PARENT SESSION
Organized Oral Session 26: From microbes to ecosystems: How do we really make the connections?
Organizer(s): J Schimel and S Frey
Wednesday, August 10, 8:00 AM - 11:30 AM, Meeting Room 510a, Level 5, Palais des congrès de Montréal

Linking microbial guilds to decomposition: A new modeling approach.

Moorhead, Daryl^*,1, Sinsabaugh, Robert², ¹ University of Toledo, Toledo, Ohio, USA² University of New Mexico, Albuquerque, NM, USA

ABSTRACT- Key processes underlying decomposition are controlled by microflora, although models seldom include more than implicit controls imposed by a generalized black-box of microorganisms. However, decomposition is an emergent property of a complex system, resulting from interactions between litter chemistry, microbial community and environment. Hence, critical controls exist at biochemical, physiological and ecological scales of hierarchical resolution. We developed a model of litter decay that explicitly includes controls at several scales: (1) defining a threshold of microbial versus litter control of decay rate, as a function of microbial metabolism and litter chemistry, (2) decoupling litter mass loss from microbial growth by adding greater flexibility in microbial physiology than normally considered, (3) adding interactive controls that both lignin and cellulose exert on each other during decomposition, (4) limiting microbial community development by apparent habitat availability underlying microbial:litter mass relationships, (5) including both N-limitations on microbial growth and N-inhibition on lignin degradation, and (6) defining three guilds of decomposer microorganisms that differ with respect to relative growth rates and capacities to degrade three key classes of litter constituents (solubles, holocellulose and lignin). Model behavior is consistent with reported patterns of litter decay, including dynamics of mass loss, changing litter chemistry, humus formation, microbial community development, and microbial:litter relationships. Moreover, this model generates differential responses to N fertilization, depending on initial litter quality and stage of decomposition, which often appear as inconsistent between field studies. Finally, this model provides a generic framework in which both contributions of specific microbial groups and their responses to perturbations can be assessed.

Key words: decomposition, model, n-deposition, lignocellulose