Does carbon allocation influence temporal dynamics of radial stem growth in conifers exposed to environmental stress?

Based on several dendroecological and dendroclimatological studies conducted coniferswithin dry inner Alpine environments, drought stress in April through June limits radial growth of coniferous species (e.g., Pichler and Oberhuber 2007, Schuster and Oberhuber 2013). In a recent study we determined intra-annual dynamics of radial growth and found that maximum growth rate of selected conifers peaked early during the growing season in May and prior to occurrence of more favourable environmental conditions, i.e., repeated high rainfall events during summer (e.g., Gruber et al. 2010). It is well known that plants can adjust carbon allocation patterns to optimize resource uptake under prevailing environmental constraints and increase carbon allocation to roots in response to drought and low nutrient supply. Hence, the early decrease in stem growth of conifers exposed to drought can be regarded as an adaptation to cope with extreme environmental conditions, which might require an early switch of carbon allocation to belowground organs. However, an experimental approach confirming this hypothesis is still missing. Because radial growth depends on a continuous supply of carbohydrates, manipulation of the carbon status of the stem can reveal source limitation of radial growth. Girdling, i.e., physical blockage of phloem transport around a tree’s outer circumference, is frequently applied to investigate carbon relationships and causes accumulation and depletion of carbohydrates above and below the girdle, respectively.

Research Questions
In a common garden experiment we will aim at determining to what extent above- and belowground growth is influenced by carbon availability under different environmental regimes. To accomplish this, we will manipulate environmental conditions (i.e., water availability and soil nutrient content) and modify tree carbon status through physical phloem blockage to test the hypotheses that (i) phloem blockage at distinct phenological stages during the growing season differently affects above- and belowground growth, (ii) altered carbon availability changes temporal dynamic of growth processes and wood formation and (iii) soil related stress factors, i.e., soil dryness and/or nutrient deficiency, induce early cessation of aboveground growth in favour of belowground root growth. Hence, results of this project will largely contribute to the understanding of the physiological growth response of conifers exposed to extreme environmental conditions.

Funding
FWF P25643-B16 [Link]

References

  • Gruber A, A Strobl, B Veit, W Oberhuber (2010) Impact of drought on the temporal dynamics of wood formation in Pinus sylvestris. Tree Physiology 30:490-501.
  • Pichler P, W Oberhuber (2007) Radial growth response of coniferous forest trees in an inner Alpine environment to heat-wave in 2003. Forest Ecology and Management 242:688-699.
  • Schuster R, W Oberhuber (2013) Drought sensitivity of three co-occurring conifers within a dry inner Alpine environment. Trees 27:61-69

Peer-reviewed scientific publications:

  1. Oberhuber W, A Hammerle, W Kofler (2015) Tree water status and growth of saplings and mature Norway spruce (Picea abies) at a dry distribution limit. Frontiers in Plant Science 6:703; DOI: 10.3389/fpls.2015.00703
  2. Oberhuber W (2017) Soil water availability and evaporative demand affect seasonal growth dynamics and use of stored water in co-occurring saplings and mature conifers under drought. Trees 31:467-478; DOI: 10.1007/s00468-016-1468-4
  3. Oberhuber W, A Gruber, G Lethaus, G Wieser, A Winkler (2017) Stem girdling indicates prioritized carbon allocation to the root system at the expense of radial stem growth in Norway spruce under drought. Environmental and Experimental Botany 138:109-118; DOI:10.1016/j.envexpbot.2017.03.004
  4. Winkler A, W Oberhuber (2017) Cambial response of Norway spruce to modified carbon availability by phloem girdling. Tree Physiology 37:1527-1535; DOI:  10.1093/treephys/tpx077
  5. Rainer-Lethaus G, W Oberhuber (2018) Phloem girdling of Norway spruce increases radial root growth and hydraulic conductivity under drought. (in review)

Personnel involved
Gruber Andreas
Oberhuber Walter
Gina Rainer-Lethaus
Andrea Winkler 

Cooperation
Universitätsdozent Dr. Gerhard Wieser [Link]
Federal Research and Training Centre for Forests, Natural Hazards and Landscape