Elevated Night-time Temperatures Research Articles

A Review: Elevated Nighttime Temperature Impacts on Rice

A Review: Elevated Nighttime Temperature Impacts on Rice

Potential for climate equity: Integrating nocturnal drainage winds into heat mitigation strategies in Portland

Limited adaptation options and local-scale heat mitigation measures to counter elevated nighttime temperatures have increased the need for effective and equitable city-scale cooling measures. I proposed that cold and dense air from surrounding high landscapes, called drainage winds, could be a potential city-scale nocturnal heat mitigation measure. I further suggest that this measure can moderate spatial disparities in heat mitigation capacity due to the unequal distribution of urban trees in Portland, Oregon. First, I conducted KLAM_21 wind simulations using grid cells of 30 m with elevation and historical and recent land use types. Then, I used census block groups including the proportion of tree canopy area, socioeconomic variables, and simulated wind attributes in statistical analysis. I found: (1) KLAM_21 simulation results generally align with actual wind observations, (2) urban development over the last two decades lowered the cold air layer, and (3) marginalized neighborhoods with less tree canopy coverage experience greater nocturnal cooling effects from drainage winds. These results emphasize the potential of drainage winds as an equitable heat mitigation option in Portland. Urban planners should integrate scenario-based simulated wind data into heat mitigation strategies to foster a more equitable and comfortable nighttime thermal environment in the long term.

Multiple physiological mechanisms involved in reproduction could be targeted for breeding heat tolerance in lima bean

AbstractWith global warming, the impact of high‐temperature stress on crop production is one of the major issues facing agriculture. Combining a series of field and controlled environment experiments, the current study aimed at understanding causes of yield loss due to heat stress in lima bean (Phaseolus lunatus L.) in order to guide breeding for heat tolerance. A growth‐stage analysis of multi‐year field trials suggested that yields were reduced by sensitivity to heat during floral transition. High nighttime temperatures during this period were also associated with delayed pod set and subsequent harvest. These effects were validated in controlled environments, with additional tests revealing how nighttime heat stress generally reduces seeds per pod but can also reduce the number of pods set. Using an intra‐plant dual temperature treatment design for vegetative and reproductive organs, it was determined that effects on pollen viability and release are primary factors underlying heat stress‐associated yield losses in lima bean. Elevated nighttime temperatures did not reduce aboveground biomass, indicating the physiological basis for temperature sensitivity was not driven by a photosynthate deficit, but instead could be attributed to changes in source–sink dynamics. Still, the basis for sensitivity to heat differed among genotypes, opening new targets for a multi‐mechanistic breeding approach for heat tolerance.

An overheating criterion for bedrooms in temperate climates: Derivation and application

Adequate sleep is crucial to human health and well-being and elevated night-time temperatures can degrade sleep quality. European countries with temperate climates use temperature thresholds between 25°C and 28°C to identify homes that are overheated. The current UK bedroom threshold of 26°C, is based on one small study, which is now over 45 years old. An extensive literature review indicated that with modern summertime bedding and bedwear, which enables body coverage to be easily adjusted, thermal comfort can be achieved for night-time bedroom temperatures up to approximately 29°C. Temperatures measured in 591 bedrooms during England’s hottest ever summer, 2018, are re-analysed. The prevalences of night-time overheating generated by alternative criteria are compared with the prevalences generated by the established adaptive overheating criterion. Comparisons are made for homes with different dwelling and household characteristics. Finally, a new overheating criterion is proposed based on the mean night-time bedroom temperature, with thresholds between 26°C and 29°C depending on the application of the criterion. The allowable exceedance of the chosen threshold is limited to seven nights between May and September. Adopting thresholds of 27°C for vulnerable households and 28°C for others, 23% (5.5 million) of the main bedrooms in English homes were deemed to be overheated in the hot summer of 2018, far fewer than the 69% obtained using the current UK bedroom criterion. Irrespective of the threshold chosen, there were clear, consistent and significant differences in overheating prevalence depending on dwelling and household characteristics. The proposed new overheating criterion is applicable to unconditioned bedrooms in temperate regions. It seeks to strike a balance between the risk that hot bedrooms will be air-conditioned and the risk of temperatures detrimental to a “good nights’ sleep”. Practical Application A new overheating criterion is proposed to identify overheated bedrooms. It adopts the familiar format of a temperature threshold and an allowable exceedance. It is applicable in temperate climates when people are asleep in unconditioned bedrooms. The criterion is intended to aid the interpretation of night-time temperatures predicted by dynamic thermal models and temperature measurements in existing bedrooms. It is applicable to individuals of different heat sensitivity, the design of new homes or the refurbishment of existing homes. With further testing and refinement, it offers a credible replacement to the existing UK bedroom criterion given in CIBSE Guide A, TM59 and in other guides. It can thus underpin the new overheating regulations, Part O, for the design of new dwellings in England.

