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At least 631 records · Page 35Linked to original sources

USGS2019

Evidence for widespread microbivory of endophytic bacteria in roots of vascularplants through oxidative degradation in root cell periplasmic spaces

In this chapter we present a hypothesis, and data supporting it, that vascular plants in diverse families possess symbiotic/endophytic bacteria that frequently vector on or within their seeds; seedlings degrade symbiotic bacteria within roots. Evidence of widespread microbivory was found in a survey for intracellular bacteria that we conducted including seedlings in 36 species of vascular plants distributed in 20 plant families. Experiments indicate that when seeds germinate, bacteria colonize seedlings and internalize into root cells where they are oxidatively-degraded in the periplasmic spaces of cells. The process of degradation of microbes in roots has been termed “rhizophagy”, and “rhizophagy cycle” or “rhizophagy symbiosis” in the case of symbiotic bacteria that alternate between a free-living soil phase and intracellular/endophytic phase. We hypothesize that microbivory could account for a significant portion of nutrients acquired by plants from soils—with one estimate suggesting that as much as 30% of the nutrients acquired by seedlings may stem from rhizophagy symbiosis. Developing a better understanding of rhizophagy symbiosis could lead to new ways to cultivate crops without reliance on excessive agrochemical applications. Learning how to manipulate rhizophagy symbiosis could result in new technologies for reducing growth of weedy or invasive plant species by inhibiting rhizophagy symbiosis.

Book chapter↗

USGS2022

Histochemical evidence for nitrogen‐transfer Endosymbiosis in non‐photosynthetic cells of leaves and inflorescence bracts of angiosperms

We used light and confocal microscopy to visualize bacteria in leaf and bract cells of more than 30 species in 18 families of seed plants. Through histochemical analysis, we detected hormones (including ethylene and nitric oxide), superoxide, and nitrogenous chemicals (including nitric oxide and nitrate) around bacteria within plant cells. Bacteria were observed in epidermal cells, various filamentous and glandular trichomes, and other non-photosynthetic cells. Most notably, bacteria showing nitrate formation based on histochemical staining were present in glandular trichomes of some dicots (e.g., Humulus lupulus and Cannabis sativa ). Glandular trichome chemistry is hypothesized to function to scavenge oxygen around bacteria and reduce oxidative damage to intracellular bacterial cells. Experiments to assess the differential absorption of isotopic nitrogen into plants suggest the assimilation of nitrogen into actively growing tissues of plants, where bacteria are most active and carbohydrates are more available. The leaf and bract cell endosymbiosis types outlined in this paper have not been previously reported and may be important in facilitating plant growth, development, oxidative stress resistance, and nutrient absorption into plants. It is unknown whether leaf and bract cell endosymbioses are significant in increasing the nitrogen content of plants. From the experiments that we conducted, it is impossible to know whether plant trichomes evolved specifically as organs for nitrogen fixation or if, instead, trichomes are structures in which bacteria easily colonize and where some casual nitrogen transfer may occur between bacteria and plant cells. It is likely that the endosymbioses seen in leaves and bracts are less efficient than those of root nodules of legumes in similar plants. However, the presence of endosymbioses that yield nitrate in plants could confer a reduced need for soil nitrogen and constitute increased nitrogen-use efficiency, even if the actual amount of nitrogen transferred to plant cells is small. More research is needed to evaluate the importance of nitrogen transfer within leaf and bract cells of plants

Biology↗

USGS2022

Ventilation systems in wetland plant species

Molecular oxygen and carbon dioxide may be limited for aquatic plants, but they have various mechanisms for acquiring these gases from the atmosphere, soil, or metabolic processes. The most common adaptations of aquatic plants involve various aerenchymatic structures, which occur in various organs, and enable the throughflow of gases. These gases can be transferred in emergent plants by molecular diffusion, pressurized gas flow, and Venturi-induced convection. In submerged species, the direct exchange of gases between submerged above-ground tissues and water occurs, as well as the transfer of gases via aerenchyma. Photosynthetic O 2 streams to the rhizosphere, while soil CO 2 streams towards leaves where it may be used for photosynthesis. In floating-leaved plants anchored in the anoxic sediment, two strategies have developed. In water lilies, air enters through the stomata of young leaves, and streams through channels towards rhizomes and roots, and back through older leaves, while in lotus, two-way flow in separate air canals in the petioles occurs. In Nypa Steck palm, aeration takes place via leaf bases with lenticels. Mangroves solve the problem of oxygen shortage with root structures such as pneumatophores, knee roots, and stilt roots. Some grasses have layers of air on hydrophobic leaf surfaces, which can improve the exchange of gases during submergence. Air spaces in wetland species also facilitate the release of greenhouse gases, with CH 4 and N 2 O released from anoxic soil, which has important implications for global warming.

