High Nighttime Temperatures Research Articles

СКРИНИНГ ОБРАЗЦОВ МЕСТНЫХ ЯЧМЕНЕЙ НА ЧУВСТВИТЕЛЬНОСТЬ К ФОТОПЕРИОДУ

Background. Earliness of barley is an important trait for increasing the yield of this crop, especially in regions where abiotic factors are determinant. This work is dedicated to the identification of the eam8 gene in local barley accessions from the VIR collection. It would be possible to find sources of weak sensitivity to photoperiod to be used in breeding practice. Materials and methods . In Pushkin and Pavlovsk Laboratories of the N. I. Vavilov All-Russian Institute of Plant Genetic Resources (VIR, St. Petersburg), 1460 local barley accessions from 26 countries with a short photoperiod of vegetation were studied. These countries are included in five centers of barley diversity: the Abyssinian, the Near East, the Mediterranean, the Central Asian, and the New World. The experiments were performed in the THERMO 818 (3751) climate chamber. Barley seeds were planted in cuvettes with moistened cotton wool. After the emergence of shoots, they were placed in the climate chamber where the plants remained until the stage of the second leaf with the 10-hour photoperiod and the temperature regime of a low daytime (+8°C) and high nighttime (+25°C) temperatures. Yellow color of a plantlet was the marker for the expression of the eam8 gene. Two varieties were used as references: 'Mari Svalofs' (k-19354; var. nutans Schubl.; Genotype eam8eam8) insensitive to photoperiod, and 'Belogorsky' (k-22089; var. pallidum Ser., var. ricotense Regel; Genotype Eam8Eam8) responding to a short day. Results and conclusions . Phenotypic screening of barley samples from 26 countries with a short photoperiod resulted in identification of 1379 forms with the Eam8Eam8 genotype (sensitive to a short day), 44 accessions with the eam8eam8 genotype (insensitive to a short photoperiod), and 37 heterogeneous accessions. Local barleys from Dagestan demonstrated the highest occurrence of forms with the eam8 gene (15.9%). The Near East and Central Asian centers of barley diversity were notable for the occurrence of local accessions with the recessive allele of the Eam8 gene. Accessions with the eam8eam8 genotype and heterogeneous forms can serve as sources of earliness in regions with short-light days. In order to include such sources in commercial barley cultivar breeding programs, they should be searched for in countries with a mountainous landscape and a short photoperiod.

High day- and night-time temperatures affect grain growth dynamics in contrasting rice genotypes.

Rice grain yield and quality are predicted to be highly vulnerable to global warming. Five genotypes including heat-tolerant and susceptible checks, a heat-tolerant near-isogenic line and two hybrids were exposed to control (31 °C/23 °C, day/night), high night-time temperature (HNT; 31 °C/30 °C), high day-time temperature (HDT; 38 °C/23 °C) and high day- and night-time temperature (HNDT; 38 °C/30 °C) treatments for 20 consecutive days during the grain-filling stage. Grain-filling dynamics, starch metabolism enzymes, temporal starch accumulation patterns and the process of chalk formation were quantified. Compensation between the rate and duration of grain filling minimized the impact of HNT, but irreversible impacts on seed-set, grain filling and ultimately grain weight were recorded with HDT and HNDT. Scanning electron microscopy demonstrated irregular and smaller starch granule formation affecting amyloplast build-up with HDT and HNDT, while a quicker but normal amylopast build-up was recorded with HNT. Our findings revealed temporal variation in the starch metabolism enzymes in all three stress treatments. Changes in the enzymatic activity did not derail starch accumulation under HNT when assimilates were sufficiently available, while both sucrose supply and the conversion of sucrose into starch were affected by HDT and HNDT. The findings indicate differential mechanisms leading to high day and high night temperature stress-induced loss in yield and quality. Additional genetic improvement is needed to sustain rice productivity and quality under future climates.

