大气CO2浓度升高对春玉米土壤呼吸的影响

Abstract

为探讨春玉米不同生育期土壤呼吸速率对大气CO₂浓度升高的响应，以黄土高原旱作春玉米为研究对象，通过改进的开顶式气室（OTC）模拟大气CO₂浓度升高的环境，在田间条件下设置自然大气CO₂浓度（CK）、OTC对照（OTC，CO₂浓度同CK）与CO₂浓度升高（OTC+CO₂，OTC系统自动控制CO₂浓度700 μmol/mol）3种处理。研究了旱区覆膜高产栽培春玉米播前（V0）、六叶期（V6）、九叶期（V9）、吐丝期（R1）、乳熟期（R3）、蜡熟期（R5）及完熟期（R6）土壤呼吸速率对大气CO₂浓度升高的响应特征，以及大气CO₂浓度升高对土壤呼吸速率的温度与水分效应的影响。研究发现，OTC+CO₂处理土壤呼吸速率，与CK相比，在R3和R5期分别增加43%、104%（P<0.05），与OTC相比，R3和R5期分别提升了63%、109%（P<0.05）；OTC处理与CK相比，在整个生育期对土壤呼吸影响不显著；3种处理条件下，土壤温度和水分随生育期变化趋势基本一致，土壤呼吸速率与土壤温度和水分分别呈指数相关和抛物线型相关；结果表明：大气CO₂浓度升高对土壤呼吸的影响因生育期而异，土壤温度和土壤水分是影响旱地农田土壤呼吸的重要因素，CO₂浓度升高会使土壤呼吸温度效应值（Q₁₀）降低，土壤呼吸对土壤水分响应的阈值提高。;Understanding the effects of elevated atmospheric CO₂ on soil respiration is crucial for predicting the greenhouse gas emission in the future. A field experiment was conducted to study the effects of elevated CO₂ on soil respiration of spring maize under three atmospheric conditions (treatments):natural atmospheric conditions with the current CO₂ concentration (marked as CK), open-top chamber (OTC) system with the current atmospheric CO₂ concentration (as the contrast, marked as OTC), and OTC system with elevated CO₂ concentration of 700 μmol/mol (marked as OTC+CO₂). Soil respiration, soil temperature and moisture were measured at the main growth stages of spring maize including pre-sowing (V0), jointing stage (V6), ninth-leaf stage (V9), silking stage (R1), milk stage (R3), dent stage (R5), and physiological maturity stage (R6). The results showed that, compared with CK, OTC+CO₂ enhanced soil respiration rates by 43% and 104% (P<0.05), respectively, at the R3 and R5 stage. Compared with OTC, OTC+CO₂ increased soil respiration rates by 63% and 109% (P<0.05) at the R3 and R5 stage, respectively. There was no significant difference in soil respiration between OTC and CK during the whole growth period of spring maize. The changing dynamics of soil temperature with growth period for the three treatments were consistent, also soil moisture changing dynamics with growth period under the three atmospheric conditions were similar. Soil respiration showed an exponential and parabolic correlation with the soil temperature and soil moisture, respectively. In conclusion, the effects of elevated CO₂ on soil respiration varied with growth stage. Soil temperature and soil moisture were the main factors affecting soil respiration, the elevated CO₂ decreased the temperature effect value (Q₁₀), and increased the threshold value of soil respiration to soil moisture.