Effects of warming and fertilization on soil organic carbon and total nitrogen contents, and δ13C and δ15N in farmland
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摘要: 农田土壤是重要的碳氮库, 对气候变化极其敏感, 但土壤碳氮循环对气候变化的响应目前还不清楚。在全球变暖背景下, 为了实现我国碳达峰、碳中和目标, 研究增温对土壤有机碳、全氮含量及其碳氮同位素的影响具有重要的现实意义。本研究采用红外辐射加热器模拟全球变暖, 使5 cm土壤温度增加约2 ℃。通过测定灌溉前后土壤有机碳和全氮含量及δ13C和δ15N值的变化, 研究增温、施氮和灌溉对华北平原小麦田土壤碳氮库的影响。试验共设4个处理: 不施氮不增温(N0T0)、不施氮增温(N0T1)、施氮不增温(N1T0)和施氮增温(N1T1)。结果表明: 灌溉前, 增温降低了土壤有机碳含量, 0~10 cm土层N1T1处理与不增温处理(N0T0和N1T0)之间差异显著(P<0.05), 10~20 cm土层N1T1处理与其他处理差异均显著(P<0.05); 灌溉后, 增温虽有降低土壤有机碳含量的趋势, 但差异不显著; 施氮条件下, 增温显著提升了δ13C值(P<0.05)。增温降低了土壤全氮含量, 并在灌溉前10~20 cm土层和灌溉后0~10 cm土层达显著水平(P<0.05); 增温提升了土壤δ15N值, 灌溉前0~10 cm土层N0T0处理与增温处理(N0T1和N1T1)差异显著(P<0.05), 灌溉后0~10 cm土层仅N0T1和N1T0处理间差异显著(P<0.05), 而10~20 cm土层增温处理(N0T1和N1T1)均与N1T0处理差异显著(P<0.05)。同一处理同一时期, 土壤有机碳和全氮的含量随土壤深度的增加而降低, δ13C和δ15N值随深度增加而升高, 但土壤有机碳和δ13C值的变化差异不显著, 全氮含量和δ15N值的变化差异显著(P<0.05)。土壤有机碳、全氮含量及δ13C和δ15N值在灌溉前后的差异均不显著。连续5年的增温施氮试验表明, 未来气候变暖可能会加快土壤有机碳和全氮的分解, 造成更多轻组有机碳损失。灌溉在短期内不会显著改变土壤碳氮含量及δ13C和δ15N值, 但其长期影响还需进一步探究。此外, 未来研究还应该重视多因素交互作用对土壤碳氮循环的影响。Abstract: Farmland soil is an essential terrestrial carbon and nitrogen pool that is highly sensitive to climate change. However, the response of soil carbon and nitrogen cycles to climate change remains unclear. Understanding the effect of warming on soil organic carbon is particularly important to achieving the goal of carbon peak and carbon neutralization in the context of global warming. Here, the infrared heaters were used to simulate warming and the soil temperature (5 cm depth) increased by approximately 2 °C. The soil organic carbon, total nitrogen, δ13C, and δ15N contents were measured to assess the effects of warming, nitrogen addition, and irrigation on the soil carbon and nitrogen cycle. The experiment consisted of four treatments: no nitrogen addition and no warming (N0T0), no nitrogen addition and warming (N0T1), nitrogen addition and no warming (N1T0), and nitrogen addition and warming (N1T1). The results showed that warming decreased the soil organic carbon content before irrigation. There were significant differences between the N1T1 and no warming (N0T0 and N1T0) treatments at 0–10 cm depth (P<0.05), and between N1T1 and the other three treatments at 10−20 cm depth (P<0.05). Warming tended to decrease soil organic carbon content after irrigation. However, the difference was not statistically significant. Warming enhanced soil δ13C in the nitrogen addition treatments (P<0.05) and decreased soil total nitrogen content, but the differences were only significant at the 10−20 cm depth before irrigation and at the 0–10 cm depth after irrigation (P<0.05). Soil δ15N was enhanced in the warming treatment. However, the defferences were only significant between the N0T0 and warming (N0T1 and N1T1) treatments at 0−10 cm depth before irrigation (P<0.05), between N0T1 and N1T0 at 0−10 cm depth (P<0.05), and between N1T0 and the warming (N0T1 and N1T1) treatments at 10−20 cm after irrigation (P<0.05). The soil organic carbon and total nitrogen contents decreased with increasing soil depth, while δ13C and δ15N increased with increasing soil depth. However, only the changes in total nitrogen and δ15N were significant. Irrigation had no significant effects on soil organic carbon, total nitrogen, δ13C, and δ15N. The 5-year continuous warming and nitrogen addition experiments suggest that future climate warming may accelerate the decomposition of soil organic carbon and total nitrogen, resulting in a greater loss of the light fraction carbon. Irrigation did not significantly alter the soil organic carbon and total nitrogen contents and the δ13C, and δ15N values in the short term; however, its long-term effects need to be further explored. In addition, future research should focus on the effect of multi-factor interactions on soil carbon and nitrogen cycles.
