基于Biome-BGC模型的北方杨树人工林碳水通量对气候变化的响应研究

研究中国北方杨树人工林碳水通量对气候变化的响应,对于制定合理的经营管理措施以应对区域的气候变化具有重要意义。基于对杨树人工林碳水通量的连续监测数据和对Biome-BGC模型参数的校准,模拟分析杨树人工林碳水通量及水分利用效率(WUE)对气候变化(气温上升、降水变化和大气CO_2浓度上升)的响应规律。结果表明,Biome-BGC模型校准后显著提升了其对杨树人工林碳水通量的模拟精度,对GPP、ET模拟结果的Nash-Sutcliffe效率系数(NS)分别为0.69和0.63,各自提高了64.3%和80%,均方根误差(RMSE)则分别降低至1.94 g C m~(-2) d~(-1)和0.88 mm/d,分别下降了26.5%和25.4%。在未来气候变化情景中,单独的气温上升、降水增加和大气CO_2浓度上升分别造成GPP的降低、升高和升高,其中GPP对大气CO_2浓度上升的响应程度(28%—44%)远高于对气温上升(1%—5%)和降水变化(3%—10%)的,ET则主要受降水的影响,响应程度在5%—14%之间。GPP和ET对气候变化的响应则受不同水平的气温上升、降水变化和大气CO_2浓度上升三者综合作用的影响。基于GPP和ET对气候变化的响应,WUE随气温上升、降水增加表现为降低趋势,随降水减少和大气CO_2浓度升高则呈升高趋势;其对未来气候中大气CO_2浓度升高的响应程度为27.7%—43.6%,远高于对气温上升(1.2%—5.8%)和降水变化(1.2%—3.5%)的,说明未来气候变化中大气CO_2浓度上升是促进杨树生长的主要因素;其中相对于当前WUE(2.8 g C/kg H_2O),C2T2P1和C0T3P0情景下WUE的升高和降低幅度最大,分别为45.4%和5.8%。

Modelling the responses of carbon and water fluxes with climate change for a poplar plantation in northern China based on the Biome-BGC model

It is of great importance to project the response of carbon and water fluxes of terrestrial ecosystems with climate change and to develop science-based biological climate change mitigation strategies. We used our continuously measured long-term carbon and water flux data for a poplar plantation (Populus euramericana CV. "74/76") to calibrate and validate a widely applied Biome-BGC model to accurately simulate gross primary productivity (GPP), evapotranspiration (ET), and water use efficiency (WUE) and to project their responses to climate change. The climate change scenarios were designed with different levels of rising temperature (T), precipitation change (P), and atmospheric CO₂ concentration (C). Results showed that the Nash-Sutcliffe coefficient (NS) of the simulated GPP and ET were 0.69 and 0.63, respectively, with a root mean square error (RMSE) of 1.94 g C m^-2·^-1 and 0.88 mm/d, respectively, which indicated that the calibrated Biome-BGC model could be effectively used for modeling their responses to climate change. Under future climate change scenarios, the overall responses of GPP and ET were influenced by a combined effect of C, T, and P. In addition, the individual responses of GPP and ET to these climatic factors varied. Rising temperature and decreasing precipitation caused a decrease in GPP, while an increase in precipitation and atmospheric CO₂ concentration resulted in an increase in GPP. The enhancement of GPP with increasing atmospheric CO₂ concentration was 28%-44%, which was much higher than that of rising temperature (1%-5%) and precipitation (3%-10%). However, the variations in ET only responded to a precipitation change of 5%-14%. As a result, WUE (GPP/ET) decreased with rising temperature and an increase in precipitation, while increased with a decrease in precipitation and rising atmospheric CO₂ concentration. The rising atmospheric CO₂ concentration enhanced WUE by 27.7%-43.6%, which was much higher than that effect of rising temperature (1.2%-5.8%) and precipitation (1.2%-3.5%). Compared with the current WUE (2.8 g C/kg H₂O), the largest increase and decrease in WUE would occur under scenarios C2T2P1 and C0T3P0, which are 45.4% and 5.8%, respectively.