Urban green spaces play a crucial role in cities by providing near-natural environments that greatly impacts the health of residents. However, these green spaces have recently been scrutinized as ...potential reservoirs of antibiotic resistance genes (ARGs), posing significant ecological risks. Despite this concern, our understanding of the distribution, sources, and ecological risks associated with ARGs remains limited. In this study, we investigated the spatial distribution of soil ARGs using spatial interpolation and auto-correlation analysis. To apportion the source of soil ARGs in urban green spaces of Tianjin, Geo-detector method (GDM) was employed. Furthermore, we evaluated the ecological risk posed by ARGs employing risk quotients (RQ). The results of our study showed a significantly higher abundance of Quinolone resistance genes in the soil of urban green spaces in Tianjin. These genes were mainly found in the northwest, central, and eastern regions of the city. Our investigation identified three main factors contributing to the presence of soil ARGs: antibiotic production, precipitation, livestock breeding, and hospital. The results of ecological risk in RQ value showed a high risk associated with Quinolone resistance genes, followed by Aminoglycoside, Tetracycline, Multidrug, MLSB, Beta Lactam, Sulfonamide, and Chloramphenicol. Mantel-test and correlation analysis revealed that the ecological risk of ARGs was greatly influenced by soil properties and heavy metals. This study provides a new perspective on source apportionment and the ecological risk assessment of soil ARGs in urban green spaces.
•Explore the spatial distribution of soil antibiotic resistance genes.•Identify the sources of soil antibiotic resistance genes via multiple models.•Assess the ecological risk of soil antibiotic resistance genes in urban green space.
Precipitation patterns including the magnitude, timing, and seasonality of rainfall are predicted to undergo substantial alterations in arid regions in the future, and desert organisms may be more ...responsive to such changes than to shifts in only mean annual rainfall. Soil biocrust communities (consisting of cyanobacteria, lichen, and mosses) are ubiquitous to desert ecosystems, play an array of ecological roles, and display a strong sensitivity to environmental changes. Crust mosses are particularly responsive to changes in precipitation and exhibit rapid declines in biomass and mortality following the addition of small rainfall events. Further, loss of the moss component in biocrusts leads to declines in crust structure and function. In this study, we sought to understand the physiological responses of the widespread and often dominant biocrust moss
Syntrichia caninervis
to alterations in rainfall. Moss samples were collected during all four seasons and exposed to two rainfall event sizes and three desiccation period (DP) lengths. A carbon balance approach based on single precipitation events was used to define the carbon gain or loss during a particular hydration period. Rainfall event size was the strongest predictor of carbon balance, and the largest carbon gains were associated with the largest precipitation events. In contrast, small precipitation events resulted in carbon deficits for
S. caninervis
. Increasing the length of the DP prior to an event resulted in reductions in carbon balance, probably because of the increased energetic cost of hydration following more intense bouts of desiccation. The season of collection (i.e., physiological status of the moss) modulated these responses, and the effects of DP and rainfall on carbon balance were different in magnitude (and often in sign) for different seasons. In particular,
S. caninervis
displayed higher carbon balances in the winter than in the summer, even for events of identical size. Overall, our results suggest that annual carbon balance and survivorship in biocrust mosses are largely driven by precipitation, and because of the role mosses play in biocrusts, changes in intra-annual precipitation patterns can have implications for hydrology, soil stability, and nutrient cycling in dryland systems.
It is increasingly recognized that macro-organisms (corals, insects, plants, vertebrates) consist of both host tissues and multiple microbial symbionts that play essential roles in their host's ...ecological and evolutionary success. Consequently, identifying benefits and costs of symbioses, as well as mechanisms underlying them are research priorities. All plants surveyed under natural conditions harbor foliar endophytic fungi (FEF) in their leaf tissues, often at high densities. Despite producing no visible effects on their hosts, experiments have nonetheless shown that FEF reduce pathogen and herbivore damage. Here, combining results from three genomic, and two physiological experiments, we demonstrate pervasive genetic and phenotypic effects of the apparently asymptomatic endophytes on their hosts. Specifically, inoculation of endophyte-free (E-) Theobroma cacao leaves with Colletotrichum tropicale (E+), the dominant FEF species in healthy T. cacao, induces consistent changes in the expression of hundreds of host genes, including many with known defensive functions. Further, E+ plants exhibited increased lignin and cellulose content, reduced maximum rates of photosynthesis (Amax), and enrichment of nitrogen-15 and carbon-13 isotopes. These phenotypic changes observed in E+ plants correspond to changes in expression of specific functional genes in related pathways. Moreover, a cacao gene (Tc00g04254) highly up-regulated by C. tropicale also confers resistance to pathogen damage in the absence of endophytes or their products in host tissues. Thus, the benefits of increased pathogen resistance in E+ plants are derived in part from up-regulation of intrinsic host defense responses, and appear to be offset by potential costs including reduced photosynthesis, altered host nitrogen metabolism, and endophyte heterotrophy of host tissues. Similar effects are likely in most plant-endophyte interactions, and should be recognized in the design and interpretation of genetic and phenotypic studies of plants.
