Photoperiod Regimes Research Articles

Alterations of circadian rhythms of thyroid-stimulating hormone, thyroid, adrenal and insulin hormones, and blood glucose profiles following lithium treatment in alternate Light–Dark, constant Light and constant Dark regimens in rats

Lithium, widely used for the treatment of mania, has adverse side effects on circadian rhythms of pineal and testicular hormones. Objective was to examine the role of lithium on circadian rhythms of other hormones and glucose profiles in light–dark (12L:12D), constant light (12L:12L) and constant dark (12D:12D) regimens in rats. Intraperitoneal injection of lithium (2 mEq/kg body wt daily for 15 days) sustained circadian rhythms of T3, T4, thyroid-stimulating hormone (TSH), corticosterone, norepinephrine and epinephrine in light–dark and constant dark but not in constant light. But it abolished circadian rhythms of insulin and blood glucose in all the photoperiodic regimens, except insulin, without changing their pattern in constant dark. Patterns of circadian rhythms of thyroid and TSH, and adrenal hormones remained unchanged after lithium treatment in L–D or D–D, except TSH in L–D. The probable role of photoperiodic cue and lithium on circadian and/or nycthemeral (daily) rhythms of hormones and blood glucose profiles is discussed.

Osteology of the axial and appendicular skeletons of the meagre Argyrosomus regius (Sciaenidae) and early skeletal development at two rearing facilities

Summary The meagre (Argyrosomus regius) is a new species for aquaculture diversification, presenting a high economic value and a high growth rate, reaching 1 kg year )1 . The occurrence of deformities, which generally appear in cultured larvae at early stages, is problematic for aquaculture since they reduce fish fitness and profitability. Knowledge about the stages of skeletal formation is essential to accurately assess deformities in hatchery produced fish. Here, we describe the osteology of the axial skeleton and unpaired fins of the meagre. Based on this data, the osteological development of meagre larvae reared at the IPIMAR and IRTA-SCR, under different rearing conditions, was compared. Although little literature is available on the osteology of teleosts from the same taxonomic group, the skeletal composition of the meagre is comparable to that of other Sciaenidae. All skeletal structures considered appeared at earlier stages in larvae reared at IPIMAR, which presented a more advanced skeletal development in comparison to larvae of comparable length reared at IRTA-SCR that were submitted to lower temperature and light intensity, and reduced photoperiod regimes.

Reproductive and metabolic responses of desert adapted common spiny male mice (Acomys cahirinus) to vasopressin treatment

Sufficient amounts of water and food are important cues for reproduction in an unpredictable environment. We previously demonstrated that increased osmolarity levels, or exogenous vasopressin (VP) treatment halt reproduction of desert adapted golden spiny mice Acomys russatus. In this research we studied gonad regulation by VP and food restriction (FR) in desert adapted common spiny mouse (A. cahirinus) males, kept under two different photoperiod regimes—short (SD—8L:16D) and long (LD—16L:8D) days. Mice were treated with VP, FR, and VP+FR for three weeks. Response was assessed from changes in relative testis mass, serum testosterone levels and mRNA receptor gene expression of VP, aldosterone and leptin in treated groups, compared with their controls. SD-acclimation increased testosterone levels, VP treatment decreased expression of aldosterone mRNA receptor in the testes of SD-acclimated males. FR under SD-conditions resulted in testosterone decrease and elevation of VP- receptor gene expression in testes. Aldosterone receptor mRNA expression was also detected in WAT. These results support the idea that water and food availability in the habitat may be used as signals for activating the reproductive system through direct effects of VP, aldosterone and leptin on the testes or through WAT by indirect effects.

