Stomatal Responses of Douglas-Fir Seedlings to Elevated Carbon Dioxide and Temperature During the Third and Fourth Years of Exposure

Two major components of climate change, increasing atmospheric [CO2] and increasing temperature, may substantially alter the effects of water availability to plants through effects on the rate of water loss from leaves. We examined the interactive effects of elevated [CO2] and temperature on seasonal patterns of stomatal conductance (gs), transpiration (E) and instantaneous transpiration efficiency (ITE) in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings. Seedlings were grown in sunlit chambers at either ambient CO2 (AC) or ambient + 180 µmol mol-1 CO2 (EC), and at ambient temperature (AT) or ambient + 3.5° C (ET) in a full-factorial design. Needle gas exchange at the target growth conditions was measured approximately monthly over 21 months. Across the study period and across temperature treatments, growth in elevated [CO2] decreased E by an average of 12% and increased ITE by an average of 46%. The absolute reduction of E associated with elevated [CO2] significantly increased with seasonal increases in the needle-to-air vapour pressure deficit (D). Across CO2 treatments, growth in elevated temperature increased E an average of 37%, and did not affect ITE. Combined, growth in elevated [CO2] and elevated temperature increased E an average of 19% compared with the ACAT treatment. The CO2 supply and growth temperature did not significantly affect stomatal sensitivity to D or the relationship between gs and net photosynthetic rates. This study suggests that elevated [CO2] may not completely ameliorate the effect of elevated temperature on E, and that climate change may substantially alter needle-level water loss and water use efficiency of Douglas-fir seedlings

Foliar nitrogen concentrations and natural abundance of ¹⁵N suggest nitrogen allocation patterns of Douglas-fir and mycorrhizal fungi during development in elevated carbon dioxide concentration and temperature

seudotsuga menziesii (Mirb.) Franco (Douglas-fir) seedlings were grown in a 2 × 2 factorial design in enclosed mesocosms at ambient temperature or 3.5 °C above ambient, and at ambient CO2 concentration ([CO2]) or 179 ppm above ambient. Two additional mesocosms were maintained as open controls. We measured the extent of mycorrhizal infection, foliar nitrogen (N) concentrations on both a weight basis (%N) and area basis (Narea), and foliar δ15N signatures (15N/14N ratios) from summer 1993 through summer 1997. Mycorrhizal fungi had colonized nearly all root tips across all treatments by spring 1994. Elevated [CO2] lowered foliar %N but did not affect Narea, whereas elevated temperature increased both foliar %N and Narea. Foliar δ15N was initially –1‰ and dropped by the final harvest to between –4 and –5‰ in the enclosed mesocosms, probably because of transfer of isotopically depleted N from mycorrhizal fungi. Based on the similarity in foliar δ15N among treatments, we conclude that mycorrhizal fungi had similar N allocation patterns across CO2 and temperature treatments. We combined isotopic and Narea data for 1993–94 to calculate fluxes of N for second- and third-year needles. Yearly N influxes were higher in second-year needles than in third-year needles (about 160 and 50% of initial leaf N, respectively), indicating greater sink strength in the younger needles. Influxes of N in second-year needles increased in response to elevated temperature, suggesting increased N supply from soil relative to plant N demands. In the elevated temperature treatments, N effluxes from third-year needles were higher in seedlings in elevated [CO2] than in ambient [CO2], probably because of increased N allocation below ground. We conclude that N allocation patterns shifted in response to the elevated temperature and [CO2] treatments in the seedlings but not in their fungal symbionts

Relative Sensitivity of Avocado Varieties to Photochemical Smog (Ozone) and Sulfur Dioxide

ABSTRACT A preliminary study was conducted to gain general information as to the sensitivity of avocado varieties (Persea americana L.) to the primary component of smog, ozone (O 3 ), and sulfur dioxide (SO 2 ). Varieties on both seedling 'G6' and clonal 'Borchard' rootstocks were exposed to 0, 0.1, 0.2, 0.3, or 0.4 ppm O 3 for eight hours; or 0, 0.25, 0.5, or 1.0 ppm SO 2 for 24 hours; for two days. 'Hass', 'Whitsell', and 'Gwen' were generally more sensitive than Fuerte' and 'G6'. Mexican-race cultivars tended to be less sensitive to O 3 than Guatemalan-race cultivars. Larger, older trees on 'G6' rootstocks had less injury than smaller, younger trees on 'Borchard' rootstocks. A minimum of 0.2 ppm O 3 or 0.5 ppm SO 2 was required for acute leaf injury to avocados. Ozone injury was characterized as a brown flecking on upper leaf surfaces; and SO 2 injury as large areas of brown, dead tissue through both upper and lower leaf surfaces

Relationships Between Needle Nitrogen Concentration and Photosynthetic Responses of Douglas-Fir Seedlings to Elevated CO2 and Temperature

Here we examined correlations between needle nitrogen concentration ([N]) and photosynthetic responses of Douglas-fir (Pseudotsuga menziesii) seedlings to growth in elevated temperatures and atmospheric carbon dioxide concentrations ([CO2]). Seedlings were grown in sunlit, climate-controlled chambers at ambient or ambient+3.5° C and ambient or ambient +180 μmol mol-1 CO2 in a full factorial design. Photosynthetic parameters and needle [N] were measured six times over a 21-month period. Needle [N] varied seasonally, and accounted for 30–50% of the variation in photosynthetic parameters. Across measurement periods, elevated temperature increased needle [N] by 26% and light-saturated net photosynthetic rates by 17%. Elevated [CO2] decreased needle [N] by 12%, and reduced net photosynthetic rates measured at a common [CO2], maximum carboxylation activity (Vc,max) and electrontransport capacity (Jmax), indicating photosynthetic acclimatization. Even so, elevated [CO2] enhanced net photosynthesis, and this effect increased with needle [N]. These results suggest that needle [N] may regulate photosynthetic responses of Douglas-fir to climate change. Further, needle [N] may be altered by climate change. However, effects of elevated [CO2] on photosynthesis may be similar across growth temperatures