Allometric Models to Estimate Carbon Content in Arecaceae Based on Seven Species of Neotropical Palms

We present allometric models to estimate total carbon content and above ground carbon (AGC) for the family Arecaceae, and for 7 abundant neotropical palm species (the canopy species Socratea exorrhiza and Iriartea deltoidea , the sub-canopy palm Euterpe precatoria , and the understory species Asterogyne martiana , Prestoea decurrens , Geonoma interrupta and Chamaedorea tepejilote ). The study was done in the tropical rainforests of the Caribbean slope of Costa Rica. We harvested 87 individuals of a wide range of sizes, and divided them into roots, stems, and leaves, weight their fresh and dry biomass, calculated the carbon content, tissue density, leaf area, and shoot:root ratios (based on biomass and carbon content). The general palm model estimating total carbon content accounted for 92% of the variation and had diameter at breast height, stem height, and dry mass fraction as predictor variables. We generated a similar model to estimate AGC, which included the same variables and explained 91% of the variation. We compared our AGC model with two models used to estimate palm carbon content: Goldman et al. (2013)´s and Chave et al. (2014)´s models and found a range of R 2 values ​​of 0.87 to 0.91. Understory palm allometry was centered around biomass allocation, whereas sub-canopy and canopy species were associated with traits related to palm size (mainly DBH, total height, and leaf area). The efficiency the allometric models depends on species identity, sample size, and size range.

Spheres of Influence: Host Tree Proximity and Soil Chemistry Shape rRNA, but Not DNA, Communities of Symbiotic and Free-Living Soil Fungi in a Mixed Hardwood-Conifer Forest

Host and symbiont diversity are inextricably linked across partnerships and ecosystems, with degree of partner reliance governing the strength of this correlation. In many forest soils, symbiotic ectomycorrhizal fungi coexist and compete with free-living saprotrophic fungi, with the outcomes of these interactions shaping resource availability and competitive outcomes for the trees aboveground. Traditional approaches to characterizing these communities rely on DNA sequencing of a ribosomal precursor RNA gene (the internal transcribed spacer region), but directly sequencing the precursor rRNA may provide a more functionally relevant perspective on the potentially active fungal communities. Here, we map ectomycorrhizal and saprotrophic soil fungal communities through a mixed hardwood-conifer forest to assess how above- and belowground diversity linkages compare across these differently adapted guilds. Using highly spatially resolved transects (sampled every 2 m) and well-mapped stands of varying host tree diversity, we sought to understand the relative influence of symbiosis versus environment in predicting fungal diversity measures. Canopy species in this forest included two oaks (Quercus agrifolia and Quercus douglasii) and one pine (Pinus sabiniana). At the scale of our study, spatial turnover in rRNA-based communities was much more predictable from measurable environmental attributes than DNA-based communities. And while turnover of ectomycorrhizal fungi and saprotrophs were predictable by the presence and abundance of different canopy species, they both responded strongly to soil nutrient characteristics, namely pH and nitrogen availability, highlighting the niche overlap of these coexisting guilds and the strong influence of aboveground plants on belowground fungal communities.

Interspecific Variation in the Timing and Magnitude of Hydraulic Redistribution in a Forest With Distinct Water Sources

Aims Trees regulate water availability among their rooting strata through a nocturnal, passive transference of water known as hydraulic redistribution (HR). This study investigates differences in HR and groundwater use among common canopy species in longleaf pine ( Pinus palustris Mill., Pinaceae) woodlands and explores environmental factors influencing HR. Methods HR was estimated by sap flux of lateral roots and main stems of three mature canopy species ( P. palustris , Quercus laevis Walter., Fagaceae and Quercus margarettae Ashe., Fagaceae). We used δ 18 O and δD of xylem water, soil water, and groundwater to determine water source. Finally, we related HR to environmental factors (Temperature, VWC, VPD) to better understand controls of HR dynamics. Results Pinus palustris had higher water use than either Quercus species, and also redistributed significantly more water as a nocturnal subsidy. HR fluxes were inversely related with mean daily temperature and independent of shallow soil moisture. Stable isotope mixing models, based on δ 18 O and δD, indicated that all species have access to groundwater, but utilized shallow soil water in differing amounts when available. Conclusions In systems with strong water potential gradients among soil strata, any species with access to a groundwater source is likely capable of HR; however, the magnitude of HR varies significantly by species, even among closely related taxa.

Funtumia elastica (west African rubber tree).

Funtumia elastica is a medium-sized rubber tree native to tropical West Africa. It is considered an invasive species in forest understorey and naturally disturbed areas in Samoa and Martinique. It produces an immense quantity of seeds that are adapted for wind dispersal and its establishment has been favoured by fire and cyclones or hurricanes on these islands. This species can form monospecific stands, outcompeting native species. In some of its native habitats in Africa, F. elastica is a rare canopy species of primary and secondary forests, even being considered an endangered species in some Nigerian forests.