Adaptive responses to fescue toxicosis under thermoneutral and heat stress conditions

This study determined the potential for short-term adaptation to fescue toxicosis and heat stress in rats. Male CD outbred rats (n=24) were implanted with temperature transmitters (Respironics, Bend, OR) to measure core temperature (Tc) and general activity. All rats were initially fed diets with ground, uninfected tall fescue seed (E−) and exposed to 21 °C (thermoneutral, TN) to establish baseline values. In Period 1, all groups were maintained at TN for 7 days, with one group fed a diet containing ground, endophyte-infected tall fescue seed (E+, approximately 165 μg ergovaline/kg BW/d) and two groups fed E− diet. Ergovaline is thought to be the primary toxin responsible for many symptoms associated with fescue toxicosis. Period 1 was followed by 7 days at 31 °C (heat stress, HS, Period 2) on the same diets. All animals were fed E− diet during the second 7 day of HS (Period 3). In the final 7 day (Period 4), E+ diet was returned to the original group and fed to one of the previously E− groups, with the third group remaining on E− diet. A 40% decrease in FI occurred with E+ treatment at TN (P<0.05), with a comparable BW reduction (P<0.05) after 4 day. Both responses worsened during HS. Treatment with E+ in Period 4 indicated that FI and BW had not adapted to fescue toxicosis. A reduction in daily Tc occurred with E+ treatment at TN (P<0.05) followed by hyperthermia during the initial stage of HS (P<0.05). Although feed intake and growth rate showed no change over time, there was a reduction in fescue toxicosis-induced hyperthermia in the heat with repeat treatment. Conditioning animals to fescue toxicosis and heat stress prior to exposure may be beneficial in reducing impacts on thermal status of the animal.     

Short- and long-term responses to fescue toxicosis at different ambient temperatures

Intake of endophyte-infected tall fescue by cattle results in fescue toxicosis, which is characterized by increased hyperthermia during heat stress and concomitant reductions in feed intake and growth. Rats were monitored at 21 or 31 °C for short- or long-term periods to determine temporal changes associated with the intake of endophyte-infected (E+) or uninfected (E−) fescue seed diets. Core temperature only changed in rats fed E+ diet at 31 °C. Intake of E+ diet reduced feed intake, daily gain, and serum prolactin. There were temporal and thermal differences in the response to endophytic toxins, with short-term changes diminishing over time at 21 °C, but increasing for certain parameters at 31 °C.     

Benefit of dietary seaweed (Ascophyllum nodosum) extract in reducing heat strain and fescue toxicosis: a comparative evaluation

Much of the fescue throughout the world contains an endophytic fungus which protects the plant from heat and drought, but produces a condition known as fescue toxicosis when consumed by animals. Major symptoms include reduced feed intake and growth, and increased hyperthermia during heat stress. Seaweed extract was tested, using both rodent and bovine models, to determine potential for reduction of fescue toxicosis-induced hyperthermia. Results show that the seaweed extract reduces hyperthermia associated with fescue toxicosis.     

Effect of thermal stress on physiological parameters, feed intake and plasma thyroid hormones concentration in Alentejana, Mertolenga, Frisian and Limousine cattle breeds

The aim of the present study was to assess the heat tolerance of animals of two Portuguese (Alentejana and Mertolenga) and two exotic (Frisian and Limousine) cattle breeds, through the monitoring of physiological acclimatization reactions in different thermal situations characterized by alternate periods of thermoneutrality and heat stress simulated in climatic chambers. In the experiment, six heifers of the Alentejana, Frisian and Mertolenga breeds and four heifers of the Limousine breed were used. The increase in chamber temperatures had different consequences on the animals of each breed. When submitted to heat stress, the Frisian animals developed high thermal polypnea (more than 105 breath movements per minute), which did not prevent an increase in the rectal temperature (from 38.7°C to 40.0°C). However, only a slight depression in food intake and in blood thyroid hormone concentrations was observed under thermal stressful conditions. Under the thermal stressful conditions, Limousine animals decreased food intake by 11.4% and blood triiodothyronine (T3) hormone concentration decreased to 76% of the level observed in thermoneutral conditions. Alentejana animals had similar reactions. The Mertolenga cattle exhibited the highest capacity for maintaining homeothermy: under heat stressful conditions, the mean thermal polypnea increased twofold, but mean rectal temperature did not increase. Mean food intake decreased by only 2% and mean T3 blood concentration was lowered to 85,6% of the concentration observed under thermoneutral conditions. These results lead to the conclusion that the Frisian animals had more difficulty in tolerating high temperatures, the Limousine and Alentejana ones had an intermediate difficulty, and the Mertolenga animals were by far the most heat tolerant.     