The Effects of Night-time Temperatures on Physiological and Biochemical Traits in Rice

High nighttime temperatures impair rice yield. Additionally, heat stress periods have increased during the last years in the rice areas of the tropics. The aim of this study was to physiologically characterize six genotypes of rice (a commercial cultivar (ʻF60ʼ) and five selected lines (ʻIR 1561ʼ, ʻFLO 2764ʼ, ʻLV447-1ʼ, ʻCT19021ʼ, and ʻLV1401ʼ) subjected to two nighttime temperatures (24 and 30 °C), based on different physiological traits. When the collar formed on leaf 6 of the main stem, one group of six plants in each genotype was subjected to 30 °C from 18:00 to 24:00 hours for eight days, while the other group remained at 24 °C. Differences were found in the interaction between genotype and nighttime temperatures, where a high night temperature reduced leaf photosynthesis by approximately 50% in all genotypes compared to the controls (20 µmol vs. 10 µmol CO2 m-2 s-1, respectively). In general, higher plant respiration was also observed in almost all genotypes when the plants were exposed to 30 °C. However, rice plants of the genotype ʻF60ʼ showed a constant respiration under two different night temperatures. A high nighttime temperature increased the electrolyte leakage and malondialdehyde content only in the ʻLV1401ʼ plants. Plant growth and Fv/Fm ratio were separately conditioned by the night temperature or the genotype factor. A lower total plant dry weight was found at 30 °C (620.36 mg) than in rice plants exposed to 24 °C (254.16 mg). The Fv/Fm ratio was slightly diminished at a high nighttime temperature. These results suggest that physiological variables, such as leaf photosynthesis, plant respiration, malondialdehyde content and leaf photosynthetic pigments, can be considered markers for characterizing tolerant genotypes in earlier growth phases during plant breeding programs.

Assessing Weather-Yield Relationships in Rice at Local Scale Using Data Mining Approaches.

Seasonal and inter-annual climate variability have become important issues for farmers, and climate change has been shown to increase them. Simultaneously farmers and agricultural organizations are increasingly collecting observational data about in situ crop performance. Agriculture thus needs new tools to cope with changing environmental conditions and to take advantage of these data. Data mining techniques make it possible to extract embedded knowledge associated with farmer experiences from these large observational datasets in order to identify best practices for adapting to climate variability. We introduce new approaches through a case study on irrigated and rainfed rice in Colombia. Preexisting observational datasets of commercial harvest records were combined with in situ daily weather series. Using Conditional Inference Forest and clustering techniques, we assessed the relationships between climatic factors and crop yield variability at the local scale for specific cultivars and growth stages. The analysis showed clear relationships in the various location-cultivar combinations, with climatic factors explaining 6 to 46% of spatiotemporal variability in yield, and with crop responses to weather being non-linear and cultivar-specific. Climatic factors affected cultivars differently during each stage of development. For instance, one cultivar was affected by high nighttime temperatures in the reproductive stage but responded positively to accumulated solar radiation during the ripening stage. Another was affected by high nighttime temperatures during both the vegetative and reproductive stages. Clustering of the weather patterns corresponding to individual cropping events revealed different groups of weather patterns for irrigated and rainfed systems with contrasting yield levels. Best-suited cultivars were identified for some weather patterns, making weather-site-specific recommendations possible. This study illustrates the potential of data mining for adding value to existing observational data in agriculture by allowing embedded knowledge to be quickly leveraged. It generates site-specific information on cultivar response to climatic factors and supports on-farm management decisions for adaptation to climate variability.

Quantifying source-sink relationships of rice under high night-time temperature combined with two nitrogen levels

High night-time temperature (HNT) disturbs processes of both assimilate production (source) and assimilate accumulation (sink), and as a result substantially reduces yields of cereal crops. There have been reports that increasing nitrogen application can alleviate the negative impact of high-temperature stress on yield in rice (Oryza sativa L.). However, little is known about the interactive effect of HNT and nitrogen (N) supply on rice grain yield and its underlying source-sink relationships. We conducted two field experiments at the International Rice Research Institute in both the dry (DS) and wet (WS) season of 2012, in which three cultivars with contrasting responses to HNT were grown under two levels of night-time temperature and two levels of N application. HNT significantly decreased grain yield of cv. Gharib at both N levels and in both seasons, while grain yield of cv. PSBRc4 was significantly reduced by HNT at the higher N level only. Among the yield components, grain weight was consistently reduced by HNT in all three cultivars across two seasons while spikeletsm−2 and seed-set were affected by HNT during DS and WS, respectively. In most cases, higher N application reduced grain yield and its components. Thus, in our study, increasing the total N fertilizer did not alleviate the adverse effects of HNT on rice yield. Using a novel modelling approach that quantifies source-sink relationships during grain filling, we found that increased nitrogen did not alleviate the negative impact of HNT on source-sink interactions during grain growth across cultivars and seasons. Nevertheless, the model showed that there were significant differences among cultivars in grain filling duration, grain filling rate and total sink size, modulated by their source-sink relationship in response to HNT, suggesting that breeding programs should select for sink-related traits to improve rice tolerance to HNT.

