Martha E. Apple

Morphology and Stomatal Function of Douglas Fir Needles Exposed to Climate Change: Elevated CO2 and Temperature1

Climate change may have an impact on the productivity of conifer trees by influencing the morphology (size and surface characteristics) and function (capacity for gas exchange) of conifer needles. In order to test the responses of needles to climatic variables, Douglas fir (Pseudotsuga menziesii [Mirb.] Franco), saplings were grown in sunlit controlled environment chambers at ambient or elevated (+200 parts per million above ambient) CO2 and at ambient or elevated temperature (+4°C above ambient). Needle characteristics, including length, width, area, stomatal density (stomata per mm2), percentage of stomatal occlusion, and the morphology of epicuticular wax, were evaluated. Needle function was evaluated as stomatal conductance to water vapor and transpiration. Needle length increased significantly with elevated temperature but not with elevated CO2. Neither elevated CO2 nor elevated temperature affected stomatal density or stomatal number in these hypostomatous needles. Epicuticular wax was less finely granular at elevated than at ambient temperature and was similar in appearance at elevated and ambient CO2. Stomatal conductance and transpiration increased with elevated temperature and associated increased vapor pressure deficit; however, neither conductance nor transpiration was affected by elevated CO2. These results indicate that simulated climate change influences Douglas fir needle structure and function.

Aspects of Mycorrhizae in Desert Plants

Mycorrhizal symbioses are critical to desert plants since they face the challenges of scarce, sporadic precipitation, nutrient deficiencies, intense solar radiation, and the high temperatures found in hot deserts. Deserts are covering increasingly more of the Earths surface area as desertification increases globally. Mycorrhizal desert plants have a greater chance of survival in the harsh desert environment. Desert plants form mycorrhizae with endomycorrhizal arbuscular fungi and with ectomycorrhizal fungi. Both form extensive networks of hyphae in the soil, and glomalin, a glycoprotein produced by hyphae of arbuscular mycorrhizal fungi, is crucial in soil structure and carbon storage. Mycorrhizal desert plants are important in agriculture, ecosystem biology, and conservation of the deserts.