Scaling leaf respiration with nitrogen and phosphorus in tropical forests across two continents

Abstract

Leaf dark respiration (R_dark ) represents an important component controlling the carbon balance in tropical forests. Here, we test how nitrogen (N) and phosphorus (P) affect R_dark and its relationship with photosynthesis using three widely separated tropical forests which differ in soil fertility. R_dark was measured on 431 rainforest canopy trees, from 182 species, in French Guiana, Peru and Australia. The variation in R_dark was examined in relation to leaf N and P content, leaf structure and maximum photosynthetic rates at ambient and saturating atmospheric CO₂ concentration. We found that the site with the lowest fertility (French Guiana) exhibited greater rates of R_dark per unit leaf N, P and photosynthesis. The data from Australia, for which there were no phylogenetic overlaps with the samples from the South American sites, yielded the most distinct relationships of R_dark with the measured leaf traits. Our data indicate that no single universal scaling relationship accounts for variation in R_dark across this large biogeographical space. Variability between sites in the absolute rates of R_dark and the R_dark : photosynthesis ratio were driven by variations in N- and P-use efficiency, which were related to both taxonomic and environmental variability.

Keywords: leaf respiration; nitrogen (N); phosphorus (P); photosynthesis; tropical forest.

Figure 1

Boxplots of leaf nitrogen (N) on an area (a) and mass (b) basis, leaf phosphorus (P) on an area (c) and mass (d) basis, leaf mass per area (LMA, e) and leaf N to P ratio (N : P, f). Pairwise Wilcoxon tests were performed and site means which were not significantly different at the P < 0.05 level are shown by #. The thick line shows the median, the box extends to the lower and upper quartiles, the dashed lines indicate the nominal range (1.5 times the interquartile range below and above the upper and lower quartiles) and the circles indicate points which lie outside of the nominal range.

Figure 2

Log–log plots of leaf mass per area (LMA) against leaf phosphorus (P; c) and nitrogen (N; a) on an area basis and specific leaf area (SLA) against leaf P (d) and leaf N (b) on a mass basis. Data for individual leaves are shown as points separated by country: green (Peru), red (French Guiana) and blue (Australia). Standardized major axis (SMA) lines are shown for the relationships of each country. Tests for significant differences in the slope and y‐axis of the SMA lines are shown in Table 3. Note: if the linear relationship between variables is not significant, SMA lines are not shown.

Figure 3

Boxplots of saturating photosynthesis on an area (A _{sat_a}; a) and mass (A _{sat_m}; b) basis and respiration in the dark on an area (R _{dark_a}; c) and mass (R _{dark_m}; d) basis. Pairwise Wilcoxon tests were performed and datasets which were not significantly different at the P < 0.05 level are shown by #. The thick line shows the median, the box extends to the lower and upper quartiles, the dashed lines indicate the nominal range (1.5 times the interquartile range below and above the upper and lower quartiles) and the circles indicate points which lie outside of the nominal range. FG, French Guiana; AUS, Australia.

Figure 4

Boxplots of respiration in the dark divided by saturating photosynthesis (R _dark : A _sat). Pairwise Wilcoxon tests were performed and all datasets were significantly different at the P < 0.05 level. The thick line shows the median, the box extends to the lower and upper quartiles, the dashed lines indicate the nominal range (1.5 times the interquartile range below and above the upper and lower quartiles) and the circles indicate points which lie outside of the nominal range. FG, French Guiana; AUS, Australia.

Figure 5

Log–log plots of respiration in the dark on an area basis (R _{dark_a}) against leaf mass per area (LMA; a), leaf nitrogen (N_a; b) and leaf phosphorus (P_a; c), and respiration in the dark on a mass basis (R _{dark_m}) against specific leaf area (SLA; d), leaf nitrogen (N_m; e) and leaf phosphorus (P_m; f). Data for individual leaves are shown as points separated by country: green (Peru), red (French Guiana) and blue (Australia). Standardized major axis (SMA) lines are shown for the relationships of each country. Tests for significant differences in the slope and y‐axis of the SMA lines are shown in Table 4. Note: if the linear relationship between variables is not significant, SMA lines are not shown.

Figure 6

Log–log plots of respiration in the dark on an area basis (R _dark__a) against saturating photosynthesis on an area basis (A _{sat_a}) (a) and respiration in the dark on a mass basis (R _dark__m) against saturating photosynthesis on a mass basis (A _{sat_m}) (b). Data for individual leaves are shown as points separated by country: green (Peru), red (French Guiana) and blue (Australia). Standardized major axis (SMA) lines are shown for the relationships of each country. Tests for significant differences in the slope and y‐axis of the SMA lines are shown in Table 5. Note: if the linear relationship between variables is not significant, SMA lines are not shown.

Figure 7

Bar plot showing the mean ± SE for light‐saturated photosynthesis (A _sat; a), leaf respiration in darkness (R _dark; b) and R _dark divided by A _sat (c) on an area basis for species common to French Guiana (FG; white bars) and Peru (grey bars): Licania heteromorpha (LH), Eschweilera coriacea (EC) and Symphonia globulifera (SG).