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Soil degradation during construction often results in soil loss through erosion and reduced vegetation establishment. Composted organic materials are used to restore soil health of compromised urban soils when planting trees and shrubs; however, less is known about compost amendments for turfgrass establishment. The objective of this trial was to determine the effects of differing compost incorporation rates in two soil types on perennial ryegrass [PR (Lolium perenne)] establishment. The hypothesis was that as compost incorporation rates increase, turfgrass germination would increase until the compost rate becomes detrimental to turfgrass germination because of increased nitrate content and electrical conductivity (EC) levels. A salt-sensitive PR cultivar and a salt-tolerant PR cultivar were seeded into a loam topsoil and a clay subsoil at soil:compost volume ratios of 100:0, 80:20, 70:30, 60:40, 50:50, 40:60, and 0:100 using a mixed-source mature compost. Percent green cover (PGC) and leachate pH, EC, and nitrate content were measured during the 5-week establishment period. This trial showed that with a suitable topsoil, compost incorporation may be unnecessary to obtain acceptable PGC, but that compost additions (30% to 40%) to a clay subsoil achieve faster establishment while limiting the potential for reduced establishment because of increased nitrate content or EC associated with greater levels of compost incorporation. The EC or pH of soil:compost leachate was not found to predict turfgrass establishment. This trial suggests that soil type should be considered when making compost use rate recommendations; however, further research is needed to link compost physiochemical properties to compost use rates.

Land-use change is highly dynamic globally and there is great uncertainty about the effects of land-use legacies on contemporary environmental performance. We used a chronosequence of urban grasslands (lawns) that were converted from agricultural and forested lands from 10 to over 130 years prior to determine if land-use legacy influences components of soil biodiversity and composition over time. We used historical aerial imagery to identify sites in Baltimore County, MD (USA) with agricultural versus forest land-use history. Soil samples were taken from these sites as well as from existing well-studied agricultural and forest sites used as historical references by the National Science Foundation Long-Term Ecological Research (NSF-LTER) Baltimore Ecosystem Study program. We found that the microbiomes in lawns of agricultural origin were similar to those in agricultural reference sites, which suggests that the ecological parameters on lawns and reference agricultural systems are similar in how they influence soil microbial community dynamics. In contrast, lawns that were previously forest showed distinct shifts in soil bacterial composition upon recent conversion but reverted back in composition similar to forest soils as the lawns aged over decades. Soil fungi did not follow similar trends as the bacteria in the previously forested lawns. Our results show that components of bacterial biodiversity and composition are resistant to change in previously forested lawns despite urbanization processes. Therefore land-use legacy, depending on the prior use, is an important factor to consider when examining urban ecological homogenization.

Climate change-related soil salinization increases plant stress and decreases productivity. Soil microorganisms are thought to reduce salt stress through multiple mechanisms, so diverse assemblages could improve plant growth under such conditions. Previous studies have shown that microbiome selection can promote desired plant phenotypes, but with high variability. We hypothesized that microbiome selection would be more consistent in saline soils by increasing potential benefits to the plants. In both salt-amended and untreated soils, we transferred forward Brassica rapa root microbiomes (from high-biomass or randomly selected pots) across six planting generations while assessing bacterial (16S rRNA) and fungal (ITS) composition in detail. Uniquely, we included an add-back control (re-adding initial frozen soil microbiome) as a within-generation reference for microbiome and plant phenotype selection. We observed inconsistent effects of microbiome selection on plant biomass across generations, but microbial composition consistently diverged from the add-back control. Although salt amendment strongly impacted microbial composition, it did not increase the predictability of microbiome effects on plant phenotype, but it did increase the rate at which microbiome selection plateaued. These data highlight a disconnect in the trajectories of microbiomes and plant phenotypes during microbiome selection, emphasizing the role of standard controls to explain microbiome selection outcomes.

Despite the abundance of tree diversity in the natural world, and generally high tree species richness in urban areas, urban forests continue to be dominated by a limited number of species. As socio-ecological systems, urban forests are shaped by historical and current management efforts and decision-making of a wide range of human actors. Drawing on past research, we offer a conceptual framework for describing the complex interactions among tree producers and consumers as trees are selected, grown, specified, and planted in private and public urban areas. We illustrate how multiple layers of selection criteria filter down the entirety of potential local tree diversity to a handful of commonly used and accepted tree species. We detail the actors and decision makers who impact tree composition and diversity across several land types. Finally, we identify research, education and outreach needs as they relate to creating more diverse and resilient urban forest ecosystems.

