Increasing nitrogen availability and soil temperature: effects on xylem phenology and anatomy of mature black spruce¹This article is one of a selection of papers from the 7th International Conference on Disturbance Dynamics in Boreal Forests.

Abstract

Since plant growth in the boreal forest is often considered to be limited by low temperatures and low N availability and these variables are projected to increase due to climate warming and increased anthropogenic activities, it is important to understand whether and to what extent these disturbances may affect the growth of boreal trees. In this study, the hypotheses that wood phenology and anatomy were affected by increased soil temperatures and N depositions have been tested in two mature black spruce ( Picea mariana (Mill.) BSP) stands at different altitudes in Quebec, Canada. For 3 years, soil temperature was increased by 4 °C during the first part of the growing season and precipitations containing three times the current N concentration were added in the field by frequent canopy applications. Soil warming resulted in earlier onsets of xylogenesis and interacted with N addition producing longer durations of xylogenesis for the treated trees. The effect of warming was especially marked in the phenology of roots, while wood production, in terms of number of tracheids, was not affected by the treatment. Xylem anatomy and soil and needle chemistry showed no effect of the treatments, except for an increase of cell wall thickness in earlywood of treated trees. This short-term experiment with black spruce suggested that previous fertilization studies that used large and unrealistic rates of N addition may have overestimated the impact of N depositions on boreal forest productivity.

Diverging shifts in spring phenology in response to biodiversity loss in a subtropical forest

“…Although nitrogen availability is one of the cues most often associated with human-caused phenological changes, phenology may also respond to other abiotic variables (e.g., solar radiation, other nutrient concentrations) that we did not measure. For example, soil surface temperature and water availability were found to correlate with the PFD of most species in the BEF grasslands in California (Wolf et al, 2017) and in other soil-warming experiments (Lupi, Morin, Deslauriers, Rossi, & Houle, 2012). Our findings indicate that abiotic variables may be more important than biotic variables (species diversity) in determining LD in subtropical forests.…”

A 6-Year-Long Manipulation with Soil Warming and Canopy Nitrogen Additions does not Affect Xylem Phenology and Cell Production of Mature Black Spruce

“…Volumetric water content of heated and non-heated plots was measured in July 2009 using a CS-616 probe (Campbell Scientific Corporation, Canada) mounted on a portable device to check for differences in soil moisture content. No significant difference was found between heated (H and NH) and non-heated trees (C and N) ( Lupi et al, 2012 ).…”

“…Most experimental investigations of N deposition and warming on plant growth have examined juvenile wood or used unrealistically high rates of N addition, so it is not possible to extrapolate the results to the conditions occurring in natural forest ecosystems. 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 ).…”

Age, competition, disturbance and elevation effects on tree and stand growth response of primary Picea abies forest to climate

“…Warm winter temperatures and high spring precipitation enhanced RWIs in low-density stands at high elevations, but RWIs responded more to those variables in high-density stands at low elevations. During winter, lower air and soil temperature can occur more frequently and be more extreme in open areas than under forest canopy (Aussenac, 2000), which may constrain tree photosynthesis (Wu et al, 2012), lead to delayed onsets of xylogenesis (Lupi et al, 2012), and also result in freeze-thaw cycles causing xylem embolism and damaging the cambium in the most extreme cases such as those related to frost drought (Lens et al, 2013;Mayr et al, 2006). At high elevations, trees in open stands might thus …”