Scaling relationship between tree respiration rates and biomass

Abstract

The WBE theory proposed by West, Brown and Enquist predicts that larger plant respiration rate, R , scales to the three-quarters power of body size, M . However, studies on the R versus M relationship for larger plants (i.e. trees larger than saplings) have not been reported. Published respiration rates of field-grown trees (saplings and larger trees) were examined to test this relationship. Our results showed that for larger trees, aboveground respiration rates R A scaled as the 0.82-power of aboveground biomass M A , and that total respiration rates R T scaled as the 0.85-power of total biomass M T , both of which significantly deviated from the three-quarters scaling law predicted by the WBE theory, and which agreed with 0.81–0.84-power scaling of biomass to respiration across the full range of measured tree sizes for an independent dataset reported by Reich et al . (Reich et al . 2006 Nature 439 , 457–461). By contrast, R scaled nearly isometrically with M in saplings. We contend that the scaling exponent of plant metabolism is close to unity for saplings and decreases (but is significantly larger than three-quarters) as trees grow, implying that there is no universal metabolic scaling in plants.