Aridity, not fire, favors nitrogen‐fixing plants across tropical savanna and forest biomes

Pellegrini, Adam F. A.; Staver, A. Carla; Hedin, Lars O.; Charles‐Dominique, Tristan; Tourgee, Amy

doi:10.1002/ecy.1504

Cited by 59 publications

(70 citation statements)

References 35 publications

(85 reference statements)

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“…The extent to which our findings of a lack of effect of N 2 fixers on biomass accumulation during secondary forest succession are consistent across Neotropical forests that vary widely in environmental conditions (Quesada et al, 2010(Quesada et al, , 2012, biomass accumulation rates , fixer abundance (Gei et al, in review;Liao, Menge, Lichstein, & Ángeles-Pérez, 2017;Pellegrini, Staver, Hedin, Charles-Dominique, & Tourgee, 2016;ter Steege et al, 2006) and fixer species community composition (S. A. Batterman, pers. comm.)…”

Section: No Evidence For Net Facilitative or Competitive Effects Ofmentioning

confidence: 59%

Nitrogen fixer abundance has no effect on biomass recovery during tropical secondary forest succession

et al. 2018

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Abstract1. Nitrogen-fixing trees (N 2 fixers) provide new nitrogen critical for rapid biomass accumulation of tropical forests during early secondary succession, but it remains unclear how the abundance of N 2 fixers in the forest community affects the growth of non-fixers or the primary productivity of the whole forest.2. On the one hand, N 2 fixers may enhance forest productivity by providing a facilitative effect through the provision of plant-available nitrogen to non-fixing trees. On the other hand, N 2 fixers may suppress the growth of non-fixers by growing faster and competing more vigorously for light and other resources. A third alternative is that the growth of N 2 fixers themselves accumulate biomass rapidly, while having a neutral effect on non-fixers, leading to an overall increase in forest biomass.3. We examine these alternative hypotheses using 5-year tree census data from 88 plots in 44 seasonal tropical moist secondary forests (3-32 years old) across a human-modified landscape in central Panama. We examined whether N 2 fixers accumulated biomass more rapidly than non-fixers, and how relative biomass of N 2 fixers as a functional group and as individual species influenced the growth of non-fixer and whole stand primary productivity.4. Surprisingly, we found no evidence for either a net competitive or a facilitative effect of N 2 fixers as a functional group or individual species on the biomass recovery in these young forests. N 2 fixers did not grow faster than non-fixers. Individual mortality rates were lower among N 2 fixers, but biomass losses due to mortality were similar between the two groups. Overall, we found no relationship between the relative abundance of N 2 fixers and stand primary productivity during succession. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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Section: No Evidence For Net Facilitative or Competitive Effects Ofmentioning

confidence: 59%

Nitrogen fixer abundance has no effect on biomass recovery during tropical secondary forest succession

et al. 2018

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“…We have not directly addressed drivers of this variation, but aridity is an intriguing possibility. Our lower-latitude sites range from arid to exceptionally wet (Liao et al 2017), and recent work has established that N-fixing and particularly rhizobial trees are more abundant in drier sites, both in these datasets (Liao et al 2017) and elsewhere in the tropics (Pellegrini et al 2016).…”

Section: Discussionmentioning

confidence: 99%

Nitrogen‐fixing tree abundance in higher‐latitude North America is not constrained by diversity

et al. 2017

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The rarity of nitrogen (N)-fixing trees in frequently N-limited higher-latitude (here, > 35°) forests is a central biogeochemical paradox. One hypothesis for their rarity is that evolutionary constraints limit N-fixing tree diversity, preventing N-fixing species from filling available niches in higher-latitude forests. Here, we test this hypothesis using data from the USA and Mexico. N-fixing trees comprise only a slightly smaller fraction of taxa at higher vs. lower latitudes (8% vs. 11% of genera), despite 11-fold lower abundance (1.2% vs. 12.7% of basal area). Furthermore, N-fixing trees are abundant but belong to few species on tropical islands, suggesting that low absolute diversity does not limit their abundance. Rhizobial taxa dominate N-fixing tree richness at lower latitudes, whereas actinorhizal species do at higher latitudes. Our results suggest that low diversity does not explain N-fixing trees' rarity in higher-latitude forests. Therefore, N limitation in higher-latitude forests likely results from ecological constraints on N fixation.

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“…Among the ecological mechanisms that could drive the latitudinal pattern of N-fixing tree abundance, climate (Jenny's other proposed driver) has often been invoked. N-fixing trees are more abundant in hotter (Liao et al 2017) and more arid (Pellegrini et al 2016, Liao et al 2017) ecosystems, but the mechanisms underlying these patterns are not well established. One previously proposed possibility is that a direct temperature constraint on the process of N fixation confines N-fixing trees to lower latitudes (Houlton et al 2008).…”

Section: Introductionmentioning

confidence: 99%

Why are nitrogen‐fixing trees rare at higher compared to lower latitudes?

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et al. 2017

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Symbiotic nitrogen (N) fixation provides a dominant source of new N to the terrestrial biosphere, yet in many cases the abundance of N-fixing trees appears paradoxical. N-fixing trees, which should be favored when N is limiting, are rare in higher latitude forests where N limitation is common, but are abundant in many lower latitude forests where N limitation is rare. Here, we develop a graphical and mathematical model to resolve the paradox. We use the model to demonstrate that N fixation is not necessarily cost effective under all degrees of N limitation, as intuition suggests. Rather, N fixation is only cost effective when N limitation is sufficiently severe. This general finding, specific versions of which have also emerged from other models, would explain sustained moderate N limitation because N-fixing trees would either turn N fixation off or be outcompeted under moderate N limitation. From this finding, four general hypothesis classes emerge to resolve the apparent paradox of N limitation and N-fixing tree abundance across latitude. The first hypothesis is that N limitation is less common at higher latitudes. This hypothesis contradicts prevailing evidence, so is unlikely, but the following three hypotheses all seem likely. The second hypothesis, which is new, is that even if N limitation is more common at higher latitudes, more severe N limitation might be more common at lower latitudes because of the capacity for higher N demand. Third, N fixation might be cost effective under milder N limitation at lower latitudes but only under more severe N limitation at higher latitudes. This third hypothesis class generalizes previous hypotheses and suggests new specific hypotheses. For example, greater trade-offs between N fixation and N use efficiency, soil N uptake, or plant turnover at higher compared to lower latitudes would make N fixation cost effective only under more severe N limitation at higher latitudes. Fourth, N-fixing trees might adjust N fixation more at lower than at higher latitudes. This framework provides new hypotheses to explain the latitudinal abundance distribution of N-fixing trees, and also provides a new way to visualize them. Therefore, it can help explain the seemingly paradoxical persistence of N limitation in many higher latitude forests.

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Aridity, not fire, favors nitrogen‐fixing plants across tropical savanna and forest biomes

Cited by 59 publications

References 35 publications

Nitrogen fixer abundance has no effect on biomass recovery during tropical secondary forest succession

Nitrogen fixer abundance has no effect on biomass recovery during tropical secondary forest succession

Nitrogen‐fixing tree abundance in higher‐latitude North America is not constrained by diversity

Why are nitrogen‐fixing trees rare at higher compared to lower latitudes?

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