Soil biotic quality lacks spatial structure and is positively associated with fertility in a northern grassland

Abstract

Abstract1. When placing roots in the soil, plants integrate information about soil nutrients, plant neighbours and beneficial/detrimental soil organisms. While the fine-scale spatial heterogeneity in soil nutrients and plant neighbours have been described previously, virtually nothing is known about the spatial structure in soil biotic quality (measured here as a soil Biota-Induced plant Growth Response, or BIGR), or its correlation with nutrients or neighbours. Such correlations could imply trade-offs in root placement decisions.2. Theory would predict that soil BIGR is (1) negatively related to soil fertility and (2) associated with plant community structure, such that plants influence soil biota (and vice versa) through plant-soil feedbacks. We would also expect that since plants have species-specific impacts on soil organisms, spatially homogeneous plant communities should also homogenize soil BIGR.3. Here, we test these hypotheses in a semi-arid grassland by (1) characterizing the spatial structure of soil BIGR at a scale experienced by an individual plant and (2) correlating it to soil abiotic properties and plant community structure. We do so in two types of plant communities: (1) low-diversity patches dominated by an invasive grass (Bromus inermis Leyss.) and (2) patches covered mostly by native vegetation, with the expectation that dominance by Bromus would homogenize soil BIGR. 4. Soil BIGR was spatially heterogeneous, but not autocorrelated. This was true in both vegetation types (Bromus-invaded vs. native patches). Conversely, soil abiotic properties and plant community structure were frequently spatially autocorrelated at similar scales. Also, contrary to many studies, we found a positive correlation between soil BIGR and soil fertility. Soil BIGR was also associated with plant community structure. 5.Synthesis. The positive correlation between soil BIGR and some soil nutrient levels suggests that plants do not necessarily trade-off between foraging for nutrients vs.biotic interactions: nutritional cues could rather indicate the presence of beneficial soil biota. Moreover, the spatial structure in plant communities, coupled with their correlation with soil BIGR, jointly suggest that plant-soil feedbacks operate at local scales in the field: this has been identified in modelling studies as an important driver of plant coexistence. K E Y W O R D Sinformation integration, mutualisms, nutritional cues, phenotypic plasticity, plant coexistence, plant-soil feedbacks, root foraging behaviour, soil biota, soil micro-organisms, spatial scale

Biotic homogenization within and across eight widely distributed grasslands following invasion by Bromus inermis

“…However, at least within patches, the soil biotic quality experienced by plants appears to be equally variable within and outside B. inermis –invaded areas (Chagnon et al. ). The consequences of biotic homogenization within and across sites due to B. inermis invasion should be further investigated, as they could lead to losses in ecosystem function (Zak et al.…”

“…Piper et al (2015b) found microbial communities to be more homogeneous among B. inermis-invaded areas, compared to uninvaded areas. However, at least within patches, the soil biotic quality experienced by plants appears to be equally variable within and outside B. inermis-invaded areas (Chagnon et al 2018). The consequences of biotic homogenization within and across sites due to B. inermis invasion should be further investigated, as they could lead to losses in ecosystem function (Zak et al 2003, Lamb et al 2011, Hautier et al 2018) and increase the vulnerability of these communities to large-scale disturbances (Olden et al 2004).…”

Species‐specific size vulnerabilities in a competitive arena: Nutrient heterogeneity and soil fertility alter plant competitive size asymmetries

“…In the high‐nutrient‐heterogeneous soil treatment, fertilizer was distributed along the outside of the mesocosm with no nutrients placed in the centre of the mesocosm (low‐quality patch). For the initial microbial suppression treatment, soil was autoclaved at 121°C for 3 hr (Chagnon, Brown, Stotz, & Cahill, ) prior to nutrient addition to reduce any positive effects of sterilization on nutrient concentrations (Powlson & Jenkinson, ). Although autoclaving soil prior to nutrient addition cannot fully control for differences in nutrient concentrations among sterilized and non‐sterilized treatments, this should be minimized here due to the low fertility of the soil mixture (Powlson & Jenkinson, ).…”

A survey of invasive plants on grassland soil microbial communities and ecosystem services

“…Smooth brome invasion into intact native grasslands has been extensively studied [9][10][11][12][13][14][15][16][17] . Smooth brome invasion radically changes plant community structure 15,16 , and subsequently causes changes in soil nutrient cycling and soil microbial community structure and function [9][10][11]18,19 .…”