Molecular mapping and characterization of QTLs for grain quality traits in a RIL population of US rice under high nighttime temperature stress

Elevated nighttime temperatures resulting from climate change significantly impact the rice crop worldwide. The rice (Oryza sativa L.) plant is highly sensitive to high nighttime temperature (HNT) during grain-filling (reproductive stage). HNT stress negatively affects grain quality traits and has a major impact on the value of the harvested rice crop. In addition, along with grain dimensions determining rice grain market classes, the grain appearance and quality traits determine the rice grain market value. During the last few years, there has been a major concern for rice growers and the rice industry over the prevalence of rice grains opacity and the reduction of grain dimensions affected by HNT stress. Hence, the improvement of heat-stress tolerance to maintain grain quality of the rice crop under HNT stress will bolster future rice value in the market. In this study, 185 F12-recombinant inbred lines (RILs) derived from two US rice cultivars, Cypress (HNT-tolerant) and LaGrue (HNT-sensitive) were screened for the grain quality traits grain length (GL), grain width (GW), and percent chalkiness (%chalk) under control and HNT stress conditions and evaluated to identify the genomic regions associated with the grain quality traits. In total, there were 15 QTLs identified; 6 QTLs represented under control condition explaining 3.33% to 8.27% of the phenotypic variation, with additive effects ranging from − 0.99 to 0.0267 on six chromosomes and 9 QTLs represented under HNT stress elucidating 6.39 to 51.53% of the phenotypic variation, with additive effects ranging from − 8.8 to 0.028 on nine chromosomes for GL, GW, and % chalk. These 15 QTLs were further characterized and scanned for natural genetic variation in a japonica diversity panel (JDP) to identify candidate genes for GL, GW, and %chalk. We found 6160 high impact single nucleotide polymorphisms (SNPs) characterized as such depending on their type, region, functional class, position, and proximity to the gene and/or gene features, and 149 differentially expressed genes (DEGs) in the 51 Mbp genomic region comprising of the 15 QTLs. Out of which, 11 potential candidate genes showed high impact SNP associations. Therefore, the analysis of the mapped QTLs and their genetic dissection in the US grown Japonica rice genotypes at genomic and transcriptomic levels provide deep insights into genetic variation beneficial to rice breeders and geneticists for understanding the mechanisms related to grain quality under heat stress in rice.

Plant photosynthetic overcompensation under nocturnal warming: lack of evidence in subtropical evergreen trees.

