Beech leaf disease reduces nitrogen retranslocation at leaf fall, altering litter chemistry

Area of Science:

• Forest Pathology
• Ecology
• Plant-Soil Interactions

Background:

• Beech leaf disease (BLD), caused by invasive nematodes, is a significant threat to North American beech forests.
• BLD has rapidly spread across the northeastern USA and Canada since its first detection in 2012.
• Understanding BLD's impact on forest ecosystems, including nutrient cycling and decomposition, is crucial.

Purpose of the Study:

• To investigate the effects of BLD on leaf and litter chemistry (carbon and nitrogen content).
• To assess the impact of BLD-altered leaf litter on decomposition rates.
• To determine if BLD affects nutrient retranslocation in beech leaves.

Main Methods:

• Collected attached leaves and fallen litter from BLD-infected and asymptomatic beech stands in Massachusetts.
• Analyzed leaf and litter samples for carbon (C) and nitrogen (N) content, including stable isotopes (δ¹³C, δ¹⁵N).
• Conducted short-term soil incubations using ground leaf litter to measure decomposition rates (CO₂ evolution).

Main Results:

• Severely infected beech litter exhibited significantly higher percent Nitrogen (%N) compared to asymptomatic litter.
• Severely infected leaves had lower %N than asymptomatic green leaves, but similar %N to fallen litter, indicating reduced N retranslocation.
• Despite lower C:N ratios in infected litter, short-term decomposition rates showed negligible differences between infected and asymptomatic litter.

Conclusions:

• BLD alters beech leaf and litter chemistry, notably increasing nitrogen content in symptomatic litter.
• Trees exhibit reduced nitrogen retranslocation from BLD-infected leaves prior to abscission.
• BLD-induced changes in litter chemistry did not significantly affect short-term decomposition rates in this study.