Optimal Harvest Moisture Content for Maximizing Mid‐South Rice Milling Yields and Returns

Rice (Oryza sativa L.) is unique from other major row crops in the United States in that it requires postharvest milling before pricing. As a result, profitability is based on mass yield (paddy yield) and kernel integrity, or head rice yield (HRY). A common dilemma rice producers confront is the selection of a harvest moisture content (HMC) to begin harvesting. Although harvesting with a high HMC can improve HRY, it also increases drying costs at the mill. Conversely, harvesting with a low HMC can save in drying costs but decreases HRY due to fissuring. This study determines the optimal harvest HMC that maximizes net value, accounting for both HRY and drying costs per megagram of rice, considering genetic differences across cultivars and the effects of exposure to nighttime heat stress during the growing season, which is known to reduce overall yield and quality of milling. The effects of imbedded genetic technology and high nighttime temperatures on HRY were estimated via multiple regression analysis using 522 paddy/milling yield observations across the Mississippi and Arkansas Deltas as well as corresponding location‐specific weather data from 2003–2013. For the nine most commonly produced cultivars in Arkansas and Mississippi in 2013, the optimal HMC for maximizing HRY ranged from 17 to 22%, and the optimal HMC for maximizing net value ranged from 16 to 20%. The results show that, on average, conventional cultivars experienced larger decreases than their hybrid counterparts in net value per hectare when producers deviated from the optimal HMC for maximizing net value.

Climate Influences on Yield, Berry and Wine Quality in Monastrell Wine Grapes in a Warm Winegrowing Region (Jumilla Area, SE Spain)

The effects of climatic factors on yield, berry, and wine quality for long-term (7 years) deficit irrigated (DI) Monastrell wine grapes under the semiarid conditions of SE Spain were analyzed. The relationships between climatic variables and the yield, berry (QIoverallberry), and wine quality (QIwine) novel indices confirmed that the most important climatic factors were rainfall, temperature, and radiation. Climate was more influential in determining yield, berry, and wine composition in some important physiological periods, such as early season (budburst-fruit set) and ripening (veraison-harvest). Greater rainfall during dormancy and early season was related with greater yield, QIoverallberry, and QIwine; in contrast, rainfall late in the season, during the veraison-harvest period, was related negatively with berry and wine quality. Similarly, solar radiation impacted positively during dormancy and early season and negatively during late season. In addition, greater Tªmax during the dormancy, early season (budburst-fruit set) and veraison-harvest periods influenced negatively the QIoverallberry and QIwine, while greater Tªmax during other periods, such as fruit set-veraison were - in general - positive for berry and wine quality. Besides greater Tªmin (high nighttime temperatures) also exerted a negative influence, reducing QIphenolicberry, although had positive effects in yield, QItechnologicalberry and QIwine. In general, climate had more influence on berry quality than on wine quality.

Increased Temperatures Have Dramatic Effects on Growth and Grain Yield of Three Maize Hybrids

Core Ideas Projected Corn Belt temps by the end of the 21st century increase the rate of phenological development. Temperature increases reduce grain production but not vegetative production. There were differences in corn hybrid response to yield impacts. Rising temperatures under climate change are projected to have negative impacts on crop growth and production. These conclusions are not based on direct observations but on projected model results. A study conducted comparing normal seasonal temperatures (1980–2010) for Ames, IA, to a normal + 4°C environment with the same water vapor deficit evaluated the impacts of temperature on maize (Zea mays L.) development and production. The rate of phenological development increased at higher temperatures; however, the relationship of leaf collar and leaf tip appearance to growing degree days was the same between temperature regimes. There was no effect on total leaf area or vegetative dry matter production, but grain yields decreased from 84 to 100% because of exposure to high nighttime temperatures and disruption of the pollination process as evidenced by the large reduction in kernels per ear. Projected increases in temperature will negatively affect grain production and threaten food security.

