长期垄作稻田腐殖质稳定碳同位素丰度(δ13C)分布特征

研究了四川盆地丘陵区连续16年垄（宽垄）作稻田土壤稳定碳库腐殖质组分的稳定碳同位素(δ¹³C)分布特征.结果表明： 稻田土壤有机碳含量为宽垄作＞垄作＞水旱轮作.腐殖质碳以胡敏素为主，占土壤碳含量的21%～30%，提取碳以胡敏酸为主，分别占土壤有机碳和腐殖质的17%～21%和38%～65%.土壤有机碳的δ¹³C值介于-27.9‰～-25.6‰，20～40 cm和0～5 cm土壤有机碳δ¹³C值之差约为1.9‰.土壤胡敏酸δ¹³C值比土壤有机碳低1‰～2‰，更接近于油菜和水稻秸秆及根系的δ¹³C值.土壤富里酸δ¹³C值分别较土壤有机碳和胡敏酸高2‰和4‰.耕作层和犁底层胡敏素δ¹³C值分别介于-23.7‰～-24.9‰和-22.6‰～-24.2‰，δ¹³C值的变化反映了耕层中腐殖质的新老混合现象.各有机组分δ¹³C值递减顺序为：胡敏素＞富里酸＞土壤有机碳＞稻草（油菜）残体＞胡敏酸.长期水稻种植有利于增加土壤有机碳含量，同时，耕作方式影响土壤腐殖质δ¹³C在耕作层和犁底层中的分布格局.

Distribution characteristics of soil humus fractions stable carbon isotope natural abundance (δ13C) in paddy field under long-term ridge culture.

A 16-year field experiment was conducted in a ridge culture paddy field in the hilly region of Sichuan Basin, aimed to investigate the distribution characteristics of stable carbon isotope natural abundance (δ¹³C) in soil humus fractions. The soil organic carbon (SOC) content in the paddy field under different cultivation modes ranked in the order of wide ridge culture ＞ ridge culture ＞ paddy and upland rotation. In soil humus substances (HS), humin (HU) was the main composition, occupying 21%-30% of the total SOC. In the extracted soil carbon, humic acid (HA) dominated, occupying 17%-21% of SOC and 38%-65% of HS. The δ¹³C value of SOC ranged from -27.9‰ to -25.6‰, and the difference of the δ¹³C value between 0-5 cm and 20-40 cm soil layers was about 1.9‰. The δ¹³C value of HA under different cultivation modes was 1‰-2‰ lower than that of SOC, and more approached to the δ¹³C value of rapeseed and rice residues. As for fulvic acid (FA), its δ¹³C value was about 2‰ and 4‰ higher than that of SOC and HA, respectively. The δ¹³C value of HU in plough layer (0-20 cm) and plow layer (20-40 cm) ranged from -23.7‰--24.9‰ and -22.6‰--24.2‰, respectively, reflecting the admixture of young and old HS. The δ¹³C value in various organic carbon fractions was HU＞FA＞SOC＞rapeseed and rice residues＞HA. Long-term rice planting benefited the increase of SOC content, and cultivation mode played an important role in affecting the distribution patterns of soil humus δ¹³C in plough layer and plow layer.