Contrasting Dependencies of Photosynthetic Capacity on Leaf Nitrogen in Early- and Late-Successional Tropical Montane Tree Species

Camille Ziegler; Mirindi Eric Dusenge; Brigitte Nyirambangutse; Etienne Zibera; Göran Wallin; Johan Uddling

doi:10.3389/fpls.2020.500479

Contrasting Dependencies of Photosynthetic Capacity on Leaf Nitrogen in Early- and Late-Successional Tropical Montane Tree Species

Front Plant Sci. 2020 Sep 17:11:500479. doi: 10.3389/fpls.2020.500479. eCollection 2020.

Authors

Camille Ziegler^{1

2

3}, Mirindi Eric Dusenge^{1

4

5}, Brigitte Nyirambangutse^{1

4}, Etienne Zibera⁴, Göran Wallin¹, Johan Uddling¹

Affiliations

¹ Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden.
² UMR EcoFoG, AgroParisTech, CNRS, CIRAD, INRAE, Université des Antilles, Université de Guyane, Kourou, France.
³ Université de Lorraine, AgroParisTech, INRAE, UMR Silva, Nancy, France.
⁴ Department of Biology, University of Rwanda, Huye, Rwanda.
⁵ Department of Biology, The University of Western Ontario, London, ON, Canada.

Abstract

Differences in photosynthetic capacity among tree species and tree functional types are currently assumed to be largely driven by variation in leaf nutrient content, particularly nitrogen (N). However, recent studies indicate that leaf N content is often a poor predictor of variation in photosynthetic capacity in tropical trees. In this study, we explored the relative importance of area-based total leaf N content (N_tot) and within-leaf N allocation to photosynthetic capacity versus light-harvesting in controlling the variation in photosynthetic capacity (i.e. V _cmax, J _max) among mature trees of 12 species belonging to either early (ES) or late successional (LS) groups growing in a tropical montane rainforest in Rwanda, Central Africa. Photosynthetic capacity at a common leaf temperature of 25˚C (i.e. maximum rates of Rubisco carboxylation, V _cmax25 and of electron transport, J _max25) was higher in ES than in LS species (+ 58% and 68% for V _cmax25 and J _max25, respectively). While N_tot did not significantly differ between successional groups, the photosynthetic dependency on N_tot was markedly different. In ES species, V _cmax25 was strongly and positively related to N_tot but this was not the case in LS species. However, there was no significant trade-off between relative leaf N investments in compounds maximizing photosynthetic capacity versus compounds maximizing light harvesting. Both leaf dark respiration at 25˚C (+ 33%) and, more surprisingly, apparent photosynthetic quantum yield (+ 35%) was higher in ES than in LS species. Moreover, R_d25 was positively related to N_tot for both ES and LS species. Our results imply that efforts to quantify carbon fluxes of tropical montane rainforests would be improved if they considered contrasting within-leaf N allocation and photosynthetic N_tot dependencies between species with different successional strategies.

Keywords: allocation; early successional; late successional; nitrogen; photosynthesis; tropical montane forests.