Variation in Canopy Litterfall Along a Precipitation and Soil Fertility Gradient in a Panamanian Lower Montane Forest

Abstract

Fertilization experiments in tropical forests have shown that litterfall increases in response to the addition of one or more soil nutrients. However, the relationship between soil nutrient availability and litterfall is poorly defined along natural soil fertility gradients, especially in tropical montane forests. Here, we measured litterfall for two years in five lower montane 1-ha plots spanning a soil fertility and precipitation gradient in lower montane forest at Fortuna, Panama. Litterfall was also measured in a concurrent nitrogen fertilization experiment at one site. Repeated-measures ANOVA was used to test for site (or treatment), year, and season effects on vegetative, reproductive and total litterfall. We predicted that total litterfall, and the ratio of reproductive to leaf litterfall, would increase with nutrient availability along the fertility gradient, and in response to nitrogen addition. We found that total annual litterfall varied substantially among 1-ha plots (4.78 Mg/ha/yr to 7.96 Mg/ha/yr), and all but the most aseasonal plot showed significant seasonality in litterfall. However, litterfall accumulation did not track soil nutrient availability; instead forest growing on relatively infertile soil, but dominated by an ectomycorrhizal tree species, had the highest total litterfall accumulation. In the fertilization plots, significantly more total litter fell in nitrogen addition relative to control plots, but this increase in response to nitrogen (13%) was small compared to variation observed among 1-ha plots. These results suggest that while litterfall at Fortuna is nutrient-limited, compositional and functional turnover along the fertility gradient obscure any direct relationship between soil resource availability and canopy productivity.Abstract in Spanish is available in the online version of this article.

Soils and rainfall drive landscape‐scale changes in the diversity and functional composition of tree communities in premontane tropical forest

“…The slow leaf production rate and tall stature (>25 m) achieved by these palms, particularly Colpothrinax aphanopetalum (Heineman et al. ), suggests that they may be particularly strong competitors under extremely infertile conditions, where long‐lived leaves with low nutrient concentrations, as well as reduced investment in wood, results in higher nutrient use efficiency and potentially allows greater allocation to reproductive biomass than dicot trees (Heineman et al. ).…”

Plasticity in nitrogen uptake among plant species with contrasting nutrient acquisition strategies in a tropical forest

“…, Heineman et al. ). Thus, the co‐occurrence of species with divergent nutrient acquisition strategies may alleviate competition for nutrients in this ECM‐dominated forest.…”

“…Total litterfall accumulation is higher in Oreomunnea dominated forests than surrounding forests on the same soil type (Heineman et al. ). The organic soil horizon (4.2 ± 0.4 cm thick) has a high surface root density (135 ± 9 g/m 2 root biomass) in comparison with the top 10 cm of underlying mineral soil (236 ± 18 g/m 2 ) (Adamek et al.…”

“…Soil inorganic N and δ 15 N concentrations within Oreomunnea-dominated areas are low compared to surrounding forests and depletion of N in the soil organic matter by Oreomunnea-associated ECM fungi may reduce inorganic N availability for free-living microbes and other plant species (Corrales et al 2016a). Total litterfall accumulation is higher in Oreomunnea dominated forests than surrounding forests on the same soil type (Heineman et al 2015). The organic soil horizon (4.2 ± 0.4 cm thick) has a high surface root density (135 ± 9 g/m 2 root biomass) in comparison with the top 10 cm of underlying mineral soil (236 ± 18 g/m 2 ) (Adamek et al 2011).…”

“…Net N mineralization and nitrification rates are greater in the organic soil horizon (258 ± 33 ng N·cm −2 ·h −1 and 15 ± 9 ng N·cm −2 ·h −1 , respectively) compared to the underlying mineral soil (41 ± 27 ng N·cm −2 ·h −1 and −3 ± 3 ng N·cm −2 ·h −1 , respectively), indicating that substantial inorganic and organic N may be supplied by the soil organic layer to plants and microbes in this forest (Koehler et al 2009). In an N fertilization experiment at the same site, root vertical distribution shifts from the organic to mineral soil layers (Adamek et al 2011) and litter production increases with N addition (Adamek et al 2009, Heineman et al 2015. Thus, the co-occurrence of species with divergent nutrient acquisition strategies may alleviate competition for nutrients in this ECM-dominated forest.…”