Relationships of leaf dark respiration to leaf nitrogen, specific leaf area and leaf life-span: a test across biomes and functional groups

Based on prior evidence of coordinated multiple leaf trait scaling, we hypothesized that variation among species in leaf dark respiration rate (R-d) should scale with variation in traits such as leaf nitrogen (N), leaf life-span, specific leaf area (SLA), and net photosynthetic capacity (A(max)). However, it is not known whether such scaling if it exists, is similar among disparate biomes and plant functional types. We tested this idea by examining the interspecific relationships between R-d measured at a standard temperature and leaf life-span, N, SLA and A(max) for 69 species from four functional groups (forbs, broad-leafed trees and shrubs, and needle-leafed conifers) in six biomes traversing the Americas. alpine tundra/subalpine forest, Colorado; cold temperate forest/ grassland, Wisconsin; cool temperate forest, North Carolina; desert/shrubland, New Mexico; subtropical forest, South Carolina; and tropical rain forest, Amazonas, Venezuela. Area-based R-d was positively related to area-based leaf N within functional groups and for all species pooled, but not when comparing among species within any site. At all sites, mass-based R-d (Rd-mass) decreased sharply with increasing leaf life-span and was positively related to SLA and mass-based A(max) and leaf N (leaf N-mass). These intra-biome relationships were similar in shape and slope among sites, where in each case we compared species belonging to different plant functional groups. Significant Rd-mass-N-mass relationships were observed in all functional groups (pooled across sites), but the relationships differed, with higher R-d at any given leaf N in functional groups (such as forbs) with higher SLA and shorter leaf life-span. Regardless of biome or functional group, Rd-mass was well predicted by all combinations of leaf life-span, N-mass and/or SLA (r(2) > 0.79, P < 0.0001). At any given SLA, Rd-mass rises with increasing N-mass and/or decreasing leaf life-span and at any level of N-mass, Rd-mass rises with increasing SLA and/or decreasing leaf life-span. The relationships between R-d and leaf traits observed in this study support the idea of a global set of predictable interrelationships between key leaf morphological, chemical and metabolic traits.