Increased plant photosynthesis under nocturnal warming is a negative feedback mechanism to overcompensate for night-time carbon loss to mitigate climate warming. This photosynthetic overcompensation effect has been observed in dry deciduous ecosystems but whether it exists in subtropical wet forest trees is unclear. Two subtropical evergreen tree species (Schima superba and Castanopsis sclerophylla) were grown in a greenhouse and exposed to ambient and elevated night-time temperature. The occurrence of the photosynthetic overcompensation effect was determined by measuring daytime and night-time leaf gas exchange and non-structural carbohydrate (NSC) concentration. A reduction in leaf photosynthesis for both species and an absence of persistent photosynthetic overcompensation were observed. The photosynthetic overcompensation effect was transient in S. superba due to respiratory acclimation and stomatal limitation. For S. superba, nocturnal warming resulted in insufficient changes in night-time respiration and NSC concentration to stimulate overcompensation and inhibited leaf stomatal conductance by increasing the leaf-to-air vapour pressure deficit. The results indicate that leaf stomatal conductance is important for the photosynthetic overcompensation effect in different tree species. The photosynthetic overcompensation effect under nocturnal warming may be a transient occurrence rather than a persistent mechanism in subtropical forest ecosystems.

Nocturnal warming accelerates drought-induced seedling mortality of two evergreen tree species.

Extreme drought is one of the key climatic drivers of tree mortality on a global scale. However, it remains unclear whether the drought-induced tree mortality will increase under nocturnal climate warming. Here we exposed seedlings of two wide-ranging subtropical tree species, Castanopsis sclerophylla and Schima superba, with contrasting stomatal regulation strategies to prolonged drought under ambient and elevated night-time temperature by 2°C. We quantified the seedling survival time since drought treatment by measuring multiple leaf traits such as leaf gas exchange, predawn leaf water potential and water-use efficiency. The results showed that all seedlings in the ambient temperature died within 180days and 167days of drought for C. sclerophylla and S. superba, respectively. Night warming significantly shortened the survival time of C. sclerophylla, by 31days, and S. superba by 28days, under the drought treatment. A survival analysis further showed that seedlings under night warming suffered a 1.6 times greater mortality risk than those under ambient temperature. Further analyses revealed that night warming suppressed net leaf carbon gain in both species by increasing the nocturnal respiratory rate of S. superba across the first 120days of drought and decreasing the photosynthetic rate of both species generally after 46days of drought. These effects on net carbon gain were more pronounced in S. superba than C. sclerophylla. After 60days of drought, night warming decreased the predawn leaf water potential and leaf water-use efficiency of C. sclerophylla but not S. superba. These contrasting responses are partially due to variations in stomatal control between the two species. These findings suggest that stomatal traits can regulate the response of leaf gas exchange and plant water-use to nocturnal warming during drought. This study indicates that nocturnal warming can accelerate tree mortality during drought. Night warming accelerates the mortality of two subtropical seedlings under drought.Night warming differently affects the drought response of leaf gas exchange and plant water-use between the two species due to species-specific stomatal morphological traits.Carbon metabolism changes and hydraulic damage play differential roles in driving night-warming impacts on the drought-induced mortality between the two species.

Elevated nighttime temperature affects fiber bundle strength via altering cellulose deposition rate during early fiber development

The Xinjiang Region is China's major concentrated cotton growing area. But nighttime temperature during the late growing season is a crucial factor affecting fiber quality, especially fiber bundle strength. The objective of this study was to determine the effects of nighttime temperature on fiber bundle strength and cellulose deposition via elevating nighttime temperature at different fiber development stages. The results indicated that elevated nighttime temperature from anthesis to the boll opening stage (Na) significantly advanced the time of cellulose deposition, the onset time and termination time of rapid cellulose deposition were all significant by 4.5 d in advance, and the deposition rate (V1) significant was increased by 0.65%/d in the initial period from anthesis to the onset of rapid cellulose deposition. And these resulted in an increase of fiber bundle strength. When nighttime temperature was elevated either from anthesis to the onset of rapid cellulose deposition (N1) or between the onset and termination of rapid cellulose deposition (N2), it had a significantly shorter duration of rapid cellulose deposition by 3.6–5.7 d, and the deposition rate of rapid cellulose deposition significantly increased by 0.8–1.0%/d. Compared with N1, the V1 was significantly reduced by 7.9% and the maximum cellulose content was increased by 7.3% in N2. Fiber bundle strength was significantly increased at the N2, but significantly decreased by 1.3 cN/tex at the N1. Elevated nighttime temperatures from the termination of rapid cellulose deposition to boll opening (N3) had no significant effect on fiber bundle strength or cellulose deposition characteristics. In conclusion, the effects of nighttime temperature on fiber bundle strength mainly depended on the average cellulose deposition rate from anthesis to the onset of rapid cellulose deposition (V1).

