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Title: Leaf nitrogen affects photosynthesis and water use efficiency similarly in nitrogen‐fixing and non‐fixing trees
Abstract

Nitrogen (N)‐fixing trees are thought to break a basic rule of leaf economics: higher leaf N concentrations do not translate into higher rates of carbon assimilation. Understanding how leaf N affects photosynthesis and water use efficiency (WUE) in this ecologically important group is critical.

We grew six N‐fixing and four non‐fixing tree species for 4–5 years at four fertilization treatments in field experiments in temperate and tropical regions to assess how functional type (N fixer vs. non‐fixer) and N limitation affected leaf N and how leaf N affected light‐saturated photosynthesis (Asat), stomatal conductance (gsw) and WUE (WUEiand δ13C).

Asat, WUEiand δ13C, but notgsw, increased with higher leaf N. Surprisingly, N‐fixing and non‐fixing trees displayed similar scaling between leaf N and these physiological variables, and this finding was supported by reanalysis of a global dataset. N fixers generally had higher leaf N than non‐fixers, even when non‐fixers were not N‐limited at the leaf level. Leaf‐level N limitation did not alter the relationship ofAsat,gsw, WUEiand δ13C with leaf N, although it did affect the photosynthetic N use efficiency. Higher WUE was associated with higher productivity, whereas higherAsatwas not.

Synthesis: The ecological success of N‐fixing trees depends on the effect of leaf N on carbon gain and water loss. Using a field fertilization experiment and reanalysis of a global dataset, we show that high leaf‐level photosynthesis and WUE in N fixers stems from their higher average leaf N, rather than a difference between N fixers and non‐fixers in the scaling of photosynthesis and WUE with leaf N. By clarifying the mechanism by which N fixers achieve and benefit from high WUE, our results further the understanding of global N fixer distributions.

 
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NSF-PAR ID:
10472173
Author(s) / Creator(s):
 ;  ;  ;  ;  
Publisher / Repository:
Wiley-Blackwell
Date Published:
Journal Name:
Journal of Ecology
Volume:
111
Issue:
11
ISSN:
0022-0477
Format(s):
Medium: X Size: p. 2457-2471
Size(s):
["p. 2457-2471"]
Sponsoring Org:
National Science Foundation
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