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

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. 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. 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). 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.