Anaerobic respiration and antioxidant responses of Corythucha ciliata (Say) adults to heat-induced oxidative stress under laboratory and field conditions

High temperature often induces oxidative stress and antioxidant response in insects. This phenomenon has been well documented under controlled laboratory conditions, but whether it happens under fluctuating field conditions is largely unknown. In this study, we used an invasive lace bug (Corythucha ciliata) as a model species to compare the effects of controlled thermal treatments (2 h at 33–43 °C with 2 °C intervals in the laboratory) and naturally fluctuating thermal conditions (08:00–14:00 at 2-h intervals (29.7–37.2 °C) on a hot summer day in a field in Shanghai, China) on lipid peroxidation (malondialdehyde (MDA) was the marker) and anaerobic respiration (lactate dehydrogenase (LDH) was the marker), as well as superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), and glutathione reductase (GR). The results show that MDA concentration increased significantly in response to heat stresses with similar trend in the laboratory and field. LDH activities did not significantly vary across temperatures in the laboratory-exposed individuals, but they significantly increased by rising temperature in the field. The activities or concentrations of SOD, CAT, GSH, and GR all significantly increased with increasing temperature in the two populations. These findings indicate that high temperature induces oxidative stress, resulting in high anaerobic respiration and antioxidant defenses in C. ciliata under both the laboratory and field conditions, which likely provide a defense mechanism against oxidative damage due to the accumulation of ROS.     

Analyses of thermoregulatory responses of feeder cattle exposed to simulated heat waves

Heat stress in feedlot cattle causes reduced performance, and in the most severe cases, death of the animals, thus causing the loss of millions of dollars in revenue to the cattle industry. A study was designed to evaluate dynamics of thermoregulation and feeding activities when feeder cattle were exposed to simulated heat waves, in comparison with repeated sinusoidal hot and thermoneutral environments. Nine beef steers were randomly assigned to an individual pen in one of three environmental chambers. Each chamber was subjected to each of three temperature regimes (Heatwave simulation from Rockport, Mo., 1995, Heatwave simulation from Columbia, Mo., 1999, and Controlled heat stress treatment of 32±7°C) for a period of 18 days, according to a Latin square treatment design, with a 10-day thermoneutral period (18±7°C) separating treatment periods. Respiration rate, core body temperature, heat production, feed intake, and feeding behavior were measured on each animal for the duration of the experiment. Differences were found in all treatments for all parameters except feeding behavior. It was shown that the two simulated heat waves elicited very different thermoregulatory responses. Based on these results the heat wave centered at Rockport, Mo. in 1995 was devastating because the animals were not acclimated to hot conditions, thus causing an acute response to heat stress. The responses of cattle to conditions at Columbia, Mo. showed some acclimation to heat prior to the peak stress days, and therefore a dampened response was seen. It appears the extreme conditions at Columbia, Mo., 1999 were made severe by environmental conditions not simulated during this study (low wind speed and intensive solar radiation). Overall, it was determined while a cyclic heat stress treatment is a representative model to test heat stress in cattle, further heat stress experiments should be conducted in an actual feedlot.Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. 9th Street Drive, West Palmetto, FL 34221, USA.     

Physiological responses of Corythucha ciliata adults to high temperatures under laboratory and field conditions

Under high temperature conditions, insects can tolerate to survive through various physiological mechanisms, which have been well documented in laboratory studies. However, it is still unclear as to whether these laboratory data can scale up to those in the field. Here we studied dynamics of heat-induced metabolites in Corythucha ciliata adults under both laboratory and field conditions to examine their significance in thermal tolerance of the species. We compared the effects of controlled thermal treatments (2 h at 33–43 °C at 2 °C intervals in the laboratory) and naturally increasing thermal conditions (10:00–14:00 at 2-h intervals (33.5–37.2 °C) on a hot summer day in a field in Shanghai, China) on water content and levels of water-soluble protein, triglycerides, mannitol, and sorbitol in the adult bodies. The results showed that water content significantly decreased and all other metabolic parameters significantly increased in response to temperature stresses with similar patterns in both the laboratory and field, although the respective threshold temperatures were different under the two conditions. The close linkage observed in the two conditions suggests that a short period of heat stress induces water loss and accumulation of thermal metabolites in C. ciliata adults. This heat-resistance provides a defense mechanism counteracting thermal damage in C. ciliata.     

