Asymmetrical warming of growing/non-growing season increases soil respiration during growing season in an alpine meadow

Soil respiration (R_s) is an important carbon flux in the global carbon cycle, and understanding the influence of global warming on R_s is critical for precise prediction future climate change. Actually, global warming is expected to be seasonally asymmetric, however, it is still unclear on the response of R_s to asymmetrical warming of growing/non-growing season in alpine regions. In this study, an experiment with asymmetrical warming of growing/non-growing season (including three treatments, CK: control; GLNG: warming magnitude of growing season lower than non-growing season; GHNG: warming magnitude of growing season higher than non-growing season) was performed in an alpine meadow of the Northern Tibet since June 2015. The 'GLNG' and 'GHNG' treatments increased mean R_s by 71.22% (1.89 μmol CO₂ m^-2 s^-1) and 34.32% (0.91 μmol CO₂ m^-2 s^-1) during growing season in 2019, respectively. However, the 'GLNG' and 'GHNG' treatments did not significantly affect mean R_s during growing season in 2015, 2016, 2017 and 2018, respectively. The variation coefficient of growing season mean R_s was 32.95% under the CK treatment in 2015-2019. Therefore, warming may have a lagging effect on R_s. The warming scene with a greater warming during non-growing season may have a stronger effect on R_s than the warming scene with a greater warming during growing season. Inter-annual variation of R_s may be greater than the warming effect on R_s in alpine meadows.

Conservation management improves agroecosystem function and resilience of soil nitrogen cycling in response to seasonal changes in climate

Understanding how conservation agricultural management improves soil nitrogen (N) stability in the face of climate change can help increase agroecosystem productivity and mitigate runoff, leaching and downstream water quality issues. We conducted a 2-year field study in a 36-year-old rain-fed cotton production system to evaluate the impacts of changing climatic factors (temperature and precipitation) on soil N under conservation management, including moderate inorganic N fertilizer application (0 and 67 kg N ha^-1), winter cover crops (fallow; winter wheat, Triticum aestivum L.; hairy vetch, Vicia villosa Roth), and reduced tillage (no-till; disk tillage). Structural equation modeling (SEM) was used to quantify and compare the effects of conservation management and climatic factors on soil N concentrations. Fertilizer and vetch cover crops increased soil total N concentration by 16% and 18%, respectively, and also increased microbial N transformation rate by 41% and 168%. In addition, vetch cover crops also increased soil labile N concentrations by 57%, 21%, and 79%, i.e., extractable organic N, ammonium, and nitrate, respectively. The highest soil δ¹⁵N value (6.4 ± 0.3‰) was observed under the 67 kg N ha^-1 fertilizer-wheat-disk tillage treatment, and the lowest value (4.8 ± 0.3‰) under the zero-fertilizer-wheat-no-till treatment, indicating fertilizer and tillage might accelerate microbial N transformation. The SEM showed positive effects of temperature and precipitation on labile N concentrations, suggesting destabilization of soil N and the potential for soil N loss under increased temperature and intensified precipitation. Fertilizer and vetch use might mitigate some of the effects of temperature by accelerating microbial N transformations, with vetch having a larger effect than fertilizer (0.35 vs. 0.15, Table 1). No-till can reduce some of the effects of precipitation on soil labile N by maintaining soil structure. Our study suggests that fertilizer, vetch cover crop, and no-till might help improve function and resilience of agroecosystems in relation to soil N cycling. Soil N stabilization in cropping systems can be enhanced by adjusting agricultural management.

Enhanced phytoextraction of multi-metal contaminated soils under increased atmospheric temperature by bioaugmentation with plant growth promoting Bacillus cereus

The co-occurrence of environmental stresses such as heavy metals (HM) and increased atmospheric temperature (IAT) pose serious implications on plant growth and productivity. In this work, we evaluated the role of plant growth-promoting bacteria (PGPB) and its effectiveness on Zea mays growth, stress tolerance and phytoremediation potential in multi-metal (MM) contaminated soils under IAT stress conditions. The PGPB strain TCU11 was isolated from metal contaminated soils and identified as Bacillus cereus. TCU11 was able to resist abiotic stresses such as IAT (45 °C), MM (Pb, Zn, Ni, Cu, and Cd), antibiotics and induced in vitro plant growth promotion (PGP) by producing siderophores (catechol and hydroxymate) and indole 3-acetic acid even in the presence of MM under IAT. Inoculation of TCU11 significantly increased the biomass, chlorophyll, carotenoids, and protein content of Z. mays compared to the respective control under MM, IAT, and MM + IAT stress. A decrease of malondialdehyde and over-accumulation of total phenolics, proline along with the increased activity of superoxide dismutase, catalase and ascorbic peroxidase were observed in TCU11 inoculated plants under stress conditions. These results suggested MM and/or IAT significantly reduced the maize growth, whereas TCU11 inoculation mitigated the combined stress effects on maize performance. Moreover, the inoculation of TCU11 under IAT stress increased the MM (Pb, Zn, Ni, Cu, and Cd) accumulation in plant tissues and also increased the translocation of HM from root to shoot except for Ni. The results of soil HM mobilization further indicates that IAT increased the HM mobilizing activity of TCU11, thus increasing the concentrations of bio-available HM in soil. These results suggested that TCU11 not only alleviates MM and IAT stresses but also enhances the biomass production and HM accumulation in plants. Therefore, TCU11 can be exploited as inoculums for improving the phytoremediation efficiency in MM polluted soils under IAT conditions.

