Abstract
The predicted climate warming and increased atmospheric inorganic nitrogen deposition are expected to have dramatic impacts on plant growth. However, the extent of these effects and their interactions remains unclear for boreal forest trees. The aim of this experiment was to investigate the effects of increased soil temperature and nitrogen (N) depositions on stem intra-annual growth of two mature stands of black spruce [Picea mariana (Mill.) BSP] in Québec, QC, Canada. During 2008–2013, the soil around mature trees was warmed up by 4°C with heating cables during the growing season and precipitations containing three times the current inorganic N concentration were added by frequent canopy applications. Xylem phenology and cell production were monitored weekly from April to October. The 6-year-long experiment performed in two sites at different altitude showed no substantial effect of warming and N-depositions on xylem phenological phases of cell enlargement, wall thickening and lignification. Cell production, in terms of number of tracheids along the radius, also did not differ significantly and followed the same patterns in control and treated trees. These findings allowed the hypothesis of a medium-term effect of soil warming and N depositions on the growth of mature black spruce to be rejected.
Highlights
Surface temperature is projected to rise over the 21st century under all assessed emission scenarios (IPCC, 2014)
Few studies have used an accurate quantity of the additional N inputs that are expected in boreal forest ecosystems in the future, and together with soil warming or singly, the results indicated limited effects on the N status and growth rate after 3-year studies (Lupi et al, 2012; D’Orangeville et al, 2013)
This study conducted in two matured black spruce stands of the boreal forest of Quebec, Canada tested the hypothesis that xylem phenology and cell production were affected by increased soil temperature and inorganic N availability in precipitation
Summary
Surface temperature is projected to rise over the 21st century under all assessed emission scenarios (IPCC, 2014). The timings of plant development and growth, is one of the traits sensitive to regional climate warming (Schwartz et al, 2006; Cleland et al, 2007). Apart from higher average temperatures, plants may have to cope with other effects of global change, especially enhanced atmospheric nitrogen (N) deposition. Soil warming and nitrogen impact centuries and are projected to increase in the future (Thomas et al, 2010). In the boreal forest, plant growth is often considered to be limited by low temperatures and the availability of N (Reich et al, 2006). Understanding the combined effects of warming and increased N depositions on xylem phenology, tree growth and the amount of cells produced, is critical for improving the prediction of tree responses to future climate
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