Because of public concern about exposing children to pesticides, legislation restricting its use on school playing fields has increased. One way to manage weeds without chemical herbicides is overseeding or the practice of repetitively seeding with a rapidly germinating turfgrass species. Overseeding for broadleaf weed control was tested on eight fields in Central New York (CNY) for three seasons and 40 fields across the northeastern United States for two seasons. Half of each field was treated each season by overseeding Lolium perenne L. (perennial ryegrass) three to five times each season for a total of 731 kg seed/ha (15 lb per 1000 ft2). Changes in the percent broadleaf weeds, grass, bare ground, soil moisture, Dark Green Color Index (DGCI) of grass cover, depth to soil compaction, and shear strength were measured after each treatment. The percent broadleaf weeds decreased and the percent grass cover increased due to overseeding in the Northeast fields, but not in CNY fields. Depth to compaction, percent soil moisture, and shear strength varied over time in the Northeast fields, and the percent bare ground, DGCI, and soil moisture varied over time in CNY fields. DGCI in the Northeast and soil compaction in CNY were affected by the interaction of overseeding × time. Although overseeding can be a beneficial weed management tool and affect other turf and soil traits in an integrated turf management program, monitoring environmental conditions and supporting field maintenance routines are critical weed management strategies for maintaining healthy turfgrass.

Agricultural over-fertilization may adversely impact plant−microbial interactions affecting crop yield. It is unclear if soil microbiomes respond quickly to changes in fertilizer inputs once conditioned to specific nutrient regimes. We conducted a growth chamber study assessing the compositional and functional resilience of root-associated microbiomes of Medicago sativa to nutrient regime changes, and consequences for plant growth. Plants were grown with a common starting soil microbiome under four nutrient treatments: control (no fertilizer), organic phosphorus (compost added), low inorganic P (low triple superphosphate, TSP) and high inorganic P (high TSP). After several conditioning generations, in which microbiomes from rhizospheres of high biomass plants were transferred forward, microbiome composition was distinct across the four treatments. The resulting microbiomes were then transplanted into each of the nutrient treatments, leading generally to functional changes in hydrolytic enzyme activity and taxonomic convergence with other microbiomes transplanted into the same nutrient regime. However, high inorganic P-conditioned microbiomes were resistant to compositional change. Correspondingly, M. sativa grown with high inorganic P-conditioned microbiomes had lower biomass, fewer nodules, and lower %N than plants grown under the same nutrient regime with other microbiomes. These findings suggest that excessive inorganic P fertilization may change microbiomes such that they negatively affect plant growth.

European swallowwort [Vincetoxicum rossicum(Kleopow) Barbarich] is found in the northeastern United States and southeastern Canada. It forms dense growth patterns that reduce plant and insect biodiversity, and lab assays show that it produces allelopathic compounds that affect microbial activity. Consequently, we hypothesized thatV. rossicumalters soil microbiome composition and activity in invaded habitats, which may impact ecosystem properties and processes. We sampled soil from a similar time point within a growing season at each of five sites in New York State whereV. rossicumwas both present and absent. We measured bacterial and fungal microbiome composition, available soil nitrogen (N), soil respiration (CO2flux), and soil extracellular enzyme activities. Microbial composition varied across field sites, but only fungal composition was affected by invasion. No significant differences were found between the invaded and uninvaded plots at any of the sites for available soil ammonium, nitrate, or respiration, though extractable N varied greatly between sites. Microbial hydrolytic extracellular enzyme activities suggest decreased protein degradation and increased oxidative enzyme activity withV. rossicuminvasion, which is relevant to soil N and carbon cycling processes. AlthoughV. rossicumimpacted rhizosphere microbial composition and activity, it was not associated with large perturbations in ecosystem function when examined across multiple invasion sites during this short-term study.

