改种玉米连续3年后稻田土壤有机碳分布和^(13)C自然丰度变化  

TOPSOIL ORGANIC CARBON POOL AND ^(13)C NATURAL ABUNDANCE CHANGES FROM A PADDY AFTER 3 YEARS CORN CULTIVATION

作　　者：李志鹏[1] 潘根兴[1] 张旭辉[1] 

机构地区：[1]南京农业大学农业资源与生态环境研究所,南京210095

出　　处：《土壤学报》2007年第2期244-251,共8页Acta Pedologica Sinica

基　　金：国家自然科学基金重大项目(40231016)资助

摘　　要：耕作制更替下土壤有机碳的变化是阐明土地利用变化下土壤碳循环改变及其全球变化效应的重要方面。本研究选择了太湖地区毗邻的一块长期稻油轮作的稻田和一块稻田改种玉米3年的旱田,采集其剖面不同深度的土壤样品,分别测定全土和分离的土壤团聚体颗粒组中总有机碳(TOC)、土壤溶解有机碳(DOC)和微生物生物量碳(SMBC),并对选择性样本测定了有机质的δ13C值,分析改种玉米后水稻土有机碳储量及其同位素组成的变化。结果表明,改种玉米3年后,耕层土壤TOC明显下降,而DOC和SMBC都有增加的趋势;改种玉米后2~0.2 mm粗团聚体颗粒组的TOC含量降低,而其他团聚体颗粒组TOC无显著变化。玉米地表层土壤(0~15 cm)原土及各粒级团聚体的δ13C值均明显高于原稻田。改种玉米后进入水稻土中的源于玉米的新碳绝大部分集中在0~20 cm土层,且主要富集在粗团聚体颗粒组中。计算表明,粗团聚体颗粒组中有机碳更新周期明显较短。水田转变成旱地后,耕层土壤有机碳分解加速,碳储量快速减少。这说明水稻土中物理保护的有机碳可能因耕作改变下团聚体破坏而快速分解。Dynamics of soil organic carbon （SOC） under cultivation shifts has been in debate in soil C cycling studies. In this study, 2 adjacent fields of Wunitu paddy soil （one with rice-rape rotation and another with double corn for 3 years after rice and rape） were chosen to study the SOC dynamics. Both topsoil and whole profile was sampled. C pools of total organic carbon （TOC）, dissolved organic carbon （DOC） and soil microbial biomass carbon （SMBC） was determined for bulk soils from the two fields respectively. Soil particle size factions （PSFs） were separated using low energy ultrasonic dispersion and the TOC of them determined using CNS analyzer. Selected samples of bulk soil and PSFs from both rice and corn fields were used for ^13 C natural abundance measurement with Finnigan MAT251 mass spectrometer. TOC of topsoil decreased drastically after 3 years of continuous corn cultivation although marked increase of DOC and SMBC was observed in the corn field. This was in coincident with the decrease of SOC in the sand PSF despite no remarkable changes in the other PSFs from the corn filed. Significantly heavier carbon could be detected either in bulk samples or in a single PSF from the corn field than from rice field. Calculation using the data of δ^13C‰（PDB） indicated that 80% of young carbon inputted by corn residues was allocated in the topsoil of 0- 20cm and mainly found in the coarse PSF as well as in the pools of DOC and SMBC. The calculated short mean residence time （MRT） found with bulk sample and coarse fraction from the corn field in contrast to from the rice field suggested a coupling of rapid TOC decrease and fast aggregate turnover in the cornfield. Therefore, the TOC decline in the corn field was attributed to the disruption of aggregates that, in turn, released labile carbon from physical protection. Drastic decline of indigenous SOC at C 4 t hm^- 2 a^- 1 in the paddy soil after corn cultivation was in disagreement with the findings reported for American and European dry

关 键 词：^13C 更新速率 水稻土 碳库 团聚体 总有机碳 

分 类 号：S153.6[农业科学—土壤学]