Diversity↗

USGS2022

Plant community trajectories following livestock exclusion for conservation vary and hinge on initial invasion and soil-biocrust conditions in shrub steppe

Adjustments or complete withdrawal of livestock grazing are among the most common conservation actions in semiarid uplands, but outcomes can vary considerably with ecological context. Invasion by exotic annual grasses and the excessive wildfire they promote are increasing threats to semiarid shrub-steppe, and plant-community response to livestock exclusion in these areas may be complicated by the rapid colonization ability of invaders. We evaluated vegetation-community changes over 14-year interval (2007–2021) in a shrub-steppe landscape where a >100-year history of livestock grazing had been terminated in 1996. Field surveys revealed that bare-soil exposure decreased >20% over the 14 years owing to biomass accumulation, but this was primarily due to large increases in exotic annual “cheatgrass” ( Bromus tectorum , +1.8-fold) and the litter it produces (+1.5-fold). Soil biocrusts increased 11.9% and perennial bunchgrasses increased 3% over the 14 years. These community changes varied at the patch scale and entailed inverse relationships of (1) both cheatgrass and biocrusts to plant-community basal cover, (2) cheatgrass to both biocrusts and perennial grasses, and (3) biocrusts to cheatgrass and litter. The spatiotemporal variability in vegetation constituted changes in plant-community states, according to cluster analysis. The modeled probability of a community transitioning to a cheatgrass state was (1) strongly and positively related to the initial (2007) cover of cheatgrass in hotspots where initial cheatgrass cover was >20%, and (2) negatively related to biocrust cover where initial biocrust cover was >4% of ground area. The decision space for this landscape can be framed as a shifting from acceptance towards resisting further degradation by removing livestock and their trampling of soil surfaces and utilization of perennial herbs. However, cheatgrass appears to be the most impactful agent of change and continued invasion appears imminent. Active restoration may help resist further degradation and direct change towards tolerable conditions.

Colorado↗

USGS2022

Piñon and juniper tree removal increases available soil water, driving understory response in a sage-steppe ecosystem

Over the past century, piñon and juniper trees have encroached into sagebrush steppe lands of the interior United States, and managers have for many years removed trees to stimulate the favored understory. While consistent understory response to tree removal in these semiarid lands suggests that trees outcompete other plants for water, no studies have linked increased soil water to understory response after tree removal. We tested the hypothesis that tree removal at six sagebrush steppe sites increased soil water, leading to increased understory plant cover. Using a structural equation model, we found that before tree removal, trees suppressed shrubs (standardized coefficient [SC] = −0.87), perennial deep-rooted (SC = −0.50) and shallow-rooted bunchgrasses (SC = −0.36), but had no influence on cheatgrass. The model explained between 2% (cheatgrass) and 40% (shrubs) of pretreatment cover variation. Measurement of the same plots six years post-treatment showed that most cover variation was due directly to plant growth, with standardized coefficients between 0.51 (perennial shallow-rooted grasses) and 0.72 (cheatgrass). Competition between cheatgrass and perennial deep-rooted grasses was evident, with perennials having twice the influence on cheatgrass than vice-versa (SC = −0.24 vs. −0.11). Spring soil water (wet-degree days) increased significantly after tree removal, measured as cumulative over 6 years (SC = 0.30), and in the early Spring of year six (SC = 0.16). Treatment-induced increase of cumulative Spring wet degree-days explained variation in shrub cover at year 6 (SC = 0.12) and the increase of early Spring wet degree-days at year 6 led to increases in perennial deep-rooted grasses (SC = 0.24) and cheatgrass (SC = 0.23). We detected no influence of Spring wet degree-days on perennial shallow-rooted grasses. The post-treatment model explained between 34% (shallow-rooted perennial grasses) and 69% (deep-rooted perennial grasses) of variation in understory cover. Most variation was explained by re-measurement of the same populations, followed by treatment effects mediated through increased soil water availability, soil factors, and direct effects of the treatment itself. In conclusion, our model is consistent with the a priori hypothesis that additional wet degree-days due to tree removal is a significant mechanism behind observed increases in understory cover.

