Extended Data Fig. 4: Site-specific results for direct and total CO2 effects, along with the trend slope of peak leaf area index.
From: Reduced water loss rather than increased photosynthesis controls CO2-enhanced water-use efficiency
Peak leaf area index (LAIpeak) is defined as the 95th percentile of LAI for each year. Cross symbols (×) denote sites with significant LAIpeak trends (P < 0.05), based on a two-sided Mann-Kendall trend test. Dot (•) symbols indicate sites with detectable CO2 effects. The CO2 effect is considered detectable when \(\left|{\rm{SNR}}\right|\ge 1\), where SNR measures the relative strength of CO2 effects (signal) against inherent variability in data (noise). Red boxes highlight the seven sites that support the canopy size affects leaf physiology hypothesis, specifically, they (1) exhibit an increasing trend in the annual peak LAI, (2) show a notable direct CO2 effect on GPP (to ensure the enhanced LAIpeak is more likely driven by CO2 rather than other factors), and (3) exhibit a less responsive GPP enhancement than Gc reduction (\(\left|{{{\upbeta }}}_{{\rm{GPP}},{\rm{total}}}\right| < \left|{{{\upbeta }}}_{{\rm{Gc}},{\rm{total}}}\right|\), where the ‘total’ subscript indicates total CO2 effects).
