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USGS1994

Prospects for increasing the salt tolerance of forest trees: A review

Three major themes related to the improvement of salt tolerance in forest tree species are examined. First, evidence demonstrating that substantial intraspecific variation in salt tolerance exists in many species is presented. This evidence is important because it suggests that efforts to improve salt tolerance through conventional plant breeding techniques are justified. Second, the physiological and genetic mechanisms controlling salt tolerance are discussed briefly. Although salt tolerance involves the integration of numerous physiological processes, there is considerable evidence that differences in the ability to exclude Na + and Cl - from leaves are the most important factors underlying intraspecific differences in tolerance . It is also becoming apparent that, although salt tolerance is a multigenic trait, major genes play an important role. Third, progress to date in improving salt tolerance of forest tree species is assessed. Compared with agricultural crops, relatively little progress has been made with either conventional or biotechnological methods, but field trials designed to test clones identified as salt tolerant in screening trials are underway now in several countries. We conclude that there is justification for cautious optimism about the prospects for improving salt tolerance in forest tree species. © 1994 Heron Publishing.

Tree Physiology↗

USGS2020

Negative effects of an allelopathic invader on AM fungal plant species drive community‐level responses

The mechanisms causing invasive species impact are rarely empirically tested, limiting our ability to understand and predict subsequent changes in invaded plant communities. Invader disruption of native mutualistic interactions is a mechanism expected to have negative effects on native plant species. Specifically, disruption of native plant‐fungal mutualisms may provide non‐mycorrhizal plant invaders an advantage over mycorrhizal native plants. Invasive Alliaria petiolata (garlic mustard) produces secondary chemicals toxic to soil microorganisms including mycorrhizal fungi, and is known to induce physiological stress and reduce population growth rates of native forest understory plant species. Here, we report on a 11‐yr manipulative field experiment in replicated forest plots testing if the effects of removal of garlic mustard on the plant community support the mutualism disruption hypothesis within the entire understory herbaceous community. We compare community responses for two functional groups: the mycorrhizal vs. the non‐mycorrhizal plant communities. Our results show that garlic mustard weeding alters the community composition, decreases community evenness, and increases the abundance of understory herbs that associate with mycorrhizal fungi. Conversely, garlic mustard has no significant effects on the non‐mycorrhizal plant community. Consistent with the mutualism disruption hypothesis, our results demonstrate that allelochemical producing invaders modify the plant community by disproportionately impacting mycorrhizal plant species. We also demonstrate the importance of incorporating causal mechanisms of biological invasion to elucidate patterns and predict community‐level responses.

Ecology↗

USGS1991

Effects of dietary boron and arsenic on the behavior of mallard ducklings

High concentrations of boron and arsenic have been associated with irrigation drain water and aquatic plants consumed by waterfowl. Both compounds affect the central nervous system and cause generalized physiological distress in mammals and waterfowl. We examined sublethal effects of boron and arsenic on the behavior of developing mallard ducklings (Anas platyrhynchos). Day-old ducklings received an untreated diet (control) or a diet containing 100, 400, or 1,600 ppm boron, added as boric acid, or 30, 100, or 300 ppm arsenic, added as sodium arsenate. Activity schedules and behavior durations were analyzed for effects at the various treatment levels. Both boron and arsenic at the highest levels had significant effects on the activity schedules of developing ducklings, including increased time at rest and under the provided heat lamp. We also observed decreases in the amount of time treated ducklings spent in alert behaviors and in the water in comparison to control ducklings. High levels of boron (1,600 ppm) increased feeding time overall but did not increase the amount of food consumed. Arsenic had no effect on feeding behavior. There were no differences found in the durations of behaviors as a result of treatment. These findings, in combination with reported effects on the growth and physiology of ducklings under identical treatments, suggest that reported concentrations of these compounds in aquatic plants in the Central Valley of California could adversely affect normal duckling development and survival.