California, Idaho, Nevada, Oregon, Utah↗

USGS2009

Heavy metal distribution in soils near Palapye, Botswana: An evaluation of the environmental impact of coal mining and combustion on soils in a semi-arid region

Morupule Colliery near Palapye in eastern Botswana is the only coalmine in production in Botswana at present. Its coal is mainly used in the nearby coal-fired Morupule Power Station, which generates approximately 1,000 GWh of electricity per annum. After more than 30 years mining and more than 20 years of combustion, the sedimentation of outlet fly ash from the Morupule Power Station has increased concentrations of Cr, Ni, Zn and As by 13, 2.5, 16 and 5 ppm, respectively, in the fine portion (<53 ??m) of surface soils for approximately 9 km downwind. Elements that have higher concentrations in coal have stronger small-particle association during coal combustion and are less mobile in surface soils, thus showing stronger contaminations in surface soils around the coal-fired plant. Although the degree of contamination of Cr, Ni, Zn and As from coal combustion in the Palapye area at present is low, it is necessary to monitor concentrations of these elements in surface soils routinely in the future. This study also reveals moderate Pb and Zn contaminations in the Palapye area. The former is due to the use of leaded petroleum in motor vehicle traffic and the latter is mainly due to the use of galvanized iron sheets in construction. ?? 2009 Springer Science+Business Media B.V.

Environmental Geochemistry and Health↗

USGS2017

Stable isotopic composition of perchlorate and nitrate accumulated in plants: Hydroponic experiments and field data

Natural perchlorate (ClO 4 − ) in soil and groundwater exhibits a wide range in stable isotopic compositions (δ 37 Cl, δ 18 O, and Δ 17 O), indicating that ClO 4 − may be formed through more than one pathway and/or undergoes post-depositional isotopic alteration. Plants are known to accumulate ClO 4 − , but little is known about their ability to alter its isotopic composition. We examined the potential for plants to alter the isotopic composition of ClO 4 − in hydroponic and field experiments conducted with snap beans ( Phaseolus vulgaris L.). In hydroponic studies, anion ratios indicated that ClO 4 − was transported from solutions into plants similarly to NO 3 − but preferentially to Cl − (4-fold). The ClO 4 − isotopic compositions of initial ClO 4 − reagents, final growth solutions, and aqueous extracts from plant tissues were essentially indistinguishable, indicating no significant isotope effects during ClO 4 − uptake or accumulation. The ClO 4 − isotopic composition of field-grown snap beans was also consistent with that of ClO 4 − in varying proportions from irrigation water and precipitation. NO 3 − uptake had little or no effect on NO 3 − isotopic compositions in hydroponic solutions. However, a large fractionation effect with an apparent ε ( 15 N/ 18 O) ratio of 1.05 was observed between NO 3 − in hydroponic solutions and leaf extracts, consistent with partial NO 3 − reduction during assimilation within plant tissue. We also explored the feasibility of evaluating sources of ClO 4 − in commercial produce, as illustrated by spinach, for which the ClO 4 − isotopic composition was similar to that of indigenous natural ClO 4 − . Our results indicate that some types of plants can accumulate and (presumably) release ClO 4 − to soil and groundwater without altering its isotopic characteristics. Concentrations and isotopic compositions of ClO 4 − and NO 3 − in plants may be useful for determining sources of fertilizers and sources of ClO 4 − in their growth environments and consequently in food supplies.

Science of the Total Environment↗

USGS2025

Patterns of water-extractable soil organic matter in the US Great Plains: Insights from the Haas Soil Archive

