Isoprene and monoterpene emissions from an Inner Mongolia grassland

Abstract

Terpenoid emissions were measured at a grassland site in Inner Mongolia, China during four campaigns over a 2-year period. Emissions were strongly correlated with light and temperature and the variations could be simulated using a canopy emission model. Substantial seasonal and interannual variations in isoprene emissions were also observed. Area averaged isoprene emissions normalized to standard above-canopy temperature and light conditions (30 1C and 1500 mmol m À2 s À1) ranged from about 50 to 500 mg m À2 h À1. These rates are more than an order of magnitude higher than those previously reported for temperate grasslands but are lower than emission rates observed from ground cover vegetation at higher latitudes. Isoprene emissions from this Inner Mongolia grassland may be dominated by emissions from sedges, e.g. Carex appendiculata. Total monoterpene emissions normalized to a standard temperature of 30 1C were only about 3 mg m À2 h À1 and consisted primarily of carene and limonene with smaller contributions of a-pinene and b-pinene. A model sensitivity study showed that grass and other herbaceous ground cover can contribute 410% of the total isoprene emission from certain regions, such as Inner Mongolia, but areo4% on a global annual scale. r

Evident elevation of atmospheric monoterpenes due to degradation-induced species changes in a semi-arid grassland

“…Based on the regression analysis, sedge was the main contributor, although only small sedge patches existed in our study areas. Bai et al (2006) also found that isoprene emission from grassland in Inner Mongolia mainly came from sedge (Bai et al, 2006). Different from ambient samples collected by canisters, we found much higher isoprene concentration roughly at zero minute in the chamber.…”

Evaluation of a photosynthesis-based biogenic isoprene emission scheme in JULES and simulation of isoprene emissions under present-day climate conditions

“…Nevertheless observations collected at a grassland site in Inner Mongolia reach values comparable to a tree-dominated environment (Bai et al, 2006), while summer-time maxima in a sub-arctic Swedish wetland reach values similar to boreal and temperate forest locations (Holst et al, 2010). We have been unable to make a simulation for this these sites because of the lack of local meteorological data; in particular downward longwave and shortwave radiation were not available for a time period long enough to perform a local simulation.…”

Why are estimates of global terrestrial isoprene emissions so similar (and why is this not so for monoterpenes)?

“…Although some C3 grasses, sedges or herbaceous vegetation emit significant amounts of isoprene (Kesselmeier and Staudt, 1999;Bai et al, 2006;Ekberg et al, 2008), by far the largest proportion of isoprene emission originates from woody vegetation. Azolla, a highly emitting fern is frequently found growing alongside non-emitting rice in aquaculture.…”