ALBERT

Description: White oak (Quercusalba L.) seedlings grown in a silt loam soil inoculated with Pisolithustinctorius (Pers.) Coker and Couch exhibited 80% ectomycorrhizal development after a 6-month establishment period whereas the noninoculated controls exhibited less than 5%.When water was withheld and soil water potential decreased as the soil dried, xylem pressure potential and leaf conductance of both the inoculated and noninoculated seedlings declined gradually. At the peak of the drying cycle, the inoculated seedlings exhibited mean prelight and midlight xylem pressure potential values which were 0.2 MPa and 0.15 MPa, respectively, more negative than the noninoculated seedlings. Although the inoculated seedlings had a mean leaf surface area 1.5 times larger than that of the noninoculated seedlings, there were no significant differences in leaf conductance at the peak of the dehydration cycle. Mean rates of root elongation were greater among the inoculated seedlings during the drying cycle. Following reirrigation of the soil, the inoculated seedlings yielded significantly less negative values of prelight and midlight xylem pressure potential and greater leaf conductance when compared to the noninoculated seedlings.

Description: Predicted future changes in air temperature and atmospheric CO 2 concentration ([CO 2 ]), coupled with altered precipitation, are expected to substantially affect tree growth. Effects on growth may vary considerably across a species range, as temperatures vary from sub-optimal to supra-optimal for growth. We performed an experiment simultaneously at two locations in the current range of loblolly pine, a cool site and a warm site, to examine the effect of future climate conditions on growth of loblolly pine seedlings in contrasting regions of the species range. At both sites 1-year-old loblolly pine seedlings were grown in current (local ambient temperature and [CO 2 ]) and predicted future atmospheric conditions (ambient +2 °C temperature and 700 mol mol –1 [CO 2 ]). Additionally, high and low soil moisture treatments were applied within each atmospheric treatment at each site by altering the amount of water provided to the seedlings. Averaged across water treatments, photosynthesis ( A net ) was 31% greater at the cool site and 34% greater at the warm site in elevated temperature and [CO 2 ] compared with ambient temperature. Biomass accumulation was also stimulated by 38% at the cool site and by 24% at the warm site in that treatment. These results suggest that a temperature increase of 2 °C coupled with an increase in [CO 2 ] (predicted future climate) will create conditions favorable for growth of this species. Reduced soil moisture decreased growth in both current and predicted atmospheric conditions. Biomass accumulation and A net were reduced by ~39 and 17%, respectively, in the low water treatment. These results suggest that any benefit of future atmospheric conditions may be negated if soil moisture is reduced by altered precipitation patterns.

Description: If an increase in temperature will limit the growth of a species, it will be in the warmest portion of the species distribution. Therefore, in this study we examined the effects of elevated temperature on net carbon assimilation and biomass production of northern red oak ( Quercus rubra L.) seedlings grown near the southern limit of the species distribution. Seedlings were grown in chambers in elevated CO 2 (700 µmol mol –1 ) at three temperature conditions, ambient (tracking diurnal and seasonal variation in outdoor temperature), ambient +3 °C and ambient +6 °C, which produced mean growing season temperatures of 23, 26 and 29 °C, respectively. A group of seedlings was also grown in ambient [CO 2 ] and ambient temperature as a check of the growth response to elevated [CO 2 ]. Net photosynthesis and leaf respiration, photosynthetic capacity ( V cmax , J max and triose phosphate utilization (TPU)) and chlorophyll fluorescence, as well as seedling height, diameter and biomass, were measured during one growing season. Higher growth temperatures reduced net photosynthesis, increased respiration and reduced height, diameter and biomass production. Maximum net photosynthesis at saturating [CO 2 ] and maximum rate of electron transport ( J max ) were lowest throughout the growing season in seedlings grown in the highest temperature regime. These parameters were also lower in June, but not in July or September, in seedlings grown at +3 °C above ambient, compared with those grown in ambient temperature, indicating no impairment of photosynthetic capacity with a moderate increase in air temperature. An unusual and potentially important observation was that foliar respiration did not acclimate to growth temperature, resulting in substantially higher leaf respiration at the higher growth temperatures. Lower net carbon assimilation was correlated with lower growth at higher temperatures. Total biomass at the end of the growing season decreased in direct proportion to the increase in growth temperature, declining by 6% per 1 °C increase in mean growing season temperature. Our observations suggest that increases in air temperature above current ambient conditions will be detrimental to Q. rubra seedlings growing near the southern limit of the species range.