Patterns of heat response and adaptation on summer pasture: A comparison of heat-sensitive (Angus) and -tolerant (Romosinuano) cattle

Heat stress in Bos taurus cattle is a problem that affects many regions of the world. Numerous studies have focused on heat stress in feedlots or environmental chambers; but few have looked at undisturbed cattle on pasture. The present study followed two Bos taurus cattle breeds throughout a mid-Missouri summer to determine thermoregulatory responses to fluctuating summer air temperature (T_a), as well as differences in adaptation to heat. Heat-sensitive Angus steers (ANG; n=22; 480±7.15 kg BW), and heat-tolerant Romosinuano steers (RO; n=11; 352±6 kg BW) were monitored on 12 day from June through August of 2009 in an endophyte free tall fescue pasture. Data were grouped into two, six-day periods representing peak (Period 1) and late (Period 2) summer for determination of adaptation. Respiration rate (RR) was measured via flank counting and telemetric temperature transmitters in the rumen of each animal monitored core temperature (T_rum). Romosinuano sustained a lower (P<0.05) RR and T_rum compared to ANG during both periods. Linear relationships for RR and T_rum, compared against T_a for both Periods were determined. Slopes of RR to T_a from Period 1 to Period 2 decreased (P<0.05) from 2.63 to 1.08 bpm/°C and 2.25 to 0.49 bpm/°C for ANG and RO, respectively. Slopes of T_rum to T_a also decreased (P<0.05) from Periods 1 to 2 from 0.12 to 0.02 °C T_rum/°C T_a for ANG; however, RO showed no differences between periods. Although Romosinuano have a lower respiration rate and ruminal temperature than Angus, they share a similar pattern of respiration rate adaptation from early to late summer periods.     

Role of oxidative stress on growth responses of spring barley exposed to different environmental stressors

Aims Oxidative stress is one of the most important mechanisms in a plant's reaction to the effects of different stressors; however, its role in plants' resistance is still poorly understood. The objective of this study is to evaluate an influence of oxidative stress induced by stress factors of different origin—ozone, ultraviolet (UV)-B radiation, drought, cadmium (Cd) and copper (Cu), to growth of spring barley and to check the hypothesis, that intensification of oxidative stress is the main factor of growth depression induced by strong treatments of different stressors; meanwhile, mitigation of oxidative stress determines eustress-induced growth stimulation.Methods A pot experiment was carried out in phytotron chambers with a controlled environment. Spring barley (Hordeum vulgare L.) plants were exposed to different doses of investigated environmental stress factors (O 3, UV-B radiation, drought, Cd and Cu), and their effects on shoots growth, accumulation of superoxide (O 2 .?), intensification of lipid peroxidation and antioxidative protection (superoxide dismutase, glutathione reductase and catalase activities and concentration of carotenoids) were measured. Analysis of variance (ANOVA) with classical eta-squared (η 2) values was used to evaluate and to compare the contribution of non-specific oxidative stress and stressor-specific mechanisms on plants growth.Important findings Low doses of most stressors stimulated antioxidative protection and growth of barley shoots, reduced the concentration of O 2 .? and/or intensity of lipid peroxidation. Whereas an impairment of growth and intensification of oxidative stress as well as a reduction in concentration of carotenoids and further increase in activity of antioxidative enzymes were noticed when the intensity of the stressors was increased. In the cases of ozone and UV-B stress, the effects of oxidative stress on plant growth was mitigated by strong antioxidative protection—highly increased catalase (CAT) and superoxide dismutase (SOD) activities, respectively. In the cases of drought and Cu, relatively strong oxidative stress was the major cause of plant growth depression. Additionally, mitigation of oxidative stress due to increased SOD activity was likely to be one of the main causes of growth stimulation induced by low doses of UV-B, Cd and Cu stress. Possible reasons for O 3 -induced growth stimulation were increased CAT activity and concentration of carotenoids. Generalizing the effects of different stressors, the contribution of non-specific oxidative stress on plant growth was stronger compared with stressor-specific action mechanisms: oxidative stress determined 42% of the changes in plants' dry biomass, whereas the contribution of stressor-specific mechanisms accounted for 35% of variability in barley growth.     