Does global warming intensify cost of antipredator reaction? A case study of freshwater amphipods

Global warming is a worldwide phenomenon affecting the functioning of diverse ecosystems, including fresh waters. Temperature increase affects physiology and behaviour of ectotherms due to growing energetic demands necessary to sustain increased metabolic rate. Anti-predator responses may resemble temperature-induced changes in organisms, suggesting synergism between these factors. To check how temperature shapes physiological and behavioural responses of ectotherms to predation risk, we exposed amphipods: Dikerogammarus villosus and Gammarus jazdzewskii to fish kairomones at 10, 17 or 24 °C. Animals were placed in tanks where temperature was gradually adjusted to the desired test temperature and acclimated under such conditions for 3 subsequent days. Then they were exposed to the predator cue (the Eurasian perch kairomone) for 35 min to test their acute responses. We measured metabolic rate (as respiration), antioxidant defence (CAT: catalase activity, TAS: total antioxidant status), oxidative molecules (TOS: total oxidative status), oxidative damage (TBARS: thiobarbituric acid reactive substances) and behaviour (locomotor activity). Amphipods increased respiration with raising temperature and when exposed to predation risk (all temperatures). Only G. jazdzewskii exhibited increased TOS when exposed to 24 °C or to predation risk at all temperatures. Antioxidant defence increased with raising temperature (CAT, TAS) and decreased under predation risk (CAT). Cellular damage increased in G. jazdzewskii under predation risk at 10 and 24 °C, but raised temperature itself did not generate any damage. Amphipods reduced locomotor activity at 24 °C. Thus, at elevated temperatures, amphipods minimized their cellular damage at the cost of increased antioxidant defence and lower locomotor activity (potentially disadvantageous under higher energetic demands). Under predation risk, the performance of antioxidant systems was reduced, probably due to energy allocation into anti-predatory mechanisms, leading to increased cellular damage at suboptimum temperatures. Thus, negative consequences of elevated temperature for organisms may be amplified by changes in behaviour (compromising food acquisition) and non-consumptive predator effects.

Chronic exposure to venlafaxine and increased water temperature reversibly alters microRNA in zebrafish gonads (Danio rerio)

MicroRNA (miRNA) are short, non-coding RNA that act by downregulating targeted mRNA transcripts. Only recently have they been used as endpoints in studies of aquatic toxicology. The purpose of this study was to determine the effect of an antidepressant contaminant, venlafaxine (VFX), and increased temperature on specific microRNA levels in zebrafish (Danio rerio) reproductive tissue. Adult zebrafish were exposed to one of four conditions; control, 1 μg/L VFX (VFX), 32 °C (Temp), or 1 μg/L VFX + 32 °C (VFX & Temp) for 21 days. Half of the fish were returned to control conditions for a 21-day recovery period. RT-qPCR was performed to measure relative abundances of several miRNAs known to respond to antidepressant exposure: dre-miR-22b-3p, dre-miR-301a, dre-miR-140-5p, dre-let-7d-5p, dre-miR-210-5p, and dre-miR-457b-5p. After the exposure period, dre-miR-22b-3p and dre-miR-301a showed a significant downregulation in response to all treatments. In contrast, after the recovery period, there were no significant differences in microRNA abundance. These altered microRNA are predicted to target several genes, including phosphofructokinase, and are associated with ovarian pathologies. Combined, we have shown that VFX and increased water temperature alter miRNA abundances in zebrafish reproductive tissue, an effect correlated with a functional stress response and cell cycle dysregulation.

Will temperature increases associated with climate change potentiate toxicity of environmentally relevant concentrations of chloride on larval green frogs (Lithobates clamitans)?