Environmental Toxicology and Chemistry↗

USGS2009

Dust deposition effects on growth and physiology of the endangered Astragalus jaegerianus (Fabaceae)

Human expansion into the Mojave Desert is a significant threat to rare desert plants. While immediate habitat loss is often the greatest concern, rare plants situated near areas where soil surfaces experience frequent disturbance may be indirectly impacted when fine particulate dust accumulates on leaf surfaces. Remaining populations of the federally listed Astragalus jaegerianus (Lane Mountain milkvetch) occur on land open to expanding military activities and on adjacent public land with increasing recreational use. This study was initiated to determine whether dust accumulation could decrease the vigor and fitness of A. jaegerianus through reduced growth. Beginning in early May 2004, plants located on Bureau of Land Management (BLM) land were dusted bimonthly at canopy-level dust concentrations ranging from 0 to 32 g/m 2 , and physiology and growth were monitored until late June when plants senesced. The maximum experimental dust level simulates dust concentrations of Mojave Desert perennials neighboring military activities at a nearby army training center. Average shoot growth declined with increasing dust accumulation, but seasonal net photosynthesis increased. Further investigation of plants grown in a greenhouse supported similar trends. This pattern of greater net photosynthesis with increasing dust accumulation may be explained by higher leaf temperatures of dusted individuals. Ambient dust deposition measured in traps near field plants (May 2004–July 2004) ranged from 0.04–0.17 g/m 2 / d, which was well below the lowest level of dust on experimental plants (3.95 g/m 2 /d). With this low level of ambient deposition, we expect that A. jaegerianus plants in this population were not greatly affected by the dust they receive at the level of recreational use during the study.

Madroño↗

USGS2014

Plants in alpine environments

Alpine and subalpine plant species are of special interest in ecology and ecophysiology because they represent life at the climate limit and changes in their relative abundances can be a bellwether for climate-change impacts. Perennial life forms dominate alpine plant communities, and their form and function reflect various avoidance, tolerance, or resistance strategies to interactions of cold temperature, radiation, wind, and desiccation stresses that prevail in the short growing seasons common (but not ubiquitous) in alpine areas. Plant microclimate is typically uncoupled from the harsh climate of the alpine, often leading to substantially warmer plant temperatures than air temperatures recorded by weather stations. Low atmospheric pressure is the most pervasive, fundamental, and unifying factor for alpine environments, but the resulting decrease in partial pressure of CO 2 does not significantly limit carbon gain by alpine plants. Factors such as tree islands and topographic features create strong heterogeneous mosaics of microclimate and snow cover that are reflected in plant community composition. Factors affecting tree establishment and growth and formation of treeline are key to understanding alpine ecology. Carbohydrate and other carbon storage, rapid development in a short growing season, and physiological function at low temperature are prevailing attributes of alpine plants. A major contemporary research theme asks whether chilling at alpine-treeline affects the ability of trees to assimilate the growth resources and particularly carbon needed for growth or whether the growth itself is limited by the alpine environment. Alpine areas tend to be among the best conserved, globally, yet they are increasingly showing response to a range of anthropogenic impacts, such as atmospheric deposition.

Book chapter↗

USGS2019

Freezing resistance, safety margins, and survival vary among big sagebrush populations across the western United States

Premise Physiological responses to temperature extremes are considered strong drivers of species’ demographic responses to climate variability. Plants are typically classified as either avoiders or tolerators in their freezing‐resistance mechanism, but a gradient of physiological‐threshold freezing responses may exist among individuals of a species. Moreover, adaptive significance of physiological freezing responses is poorly characterized, particularly under warming conditions that relax selection on cold hardiness. Methods Freezing responses were measured in winter and again for new foliage in spring for 14 populations of Artemisia tridentata collected throughout its range and planted in a warm common garden. The relationships of the freezing responses to survival were evaluated in the warm garden and in two colder gardens. Results Winter and spring freezing resistance were not correlated and appeared to be under differing selection regimes, as evident in correlations with different population climate of origin variables. All populations resisted considerably lower temperatures in winter than in spring, with populations from more continental climates showing narrower freezing safety margins (difference in temperatures at which ice‐nucleation occurs and 50% reduction in chlorophyll fluorescence occurs) in spring. Populations with greater winter freezing resistance had lower survivorship in the warmest garden, while populations with greater spring freezing resistance had lower survivorship in a colder garden. Conclusions These survivorship patterns relative to physiological thresholds suggest excess freezing resistance may incur a survival cost that likely relates to a trade‐off between carbon gain and freezing resistance during critical periods of moisture availability. This cost has implications for seed moved from cooler to warmer environments and for plants growing in warming environments.

