Pacific Southwest

Title: Using ¹³C and ¹⁵N isotopes to study allocation patterns in oak seedlings

Author: Suz, Laura M.; Albarracín, María V.; Bledsoe, Caroline S.

Date: 2008

Source: In: Merenlender, Adina; McCreary, Douglas; Purcell, Kathryn L., tech. eds. 2008. Proceedings of the sixth California oak symposium: today's challenges, tomorrow's opportunities. Gen. Tech. Rep. PSW-GTR-217. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: p. 117-130

Station ID: GTR-psw-217

Description: In California’s oak woodlands, survival and growth of oaks may depend on a symbiosis between oak roots and fungi that form ectomycorrhizas. Ectomycorrhizal (ECM) fungi are major players in carbon (C) and nitrogen (N) utilization and cycling because they facilitate water and nutrient uptake from the soil into the plant. The ECM fungi also benefit because plants supply carbohydrates to their fungal partners. Little is known about the stoichiometry of N and C exchange within ECM plants. It is not known whether N uptake and transfer from ECM fungi to their plant host is related to C flow from host to ECM fungi. We considered several questions. Do plants "reward" those ECM fungal species that supply more N to the plant by providing more C to these ECM species? Are N and C transfers linked? Are ECM roots that take up more N from soils greater sinks for C? What are the longterm and short-term transfers of N and C, as measured by natural abundance (long-term) and tracer studies (short-term)? The natural abundance (background levels) of ¹⁵N and ¹³C in oak seedlings sheds light on what are the N sources for oaks, and how oaks allocate C over the long term (years to decades). Tracer data shed light on short-term processes of N and C allocation in oaks. In this study, we explored these questions by tracking C and N transfers within ECM blue oak seedlings of Quercus douglasii Hook&Arn. First, we determined the natural abundance (background) of N and C in control seedlings. N natural abundance was higher in ECM roots than in other tissues, while C natural abundance was higher in leaves than in other tissues. We traced C transfer from oak shoots into oak ECM roots, as well as N transfer from soil into oak ECM roots and into oak shoots. Our results suggest that both leaves and ECM tips were strong sinks for C and N. The stoichiometry of N and C into and out of ECM roots can help us understand how ECM fungi affect C allocation within oaks and how oaks respond to N supply from ECM roots.

Keywords: blue oak, carbon allocation, nitrogen uptake, stable isotopes, stoichiometry

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Citation

Suz, Laura M.; Albarracín, María V.; Bledsoe, Caroline S.  2008.  Using ¹³C and ¹⁵N isotopes to study allocation patterns in oak seedlings.   In: Merenlender, Adina; McCreary, Douglas; Purcell, Kathryn L., tech. eds. 2008. Proceedings of the sixth California oak symposium: today's challenges, tomorrow's opportunities. Gen. Tech. Rep. PSW-GTR-217. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: p. 117-130.