The carbon charging of pines at the climatic treeline: a global comparison

Abstract

The carbon charging of pines across the treeline ecotone of three different climatic zones (Mexico 19 degrees N Pinus hartwegii, Swiss Alps 46 degrees N P. cembra and northern Sweden 68 degrees N P. sylvestris) was analyzed, to test whether a low-temperature-driven carbon shortage can explain high-elevation tree limits, and whether the length of the growing season affects the trees' carbon balance. We quantified the concentrations of non-structural carbohydrates (NSC) and lipids (acylglycerols) in all tree organs at three dates during the growing seasons across elevational transects from the upper end of the closed, tall forest (timberline) to the uppermost location where groups of trees > or =3 m in height occur (treeline). Mean ground temperatures during the growing season at the treelines were similar (6.1+/-0.7 degrees C) irrespective of latitude. Across the individual transects, the concentrations of NSC and lipids increased with elevation in all organs. By the end of the growing season, all three species had very similar total mobile carbon (TMC) concentrations at the treeline (ca. 6% TMC in the aboveground dry biomass), suggesting no influence of the length of the growing season on tree carbon charging. At a temperate lowland reference site P. sylvestris reached only ca. 4% TMC in the aboveground dry biomass, with the 2% difference largely explained by higher lipid concentrations of treeline pines. We conclude that carbon availability is unlikely to be the cause of the altitudinal tree limit. It seems rather that low temperatures directly affect sink activity at the treeline, with surplus carbon stored in osmotically inactive compounds.

Lichen, moss and soil in resolving the occurrence of semi-volatile organic compounds on the southeastern Tibetan Plateau, China

“…This might be due to the stronger synthesis of fat for their stronger frost resistances in the higher altitudes. Similar findings were also observed for pine needles, tree bark and xylem tissues (Hoch and Korner, 2003;Yang et al, 2013). To avoid the influence of altitudes on the concentration and lipid (or TOC) content, partial correlation analysis was carried out and indicated that there was no significant correlation between the soil TOC and the concentrations of each targeted compound, which was different from the observation of Yang's work where most of OCPs were significantly linearly correlated with the soil TOC (Yang et al, 2013).…”

“…Lichen is a complex life form that lives symbiotically with fungi and algae; thus, the decreasing temperature with increasing altitude might be related to the altitude-dependent gradient trend of SVOCs in lichens. Additionally, the host trees at the higher altitudes might ooze more hydrophobic oils to resist frost than those at lower altitudes, which may increase the lipid contents of lichens, further improving the uptake capacity of SVOCs for lichens in the higher altitude regions (Hoch and Korner, 2003;Yang et al, 2013). Conversely, a range of other studies also noted similar altitude-dependent gradient trend/cold-trapping effects for HCHs (Blais et al, 1998;Blais et al, 2003;Davidson et al, 2003;Shen et al, 2004), DDTs Davidson et al, 2003;Shen et al, 2005), endosulfan II and PCBs (Blais et al, 1998) in the Canadian Rocky Mountains and the Alps.…”

Feedback effects of clonal groups and tree clusters on site conditions at the treeline: implications for treeline dynamics

“…On the other hand, nonstructural carbon reserves (e.g. Sveinbjörnsson et al 1992, Skre 1993, Grace et al 2002, Hoch & Körner 2003, Shi et al 2006) may compensate for the effects of low soil temperature during the early growing season. In dry climates and during dry summers, moisture supply from melting snow drifts may mitigate moisture stress in late spring and early summer.…”

Winter crop growth at low temperature may hold the answer for alpine treeline formation

“…build new structures (< 5 °C; Körner 2003). As a consequence of limits to tissue growth, plants accumulate non-structural carbohydrates and even lipids (Hoch and Körner 2003). For leaf starch formation this observation dates back to the mid-nineteenth century (Krause 1869).…”