The sleep architecture of Australian volunteer firefighters during a multi-day simulated wildfire suppression: Impact of sleep restriction and temperature

Wildland firefighting exposes personnel to combinations of occupational and environmental stressors that include physical activity, heat and sleep restriction. However, the effects of these stressors on sleep have rarely been studied in the laboratory, and direct comparisons to field scenarios remain problematic. The aim of this study was to examine firefighters’ sleep during a three-day, four-night simulated wildfire suppression that included sleep restriction and physical activity circuits representative of firefighting wildfire suppression tasks in varied temperatures. Sixty-one volunteer firefighters (37.5±14.5 years of age, mean±SD) were assigned to one of three conditions: control (n=25; 8h sleep opportunities and 18–20°C), awake (n=25; 4h sleep opportunities and 18–20°C) or awake/hot (n=11; 4h sleep opportunities and 33–35°C during the day and 23–25°C during the night). Results demonstrated that amounts of N1, N2 and R sleep, TST, SOL and WASO declined, whilst sleep efficiency increased significantly in the awake and awake/hot conditions compared to the control condition. Results also demonstrated that SWS sleep remained relatively stable in the awake and awake/hot conditions compared to control values. Most importantly, no significant differences were found for any of the sleep measures between the awake and awake/hot conditions. Thus, working in hot daytime temperatures in combination with sleep restriction during the night did not affect patterns of sleep compared to working in temperate conditions in combination with sleep restriction during the night. However, the effects on sleep of high (>25°C) night-time temperatures with sleep restriction in addition to physical activity remains to be studied.

Grain yield and quality responses of tropical hybrid rice to high night-time temperature

High temperature has a pronounced effect on grain yield and quality in rice. Climate change has increased night temperature more than day temperature in many parts of the world. How rice responds to high night-time temperature (HNT) is largely unknown. This study presents the first effort to assess the response of tropical hybrid rice to HNT. Six commercial tropical hybrid rice cultivars together with a tolerant (N22-aus) and a susceptible (Gharib-indica) genotype were evaluated under control temperature (23°C) and HNT (29°C) starting from panicle initiation until maturity under field conditions at the International Rice Research Institute during the dry (DS) and wet (WS) seasons of 2013. Overall, HNT significantly decreased grain yield of Gharib and all tested hybrids across both seasons, with less average reduction in the DS (13.4%) than in the WS (18.6%). Among the yield components, spikelets m−2 most significantly contributed to yield variation under control and/or HNT during both DS and WS followed by grain weight, while the contribution of seed-set was low and season-specific. Grain quality in most hybrids was also strongly affected by HNT, with decreased head rice yield, increased chalkiness and reduced grain width. Given this vulnerability to HNT, there is an urgent need to explore options for improving the adaptation of rice hybrids to increasingly warmer nights.

A biochar application protects rice pollen from high-temperature stress

The influences of high temperature and fertilization with biochar and phosphorus (P) on the pollen characteristics of two rice cultivars (IR-64 and Huanghuazhan) were examined in controlled growth chambers. Temperature treatments included high daytime temperature (HDT), high nighttime temperature (HNT) and ambient temperature (AT). The fertilization treatments were control, biochar alone, P alone and biochar + P. High temperature severely reduced pollen fertility, anther dehiscence, pollen retention and pollen germination of both rice cultivars, with HNT more destructive than HDT. The Huanghuazhan cultivar performed better than IR-64 under high temperature, with higher pollen fertility, better anther dehiscence and greater pollen retention and germination rates. In both cultivars, the pollen of plants treated with biochar + P were more resistant to heat induced stress. Further studies are needed to test the ability of biochar to ameliorate the effects of different abiotic stresses in rice and other crops.

