable insights into the sustainable and efficient utilization of agricultural by-products. However, meticulous control of extraction alkali concentration and A-HA precipitation pH is essential. • Preparation methods of straw-derived artificial humic acid (A-HA) were compared. • Too high a concentration of alkali extract inhibits A-HA to stimulate maize growth. • Lowering the precipitation endpoint pH decreases the biological activity of A-HA. • 1 % alkali solution and precipitated at pH 3 is optimal for A-HA bio-stimulation. • A-HA improved plasma membrane H + -ATPase activity and NO 3 - inflows into root cells.
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Claims 11
Claim · model-written summary
A-HA1–1 at 2.5–10 mg/L significantly increased maize biomass by 13.8 %–24.1 %.
- Treatment
- A-HA1–1 (one of the six A-HAs), at concentrations of 2.5–10 mg/Le0
- Outcome
- maize biomasse0
- Direction
- enhancede0
- Value
- 13.8 %–24.1 %e0
Zea maysNot reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“A-HA1–1 (one of the six A-HAs), at concentrations of 2.5–10 mg/L, significantly enhanced maize biomass by 13.8 %–24.1 % and N uptake by 13.8 %–25.0 %”
Claim · model-written summary
A-HA1–1 at 2.5–10 mg/L significantly increased maize N uptake by 13.8 %–25.0 %.
- Treatment
- A-HA1–1 (one of the six A-HAs), at concentrations of 2.5–10 mg/Le0
- Outcome
- N uptakee0
- Direction
- enhancede0
- Value
- 13.8 %–25.0 %e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“A-HA1–1 (one of the six A-HAs), at concentrations of 2.5–10 mg/L, significantly enhanced maize biomass by 13.8 %–24.1 % and N uptake by 13.8 %–25.0 %”
Claim · model-written summary
Increased root plasma membrane H + -ATPase activity was attributed as contributing to maize growth and N uptake increases.
- Organ / stage
- roote0
- Gene
- H + -ATPasee0
- Outcome
- increased root plasma membrane H + -ATPase activitye0
- Direction
- increasede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“This increase was attributed to increased root plasma membrane H + -ATPase activity and enhanced nitrate ion influx into root cells”
t0“maize growth and nitrogen uptake”
Claim · model-written summary
Enhanced nitrate ion influx into root cells was attributed as contributing to maize growth and N uptake increases.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“This increase was attributed to increased root plasma membrane H + -ATPase activity and enhanced nitrate ion influx into root cells”
t0“maize growth and nitrogen uptake”
Claim · model-written summary
A-HA promotion of maize growth decreased as extraction alkali concentration rose from 1 % to 10 %.
- Treatment
- extraction solution alkali concentration from 1 % to 10 %e0
- Outcome
- A-HA biological activity in promoting maize growthe0
- Direction
- decreasede0
- Value
- 1 % to 10 %e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“A-HA biological activity in promoting maize growth decreased with a rise in extraction solution alkali concentration from 1 % to 10 %”
Claim · model-written summary
The reduced proportion of low-molecular-weight components was attributed as the main reason for lower A-HA activity.
- Outcome
- reduction in the proportion of low-molecular-weight components in A-HAe0
- Qualifier
- low-molecular-weight componentse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“primarily due to a reduction in the proportion of low-molecular-weight components in A-HA”
t0“maize growth and nitrogen uptake”
Claim · model-written summary
A-HA precipitated at pH 3 stimulated maize growth more than A-HA precipitated at pH 1.
- Treatment
- A-HA precipitated at pH 3e0
- Outcome
- maize growthe0
- Direction
- superiore0
- Comparator
- that at pH 1e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“A-HA precipitated at pH 3 exhibited superior stimulation of maize growth and N uptake compared with that at pH 1”
Claim · model-written summary
A-HA precipitated at pH 3 stimulated maize N uptake more than A-HA precipitated at pH 1.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“A-HA precipitated at pH 3 exhibited superior stimulation of maize growth and N uptake compared with that at pH 1”
Claim · model-written summary
Higher contents of O-alkyl-C, O-substituted aromatics-C, carboxylic-C, and amide-C were attributed as the reason for greater activity of pH 3 precipitate.
- Outcome
- higher contents of O-alkyl-C, O-substituted aromatics-C, carboxylic-C, and amide-Ce0
- Qualifier
- higher contentse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“owing to higher contents of O-alkyl-C, O-substituted aromatics-C, carboxylic-C, and amide-C”
t0“maize growth and nitrogen uptake”
Claim · model-written summary
The authors recommend controlling alkali concentration and precipitation pH when preparing A-HA for maize stimulation.
- Outcome
- meticulous control of extraction alkali concentration and A-HA precipitation pHe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“meticulous control of extraction alkali concentration and A-HA precipitation pH is essential”
t0“maize growth and nitrogen uptake”
Claim · model-written summary
A-HA made with 1 % alkali and precipitated at pH 3 was described as optimal for stimulation.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“1 % alkali solution and precipitated at pH 3 is optimal for A-HA bio-stimulation”
t0“maize growth and nitrogen uptake”
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