The dynamic process of forest succession is important for terrestrial ecosystems where soil organic matter (SOM) primarily controls biogeochemical cycles and is driven by soil microorganisms. Carbon (C) incorporation into SOM occurs along two different microbial metabolic pathways: ex vivo mostly extracellular enzymatic modification and in vivo turnover within the cells, highlighting the importance of microbial catabolism and anabolism respectively during soil C transformation and sequestration. However, identifying the dual C pathways and understanding the microbially-mediated SOM transformation during forest succession remains elusive, particularly with respect to interactions in the rhizosphere. Here, we used a series of biomarkers, including amino sugars, phospholipid fatty acids, and neutral sugars, to explore how forest succession and rhizosphere dynamics affect microbial contribution to soil organic carbon (SOC) in three successional stages of a subtropical forest ecosystem. We observed generally consistent increases in amino sugar and SOC with forest age in both bulk and rhizosphere soil, demonstrating that microorganisms facilitate SOC accumulation through the in vivo pathway along the successional gradient. The ratio of amino sugar-C to SOC (AS-C/SOC) exhibited a greater increase in bulk than in rhizosphere soil along the successional gradient, indicating the microbial in vivo pathway was relatively more important for SOC accumulation in bulk than in rhizosphere soil. Given there was a significant decrease in the ratios of hexose-to-pentose sugars [(galactose + mannose)/(arabinose + xylose), indicating the contribution of sugars derived from microbes and plants to labile soil C], we hold the opinion that relatively limited microbial C processing occurred in the rhizosphere along the forest successional gradient. Therefore, the microbial ex vivo pathway where microorganisms decomposed (structurally modified) fine root litter that was incorporated into SOC was relatively more important in rhizosphere than in bulk soil for SOC variation during forest succession. Our findings emphasize the role of microbes transforming organic matter in both bulk and rhizosphere soil in a subtropical forest successional gradient and help to enhance our understanding of the function and ecosystem services of these environments.

Urban forests are valuable assets to a community from multiple perspectives. Diversifying urban forests is a common and important management goal to increase resilience in the face of biotic pests and diseases, climate change, and to increase ecosystem services. Multiple design and engineering consultants develop site plans and specify trees for public and private projects, and consultant disciplines differ in their training plant material selection and diversity. Publicly available site plans from Des Moines (79) and Iowa City, Iowa, USA (70) between 2015–2018 that passed planning and zoning review were analyzed to determine the associations between practitioner disciplinary training and the diversity of specified trees at site, city, and landscape scales. We found that consultant discipline was not related to the alpha diversity of a site until site size was greater than 2.42 ha, then civil engineers were associated with lower tree diversity than other consultants. Landscape architects completed a majority of the project plans (43 %), specified the most trees (62 %), and utilized the most diverse plant palette, including 30 species not used by other consultants. However, landscape architects also frequently specified clonally produced cultivars (62 % of all selections) which may limit genetic diversity at a landscape scale, thus potentially undermining diversification efforts by repeating genotypes. Findings from this study suggest that messages pertaining diversification efforts, plant selection, and reduction of genetic diversity resulting from cultivar specification are important for all consultants, but especially for landscape architects who were responsible for specifying a majority of trees and sites. This case study of two Iowa (USA) communities provides evidence of landscape-scale diversity outcomes associated with consultant discipline and the potential for use of public site plan documents to assess such relationships. Further research is needed to determine if these findings are generalizable to other municipalities or states.

Urban grasslands are turfgrass dominated landscapes of varying functions and uses that are ubiquitous in areas associated with human population growth and urbanization. While these landscapes are perceived to serve a primarily aesthetic function, they provide a multitude of beneficial ecosystem functions that impervious surfaces do not provide. Urban grassland soils have been shown to accumulate carbon (C) and nitrogen (N) for decades, matching native grasslands and eastern hardwood forest soils in terms of C and N densities. The establishment and maintenance of urban grasslands alters many microbially-mediated biogeochemical processes in soils, including soil organic matter (SOM) dynamics. Despite strong evidence of alterations to soil C and N cycling, the impacts of maintaining urban grasslands on soil microbiomes and their functions remain understudied compared to other ecosystems. Typical management practices can directly and indirectly affect edaphic factors in urban grasslands, which in turn, could impact soil processes mediated by microorganisms. We reviewed the existing literature on urban grassland management, focusing on how mowing, fertilization, irrigation, grass species composition, and soil cultivation could impact the composition and function of soil microorganisms. Although sparse, the literature indicates that the techniques used to maintain urban grassland habitats broadly select for copiotrophic microorganisms adapted to higher resource availability. Additionally, the studies indicate that greater soil fertility and plant productivity found in urban grasslands facilitate the accumulation of soil C and N, as well as SOM as compared to other land-use types. However, effects on soil biology and biogeochemistry depend on specific management practices, which are quite variable. Future research on soil C and N dynamics in urban grasslands should focus on the dominant component of this ecosystem—residential lawns—however, much of the existing scientific literature featuring turfgrass systems focus heavily on golf courses, athletic fields, and major tourist parks.

