干湿交替灌溉改善稻田根际氧环境进而促进氮素转化和水稻氮素吸收

曹小闯; 刘晓霞; 马超; 田仓; 朱练峰; 吴龙龙; 张均华; 金千瑜; 朱春权; 孔亚丽; 虞轶俊

doi:10.11674/zwyf.2021294

干湿交替灌溉改善稻田根际氧环境进而促进氮素转化和水稻氮素吸收

Alternative dry-wet irrigation improves the rhizospheric oxygen environment and nitrogen transformation, and increases nitrogen absorption by rice plants

摘要

摘要:
目的阐明不同水氮管理模式下水稻根际内外氧环境变化特征及其对土壤碳氮转化和水稻氮吸收利用的影响，以期从稻田“根际氧环境”调控角度揭示适宜水氮耦合促进水稻生长和提高氮素利用效率的内在机制。
方法在长期定位试验基础上，采用根箱模拟培养以及Unisense微电极系统和¹⁵N同位素示踪相结合的研究方法，以常规粳稻日本晴和常规籼稻扬稻6号为供试材料，试验设常规淹灌 (conventional flood irrigation，CF)、干湿交替(alternate wet and dry irrigation，AWD) 两种灌溉模式，以及无氮 (0 g/kg, N₀)、中氮(0.8 g/kg, N_0.8)、高氮(1.2 g/kg, N_1.2) 3个施氮水平。对比分析了不同水氮耦合下水稻根际内外氧环境、可溶性有机碳、微生物量碳氮和碳氮转化相关酶活性，并分析了水稻生长和氮吸收利用的关系。
结果 1)与CF相比，AWD显著增加了水稻根际内外溶氧量和氧化还原电位，扬稻6号根际土壤的增加量高于日本晴；2)与N₀相比，在N_0.8、N_1.2水平下，AWD显著增加了两个水稻品种根际微生物量碳氮和可溶性有机碳含量，增加了水稻根际碳氮代谢相关酶活性 (脲酶、蔗糖酶、过氧化氢酶和N-乙酰-β-D-葡萄糖苷酶)；3)与N₀相比，在N_0.8、N_1.2水平下，AWD显著增加了水稻根际硝化速率和提取态总氮、硝态氮和游离氨基酸含量，但降低了其铵态氮含量；同时，增加了2个水稻品种根系铵态氮吸收速率、干物质重和氮素利用指数，且上述各指标扬稻6号均显著高于日本晴；4)相关性分析结果表明，水稻生物量和氮素利用指数与根际土壤硝化速率、微生物量碳氮、可溶性碳氮有效性和根系铵态氮/硝态氮吸收速率均呈显著正相关。
结论 AWD管理可通过提高溶解氧含量和氧化还原电位，创造良好的根际环境，进而提高根际可溶性有机碳、微生物量碳氮和碳氮代谢相关酶活性，增强根际硝化速率及根系铵态氮和硝态氮吸收速率，提高水稻干物质累积和氮素利用效率。

Abstract:
Objectives This study investigated the characteristics of the oxygen environment in rice rhizospheric and non-rhizospheric soils, its effects on soil C and N transformation, and rice N utilization under different irrigation and fertilization regimes. The aim was to reveal the intrinsic mechanism of suitable water and N coupling management to improve rice growth and N use efficiency.
Methods The test soils were collected from a long-term field experiment, including two irrigation regimes, i.e. conventional flood irrigation (CF) and alternate wet and dry irrigation (AWD), and three N application levels, i.e. N₀ (N 0 g/kg), N_0.8 (N 0.8 g/kg), and N_1.2 (N 1.2 g/kg). Japonica rice cultivar of nipponbare (Nip) and indica rice cultivar Yangdao 6 were grown in root boxes. The unisense microelectrode system and ¹⁵N isotope tracer techniques were used to detect soil oxygen environment, soluble organic C, and microbial biomass C and N. Enzyme activities related to C and N transformation and their relationships with rice growth and N utilization were also analyzed.
Results 1) Compared to CF, AWD (P < 0.05) increased the dissolved oxygen content and redox potential in rhizospheric and non-rhizospheric soils. However, the dissolved oxygen content in the rhizospheric soil of Yangdao 6 was higher than Nip. 2) AWD (P < 0.05) increased the soil microbial biomass C and N and the soluble organic C content in the rhizospheric soil of Nip and Yangdao 6 under N_0.8 and N_1.2 levels compared with N₀. AWD conditions increased the activities of urease, invertase, atalase and N-acetyl-β-D-glucosaminidase in Nip under N_0.8 and N_1.2 and Yangdao 6 under N_0.8. 3) AWD (P < 0.05) increased soil nitrification rate, extracted total N, NO₃^– and free amino acids under N_0.8 and N_1.2 compared with N₀, but decreased NH₄⁺ content in the rhizosphere. AWD also increased root NH₄⁺ uptake rate, rice dry matter weight and N utilization index. The increments mentioned above were higher in Yangdao 6 than Nip. 4) Rice biomass and N use index were (P < 0.05) positively correlated to soil nitrification rate, microbial biomass C and N, the availability of soil soluble organic C and N, and root NH₄⁺/NO₃^– uptake rate in the rhizosphere.
Conclusions AWD could improve the dissolved oxygen and redox potential in the rhizosphere, establish a well rhizospheric environment, thus improve the content of soil soluble organic carbon, soil microbial biomass-carbon/nitrogen and the enzyme activity related to C/N metabolism. This benefits the rhizosphere nitrification rate and root NH₄⁺/NO₃^– uptake and the improvement of the accumulation of rice dry matter and nitrogen use efficiency.

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