Isoprene emission capacity for US tree species

Isoprene emission capacity measurements are presented from 18 North America n oak (Quercus) species and species from six other genera previously found to emit significant quantities of isoprene. Sampling was conducted at physi ographically diverse locations in North Carolina, Central California, and N orthern Oregon. Emissions from several sun leaves of each species were meas ured at or near standard conditions (leaf temperature of 30 degreesC and ph otosynthetically active radiation of 1000 mu mol m(-2) s(-1)) using environ mentally controlled cuvette systems and gas chromatography with reduction g as detectors. Species mean emission capacity ranged from 39 to 158 mug C g( -1) h(-1) (mean of 86), or 22 to 79 nmol m(-2) s(-1) (mean of 44). These ra tes are 2-28 times higher than those previously reported from the same spec ies, which were summarized in a recent study where isoprene emission rates were assigned based on published data and taxonomy. These discrepancies wer e attributed to differences in leaf environment during development, measure ment technique (branch or plant enclosure versus leaf enclosure), and lack of environmental measurements associated with some of the earlier branch en closure measurements. Mass-based emission capacities for 15 of 18 oak speci es. sweetgum (Liquidambar styraciflua), and poplars (Populus trichocarpa an d P. deltoides) were within ranges used in current biogenic volatile organi c compound (BVOC) emission models, while measured rates for the remaining t hree oak species, Nyssa sylvatica, Platanus occidentalis. Robinia pseudoaca cia, Salix nigra, and Populus hybrids (Populus trichocarpa x P. deltoides) were considerably higher. In addition, mean specific leaf mass of the oak s pecies was 30% higher than assumed in current emission models. Emission rat es reported here and in other recent studies support recent conclusions tha t isoprene emission capacities for sun leaves of high emitting species may be better represented by a value of 100 +/- 50 mug C g(-1) h(-1) during hot summer conditions. We also find that intermediate isoprene emission rates previously suggested for some tree species may not represent their true emi ssion capacities, and that broadleaf plant species may have either low (< 1 .0 mug C g(-1) h(-1)) or very high (similar to 100 mug C g(-1) h(-1)) genet ic capacity to emit isoprene when mature foliage is exposed to a high ambie nt temperature and light environment. Published by Elsevier Science Ltd.