Short-term exposure to continuous light delays sexual maturation and increases growth of Atlantic cod in sea pens

Atlantic cod Gadus morhua L. (initial weight 130 g, final weight 2800 g) was exposed to continuous light at different stages during the production cycle, and the effect on growth performance, age at first maturation, plasma sex steroid levels and flesh quality were investigated. The entire photoperiod experiment was divided into five phases where the fish in each phase were exposed to either natural photoperiod (N, 65°28′) or continuous light (C). Thus, the following five photoperiod combinations were tested: (a) control group (NNNNN), (b) group 2A (NCNNN), (c) group 2B (NNCNN), (d) group 2C (NNNCN) and (e) continuous light group (CCCCC). Short-term exposure to continuous light in the first (group 2A) and second (group 2B) growth phases stimulated growth, as the final mean weights of groups 2A and 2B were 11% and 19% higher than those of the control group (NNNNN). Growth in the control group and group 2C was arrested from January to May in the second year. Continuous light (CCCCC) stimulated growth at the beginning of the trial, but the effect diminished at the end. Reduced male plasma 11-ketotestosterone (11-KT) and female estradiol 17β (E2) levels were found in groups 2A and 2B and continuous light group, as compared with the control group and group 2C at 26 months post hatch, indicating a higher age at first maturation in these groups. The 11-KT and E2 levels increased in May–June in group 2A indicating that first maturation was postponed by 6 months in this group, whereas first maturation was postponed by 1 year in group 2B and in the continuous light group. Photoperiod regime only had minor effects on flesh quality traits of the fish.

Metamorphosis Induces a Light-Dependent Switch in Senegalese Sole (Solea senegalensis) from Diurnal to Nocturnal Behavior

Light plays a key role in the development of biological rhythms in fish. Recent research in Senegal sole has revealed that spawning and hatching rhythms, larval development, and growth performance are strongly influenced by lighting conditions. However, the effect of light on the daily patterns of behavior remains unexplored. Therefore, the aim of this study was to investigate the impact of different photoperiod regimes and white, blue, and red light on the activity rhythms and foraging behavior of Solea senegalensis larvae up to 40 days posthatching (DPH). To this end, eggs were collected immediately after spawning during the night and exposed to continuous white light (LL), continuous darkness (DD), or light-dark (LD) 12L:12D cycles of white (LD(W)), blue (LD(B), λ(peak) = 463 nm), or red light (LD(R), λ(peak) = 685 nm). A filming scenario was designed to video record activity rhythms during day and night times using infrared lights. The results revealed that activity rhythms in LD(B) and LD(W) changed from diurnal to nocturnal on days 9 to 10 DPH, coinciding with the onset of metamorphosis. In LD(R), sole larvae remained nocturnal throughout the experimental period, while under LL and DD, larvae failed to show any rhythm. In addition, larvae exposed to LD(B) and LD(W) had the highest prey capture success rate (LD(B) = 82.6% ± 2.0%; LD(W) = 75.1% ± 1.3%) and attack rate (LD(B) = 54.3% ± 1.9%; LD(W) = 46.9% ± 3.0%) during the light phase (ML) until 9 DPH. During metamorphosis, the attack and capture success rates in these light conditions were higher during the dark phase (MD), when they showed the same nocturnal behavioral pattern as under LD(R) conditions. These results revealed that the development of sole larvae is tightly controlled by light characteristics, underlining the importance of the natural underwater photoenvironment (LD cycles of blue wavelengths) for the normal onset of the rhythmic behavior of fish larvae during early ontogenesis.

Identification of a photolabile period for reducing sexual maturation in juvenile male sea bass (Dicentrarchus labrax) by means of a continuous light regime

The objective of this study was to identify a photolabile period suitable for reducing precocious gonadal maturation in juvenile male sea bass (Dicentrarchus labrax) through the exploration of discrete windows of continuous light (LL), 1–2 months in duration, in late summer-early autumn. Somatic growth, 11-ketotestosterone plasma levels, and the rates of testicular maturation and spermiation were analyzed to evaluate the effect of the applied photoperiodic regimes. Three LL treatments, with duration of 2 months each, were previously screened between the months of August and November. Administration of LL during the October–November period failed to show any differential effects in reducing early maturation, as compared to the simulated natural photoperiod. However, the August–September period was considered to be a likely candidate for photolability. To define this photolabile period, four LL treatments with duration of 1 month were then screened within the same late summer period. Our results demonstrate that the time interval including the month of September is the most sensitive photolabile period in order to reduce precocious gametogenesis in sea bass.