American Journal of Botany↗

USGS2023

Temperature and winter duration requirements for reproductive success in johnny darter Etheostoma nigrum in the South Platte River basin, Colorado

Changes in water temperature and its seasonal timing influences the physiological processes of many aquatic ectotherms. Wastewater treatment plants (WWTP) contribute to warmer and more consistent water temperatures in streams draining the North American Great Plains, particularly during winter months. Reduced variation in seasonal water temperature may adversely affect fishes that rely on temperature fluctuation or specific overwintering temperatures for reproductive cues. We used johnny darter Etheostoma nigrum (Family Percidae), a thermally sensitive species native to the South Platte River Basin, as a focal species to assess the effects of winter water temperature regulations in Colorado. Our objective was to evaluate the effects of winter stream temperature and winter duration on reproductive success of johnny darter in the laboratory to inform development of water quality criteria for the South Platte River Basin. Winter duration (60, 90 or 120 days) and temperature (4 or 12°C) were crossed in a factorial design of six treatments that simulated warmed effluent-impacted streams as well as streams with a more natural thermal regime. We defined reproductive success in johnny darter by examining four reproductive endpoints: (1) spawning timing, (2) egg and larvae production, (3) egg success, and (4) egg development. Across the four endpoints, seven main response variables were measured: spawning initiation date, eggs per gram of female per week, live larvae per gram of female per week, fertilisation success, hatching success, egg-to-larva survival and days to hatch. Winter temperature and duration influenced spawning timing and egg development. Earlier spawning initiation dates were observed in fish exposed to 12°C winters and was associated with a higher number of days to hatch. Eggs per gram of female per week, live larvae per gram of female per week, fertilisation success, hatching success, and egg-to-larva survival were similar among winter treatments. Although the State of Colorado chronic winter water temperature standard of 12°C appears to be adequate for egg and larvae production in johnny darter, our results showed that fish exposed to the standard began spawning significantly earlier than fish exposed to 4°C winters. Evaluating reproductive output in the context of seasonal timing is valid because spawning timing has the potential to affect overall production and egg development, and consequently recruitment and population sustainability. Therefore, spawning timing should be considered when making management decisions and revising water temperature standards. The warming of streams and rivers from WWTP effluent is a global issue, especially in areas that are undergoing rapid urbanisation. Fishes are particularly sensitive to water temperature and many fishes worldwide are likely to be experiencing changes in important physiological processes, affecting both reproduction and survival. Our study indicates that reproductive timing could be influenced by stream warming and stresses the need for further studies on the influence of anthropogenic effects on stream warming.

Colorado↗

USGS2014

Desert shrub responses to experimental modification of precipitation seasonality and soil depth: relationship to the two-layer model and ecohydrological niche

