Carbon allocation and water use in juvenile Douglas fir under elevated CO₂

Abstract

SUMMARYIn this study the impact of an elevated CO, level on allocation of assimilates and water use efficiency of Douglas fir [Pseudotsiiga menziesii (Mirb.) Franco] was investigated. Juvenile Douglas firs were exposed to a long-term treatment at 350 and 700^1 T' CO^ for 14 months and subsequently crosswise transferred to phytotrons for a short-term treatment with 350 and 700 fi\ 1"^ COj for 4 wk in an atmosphere continuously labelled with "CO^. No interactive efTects on total net uptake of ^^COj between long-term treatment and short-term treatment were observed. The short-term treatment with 700 n\ 1"' COj increased the total net uptake of "CO^ by 22 %, compared with the 350 //I 1"^ CO^ treatment. The long-term pretreatment did not affect the total net uptake, suggesting that photosynthetic acclimation had not occurred. However, expressed per unit of needle mass a 14% reduction was observed in the trees pretreated at 700 /tl 1"^ COj. This was not because of a reduced sink strength of the root system. This reduced uptake per unit of needle mass after long-term treatment may have implications for carbon storage in forest ecosystems. The results showed that an initial growth stimulation can eventually be annulled by developing physiological or morphological adaptions. "CO^ in the root/soil respiration increased in the short-term treatment with 700 //I 1"^ CO^, indicating a stimulated use of current carbon compounds either by roots or microorganisms. The water use efficiency during the short-term treatment with 700 /tl T' COg increased by 32 %, but was not affected by the long-term pretreatment. Water use per unit needle mass during the short-term treatment was decreased both by the short-term treatment and by the long-term pretreatment by about 15%. Some of the observed effects appeared to be persistent, such as decreased water use per unit needle mass, whereas others, stimulation of total net "CO2 uptake and water use efficiency, were transient.

Whole-seedling biomass allocation, leaf area, and tissue chemistry for Douglas-fir exposed to elevated CO2 and temperature for 4 years

“…Elevated CO 2 may have stimulated early growth of the seedlings with the effect disappearing over time as observed previously in Douglas-fir by Gorissen et al (1995). In our study, root biomass was higher from soil cores taken in elevated compared with the ambient CO 2 chambers in fall Table 1.…”

“…Franco) is the most important timber species in the Pacific Northwest of the United States and southern British Columbia, Canada (Little 1971), yet Douglas-fir has not been intensively studied in terms of responses to global climate change (Mote et al 1999;Franklin et al 1991). There have been a few studies on the short-term responses (~3-14 months) of Douglas-fir to elevated CO 2 in containers under controlled environments (Gorissen et al 1995;Mortensen 1994;Hollinger 1987). In general, these studies showed little effect of elevated CO 2 on growth or biomass accumulation or allocation for seedlings.…”

Xeromorphy increases in shoots of Pseudotsuga menziesii (Mirb.) Franco seedlings with exposure to elevated temperature but not elevated CO2

“…Hollinger (1987) found no difference in dry mass or relative mass allocation for P. menziesii with elevated compared to ambient CO 2 . Gorissen et al (1995) indicated that elevated CO 2 can have a short-term stimulatory effect on P. menziesii shoot growth, but that this effect may disappear over time. Brix (1967) reported more xerophytic P. menziesii leaves with higher temperatures (i.e., thicker, narrower, and heavier), but no effect of temperature on allocation of mass to stems and branches from roots.…”

Elevated CO2 and tree root growth: contrasting responses in Fraxinus excelsior, Quercus petraea and Pinus sylvestris

“…However, the results observed from direct measurements of root respiration in response to elevated atmospheric CO # are varied (Rogers et al, 1994), with increases (Gorrisen, Kuikman & Van de Beek, 1995), decreases (Callway et al, 1994 ;Gifford, Lambers & Morison, 1985 ;Gonza ' lez-Meler et al, 1996) and no change (Stulen & Den Hertog, 1993) reported. Interestingly, Ryan et al (1996) have shown that for fine roots there is a strong relationship between root respiration and nitrogen content, suggesting that root activity varies with the protein content of the tissue.…”