Towards a Characterization of the Locomotor Activity Rhythm of the Supralittoral Isopod Tylos europaeus

Freshly collected samples of Tylos europaeus from Korba beach (northeast of Tunisia) were housed in an environmental cabinet at controlled temperature (18°C ± .5°C) and photoperiod. Locomotor activity was recorded under two photoperiodic regimens by infrared actography every 20 min by multichannel data loggers. One regimen simulated the natural light-dark cycle on the day of collection, whereas the second imposed a state of continuous darkness on all individuals. Under entraining conditions, the animals displayed rhythmic activity, in phase with the period of darkness, whereas in continuous darkness these isopods exhibited a strong endogenous rhythm with circadian and semidiurnal components at mean periods of τ (h:min) = 25:09 ± 01:02 h and τ = 12:32 ± 00:26 h, respectively. Under free-running conditions, this endogenous rhythm showed significant intraspecific variability. (Author correspondence: bohli.dhouha@gmail.com)

Melatonin modulates cytoskeletal organization in the rat brain hippocampus

Melatonin concentration in plasma reaches high levels during the night and synchronizes body rhythms with the photoperiod. Previous evidence obtained in cultured cells suggests that melatonin synchronizes cytoskeletal re-arrangements at nocturnal plasma concentration. In this study, we determined the amount of microtubules and microfilaments in the rat hippocampus as an index of cytoskeletal organization in rats submitted to a photoperiodic regime. Additionally, these parameters were determined in control rats, sham rats, pinealectomized rats, and rats that were pinealectomized and treated with melatonin for 1 week. The results showed an increase in both the amount of microfilaments in the hippocampus of rats sacrificed in the dark phase, and in melatonin levels. In addition, a decrease in both microfilament and microtubule amounts occurred in pinealectomized rats. In contrast, melatonin treatment partially reestablished actin and tubulin proportions organized in microfilaments and microtubules, respectively. The results indicate that actin organization in microfilaments was associated with both the photoperiod and with melatonin levels. Together, the data support that cytoskeletal organization is regulated rhythmically by melatonin in synchrony with the photoperiod.

Photoperiod has a stronger impact than irradiance on the source–sink relationships in the sink-limited species Erythronium americanum

Under sink-limited conditions, source activity is modulated to remain in balance with the use of carbohydrates by the sink, but this feedback control has been studied in only a few systems so far. Sink and source activities were investigated throughout the season. Plants were subjected to two photoperiod regimes combined with two irradiance levels to produce three different daily amounts of photons. Net photosynthetic rate and the photochemical efficiency of photosynthesis were initially higher under a long photoperiod, but decreased early in the growth season, whereas they remained fairly constant until a few days before leaf senescence under a short photoperiod. The rates of starch and biomass accumulation in the bulb were also faster under a long photoperiod at the beginning of the season but reached similar levels under both short and long photoperiods later on. Response to photoperiod cannot be explained by changes in daily amounts of photons, as none of the variables reported were affected by instantaneous or daily irradiance. It appears that the total amount of carbohydrate synthesized under a long photoperiod was in excess compared to the ability of the sink to store or use them, inducing a feedback inhibition of net photosynthetic rate to restore the source–sink balance.

