PARENT SESSION
Friday, August 11, 8:00-11:30 am
COS 113 - Uses of stable isotopes in ecology
L-12, Lobby Level, Cook Convention Center
Presiders: B Hough

Can ¹³C and ¹⁵N of leaf litter be used to infer canopy isotopic composition?

Marshall, John^*,1, Kavanagh, Kathleen¹, Alisa, Schotzko¹, Duursma, Remko², ¹ Department of Forest Resources, Moscow, ID, USA² Department of Forest Ecology, Helsinki, Finland

ABSTRACT- Foliar stable isotope composition can be used to parameterize models of photosynthetic gas exchange and nitrogen biogeochemistry. But obtaining a sample representative of the whole canopy is difficult, especially in large evergreen trees with deep canopies and multiple leaf cohorts. We tested the use of leaf litter to estimate stable isotope composition for the whole canopy of mature, individual trees in a natural forest in northern Idaho. Leaves and litter of Douglas-fir (Pseudotsuga menziesii), western hemlock (Tsuga heterophylla), and western larch (Larix occidentalis) were compared. We first compared foliage collected three years ago on large standing trees to litter collected in the fall of 2005. The litter had less negative ¹³C (P<0.006) and slightly more enriched ¹⁵N (P=0.02). A regression line using litter ¹⁵N to predict green ¹⁵N had high predictive power (R² =0.91). We next compared age trends among foliage cohorts along branches of smaller trees. These showed reductions in ¹⁵N (P = 0.03) and constant ¹³C (P = 0.40). Again, the litter isotopic data predicted the canopy values well (R² = 0.86). We conclude that the change in ¹³C from green foliage to litter is negligible, and that the change in ¹⁵N is small, consistent, and predictable. It appears that litter isotopic data can be used to estimate mean stable isotope composition of complex forest canopies.

Key words: stable isotope, canopy, litter