1. Ecohydrological niches are important for understanding plant community responses to climate shifts, particularly in dry lands. According to the two-layer hypothesis, selective use of deep-soil water increases growth or persistence of woody species during warm and dry summer periods and thereby contributes to their coexistence with shallow-rooted herbs in dry ecosystems. The resource-pool hypothesis further suggests that shallow-soil water benefits growth of all plants while deep-soil water primarily enhances physiological maintenance and survival of woody species. Few studies have directly tested these by manipulating deep-soil water availability and observing the long-term outcomes. 2. We predicted that factors promoting infiltration and storage of water in deep soils, specifically greater winter precipitation and soil depth, would enhance Artemisia tridentata (big sagebrush) in cold, winter-wet/summer-dry desert. Sagebrush responses to 20 years of winter irrigation were compared to summer- or no irrigation, on plots having relatively deep or shallow soils (2 m vs. 1 m depths). 3. Winter irrigation increased sagebrush cover, and crown and canopy volumes, but not density (individuals/plot) compared to summer or no irrigation, on deep-soil plots. On shallow-soil plots, winter irrigation surprisingly decreased shrub cover and size, and summer irrigation had no effect. Furthermore, multiple regression suggested that the variations in growth were related (i) firstly to water in shallow soils (0-0.2 m) and secondly to deeper soils (> 1 m deep) and (ii) more by springtime than by midsummer soil water. Water-use efficiency increased considerably on shallow soils without irrigation and was lowest with winter irrigation. 4. Synthesis . Sagebrush was more responsive to the seasonal timing of precipitation than to total annual precipitation. Factors that enhanced deep-water storage (deeper soils plus more winter precipitation) led to increases in Artemisia tridentata that were consistent with the two-layer hypothesis, and the contribution of shallow water to growth on these plots was consistent with the resource-pool hypothesis. However, shallow-soil water also had negative effects on sagebrush, suggesting an ecohydrological trade-off not considered in these or related theories. The interaction between precipitation timing and soil depth indicates that increased winter precipitation could lead to a mosaic of increases and decreases in A. tridentata across landscapes having variable soil depth.

Idaho↗

USGS2010

Do competitors modulate rare plant response to precipitation change?

Ecologists increasingly suspect that climate change will directly impact species physiology, demography, and phenology, but also indirectly affect these measures via changes to the surrounding community. Unfortunately, few studies examine both the direct and indirect pathways of impact. Doing so is important because altered competitive pressures can reduce or magnify the direct responses of a focal species to climate change. Here, we examine the effects of changing rainfall on three rare annual plant species in the presence and absence of competition on the California Channel Islands. We used rain-out shelters and hand watering to exclude and augment early, late, and season-long rainfall, spanning the wide range of precipitation change forecast for the region. In the absence of competition, droughts reduced the population growth rates of two of three focal annuals, while increased rainfall was only sometimes beneficial, As compared to the focal species, the dominant competitors were more sensitive to the precipitation treatments, benefiting from increased season-long precipitation and harmed by droughts. Importantly, the response of two of three competitors to the precipitation treatments tended to be positively correlated with those of the focal annuals. Although this leads to the expectation that increased competition will counter the direct benefits of favorable conditions, such indirect effects of precipitation change proved weak to nonexistent in our experiment. Competitors had little influence on the precipitation response of two focal species, due to their low sensitivity to competition and highly variable precipitation responses. Competition did affect how our third focal species responded to precipitation change, but this effect only approached significance, and whether it truly resulted from competitor response to precipitation change was unclear. Our work suggests that even when competitors respond to climate change, these responses may have little effect on the focal species. Ultimately, the strength of the indirect effect depends on how strongly climate change alters competition, and how sensitive focal species are to changes in competition. ?? 2010 by the Ecological Society of America.

Ecology↗

USGS2001

Species and population variation to salinity stress in Panicum hemitomon, Spartina patens, and Spartina alterniflora: Morphological and physiological constraints

