大气CO_2浓度和温度升高对稻麦轮作生态系统N_2O排放的影响

【目的】研究大气CO_2浓度和温度升高条件下稻麦轮作生态系统N_2O排放的响应规律,以期科学评估未来气候变化情境下,CO_2浓度和温度升高对稻麦轮作生态系统N_2O排放的影响,为中国应对未来气候变化提供数据支持。【方法】依托同步模拟自由大气CO_2浓度升高和温度升高的T-FACE试验平台,设置本底大气CO_2浓度和温度(Ambient)、500μmol·mol~(-1) CO_2+本底大气温度(C)、本底大气CO_2浓度+温度增加2℃(T)和500μmol·mol-1 CO_2+温度增加2℃(C+T)等4个处理。采用静态暗箱-气相色谱法原位观测稻麦轮作生态系统N_2O排放通量,研究稻麦轮作生态系统N_2O排放对大气CO_2浓度和温度升高的响应规律。【结果】(1)CO_2浓度升高使水稻和小麦生物量和产量分别显著增加9.7%、11.3%和5.6%、5.7%(P0.05);温度升高使水稻和小麦生物量和产量分别显著减少21.1%、18.0%和31.6%、17.7%(P0.05);CO_2浓度和温度的同步升高使水稻和小麦生物量和产量分别显著降低13.5%、8.7%和26.0%、10.3%(P0.05)。(2)CO_2浓度和温度升高,均未改变稻麦轮作系统N_2O的季节排放模式。CO_2浓度升高条件下,水稻季和小麦季N_2O排放分别增加15.2%和39.9%,其中后者达显著水平(P0.05);温度升高未显著影响水稻季N_2O排放,但显著增加小麦季N_2O排放20.5%(P0.05);CO_2浓度和温度同步升高对水稻季N_2O排放的影响存在较大的年际差异,但总体上有促进N_2O排放的趋势;CO_2浓度和温度同步升高极显著增加小麦季N_2O排放(46.0%,P0.01)。(3)小麦季N_2O排放与小麦生物量密切相关,在CO_2浓度和温度升高条件下,小麦季N_2O排放与小麦地下部生物量和ΔSOC之间具有显著的正相关关系。(4)与对照组相比,CO_2浓度升高、温度升高以及两者的共同作用,分别导致稻麦轮作系统单位产量的N_2O排放强度(GHGI)分别增加29.1%、66.3%和81.8%,其中温度升高和CO_2浓度和温度同步升高处理达显著水平(P0.05)。【结论】CO_2浓度升高和温度升高均未改变稻麦轮作生态系统N_2O的季节排放模式。CO_2浓度升高导致稻麦轮作系统N_2O排放显著增加;温度升高显著增加小麦季N_2O排放,但未显著影响水稻季N_2O排放。CO_2浓度和温度升高导致稻麦轮作系统温室气体排放强度增加,各处理条件下温室气体排放强度的响应从大小依次为:C+TTC。可见,在未来CO_2浓度和温度升高情境下,为保证现有粮食供应水平不变,由稻麦生产所导致的N_2O排放强度变化可能会进一步加剧气候变化进程。

Response of N2O Emissions to Elevated Atmospheric CO2 Concentration and Temperature in Rice-wheat Rotation Agroecosystem

【Objective】This study was conducted to examine the effects of elevated atmospheric carbon dioxide (CO₂) concentration and temperature on nitrous oxide (N₂O) emissions from annual rice-wheat rotation systems, so as to gain an insight into N₂O fluxes response to climate change.【Method】An in-situ field experiment was established in annual rice-winter wheat rotation systems under a T-FACE platform, consisting of four treatments under different CO₂ concentration and temperature levels (ambient CO₂ + ambient temperature, ambient; 500 μmol·mol^-1 CO₂ + ambient temperature, C; ambient CO₂ + temperature increased by 2℃, T; 500 μmol·mol^-1 CO₂ + temperature increased by 2℃, C+T) during 2012-2015. The fluxes of N₂O from rice-wheat rotation fields were measured using static opaque chamber-gas chromatograph method.【Result】(1) On an average of two rice-growing seasons, elevated atmospheric CO₂ concentration significantly increased the biomass and yield of rice by 9.7% and 5.6%, respectively, and those increments of wheat were 11.3% and 5.7% over the three wheat-growing seasons（P＜0.05）, respectively; Elevated temperature significantly reduced the biomass and yield of rice by 21.1% and 31.6%, and those reductions of wheat were 18.0% and 17.7%, respectively; The combination of elevated CO₂ and temperature significantly reduced the biomass and yield of rice by 13.5%（P＜0.05）and 26.0%, and those reductions of wheat were 8.7% and 10.3%（P＜0.05）, respectively. (2) Either elevated CO₂ concentration or temperature did not affect the seasonal patterns of N₂O emission from rice-wheat rotation system. Elevated CO₂ concentration increased N₂O emissions in rice and wheat season by 15.2% and 39.9%, respectively. Elevated temperature did not affect N₂O emissions in rice season, but it significantly increased N₂O emissions in wheat season by 20.5% (P＜0.05). Despite of a considerable interannual variability, N₂O emissions tended to be increased by the combined effect of elevated CO₂ concentration and temperature in rice season; the emissions of N₂O in wheat season were significantly increased by 46.0% under the condition of C+T treatment. (3) The cumulative N₂O emissions in wheat were positively correlated with belowground biomass of wheat and ΔSOC. (4) Elevated atmospheric CO₂ concentration, elevated temperature and their combination increased GHGI of rice-wheat rotation field by 29.1%, 66.3% and 81.8%, respectively.【Conclusion】All of these results showed that both elevated CO₂ concentration and temperature had a strong impact on the emission of N₂O in rice-wheat rotation field. Elevated CO₂ concentration significantly increased the emission of N₂O in both rice and wheat seasons; Elevated temperature significantly increased N₂O emission in wheat season, but no significant change was observed in rice season. Elevated CO₂ concentration increased N₂O-derived GHGI from rice-wheat rotation field, but it was not significantly different; Elevated temperature and the interactive between elevated CO₂ concentration and temperature significantly increased GHGI. The effects of different applied treatments on N₂O-derived GHGI from rice-wheat rotation field from high to low in order were: C+T>T>C. It was suggested from this study that to ensure present crop supply level under the condition of high atmospheric CO₂ concentration and temperature would likely to exacerbate climate change by increasing N₂O emission.