Biological functions as affected by summer season-related multiple environmental stressors (heat,nutritional and walking stress) in Malpura rams under semi-arid tropical environment

The study was conducted with the primary objective to establish the impact of simultaneously imposed multiple stressors (thermal, nutritional and walking) on various biological functions in Malpura rams. The study was conducted for a period of 45 days. Twenty adult Malpura rams (average BW 44.9 Kg) were used in the present study. The rams were divided into two groups, CON (n = 10; Control) and MS (n = 10; multiple stressors). Both body weight (p < 0.05) and body condition scoring (p < 0.01) were lower in MS compared with CON rams. All the scrotal measurements reduced significantly (p < 0.01) in MS rams. All the testicular measurements also reduced significantly (p < 0.01) in MS as compared to CON rams. The seminal attributes, individual motility (p < 0.05), rapid motility (p < 0.05) and curvilinear velocity (p < 0.05) were significantly reduced in CON rams. However, slowness (p < 0.05), linearity (p < 0.05) and straightness (p < 0.05) parameters significantly increased in MS as compared to CON rams. In addition, plasma testosterone concentration was lower (p < 0.05) in MS rams. The study established the impact of multiple stressors on growth and reproductive performance of Malpura rams. Further, the results revealed that the only semen quality was affected by multiple stressors, but the semen production remained intact between the groups, indicating the extreme adaptive capability of Malpura rams to hot semi-arid tropical environment.     

Results from measurements of nitrogen and energy metabolism in adaptive different cattle

In experiments with Galloway (G), Highland (H) and Black‐White Dairy (B) cattle no significant differences between the breeds were measured in the energy and nutrient digestibility and energy metabolizability of rations with high variation in the nutrient composition. In H and B cattle no differences existed in digestibility in relation to the environmental temperature (30, 18 and 3 °C). Lowering the environmental temperature from 18 to 12 and 4–6 °C resulted in no changes of heat production in G and H but in B heat production increased about 6% and 20% respectively.     

Describing and understanding behavioral responses to multiple stressors and multiple stimuli

Understanding the effects of environmental change on natural ecosystems is a major challenge, particularly when multiple stressors interact to produce unexpected “ecological surprises” in the form of complex, nonadditive effects that can amplify or reduce their individual effects. Animals often respond behaviorally to environmental change, and multiple stressors can have both population‐level and community‐level effects. However, the individual, not combined, effects of stressors on animal behavior are commonly studied. There is a need to understand how animals respond to the more complex combinations of stressors that occur in nature, which requires a systematic and rigorous approach to quantify the various potential behavioral responses to the independent and interactive effects of stressors. We illustrate a robust, systematic approach for understanding behavioral responses to multiple stressors based on integrating schemes used to quantitatively classify interactions in multiple‐stressor research and to qualitatively view interactions between multiple stimuli in behavioral experiments. We introduce and unify the two frameworks, highlighting their conceptual and methodological similarities, and use four case studies to demonstrate how this unification could improve our interpretation of interactions in behavioral experiments and guide efforts to manage the effects of multiple stressors. Our unified approach: (1) provides behavioral ecologists with a more rigorous and systematic way to quantify how animals respond to interactions between multiple stimuli, an important theoretical advance, (2) helps us better understand how animals behave when they encounter multiple, potentially interacting stressors, and (3) contributes more generally to the understanding of “ecological surprises” in multiple stressors research.     

Association analysis of HSP70A1A haplotypes with heat tolerance in Chinese Holstein cattle

Single-nucleotide polymorphisms (SNPs) in the coding and untranslated regions of heat shock 70 kDa protein 1A (HSP70A1A), an inducible molecular chaperone that is responsible for cellular protection against heat stress, have been reported as being associated with heat tolerance. A fragment of the HSP70A1A gene was amplified in Chinese Holstein cattle and eight novel mutations were found. We performed comprehensive linkage disequilibrium (LD) and haplotype analyses of the eight SNPs of the HSP70A1A gene and examined their involvement in heat resistance in 600 Chinese Holstein cattle. Our results revealed the presence of significant differences between individuals carrying haplotype 1 and those without haplotype 1 for most of the heat-tolerance traits. Haplotype 1 increased the risk of heat stress; however, association analysis of its combination with haplotype 2 showed the lowest rectal temperature and red blood cell K⁺ level, moderate respiratory rate, and the highest red blood cell NKA level, suggesting a heterozygote advantage in the penetration of the phenotype. Protein expression levels in white blood cells among haplotype combinations further confirmed the hypothesis that heterozygotes for haplotypes 1 and 2 are more sensitive to heat stress. We presume that these mutations may be useful in the future as molecular genetic markers to assist selection for heat tolerance in cattle.     

