Soil microbiomes of hardwood‐ versus pine‐dominated stands: Linkage with overstory species

Abstract

Biodiversity in forest ecosystems is paradoxical. Whereas their most apparent component-the woody overstory-is the least diverse with respect to numbers of species, the least apparent component is the biotic community of highest diversity-the soil microbiome. Numerous factors influence the composition and diversity of soil microbial communities, which in turn exert a profound impact on plant species occupying the soil and the biogeochemistry of essential plant nutrients. Of interest in forest ecosystems is how the soil microbiome interacts with the overstory, a phenomenon referred to as linkage. This study compared the soil microbiome of two adjacent stand types-hardwood-and longleaf pine (Pinus palustris)-dominated-and addressed the following questions: (1) How does soil microbiome vary with stand type? (2) Do the forest overstory community and soil microbiome exhibit linkage? Twelve 0.04-ha circular plots were established in each stand type to assess tree community composition and structure and to sample mineral soil for three separate analyses: assessment of soil fertility, measurement of total carbon and nitrogen (N), and extraction of genomic DNA for assessment of microbiome communities. All live stems ≥2.5 cm dbh in each plot were identified to species and measured for dbh to the nearest 0.1 cm. Mineral soil was taken from a depth of 5 cm and oven-dried at 38 C prior to analyses. Hardwood stands were dominated by flowering magnolia (Magnolia grandiflora) and southern evergreen oaks, whereas pine stands were dominated by longleaf pine and live oak (Quercus virginiana). Although soils of both stand types were highly acidic, the hardwood stands were generally higher in fertility, especially for total and available N. The overstory and soil microbial communities exhibited evidence of linkage among all sample plots combined. When assessed separately by stand type, only hardwood-dominated stands displayed evidence of overstory/microbial linkage. These results have broader implications for future scenarios given the sensitivity of soil microbes to climate change.

Chronic Exclusion of Fire in Longleaf Pine Stands of an Urban Interface: The University of West Florida Campus Ecosystem Study

“…Live oak has been particularly ubiquitous in these stands, which inhibits longleaf regeneration. Indeed, it is notable that this was found in all stands, regardless of the presence of longleaf pine [22]. The data also suggest that soil fertility declined significantly with chronic fire exclusion.…”

“…Linear regression was used to compare the age of longleaf stems to the measured DBH for 50 stems to yield a model allowing an estimation of the stem age based on DBH. The age of each measured longleaf pine stem was estimated from DBH with the following model based on this analysis [22]: Age = 1.76 × DBH + 0.83 (r 2 = 0.82; p < 0.00001) where Age is the stem age in years; DBH is in cm. The mean age of longleaf pine was compared among the main campus, Ball Trails, Sanctuary, and Side Trails sites via an analysis of variance and Least Significant Difference tests [33].…”

“…The Troup soils are loamy, kaolinitic, thermic Grossarenic Kandiudults with a chronically high seasonal water table below 2 m in depth [32]. Previous works have shown these soils to be acidic and infertile [22].…”

“…Thus, the UWF Campus Ecosystem Study (CES) was established as an interconnected series of research projects. To date, there have been five investigations, with four as part of the original focus on the ecology of longleaf pine [19][20][21][22] and one study [23] that monitored the freshwater stream that flows through the campus and joins the Escambia River (Figure 1). ] and one study [23] that monitored the freshwater stream that flows through the campus and joins the Escambia River (Figure 1).…”

“…In the summer of 2020, sample plots were established and sampled in two of the UWF campus' natural areas: Ball Trails (T) and Baars-Firestone Wildlife Sanctuary (S) [20]. The most recent study [22] is indicated by the red circle.…”