Extended Data Fig. 1: Site example and aggregated results for the differencing method.
From: Reduced water loss rather than increased photosynthesis controls CO2-enhanced water-use efficiency
Panels a-c show the isolated CO2 effects for iWUE, Gc, and GPP at an example site, illustrating the quantification of \(\beta\) and \({\rm{SNR}}\) based on actual data. Dark solid lines represent the regression lines fitted between CO2 and \(\delta\) (that is, the difference between the with-CO2 model \({f}_{2}\) and the without-CO2 model \({f}_{1}\)). Shaded areas around the zero horizontal lines (shown as dark dashed lines) indicate the standard deviation of the detrended \(\delta\), which serves as the denominator in the SNR calculation (equation 4 in the main text). Panel d shows the aggregated \(\beta\) values across 63 EC sites. Each row corresponds to a target variable (Gc, GPP, and iWUE), and each column represents an EC site. The sites are categorized into three groups, denoted by different font colours, based on their divergent response patterns (the joint-response pattern, Gc-only pattern, and minimal-response pattern). The colourmap for Gc is inverted relative to GPP and iWUE, so that more bluish colours consistently represent stronger CO2 effects.
