No evidence that boron influences tree species distributions in lowland tropical forests of Panama

Abstract

SummaryIt was recently proposed that boron might be the most important nutrient structuring tree species distributions in tropical forests. Here we combine observational and experimental studies to test this hypothesis for lowland tropical forests of Panama.Plant-available boron is uniformly low in tropical forest soils of Panama and is not significantly associated with any of the > 500 species in a regional network of forest dynamics plots. Experimental manipulation of boron supply to seedlings of three tropical tree species revealed no evidence of boron deficiency or toxicity at concentrations likely to occur in tropical forest soils. Foliar boron did not correlate with soil boron along a local scale gradient of boron availability.Fifteen years of boron addition to a tropical forest increased plant-available boron by 70% but did not significantly change tree productivity or boron concentrations in live leaves, wood or leaf litter. The annual input of boron in rainfall accounts for a considerable proportion of the boron in annual litterfall and is similar to the pool of plant-available boron in the soil, and is therefore sufficient to preclude boron deficiency.We conclude that boron does not influence tree species distributions in Panama and presumably elsewhere in the lowland tropics.

Dynamic of boron in forest ecosystems traced by its isotopes: A modeling approach

“…For instance, the ratio between the living coarse root/wood biomass and the leaf biomass varies from 3 to 8 for birch, pine and spruce stands between 40 years old and 100 years old on drained mire in Finland (Finer, 1989). In addition, Turner et al (2017) report a ratio of nearly 9 for a lowland tropical forest in Panama of at least 200 years old.…”

“…Due to the relative large range of boron uptake rates measured or estimated for forest ecosystems (Finner, 1998;Cividini et al, 2010;Turner et al, 2017;Gaillardet and Lemarchand, 2018), we tested the effects of plant requirement on the boron dynamic in relation with inter species variability and/or in responses to various stresses. For different plant demands, Dem, we postulated that the maximal influx of boron, J max , will change accordingly.…”

“…Although the fundamental role of boron for the growth of plants has been recognized since 1920's (Warington,1923), its biogeochemical cycle in ecosystem has retained little attention. It has been proposed that boron along with K was the most important nutrient influencing tree species distribution in tropical regions (John et al, 2007;Steidinger et al, 2015) although this conclusion has been recently refuted by Turner et al (2017).…”

“…For instance, Turner et al (2017) estimated that the flux of boron supplied by rainfall to tropical forest ecosystem in Panama was equivalent to the annual amount of B returning to the forest floor in litter fall, suggesting that B was not a limiting nutrient. They concluded that the plant requirement for B was considerably less than for phosphorus for example J o u r n a l P r e -p r o o f By contrast, Gaillardet and Lemarchand (2018) reported fluxes for vegetation cycling 5 to 10 times greater than the total B supply to the ecosystems by atmospheric depositions and chemical weathering for two ecosystems developed under tropical and temperate climates.…”

Boron application increases growth of Brazilian Cerrado grasses

“…Cerrado soils are B deficient, and its addition can promote yield increase in crop plants (Shorrocks, 1997). Ecologically, however, B has only recently been proposed as a key element for structuring natural tree communities in rainforests in Panama (Steidinger, 2015), but contrasting results were reported from a long‐term experiment in the field (Turner et al., 2017). Yet, no convincing evidences of B limitation in natural plant communities have been reported.…”