Soil organic nitrogen endows invasive Solidago canadensis with greater advantages in low‐phosphorus conditions

Nitrogen acquisition strategy and its effects on invasiveness of a subtropical invasive plant

Introduction

Preference and plasticity in nitrogen (N) form uptake are the main strategies with which plants absorb soil N. However, little effort has been made to explore effects of N form acquisition strategies, especially the plasticity, on invasiveness of exotic plants, although many studies have determined the effects of N levels (e.g. N deposition).

Methods

To address this problem, we studied the differences in N form acquisition strategies between the invasive plant Solidago canadensis and its co-occurring native plant Artemisia lavandulaefolia, effects of soil N environments, and the relationship between N form acquisition strategy of S. canadensis and its invasiveness using a 15N-labeling technique in three habitats at four field sites.

Results

Total biomass, root biomass, and the uptakes of soil dissolved inorganic N (DIN) per quadrat were higher for the invasive relative to the native species in all three habitats. The invader always preferred dominant soil N forms: NH4 + in habitats with NH4 + as the dominant DIN and NO3 - in habitats with NO3 - as the dominant DIN, while A. lavandulaefolia consistently preferred NO3 - in all habitats. Plasticity in N form uptake was higher in the invasive relative to the native species, especially in the farmland. Plant N form acquisition strategy was influenced by both DIN levels and the proportions of different N forms (NO3 -/NH4 +) as judged by their negative effects on the proportional contributions of NH4 + to plant N (f NH4 +) and the preference for NH4 + (β NH4 +). In addition, total biomass was positively associated with f NH4 + or β NH4 + for S. canadensis, while negatively for A. lavandulaefolia. Interestingly, the species may prefer to absorb NH4 + when soil DIN and/or NO3 -/NH4 + ratio were low, and root to shoot ratio may be affected by plant nutrient status per se, rather than by soil nutrient availability.

Discussion

Our results indicate that the superior N form acquisition strategy of the invader contributes to its higher N uptake, and therefore to its invasiveness in different habitats, improving our understanding of invasiveness of exotic plants in diverse habitats in terms of utilization of different N forms.

A shift from inorganic to organic nitrogen-dominance shapes soil microbiome composition and co-occurrence networks

Soil microbiomes are characterized by their composition and networks, which are linked to soil nitrogen (N) availability. In nature, inorganic N dominates at one end and organic N dominates at the other end along soil N gradients; however, little is known about how this shift influences soil microbiome composition and co-occurrence networks, as well as their controls. To this end, we conducted an experiment with the host plant Solidago canadensis, which was subject to three N regimes: inorganic N-dominated, co-dominated by inorganic and organic N (CIO), and organic N-dominated. Organic N dominance exhibited stronger effects on the composition and co-occurrence networks of soil microbiomes than inorganic N dominance. The predominant control was plant traits for bacterial and fungal richness, and soil pH for keystone species. Relative to the CIO regime, inorganic N dominance did not affect fungal richness and increased keystone species; organic N dominance decreased fungal richness and keystone species. Pathogenic fungi and arbuscular mycorrhizal fungi were suppressed by organic N dominance but not by inorganic N dominance. These findings suggest that the shift from soil inorganic N-dominance to soil organic N-dominance could strongly shape soil microbiome composition and co-occurrence networks by altering species diversity and topological properties.

Arbuscular Mycorrhizal Fungi Compete Asymmetrically for Amino Acids with Native and Invasive Solidago

Arbuscular mycorrhizal fungi (AMF) and soil amino acids both affect plant performance. However, little is known about how AMF compete for amino acids with native and invasive congeners. We conducted a factorial experiment (inoculation, native and invasive species, and amino acids) to examine the competition for amino acids between soil microbes and both native and invasive congeners. The competition for amino acids between AMF and invasive Solidago canadensis was weaker than that observed between AMF and native S. decurrens. This asymmetric competition increased the growth advantage of S. canadensis over S. decurrens. The efficacy (biomass production per unit of nitrogen supply) of amino acids compared to ammonium was smaller in S. canadensis than in S. decurrens when both species were grown without inoculation, but the opposite was the case when both species were grown with AMF. AMF and all microbes differentially altered four phenotypic traits (plant height, leaf chlorophyll content, leaf number, and root biomass allocation) and the pathways determining the effects of amino acids on growth advantages. These findings suggest that AMF could enhance plant invasiveness through asymmetric competition for amino acids and that amino acid-driven invasiveness might be differentially regulated by different microbial guilds.

Arbuscular Mycorrhizal Fungi Contribute to Phosphorous Uptake and Allocation Strategies of Solidago canadensis in a Phosphorous-Deficient Environment

Arbuscular mycorrhizal fungi (AMF) can facilitate the uptake of limiting or inaccessible nutrients by plants. However, the importance of AMF for invasive plants under phosphorus (P) limitation is poorly well understood because of the presence of non-focal microorganisms, such as endophytes or rhizosphere bacteria. In this study, we investigated how an invasive clonal plant Solidago canadensis benefits from the AMF Glomus intraradices by using a completely sterile culturing system, which is composed of aseptic seedlings, a pure AMF strain, and a sterile growth environment. We found that the colonization rate, abundance, and spore production of AMF in the insoluble P treatment was more than twice as much as in the available P treatment. Plant above-ground growth was enhanced almost 50% by AMF in the insoluble P treatment. Importantly, AMF were able to facilitate P acquisition by the plant in insoluble P conditions, allowing plants to have lower investment into below-ground biomass and higher benefit/return for above-ground biomass. This study demonstrated the important contribution that AMF make to plants in phosphate-deficient environments eliminating interference from non-focal microorganisms. Our results also suggest that interaction with AMF could contribute to the invasiveness of clonal plant S. canadensis in a resource-deficient environment.