A Simple System for Promoting Flowering of Upland Switchgrass in the Greenhouse

ABSTRACTThe transition from vegetative to reproductive development in switchgrass (Panicum virgatum L.) has been described as a photoperiod‐mediated process. With its extensive native range, photoperiod response varies widely within the species. To synchronize flowering among cultivars of distinct origin, disparities in light‐driven developmental responses often require breeders to develop elaborate photoperiod regimens. The objective of this research was to identify a simple photoperiod treatment that could be used to evoke sexual reproductive development for three upland cultivars of switchgrass: Cave‐In‐Rock (origin 37°N), Sunburst (origin 42°N), and Dacotah (origin 46°N). To evaluate photoperiod sensitivity, switchgrass clones were grown in the greenhouse under various local natural ambient photoperiods, as well as under a 24‐h low‐irradiance daylight extension. Despite previously being described as a short‐day plant, these upland cultivars of switchgrass were induced to flower under 24‐h low‐irradiance daylight‐extended photoperiod. This daylight extension method was valid for use in addition to any ambient photoperiod. These results identified a simple system that used inexpensive equipment (common fluorescent bulbs) and required no alternating light and dark periods to promote panicle production in switchgrass. This system will be useful for improving seed yield components, via controlled pollination in the greenhouse, most especially when the ambient photoperiods are not favorable for floral induction.

Photoperiodicity and increasing salinity as environmental cues for reproduction in desert adapted rodents

Understanding the ways environmental signals, regulate reproduction and reproductive behavior of desert adapted rodents is a major gap in our knowledge. In this study, we assessed the roles of photoperiod and diet salinity, as signals for reproduction. We challenged desert adapted common spiny mice, Acomys cahirinus, males and females with osmotic stress, by gradually increasing salinity in their water source — from 0.9% to 5% NaCl under short and long days (SD and LD, respectively). Photoperiodicity affected testosterone levels, as under LD-acclimation, levels were significantly (p < 0.05) higher than under SD-acclimation. Salinity treatment (ST) significantly reduced SD-acclimated male body mass (W b) and testis mass (p < 0.005; normalized to W b). ST-LD-females significantly (p < 0.005) decreased progesterone levels and the numbers of estrous cycles. A reduction in white adipose tissue (WAT) to an undetectable level was noted in ST-mice of both sexes under both photoperiod regimes. Receptors for vasopressin (VP) and aldosterone were revealed on testes of all male groups and on WAT in control groups. Our results suggest that photoperiod serves as an initial signal while water availability, expressed by increased salinity in the water source, is an ultimate cue for regulation of reproduction, in both sexes of desert-adapted A. cahirinus. We assume that environmental changes also affect behavior, as water seeking behavior by selecting food items, or locomotor activity may change in extreme environment, and thus indirectly affect reproduction and reproductive behavior. The existence of VP and aldosterone receptors in the gonads and WAT suggests the involvement of osmoregulatory hormones in reproductive control of desert adapted rodents.

A new laboratory radio frequency identification (RFID) system for behavioural tracking of marine organisms.

Radio frequency identification (RFID) devices are currently used to quantify several traits of animal behaviour with potential applications for the study of marine organisms. To date, behavioural studies with marine organisms are rare because of the technical difficulty of propagating radio waves within the saltwater medium. We present a novel RFID tracking system to study the burrowing behaviour of a valuable fishery resource, the Norway lobster (Nephrops norvegicus L.). The system consists of a network of six controllers, each handling a group of seven antennas. That network was placed below a microcosm tank that recreated important features typical of Nephrops’ grounds, such as the presence of multiple burrows. The animals carried a passive transponder attached to their telson, operating at 13.56 MHz. The tracking system was implemented to concurrently report the behaviour of up to three individuals, in terms of their travelled distances in a specified unit of time and their preferential positioning within the antenna network. To do so, the controllers worked in parallel to send the antenna data to a computer via a USB connection. The tracking accuracy of the system was evaluated by concurrently recording the animals’ behaviour with automated video imaging. During the two experiments, each lasting approximately one week, two different groups of three animals each showed a variable burrow occupancy and a nocturnal displacement under a standard photoperiod regime (12 h light:12 h dark), measured using the RFID method. Similar results were obtained with the video imaging. Our implemented RFID system was therefore capable of efficiently tracking the tested organisms and has a good potential for use on a wide variety of other marine organisms of commercial, aquaculture, and ecological interest.

