Prospective evidence for independent nitrogen and phosphorus limitation of grasshopper (Chorthippus curtipennis) growth in a tallgrass prairie

Schizachyrium scoparium (C4) better tolerates drought than Andropogon gerardii (C4) via constant CO2 supply for photosynthesis during water stress

Climate change is dramatically altering global precipitation patterns across terrestrial ecosystems, making it critically important that we understand both how and why plant species vary in their drought sensitivities. Andropogon gerardii and Schizachyrium scoparium, both C4 grasses, provide a model system for understanding the physiological mechanisms that determine how species of a single functional type can differ in drought responses, an issue remains a critical gap in our ability to model and predict the impacts of drought on grassland ecosystems. Despite its greater lability of foliar water content, previous experiments have demonstrated that S. scoparium maintains higher photosynthetic capacity during droughts. It is therefore likely that the ability of S. scoparium to withstand drought instead derives from a greater metabolic resistance to drought. Here, we tested the following hypotheses: (H1) A. gerardii is more vulnerable to drought than S. scoparium at both the population and organismal levels, (H2) A. gerardii is less stomatally flexible than S. scoparium, and (H3) A. gerardii is more metabolically limited than S. scoparium. Our results indicate that it is actually stomatal limitations of CO2 supply that limit A. gerardii photosynthesis during drought. Schizachyrium scoparium was more drought-resistant than A. gerardii based on long-term field data, organismal biomass production and physiological gas exchange measurements. While both S. scoparium and A. gerardii avoided metabolic limitation of photosynthesis, CO2 supply of A. gerardii was greatly reduced during late-stage drought stress. That two common, co-occurring C4 species possess such different responses to drought highlights the physiological variability inherent within plant functional groups and underscores the need for more studies of C4 drought tolerance.

How Nutrients Mediate the Impacts of Global Change on Locust Outbreaks

Locusts are grasshoppers that can migrate en masse and devastate food security. Plant nutrient content is a key variable influencing population dynamics, but the relationship is not straightforward. For an herbivore, plant quality depends not only on the balance of nutrients and antinutrients in plant tissues, which is influenced by land use and climate change, but also on the nutritional state and demands of the herbivore, as well as its capacity to extract nutrients from host plants. In contrast to the concept of a positive relationship between nitrogen or protein concentration and herbivore performance, a five-decade review of lab and field studies indicates that equating plant N to plant quality is misleading because grasshoppers respond negatively or neutrally to increasing plant N just as often as they respond positively. For locusts specifically, low-N environments are actually beneficial because they supply high energy rates that support migration. Therefore, intensive land use, such as continuous grazing or cropping, and elevated ambient CO2 levels that decrease the protein:carbohydrate ratios of plants are predicted to broadly promote locust outbreaks.

Assessment of biological community in riparian zone contaminated by PAHs: Linking source apportionment to biodiversity

Riparian zone, an important land-water interface, plays an essential role in maintaining the ecological health of rivers, whereas the effects of Polycyclic aromatic hydrocarbons (PAHs) on the health of biological communities in riparian groundwater remain undetermined. To understand the responses of multiple communities to environmental variables, the distribution and ecosystem risk of 16 PAHs have been investigated in the Beiluo River, China. The distribution of multiple communities in riparian groundwater was investigated by environmental DNA metabarcoding, including 16S rRNA, 18S rRNA, and COI gene sequencing for bacteria, microbial eukaryotes (including algae, fungi, and protozoa), and metazoan, respectively, followed by correlation analysis between multiple communities and PAH contamination levels. The concentration of PAHs in the Beiluo River ranged largely from 35.32 to 728.59 ng/L. Here, the Shannon's diversity index of bacteria (Firmicutes) decreased possibly due to the occurrence of Pyrene, which mainly derives from coal and biomass combustion. Furthermore, the reduced richness of fungi (Ascomycota, Basidiomycota) and algae (Chlorophyta, Chrysophyceae) can be attributed to the presence of medium molecular weight (MMW) PAHs (Pyrene, Benz(a)anthracene, Chrysene), and low molecular weight (LMW) PAHs (Naphthalene, Fluorene, Phenanthrene). The richness and Shannon's diversity index of metazoan (Arthropoda) were promoted owing to MMW PAHs (Chrysene, Fluoranthene) generated from coal and biomass combustion and traffic emission. The ecological risk of PAHs in the groundwater environment of the Beiluo River was characterized as low to medium, where LMW and MMW PAHs posed higher risk than the high molecular weight (HMW) compounds. Overall, this study provides insights into the structures of riparian multi-biological communities altered by PAHs.