Survey of the Solidago canadensis L. Morphological Traits and Essential Oil Production: Aboveground Biomass Growth and Abundance of the Invasive Goldenrod Appears to Be Reciprocally Enhanced within the Invaded Stands

Canadian goldenrod is one of the most widespread invasive neophytes in Europe with proven ecological and environmental consequences for the invaded plots. The morphological traits and productive features survey can offer a better insight view into the S. canadensis population ecology and the dynamic of its aboveground biomass growth. Equally, it can serve as a foundation for a balanced management proposal, with the aim of keeping an acceptable degree of Canadian goldenrod invasion. In the study, 600 specimens, collected at various phenological phases, from the twelve sampling stands in the eastern Slovakia, were processed. The obtained data were related to the degree of invasion, pH, soil moisture, overall stand area, and measure of interventions. Plants from the stands with a mild degree of goldenrod invasion (<50%), lower pH, and higher stand area were significantly lower and lighter; had a significantly lower number and weight of leaves; significantly shorter and lighter stems, in comparison to the plants from the stands with a heavy degree of invasion (>50%); a higher pH; and a smaller area. These plants also showed smaller essential oil productivity rate, and they achieved the growth peak a significantly later. Conversely, as the stand area decreased, and the S. canadensis % representation and soil reaction increased, goldenrods became significantly taller and heavier, with a higher number of leaves and a higher essential oil productivity rate. Canadian goldenrod shows, somewhat, a cyclical, self-growth-reinforcing feedback: the consecutive increase of the goldenrod’s aboveground biomass leads to an increase of its relative % abundance within the invaded stands. Consequently, the increase of the goldenrod’s relative % abundance leads to the plants aboveground biomass consecutive growth, and so on.

Impacts of soil properties and functional diversity on the performance of invasive plant species Solidago canadensis L. on post-agricultural wastelands

Amongst the numerous consequences of the rapid development of agriculture and urbanization, biological invasions are highlighted as having the biggest impact on the functioning of ecosystems. One of the alien plant species, considered in Europe and Asia to be highly invasive, is Solidago canadensis L.; and its impact on the functioning of ecosystems has been studied in numerous respects. However, knowledge about how the physico-chemical parameters of soils and biotic interactions between species shape the performance of S. canadensis in a transformed landscape is still insufficient. The aim of this study was to assess how complex soil abiotic conditions and the functional diversity of co-occurring vegetation shape the performance of S. canadensis on the wastelands abandoned by agriculture. Apart from detailed investigations of soil properties and S. canadensis biomass, to achieve our study aims, we used parameters of functional diversity, which allowed us to identify the main ecological processes determining the community assembly processes. Under higher contents of loamy fractions in soil, but lower functional richness in surroundings, S. canadensis achieved larger cover. Alongside increasing functional richness and dispersion in co-occurring vegetation, this species has demonstrated sturdy attributes when competing for water and nutrients, expressed by a higher production of rhizomes and roots. Under elevated zinc and lead levels, as well as higher functional evenness in the surroundings, the flower biomass decreased, while the biomass of stems increased. Thus, S. canadensis exhibits a highly adaptive capacity to grow in soils contaminated by heavy metals, due to the buffer properties and life strategies allowing the use of resources absorbed in loamy soils. Environmental factors seem to be more responsible for the shaping of the performance and for the colonization success of S. canadensis than biotic interactions with plants occurring in the surroundings.

Common mycorrhizal networks influence the distribution of mineral nutrients between an invasive plant, Solidago canadensis, and a native plant, Kummerowa striata

Invasive species often reduce ecosystem services and lead to a serious threat to native biodiversity. Roots of invasive plants are often linked to roots of native plants by common mycorrhizal networks (CMNs) of arbuscular mycorrhizal (AM) fungi, but whether and how CMNs mediate interactions between invasive and native plant species remains largely uninvestigated. We conducted two microcosm experiments, one in which we amended the soil with mineral N and another in which we amended the soil with mineral P. In each experiment, we grew a pair of test plants consisting of Kummerowia striata (native to our research site) and Solidago canadensis (an invasive species). CMNs were established between the plants, and these were either left intact or severed. Intact CMNs increased growth and nutrient acquisition by S. canadensis while they decreased nutrient acquisition by K. striata in comparison with severed CMNs. ¹⁵N and P analyses indicated that compared to severed CMNs, intact CMNs preferentially transferred mineral nutrients to S. canadensis. CMNs produced by different species of AM fungi had slightly different effects on the interaction between these two plant species. These results highlight the role of CMNs in the understanding of interactions between the invasive species S. canadensis and its native neighbor.

Dissecting Solidago canadensis-soil feedback in its real invasion

The importance of plant-soil feedback (PSF) has long been recognized, but the current knowledge on PSF patterns and the related mechanisms mainly stems from laboratory experiments. We aimed at addressing PSF effects on community performance and their determinants using an invasive forb Solidago canadensis. To do so, we surveyed 81 pairs of invaded versus uninvaded plots, collected soil samples from these pairwise plots, and performed an experiment with microcosm plant communities. The magnitudes of conditioning soil abiotic properties and soil biotic properties by S. canadensis were similar, but the direction was opposite; altered abiotic and biotic properties influenced the production of subsequent S. canadensis communities and its abundance similarly. These processes shaped neutral S. canadensis-soil feedback effects at the community level. Additionally, the relative dominance of S. canadensis increased with its ability of competitive suppression in the absence and presence of S. canadensis-soil feedbacks, and S. canadensis-induced decreases in native plant species did not alter soil properties directly. These findings provide a basis for understanding PSF effects and the related mechanisms in the field conditions and also highlight the importance of considering PSFs holistically.