Wednesday, November 7, 2007 - 9:50 AM
239-2
Soil-Plant-Atmosphere Research (SPAR) Chambers: Systems for Defining Crop Responses to the Environment in An Era of Global Climate Change.
Soil-Plant-Atmosphere Research (SPAR) chambers had their origins in enclosures designed to measure photosynthesis by “clumps” of vegetation in outdoor conditions. Current SPAR chamber systems are outdoor, sunlit, closed-circulation, controlled environment enclosures for growing plants throughout the entire life cycle (annuals) or across multiple seasons (perennials or trees). The same natural solar irradiance impinges on all chambers at a given location. Light quality reaching the plants depends on the covering material. Rooting volumes of most systems are large, certainly in comparison with pots. SPAR systems control carbon dioxide concentrations, dry-bulb air temperature, and dewpoint temperature to precise setpoints that can be constant or vary according to selected conditions throughout daily cycles. Carbon dioxide is replenished during light conditions via mass flow controllers. Dewpoint temperature is controlled by circulation through chilled water heat exchangers. Condensate is collected and measured by tipping bucket raingauges. Air temperature is restored by electrical heaters. Evapotranspiration and net canopy photosynthetic rates can be measured throughout the daytime by carbon dioxide and water balances at 5-min intervals. Canopy dark respiration rates can be measured at hourly intervals at night by a ventilation system. Recent success of SPAR systems has been for measuring responses of crop plants to a range of temperatures from optimum to the failure point of reproductive processes, which is important to establish curves of crop yields versus temperature. Failures of reproductive processes and seed yield of several important crops have been firmly established with SPAR chamber research. Outdoor Free Air CO2 Enrichment (FACE) systems cannot provide large ranges of temperatures at a given location. SPAR chamber research has established that the most important factor in Global Climate Change will be adverse impacts of rising temperatures rather than beneficial effects of rising carbon dioxide.
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