Description: To accurately estimate stem respiration ( R S ), measurements of both carbon dioxide (CO 2 ) efflux to the atmosphere ( E A ) and internal CO 2 flux through xylem ( F T ) are needed because xylem sap transports respired CO 2 upward. However, reports of seasonal dynamics of F T and E A are scarce and no studies exist in Mediterranean species under drought stress conditions. Internal and external CO 2 fluxes at three stem heights, together with radial stem growth, temperature, sap flow and shoot water potential, were measured in Quercus pyrenaica Willd. in four measurement campaigns during one growing season. Substantial daytime depressions in temperature-normalized E A were observed throughout the experiment, including prior to budburst, indicating that diel hysteresis between stem temperature and E A cannot be uniquely ascribed to diversion of CO 2 in the transpiration stream. Low internal [CO 2 ] (〈0.5%) resulted in low contributions of F T to R S throughout the growing season, and R S was mainly explained by E A (〉90%). Internal [CO 2 ] was found to vary vertically along the stems. Seasonality in resistance to radial CO 2 diffusion was related to shoot water potential. The low internal [CO 2 ] and F T observed in our study may result from the downregulation of xylem respiration in response to a legacy of coppicing as well as high radial diffusion of CO 2 through cambium, phloem and bark tissues, which was related to low water content of stems. Long-term studies analyzing temporal and spatial variation in internal and external CO 2 fluxes and their interactions are needed to mechanistically understand and model respiration of woody tissues.

Description: Responses of CO2 and water vapor exchange to absolute humidity deficit (AHD) were measured for seedlings of Pinustaeda L. at high and low irradiance in the laboratory. Diurnal patterns of CO2 and water vapor exchange of P. taeda seedlings and trees were monitored in the field. Stomatal behavior was evaluated in relation to a recent hypothesis of "optimal" stomatal behavior, in which changes in stomatal conductance in response to environmental variation are such that water loss is minimized for a given amount of carbon gain. That is, when stomatal behavior is "optimal," the ratio (gain ratio) of the sensitivities of transpiration and net photosynthesis to changes in stomatal conductance [Formula: see text] is constant.Laboratory and field stomatal behavior generally did not conform with this hypothesis. Under controlled conditions, at high irradiance, the gain ratio increased with AHD. In the field, the gain ratio increased diurnally on most days. Increasing gain ratios were associated with increasing [Formula: see text] values but relatively uniform [Formula: see text] values. Uniform gain ratios in the field were observed on some days, associated with uniform environment, constant [Formula: see text], or varying [Formula: see text] values.

Description: Seasonal changes in water relations and net photosynthesis were measured over a year in current and 1-year-old foliage of Abiesamabilis (Dougl.) Forbes, a subalpine conifer. Responses were compared with maximum rates achieved in older foliage. Current-year foliage developed slowly during the growing season. Although growth began on 22 June, highest rates of stomatal conductance and net photosynthesis did not occur until September and October. One-year-old foliage had the highest rates of net photosynthesis (12.9 mg CO2•dm−2•h−1) and stomatal conductance (3.1 mm•s−1) during the summer. Net photosynthesis decreased with needle age, but foliage as old as 7 years had rates of net photosynthesis as high as 5.0 mg CO2•dm−2•h−1. There was no evidence of photosynthetic adjustment to seasonal change in temperature. The optimum temperature for photosynthesis remained at 15 ± 1.5 °C throughout the year. No water stress was observed during the summer. Xylem water potential never decreased below −1.65 MPa and was always well above the turgor loss point. The lack of any apparent water stress, combined with photosynthetic characteristics, indicated that summer was the most important season for carbon gain. These results also suggested that a strategy for competitive success by Abiesamabilis in this cold, stressful environment is minimum dependence on the carbon gain of any individual age-class of foliage. Instead trees rely on the combined photosynthetic capacity of many years of foliage.