Guidelines for measuring and reporting environmental factors in controlled environment facilities

Abstract

Guidelines for measuring and reporting environmental factors in growth chamber and other controlled environment studies of plant growth are listed. These guidelines were developed by researchers on the North Central Regional Committee NCR‐101 on Growth Chamber Use concerned with the use of controlled environment facilities for plant research. Adoption of these standardized guidelines should improve the quality of plant research in such facilities.     

Measuring forest floor CO2 fluxes in a Douglas-fir forest

CO₂ exchange was measured on the forest floor of a coastal temperate Douglas-fir forest located near Campbell River, British Columbia, Canada. Continuous measurements were obtained at six locations using an automated chamber system between April and December, 2000. Fluxes were measured every half hour by circulating chamber headspace air through a sampling manifold assembly and a closed-path infrared gas analyzer. Maximum CO₂ fluxes measured varied by a factor of almost 3 between the chamber locations, while the highest daily average fluxes observed at two chamber locations occasionally reached values near 15 μmol C m⁻² s⁻¹. Generally, fluxes ranged between 2 and 10 μmol C m⁻² s⁻¹ during the measurement period. CO₂ flux from the forest floor was strongly related to soil temperature with the highest correlation found with 5 cm depth temperature. A simple temperature dependent exponential model fit to the nighttime fluxes revealed Q₁₀ values in the normal range of 2–3 during the warmer parts of the year, but values of 4–5 during cooler periods. Moss photosynthesis was negligible in four of the six chambers, while at the other locations, it reduced daytime half-hourly net CO₂ flux by about 25%. Soil moisture had very little effect on forest floor CO₂ flux. Hysteresis in the annual relationship between chamber fluxes and soil temperatures was observed. Net exchange from the six chambers was estimated to be 1920±530 g C m⁻² per year, the higher estimates exceeding measurement of ecosystem respiration using year-round eddy correlation above the canopy at this site. This discrepancy is attributed to the inadequate number of chambers to obtain a reliable estimate of the spatial average soil CO₂ flux at the site and uncertainty in the eddy covariance respiration measurements.     

Are seedlings reasonable surrogates for trees? An analysis of ozone impacts on Quercus rubra

The appropriateness of using seedling responses to predict mature tree responses to ozone is questionable considering the long life span of trees. To determine if northern red oak (Quercus rubra L.) seedlings and mature trees respond similarly to ozone, 30-year-old trees and two-year-old seedlings were fumigated with subambient, ambient, and twice ambient concentrations of ozone for three growing seasons using an open-top chamber facility. Ozone reduced leaf physiological function of mature trees. However, stem diameter growth and leaf mass of mature trees were not significantly reduced by ozone. Photosynthesis in seedling leaves was slightly reduced by ozone, but seedling growth and biomass were unaffected. Mature tree fine-root biomass responded negatively to increasing ozone, while seedlings exhibited increases in biomass. Carbon retention was enhanced in leaves and branches of mature trees by ozone treatment, while seedlings were unresponsive. Differences in ozone uptake, recurrent flushing and carbon dynamics rather than microclimate may explain differences in ozone sensitivity between seedlings and mature trees. These results indicate that seedlings may not reflect the ozone sensitivity of larger more physiologically mature trees.     

矮嵩草(Kobresia humilis)草甸内架设开顶式增温小室对微气候的影响

矮嵩草 (Kobresiahumilis)草甸内架设开顶式增温小室后 ,在牧草生长季节 ,增温小室内的气温平均提高 1 .47℃ ,土温平均提高 1 .0 0℃ ,地表温度平均提高 1 .5 4℃ ;增温小室外的湿度略高于其内部 ;增温小室外的风速明显高于其内部 ;增温小室内外的太阳水平总辐射、反射系数和极端温度差异不显著 ,但变化趋势各有异同 ;增温小室的修建对地温与湿度间、气温与空气湿度间的相关显著性有影响 ,对温度与其他气候因子间的相关关系影响不大