李新悦(1997—),女,博士研究生,主要研究从事土壤肥力和质量可持续研究。E-mail:
土壤团聚体有机碳和胞外酶对于改善土壤结构和提高土壤碳固存能力至关重要,且易受农艺生产措施的影响。为探讨秸秆还田下土壤有机碳组分及胞外酶活性变化,开展了35年水稻-小麦轮作试验。本试验设置了无肥区(CK)、化肥区(NPK)和秸秆还田+化肥区(NPKS),研究了不同农艺措施对土壤团聚体有机碳(SOC)及其活性组分(可溶性有机碳(DOC)、易氧化有机碳(EOC)、微生物生物量碳(MBC))含量与碳循环相关胞外酶(β-1,4-葡萄糖苷酶(BG)、β-1,4-木糖苷酶(BX)、β-D-纤维二糖水解酶(CBH))活性的影响。结果发现,大于0.25 mm团聚体中SOC、DOC和MBC含量显著高于小于0.25 mm粒级,且均以NPKS处理的效果最优,促进了土壤大团聚体有机碳组分更新。各粒级团聚体中MBC/SOC和DOC/SOC比值相对稳定,这表明MBC和DOC与SOC的动态变化趋势较为一致,可作为评价土壤有机碳的敏感指标。2~0.25 mm粒级是团聚体胞外酶主要载体,均以NPKS处理活性最高;但大于2 mm团聚体酶活性在不同农艺措施之间差异不显著。土壤团聚体中有机碳组分与胞外酶表现为互相促进的关系,其中SOC、DOC和MBC分配差异的主要影响因子为CBH,次要影响因子是BG;而EOC仅受到CBH的正向影响。CBH和BG可促进土壤有机碳周转,且在2~0.25 mm大团聚体中互促作用更剧烈。综上,长期秸秆还田配施化肥不仅有利于提升大团聚体碳的更新和周转速率,还提高了SOC含量,是稻田土壤可持续固碳的重要农艺途径。
Soil aggregate organic carbon and extracellular enzymes play an important role in improving soil structure and carbon sequestration, which are easily affected by agronomic management practices. In order to study the effects of long-term straw returning combined with chemical fertilization on organic carbon components and extracellular enzymes in soil aggregates, a 35-year field positioning experiment was carried out.
The field experiment was designed to have three treatments in a rice-wheat rotation system: no chemical fertilizer (CK), chemical fertilizer only (NPK), and straw plus chemical fertilizer (NPKS). The contents of soil organic carbon (SOC) and its labile components (dissolved organic carbon (DOC), easily oxidizable organic carbon (EOC) and microbial biomass carbon (MBC)) in soil aggregate were analyzed, as well as the activities of extracellular enzymes related to carbon cycle (β-1, 4-Glucosidase (BG), β-1, 4-Xylosidase (BX) and β-D-Cellobiohydrolase (CBH)).
The contents of SOC, DOC and MBC in > 0.25 mm aggregates were significantly higher than those in < 0.25 mm aggregates, and their contents of NPKS treatment were the highest. This showed that NPKS promoted soil macro-aggregates organic carbon regeneration. The values of MBC/SOC and DOC/SOC in each particle size aggregate were relatively stable, which indicated that dynamic change trends of MBC and DOC were consistent with that of SOC. Thus, MBC and DOC could be used as sensitive indexes to evaluate soil organic carbon. The 2-0.25 mm aggregates were the main carriers of extracellular enzymes, and their activities in NPKS treatment were the highest. However, the enzymes activities in > 2 mm aggregates had no significant difference among treatments. The soil organic carbon components and extracellular enzymes in soil aggregates promoted each other, in which the contents of SOC, DOC and MBC in aggregates were mainly affected by CBH, followed by BG; while EOC was only positively affected by CBH. These two extracellular enzymes (CBH and BG) could promote soil organic carbon turnover and the interaction was enhanced in 2-0.25 mm aggregate.
Long-term application of straw returning combined with chemical fertilizer could increase organic carbon regeneration and turnover rate, and increase soil organic carbon content, which is an important agronomic way for sustainable carbon sequestration in paddy soil.