Seasonality Directs Contrasting Food Collection Behavior and Nutrient Regulation Strategies in Ants

Long-lived animals, including social insects, often display seasonal shifts in foraging behavior. Foraging is ultimately a nutrient consumption exercise, but the effect of seasonality per se on changes in foraging behavior, particularly as it relates to nutrient regulation, is poorly understood. Here, we show that field-collected fire ant colonies, returned to the laboratory and maintained under identical photoperiod, temperature, and humidity regimes, and presented with experimental foods that had different protein (p) to carbohydrate (c) ratios, practice summer- and fall-specific foraging behaviors with respect to protein-carbohydrate regulation. Summer colonies increased the amount of food collected as the p:c ratio of their food became increasingly imbalanced, but fall colonies collected similar amounts of food regardless of the p:c ratio of their food. Choice experiments revealed that feeding was non-random, and that both fall and summer ants preferred carbohydrate-biased food. However, ants rarely ate all the food they collected, and their cached or discarded food always contained little carbohydrate relative to protein. From a nutrient regulation strategy, ants consumed most of the carbohydrate they collected, but regulated protein consumption to a similar level, regardless of season. We suggest that varied seasonal food collection behaviors and nutrient regulation strategies may be an adaptation that allows long-lived animals to meet current and future nutrient demands when nutrient-rich foods are abundant (e.g. spring and summer), and to conserve energy and be metabolically more efficient when nutritionally balanced foods are less abundant.

Quantitative genetic analysis of flowering time, leaf number and photoperiod sensitivity in maize (Zea mays L.)

Photoperiod sensitivity is a major difficulty of broadening the resources of breeding germplasms and widening the planting area of varieties in maize. The objective of this study was to dissect the quantitative genetic control of days to pollen shed (DPS), days to silking (DS), anthesis-silking interval (ASI), LNB (the leaf number below the top ear), LN (the total leaf number), and photoperiod sensitivity index (PSIs) of these traits into the main-effect quantitative trait loci (QTL) in an F2 population consisting of 232 F2:3lines from the cross between HZ32 (low sensitive to photoperiod) and Huangzao4 (high sensitive to photoperiod). DPS, DS, LNB and LN of the F2:3 families and parents were investigated in two locations, Beijing (with a longer photoperiod regime, east longitude 117, northern latitude 41) and Wuhan (with a shorter photoperiod regime, east longitude 113, northern latitude 29) in 2007. Further QTL analysis resolved the genetic components of DPS, DS, ASI, LNB and LN into the main-effect QTLs and gene × environment interactions. A total of fifty-nine QTLs for all PS related traits were found in the two photoperiod environments, twenty-two QTLs for PSIs and twenty-two QTLs for QTL × environment were included, respectively. Some important genes associated with photoperiod response and flowering time are found in the regions. The known QTLs and the implications of the results for maize breeding have been discussed. Key words: Maize (Zea mays), photoperiod sensitivity, quantitative trait loci.

Effects of constant and changing temperature conditions on diapause induction inHelicoverpa armigera(Lepidoptera: Noctuidae)

The effects of photoperiod and temperature on the induction and termination of facultative pupal diapause in Helicoverpa armigera (Lepidoptera: Noctuidae) were investigated under laboratory conditions. Exposing H. armigera larvae to both constant and fluctuating temperature regimes with a mean of 25°C and 20°C resulted in a type-III photoperiodic response curve of a short-long day insect. The long-day critical daylengths for diapause induction were ten hours and 12 hours at the constant temperatures of 25°C and 20°C, respectively. Higher incidences of diapause and higher values both for the longer and the shorter critical photoperiods for diapause induction were observed at fluctuating regimes compared with the corresponding constant ones. At alternating temperatures, the incidence of diapause ranged from 4.2% to 33.3% and was determined by the temperature amplitude of the thermoperiod and by the interaction of cryophase or thermophase with the photoperiod. Helicoverpa armigera larvae seem to respond to photoperiodic stimuli at temperatures >15°C and <30°C; all insects entered diapause at a constant temperature of 15°C, whereas none did so at a constant temperature of 30°C under all the photoperiodic regimes examined. Although chilling was not a prerequisite for diapause termination, exposure of diapausing pupae to chilling conditions significantly accelerated diapause development and the time of adult emergence. Therefore, temperature may be the primary factor controlling the termination of diapause in H. armigera.

