Microbiomes in Suspended Soils of Vascular Epiphytes Differ from Terrestrial Soil Microbiomes and from Each Other

Abstract

Microbial biodiversity parameters for tropical rainforests remain poorly understood. Whilst the soil microbiome accounts up to 95% of the total diversity of microorganisms in terrestrial ecosystems, the microbiome of suspended soils formed by vascular epiphytes remains completely unexplored. Samples of ground and suspended soils were collected in Cat Tien National Park, southern Vietnam. DNA extraction and sequencing were performed, and libraries of 16s rDNA gene sequences were analyzed. Alpha diversity indices of the microorganisms were the highest in the forest ground soil. In general, the microbiological diversity of all the soil types was found to be similar at the phylum level. Taxonomic composition of the bacterial communities in the suspended soils of plants from the same species are not closer than the taxonomic compositions of the communities in the suspended soils of different plant species. However, the beta diversity analysis revealed significant differences in the movement of mineral elements in terrestrial versus suspended soils. Our data showed that the suspended soils associated with vascular epiphytes were a depository of unique microbiological biodiversity. A contributing factor was the presence of large amounts of organic matter in the suspended soils—deposits collected by the epiphytes—which would have been degraded by termites if it had reached the ground. Further, the nutrient content of the suspended soils was prime for soil respiration activity and taxonomic microbial community biodiversity.

Characteristic of the material deposits, microclimate profile, epiphyte abundance, and bacteria populations in the above-ground ecosystem of oil palm

“…Therefore, the nutrient and C-organic levels in the lower leaf pocket were lower than in the upper. Dried leaves, reproductive organs, fruits, dust, epiphyte, living microbial biomass, and a small portion of the soil are the most common organic materials found in the leaf pockets (Allen et al 2018;Mildaryani et al 2019;Sofiyanti et al 2013;Eskov et al 2021). Different C/N ratios and organic material types at different leaf pocket heights may influence epiphyte plants and fauna (Potapov et al 2020).…”

“…The unique configuration of the leaf pocket causes a small basin to accumulate litter from oil palm reproductive organs and the decayed epiphytic plants (Potapov et al 2020). Decomposed organic contents trapped in the leaf pocket are known as material deposits (Mildaryani et al 2019), canopy (Allen et al 2018), or suspended soils (Eskov et al 2021). The axils can also intercept rain, providing a water source for epiphytic plants (Tarigan et al 2018;Luke et al 2019).…”

“…Vascular epiphytes are commonly attached to the oil palm stem (Suzanti et al 2016), where microfauna, mesofauna, macrofauna, and different types of amoeba, are also observed (Potapov et al 2020). Each material deposits microbiome will differ from terrestrial soils (Eskov et al 2021). Material deposits have unique microbial biodiversity (Zytynska et al 2011) than tropical terrestrial soils (Lindo and Winchester 2007).…”

Tree Species and Epiphyte Taxa Determine the “Metabolomic niche” of Canopy Suspended Soils in a Species-Rich Lowland Tropical Rainforest

“…Epiphyte species composition and canopy accumulation of organic matter are a positive feedback of appropriate microclimate conditions, such as lower temperature and greater levels of humidity [74], that create environmental niches occupied by organisms, which may not otherwise persist [53,75,76]. For example, variation in levels of light penetration and moisture among canopy strata have been linked with contrasting epiphyte communities and function [77][78][79][80][81], supporting our finding that suspended soil metabolic profiles are associated with epiphyte taxa, while a study exploring microbe communities of suspended soils using artificial soil microcosms found a negative relationship between the volume of suspended soil and microbe diversity [36].…”

Composition and Dynamics of Plant- and Soil-Associated Microbial Communities in Forest and Agricultural Ecosystems

“…Vascular epiphytes, non-parasitic plants that grow and are dependent on other plants, form their own “suspended” soil that is not in contact with the terrestrial soil. Eskov et al [ 8 ] examined such soils, providing the first glimpse of these unique microbial communities. Remarkably, the suspended soils house a treasure trove of microbial diversity, primarily due to the accumulation of organic matter that was protected from insect (termite) degradation as a result of its location off of the ground.…”