Effects of Dryland-to-paddy Conversion on Soil Microbial Necromass Carbon Accumulation in Karst Area of Southern Guizhou

doi:10.11924/j.issn.1000-6850.casb2025-0164

Abstract

Abstract:

Microbial necromass carbon (MNC) is a crucial component of soil organic carbon (SOC). The conversion of large-scale dryland to paddy fields has been recently implemented to improve farmland quality and security. However, the accumulation patterns and underlying mechanisms of MNC following such conversions are still unclear. In this study, the paddy field reconstruction project in Pingtang County, Guizhou Province was taken as the research object. The changes of soil physicochemical properties, organic carbon content, microbial biomass carbon and microbial necromass carbon before and after the convertion were systematically analyzed, and the effect of paddy field reconstruction on the accumulation of microbial necromass carbon was discussed. Through analysis of soil physicochemical properties, SOC, total nitrogen (TN), total phosphorus (TP), available phosphorus (AP), alkali-hydrolyzable nitrogen (AN), available potassium (AK), microbial biomass carbon (MBC) and MNC, we elucidated conversion-induced impacts on MNC sequestration. The results showed dryland-to-paddy conversion significantly reduced the contents of TN, TP, AP, AN and AK by 33.1%, 28.3%, 70.4%, 41.0% and 65.1%, respectively. After dryland to paddy fields conversion, SOC, MBC and MNC significantly decreased, with reductions of 39.3%, 29.8%, and 25.6%, respectively. However, the relative contribution of bacterial necromass carbon (BNC) to SOC increased significantly by 50%. Correlation analysis and random forest modeling identified AP, MBC, AN, TN, pH and SOC as key drivers regulating MNC dynamics. Partial least squares structural equation modeling (PLS-SEM) revealed that dryland-to-paddy conversion primarily affected fungal and bacterial necromass carbon content through modifications in soil physicochemical properties, SOC, and MBC, thereby controlling MNC accumulation. Short-term observations indicated that dryland-to-paddy conversion significantly reduced SOC, MBC, MNC and several soil physicochemical properties. In the post-conversion management phase, it is necessary to increase soil nutrient inputs to promote the accumulation of stable organic carbon. Long-term monitoring is essential to generate robust scientific data for guiding sustainable land consolidation and improving agricultural management practices.

Key words: dryland-to-paddy conversion, soil organic carbon, microbial necromass carbon, influence mechanism

CAI Yu, XIAO Jiujun, LIAO Xiaofeng, DONG Yanyan, PAN Bojuan, XIE Yuangui. Effects of Dryland-to-paddy Conversion on Soil Microbial Necromass Carbon Accumulation in Karst Area of Southern Guizhou[J]. Chinese Agricultural Science Bulletin, 2025, 41(27): 85-93.

Figures/Tables 7

References 32

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项目区	土地利用类型	坡度/°	坡向/°	平均海拔/m	田块平均面积/m²	土壤类型	植被类型
摆图	旱地	15	西	1049	731.45	黄壤	玉米
	水田	15	西	1038	526.9	黄壤	水稻
	未利用地	20	西	1030	413.32	黄壤	荒草
李山	旱地	5	西	963	522.56	黄棕壤	玉米
	水田	5	西	967	807.07	黄棕壤	水稻
	未利用地	5	西	969	398.08	黄棕壤	荒草
黄平	旱地	10	东	861	634.41	黄壤	玉米
	水田	10	东	860	766.81	黄壤	水稻
	未利用地	10	东	873	342.26	黄壤	荒草

项目区	土地利用类型	坡度/°	坡向/°	平均海拔/m	田块平均面积/m²	土壤类型	植被类型
摆图	旱地	15	西	1049	731.45	黄壤	玉米
	水田	15	西	1038	526.9	黄壤	水稻
	未利用地	20	西	1030	413.32	黄壤	荒草
李山	旱地	5	西	963	522.56	黄棕壤	玉米
	水田	5	西	967	807.07	黄棕壤	水稻
	未利用地	5	西	969	398.08	黄棕壤	荒草
黄平	旱地	10	东	861	634.41	黄壤	玉米
	水田	10	东	860	766.81	黄壤	水稻
	未利用地	10	东	873	342.26	黄壤	荒草

指标	旱地	水田	CK
pH	5.71±0.40 a	5.75±0.35 a	6.02±0.51 a
容重BD/(g/cm³)	1.79±0.06 a	1.86±0.03 a	1.84±0.06 a
全氮TN/(g/kg)	1.27±0.12 a	0.85±0.10 b	0.74±0.11 b
全磷TP/(g/kg)	0.53±0.04 a	0.38±0.04 b	0.35±0.02 b
全钾TK/(g/kg)	7.27±0.79 a	7.72±0.82 a	9.71±1.00 a
有效磷AP/(mg/kg)	20.17±0.78 a	5.97±0.26 b	4.49±0.52 c
碱解氮AN/(mg/kg)	101.49±8.34 a	59.91±6.32 b	41.72±8.25 b
速效钾AK/(mg/kg)	169.14±26.52 a	59.02±12.57 b	81.08±12.09 b
有机碳SOC/(g/kg)	13.86±1.16 a	8.41±0.84 b	7.44±1.38 b
微生物量碳MBC/(mg/kg)	904.04±35.98 a	635.12±27.47 b	339.46±32.61 c

指标	旱地	水田	CK
pH	5.71±0.40 a	5.75±0.35 a	6.02±0.51 a
容重BD/(g/cm³)	1.79±0.06 a	1.86±0.03 a	1.84±0.06 a
全氮TN/(g/kg)	1.27±0.12 a	0.85±0.10 b	0.74±0.11 b
全磷TP/(g/kg)	0.53±0.04 a	0.38±0.04 b	0.35±0.02 b
全钾TK/(g/kg)	7.27±0.79 a	7.72±0.82 a	9.71±1.00 a
有效磷AP/(mg/kg)	20.17±0.78 a	5.97±0.26 b	4.49±0.52 c
碱解氮AN/(mg/kg)	101.49±8.34 a	59.91±6.32 b	41.72±8.25 b
速效钾AK/(mg/kg)	169.14±26.52 a	59.02±12.57 b	81.08±12.09 b
有机碳SOC/(g/kg)	13.86±1.16 a	8.41±0.84 b	7.44±1.38 b
微生物量碳MBC/(mg/kg)	904.04±35.98 a	635.12±27.47 b	339.46±32.61 c