Atmospheric Feedback of Urban Boundary Layer with Implications for Climate Adaptation.

Atmospheric structure changes in response to the urban form, land use, and the type of land cover (LULC). This interaction controls thermal and air pollutant transport and distribution. The interrelationships among LULC, ambient temperature, and air quality were analyzed and found to be significant in a case study in Cincinnati, Ohio, U.S.A. Within the urban canopy layer (UCL), traffic-origin PM2.5 and black carbon followed Gaussian dispersion in the near road area in the daytime, while higher concentrations, over 1 order of magnitude, were correlated to the lapse rate under nocturnal inversions. In the overlying urban boundary layer (UBL), ambient temperature and PM2.5 variations were correlated among urban-wide locations indicating effective thermal and mass communications. Beyond the spatial correlation, LULC-related local urban heat island effects are noteworthy. The high-density urbanized zone along a narrow highway-following corridor is marked by higher nighttime temperature by ∼1.6 °C with a long-term increase by 2.0 °C/decade, and by a higher PM2.5 concentration, than in the low-density residential LULC. These results indicate that the urban LULC may have contributed to the nocturnal thermal inversion affecting urban air circulation and air quality in UCL and UBL. Such relationships point to the potentials of climate adaptation through urban planning.

Ontogeny and aging of the distal skin temperature rhythm in humans.

In circadian terms, human ontogeny is characterized by the emergence of a daily pattern, from a previous ultradian pattern, for most variables during the first 6 months of life. Circadian aging in humans is characterized by a phase advance, accompanied by rhythm fragmentation and flattening. Despite an expanding body of literature focused on distal skin temperature, little information is available about the ontogeny and practically nothing about age-related changes in this rhythm. Thus, the aim was to evaluate the degree of maturation and aging of the circadian pattern of distal skin temperature to identify those parameters that are modified throughout life and could be used to differentiate subjects according to their age. For this, distal skin temperature was measured in 197 volunteers (55 % women), including babies aged 15 days (30 subjects), 1 month (28 subjects), 3 months (31 subjects), and 6 months (10 subjects); young adults aged 19 years (37 subjects); middle-aged persons aged 46 years (27 subjects); older people aged 72 (34 subjects). Circadian system maturation was associated with an increase in amplitude and a reduction in skin temperature during sleep. During adulthood, women showed a more robust pattern (lower fragmentation, and higher night-time temperature, amplitude, circadian function index, and first harmonic relative power); however, these differences were lost with aging, a period of life that was consistently associated with a phase advance of the rhythm. In summary, distal skin temperature pattern can be used as a robust variable to discern between different ages throughout the life.

Transcriptome changes in rice (Oryza sativa L.) in response to high night temperature stress at the early milky stage.

BackgroundRice yield and quality are adversely affected by high temperatures, especially at night; high nighttime temperatures are more harmful to grain weight than high daytime temperatures. Unfortunately, global temperatures are consistently increasing at an alarming rate and the minimum nighttime temperature has increased three times as much as the corresponding maximum daytime temperature over the past few decades.ResultsWe analyzed the transcriptome profiles for rice grain from heat-tolerant and -sensitive lines in response to high night temperatures at the early milky stage using the Illumina Sequencing method. The analysis results for the sequencing data indicated that 35 transcripts showed different expressions between heat-tolerant and -sensitive rice, and RT-qPCR analyses confirmed the expression patterns of selected transcripts. Functional analysis of the differentially expressed transcripts indicated that 21 genes have functional annotation and their functions are mainly involved in oxidation-reduction (6 genes), metabolic (7 genes), transport (4 genes), transcript regulation (2 genes), defense response (1 gene) and photosynthetic (1 gene) processes. Based on the functional annotation of the differentially expressed genes, the possible process that regulates these differentially expressed transcripts in rice grain responding to high night temperature stress at the early milky stage was further analyzed. This analysis indicated that high night temperature stress disrupts electron transport in the mitochondria, which leads to changes in the concentration of hydrogen ions in the mitochondrial and cellular matrix and influences the activity of enzymes involved in TCA and its secondary metabolism in plant cells.ConclusionsUsing Illumina sequencing technology, the differences between the transcriptomes of heat-tolerant and -sensitive rice lines in response to high night temperature stress at the early milky stage was described here for the first time. The candidate transcripts may provide genetic resources that may be useful in the improvement of heat-tolerant characters of rice. The model proposed here is based on differences in expression and transcription between two rice lines. In addition, the model may support future studies on the molecular mechanisms underlying plant responses to high night temperatures.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1222-0) contains supplementary material, which is available to authorized users.

