Influence of fertilization and atmospheric CO2 enrichment on ecosystem CO2 and H2O exchanges in single- and multiple-species grassland microcosms

Arthur L. Fredeen, George W. Koch, Christopher B. Field

Research output: Contribution to journalArticle

7 Scopus citations

Abstract

This paper reports on measurements of net CO2 and H2O exchange from single- and multiple-species microcosms composed of California annual grassland species grown at either ambient or elevated (ambient + 36 Pa) CO2. Microcosms consisted of grassland species grown in PVC tubes (~ 0.95 m deep x 0.2 m diameter) containing ~45 kg of either serpentine or sandstone derived soil or parent material in open-top enclosures under ambient meteorological conditions. Half of the microcosms were left unfertilized (low nutrient) while the other half received an intermediate level of a slow-release (N,P,K) fertilizer (high nutrient). Gas exchange was performed by sealing individual microcosms within a transparent chamber (on clear sunny days) and coupling this to an open gas-exchange system. In fertilized single-species microcosms, elevated CO2 consistently enhanced net 'ecosystem' CO2 exchange (NCE) on a ground area basis in both early and late spring. Among unfertilized single-species microcosms, no significant trends or differences were observed in NCE between those grown at ambient versus elevated CO2. The NCE in sandstone and serpentine multiple-species microcosms was monitored seasonally over a majority of the 1993-1994 growing season. Rates were largely unaffected by growth CO2 or fertilization until after mid-February, 1994. Water-use efficiency (WUE = NCE/evapotranspiration (ET)) was generally enhanced by elevated CO2, but this was primarily a result of enhancements in NCE as opposed to decreases in ET. Enhancements in NCE by elevated CO2 in fertilized single-species microcosms at the growth-CO2 concentration were partially explained by higher above-ground biomass in elevated CO2 microcosms. However, ecosystem-level 'acclimation' occurred such that microcosms grown at elevated CO2 consistently had lower NCE than ambient CO2 treatments at a single measurement CO2 concentration (ambient or elevated). The reduction in apparent ecosystem-level photosynthetic capacity in elevated CO2 microcosms was accompanied by decreases in foliar Rubisco activity, such that NCE measured at ambient CO2 was highly correlated. (r = 0.98) with foliar Rubisco activity across the three single-species microcosms in which it was measured.

Original languageEnglish (US)
Pages (from-to)147-157
Number of pages11
JournalEnvironmental and Experimental Botany
Volume40
Issue number2
DOIs
StatePublished - Oct 1 1998

Keywords

  • California annual grassland
  • Ecosystem WUE
  • Ecosystem photosynthesis
  • Elevated CO
  • Grassland microcosms
  • Mediterranean climate

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Agronomy and Crop Science
  • Plant Science

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