Population dynamics of herbivorous insects in polluted landscapes

Environmental pollution is one cause of insect decline in the Anthropocene, but the underlying mechanisms remain obscure due to a paucity of pollution-impact studies on insects that address density-dependent processes. Long data series (19-26 years) are available only for a few species monitored around two industrial polluters in north-western Russia. A particularly exciting current finding is that industrial pollution determines the relative strength of rapid (stabilising) and delayed (destabilising) density dependence operating on a herbivore population. Most studies address acute effects of traditional pollutants (e.g. sulphur dioxide and trace elements) and nitrogen deposition on agricultural pests, whereas the effects of realistic concentrations of ozone, particulate matter and emerging pollutants on insects feeding on noncultivated plants are unknown. The accumulated evidence remains insufficient to predict the effects of pollutants of global concern on the population dynamics of herbivorous insects.

Measuring and modelling crop yield losses due to invasive insect pests under climate change

Climate change and agriculture are strongly correlated, and the fast pace of climate change will have impacts on agroecosystems and crop productivity. This review summarizes potential impacts of rising temperatures and atmospheric CO₂ concentrations on insect pest-crop interactions and provides two-way approaches for integrating these impacts into crop models for sustainable pest management strategies designing. Rising temperatures and CO₂ levels affect insect physiology, accelerate their metabolism and increase their consumption, ultimately increasing population densities, which result in greater crop injury and damage, and yield loss. Whereas these direct effects are empirically demonstrated for temperature rises, they are less straightforward for CO₂ increases. Furthermore, indirect effects of rising temperatures and CO₂ levels remain largely unexploited and therefore unknown. Coupling insect pests and crops using a two-way feedback system model, whereby pest variables drive crop variables and vice versa, will improve analysis and forecasting of yield losses to better guide preparedness and intervention strategies.

Trophic differences regulate grassland food webs: herbivores track food quality and predators select for habitat volume

The impacts of altered biogeochemical cycles on ecological systems are likely to vary with trophic level. Predicting how these changes will affect ecological food webs is further complicated by human activities, which are simultaneously altering the availability of macronutrients like nitrogen (N) and phosphorus (P), and micronutrients such as sodium (Na). Here we contrast three hypotheses that predict how increasing nutrient availability will shape grassland food webs. We conducted a distributed factorial fertilization experiment (N and P crossed with NaCl) across four North American grasslands, quantifying the responses of aboveground plant biomass and volume, plant tissue and soil elemental concentrations, as well as the abundance of five arthropod functional groups. Fertilization with N and P increased plant biomass and foliar N and P concentrations in grasses but not forbs. Fertilization with Na had no effect on plant biomass but increased foliar Na concentrations. Consistent with the nutrient limitation hypothesis, we found strong evidence of nutrient limitation for insect herbivores across the four sites with sucking (phloem and xylem feeding) herbivores increasing in abundance with NP fertilization and chewing herbivores increasing in response to both Na and NP fertilization, and a trend for increased response of arthropods to lower plant nutrient availability. We found no evidence for an interaction of NaCl and NP on arthropod abundance as predicted by the serial colimitation hypothesis. Finally, consistent with the ecosystem size hypothesis, predator and parasitoid abundances increased with plant volume, but not fertilization. Our results suggest these functional group-specific responses to changes in plant nutrients and structure are key to predicting the future of grassland food webs in an era with increasing use of N and P fertilizers, and increasing terrestrial inputs of Na from road salt, saline irrigation water, and aerosols due to rising sea levels.

Introduced ecological engineers drive behavioral changes of grasshoppers, consequently linking to its abundance in two grassland plant communities

Introduced ecosystem engineers are expected to have extensive ecological impacts on a broad range of resident biota by altering the physical-chemical structure of ecosystems. Livestock that are potentially important introduced ecosystem engineers in grassland systems could create and/or modify habitats for native plant-dwelling insects. Yet, there is little knowledge of how insects respond to engineering effects of introduced livestock. To bridge this gap, we tested how domestic sheep affects the behavior and abundance of a native grasshopper Euchorthippus unicolor at both low (11.8 ± 0.4 plant species per plot) and high (19.8 ± 0.5 plant species per plot) diversity sites. Results found grasshoppers shifted their resting and feeding locations from the upper to the intermediate or low layers of vegetation, and fed on more plants species following livestock engineering effects. In the low plant diversity habitats, grazing caused grasshoppers to increase switching frequency, spend more time searching for host plants, and reduce time spent feeding, but had opposite effects on all the three behaviors in the high-diversity habitats. Moreover, grazing engineering effects on behavioral changes of grasshoppers were potentially related to their abundance. Overall, this study highlights native insect species' behavior and abundance in responses to introduced ecological engineers, and suggests that ecosystem engineers of non-native species have strong and important impacts extending beyond their often most obvious and frequently documented direct ecological effects.