Novel approaches that are fast and sensitive are needed to evaluate soil change and integrate soil ecosystem properties. Carbon (C) and nitrogen (N) extracted from soil with water are associated with plant nutrients and microbial activity but information about change over time in the US Great Plains is sparse. We used cool (20°C) and hot (80°C) water extracts from historic (1947) and contemporary (2018) soil samples collected at Moccasin, MT; Akron, CO; and Big Spring, TX; to examine changes to labile C and N and optical properties after 71 years of dryland cropping. Concentrations of C and N extracted with cool water decreased between 1947 and 2018 in surface (0–15.2 cm) samples from Moccasin, by 52% and 35%, and Big Spring, by 37% and 32%, but remained unchanged at Akron. Conversely, net (hot−cool) extractable C did not change at Moccasin or Big Spring but increased at Akron by 26%. Net extractable N decreased at Moccasin by 22% but did not change elsewhere. Sequential principal component analysis and stepwise discriminant analysis identified three important optical properties. Values of SUVA 254 (where SUVA 254 is the specific ultraviolet absorbance at 254 nm) in extracts did not change at Moccasin between 1947 and 2018 but increased at Akron, indicating increased aromaticity. Conversely, SUVA 254 decreased at Big Spring. Values for Sag 350–400 (where Sag 350–400 is the slope from a nonlinear fit of an exponential function to the absorption spectrum over the wavelength range from 350 to 400 nm), inversely related to extract molecular weight and aromaticity, decreased at Moccasin but not elsewhere. The proportion of recalcitrant to labile compounds, C:T (where C:T is the ratio of fluorescence intensity from Peak C [ex340/em440] to Peak T [ex275/em340]), increased in extracts from all sites but especially at Akron. Together, these methods provided insights into soil change while conserving samples.

Colorado, Kansas, Montana, Nebraska, New Mexico, N↗

USGS2016

Soil microbial community profiles and functional diversity in limestone cedar glades

Rock outcrop ecosystems, such as limestone cedar glades (LCGs), are known for their rare and endemic plant species adapted to high levels of abiotic stress. Soils in LCGs are thin (< 25 cm), soil-moisture conditions fluctuate seasonally between xeric and saturated, and summer soil temperatures commonly exceed 48 °C. The effects of these stressors on soil microbial communities (SMC) remain largely unstudied, despite the importance of SMC-plant interactions in regulating the structure and function of terrestrial ecosystems. SMC profiles and functional diversity were characterized in LCGs using community level physiological profiling (CLPP) and plate-dilution frequency assays (PDFA). Most-probable number (MPN) estimates and microbial substrate-utilization diversity (H) were positively related to soil thickness, soil organic matter (OM), soil water content, and vegetation density, and were diminished in alkaline soil relative to circumneutral soil. Soil nitrate showed no relationship to SMCs, suggesting lack of N-limitation. Canonical correlation analysis indicated strong correlations between microbial CLPP patterns and several physical and chemical properties of soil, primarily temperature at the ground surface and at 4-cm depth, and secondarily soil-water content, enabling differentiation by season. Thus, it was demonstrated that several well-described abiotic determinants of plant community structure in this ecosystem are also reflected in SMC profiles.

Tennessee↗

USGS2009

DayCent-Chem simulations of ecological and biogeochemical processes of eight mountain ecosystems in the United States

Atmospheric deposition of nitrogen (N) and sulfur (S) cause complex responses in ecosystems, from fertilization to forest ecosystem decline, freshwater eutrophication to acidification, loss of soil base cations, and alterations of disturbance regimes. DayCent-Chem, an ecosystem simulation model that combines ecosystem nutrient cycling and plant dynamics with aqueous geochemical equilibrium calculations, was developed to address ecosystem responses to combined atmospheric N and S deposition. It is unique among geochemically-based models in its dynamic biological cycling of N and its daily timestep for investigating ecosystem and surface water chemical response to episodic events. The model was applied to eight mountainous watersheds in the United States. The sites represent a gradient of N deposition across locales, from relatively pristine to N-saturated, and a variety of ecosystem types and climates. Overall, the model performed best in predicting stream chemistry for snowmelt-dominated sites. It was more difficult to predict daily stream chemistry for watersheds with deep soils, high amounts of atmospheric deposition, and a large degree of spatial heterogeneity. DayCent-Chem did well in representing plant and soil carbon and nitrogen pools and fluxes. Modeled stream nitrate (NO 3 - ) and ammonium (NH 4 + ) concentrations compared well with measurements at all sites, with few exceptions. Simulated daily stream sulfate (SO 4 2- ) concentrations compared well to measured values for sites where SO 4 2- deposition has been low and where SO 4 2- adsorption/desorption reactions did not seem to be important. The concentrations of base cations and silica in streams are highly dependent on the geochemistry and weathering rates of minerals in each catchment, yet these were rarely, if ever, known. Thus, DayCent-Chem could not accurately predict weathering products for some catchments. Additionally, few data were available for exchangeable soil cations or the magnitude of base cation deposition as a result of dry and fog inputs. The uncertainties related to weathering reactions, deposition, soil cation exchange capacity, and groundwater contributions influenced how well the simulated acid neutralizing capacity (ANC) and pH estimates compared to observed values. Daily discharge was well represented by the model for most sites. The chapters of this report describe the parameterization for each site and summarize model results for ecosystem variables, stream discharge, and stream chemistry. This intersite comparison exercise provided insight about important and possibly not well understood processes.