Black widows on an urban heat island: extreme heat affects spider development and behaviour from egg to adulthood

Urbanization rapidly alters the environment, often leading to decreased biodiversity. One abiotic selection pressure uniquely associated with urbanization is the urban heat island (UHI) effect—wherein built structures (e.g. paved surfaces) capture heat during the day, retain it through the dark cycle and result in significantly elevated night-time temperatures. Relatively few studies have asked what effects the UHI might have on the development and behaviour of urban animals, and even fewer have asked this question of urban arthropod pests who rely on external heat sources and can experience explosive urban population growth rates. In particular, behavioural plasticity is often cited as a critical phenotype for organisms to thrive after rapid environmental change such as urbanization. Here, the relationship between elevated urban temperatures and behaviour was examined in the western black widow spider, Latrodectus hesperus. With regard to the UHI, young spiderlings raised at urban, elevated temperatures showed significantly reduced life span, reduced body mass, elevated web building, heightened voracity towards heterospecific prey and sibling cannibalism. In contrast, males studied later in the final prereproductive moults and raised at urban, elevated temperatures showed reduced life span, decreased adult body condition and increased voracity towards prey. We found no effects of temperature on late-stage male web building or courtship behaviour. UHI temperatures simulated in the laboratory present black widow spiders with a myriad of developmental problems, but our data suggest these spiders use temperature-sensitive behavioural plasticity to attempt to accommodate this stressor.

Effects of solar irradiation and night-time temperature on the thinning efficacy of metamitron (Brevis®) in apple

Trials with metamitron (Brevis®) were conducted at different phenological stages of apple fruit (7-18 mm fruit diameter) in the 2014-2016 seasons. Within each season, the same dosages were used at all application dates for all tested cultivars. On the basis of the obtained results a model was developed in order to estimate the efficacy of Brevis® at the established treatment. Metamitron causes a measurable reduction of electron transport in photosystem II for about 10 days, leading to a reduced photosynthetic output. In addition when elevated night-time temperatures (>10°C) occur a further fruit abscission can be enhanced.

Limits on Dione's Activity Using Cassini/CIRS Data

AbstractWe use nighttime Cassini Composite Infrared Spectrometer (CIRS) data to look for discrete regions of elevated nighttime temperatures indicative of endogenic activity on Dione's surface. This is achieved by producing low latitude and midlatitude (less than 60°) maps of Dione's nighttime surface temperature, derived from 10 to 1,100‐cm−1 CIRS data. The surface temperatures observed do not show evidence of any small discrete regions of elevated nighttime temperatures and are comparable to temperatures predicted by a passive thermophysical model of Dione's surface. Thus, we conclude that no evidence for activity exists on Dione at midlatitude to low latitude. Using the derived surface temperature maps, we set upper limits for the temperature at which a 50‐, 100‐, or 200‐km2 hot spot would remain undetected by this study. We find the mean temperature of such a hot spot would be 117.1 ± 47.2 K (−249 F), 104.8 ± 27.7 K (−272 F), and 95.4 ± 19.5 K (−288 F) for a 50‐, 100‐, and 200‐km2 hot spot, respectively, corresponding to endogenic emission of 1.07, 0.68, and 0.47 GW.

Influence of arbuscular mycorrhizal colonization on whole-plant respiration and thermal acclimation of tropical tree seedlings.

