Invasive legume management strategies differentially impact mutualist abundance and benefit to native and invasive hosts

Abstract

Determining the best management practices for plant invasions is a critical, but often elusive goal. Invasive removals frequently involve complex and poorly understood biotic interactions. For example, invasive species can leave potent legacies that influence the success of native species restoration efforts, and positive plant‐microbial feedbacks may promote continued reinvasion by an exotic species following restoration. Removal methods can vary in their effects on plant–soil feedbacks, with consequences for restoration of native species. We determined the effects of invasion by a leguminous shrub (French broom; Genista monspessulana) on the density and community composition of, and benefit conferred by, its microbial mutualists in its invading range. Densities of soil‐dwelling rhizobia were much higher in areas invaded by G. monspessulana relative to uninvaded areas, and this increased density of rhizobia fed back to increase seedling growth of both the invader and native legumes. We further compared how three techniques for removing G. monspessulana affected the densities of rhizobia relative to areas where G. monspessulana was still present. Removal by hand‐pulling reduced soil rhizobial densities, and reduced growth of one native legume, while having no effect on the growth of the invader. Overall, our results show that the consequences of restoration techniques, both above‐ and belowground, could be critical for the successful removal of an invasive legume and restoration of native species.

Invasive plant species interact with drought to shift key functions and families in the native rhizosphere

“…While we did not find that here, it is possible that intra-group interactions (i.e., interactions between native forbs or between invasive grasses) in the field mask differences between natives and invasives as plants compete for limited nutrients (Hawkins & Crawford, 2018). Despite this, our findings that invasive competition shifts native rhizosphere microbes is generally well-supported (Komatsu & Simms, 2019;LaForgia et al, 2022;Rodríguez-Caballero et al, 2020), and we speculate that these invasive-associated microbial shifts play a role in the direction and magnitude of native-invasive interactions as seen elsewhere (Emam et al, 2014;Klironomos, 2002). The sole function that increased in abundance under invasive competition was OprP.…”

Invasive Grass Dominance over Native Forbs Is Linked to Shifts in the Bacterial Rhizosphere Microbiome

“…Shifts in the microbiome are a potentially important contributor to the dominance of invasive plants. Although there is strong evidence for local adaptation between plants and their home microbiome, invasive plants are relatively novel players, causing disruptions in important plant-microbe interactions by increasing soil microbial activity [31], reducing microbial biomass [32] and diversity [33], increasing nitrification rates [24], and changing microbiome composition [34,35]. These plant-soil feedbacks can benefit the invader [35,36], selectively harm natives [37], and/or benefit other invaders [38].…”

Legume germination is delayed in dry soils and in sterile soils devoid of microbial mutualists: Species‐specific implications for upward range expansions

“…Soils and seeds were collected within 10 m of transects that traverse the Washington Gulch (403), Gothic Mountain, and Baldy Mountain trails (3200–3500 m in elevation; Figure 2 ). Within the current range of our focal legume species, soils were collected from within a 10 cm radius of the nearest legume to a depth of 15 cm, just past the rooting depth of L. leucanthus and V. americana , and where beneficial soil microbial species are likely to be at higher densities in the soil (Komatsu & Simms, 2020 ). A soil corer was centered over a focal legume and soils were exhumed from that core.…”