Wagner S W, Reicosky D C, Alessi R S
USDA-ARS, North Central Soil Conservation Res. Lab., Morris, MN 56267, USA.
Agron J. 1997 Mar-Apr;89(2):279-84. doi: 10.2134/agronj1997.00021962008900020021x.
Portable closed chambers provide a valuable tool for measuring crop photosynthesis and evapotranspiration. Typically, the rates of change of CO2 and water vapor concentration are assumed to be constant in the short time required to make the closed-chamber measurement, and a linear regression model is used to estimate the CO2 and H2O fluxes. However, due to the physical and physiological effects the measurement system has on the measured process, assuming a constant rate and using a linear model may underestimate the flux. Our objective was to provide a model that estimates the CO2 and H20 exchange rates at the time of chamber closure. We compared the linear regression model with a quadratic regression model using field measurements from two studies. Generally, 60 to 100% of all chamber measurement data sets were significantly nonlinear, causing the quadratic model to yield fluxes 10 to 40% greater than those calculated with the linear regression model. The frequency and degree of nonlinearity were related to the measured rate and chamber volume. Closed-chamber data should be tested for nonlinearity and an appropriate model used to calculate flux. The quadratic model provides users of well-mixed closed chambers an alternative to a simple linear model for data sets with significant nonlinearity.
便携式封闭气室为测量作物光合作用和蒸散作用提供了一种有价值的工具。通常，在进行封闭气室测量所需的短时间内，假定二氧化碳和水汽浓度的变化速率是恒定的，并使用线性回归模型来估算二氧化碳和水的通量。然而，由于测量系统对被测过程存在物理和生理影响，假定速率恒定并使用线性模型可能会低估通量。我们的目标是提供一个模型，用于估算气室封闭时刻的二氧化碳和水的交换速率。我们使用两项研究的田间测量数据，将线性回归模型与二次回归模型进行了比较。一般来说，所有气室测量数据集的60%至100%都存在显著的非线性，这使得二次模型得出的通量比用线性回归模型计算出的通量高出10%至40%。非线性的频率和程度与测量速率和气室体积有关。应对封闭气室数据进行非线性检验，并使用合适的模型来计算通量。对于具有显著非线性的数据集，二次模型为充分混合的封闭气室的用户提供了一种替代简单线性模型的方法。
