Effects of the Permo-Carboniferous pO2 rise
at two different pCO2 levels on annual
(a) terrestrial NPP, (b) canopy
transpiration (Et), and (c)
water-use efficiency (WUE, defined as NPP divided by
Et) during the late Carboniferous, analyzed
on a site-by-site basis. Open symbols represent results from case 2
(35% O2, 0.03% CO2); solid symbols represent
results from case 4 (35% O2, 0.06% CO2). All
values are expressed as the differences between results from the
specified atmospheric composition and the control (case 1).