土壤碳库的微小波动能显著影响全球碳循环,引起全球气候变化[
农作物秸秆是土壤中重要的有机质来源,影响着SOC的分解和积累[
长江上游耕地多分布于丘陵山区(以紫色土为主),四川盆地是典型的集约化水稻-小麦轮作种植区[
试验地位于四川省德阳市玉兴镇国家级耕地质量监测点(30°59′43″ N,104°57′12″ E),属于四川盆地中部浅丘地带,亚热带季风性湿润气候。试验区年降水量1 000~1 300 mm,年均气温16.7℃,年有效积温5 304℃,年无霜期281 d。长期定位试验点建于1984年,成土母质属白垩系下统薄砂厚页岩互层风化的坡积-洪积物,土壤发生类型为水稻土。初始耕层土壤(0~20 cm)基本理化性质见
耕层土壤基本理化性质
Basic physical and chemical properties of topsoil
土壤类型 |
砂粒 |
粉粒 |
黏粒 |
pH | 阳离子 |
有机质SOM/(g·kg–1) | 全氮 |
碱解氮 |
有效磷 |
速效钾 |
注:砂粒、粉粒和黏粒含量采用比重计法测定。Note:The contents of sand,silt and clay were determined by hydrometer method. ① Paddy soil. | ||||||||||
水稻土① | 350.0 | 440.0 | 210.0 | 7.6 | 15.38 | 24.40 | 1.46 | 138.00 | 10.80 | 122.00 |
设置3个试验区:无肥区(CK)、化肥区(NPK)和秸秆还田+化肥区(NPKS),1984年建立长期定位试验点后无重大变更。试验区面积866 m2,种植制度采用一年两熟夏水稻-冬小麦轮作模式。无肥区和化肥区在作物收获后移除地上部秸秆。化肥区施入复合肥,2019年小麦季肥料用量为:N 132.2 kg·hm–2、P2O5 34.54 kg·hm–2、K2O 48.88 kg·hm–2;水稻季肥料用量为N 183.5 kg·hm–2、P2O5 34.54 kg·hm–2、K2O 48.88 kg·hm–2。化肥+秸秆还田区在施化肥的基础上,于每季作物收获时将原小区内水稻或小麦秸秆机械粉碎还田(秸秆长度约5~10 cm),其中水稻秸秆还田量约5 000 kg·hm–2,小麦秸秆还田量约3 000 kg·hm–2。化肥均作为基肥在小麦播种或水稻移栽前1周均匀施入土壤,田间管理以当地习惯方式进行。
2019年9月中旬水稻收获后,将每个试验区等体积划分为3个重复样区。每个样区按照“五点法”选择样点,采集0~20 cm土层原状土于无菌硬质塑料盒内,并放于低温保温箱中及时送回实验室。去除可见的动植物残体、石块等杂物后,部分土样保存于低温无菌环境,用干筛法制备新鲜土样团聚体;另取部分土样于阴凉通风处自然风干,并当土壤含水量降低至塑限时,沿原状土自然结构裂隙轻轻掰开为约1 cm3的小块,用湿筛法制备风干土样团聚体。
风干土样团聚体分级采用湿筛法[
新鲜土样团聚体分级采用改进的干筛法[
土壤有机碳(SOC)采用重铬酸钾—容量法[
采用微孔板荧光法测定参与土壤碳循环的3种胞外酶活性(β-1,4-葡萄糖苷酶,BG;β-1,4-木糖苷酶,BX;β-D-纤维二糖水解酶,CBH)[
在SPSS 19.0软件中进行数据统计分析,采用单因素(one-way ANOVA)方差分析,并用最小显著差异法(LSD)和q检验(S-N-K,Student Newman Keuls)进行差异显著性检验(α = 0.05)。在Excel 2010中制图,柱状图误差线表示平均值的标准误差,用不同字母表示差异性显著(
由
不同处理下土壤团聚体有机碳及其活性组分含量
The contents of organic carbon and its labile fractions in soil aggregates under different treatments
与SOC变化特征相似,不同处理对团聚体可溶性有机碳(DOC)含量有强烈影响(
从
土壤团聚体微生物生物量碳(MBC)分布规律与SOC类似(
水稻土团聚体各活性有机碳组分比例如
不同处理下土壤团聚体活性有机碳组分比例
The ratios of labile organic carbon fractions in soil aggregates under different treatments
由
EOC/SOC明显高于DOC/SOC和MBC/SOC,表明EOC是土壤活性有机碳主要存在形式(
土壤团聚体MBC/SOC变化趋势与DOC、EOC不同(
总体而言,LOC/SOC和EOC/SOC随团聚体粒径减小而增大,而DOC/SOC和MBC/SOC在各粒级团聚体间变幅较小;与CK处理相比,NPKS可明显提高土壤团聚体各活性有机碳组分比例,而NPK降低了小于0.25 mm粒级LOC/SOC和EOC/SOC。
由
不同处理下土壤团聚体胞外酶活性
Extracellular enzyme activities in soil aggregates under different treatments
从
随团聚体粒径减小,NPK和NPKS处理下土壤β-D-纤维二糖水解酶(CBH)活性呈先升后降趋势,在2~1 mm粒级处出现拐点(
不同处理间土壤团聚体胞外酶活性冗余分析(RDA)结果(
稻田土壤团聚体酶活性与有机碳组分的冗余分析(RDA)
Redundancy analysis(RDA)between enzyme activities and organic carbon fractions at the aggregate size
采用逐步多元回归线性方程分析了胞外酶对有机碳及其活性组分的主次效应。如
土壤碳循环胞外酶与有机碳组分关系的逐步多元回归分析
Stepwise multiple regression analysis of the relationships between soil extracellular enzymes and organic carbon fractions
项目Term | 模型Models | ||
SOC | 0.526 | < 0.001 | |
DOC | 0.543 | < 0.001 | |
EOC | 0.413 | < 0.001 | |
MBC | 0.504 | < 0.001 |
土壤各活性有机碳组分(LOCs)是土壤有机碳(SOC)演变的重要控制因子,且容易受到农田土壤管理措施的影响[
农田管理措施会显著影响土壤碳输入与输出平衡,从而改变土壤SOC和LOCs组成。LOCs和SOC的比值在一定程度上可反映土壤有机碳的更新速率[
微生物作为土壤团聚体形成过程以及有机碳循环过程中最活跃的生物因素[
土壤胞外酶催化有机质的分解和组成,从而影响有机碳组分分配[
团聚体中有机碳组分与碳循环胞外酶互相促进,其中可溶性有机碳和微生物生物量碳主要受到β-D-纤维二糖水解酶的影响,其次是β-1,4-葡萄糖苷酶。2~0.25 mm粒级大团聚体中有机碳各组分含量与胞外酶活性均处于较高水平,这为有机碳更新和周转提供了良好的微环境。农艺措施改变了土壤碳在团聚体中的赋存机制,长期化肥处理显著降低了小于0.25 mm团聚体中有机碳及其活性组分含量。秸秆还田配施化肥处理则提高了大团聚体中有机碳及其活性组分含量,有利于可持续的土壤碳增加。
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