Panicum hemitomon, Spartina patens, and Spartina alterniflora are wide-spread dominant grasses of fresh, brackish, and salt marsh plant communities, respectively. Our previous research identified significant intraspecific variation in salt tolerance and morphology among populations within each species. In this study our objectives were to determine shorter-term physiological/biochemical responses to salinity stress and identify potential indicators of salt tolerance, with the ultimate goal of discerning similarities and differences in the mechanisms of salinity stress resistance. We subjected a subset of six populations within each species, ranging from high to low salt tolerance, to sublethal salinity levels (4, 20, and 30 ppt, respectively, for species) and monitored physiological and growth responses after 1 week (early harvest) and 5 weeks (late harvest). In all three species sublethal salinity levels generally resulted in significantly reduced net CO2 assimilation, leaf expansion, midday leaf xylem pressure, water use efficiency, and live and total biomass; and significantly increased leaf Na+/K+ ratio, leaf proline, leaf glycine betaine, leaf sucrose, root-to-shoot ratio, and dead:total aboveground biomass ratio. All three species displayed significant population (intraspecific) variation in net CO2 assimilation, leaf expansion, water use efficiency, midday leaf xylem pressure, leaf proline, leaf glycine betaine (except Panicum, where it could not be accurately determined), leaf Na+/K+ ratio, leaf sucrose, total plant biomass, dead:total aboveground biomass ratio, and root-to-shoot ratio. General indicators of salt tolerance (regardless of species) included high net CO2 assimilation rates and water use efficiencies, and low ratios of root-to-shoot and dead:total aboveground biomass. Factor analysis and a-priori linear contrasts revealed some unique differences between species in terms of the relative importance of morphology and physiology in explaining intraspecific variation in salt tolerance. Plant morphology (size attributes) were strongly associated with salt tolerance in P. hemitomon, weakly associated with salt tolerance in S. patens, and not associated with salt tolerance in S. alterniflora. Highly salt-tolerant populations of Spartina alterniflora displayed the greatest ion selectivity (lower leaf Na+/K+ ratios), which was not displayed by the other two species. These results suggest that plant size attributes can be very important in explaining population differences in salt tolerance in glycophytes, but may be independent of salt tolerance in halophytes, which have specialized physiological (and/or anatomical) adaptations that can confer salinity stress resistance through mechanisms such as selective ion exclusion and secretion. ?? 2001 Elsevier Science B.V. All rights reserved.

Conference Paper↗

USGS2023

Respiratory acclimation of tropical forest roots in response to in situ experimental warming and hurricane disturbance

Climate projections predict higher temperatures and more frequent hurricanes in the tropics. Tropical plants subjected to these stresses may respond by acclimating their physiology. We investigated tropical forest root respiration in response to in situ experimental warming and hurricane disturbance in eastern Puerto Rico. We measured mass-normalized root specific respiration, root biomass, and root traits at the Tropical Responses to Altered Climate Experiment (TRACE), where understory vegetation is warmed + 4 °C above ambient. Our measurements span 5 years, including before and after two major hurricanes, to quantify root contributions to ecosystem carbon fluxes. Experimental warming did not affect root specific respiration at a standard temperature of 25° (RSR 25 , mean = 3.89 nmol CO 2 g −1 s −1 ) or the temperature sensitivity of root respiration (Q 10 , mean = 1.75), but did result in decreased fine-root biomass, thereby decreasing area-based estimations of ecosystem-level root respiration in warmed plots by ~ 35%. RSR 25 of newer roots, which increased with increasing root nitrogen, showed greater rates 6 months after the hurricanes, but subsequently decreased after 12 months. Root specific respiration did not acclimate to higher temperatures, based on lack of adjustments in either Q 10 or RSR 25 in the warmed plots; however, decreased root biomass indicates the root contribution to soil carbon dioxide efflux was overall lower with warming. Lower root biomass may also limit nutrient and water uptake, having potential negative effects on carbon assimilation. Our results show that warming and hurricane disturbance have strong potential to affect tropical forest roots, as well as ecosystem carbon fluxes.