Environmental Nutrients Alter Bacterial and Fungal Gut Microbiomes in the Common Meadow Katydid, Orchelimum vulgare

Insect gut microbiomes consist of bacteria, fungi, and viruses that can act as mutualists to influence the health and fitness of their hosts. While much has been done to increase understanding of the effects of environmental factors that drive insect ecology, there is less understanding of the effects of environmental factors on these gut microbial communities. For example, the effect of environmental nutrients on most insect gut microbiomes is poorly defined. To address this knowledge gap, we investigated the relationship between environmental nutrients and the gut microbial communities in a small study of katydids (n = 13) of the orthopteran species Orchelimum vulgare collected from a costal prairie system. We sampled O. vulgare from unfertilized plots, as well as from plots fertilized with added nitrogen and phosphorus or sodium separately and in combination. We found significantly higher Shannon diversity for the gut bacterial communities in O. vulgare from plots fertilized with added sodium as compared to those collected from plots without added sodium. In contrast, diversity was significantly lower in the gut fungal communities of grasshoppers collected from plots with added nitrogen and phosphorus, as well as those with added sodium, in comparison to those with no added nutrients. There was also a strong positive correlation between the gut bacterial and gut fungal community diversity within each sample. Indicator group analysis for added sodium plots included several taxa with known salt-tolerant bacterial and fungal representatives. Therefore, despite the small sample number, these results highlight the potential for the gut bacterial and fungal constituents to respond differently to changes in environmental nutrient levels. Future studies with a larger sample size will help identify mechanistic determinants driving these changes. Based on our findings and the potential contribution of gut microbes to insect fitness and function, consideration of abiotic factors like soil nutrients along with characteristic gut microbial groups is necessary for better understanding and conservation of this important insect herbivore.

Effects of biosolids amendments on American Kestrel (Falco sparverius) nest-site selection and diet

Fertilization is a common practice, as it improves plant yields. In many areas, biosolids (remains from treated wastewater) are used instead of chemical fertilizers owing to multi-year nutrient release and positive changes in soils and water retention. Little is known about whether biosolids affect animal consumers. Here, we examine diets and nesting sites of American Kestrels (Falco sparverius Linnaeus, 1758) in British Columbia, Canada. Our major study area was a large cattle ranch that has been grazed for over a century and where biosolids were applied in the previous 1–3 years. Kestrels selected nests in areas with higher Northern Flicker (Colaptes auratus (Linnaeus, 1758)) nest density and with a higher proportion of pastures with biosolids applications, but with less forest. Kestrels were observed more often on biosolids-amended pastures than in untreated areas. Kestrels primarily ate voles (genus Microtus Schrank, 1798), but also consumed grasshoppers (Orthoptera) late in the breeding season when grasshoppers were abundant. Kestrel diets were slightly more varied on a nearby control area than on the ranch. Our results suggest that biosolids applications improve prey availability for Kestrels, thus potentially acting as a restoration tool in areas with degraded habitats or where Kestrels have declined.

Drought timing, not previous drought exposure, determines sensitivity of two shortgrass species to water stress

Climate change will alter global precipitation patterns, making it increasingly important that we understand how ecosystems will be impacted by more frequent and severe droughts. Yet most drought studies examine a single, within-season drought, and we know relatively little about the impacts of multiple droughts that occur within a single growing season. This distinction is important because many plant species are able to acclimate physiologically, such that the effects of multiple droughts on ecosystem function deviate significantly from the effects of cumulative, independent droughts. Unfortunately, we know relatively little about the ability of dominant species to acclimate to drought in drought-sensitive ecosystems like semi-arid grasslands. Here, we tested for physiological acclimation to multiple drought events in two dominant shortgrass steppe species: Bouteloua gracilis (C₄) and Elymus elymoides (C₃). Neither species exhibited physiological acclimation to drought; leaf water potential, stomatal conductance, and photosynthesis rates were all similarly affected by a single, late period drought and a second, late period drought. Biomass was lowest in plants exposed to two droughts, but this is likely due to the cumulative effects of both an early and late period drought. Our results suggest that late period droughts do exert weaker effects on biomass production of two dominant shortgrass species, but that the weaker effects are due to ontogenetic changes in plant physiology as opposed to physiological acclimation against multiple droughts. As a consequence, current ecosystem models that incorporate grass phenology and seasonal physiology should provide accurate predictions of primary production under future climates.