2.4. Emission Metrics and Statistical Analysis 
Isoprenoid emission and photosynthetic rates were analyzed in common units of μgC g-1 h-1. This enabled us to produce integrated metrics related to the leaf carbon balance. We analyzed total isoprenoid emissions both as the sum of all C emitted in the form of isoprenoids, and as a percentage of photosynthetic C assimilation rates. The three compound classes vary in mass (5C isoprene, 10C monoterpenes, 15C sesquiterpenes). We developed an ‘isoprenoid mass investment’ metric to assess the partitioning of C among the different classes of emitted isoprenoids, calculated by multiplying the emission rates of each compound (in μgC g-1 h-1) by their respective masses (number of C atoms), and dividing by the combined total emission rate (i.e. the emission-rate weighted mean mass of emitted compounds). The mass investment metric reflects how much carbon is allocated to lighter versus heavier compounds. For example, the average mass investment of pure isoprene emission is 5C. Since sesquiterpenes contain three times as much C as isoprene, a 2:1 molar ratio of sesquiterpenes to isoprene yields an average mass investment of (2(15C × 3) + 1(5C × 1)) / 7 = 13.6C. Variation in metrics among habitats within species and seasons was analyzed by Tukey Honestly Significant Difference (HSD) test (alpha = 0.05). Variation between dry and wet seasons was analyzed by paired t-test (alpha = 0.05) on measurements taken from the same individuals in both seasons.