Plant physiological strategies of carbon (C) and nitrogen (N) uptake and metabolism are often regarded as outcomes of environmental selection. This is likely true, but the role of evolutionary ...history may also be important in shaping patterns of functional diversity. Here, we used leaf C and N stable isotope ratios (δ¹³C, δ¹⁵N) as integrators of physiological processes to assess the relative roles of phylogenetic history and environment in a diverse group of Ericaceae species native to North America. We found strong phylogenetic signal in both leaf δ¹³C and δ¹⁵N, suggesting that close relatives have similar physiological strategies. The signal of phylogeny was generally stronger than that of the local environment. However, within some specialized environments (e.g., wetlands, sandy soils), we found environmental effects and/or niche conservatism. Phylogenetic signal in δ¹³C appears to be most closely related to the constraints on metabolic demand and supply of C, and δ¹⁵N appears to be most strongly related to mycorrhizal associations within the family.
The objective of this study was to evaluate if aquatic pollution promote diet shifts in two livebearer fishes (Poeciliidae): an exotic species, the guppy (Poecilia reticulata), and a native ...livebearer (Phalloceros uai). The study was carried out in a Brazilian basin highly impacted by anthropogenic activities, especially discharge of domestic and industrial sewage from a region with more than five million human inhabitants. To evaluate the trophic ecology of both native and exotic species it was analysed carbon (δ13C) and nitrogen (δ15N) stable isotopes of fish tissue, food resources and, sewage. Moreover, stable isotopes analyses were coupled with gut contents of the two species to provide additional information about fish diet. Exotic guppy abundance was high in the most polluted site, where P. reticulata assimilated carbon directly from sewage. The native species was absent in the most polluted site, but presented wider niches than the exotic species in almost all other sites. Gut content analyses indicated high consumption of aquatic insects by both species. However, while the native species consumed a diverse suite of insect taxa, the exotic species consumed mainly Chironomidae larvae. We conclude that aquatic pollution promotes diet shifts in both native and exotic species, with both species changing their trophic niches in a similar way according to the level of degradation of the environment. The ability to directly assimilate sewage, together with its capacity to survive in environments with poor water quality and its reproductive strategy, may favour the establishment of exotic guppies in strongly polluted sites.
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•We tested the influence of pollution in the diet of exotic and native fish species.•We used gut contents and stable isotopes analysis to access the information.•Both species showed trophic plasticity and changed their trophic niches similarly.•Exotic species assimilated carbon directly from sewage.•Sewage consume can facilitate the exotic species establishment at polluted sites.
Savanna ecosystems are a major source of nitrogen (N) trace gases that influence air quality and climate. These systems are experiencing widespread encroachment by woody plants, frequently associated ...with large increases in soil N, with no consensus on implications for trace gas emissions. We investigated the impact of encroachment by N‐fixing tree Prosopis glandulosa on total reactive N gas flux (Nt = NO + N2O + NOy + NH3) from south Texas savanna soils over 2 years. Contrary to expectations, upland Prosopis groves did not have greater Nt fluxes than adjacent unencroached grasslands. However, abiotic conditions (temperature, rainfall, and topography) were strong drivers. Emissions from moist, low‐lying Prosopis playas were up to 3 times higher than from Prosopis uplands. Though NO dominated emissions, NH3 and NOy (non‐NO oxidized N) comprised 12–16% of the total summer N flux (up to 7.9 µg N m−2 h−1). Flux responses to soil wetting were temperature dependent for NO, NH3, and NOy: a 15 mm rainfall event increased flux 3‐fold to 22‐fold after 24 h in summer but had no effect in winter. Repeated soil wetting reduced N flux responses, indicating substrate depletion as a likely control. Rapid (<1 min) increases in NO emissions following wetting of dry soils suggested that abiotic chemodenitrification contributes to pulse emissions. We conclude that temperature and wetting dynamics, rather than encroachment, are primary drivers of N flux from these upland savannas, with implications for future emission patterns under altered precipitation regimes.
