Mistletoe-induced crown degradation in Scots pine in a xeric environment

Area of Science:

• Ecology
• Forest Pathology
• Plant Physiology

Background:

• Scots pine (Pinus sylvestris L.) mortality is increasing in the European Alps.
• Pine mistletoe (Viscum album ssp. austriacum) infection is implicated in Scots pine decline, but the mechanism is unclear.
• Drought is a known stressor for Scots pines in this region.

Purpose of the Study:

• To investigate if pine mistletoe infection weakens Scots pines through crown degradation.
• To quantify the effects of mistletoe infestation on branch growth and photosynthetic tissues.
• To understand how mistletoe impacts host vulnerability to drought.

Main Methods:

• Comparison of infested and non-infested paired branches on Scots pine trees.
• Assessment of branch length, radial increment, ramification, needle length, and needle age.
• Evaluation of photosynthetic tissue loss and its impact on primary production and carbohydrate availability.

Main Results:

• Pine mistletoe infection significantly reduced branch length, radial increment, and ramification.
• Infested branches exhibited shorter needles and fewer needle years, indicating reduced photosynthetic capacity.
• Mistletoe infestation led to decreased primary production and carbohydrate availability.
• Reduced needle length suggests lower water and nutrient availability in infected branches.

Conclusions:

• Pine mistletoe causes crown degradation in Scots pines, diminishing photosynthetic tissues and growth.
• This degradation reduces the availability of water and carbohydrates, crucial growth factors.
• In xeric environments, mistletoe infection intensifies drought stress, increasing Scots pine mortality risk.