An important challenge in amphibian ecotoxicology and conservation is that amphibian toxicity tests are usually focused on a single chemical while populations experience multiple, simultaneous stressors. For example, about 14 million tons of road de-icing salts are used each year in North America with NaCl accounting for 98% of total salt use and, hence, elevated chloride is an important environmental stressor to aquatic organisms, including amphibians. As well, higher temperature as a result of climate change is becoming an increasingly important environmental stressor. There are no data on the combined effects of chloride and temperature on amphibians hinders conservation efforts. We conducted field studies to characterize chloride concentrations and water temperatures in known amphibian breeding habitats and performed toxicity tests to explore impacts of these two stressors on a common anuran, the green frog (Lithobates clamitans). A 96-hour acute toxicity test was conducted to first determine a chloride LC50 (2587.5 mg Cl^-/L) at a single, neutral temperature, which was used to inform the treatment levels of the sub-chronic test, which also included a temperature range. In the sub-chronic study, green frog larvae were exposed to three temperatures (18, 22, and 25 °C), and four concentrations of chloride (0, 500, 1000, and 2000 mg Cl^-/L) for 35 days. At all temperatures, tadpoles exposed to 2000 mg Cl^-/L had significantly higher mortality. While there was no significant effect of temperature alone on mortality, survival of tadpoles was significantly lower at 1000 mg Cl^-/L at the two higher temperatures suggesting a potentiation of chloride ion toxicity with increasing temperature. Comparing toxicity results to field measurements of chloride and temperature suggests green frog tadpoles and other species with similar sensitivity are likely negatively affected. Data on additional species and populations would further increase our understanding of how salt and temperature may shape aquatic communities.

Effects of 7 years experimental warming on soil bacterial and fungal community structure in the Northern Tibet alpine meadow at three elevations

A warming experiment was established along an altitudinal gradient (low elevation: 4313 m, mid-elevation: 4513 m and high elevation: 4693 m) in alpine meadows of the Northern Tibet to investigate the effects of warming on soil bacterial and fungal community structure. Elevation had significant effects on vegetation community coverage (CC), soil temperature (T_s) and pH, but not soil fungal diversity. Soil bacterial diversity at the high elevation was significantly lower than that at the low and mid-elevations, whereas there was no significant difference of soil bacterial diversity between the low and mid-elevations. After seven years of warming, soil fungal diversity was significantly increased at the mid-elevation but not the low and high elevations, and soil bacterial diversity was not significantly altered at the low, mid- and high elevations. Soil bacterial community structure was significantly altered at the low and mid-elevations but not the high elevation. Soil fungal community structure was significantly altered at all the three elevations. CC, T_s and pH significantly explained 20.55%, 5.30% and 12.61% of the variation of bacterial community structure, respectively. CC and T_s significantly explained 17.40% and 5.86% of the variation of fungal community structure, respectively. Therefore, responses of soil microbial community structure to warming may vary with elevation, which was mainly attributed to different vegetation coverage, soil temperature and/or pH conditions among the three elevations in this study alpine meadows.

Response of plant production to growing/non-growing season asymmetric warming in an alpine meadow of the Northern Tibetan Plateau

A field growing/non-growing season asymmetric warming experiment (C: control, i.e., no warming in the entire year; GLNG: growing season warming lower than non-growing season warming; GHNG: growing season warming higher than non-growing season warming) was conducted in an alpine meadow of the Northern Tibetan Plateau in early June 2015. The effects of growing/non-growing season asymmetric warming on the normalized difference vegetation index (NDVI), soil adjusted vegetation index (SAVI), aboveground biomass (AGB) and gross primary production (GPP) in 2015-2017 were examined. The 'GLNG' and 'GHNG' treatments significantly increased the annual mean air temperature (T_a) by 2.95 °C and 2.76 °C, and the vapor pressure deficit (VPD) by 0.23 kPa and 0.28 kPa but significantly reduced the annual mean soil moisture (SM) by 0.02 m³ m^-3 and 0.02 m³ m^-3 respectively; however, changes in the annual mean T_a, VPD and SM were the same between the 'GLNG' and 'GHNG' treatments over the three years in 2015-2017. There were no significant differences in the SAVI and GPP among the 'C', 'GLNG' and 'GHNG' treatments over the three growing seasons in 2015-2017. The 'GLNG' and 'GHNG' treatments did not significantly affect the NDVI and AGB compared to 'C', whereas the NDVI and AGB under the 'GLNG' treatment were significantly greater than those under the 'GHNG' treatment over the three growing seasons in 2015-2017. The significant differences in NDVI and AGB between the 'GLNG' and 'GHNG' treatments may be attributed to the different effects under the 'GLNG' and 'GHNG' treatments on the non-growing season T_a, growing season water availability and soil nitrogen availability. Therefore, the non-growing season with a higher warming magnitude may have stronger effects on the aboveground plant production than did the growing season with a higher warming magnitude in the alpine meadow of the Northern Tibetan Plateau.

