Nutrient‐induced changes in root respiration in 10 woody plant species

1. Nitrogen (N) and phosphorus (P) are soil macronutrients that influence ecosystem productivity through strong impacts on plant metabolism. The influence of nutrient supply on the relationships between leaf respiration rate (R) and leaf N concentration ([N]) has been widely investigated. By contrast, how root R responds to variations in nutrient availability and whether there remains a general response across a wide range of species is less well known.

2. We conducted an experiment assessing the effects of N and P supply on root R in 10 woody plant species, with root R being determined by the in vivo rate of oxygen (O2) consumption. Maximum R (Rmax) was also quantified by O2 uptake in the presence of an exogenous substrate and a respiratory uncoupler

3. Our results showed that high-N and high-P supply significantly stimulated mass-based root R in woody plants, with the effects of N supply significant only when P supply was high. The promoting effect of high-P treatment remained consistent despite N supply. Root R-[N] bivariate relationships were altered by nutrient availability across all species, with higher root R at a given root [N] under low- than high-N supply. Similarly, root R at a given P concentration ([P]) was higher under low- than high-P supply. Root Rmax was significantly higher than in vivo R for all nutrient treatments, showing that in vivo root R was limited by substrate supply and/or adenylates, with no significant difference in R/Rmax ratios among nutrient treatments.

4. These results indicate that ecosystem models should consider different scaling relationships linking root R to root N or P concentrations for woody species when predicting the effects of nutrient availability on carbon cycle dynamics and climate–biosphere feedback.