The male effect stimulus positively influences luteinising hormone secretion in ovariectomised Criollo goats irrespective of a controlled photoperiodic regime

Present study evaluated the presence of a sexually active male buck upon the influence of an estradiol implant in ovariectomised (OVX) goats exposed to a 6-month-long controlled photoperiod in a range of 13.4–10.6 light-hours per day. Mexican-native (Criollo) goats (n=20) were randomly assigned into 2 groups: (1) goats exposed to a sexually active male buck (n=10); (2) goats not exposed to a male buck (n=10). Each experimental group of goats included ovariectomised goats (OVX, n=5), and ovariectomised and estradiol-implanted goats (OVX + E2, n=5). Blood samples were taken from OVX and OVX + E2 goats, every four weeks, during 6 h at 15 min intervals (i.e., 24 samples/day). Frequency, amplitude, and concentration of luteinising hormone (LH) were determined. While the OVX + E2 goats depicted an increased LH pulse frequency (2.0±0.5 vs. 0.7±0.1), the presence of a sexually active male increased frequency, amplitude and concentration of LH in OVX goats compared to goats not exposed to males (frequency: 3.2±0.4 vs. 0.7±0.1 pulses/6 h; amplitude: 1.6±0.1 vs. 0.8±0.3 ng/mL; concentration: 5.3±0.6 vs. 2.0±0.9 ng/mL) (P<0.001). In conclusion, the presence of a sexually active male increase LH pulse frequency, amplitude and concentration in OVX-goats (Criollo), irrespective of a controlled photoperiodic regime.

The male effect stimulus positively increased the ovarian and reproductive seasonality in Criollo goats irrespective of a controlled photoperiodic regime

Present study evaluated the presence of a sexually active male buck upon the onset of reproductive activity and estrous cycle progression in Criollo goats exposed to a 6-month long controlled photoperiod in a range of 13.4–10.6 light-hours per day. Mexican-native (Criollo) goats (n=10) were randomly assigned into 2 groups: (1) goats exposed to a male buck (n=5); (2) goats not exposed to a male buck (n=5). Blood samples were taken weekly to quantify serum-progesterone levels through radioimmunoanalysis. Male exposure increased luteal activity and estrous cycle progression reflected as a higher number of days in luteal activity (44±9.05 vs. 32.3±20.6); a reduced number of days in anestrous (4.0±4.8 vs. 51.9±28) and a greater number of luteal phases (15.7±4.4 vs. 11.3±8.7) without compromising serum progesterone levels (6.8±0.8 vs. 7.3±0.5). In conclusion, presence of a sexually active male induced a greater ovarian activity in Criollo goats, shortening seasonal anestrous irrespective of the controlled photoperiodic regime.

Daily torpor reduces mass and changes stress and power output of soleus and EDL muscles in the Djungarian hamster, Phodopus sungorus

Djungarian hamsters (Phodopus sungorus) undergo bouts of daily torpor in response to reduced photoperiod. Metabolic rate, body temperature and energy cost are reduced during torpor. The present study exposed Djungarian hamsters to two different photoperiod regimes at a room temperature of 19-21°C: long photoperiod (control, 16 h:8 h light:dark, N=8) and short photoperiod (torpor, 8 h:16 h light:dark, N=8). After 14 weeks, muscle mechanics were analyzed in each group, examining both extensor digitorum longus (EDL) muscle and soleus muscle from each individual. Control hamsters had significantly greater body mass (43%), EDL mass (24%), EDL length (9%) and soleus mass (48%) than the torpor hamsters. However, there were no significant differences between control and torpor groups in forearm length or soleus muscle length. There were no significant differences in either muscle between control and torpor hamsters in maximum twitch stress (force per unit area), tetanus force generation or relaxation times. Maximum soleus tetanic stress was 43% greater (P=0.039) and soleus work loop power output (P<0.001) was higher in torpor than in control hamsters. Maximum EDL tetanic stress was 26% greater in control than in torpor hamsters (P=0.046), but there was no significant effect on EDL power output (P=0.38). Rate of fatigue was not affected by torpor in either soleus or EDL muscles (P>0.43). Overall, extended use of daily torpor had no effect on the rate at which stress or work was produced in soleus and EDL muscles in Djungarian hamsters; however, torpor did increase the stress and power produced by the soleus.