The role of solar and UV radiation in environmental stress assessment

The purpose of this study was to evaluate the role of ultraviolet (UV) radiation in environmental assessment. Analysis of two meteorological databases, from Israel and New Zealand, used in this study revealed that the UV radiation component in the environmental stress assessment was not significant. However, because of the health hazards, an independent UV index should be implemented and used for preventing acute and chronic injuries. A prediction of UV radiation from solar radiation measurement would be a great benefit for such an index.     

Redefining physiological responses of moose (Alces alces) to warm environmental conditions

We tested the concept that moose (Alces alces) begin to show signs of thermal stress at ambient air temperatures as low as 14 °C. We determined the response of Alaskan female moose to environmental conditions from May through September by measuring core body temperature, heart rate, respiration rate, rate of heat loss from exhaled air, skin temperature, and fecal and salivary glucocorticoids. Seasonal and daily patterns in moose body temperature did not passively follow the same patterns as environmental variables. We used large changes in body temperature (≥1.25 °C in 24hr) to indicate days of physiological tolerance to thermal stressors. Thermal tolerance correlated with high ambient air temperatures from the prior day and with seasonal peaks in solar radiation (June), ambient air temperature and vapor pressure (July). At midday (12:00hr), moose exhibited daily minima of body temperature, heart rate and skin temperature (difference between the ear artery and pinna) that coincided with daily maxima in respiration rate and the rate of heat lost through respiration. Salivary cortisol measured in moose during the morning was positively related to the change in air temperature during the hour prior to sample collection, while fecal glucocorticoid levels increased with increasing solar radiation during the prior day. Our results suggest that free-ranging moose do not have a static threshold of ambient air temperature at which they become heat stressed during the warm season. In early summer, body temperature of moose is influenced by the interaction of ambient temperature during the prior day with the seasonal peak of solar radiation. In late summer, moose body temperature is influenced by the interaction between ambient temperature and vapor pressure. Thermal tolerance of moose depends on the intensity and duration of daily weather parameters and the ability of the animal to use physiological and behavioral responses to dissipate heat loads.     

The three-spined stickleback as an environmental sentinel: effects of stressors on whole-body physiological indices

Indicators of a generalized stress response (changes in cortisol, glucose, RNA: DNA ratio and total protein) when measured in whole-body preparations of individual three-spined sticklebacks Gasterosteus aculeatus displayed significant alterations in response to acute (hours) and chronic (days) disturbances and food withdrawal. In addition, changes in alkali-labile phosphorous, a specific biomarker of exposure to oestrogenic contaminants, could be detected in whole-body preparations of oestrogen-exposed three-spined sticklebacks confirming that the measurement of biomarkers normally assessed in a specific tissue can be equally possible in whole fish.     

Distinct physiological responses of two rice cultivars subjected to iron toxicity under field conditions

Iron toxicity is recognised as the most widely distributed nutritional disorder in lowland and irrigated rice, derived from the excessive amounts of ferrous ions generated by the reduction of iron oxides in flooded soils. Rice cultivars with variable degrees of tolerance to iron toxicity have been developed, and cultural practices such as water management and fertilisation can be used to reduce its negative impact. However, because of the complex nature of iron toxicity, few physiological data concerning tolerance mechanisms to excess iron in field conditions are available. To analyse the physiological responses of rice to iron excess in field conditions, two rice cultivars with distinct tolerance to iron toxicity [BR‐IRGA 409 (susceptible) and IRGA 420 (tolerant)] were grown in two areas, with a well‐established history of iron toxicity (in Camaquã, RS, Brazil) and without iron toxicity (in Cachoeirinha, RS, Brazil). Plants from the susceptible cultivar grown in the iron‐toxic site showed lower levels of chlorophylls and soluble proteins (together with higher carbonyl levels) indicating photooxidative and oxidative damage. The toxic effects observed were because of the accumulation of high levels of iron and not because of any indirectly induced shoot deficiency of other nutrients. Higher activities of antioxidative enzymes were also observed in leaves of plants from the susceptible cultivar only in the iron‐toxic site, probably as a result of oxidative stress rather than because of specific involvement in a tolerance mechanism. There was no difference between cultivars in iron accumulation in the symplastic and apoplastic space of leaves, with both cultivars accumulating 85–90% of total leaf iron in the symplast. However, susceptible plants accumulated higher levels of iron in low‐molecular‐mass fractions than tolerant plants. The accumulation of iron in the low‐molecular‐mass fraction probably has a direct influence on iron toxicity, and the adaptive strategy of tolerant plants may rely on their capacity to buffer the iron amounts present in the low mass fraction, a new parameter to be considered when evaluating tolerance to iron excess in field‐cultivated rice plants.     

