Atmospheric CO₂ enrichment of alpine treeline conifers

Abstract

Summary• Experimental CO 2 enrichment of mature Larix decidua and Pinus uncinata trees and their understory vegetation was used to test the carbon limitation hypothesis of treeline formation at the alpine treeline in Switzerland.• Forty plots (each 1.1 m 2 ) were established; half of them were exposed to elevated (566 ppm) atmospheric CO 2 using a free air CO 2 enrichment (FACE) system releasing pure CO 2 , and the other half were treated as controls at current ambient [CO 2 ].• Reliable and adequate CO 2 control was achieved, with 63% and 90% of 1-min averages having a [CO 2 ] within ± 10% and ± 20% of the target value, respectively, which is comparable to previous FACE systems. Both tree species showed higher net photosynthesis, lower stomatal conductance, and increased accumulation of nonstructural carbohydrates in response to CO 2 in the first year of treatment. Quite unexpectedly, shoot length increment increased significantly at elevated CO 2 (up to 23%) compared with controls in both species.• The pure CO 2 release technology proved suitable for CO 2 enrichment of native trees on this remote mountain slope. Our results suggest an improved C balance and growth of treeline trees in response to elevated CO 2 . However, it is unclear whether this initial growth stimulation will persist in the longer term.

A late Eocene palynological record of climate change and Tibetan Plateau uplift (Xining Basin, China)

“…Productivity of arid land plants is predicted to increase substantially with rising atmospheric carbon dioxide concentrations due to enhancement in plant water-use efficiency (Housman et al, 2006). Trees at high altitudes are also particularly sensitive to CO 2 enrichment, because they live in an atmosphere of lower partial pressure of CO 2 (Hattenschwiler et al, 2002). The current literature indicates a significantly larger average long-term biomass increment under elevated carbon dioxide for Pinaceae than for deciduous trees in studies not involving stress components (Saxe et al, 1998).…”

Nonstructural Carbon in Woody Plants

“…Although elevated CO 2 experiments are not equitably distributed across biomes or stand ages (75), this nonetheless suggests that carbon limitation is widespread. Leaf NSC concentrations show large increases (46,62), which are due primarily to starch rather than sugar accumulation (80). Fewer data are available for longer-term storage, but NSC concentrations generally increase in plants exposed to elevated atmospheric CO 2 and decrease in plants growing at low CO 2 concentrations (18,61).…”

The Potential Impact of Climate Change on Soil Properties and Processes and Corresponding Influence on Food Security

“…Early expectations were that increased atmospheric CO 2 would lead to increased plant productivity coupled with increased C sequestration by soil, meaning increased plant growth and the soil-plant system would help offset increasing atmospheric CO 2 levels [49,50]. This increase in plant growth is known as the CO 2 fertilization effect.…”