Scientific Investigations Report↗

USGS2007

Genotype, soil type, and locale effects on reciprocal transplant vigor, endophyte growth, and microbial functional diversity of a narrow sagebrush hybrid zone in Salt Creek Canyon, Utah

When addressing the nature of ecological adaptation and environmental factors limiting population ranges and contributing to speciation, it is important to consider not only the plant's genotype and its response to the environment, but also any close interactions that it has with other organisms, specifically, symbiotic microorganisms. To investigate this, soils and seedlings were reciprocally transplanted into common gardens of the big sagebrush hybrid zone in Salt Creek Canyon, Utah, to determine location and edaphic effects on the fitness of parental and hybrid plants. Endophytic symbionts and functional microbial diversity of indigenous and transplanted soils and sagebrush plants were also examined. Strong selection occurred against the parental genotypes in the middle hybrid zone garden in middle hybrid zone soil; F1 hybrids had the highest fitness under these conditions. Neither of the parental genotypes had superior fitness in their indigenous soils and habitats; rather F1 hybrids with the nonindigenous maternal parent were superiorly fit. Significant garden-by-soil type interactions indicate adaptation of both plant and soil microorganisms to their indigenous soils and habitats, most notably in the middle hybrid zone garden in middle hybrid zone soil. Contrasting performances of F1 hybrids suggest asymmetrical gene flow with mountain, rather than basin, big sagebrush acting as the maternal parent. We showed that the microbial community impacted the performance of parental and hybrid plants in different soils, likely limiting the ranges of the different genotypes.

Utah↗

USGS2017

Disease protection and allelopathic interactions of seed-transmitted endophytic pseudomonads of invasive reed grass ( Phragmites australis )

Background and aims Non-native Phragmites australis (haplotype M) is an invasive grass that decreases biodiversity and produces dense stands. We hypothesized that seeds of Phragmites carry microbes that improve seedling growth, defend against pathogens and maximize capacity of seedlings to compete with other plants. Methods We isolated bacteria from seeds of Phragmites , then evaluated representatives for their capacities to become intracellular in root cells, and their effects on: 1.) germination rates and seedling growth, 2.) susceptibility to damping-off disease, and 3.) mortality and growth of competitor plant seedlings (dandelion ( Taraxacum officionale F. H. Wigg) and curly dock ( Rumex crispus L.)). Results Ten strains (of 23 total) were identified and characterized; seven were identified as Pseudomonas spp. Strains Sandy LB4 ( Pseudomonas fluorescens ) and West 9 ( Pseudomonas sp.) entered root meristems and became intracellular. These bacteria improved seed germination in Phragmites and increased seedling root branching in Poa annua . They increased plant growth and protected plants from damping off disease. Sandy LB4 increased mortality and reduced growth rates in seedlings of dandelion and curly dock. Conclusions Phragmites plants associate with endophytes to increase growth and disease resistance, and release bacteria into the soil to create an environment that is favorable to their seedlings and less favorable to competitor plants.

Plant and Soil↗

USGS2016

Disentangling the complexities of how legumes and their symbionts regulate plant nitrogen access and storage

Nitrogen (N) availability strongly inﬂuences the structure and function of ecosystems (e.g. Vitousek & Howarth, 1991), but only a relatively small number of microbial groups have the ability to convert the N 2 in our atmosphere into biologically available forms.This process, N 2 ﬁxation, is the dominant source of new N to the biosphere outside of anthropogenic inputs (Vitousek et al., 2013).Some N 2 -ﬁxing microorganisms live independently on plant leaves, on decomposing organic material, and in soil (Reed et al.,2011), while others have co-evolved with a few higher plant taxa to form symbioses that ﬁx N 2 in root nodules (e.g. Sprent & Raven,1985). The relationship between these legumes and their root nodule symbionts (rhizobia) is one of the most well studied plant –microbe symbioses. Yet, many important questions about the controls, interactions, and implications of legume N 2 ﬁxation remain unanswered. In this issue of New Phytologist (pp. 690–699),Wolf, Funk, & Menge elegantly address a fundamental set of questions about N 2 ﬁxation in their examination of how herbaceous legumes, their symbionts, and external N availability interact to govern legume access and storage of N.