Symbiotic arbuscular mycorrhizal fungi (AMF) are ubiquitous in tropical forests. AMF play a role in the forest carbon cycle because they can increase nutrient acquisition and biomass of host plants, but also incur a carbon cost to the plant. Through their interactions with their host plants they have the potential to affect how plants respond to environmental perturbation such as global warming. Our objective was to experimentally determine how plant respiration rates and responses to warmer environment are affected by AMF colonization in seedlings of five tropical tree species at the whole plant level. We evaluated the interaction between AMF colonization and temperature on plant respiration against four possible outcomes; acclimation does or does not occur regardless of AMF, or AMF can increase or decrease respiratory acclimation. Seedlings were inoculated with AMF spores or sterilized inoculum and grown at ambient or elevated nighttime temperature. We measured whole plant and belowground respiration rates, as well as plant growth and biomass allocation. There was an overall increase in whole plant, root, and shoot respiration rate with AMF colonization, whereas temperature acclimation varied among species, showing support for three of the four possible responses. The influence of AMF colonization on growth and allocation also varied among plant species. This study shows that the effect of AMF colonization on acclimation differs among plant species. Given the cosmopolitan nature of AMF and the importance of plant acclimation for predicting climate feedbacks a better understanding of the patterns and mechanisms of acclimation is essential for improving predictions of how climate warming may influence vegetation feedbacks.

Growth and nitrogen allocation of dry season tropical rice as a result of carbon dioxide fertilization and elevated night time temperature

A field experiment was laid out on carbon dioxide (CO2) fertilization for 3 years in dry cropping seasons to investigate the effects of elevated CO2 (e-CO2) (550 µmol mol−1) and elevated CO2 (550 µmol mol−1) + elevated temperature (+2 °C over ambient) (e-CO2 + T) on biomass production, carbon (C) and nitrogen (N) concentration in plant parts, its allocation and grain quality in a tropical rice (cultivar-Naveen) under open top chambers (OTCs). The aboveground plant biomass, root biomass, leaf area index and net C assimilation rates were increased significantly under e-CO2 to that of ambient CO2 in control chamber CC by 32, 26, 21 and 37 %, respectively over the three dry cropping seasons. The grain yield was significantly higher under e-CO2 compared to CC (21.6 %), although the higher temperature in e-CO2 + T significantly reduced the yield advantage by 8.5 % overe-CO2. The amylose content was significantly increased by 10 % under e-CO2 + T over CC. In dry season, CO2 fertilization enhanced the rice yield by 21.6 % but the yield advantage of CO2 fertilization were reduced by 8.5 % due to elevated temperature. We did not found any deterioration ingrain quality in elevated temperature (2 °C) in low land rice ecologies.

Experimental climate warming enforces seed dormancy in South African Proteaceae but seedling drought resilience exceeds summer drought periods.

Two hypotheses-that elevated night-time temperatures due to climate warming would enforce post-fire dormancy of Proteaceae seed due to low moisture, and that periods without rain during summer would exceed desiccation periods tolerated by Proteaceae seedlings-were tested empirically. Enforced dormancy, i.e., the inability to germinate due to an environmental restraint, was tested by measuring seed germination in 11 Proteaceae species in experimental mesocosms whose soils were artificially elevated by 1.4 and 3.5 °C above ambient by far-red wavelength filtered infrared lamps. Diminished totality of germination and velocities were observed in 91 and 64%, respectively, of the Proteaceae species tested. Drought resilience was tested in one-year-old seedlings of 16 Proteaceae species by withholding water from potted plants during summer in a greenhouse. The most drought-resilient Proteaceae species displayed the lowest initial transpiration rates at field capacity, the smallest declines in transpiration rate with decreasing soil water content, and the lowest water losses by transpiration. Projected drought periods leading to the complete cessation of transpiration in all Proteaceae species greatly exceeded the number of days without rain per month during summer in the current distribution ranges of those species. It was therefore concluded that enforced seed dormancy induced by elevated night-time temperatures is the post-fire recruitment stage of Proteaceae that is most sensitive to climate warming.

