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

Abstract

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.

Do N‐fixing legumes promote neighbouring diversity in the tropics?

“…It also suggests that legumes do not share biologically fixed N and prefer to tolerate low level of soil N with a low N‐demanding lifestyle, which implies slow recycling rates. These results are consistent with recent findings in Panamanian forests which show that fixers do not have an effect on biomass recovery in secondary succession (Lai, Hall, Batterman, Turner, & Breugel, ). Future demographic data, such as growth and mortality rates, might provide evidence to test this finding.…”

Soil nutrients and dispersal limitation shape compositional variation in secondary tropical forests across multiple scales

“…The Smithsonian Tropical Research Institute manages three blocks of land (664 ha total) within a 3 × 5 km area, of which ~530 ha was covered by fallow vegetation and secondary forests of various ages upon property acquisition in 2008. Successional trajectories and dynamics in plant diversity and composition in these forests have been extensively studied (Barry, Schnitzer, van Breugel, & Hall, 2015;Batterman et al, 2013;van Breugel et al, 2013;Craven, Hall, Berlyn, Ashton, & van Breugel, 2015Lai, Hall, Batterman, Turner, & van Breugel, 2018;Lai, Hall, Turner, & van Breugel, 2017).…”

A Slash-And-Mulch Improved-Fallow Agroforestry System: Growth and Nutrient Budgets over Two Rotations

“…In contrast, some recent studies in moist tropical forests did not support the notion of N-fixing trees facilitating the growth or nutrient acquisition of neighboring plants during secondary succession [18] or any effect on the total biomass accumulation of the secondary forest [19]. Rather than depleting agroecosystem N capital, as happens in slash-and-burn systems due to gaseous losses of N during burning [5], the inclusion of N-fixing tree species to enhance N stocks in AFS requires continued validation.…”

“…One premise that supports the use of many forms of AFS is that the use of N fixers increases N availability in an agroecosystem, so these results are somewhat surprising. However, other recent research has similarly indicated that N-fixing trees may neither benefit nor inhibit neighboring trees [18] and may not confer a competitive or facilitative effect on secondary growth [19]. It may be necessary to convert N fixers into green manure to capture N benefits.…”