highly significantp < 0.01
The average δ 13 C of C 3 plants was −26.7‰ ( n = 434), varying from −30.7 to −22.5‰, while the average δ 13 C of C 4 plants was −11.5‰ ( n = 47), varying from −14.2 to −10.2‰ ( Figure 1 a), which is a highly significant difference ( p < 0.01).