稻麦作物呼吸作用与植株氮含量、生物量和温度的定量关系

Quantitative relationship of wheat and rice respiration with tissue nitrogen, biomass and temperature

陆地生态系统碳循环是全球变化研究的重要议题之一,准确估算植被的呼吸作用对于客观评价植被在陆地生态系统碳循环中的作用具有重要意义。为探讨作物生长、植株氮含量和环境温度对呼吸作用的综合影响,研究以盆栽为主并与大田试验相结合,基于逐步收割法和静态暗箱-气相色谱技术,于2 0 0 2年和2 0 0 3年冬小麦和水稻生长季原位测定了作物地上部分CO2 排放速率,并同时测定了作物生物量、氮含量和环境温度。试验处理分为常规管理、不同氮肥水平、不同播种期和不同种植密度。研究结果表明:稻麦作物暗呼吸系数(Rd)不是常数,而是正比于植株氮(N )含量,两者的关系可用方程Rd=4 .74 N - 1.4 5 (R2 =0 .85 ,n=12 2 ,p<0 .0 0 1)来定量表述。用方程RD=(4.74 N - 1.4 5 )×Q( T- 2 5) /1 01 0 ×W模拟的作物暗呼吸量(RD)与大田测定结果一致。用国际上著名的作物模拟模型估算的稻麦作物维持性呼吸与用此方程模拟的结果具有可比性,而采用陆地生态系统模型(TEN)估算的结果则远高于本项研究,TEM用于估算农业植被的呼吸作用可能是不适合的。

Carbon cycling in terrestrial ecosystem is of great importance in global change issue. A reliable estimation of plant respiration is essential to objectively evaluate the role of vegetation in the terrestrial ecosystem cycling. As an easily measured surrogate for protein content, nitrogen concentration plays a vital role on plant respiration. The dependence of plant respiration on nitrogen concentration for forest ecosystem has been well pronounced over the last decades. However, few studies have been dedicated to agro-ecosystem. To quantify the dependence of crop respiration on tissue N, crop growth and temperature, we conducted pot and field experiments during 2002 and 2003 wheat- and rice-growing seasons with different treatments, including fertilizer N application, planting date and planting density. Crop biomass, tissue N content, dark respiration and the corresponding environmental temperature were measured. Static opaque chamber was used for sampling gas. The respiration as CO 2 emission was detected by a gas chromatograph (Agilent 4890D) with flame ionization detector (FID). A gradual-clip-up method was employed to determine the dark respiration coefficient (R d), defined as the CO 2 emissions per unit crop biomass per unit time at a reference temperature. Results indicated that the R d of wheat and rice crops is not a constant but is positively dependent on shoot N content. Relationship between these two parameters can be well quantified by R d=4.74N-1.45 (R^2=0.85, n=122, p<0.001). The lowest and the highest values are 3.58 and 31.49 μmol kg^(-1) s^(-1) for the wheat crop over the 2002-03 growing season, and 1.04 and 29.56 μmol kg^(-1) s^(-1) for the rice crop during the 2002 growing season, respectively. Crop dark respiration (RD) associated with tissue nitrogen (N), crop biomass (W) and air temperature (T) can be quantified by RD=(4.74N-1.45)×Q^((T-25)/10) (10)×W. Q (10) is a temperature coefficient for the respiration. Computed RD applying this relationship matched field measurements well. We computed daily crop respiration over a rice-growing season and a wheat-growing season in Nanjing by using the methods in the crop model, the TEM as well as derived from this study, respectively. Calculations indicate that the estimated respiration with crop model is in general comparable to this study, while the respiration estimated by the TEM method is 59% (for rice) and 31% (for wheat) higher than that from this study. It is concluded that the tissue N content affects greatly crop dark respiration. The respiration coefficient is linearly correlated to tissue N content. Crop dark respiration can be well estimated from tissue nitrogen, crop biomass and air temperature. A further conclusion is that the simulated dark respiration of rice and wheat crops is comparable to the maintenance respiration estimated by the crop model, while the TEM method overestimated crop maintenance respiration and may be not suitable for agricultural vegetation.