Light and water-use efficiencies of pine shoots exposed to elevated carbon dioxide and temperature

An automatic gas exchange system was used to continuously measure water and carbon fluxes of attached shoots of Scots pine trees (Pinus sylvestris L.) grown in environment-controlled chambers for a 3-year period (1998-2000) and exposed to either normal ambient conditions (CON), elevated CO2 (+350 micro mol mol-1; EC), elevated temperature (+2-6 degrees C; ET) or a combination of EC and ET (ECT). EC treatment enhanced the mean daily total carbon flux per unit projected needle area (Fc.d) by 17-21 %, depending on the year. This corresponds to a 16-24 % increase in light-use efficiency (LUE) based on incident photosynthetically active radiation. The EC treatment reduced the mean daily total water flux (Fw.d) by 1-12 %, corresponding to a 13-35 % increase in water-use efficiency (WUE). The ET treatment increased Fc.d by 10-18 %, resulting in an 8-19 % increase in LUE, and Fw.d by 48-74 %, resulting in a reduction of WUE by 19-34 %. There was no interaction between CO2 and temperature elevation in connection with either carbon or water fluxes, as the carbon flux responded similarly in both ECT and EC, while the water flux in the ECT treatment was similar to that in ET. Regressions indicated that the increase in maximum LUE was greater with increasing air temperature, whereas changes in WUE were related only to high vapour pressure deficit. Furthermore, changes in LUE and WUE caused by ECT treatment displayed strong diurnal and seasonal variation.     

Seasonal variation in respiration of 1-year-old shoots of scots pine exposed to elevated carbon dioxide and temperature for 4 years

Sixteen 20-year-old Scots pine (Pinus sylvestris L.) trees growing in the field were enclosed for 4 years in environment-controlled chambers that maintained: (1) ambient conditions (CON); (2) elevated atmospheric CO2 concentration (ambient + 350 micro mol mol-1; EC); (3) elevated temperature (ambient +2-6 degrees C; ET); or (4) elevated CO2 and elevated temperature (ECT). The dark respiration rates of 1-year-old shoots, from which needles had been partly removed, were measured over the growing season in the fourth year. In all treatments, the temperature coefficient of respiration, Q10, changed with season, being smaller during the growing season than at other times. Respiration rate varied diurnally and seasonally with temperature, being highest around mid-summer and declining gradually thereafter. When measurements were made at the temperature of the chamber, respiration rates were reduced by the EC treatment relative to CON, but were increased by ET and ECT treatments. However, respiration rates at a reference temperature of 15 degrees C were reduced by ET and ECT treatments, reflecting a decreased capacity for respiration at warmer temperatures (negative acclimation). The interaction between season and treatment was not significant. Growth respiration did not differ between treatments, but maintenance respiration did, and the differences in mean daily respiration rate between the treatments were attributable to the maintenance component. We conclude that maintenance respiration should be considered when modelling respiratory responses to elevated CO2 and elevated temperature, and that increased atmospheric temperature is more important than increasing CO2 when assessing the carbon budget of pine forests under conditions of climate change.     

Total and Component Carbon Fluxes of a Scots Pine Ecosystem from Chamber Measurements and Eddy Covariance

Annals of Botany 99: 345–353, 2007 The authors regret that the     

Growth and Resource Use of Birch Seedlings Under Elevated Carbon Dioxide and Temperature

The effects of elevated CO₂and temperature on the growth, resourceacquisition and resource allocation of small birch seedlings(Betula pendula Roth.) were examined under conditions of non-limitingsoil, water and nutrient supply. Seedlings were planted in potsand placed in controlled environment chambers either under normalambient conditions (CON), or in the presence of elevated CO₂(approx.700 µmol mol^-1; Elev. C), elevated temperature (approx.3 °C above the outside ambient temperature; Elev. T) ora combination of elevated CO₂and elevated temperature (Elev.C + T). Both Elev. C and Elev. T significantly increased biomassaccumulation, but the extent of the increase depended greatlyon the stage of development of the seedlings. Furthermore, thetheoretically expected positive effect of the warmer temperatureon the CO₂-induced stimulation of growth was not observed. Byanalysing resource acquisition (i.e. CO₂ , nitrogen and wateruptake), seedling development, leaf area production and theallocation pattern, it was deduced that the CO₂-stimulated increasein biomass resulted mainly from the initial ‘fertilization’effect of CO₂while the temperature-induced increase in biomassstemmed from higher net carbon intake during the middle andlatter parts of the growing season achieved by virtue of theincreased leaf area and larger photosynthetic capacity. Thelack of positive stimulation by temperature under Elev. C +T may be related in part to (1) CO₂-induced acceleration ofseedling development, which led to a small or no response toCO₂enrichment and lower leaf area production during the latterpart of the growth season, and (2) a cumulative delay in theresponse of growth to the warmer temperature, which did notincrease net carbon intake when the seedlings were at a juvenilestage. Neither Elev. C nor Elev. T altered the root:shoot ratioduring early growth, but Elev. C increased it during the latterpart of the growth season while Elev. T decreased it, possiblyon account of a change in leaf area retention. Finally, thenitrogen and water use efficiencies of seedlings at differentstages of development are discussed. Copyright 2001 Annals ofBotany Company Photosynthesis, growth, resource acquisition and allocation, elevated CO₂and temperature, Betula pendula Roth