New Phytologist↗

USGS2017

Historical changes in organic matter input to the muddy sediments along the Zhejiang-Fujian Coast, China over the past 160 years

The burial of sedimentary organic matter (SOM) in the large river-influenced estuarine-coastal regions is affected by hydrodynamic sorting, diagenesis and human activities. Typically, the inner shelf region of the East China Sea is a major carbon sink of the Yangtze River-derived fine-grained sediments. Most of the previous work concentrated on the studies of surface sediments or used a single-proxy in this region. In this study, two cores from the Zhejiang-Fujian Coast were analyzed using bulk (TOC, TN and δ 13 C TOC ) and molecular biomarker ( n -alkane, brassicasterol, dinosterol and glycerol dialkyl glycerol tetraether lipids) techniques to clarify the sources, spatiotemporal distribution and fate of SOM in the Yangtze River Estuary and adjacent shelf. Results from this study indicated that the effects of diagenesis and diffusion on different sedimentary biomarkers resulted in overestimation of the relative contribution of terrestrial organic matter (%OM terr ), compared with those based on δ 13 C TOC . The amounts of terrestrial plant organic matter (OM plant ) and%OM terr in sediments decreased offshore. In contrast, the amounts of marine organic matter (OM marine ) increased offshore, but closer to the Yangtze River mouth, the amounts of soil organic matter (OM soil ) increased. Moreover, the amounts of TOC, OM plant and OM marine biomarkers increased, but OM soil and%OM terr decreased over time in recent decades. Our study suggests that spatial organic matter distribution patterns in marine shelf sediments were controlled primarily by hydrodynamic sorting and nutrient concentrations, and temporally diverse patterns were controlled predominantly by anthropogenic influence (e.g., dam construction and soil conservation, reclamation and agricultural plantations, anthropogenic nutrient input, dust storms, eutrophication, etc) and climate events (e.g., interdecadal climatic jump and heavy rain events) in the geological period.

Zhejiang-Fujian Coast↗

USGS2011

Soil warming alters seed-bank responses across the geographic range of freshwater Taxodium distichum (Cupressaceae) swamps

Premise of the Study: Climate warming is predicted to have far‐reaching effects on the distribution of species, but those effects may depend on the flexibility of regenerating species in responding to climate gradients. We conducted a study to determine whether the variation in the response of seed banks to temperature varied across the latitudinal range of Taxodium distichum swamps in North America. • Methods: The soil was collected in a long‐term research network and heated experimentally to three current‐day spring normal soil temperatures (average maximum daily spring normal soil temperatures during May in Illinois, Arkansas, and Louisiana, USA, respectively: 22°, 25°, and 29°C). A “normal” is the mean temperature calculated over a 30‐yr interval (1971–2000). Seed‐bank density and biomass responses were examined in relation to latitude and difference in the soil temperature of the experiment and the spring normal. • Key Results: Using first‐ and second‐order regression analysis, we determined that the variation in total germination density was lowest mid‐range and in experimental soil temperatures similar to the spring normal. For some dominant species, the variance in germination density was higher in the northern ( Cephalanthus occidentalis ) or the southern part of the network ( Saururus cernuus and Polygonum pensylvanicum ). Overall, the variance of total biomass (root, shoot, whole plant) was higher if the experimental soil temperature was warmer than the spring normal. • Conclusions: Our results suggest that the regeneration of some populations of swamp species may have more flexibility to respond to climate warming than others.