Soil invertebrates, especially larger macroinvertebrates, move soil, fragment organic matter and change resource accessibility for soil microorganisms. Macroinvertebrates also affect the formation and turnover of aggregates, which are important controls of soil organic matter dynamics because they physically protect organic matter from degradation and influence many belowground processes ranging from microbial activity to nutrient sorption and water flow. We still lack a complete understanding of how different soil invertebrate functional groups affect the incorporation of root derived carbon and nitrogen into belowground pools. We assessed the effects of macroinvertebrates on soil aggregate abundance and composition and quantified the fate of organic matter derived from roots using a two-year macroinvertebrate exclusion-based field mesocosm study coupled with stable isotope labeling in a turfgrass lawn ecosystem. We hypothesized that macroinvertebrates change soil aggregates dynamics by increasing macroaggregates and decreasing microaggregates and enhancing the incorporation of root-derived organic matter into macroaggregates. We found that within the turfgrass root zone, macroinvertebrates increased the proportion of macroaggregates and decreased free microaggregates. In addition, macroinvertebrates increased carbon and nitrogen incorporation into macroaggregates, microaggregates and coarse particulate organic matter, detected via isotopic enrichment of those soil fractions. We found that macroinvertebrates affect the fate of recently fixed root- and rhizodeposit-derived organic matter in a turfgrass lawn ecosystem, and particularly its incorporation into soil aggregates, similar to findings in forest and agricultural systems.

In the United States, there is a growing need for turfgrass management practices that protect community and environmental health. The proportion of the developed landscape in the United States covered by turfgrass is significant and, at present, covers at least 1.9% of the total land area and comprises 60% in parts of the country. As urbanization progresses, there is a critical need to re-examine turf management practices that reduce reliance on pesticide and fertilizer inputs while contributing additional beneficial ecosystem services. In this review, we discuss the functional role of turfgrass in urban ecosystems. We identify key urban ecosystem processes associated with turfgrass and evaluate the potential to integrate biodiversity into their design and management. Specifically, we summarize research on the Biodiversity and Ecosystem Function theory that shows enhanced C storage, N retention, and weed suppression in natural and managed ecosystems, which are traits that are relevant to turfgrass systems. Enhancing biodiversity in turfgrass systems could increase ecosystem services in urban landscapes and should be considered a component of sustainable management practices.

Urban grasslands, landscapes dominated by turfgrasses for aesthetic or recreational groundcovers, are rapidly expanding in the United States and globally. These managed ecosystems are often less diverse than the natural or agricultural lands they replace, leading to potential losses in ecosystem functioning. Research in non-urban systems has provided evidence for increases in multiple ecosystem functions associated with greater plant diversity. To test if biodiversity-ecosystem function findings are applicable to urban grasslands, we examined the effect of plant species and genotypic diversity on three ecosystem functions, using grassland assemblages of increasing diversity that were grown within a controlled environment facility. We found positive effects of plant diversity on reduced nitrate leaching and plant productivity. Soil microbial diversity (Mean Shannon Diversity, H') of bacteria and fungi were also enhanced in multi-species plantings, suggesting that moderate increments in plant diversity influence the composition of soil biota. The results from this study indicate that plant diversity impacts multiple functions that are important in urban ecosystems; therefore, further tests of urban grassland biodiversity should be examined in situ to determine the feasibility of manipulating plant diversity as an explicit landscape design and function trait.