Determination of the biogenic emission rates of species contributing to VOC in the San Joaquin Valley OF California. Tanner, Roger L. & Zielinska, Barbara.
As part of an extensive effort to characterize biogenic hydrocarbon emission rates in the San Joaquin Valley and surrounding areas during the SJVAQS/AUSPEX field experimental period, July-August 1990, measurements were made for the first time of isoprene, terpene, and other VOC emission rates from blue oak ( Quercus douglasii), foothill pine ( Pinus sabiniana), and a ground cover plant called tarweed ( Holocarpha sp.) at a rural site near Mariposa, CA. A flow-through plant enclosure method was used to measure the emission flux rates from these species; the plant limb or whole plant was flushed with clean air just prior to hydrocarbon sampling. Samples of the plant emissions were collected on Tenax GC or Tenax GC-Carbosieve S-I1 cartridges and analysed by gas chromatography- Fourier transform infrared-mass spectrometry (GC-FTIR-MS). Quantifiable biogenic emissions from two blue oak specimens consisted only of isoprene, with an average emission rate of 8.4 μg g -1 dry biomass h -1. Emission rates (above the detection of about 0.05 μg -1 h -1) from two foothill pine specimens consisted mostly of α-pinene; an average emission rate of 0.64 μg -1 h -1 of α-pinene was observed. The tarweed species emitted both α- and β-pinenes, along with other terpene and oxygenated species, some of which have been tentatively identified. The emission rates of biogenic hydrocarbons from foothill pine and blue oak species as determined in this study make these species potentially significant contributors to summertime VOC levels in the San Joaquin Valley of California, based on vegetation classification data and the predominant summer meteorology.
Effects of Variable Precipitation on the Strucutre and Diversity of a California Salt Marsh Community. Sabraw, Ragan M. Callaway; Craig S..
Journal of Vegetation Science:
We measured the effects of annual variation in climate and experimentally augmented rainfall on patterns of distribution and above-ground productivity in annual plant communitiesa t CarpinteriaS alt Marsh in central California. In the driest year, Hutchinsia procumbens was codominant throughout much of the upper marsh; however, Hutchinsia was very rare or not present in the wetter years. Conversely, Juncus bufonius was common in the wettest year and absent in the driest year. Elevational distributions of other annual species also differed among years with different total precipitation. In 1989-1990, an exceptionally dry season, supplemental water decreased soil salinity, increased above-ground productivity of annuals, and caused significant changes in spatial patterns and relative density. In the lowest zone, Hutchinsia occurred only in watered plots and supplemental water increased the density of Spergularia marina. At intermediate elevations Lasthenia glabrata occurred only in watered plots and supplemental ater increased the density of Spergularia, Hutchinsia, and Parapholis incurva. At upper elevations, Juncus occurred only in watered plots, and Lasthenia was the only species that increased significantly in density with watering. Unlike natural shifts in species abundance, no species declined significantly in cover in any zone in the watered treatment. Although climatic variation has complex affects on annual plant communities, our experiments isolated important affects of total annual rainfall on the structure of annual plant communities that were similar to those that occurred with natural variation in rainfall.W e conclude that variation in total annual precipitation promotes dynamic community composition and spatial distributions among years, and thus increases overall species diversity in the salt marsh.