Repeated thermal conditioning during the neonatal period affects behavioral and physiological responses to acute heat stress in chicks

ObjectiveThe aim of the present study was to investigate the effects of repeated thermal conditioning (RTC) at an early age on physiological and behavioral responses in chicks.MethodsBirds were assigned to one of the four treatments in which the RTC was exposure to 40 °C for 15 min daily. The treatments were 1) no thermal conditioning (control); 2) early exposure group (EE; RTC from 2 to 4 days of age); 3) later exposure group (LE; RTC from 5 to 7 days of age); or 4) both early and later exposure (BE; RTC from 2 to 7 days of age). All groups of chicks were challenged with high ambient temperature (40 °C for 15 min) at two weeks of age.ResultsDuring heat challenge, initiation times of dissipation behaviors (panting and wing-drooping) were measured. Rectal temperature and respiration rate were measured after and before heat challenge. Hypothalamic samples and blood were collected at the end of heat challenges. Initiation times of dissipation behaviors and rectal temperature were not affected by the treatments. Increases in respiration rate in response to heat challenge were suppressed by early RTC treatment. There was no clear pattern of glucose levels in relation to thermal conditioning, whereas plasma corticosterone levels were decreased by early treatment (EE and BE groups). Hypothalamic thyrotropin releasing hormone gene expression was suppressed by early and later thermal conditioning and suppressed further by both early and later exposure. Neuropeptide Y gene expression in the BE group was lower than in the other groups, with a similar trend for corticotropin releasing hormone expression.ConclusionOur results suggest that the effect of repeated thermal conditioning on the central thermoregulatory system depends on the number of times that chicks experienced conditioning. In addition, repeated thermal conditioning has greater effects on the acquisition of thermotolerance when conditioning occurs in chicks of two to four days of age in comparison with chicks of five to seven days of age.     

Climate warming and agricultural stressors interact to determine stream periphyton community composition

Lack of knowledge about how the various drivers of global climate change will interact with multiple stressors already affecting ecosystems is the basis for great uncertainty in projections of future biological change. Despite concerns about the impacts of changes in land use, eutrophication and climate warming in running waters, the interactive effects of these stressors on stream periphyton are largely unknown. We manipulated nutrients (simulating agricultural runoff), deposited fine sediment (simulating agricultural erosion) (two levels each) and water temperature (eight levels, 0–6 °C above ambient) simultaneously in 128 streamside mesocosms. Our aim was to determine the individual and combined effects of the three stressors on the algal and bacterial constituents of the periphyton. All three stressors had pervasive individual effects, but in combination frequently produced synergisms at the population level and antagonisms at the community level. Depending on sediment and nutrient conditions, the effect of raised temperature frequently produced contrasting response patterns, with stronger or opposing effects when one or both stressors were augmented. Thus, warming tended to interact negatively with nutrients or sediment by weakening or reversing positive temperature effects or strengthening negative ones. Five classes of algal growth morphology were all affected in complex ways by raised temperature, suggesting that these measures may prove unreliable in biomonitoring programs in a warming climate. The evenness and diversity of the most abundant bacterial taxa increased with temperature at ambient but not with enriched nutrient levels, indicating that warming coupled with nutrient limitation may lead to a more evenly distributed bacterial community as temperatures rise. Freshwater management decisions that seek to avoid or mitigate the negative effects of agricultural land use on stream periphyton should be informed by knowledge of the interactive effects of multiple stressors in a warming climate.