Effects of Understory Vegetation Conversion on Soil Greenhouse Gas Emissions and Soil C and N Pools in Chinese Hickory Plantation Forests

By inergency On Mar 19, 2024

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Figure 1.
(a,b) Schematic of the location of the test sample plots. (c) Distribution map of the test sample plots; (d) size and spacing distance of each sample plot; (e) Chinese hickory test subjects in the test sample plots; (f) field soil GHG collection tool.

Figure 2.
Effects of different understory vegetation modifications on (a) CO₂, (b) N₂O, and (c) CH₄ uptake from Chinese hickory plantation soils. Standard deviations are indicated by error lines.

Figure 3.
Effects of different understory vegetation modifications on annual cumulative (a) CO₂ emissions, (b) N₂O emissions, (c) CH₄ uptake, and (d) total soil GHG emissions from Chinese hickory plantation soils. Standard deviations are indicated by error lines. The letters a, b, c, and d are the distinctive symbols of annual emissions or annual absorption.

Figure 4.
Effects of different understory management on (a) 5 cm temperature, (b) soil moisture, and (c) pH of Chinese hickory plantation soils. Standard deviations are indicated by error lines.

Figure 5.
Effects of different understory management on (a) WSOC and (b) MBC content of Chinese hickory plantation soils. Standard deviations are indicated by error lines.

Figure 6.
Effects of different understory management conditions on (a) NO₃⁻–N, (b) NH₄⁺–N, (c) WSON, and (d) MBN contents of Chinese hickory plantation soils. Standard deviations are indicated by error lines.

Figure 7.
Structural equation modelling of soil WSOC, MBC, NO₃⁻–N, NH₄⁺–N, WSON, and MBN concentrations affecting (a) CO₂, (b) NO₂, and (c) CH₄ fluxes after forest understory vegetation conversion. Numbers next to arrows indicate correlation coefficients and significance. R² indicates the rate of model explanation, GFI is the goodness-of-fit index, NFI is the normative fit index, and CFI is the comparative fit index.

Table 1.
Weather and environmental conditions in Lin’an, Hangzhou, Zhejiang, China, from July 2022 to June 2023: average monthly temperature (°C), monthly precipitation (mm).

Weather Environment	2022						2023
Weather Environment	Jul.	Aug.	Spe.	Oct.	Nov.	Dec	Jan.	Feb.	Mar.	Apr.	May.	Jun.
Average monthly temperature (°C)	30.5	31	24	17.5	15	−4.5	−5.5	7	12.5	17	21.5	25.5
Precipitation (mm)	68.2	20	25.8	47.4	27.3	42.9	55.5	63.3	50.4	137.5	121.1	204.6

Table 2.
Stepwise regression analysis model between CO₂ flux (mg m⁻² h⁻¹) and soil temperature (T, °C), soil moisture (M, g kg⁻¹), water-soluble organic C (WSOC, mg kg⁻¹), microbial biomass C (MBC, mg kg⁻¹), NO₃⁻–N, and NH₄⁺–N under the UM1, UM2, UM3, UM4, and CK treatments. N, water-soluble organic N (WSON, mg kg⁻¹), and microbial biomass N (MBN, mg kg⁻¹) were modelled in a stepwise regression analysis. Coefficients in the model are standardized. R² indicates the rate of model explanation.

GHG	Treatment	Model	df	R²	p
CO₂	UM1	Y = 0.745T	48	0.545	**
		Y = 0.826T − 0.222WSON	48	0.579	**
		Y = 1.018T − 0.278WSON − 273WSOC	48	0.615	**
		Y = 1.251T − 0.392WSON − 426WSOC + 0.282NH₄⁺–N	48	0.662	**
	UM2	Y = 0.857T	48	0.729	**
	UM2	Y = 1.044T − 0.303MBN	48	0.783	**
	UM3	Y = 0.878T	48	0.766	**
		Y = 1.054T − 0.246MBC	48	0.792	**
		Y = 1.223T − 0.372MBC − 0.234WSON	48	0.831	**
		Y = 1.229T − 0.409MBC − 0.179WSON + 0.136pH	48	0.842	**
	UM4	Y = 0.884T	48	0.777	**
		Y = 1.019T − 0.234NO₃⁻–N	48	0.811	**
		Y = 1.143T − 0.375NO₃⁻–N + 0.293NH₄⁺–N	48	0.882	**
	CK	Y = 0.881T	48	0.772	**
		Y = 0.701T + 0.315WSOC	48	0.837	**
		Y = 0.723T + 0.358WSOC − 0.224WSON	48	0.883	**

Table 3.
Stepwise regression analysis model between N₂O flux (μg m⁻² h⁻¹) and soil temperature (T, °C), soil moisture (M, g kg⁻¹), water-soluble organic C (WSOC, mg kg⁻¹), microbial biomass C (MBC, mg kg⁻¹), NO₃⁻–N, and NH₄⁺–N in the UM1, UM2, UM3, UM4, and CK treatments. N, water-soluble organic N (WSON, mg kg⁻¹), and microbial biomass N (MBN, mg kg⁻¹) were modelled in a stepwise regression analysis. Coefficients in the model are standardized. R² indicates the rate of model explanation.