Influence of water ice clouds on nighttime tropical temperature structure as seen by the Mars Climate Sounder

AbstractAn analysis of nighttime temperature and water ice cloud extinction profiles from the Mars Climate Sounder aboard the Mars Reconnaissance Orbiter provides evidence for the close relationship between tropical temperature structure and water ice clouds. The tropical temperature structure that evolves over the spring and summer seasons is closely coupled to the waxing and waning of tropical cloud activity. The presence of strong elevated nighttime temperature inversions in the Tharsis region is a robust feature of the equatorial atmosphere during the Ls = 0–135° season, with little interannual variation seen in the three Mars years examined. Mars global circulation model simulations imply that cloud radiative forcing plays a dominant role in the seasonal modulation of the observed longitude distribution of warm and cold anomalies in surface and low‐altitude air temperatures, respectively.

The Chamber for Studying Rice Response to Elevated Nighttime Temperature in Field

An in situ temperature-controlled field chamber was developed for studying a large population of rice plant under different nighttime temperature treatments while maintaining conditions similar to those in the field during daytime. The system consists of a pipe hoop shed-type chamber with manually removable covers manipulated to provide a natural environment at daytime and a relatively stable and accurate temperature at night. Average air temperatures of 22.4 ± 0.3°C at setting of 22°C, 27.6 ± 0.4°C at 27°C, and 23.8 ± 0.7°C ambient conditions were maintained with the system. No significant horizontal and vertical differences in temperature were found and only slight changes in water temperatures were observed between the chambers and ambient conditions at 36 days after transplanting. A slight variation in CO2 concentration was observed at the end of the treatment during the day, but the 10-μmol CO2 mol−1 difference was too small to alter plant response. The present utilitarian system, which only utilizes an air conditioner/heater, is suitable for studying the effect of nighttime temperature on plant physiological responses with minimal perturbation of other environmental factors. At the same time, it will enable in situ screening of many rice genotypes.

Elevated night‐time temperatures increase growth in seedlings of two tropical pioneer tree species

Increased night-time temperatures, through their influence on dark respiration, have been implicated as a reason behind decreasing growth rates in tropical trees in the face of contemporary climate change. Seedlings of two neo-tropical tree species (Ficus insipida and Ochroma pyramidale) were grown in controlled-environment chambers at a constant daytime temperature (33°C) and a range of increasing night-time temperatures (22, 25, 28, 31°C) for between 39 d and 54 d. Temperature regimes were selected to represent a realistic baseline condition for lowland Panama, and a rise in night-time temperatures far in excess of those predicted for Central America in the coming decades. Experiments were complemented by an outdoor open-top chamber study in which night-time temperatures were elevated by 2.4°C above ambient. Increasing night-time temperatures resulted in > 2-fold increase in biomass accumulation in growth-chamber studies despite an increase in leaf-level dark respiration. Similar trends were seen in open-top chambers, in which elevated night-time temperatures resulted in stimulation of growth. These findings challenge simplistic considerations of photosynthesis-directed growth, highlighting the role of temperature-dependent night-time processes, including respiration and leaf development as drivers of plant performance in the tropics.

Leaf domatia: carbon-limited indirect defence?

