Plant Community Responses to Simultaneous Changes in Temperature, Nitrogen Availability, and Invasion

<div><p>Background</p><p>Increasing rates of change in climate have been observed across the planet and have contributed to the ongoing range shifts observed for many species. Although ecologists are now using a variety of approaches to study how much and through what mechanisms increasing temperature and nutrient pollution may influence the invasions inherent in range shifts, accurate predictions are still lacking.</p><p>Methods and Results</p><p>In this study, we conducted a factorial experiment, simultaneously manipulating warming, nitrogen addition and introduction of <i>Pityopsis aspera</i>, to determine how range-shifting species affect a plant community. We quantified the resident community using ordination scores, then used structural equation modeling to examine hypotheses related to how plants respond to a network of experimental treatments and environmental variables. Variation in soil pH explained plant community response to nitrogen addition in the absence of invasion. However, in the presence of invasion, the direct effect of nitrogen on the community was negligible and soil moisture was important for explaining nitrogen effects. We did not find effects of warming on the native plant community in the absence of invasion. In the presence of invasion, however, warming had negative effects on functional richness directly and invasion and herbivory explained the overall positive effect of warming on the plant community.</p><p>Conclusions and Significance</p><p>This work highlights the variation in the biotic and abiotic factors responsible for explaining independent and collective climate change effects over a short time scale. Future work should consider the complex and non-additive relationships among factors of climate change and invasion in order to capture more ecologically relevant features of our changing environment.</p></div

Means and (SD) for environmental factors from plots exposed to the warming treatment (data from nitrogen addition plots excluded).

<p>Factor names followed by an * were included in the structural equation models for warming plots.</p><p>Means and (SD) for environmental factors from plots exposed to the warming treatment (data from nitrogen addition plots excluded).</p

Means and (SD) for environmental factors from plots exposed to the nitrogen treatment (data from warming treatment plots excluded).

<p>Factor names followed by an * were included in the structural equation models for nitrogen plots.</p><p>Means and (SD) for environmental factors from plots exposed to the nitrogen treatment (data from warming treatment plots excluded).</p

Results of the warming SEM.

<p>Warming effects on plant community NMDS scores in the (A) absence (χ² = 15.519, d.f. = 16, <i>p</i> = 0.487) and (B) presence of invasion (χ² = 10.002, d.f. = 16, <i>p</i> = 0.867). Arrow characteristics and all values as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0123715#pone.0123715.g001" target="_blank">Fig 1</a>.</p

Results of the nitrogen SEM.

<p>Nitrogen effects on plant community NMDS scores in the (A) absence (χ² = 1.79, d.f. = 9, <i>p</i> = 0.994) and (B) presence of invasion (χ² = 6.08, d.f. = 9, <i>p</i> = 0.732). Black arrows with values indicate significant paths, gray arrows indicate insignificant paths, solid arrows indicate positive relationships, and dashed arrows indicate negative relationships. Path values indicate unstandardized (top) and standardized (bottom) coefficients. Within box values indicate R² values, which represent the proportion of variance explained for each response variable.</p

Relationship between local-scale topography and vegetation on the invasive C 4 perennial bunchgrass buffelgrass (Pennisetum ciliare) size and reproduction

Buffelgrass [Pennisetum ciliare (L.) Link] is an invasive C4 perennial bunchgrass that is a threat to biodiversity in aridlands in the Americas and Australia. Topography influences P. ciliare occurrence at large spatial scales, but further investigation into the relationship between local-scale topography and P. ciliare growth and reproduction would be beneficial. Further, density-dependent effects on P. ciliare growth and reproduction have been demonstrated in greenhouse experiments, but the extent to which density dependence influences P. ciliare in natural populations warrants further investigation. Here we present a study on the relationships between local-scale topography (aspect and slope gradient) and vegetation characteristics (shrub cover, P. ciliare cover, and P. ciliare density) and their interactions on individual P. ciliare plant size and reproduction. We measured slope gradient, aspect, shrub cover, P. ciliare cover, P. ciliare density, and the total number of live culms and reproductive culms of 10 P. ciliare plants in 33 4 by 4 m plots located in 11 transects at the Desert Laboratory at Tumamoc Hill, Tucson, AZ, USA. We modeled the relationships at the local scale of (1) P. ciliare cover and density with aspect and slope gradient and (2) P. ciliare size and reproduction with abiotic (slope gradient and aspect) and biotic (P. ciliare cover and density and native shrub and cacti cover) characteristics. Aspect and slope gradient were poor predictors of P. ciliare cover and density in already invaded sites at the scale of our plots. However, aspect had a significant relationship with P. ciliare plant size and reproduction. Pennisetum ciliare plants on south-facing aspects were larger and produced more reproductive culms than plants on other aspects. Further, we found no relationship between P. ciliare density and P. ciliare plant size and reproduction. Shrub cover was positively correlated with P. ciliare reproduction. South-facing aspects are likely most vulnerable to fast spread and infilling by new P. ciliare introductions. © 2023 The Author(s). Published by Cambridge University Press on behalf of the Weed Science Society of America.Open access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Disturbance is more important than seeding or grazing in determining soil microbial communities in a semiarid grassland

A primary goal of ecological restoration is often to return processes and functions to degraded ecosystems. Soil, while often ignored in restoration, supports diverse communities of organisms and is a fundamental actor in providing ecosystem processes and services. We investigated the impact of seeding and livestock grazing on plant communities, soil microorganisms, and soil fertility 3 years after the restoration of a disturbed pipeline corridor in southeastern Arizona. The initial soil disturbance and topsoil treatment, regardless of seeding or grazing, was the most influential factor in determining differences in both plant and microbial communities. Compared with the control, the disturbed and restored sites had greater plant species richness, greater total herbaceous plant cover, greater soil organic matter, higher pH, and differed in soil nutrients. Bacteria and fungi appeared to generally correlate with micro-environment and soil physiochemical properties rather than specific plant species. The undisturbed control had a smaller proportion of bacterial functional groups associated with the breakdown of plant biomass (polysaccharide decomposition) and a smaller proportion of arbuscular mycorrhizal fungi (AMF) compared with disturbed and restored sites. The ability of the unseeded disturbed site to recover robust vegetation may be due in part to the high presence of AMF. These differences show selection for soil microorganisms that thrive in disturbed and restored sites and may contribute to increased plant productivity. Restoration of specific plant species or ecological processes and services would both benefit from better understanding of the impacts of disturbance on soil microorganisms and soil fertility.12 month embargo; published online: 5 March 2020This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]