GHG	Treatment	Model	df	R²	p
N₂O	UM1	Y = 0.712MBC	48	0.496	**
		Y = 0.807MBC − 0.229NO₃⁻–N	48	0.531	**
		Y = 0.456MBC − 0.305NO₃⁻–N + 0.461T	48	0.587	**
		Y = 0.370MBC − 0.409NO₃⁻–N + 0.688T + 0.315NH₄⁺–N	48	0.661	**
		Y = 0.598MBC − 0.515NO₃⁻–N + 0.802T + 0.422NH₄⁺–N − 0.345WSOC	48	0.697	**
	UM2	Y = 0.729T	48	0.521	**
		Y = 0.720T + 0.334NH₄⁺–N	48	0.627	**
		Y = 0.824T + 0.458NH₄⁺–N − 0.333WSON	48	0.708	**
	UM3	Y = 0.712T	48	0.496	**
		Y = 0.785T + 0.388M	48	0.635	**
		Y = 0.755T + 0.424M + 0.237NH₄⁺–N	48	0.685	**
		Y = 0.805T + 0.298M + 0.230NH₄⁺–N − 0.215WSON	48	0.706	**
		Y = 1.108T + 0.302M + 0.147NH₄⁺–N − 0.313WSON − 0.358MBC	48	0.750	**
	UM4	Y = 0.718T	48	0.505	**
		Y = 0.754T + 0.397M	48	0.657	**
		Y = 0.788T + 0.441M + 0.206NH₄⁺–N	48	0.692	**
	CK	Y = 0.685WSOC	48	0.457	**
		Y = 0.441WSOC + 0.427T	48	0.573	**
		Y = 0.503WSOC + 0.458T − 0.324WSON	48	0.668	**
		Y = 0.551WSOC + 0.715T − 0.369WSON−0.377MBN	48	0.730	**
		Y = 0.436WSOC + 0.777T − 0.329WSON − 0.349MBN + 0.194M	48	0.756	**

Table 4.
Stepwise regression analysis model between CH₄ flux (μg m⁻² h⁻¹) and soil temperature (T, °C), soil moisture (M, g kg⁻¹), water-soluble organic C (WSOC, mg kg⁻¹), microbial biomass C (MBC, mg kg⁻¹), NO₃⁻–N, and NH4+-H in the UM1, UM2, UM3, UM4, and CK treatments. N, water-soluble organic N (WSON, mg kg⁻¹), and microbial biomass N (MBN, mg kg⁻¹) were modelled in a stepwise regression analysis. Coefficients in the model are standardized. R² indicates the rate of model explanation.

GHG	Treatment	Model	df	R²	p
CH₄	UM1	Y = 0.665MBC	48	0.430	**
		Y = 0.805MBC − 0.339NO₃⁻–N	48	0.518	**
		Y = 0.602MBC − 0.360NO₃⁻–N + 0.362MBN	48	0.599	**
	UM2	Y = 0.706MBC	48	0.488	**
		Y = 0.468MBC + 0.422MBN	48	0.603	**
		Y = 0.479MBC + 0.542MBN − 0.263NO₃⁻–N	48	0.651	**
		Y = 0.472MBC + 0.577MBN − 0.254NO₃⁻–N − 0.176M	48	0.675	**
		Y = 0.489MBC + 0.656MBN − 0.411NO₃⁻–N − 0.237M + 0.249NH₄⁺–N	48	0.711	**
	UM3	Y = 0.681MBC	48	0.466	**
		Y = 0.685MBC − 0.278WSON	48	0.535	**
		Y = 0.250MBC − 0.492WSON + 0.603T	48	0.666	**
	UM4	Y = 0.730MBC	48	0.523	**
		Y = 0.663MBC + 0.279M	48	0.589	**
		Y = 0.377MBC + 0.314M + 0.354MBN	48	0.630	**
	CK	Y = 0.665T	48	0.431	**
		Y = 0.792T + 0.296NH₄⁺–N	48	0.493	**
		Y= 0.520T + 0.346NH₄⁺–N + 0.429MBC	48	0.583	**
		Y = 0.805T + 0.486NH₄⁺–N + 0.397MBC − 0.358WSOC	48	0.649	**
		Y = 0.900T + 0.562NH₄⁺–N + 0.255MBC − 0.454WSOC + 0.308PH	48	0.719	**

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