Alabama, Arkansas, Florida, Georgia, Illinois, Ken↗

USGS2008

Plant response to nutrient availability across variable bedrock geologies

We investigated the role of rock-derived mineral nutrient availability on the nutrient dynamics of overlying forest communities (Populus tremuloides and Picea engelmanni-Abies lasiocarpa v. arizonica) across three parent materials (andesite, limestone, and sandstone) in the southern Rocky Mountains of Colorado. Broad geochemical differences were observed between bedrock materials; however, bulk soil chemistries were remarkably similar between the three different sites. In contrast, soil nutrient pools were considerably different, particularly for P, Ca, and Mg concentrations. Despite variations in nutrient stocks and nutrient availability in soils, we observed relatively inflexible foliar concentrations and foliar stoichiometries for both deciduous and coniferous species. Foliar nutrient resorption (P and K) in the deciduous species followed patterns of nutrient content across substrate types, with higher resorption corresponding to lower bedrock concentrations. Work presented here indicates a complex plant response to available soil nutrients, wherein plant nutrient use compensates for variations in supply gradients and results in the maintenance of a narrow range in foliar stoichiometry. ?? 2008 Springer Science+Business Media, LLC.

Ecosystems↗

USGS2009

Sediment losses and gains across a gradient of livestock grazing and plant invasion in a cool, semi-arid grassland, Colorado Plateau, USA

Large sediment fluxes can have significant impacts on ecosystems. We measured incoming and outgoing sediment across a gradient of soil disturbance (livestock grazing, plowing) and annual plant invasion for 9 years. Our sites included two currently ungrazed sites: one never grazed by livestock and dominated by perennial grasses/well-developed biocrusts and one not grazed since 1974 and dominated by annual weeds with little biocrusts. We used two currently grazed sites: one dominated by annual weeds and the other dominated by perennial plants, both with little biocrusts. Precipitation was highly variable, with years of average, above-average, and extremely low precipitation. During years with average and above-average precipitation, the disturbed sites consistently produced 2.8 times more sediment than the currently undisturbed sites. The never grazed site always produced the least sediment of all the sites. During the drought years, we observed a 5600-fold increase in sediment production from the most disturbed site (dominated by annual grasses, plowed about 50 years previously and currently grazed by livestock) relative to the never grazed site dominated by perennial grasses and well-developed biocrusts, indicating a non-linear, synergistic response to increasing disturbance types and levels. Comparing sediment losses among the sites, biocrusts were most important in predicting site stability, followed by perennial plant cover. Incoming sediment was similar among the sites, and while inputs were up to 9-fold higher at the most heavily disturbed site during drought years compared to average years, the change during the drought conditions was small relative to the large change seen in the sediment outputs. ?? 2009 Elsevier B.V. All rights reserved.

Aeolian Research↗

USGS2022

Geologic, geomorphic, and edaphic underpinnings of dryland ecosystems: Colorado Plateau landscapes in a changing world

Drylands represent more than 41% of the global land surface and are at degradation risk due to land use and climate change. Developing strategies to mitigate degradation and restore drylands in the face of these threats requires an understanding of how drylands are shaped by not only soils and climate, but also geology and geomorphology. However, few studies have completed such a comprehensive analysis that relates spatial variation in plant communities to all aspects of the geologic–geomorphic–edaphic–plant–climate system. The focus of this study is the Colorado Plateau, a high-elevation dryland in the southwestern United States, which is particularly sensitive to future change due to climate vulnerability and increasing land-use pressure. Here, we examined 135 long-term vegetation-monitoring sites in three national parks and characterized connections between geology, geomorphology, soils, climate, and dryland plant communities. To first understand the geologic and geomorphic influences on soil formation and characteristics, we explore associations between soil pedons, bedrock geology, and geomorphology. Then, we characterize principal axes of variation in plant communities and ascertain controls and linkages between components of the edaphic–geomorphic system and plant community ordinations. Geologic and geomorphic substrate exerted controls on important properties of the soil profile, particularly depth, water-holding capacity, rockiness, salinity, and fine sands. Ordination identified five distinct plant communities and three primary axes of variation, representing gradients of woody- to herbaceous-dominated communities (Axis 1), saline scrublands to C 3 grasslands (Axis 2), and annual to perennial communities (Axis 3). Geology, geomorphology, and soil explained a large proportion of variation in Axis 1 (74%), while climate variables largely explained Axis 2 (68%), and Axis 3 was not well explained by the random forest models. The variables identified as most influential to each axis were, respectively: (1) soil depth; (2) aridity, lithology, and soil salinity; and (3) temperature and precipitation. We posit that Axis 3 represents a land degradation gradient due to historic grazing, likely exacerbated by dry conditions. Results provide a novel framework that links the geologic and geomorphic evolution of landscapes, with the distribution of soils and plant communities that can guide ecosystem management, exemplifying an approach applicable to drylands globally.

Arizona, Colorado, New Mexico, Utah↗