Large-scale plant growth chamber design for elevated pCO2 and δ13C studies

RATIONALE: Throughout at least the next century, CO2 fertilization and environmental stresses (e.g. nutrient, moisture, insect herbivory) are predicted to affect yields of economically important crop species. Stable isotopes of carbon are used to study plant stresses, which affect yields, but a growth chamber design that can be used to isolate the effects of environmental stresses on crop-sized species through precise maintenance of pCO(2) levels and the delta C-13 values of atmospheric CO2 (delta C-13(CO2)) is lacking. METHODS: We designed and built low-cost plant growth chambers for growing staple crop species under precise pCO(2) and delta C-13(CO2) conditions. Over the course of 14 hours, we assessed for pCO(2) stability at two targeted levels (ambient, similar to 400 ppm; and 2x, similar to 800 ppm) and measured the delta C-13(CO2) value within the two chambers using a stable isotope ratio mass spectrometer. We also compared the temperature and relative humidity conditions within the two growth chambers, and in the ambient, outside air. RESULTS: Across our experimental period, we achieved delta C-13(CO2) stability (ambient: -8.05 +/- 0.17%; elevated: -12.99 +/- 0.29%) that showed nearly half the variability of any previously reported values for other chamber designs. The stability of the pCO(2) conditions (ambient: 406 +/- 3 ppm; elevated: 793 +/- 54 ppm) was comparable with that in previous studies, but our design provided similar to 8 times more growing space than previous chamber designs. We also measured nearly identical temperature and relative humidity conditions for the two chambers throughout the experiment. CONCLUSIONS: Our growth chamber design marks a significant improvement in our ability to test for plant stress across a range of future pCO(2) scenarios. Through significant improvement in delta C-13(CO2) stability and increased chamber size, small changes in carbon isotope fractionation can be used to assess stress in crop species under specific environmental (temperature, relative humidity, pCO(2)) conditions. Copyright (C) 2015 John Wiley & Sons, Ltd.