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Description
INTRODUCTION
The coastal wetland of Yellow River Delta (YRD) is one of the largest, most integrated and youngest wetlands in the warm temperate zone of China, and the YRD has the most reserve land resources in the east coast. While, soil salinization in this region induced and compounded problems like low fertility, low microbial activity, and poor soil structure, seriously affecting ecological balance and agricultural development. In consequence, the remediation and comprehensive utilization of coastal saline–alkali soils in this region are of great significance to solve the shortage of agricultural land and promote the development of ecosystem restoration and agricultural economy. At present, a large number of scholars have studied the effects of different amendments on the remediation of saline–alkali soils in the YRD, but few studies have provided technical guidance on the mechanism for the selection of effective amendments in this region.
MATERIALS AND METHODS
In this work, furfural residue (particulate; C/N: 51.87; O-alkyl C + di-O-alkyl C: 42.35%, aromatic C: 40.89%) and black liquor (dissolved; C/N: 3.11; O-alkyl C + di-O-alkyl C: 32.20%, aromatic C: 28.32%) were tested to examine their effects on chemical properties, water-stable aggregate fractions, chemical compositions of solid-state soil organic matter (SOM), gloaming-related soil protein (GRSP) contents and microbial communities of coastal saline–alkali soil under a 400-day incubation experiment. Furthermore, organic amendments mixed with mineral amendment (4:1) were employed to explore the interactions between organic and inorganic amendments. And we selected the days (R(0.25) max day) when the water-stable macroaggregate fraction (>0.25 mm, R0.25) of each treatment was the highest according to the results of water-stable aggregate fractions. Then, the solid-state SOM chemical compositions (13C NMR) and quantified soil microbial communities on the R(0.25) max and 400th days were measured. Finally, we linked these parameters to explore how organic amendment qualities and inorganic amendment addition affected the formation and stability of aggregates.
RESULTS
1) Furfural residue reduced the soil pH and increased SOC, TN, C/N, and DOC; black liquor reduced the soil pH and C/N, but increased EC, water-soluble Na+, SOC, TN, and DOC; and the addition of mineral amendment limited these effects on soil properties.
2) Furfural residue improved the water-stability of aggregates while black liquor had a slight negative effect, and mineral amendment further increased the fraction of water-stable microaggregate; Furfural residue and black liquor significantly affected the increase of GRSP, while mineral amendment slightly reduced the effect of furfural residue.
3) The chemical composition of solid-state SOM changed greatly with the input and decomposition of furfural residue, compared with black liquor.
4) Furfural residue and black liquor significantly changed the compositions of soil bacterial and fungal communities, while mineral amendment obviously influenced the effects of black liquor more than those of furfural residue; Furfural residue reduced the alpha diversities of fungi while mineral amendment limited these effects, and black liquor reduced the bacterial alpha diversities.
5) The Pearson correlation analysis showed that water-stability of aggregates were positively correlated with soil C/N and GRSP, and negatively correlated with EC, Na+, TN, and DOC. Furfural residue had obvious impacts on soil C/N, water-stability of aggregates, and GRSP, but black liquor obviously affected soil EC, Na+, TN, and DOC.
CONCLUSION
Our findings demonstrate that organic amendment qualities and inorganic amendment addition could significantly influence the formation and stabilization of aggregates in coastal saline–alkali soil. High soil C/N and the relative abundance of effective chemical compositions (O-alkyl C, di-O-alkyl C, and aromatic C) of solid-state SOM have stronger and longer effects on the water stability of aggregates by increasing the relative abundance of keystone taxa (such as orders Rhizobiales and Sordariales) and GRSP contents in soils. The qualities (primary form, C/N, and chemical composition) of organic amendment are the key factors in affecting the form, C/N, and chemical composition of SOM. In addition, O-alkyl C and di-O-alkyl C fractions of solid-state SOM promote the rapid and intense formation of macroaggregates, while aromatic C make the aggregate stability more durable. We also found that abundant N inputs have no positive or even negative influence on the formation and stability of aggregates. Inorganic amendment addition further increased the fractions of microaggregates, while having negative effects on microbial activities.
| Keywords | chemical composition; organic amendment remediation of saline–alkali soil; solid-state 13C CPMAS NMR; water-stable aggregate |
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