Ecosystems↗

USGS2000

Woody riparian vegetation response to different alluvial water table regimes

Woody riparian vegetation in western North American riparian ecosystems is commonly dependent on alluvial groundwater. Various natural and anthropogenic mechanisms can cause groundwater declines that stress riparian vegetation, but little quantitative information exists on the nature of plant response to different magnitudes, rates, and durations of groundwater decline. We observed groundwater dynamics and the response of Populus fremontii, Salix gooddingii , and Tamarix ramosissima saplings at 3 sites between 1995 and 1997 along the Bill Williams River, Arizona. At a site where the lowest observed groundwater level in 1996 (-1.97 m) was 1.11 m lower than that in 1995 (-0.86 m), 92-100% of Populus and Salix saplings died, whereas 0-13% of Tamarix stems died. A site with greater absolute water table depths in 1996 (-2.55 m), but less change from the 1995 condition (0.55 m), showed less Populus and Salix mortality and increased basal area. Excavations of sapling roots suggest that root distribution is related to groundwater history. Therefore, a decline in water table relative to the condition under which roots developed may strand plant roots where they cannot obtain sufficient moisture. Plant response is likely mediated by other factors such as soil texture and stratigraphy, availability of precipitation-derived soil moisture, physiological and morphological adaptations to water stress, and tree age. An understanding of the relationships between water table declines and plant response may enable land and water managers to avoid activities that are likely to stress desirable riparian vegetation.

Western North American Naturalist↗

USGS2004

Nutrient controls on biocomplexity of mangrove ecosystems

Mangrove forests are important coastal ecosystems that provide a variety of ecological and societal services. These intertidal, tree-dominated communities along tropical coastlines are often described as “simple systems,” compared to other tropical forests with larger numbers of plant species and multiple understory strata; however, mangrove ecosystems have complex trophic structures, and organisms exhibit unique physiological, morphological, and behavioral adaptations to environmental conditions characteristic of the land-sea interface. Biogeochemical functioning of mangrove forests is also controlled by interactions among the microbial, plant, and animal communities and feedback linkages mediated by hydrology and other forcing functions. Scientists with the U.S. Geological Survey (USGS) at the National Wetlands Research Center are working to understand more fully the impact of nutrient variability on these delicate and important ecosystems.

Fact Sheet↗

USGS1991

Effect of phosphorus deficiency on spectral reflectance and morphology of soybean plants

Soybean plants were grown in hydroponic solutions having three concentration levels of phosphorus. Spectral reflectance changes included higher reflectance in the green and yellow portions of the electromagnetic spectrum in phosphorus-deficient plants and a difference in position of the long wavelength edge (the red edge) of the chlorophyll absorption band centered near 0.68 ??m. Plants having the least phosphorus in the growing medium did not show the normal shift of the red edge to longer wavelength which occurs as leaves mature. Shoot and root biomass were significantly lower in the phosphorus-deficient plants. These results are consistent with those obtained when soybean plants are dosed with elevated concentrations of metallic elements. We hypothesize that nutrient imbalances or anomalous metal concentrations in the soil set up physiological conditions at the soil/root interface that are responsible for the reflectance differences observed in laboratory and field studies of plants growing in substrates enriched in metallic elements.

Remote Sensing of Environment↗

USGS2014

Lectins stain cells differentially in the coral, Montipora capitata

A limitation in our understanding of coral disease pathology and cellular pathogenesis is a lack of reagents to characterize coral cells. We evaluated the utility of plant lectins to stain tissues of a dominant coral, Montipora capitata , from Hawaii. Of 22 lectins evaluated, nine of these stained structures in the upper or basal body wall of corals. Specific structures revealed by lectins that were not considered distinct or evident on routine hematoxylin and eosin sections of coral tissues included apical and basal granules in gastrodermis and epidermis, cnidoglandular tract and actinopharynx cell surface membranes, capsules of mature holotrichous isorhizas, and perivitelline and periseminal cells. Plant lectins could prove useful to further our understanding of coral physiology, anatomy, cell biology, and disease pathogenesis.