Key Points
Woody legume (Prosopis) encroachment does not increase N trace gas emissions from upland savannas
Less commonly measured compounds (NH3 and NOy) contribute 12‐16% of summer N flux
Emissions controlled by topography, temperature, and wetting, including rainfall frequency
Industrialization has significantly altered atmospheric chemistry by increasing concentrations of chemicals such as nitrogen oxides (NO x ) and volatile organic carbon, which react in the presence of ...sunlight to produce tropospheric ozone (O3). Ozone is a powerful oxidant that causes both visual and physiological damage to plants, impairing the ability of the plant to control processes like photosynthesis and transpiration. Damage to photosynthesis and stomatal conductance does not always occur at the same rate, which generates a problem when using the Ball-Berry model to predict stomatal conductance because the calculations directly rely on photosynthesis rates. The goals of this work were to develop a modeling framework to modify Ball-Berry stomatal conductance predictions independently of photosynthesis and to test the framework using experimental data. After exposure to elevated O3 in open-top chambers, photosynthesis and stomatal conductance in tulip poplar changed at different rates through time. We were able to accurately model observed photosynthetic and stomatal conductance responses to chronic O3 exposure in a Ball-Berry framework by adjusting stomatal conductance in addition to photosynthesis. This led to a significant improvement in the modeled ability to predict both photosynthesis and stomatal conductance responses to O3.
The fundamental tradeoff between carbon gain and water loss has long been predicted as an evolutionary driver of plant strategies across environments. Nonetheless, challenges in measuring carbon gain ...and water loss in ways that integrate over leaf lifetime have limited our understanding of the variation in and mechanistic bases of this tradeoff. Furthermore, the microevolution of plant traits within species versus the macroevolution of strategies among closely related species may not be the same, and accordingly, the latter must be addressed using comparative phylogenetic analyses.
Here we introduce the concept of ‘integrated metabolic strategy’ (IMS) to describe the ratio between carbon isotope composition (δ13C) and oxygen isotope composition above source water (Δ18O) of leaf cellulose. IMS is a measure of leaf‐level conditions that integrate several mechanisms contributing to carbon gain (δ13C) and water loss (Δ18O) over leaf lifespan, with larger values reflecting higher metabolic efficiency and hence less of a tradeoff. We tested how IMS evolves among closely related yet ecologically diverse milkweed species, and subsequently addressed phenotypic plasticity in response to water availability in species with divergent IMS.
Integrated metabolic strategy varied strongly among 20 Asclepias species when grown under controlled conditions, and phylogenetic analyses demonstrate species‐specific tradeoffs between carbon gain and water loss. Larger IMS values were associated with species from dry habitats, with larger carboxylation capacity, smaller stomatal conductance and smaller leaves; smaller IMS was associated with wet habitats, smaller carboxylation capacity, larger stomatal conductance and larger leaves. The evolution of IMS was dominated by changes in species’ demand for carbon (δ13C) more so than water conservation (Δ18O). Although some individual physiological traits showed phylogenetic signal, IMS did not.
In response to experimental decreases in soil moisture, three species maintained similar IMS across levels of water availability because of proportional increases in δ13C and Δ18O (or little change in either), while one species increased IMS due to disproportional changes in δ13C relative to Δ18O.
Synthesis. IMS is a broadly applicable mechanistic tool; IMS variation among and within species may shed light on unresolved questions relating to the evolution and ecology of plant ecophysiological strategies.
We introduce the concept of 'integrated metabolic strategy' to describe carbon‐water tradeoffs, as measured by the relationship between δ13C and Δ18O of leaf cellulose. We tested how integrated metabolic strategies evolve among closely related yet ecologically diverse milkweed species, and subsequently addressed phenotypic plasticity in response to water availability. Variation among and within species may shed light on previously unresolved questions relating to the evoluton and ecology of plant ecophysiological strategies.
Difficulty in quantifying rates of biological N fixation (BNF), especially over long time scales, remains a major impediment to defining N budgets in many ecosystems. To estimate N additions from ...BNF, we applied a tree-scale N mass balance approach to a well-characterized chronosequence of woody legume (Prosopis glandulosa) encroachment into subtropical grasslands. We defined spatially discrete single Prosopis clusters (aged 28–99 years), and for each calculated BNF as the residual of: soil N (0–30 cm), above- and below-ground biomass N, wet and dry atmospheric N deposition, N trace gas and N₂ loss, leaching loss, and baseline grassland soil N at time of establishment. Contemporary BNF for upland savanna woodland was estimated at 10.9 ± 1.8 kg N ha⁻¹ y⁻¹, equal to a total of 249 ± 60 kg N ha⁻¹ over about 130 years of encroachment at the site. Though these BNF values are lower than previous estimates for P. glandulosa, this likely reflects lower plant density as well as low water availability at this site. Uncertainty in soil and biomass parameters affected BNF estimates by 6–11%, with additional sensitivity of up to 18% to uncertainty in other scaling parameters. Differential N deposition (higher rates of dry N deposition to Prosopis canopies versus open grasslands) did not explain N accrual beneath trees; iterations that represented this scenario reduced estimated BNF estimates by a maximum of 1.5 kg N ha⁻¹ y⁻¹. We conclude that in this relatively well-constrained system, small-scale mass balance provides a reasonable method of estimating BNF and could provide an opportunity to cross-calibrate alternative estimation approaches.
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