Root decomposition in forest ecosystems: chemical or morphological control?

Problem: Roots are the major type of plant tissue that contributes to soil organic carbon. Our study was designed to test whether variation in root chemical and morphological traits change decomposition and soil carbon sequestration rates. Compared to tulip roots (Liriodendron tulipifera), elm roots (Ulmus americana) have higher lignin:Nitrogen ratio, but finer diameter, as well as greater root tip abundance. Based on morphological traits, we expect elm roots to decompose faster because of their higher surface area and fine morphology causing them to easily break into the soil. Based on chemical properties, we expect that tulip roots will decompose faster because they have lower lignin:nitrogen ratio. Since microbial communities can adapt to the quality of locally available nutrients, it is expected that decay rates will be accelerated for tissues that have a ‘home field advantage,’ being more similar to neighboring tree species. Methods: Litterbags filled with soil and elm or tulip roots, including treatment groups of either 1st and 2nd order roots, 3rd and 4th order roots, or entire root systems, were left to decompose for 42 weeks in under trees of both species in riparian forest at Jennings Woods. Results: Tulip roots decomposed faster than elm roots, implying that root tissue chemistry has a greater effect on decomposition than morphological characteristics. The strength of our predicted relationships varied between treatment groups. Decomposition occurred faster under tulip trees regardless of the identity of the roots, giving evidence against ‘home field advantage’ theory.