Plant-based defence mutualisms utilize plant morphology to reduce the performance of plant parasites through their natural enemies. Leaf domatia primarily occur in the axials of secondary veins and are often inhabited by microbivorous and predaceous mites which often increase plant growth rates and reproductive success by controlling plant pests. Our study investigated if domatia investment is limited by plant primary productivity. To our knowledge no studies have tested if foliar domatia are resource-limited. We tested our hypothesis using the genus Coprosma (Rubiaceae), conducting correlative field surveys and manipulative experiments measuring domatia production in new leaves along temperature, nutrient and irradiance gradients. Field surveys indicated a strong positive association between leaf area, the number of secondary veins, and domatia per leaf. The number of potential sites for domatia is underutilised, with leaves on selected Coprosma species having on average 47 to 72% of the ‘maximum’ number of available sites where domatia could occur. Foliar carbon was positively associated with domatia investment. Coprosma plants held under elevated night-time temperatures showed a 34–91% decrease in daily carbon gain, a 38% decrease in domatia per leaf mass, and a positive relationship between domatia investment and integrated daily carbon gain. Under irradiance and nutrient stress, our data indicated evidence of a positive relationship between domatia investment and foliar carbon. We found a significant negative association between relative investment in domatia produced and investment in new leaf biomass. Our findings suggest investment in foliar domatia is limited by primary productivity. We propose that domatia are discretionary goods and not intrinsic structures produced automatically on leaves that mites utilize. We suggest that plants have the ability to regulate domatia formation during leaf ontogeny, with investment controlled by resource availability and some intrinsic allocation mechanism to defence.

Using rainout shelters to evaluate climate change effects on the demography of Cryptantha flava

Summary Precipitation in arid regions is temporally variable with much of it arriving in discrete, unpredictable pulses. Climate change models predict an increase in the variation of precipitation, with longer droughts and larger rainfall events, in addition to increased temperatures. A life table response experiment (LTRE) was conducted with the herbaceous arid‐land perennial Cryptantha flava (Boraginaceae) from 1997 to 2000, in order to determine how variation in precipitation affects asymptotic population growth (l) and vital rates. Variation in precipitation took two forms, through rainout shelters erected just before and during the 1999 spring growing season, and through naturally occurring variation over the 4 years. An unexpected effect of rainout shelters on l was observed that could not be attributed to drought. The l value decreased greatly in control census plots in the 1998–99 transition but did not decrease in sheltered of plots. The 1999 spring, when shelters were in place, was unusually cold, resulting in frost damage to unsheltered plants. Plants under shelters experienced elevated nighttime temperatures and escaped frost damage. The greater value of l in the sheltered plots is attributable almost entirely to greater contributions of survival, growth and stasis. There were residual effects of the 1999 drought treatment in the 1999–2000 transition as l decreased in the sheltered populations while l increased in control populations. Compared to controls, there were large negative effects of survival, growth, and stasis and a large positive effect of retrogression in the droughted plots. Natural variation in fecundity contributed considerably to inter‐annual variation in l in control plots. Annual variation in fecundity strongly paralleled annual variation in seedling establishment. The relative contributions of other vital rates varied greatly among the annual transitions. Synthesis. The study illustrates the sensitivity of this arid‐land species to early season frost events and to variation in precipitation. It suggests the importance of considering the seasonal timing of precipitation events when projecting the population‐level consequences of global climate change, with particular attention given to precipitation that triggers germination and seedling establishment. Researchers using shelters to create drought treatments should consider their nighttime warming effects.

Nocturnal warming increases photosynthesis at elevated CO2 partial pressure in Populus deltoides.

• We measured night-time respiration and daytime photosynthesis of leaves in canopies of 4m tall cottonwood (Populus deltoides) trees to investigate the link between leaf respiration and photosynthetic capacity. • Trees were grown at three CO2 partial pressures [p(CO2 )a ] (42, 80, 120Pa) and experimentally exposed to differing nocturnal temperatures (15, 20 or 25°C), but constant daytime temperatures (30-32°C), in a short-term whole-ecosystem environmental manipulation. • Rates of night-time leaf dark respiration (Rd ) increased significantly at all growth CO2 partial pressures when nocturnal temperatures were increased from 15 to 25°C. Predawn leaf nonstructural carbohydrate (soluble sugars and starch) content was significantly lower at the higher night temperatures. Photosynthetic capacity (Amax ) during the day increased significantly between 15 and 25°C at 42 and 80Pa, but not at 120Pa. • These findings indicate that the previously determined relationships between elevated night-time temperature, dark respiration and increased photosynthetic capacity may also hold at elevated p(CO2 )a . This response may have a significant influence on plant and ecosystem carbon exchange under global change scenarios.