Effects of long-term CO2 enrichment and nutrient availability in Norway spruce. I. Phenology and morphology of branches

Abstract

Branches of 30-year-old Norway spruce [Picea abies (L.) Karst.] trees were enclosed in ventilated, transparent plastic bags and flushed with air containing ambient (A≈370 µmol CO 2 mol -1 ) or ambient plus 340 µmol CO 2 mol -1 (EL). Light-saturated photosynthesis was on average 56% higher in EL compared to A. Branch phenology and morphology were strongly related to nitrogen concentration (mg g -1 dry mass) in the foliage and to elevated temperatures in the bags, but no direct effect of EL was found. In 1995, budbreak occurred on average 4 days earlier in the bags compared to the control branches, which was partly explained by the temperature elevation in the bags. No nutrient or EL effect on budbreak was found. Increases in temperature and nitrogen supply increased shoot growth: together they explained 76% of the variation in the extension rate, 63% of the variation in extension duration and 65% of the variation in final length of leading shoots. Shoot morphology was altered both by increased nitrogen availability and by the enclosure induced environmental changes inside the bags, leading to reduced mutual shading between needles. Specific needle area (SNA) was lower in EL, but this was related to lower nitrogen concentrations. Total dry mass of the branches was unaffected by EL. It is concluded that treating individual branches of Norway spruce with elevated CO 2 does not increase branch growth. The nutrient status of the branch and climate determine its growth, i.e. its sink strength for carbon. Increased export of carbohydrates to the rest of the tree is probable in EL treated branches.

Needle longevity, shoot growth and branching frequency in relation to site fertility and within-canopy light conditions in Pinus sylvestris

“…There is evidence that, in conifers, branchiness may increase with decreasing site water availability [5]. In addition, increases in soil nutrient availability generally lead to enhanced branch extension growth [47,67], as well as higher fractional biomass investment in foliage [59], and greater total plant foliar area [47,70,73]. The branching responses to nutrient availability have not been investigated extensively in trees, and it is not clear whether the nutrientrelated increase in branch extension is sufficient to support the extra foliar area, or whether the improved nutrition also leads to greater shoot production and more frequent branching.…”

Long-term effects of CO₂ enrichment on bud phenology and shoot growth patterns of Norway spruce juvenile trees

“…The effect of long-term (months and years) CO 2 enrichment on phenology of Norway spruce was investigated by few authors, and the ecosystem level approach was missing. According to results from branch investigation (Roberntz 1999) or shortterm studies , Norway spruce was found unaffected by elevated CO 2 in bud break as well as in shoot elongation growth.…”

“…However, not only the temperature (Linkosalo et al 2000) but also other environmental factors -global radiation or amount of precipitation (e.g. Bigras, D'Aoust 1993;Häkkinen 1999) and fertilization -may act as stimulators of plant growth (Roberntz 1999). For example, the increasing nutrient supply lengthened the growing season and plants flushed earlier in spring and set buds later in autumn (Murray et al 1994;Roberntz 1999).…”

“…Bigras, D'Aoust 1993;Häkkinen 1999) and fertilization -may act as stimulators of plant growth (Roberntz 1999). For example, the increasing nutrient supply lengthened the growing season and plants flushed earlier in spring and set buds later in autumn (Murray et al 1994;Roberntz 1999). Recently, earlier flowering and an extended period of active plant growth across much of the northern hemisphere have been interpreted as responses to global climate change (Cleland et al 2006).…”

“…Under elevated CO 2 conditions, an acceleration of bud phenology (Repo et al 1996;Jach, Ceulemans 1999) is reported, others showed a dilution response (i.e. the positive effect of elevated CO 2 on tree phenology is diminished over time, Linkosalo [2000]) or no effects (Olszyk et al 1998;Roberntz 1999;Kilpelainen et al 2006;Slaney et al 2007). Even among various tree species clones there is a variability of phenological responses which indicated that there are many factors reshaping the seasonality of ecosystem processes (Murray et al 1994;Johnsen, Seiler 1996;Centritto et al 1999;Bigras, Bertrand 2006).…”