Light inhibition of leaf respiration as soil fertility declines along a post-glacial chronosequence in New Zealand: An analysis using the Kok method

Background and aims: Our study quantified variations leaf respiration in darkness (R _D) and light (R _L), and associated traits along the Franz Josef Glacier soil development chronosequence in New Zealand. Methods: At six sites along the chronosequence (soil age: 6, 60, 150, 500, 12,000 and 120,000 years old), we measured rates of leaf R _D, R _L (using Kok method), light-saturated CO₂ assimilation rates (A), leaf mass per unit area (M _A), and concentrations of leaf nitrogen ([N]), phosphorus ([P]), soluble sugars and starch. Results: The chronosequence was characterised by decreasing R _D, R _L and A, reduced [N] and [P] and increasing M _A as soil age increased. Light inhibition of R occurred across the chronosequence (mean inhibition = 16 %), resulting in ratios of R _L:A being lower than for R _D:A. Importantly, the degree of light inhibition differed across the chronosequence, being lowest at young sites and highest at old sites. This resulted in R _L:A ratios being relatively constant across the chronosequence, whereas R _D:A ratios increased with increasing soil age. Log-log R-A-M _A-[N] relationships remained constant along the chronosequence. By contrast, relationships linking rates of leaf R to [P] differed among leaves with low vs high [N]:[P] ratios. Slopes of log-log bivariate relationships linking R _L to A, M _A, [N] and [P] were steeper than that for R _D. Conclusions: Our findings have important implications for predictive models that seek to account for light inhibition of R, and for our understanding of how environmental gradients impact on leaf trait relationships