The effects of different night-time temperatures and cultivation durations on the polyphenolic contents of lettuce: Application of principal component analysis

The present study was conducted to characterize the polyphenolic contents of lettuce leaves grown under different night-time temperatures (4, 12, and 20°C) and cultivation durations (5, 15, and 20days) using high performance liquid chromatography-tandem mass spectrometry (LC/MS/MS). The assay method was validated based on specificity, linearity, accuracy, precision, and the performance limit. The total polyphenolic contents were highest (2462.6mg/kg) after transplantation at a night temperature of 20°C on day 20 and lowest (1132.7mg/kg) at the same temperature on day 5. Quantification and principal component analysis showed that the relative contents of quercetin and kaempferol were markedly higher during the early stage of cultivation (day 5) than those of day 15 and 20, and that night-time temperatures of 12 and 20°C on day 20 were favorable for producing polyphenol-rich lettuce containing caffeic acid. In conclusion, a synergistic effect between high night-time temperatures (12 and 20°C) and cultivation duration (20days) produced lettuce rich in polyphenols compared to that at low temperature (4°C).

High Night Temperatures During the Floral Bud Stage Increase the Abscission of Reproductive Structures in Cotton

AbstractCotton‐producing regions throughout the world often experience high night temperatures (HNTs), affecting flowering and yield in cotton (Gossypium hirsutum). The objective of this study was to quantify the effects of high nighttime temperatures on the physiological and biochemical characteristics of cotton during the floral bud and flowering stages. Growth chamber experiments were conducted in 2011–2012 and treatments included a control (day/night temperature of 32/24 °C) and two HNT treatments (32/29 °C from 8:00 pm to 12:00 am) for 3 weeks from the beginning of each phenological stage, i.e., first floral bud (B1) and first flower (F1). The results indicated that increased night temperatures (NTs) during the floral bud and flowering stages increased the rate of flower production per plant. However, no increase was observed in the final number of reproductive structures because the rate of floral abortion also increased for both treatments compared to the control. Additionally, the increase in night temperature during the floral bud stage reduced the sucrose content in the flower, resulting in decreased pollen viability and premature abortion of reproductive structures while the onset of flowering period was also delayed and lower accumulation of reproductive dry matter was observed. HNTs during the flowering stage reduced the number of seeds per locule and the number of seeds per boll. In general, higher than optimum NTs affected sucrose metabolism of the cotton flower and consequently its pollen viability. As a result the flowering period was delayed and a reduction in reproductive dry matter accumulation was observed due to premature abortion of reproductive structures. Finally, cotton is more sensitive to HNT at floral bud stage and this finding may be important to adjust cotton planting date, management and breeding.

High Day‐ or Nighttime Temperature Alters Leaf Assimilation, Reproductive Success, and Phosphatidic Acid of Pollen Grain in Soybean [Glycine max (L.) Merr.

ABSTRACTSoybean [Glycine max (L.) Merr.] is often exposed to high daytime and nighttime temperatures during critical growth stages. Threshold mean daily temperature for photosynthesis, respiration, and reproductive process in soybean is ≥26°C. In future, the magnitude of increase in nighttime temperatures will be greater than in daytime temperatures. The objectives were to determine effects of high daytime or nighttime temperatures on (i) leaf photosynthetic and respiration rates; (ii) pollen germination, pod‐set, and seed weight; and (iii) pollen phospholipids profile. Soybean plants were exposed to high daytime temperature (39/20°C), high nighttime temperatures (30/23°C, 30/26°C, and 30/29°C), or optimum temperature (30/20°C) for 10 d at flowering stage. High daytime temperature (39/20°C) or nighttime temperatures (30/29°C) increased leaf respiration rates and decreased leaf chlorophyll content, photosynthetic rate, photochemical quenching, and electron transport rate compared to optimum temperature. Likewise, high temperature decreased pollen viability and germination. Lower pollen germination at high temperature may be due to decreased levels of saturated phospholipids and phosphatidic acid in pollen grains compared with optimum temperature. Pod‐set and seed weight were decreased by high daytime or nighttime temperature. In conclusion, high daytime (39/20°C) or nighttime (30/29°C) temperature decreased leaf photosynthetic rate and pollen germination, leading to lower pod‐set and seed weight.