Effects of experimental warming and increased precipitation on soil respiration in an alpine meadow in the Northern Tibetan Plateau

Uncertainty on the response of soil respiration (R_s) to warming and increased precipitation on the Tibetan Plateau can limit our ability to predict how alpine ecosystems will respond to future climate change. Based on a warming (control, low- and high-level) and increased precipitation (control, low- and high-level) experiment, the response of R_s to experimental warming and increased precipitation was examined in an alpine meadow in the Northern Tibetan Plateau from 2014 to 2017. The low-level warming increased soil temperature (T_s) by 1.19°C and decreased soil moisture (SM) by 0.02m³m^-3, whereas the high-level warming increased T_s by 2.88°C and decreased SM by 0.04m³m^-3 over the four growing seasons in 2014-2017. The low- and high-level increased precipitation did not affect T_s, but increased SM by 0.02m³m^-3 and 0.04m³m^-3, respectively, over the four growing seasons in 2014-2017. No significant main and interactive effects of experimental warming and increased precipitation on R_s were observed over the four growing seasons in 2014-2017. In contrast, there was a significant inter-annual variation of R_s in 2014-2017. There was a marginally significant quadratic relationship between the effect of experimental warming on R_s and warming magnitude. There was a negligible difference of R_s between the low- and high-level increased precipitation over the four growing seasons in 2014-2017 and R_s also showed a quadratic relationship with precipitation. Therefore, experimental warming and increased precipitation did not change R_s and R_s responded nonlinearly to experimental warming and increased precipitation in the alpine meadow in the Northern Tibetan Plateau. Growing season precipitation may play a more important role than experimental warming and increased precipitation in affecting R_s in the alpine meadow in the Northern Tibetan Plateau.

Impact of ocean acidification and warming on the productivity of a rock pool community

This study examined experimentally the combined effect of ocean acidification and warming on the productivity of rock pool multi-specific assemblages, composed of coralline algae, fleshy algae, and grazers. Natural rock pool communities experience high environmental fluctuations. This may confer physiological advantage to rock pool communities when facing predicted acidification and warming. The effect of ocean acidification and warming have been assessed at both individual and assemblage level to examine the importance of species interactions in the response of assemblages. We hypothesized that rock pool assemblages have physiological advantage when facing predicted ocean acidification and warming. Species exhibited species-specific responses to increased temperature and pCO₂. Increased temperature and pCO₂ have no effect on assemblage photosynthesis, which was mostly influenced by fleshy algal primary production. The response of coralline algae to ocean acidification and warming depended on the season, which evidenced the importance of physiological adaptations to their environment in their response to climate change. We suggest that rock pool assemblages are relatively robust to changes in temperature and pCO₂, in terms of primary production.

Oxidative stress and antioxidant response in a thermotolerant yeast

Stress tolerance is a key attribute that must be considered when using yeast cells for industrial applications. High temperature is one factor that can cause stress in yeast. High environmental temperature in particular may exert a natural selection pressure to evolve yeasts into thermotolerant strains. In the present study, three yeasts (Saccharomyces cerevisiae, MC4, and Kluyveromyces marxianus, OFF1 and SLP1) isolated from hot environments were exposed to increased temperatures and were then compared with a laboratory yeast strain. Their resistance to high temperature, oxidative stress, and antioxidant response were evaluated, along with the fatty acid composition of their cell membranes. The SLP1 strain showed a higher specific growth rate, biomass yield, and biomass volumetric productivity while also showing lower duplication time, reactive oxygen species (ROS) production, and lipid peroxidation. In addition, the SLP1 strain demonstrated more catalase activity after temperature was increased, and this strain also showed membranes enriched in saturated fatty acids. It is concluded that the SLP1 yeast strain is a thermotolerant yeast with less oxidative stress and a greater antioxidant response. Therefore, this strain could be used for fermentation at high temperatures.

Enhanced sludge reduction in septic tanks by increasing temperature

Septic tanks in most developing countries are constructed without drainage trenches or leaching fields to treat toilet wastewater and /or grey water. Due to the short hydraulic retention time, effluents of these septic tanks are still highly polluted, and there is usually high accumulation of septic tank sludge or septage containing high levels of organics and pathogens that requires frequent desludging and subsequent treatment. This study aimed to reduce sludge accumulation in septic tanks by increasing temperatures of the septic tank content. An experimental study employing two laboratory-scale septic tanks fed with diluted septage and operating at temperatures of 40 and 30°C was conducted. At steady-state conditions, there were more methanogenic activities occurring in the sludge layer of the septic tank operating at the temperature of 40°C, resulting in less total volatile solids (TVS) or sludge accumulation and more methane (CH4) production than in the unit operating at 30°C. Molecular analysis found more abundance and diversity of methanogenic microorganisms in the septic tank sludge operating at 40°C than at 30°C. The reduced TVS accumulation in the 40°C septic tank would lengthen the period of septage removal, resulting in a cost-saving in desluging and septage treatment. Cost-benefit analysis of increasing temperatures in septic tanks was discussed.