Plant–soil feedbacks and the dominance of conifers in a tropical montane forest in Borneo

Abstract

Abstract. We investigated consequences of plant-soil feedbacks (PSFs) in a tropical montane forest on Mt. Kinabalu in Borneo by measurements of light and soil conditions, ecophysiological analyses of tree seedlings, a long-term adult and seedling census, and a simple simulation model. The study plot (2.74 ha) is in a mixed conifer-broadleaf forest with 24% relative basal area of conifers. First, we investigated light and soil conditions beneath two dominant species, a conifer Dacrydium gracilis (Podocarpaceae, arbuscular mycorrhizal tree) and a broadleaf Lithocaprus clementianus (Fagaceae, ectomycorrhizal tree). The relative light intensity was marginally higher beneath Dacrydium tree crown than beneath Lithocarpus tree crown. The concentrations of inorganic nitrogen and labile phosphorus, and the nitrogen mineralization rate, were lower beneath Dacrydium than beneath Lithocarpus, suggesting that soils beneath Dacrydium were more nutrient deficient. Microscopic observations confirmed that conifer seedlings (including Dacrydium) harbored arbuscular mycorrhizal fungi. In addition, a molecular analysis showed that root-associated mycorrhizal fungal communities were clearly different between conifer and broadleaf seedlings, and consequently, nutrient acquisition capacity of seedlings may be different between them. Indeed, stable isotopic evidence suggested that Dacrydium seedlings are more efficient in inorganic nitrogen acquisition than Lithocarpus seedlings. These results predicted that the conifer seedlings would out-compete broadleaf seedlings and have a greater advantage beneath the conifer canopy. To test the possible advantage of conifer seedlings in performance, we developed hierarchical Bayesian models and estimated growth and mortality rates using the seedling census data during 2006-2012. We found that conifer seedlings performed better than broadleaf seedlings beneath Dacrydium canopy. On the other hand, broadleaf seedlings performed better than conifer seedlings beneath Lithocarpus canopy. The consequences of the PSFs for the tree community composition were investigated by developing a simple simulation model, and were compared with the results of a model without PSFs. After a 10 000-year simulation, the relative abundance of conifers with PSFs converged to 22%, which was consistent with the actual abundance; the model without effects of PSFs predicted a relative abundance of only ~10%. The results suggested that PSFs contributed to the maintenance of the conifer dominance in the tropical montane forest.

Spatial structure of fungal DNA assemblages revealed with eDNA metabarcoding in a forest river network in western Japan

“…For MiSeq sequencing, the fungal internal transcribed spacer 1 (ITS1) region of rDNA was amplified (Schoch et al 2012). The methods of DNA analysis followed those described by Ushio et al (2017) with some modifications, such as number of PCR cycles. The first-round PCR (first PCR) amplified the ITS1 region using the ITS1-F-KYO2 (5′-TAG AGG AAG TAA AAG TCG TAA -3′) and ITS2-KYO2 (5′-TAG AGG AAG TAA AAG TCG TAA -3′) primer set (Toju et al 2012) fused with an Illumina sequencing primer and six random bases (N).…”

“…The procedures used for bioinformatics and data analyses followed those described previously (Matsuoka et al 2016a;Ushio et al 2017). The raw MiSeq data were converted into FASTQ files using the bcl2fastq program provided by Illumina.…”

Plant–soil interactions maintain biodiversity and functions of tropical forest ecosystems

“…The figure was drawn based on Fujii (2014) seedlings of some conifers (e.g. Dacrydium) and broadleaved trees can successfully explain shift in plant community structure with soil aging (Ushio et al 2017). Identifying the main driving mechanisms of plant soil interactions would contribute to better understanding or prediction of forest dynamics and soil formation.…”

Interaction capacity underpins community diversity

“…Community diversity, or species diversity, a surrogate of biodiversity that is most commonly focused on (Willig et al 2003), is a collective consequence of community assembly. Among the community assembly processes, interspecific interactions, which contribute to the process of selection, play an important role in shaping community diversity, particularly at a local (i.e., small/short spatiotemporal) scale, and thus they have played a central role when devising theories of ecological communities (Vellend 2016), including modern coexistence theory (Chesson 2000), niche theory (Chase & Leibold 2003), plant-soil feedbacks (Comita et al 2010;Mangan et al 2010;Ushio et al 2017), and many others. Understanding how interspecific interactions shape community diversity is key to understanding how patterns in an ecological community emerge in nature.…”