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Key words:
- Global warming /
- Nitrogen application /
- Soil organic carbon /
- Soil total nitrogen /
- δ13C /
- δ15N
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图 1 2012—2013年冬小麦季大气温度和降雨量
Figure 1. Daily mean air temperature and precipitation during wheat growing season of 2012 to 2013
图 2 2013年灌溉前(3月28日, A)和灌溉后(4月26日, B)不同增温和施氮处理下不同土层的有机碳含量
N0T0: 不施氮不增温; N0T1: 不施氮增温; N1T0施氮不增温; N1T1: 施氮增温。不同小写字母表示同一土层不同处理间差异显著(P<0.05), 不同大写字母表示同一处理两个土层间差异显著。N0T0: no nitrogen and no warming; N0T1: no nitrogen and warming; N1T0: nitrogen application and no warming; N1T1: nitrogen application and warming. Different lowercase letters mean significant differences among treatments in the same soil depth at P<0.05 level. Different capital letters mean significant differences between two soil layers for the same treatment at P<0.05 level.
Figure 2. Contents of soil organic carbon at two depths before (on March 28, A) and after (on April 26, B) irrigation under different fertilization and warming treatments in 2013
图 3 2013年灌溉前(3月28日, A)和灌溉后(4月26日, B)不同增温和施氮处理下不同土层的有机碳δ13C值
N0T0: 不施氮不增温; N0T1: 不施氮增温; N1T0施氮不增温; N1T1: 施氮增温。不同小写字母表示同一土层不同处理间差异显著(P<0.05), 不同大写字母表示同一处理两个土层间差异显著。N0T0: no nitrogen and no warming; N0T1: no nitrogen and warming; N1T0: nitrogen application and no warming; N1T1: nitrogen application and warming. Different lowercase letters mean significant differences among treatments in the same soil depth at P<0.05 level. Different capital letters mean significant differences between two soil layers for the same treatment at P<0.05 level.
Figure 3. δ13C natural abundances at two depths before (on March 28, A) and after (on April 26, B) irrigation under different fertilization and warming treatments in 2013
图 4 2013年灌溉前(3月28日, A)和灌溉后(4月26日, B)不同增温和施氮处理下不同土层的全氮含量
N0T0: 不施氮不增温; N0T1: 不施氮增温; N1T0施氮不增温; N1T1: 施氮增温。不同小写字母表示同一土层不同处理间差异显著(P<0.05), 不同大写字母表示同一处理两个土层间差异显著。N0T0: no nitrogen and no warming; N0T1: no nitrogen and warming; N1T0: nitrogen application and no warming; N1T1: nitrogen application and warming. Different lowercase letters mean significant differences among treatments in the same soil depth at P<0.05 level. Different capital letters mean significant differences between two soil layers for the same treatment at P<0.05 level.
Figure 4. Contents of soil nitrogen at two depths before (on March 28, A) and after (on April 26, B) irrigation under different fertilization and warming treatments in 2013
图 5 2013年灌溉前(3月28日, A)和灌溉后(4月26日, B)不同增温和施氮处理下不同土层的δ15N值
N0T0: 不施氮不增温; N0T1: 不施氮增温; N1T0施氮不增温; N1T1: 施氮增温。不同小写字母表示同一土层不同处理间差异显著(P<0.05), 不同大写字母表示同一处理两个土层间差异显著。N0T0: no nitrogen and no warming; N0T1: no nitrogen and warming; N1T0: nitrogen application and no warming; N1T1: nitrogen application and warming. Different lowercase letters mean significant differences among treatments in the same soil depth at P<0.05 level. Different capital letters mean significant differences between two soil layers for the same treatment at P<0.05 level.
Figure 5. δ15N natural abundances at two depths before (on March 28, A) and after (on April 26, B) irrigation under different fertilization and warming treatments in 2013
图 6 2013年灌溉前(3月28日, A)和灌溉后(4月26日, B)不同增温和施氮处理下不同土层的碳氮比
N0T0: 不施氮不增温; N0T1: 不施氮增温; N1T0施氮不增温; N1T1: 施氮增温。不同小写字母表示同一土层不同处理间差异显著(P<0.05), 不同大写字母表示同一处理两个土层间差异显著。N0T0: no nitrogen and no warming; N0T1: no nitrogen and warming; N1T0: nitrogen application and no warming; N1T1: nitrogen application and warming. Different lowercase letters mean significant differences among treatments in the same soil depth at P<0.05 level. Different capital letters mean significant differences between two soil layers for the same treatment at P<0.05 level.
Figure 6. C/N ratios at two depths before (on March 28, A) and after (on April 26, B) irrigation under different fertilization and warming treatments in 2013
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