GROWTH AND MAINTENANCE RESPIRATION OF PERENNIAL ROOT SYSTEMS IN A DRY GRASSLAND DOMINATED BY AGROPYRON DASYSTACHYUM (HOOK.) SCRIBN.

Abstract

Respiration coefficients were determined for laboratory‐grown root systems of Agropyron dasystachyum (Hook.) Scribn. (northern wheatgrass). The growth respiration coefficient (0˙85 g g−1) was similar to published rates for species from mesic sites. The maintenance coefficient (0˙037 g g−1 d−1) was relatively low, suggesting that plants growing in semi‐arid habitats have inherently low maintenance costs per unit of biomass. The proportion of total root biomass requiring maintenance (degradable fraction) was determined by measuring the non‐structural root biomass. The degradable fraction (0˙13) was substantially lower than published measurements of functional (or ‘live’) biomass, because the latter include structural biomass, which has no maintenance requirement. Respiration parameters, root growth, degradable root fraction, soil temperature and soil moisture were used to construct a model of root respiration in field‐grown roots. The maintenance coefficient was adjusted downward during periods of water stress and low temperature when roots probably were dormant. Parameters in the model, particularly the degradable biomass fraction, explained much of the discrepancy between respiration rates of laboratory‐grown and field‐grown root systems. Maintenance respiration represents a substantial outlay in the carbon budgets of dry grasslands but is lower than expected considering the large root biomass in these systems. Copyright © 1987, Wiley Blackwell. All rights reserved