The effect of combining shading and continuous lighting on the suppression of sexual maturation in outdoor-reared Atlantic cod, Gadus morhua

Sexual maturation of Atlantic cod, Gadus morhua, is a major problem during commercial on growing as fish divert energy away from growth into gonadal development. While the photoperiod regimes that inhibit maturation are well described, when manipulations are applied in a commercial cage setting, using standard lighting technology, maturation is not completely inhibited. This has led to the hypothesis that the enhanced light sensitivity of cod allows it to perceive ambient illumination over the artificial lighting. A 13 month trial was conducted to determine the effectiveness of net shading ambient photoperiod in addition to constant lighting to suppress maturation of cod in outdoor conditions. By reducing the relative difference between day and night light intensities, it was hypothesised that maturation in cod could be inhibited as fish could not perceive, and thus use the ‘ambient daylength’ signal to entrain their reproductive cycle. Two outdoor tanks were covered in either a low density (70% reduction in ambient illumination) or a high density (90% reduction in ambient illumination) shade netting and then illuminated continuously by cathode lighting. These were compared to two indoor tanks in which ambient light was excluded and instead they were illuminated by similar lighting running either under a simulated natural photoperiod or continuous illumination. The work demonstrated that the shade netting could improve the relative performance of the artificial lighting outdoors from < 2% in a non-shaded system to 6.6% (low shade treatment) and 31.3% (high shade treatment) of the day light intensity. Importantly, both shading treatments were effective at suppressing sexual development as confirmed through histology and reduced GSI (female mean ≤ 2.18%, male mean ≤ 1.39%), oocyte diameter (mean < 400 μm) and sex steroid profiles (female 17β-estradiol mean ≤ 0.24 ng.ml − 1 , male 11-ketotestosterone mean ≤ 3.35 ng.ml − 1 ) as well as enhanced growth. These results are a promising demonstration of the potential value of shading systems to enhance the efficacy of photoperiod control.

Responses of time of anthesis and maturity to sowing dates and infrared warming in spring wheat

Reliable prediction of the potential impacts of global warming on agriculture requires accurate data on crop responses to elevated temperatures. Controlled environments can precisely regulate temperature but may impose unrealistic radiation, photoperiod and humidity regimes. Infrared warming with automatic control of temperature rise has shown potential for warming field plots above ambient temperatures, while avoiding such biases. In a field experiment conducted at Maricopa, AZ, we assessed the utility of a temperature free-air controlled enhancement (T-FACE) approach by comparing phenology of wheat from a series of six sowing date treatments using T-FACE and an additional nine sowing dates that exposed crops to an exceptionally wide range of air temperatures (<0 °C to >40 °C). The T-FACE treatments were intended to achieve a warming of +1.5 °C during the daytime and +3.0 °C at night; the achieved warming averaged +1.3 °C during daytime and +2.8 °C at night. T-FACE and sowing date treatments had large effects on phenology. A regression-based analysis of simulations with the CSM-CROPSIM-CERES model showed that effects of T-FACE on phenology were similar to what would be expected from equivalent changes in air temperature. However, systematic deviations from the expected 1-to-1 relation suggested that assumed cardinal temperatures for phenology should be revised. Based on the single cultivar and location, it appeared that the base temperature for emergence to anthesis should be reduced from 0 °C to −5 °C, whereas the base temperature for grain filling should be increased from 0 °C to 4 °C and the optimal temperature, from 30 °C to 34 °C. Both T-FACE and extreme sowing date treatments proved valuable for improving understanding of high temperature effects on plant processes, as required for accurate prediction of crop responses to elevated temperatures under climate change.