Plant–microbe interactions along a gradient of soil fertility in tropical dry forest

Abstract

Abstract:Theoretical models predict that plant interactions with free-living soil microbes, pathogens and fungal symbionts are regulated by nutrient availability. Working along a steep natural gradient of soil fertility in a Costa Rican tropical dry forest, we examined how soil nutrients affect plant–microbe interactions using two complementary approaches. First, we measured mycorrhizal colonization of roots and soil P availability in 18 permanent plots spanning the soil fertility gradient. We measured root production, root colonization by mycorrhizal fungi, phosphatase activity and Bray P in each of 144 soil cores. Next, in a full-factorial manipulation of soil type and microbial community origin, tree seedlings of Albizia guachapele and Swietenia macrophylla were grown in sterilized high-, intermediate- and low-fertility soils paired with microbial inoculum from each soil type. Seedling growth, biomass allocation and root colonization by mycorrhizas were quantified after 2 mo. In the field, root colonization by mycorrhizal fungi was unrelated to soil phosphorus across a five-fold gradient of P availability. In the shadehouse, inoculation with soil microbes had either neutral or positive effects on plant growth, suggesting that positive effects of mycorrhizal symbionts outweighed negative effects of soil pathogens. The presence of soil microbes had a greater effect on plant biomass than variation in soil nutrient concentrations (although both effects were modest), and plant responses to mycorrhizal inoculation were not dependent on soil nutrients. Taken together, our results emphasize that soil microbial communities can influence plant growth and morphology independently of soil fertility.

Ectomycorrhizal diversity and community structure in stands of Quercus oleoides in the seasonally dry tropical forests of Costa Rica

“…We documented 37 EMF taxa from Q. oleoides dominated forests. While our study may have been limited to a single sampling period and small spatial extent, this level of richness is in general agreement with previous studies of EMF communities in Q. crassifolia in montane cloud forests (n=42; Morris et al 2008) and another study of Q. oleoides stands in this region (Waring et al 2016a(Waring et al , 2016b. Similar to temperate Quercus forests and tropical angiosperm forests, the EMF community in Q. oleoides was dominated by members of the Russulaceae and Thelephoraceae (Walker et al 2005, Smith et al 2007, Tedersoo et al 2007, Peay et al 2009.…”

“…Thelephora species can utilize inorganic sources of N (Lilleskov et al 2002), which may benefit establishment of Q. oleoides during early stand development when soil inorganic N levels (as Quercus oleoides roots were also colonized by AMF; this is the first study to document dual colonization in Q. oleoides. However, AMF colonization levels did not differ significantly between Early and Late plots (Hypothesis 3), a result consistent with another study in this region that was conducted across a wider range of site ages and forest types (Waring et al 2016b). However, AMF hyphal colonization was higher in roots from Late than Early plots.…”

“…However, members of the Sebacinales and Pezizales, which are common constituents of temperate Quercus EMF communities, were not detected in our study. This outcome may reflect EMF community responses to the soil physicochemical environment (Waring et al 2016a(Waring et al , 2016b, a level of EMF-host plant specificity, or a combination of both factors (Tedersoo et al 2007). Nevertheless, our results show that EMF were common and diverse in Q. oleoides, in terms of both species and known EMF lineages.…”

“…Studies to date have shown that tropical forests harbor species-rich EMF communities (Mueller and Halling 1995, Tedersoo et al 2007, Morris et al 2008, Peay et al 2009, Smith et al 2011, but see Tedersoo et al 2010a, 2010b, and that EMF networks can enhance seedling establishment and promote monodominance (McGuire 2007). Variations in soil fertility (Peay et al 2015, Waring et al 2016a, 2016b, the size and phenology of the host plants and their distribution on the landscape can also influence EMF diversity (Morris et al 2008, Tedersoo et al 2010a, 2010b, as well as management activities such as fire suppression or restoration plantings that affect EMF host tree availability (Klemens et al 2011). For instance, trees in smaller patch size fragments might host fewer EMF taxa owing to reductions in inoculum potential and limits to root colonization (Peay et al 2007).…”

Nutrient limitation of soil microbial processes in tropical forests

“…In addition, methodological advances of deep-sequencing approaches may be used to reveal insights into differential responses of distinct soil microbial taxa or functional groups to nutrient additions (Kaspari et al 2017). A combination of the most recent molecular techniques with functional assessments of the microbial community may be particularly rewarding for the understanding of how resource availability and microbial community structure and function are interconnected (Su et al 2015, Waring et al 2016. Such knowledge on the nature of resource limitation regarding the abundance and activity of soil microorganisms is fundamental for understanding ecosystem functioning, and how it is affected by changing environmental conditions.…”