Thermal tolerance, net CO2 exchange and growth of a tropical tree species, Ficus insipida, cultivated at elevated daytime and nighttime temperatures

Global warming and associated increases in the frequency and amplitude of extreme weather events, such as heat waves, may adversely affect tropical rainforest plants via significantly increased tissue temperatures. In this study, the response to two temperature regimes was assessed in seedlings of the neotropical pioneer tree species, Ficus insipida. Plants were cultivated in growth chambers at strongly elevated daytime temperature (39°C), combined with either close to natural (22°C) or elevated (32°C) nighttime temperatures. Under both growth regimes, the critical temperature for irreversible leaf damage, determined by changes in chlorophyll a fluorescence, was approximately 51°C. This is comparable to values found in F. insipida growing under natural ambient conditions and indicates a limited potential for heat tolerance acclimation of this tropical forest tree species. Yet, under high nighttime temperature, growth was strongly enhanced, accompanied by increased rates of net photosynthetic CO2 uptake and diminished temperature dependence of leaf-level dark respiration, consistent with thermal acclimation of these key physiological parameters.

Response of rice nitrogen physiology to high nighttime temperature during vegetative stage.

The effects of night temperature on plant morphology and nitrogen accumulation were examined in rice (Oryza sativa L.) during vegetative growth. The results showed that the shoot biomass of the plants was greater at 27°C (high nighttime temperature, HNT) than at 22°C (CK). However, the increase in both shoot and root biomasses was not significant under 10 mg N/L. The shoot nitrogen concentrations were 16.1% and 16.7% higher in HNT than in CK under 160 and 40 mg N/L. These results suggest that plant N uptake was enhanced under HNT; however, the positive effect might be limited by the N status of the plants. In addition, leaf area, plant height, root maximum length, root and shoot nitrogen concentrations, soluble leaf protein content, and soluble leaf carbohydrate content were greater in HNT than in CK under 40 and 160 mg N/L, while fresh root volume, root number, and the content of free amino acid in leaf were not significantly different between HNT and CK regardless of nitrogen levels. Moreover, leaf GS activity under HNT was increased at 160 mg N/L compared with that under CK, which might partly explain the positive effect of HNT on soluble protein and carbohydrate content.

Effects of night-time warming on temperate ectotherm reproduction: potential fitness benefits of climate change for side-blotched lizards

Temperate ectotherms, especially those at higher latitudes, are expected to benefit from climate warming, but few data yet exist to verify this prediction. Furthermore, most previous studies on the effects of climate change utilized a model of uniform annual change, which assumes that temperature increases are symmetric on diurnal or seasonal time scales. In this study, we simulated observed trends in the asymmetric alteration of diurnal temperature range by increasing night-time temperatures experienced by female lizards during their ovarian cycle as well as by the resulting eggs during their incubation. We found that higher night-time temperatures during the ovarian cycle increased the probability of reproductive success and decreased the duration of the reproductive cycle, but did not affect embryo stage or size at oviposition, clutch size, egg mass or relative clutch mass. Furthermore, higher incubation temperatures increased hatchling size and decreased incubation period but had no effect on incubation success. Subsequent hatchlings were more likely to survive winter if they hatched earlier, though our sample size of hatchlings was relatively small. These findings indicate that higher night-time temperatures mainly affect rate processes and that certain aspects of life history are less directly temperature dependent. As our findings confirm that climate warming is likely to increase the rate of development as well as advance reproductive phenology, we predict that warmer nights during the breeding season will increase reproductive output as well as subsequent survival in many temperate ectotherms, both of which should have positive fitness effects.