Hawai'i↗

USGS2013

Nonstructural leaf carbohydrates dynamics of Pinus edulis during drought-induced tree mortality reveal role for carbon metabolism in mortality mechanism

* Vegetation change is expected with global climate change, potentially altering ecosystem function and climate feedbacks. However, causes of plant mortality, which are central to vegetation change, are understudied, and physiological mechanisms remain unclear, particularly the roles of carbon metabolism and xylem function. * We report analysis of foliar nonstructural carbohydrates (NSCs) and associated physiology from a previous experiment where earlier drought-induced mortality of Pinus edulis at elevated temperatures was associated with greater cumulative respiration. Here, we predicted faster NSC decline for warmed trees than for ambient-temperature trees. * Foliar NSC in droughted trees declined by 30% through mortality and was lower than in watered controls. NSC decline resulted primarily from decreased sugar concentrations. Starch initially declined, and then increased above pre-drought concentrations before mortality. Although temperature did not affect NSC and sugar, starch concentrations ceased declining and increased earlier with higher temperatures. * Reduced foliar NSC during lethal drought indicates a carbon metabolism role in mortality mechanism. Although carbohydrates were not completely exhausted at mortality, temperature differences in starch accumulation timing suggest that carbon metabolism changes are associated with time to death. Drought mortality appears to be related to temperature-dependent carbon dynamics concurrent with increasing hydraulic stress in P. edulis and potentially other similar species.

New Phytologist↗

USGS2011

Evidence of shift in C 4 species range in central Argentina during the late Holocene

Aim Millennial-scale biogeographic changes are well understood in many parts of the world, but little is known about long-term vegetation dynamics in subtropical regions. Here we investigate shifts in C 3 /C 4 plant abundance occurred in central Argentina during the past few millennia Methods We determined present day soil organic matter δ 13 C signatures of grasslands, shrublands and woodlands, containing different mixtures of C 3 and C 4 plants. We measured past changes in the relative cover of C 3 /C 4 plants by comparing δ 13 C values in soil profiles with present day δ 13 C signatures. We analyzed 14 C activity in soil depths that showed major changes in vegetation. Results Present day relative cover of C 3 /C 4 plants determines whole ecosystem δ 13 C signatures integrated as litter and superficial soil organic matter (R 2 = 0.78; p < 0.01). Deeper soils show a consistent shift in δ 13 C, indicating a continuous replacement of C 4 by C 3 plants since 3,870 (±210) YBP. During this period, the relative abundance of C 3 plants increased 32% (average across sites) with significant changes being observed in all studied ecosystems. Conclusions Our results show that C 4 species were more abundant in the past, but C 3 species became dominant during the late Holocene. We identified increases in the relative C 3 /C 4 cover in grasslands, shrublands and woodlands, suggesting a physiological basis for changes in vegetation. The replacement of C 4 by C 3 plants coincided with changes in climate towards colder and wetter conditions and could represent a climatically driven shift in the C 4 species optimum range.

Plant and Soil↗

USGS2015

Landscape genomics of Sphaeralcea ambigua in the Mojave Desert: a multivariate, spatially-explicit approach to guide ecological restoration

Local adaptation influences plant species’ responses to climate change and their performance in ecological restoration. Fine-scale physiological or phenological adaptations that direct demographic processes may drive intraspecific variability when baseline environmental conditions change. Landscape genomics characterize adaptive differentiation by identifying environmental drivers of adaptive genetic variability and mapping the associated landscape patterns. We applied such an approach to Sphaeralcea ambigua , an important restoration plant in the arid southwestern United States, by analyzing variation at 153 amplified fragment length polymorphism loci in the context of environmental gradients separating 47 Mojave Desert populations. We identified 37 potentially adaptive loci through a combination of genome scan approaches. We then used a generalized dissimilarity model (GDM) to relate variability in potentially adaptive loci with spatial gradients in temperature, precipitation, and topography. We identified non-linear thresholds in loci frequencies driven by summer maximum temperature and water stress, along with continuous variation corresponding to temperature seasonality. Two GDM-based approaches for mapping predicted patterns of local adaptation are compared. Additionally, we assess uncertainty in spatial interpolations through a novel spatial bootstrapping approach. Our study presents robust, accessible methods for deriving spatially-explicit models of adaptive genetic variability in non-model species that will inform climate change modelling and ecological restoration.

California, Nevada↗