Nighttime Respiration Research Articles

Distinguishing High Daytime From Nighttime Temperature Effects During Early Vegetative Growth in Cotton

ABSTRACTHigh‐temperature limits early season vegetative growth of cotton, and the physiological response of cotton (Gossypium hirsutum L.) to high daytime or nighttime temperature needs to be explored. The objectives of the current study were to determine (1) plant growth response, (2) physiological contributors to variation in biomass production and (3) mechanisms driving variation in net photosynthetic rate (AN) in response to different combinations of high daytime and nighttime temperatures. Beginning at planting, cotton was exposed to four different growth temperature regimes: (1) optimum (30/20°C day/night), (2) high nighttime (30/30°C), (3) high daytime (40/20°C) and combined high daytime and nighttime (40/30°C) for 4 weeks. Relative to the 30/20°C treatment, plant growth was positively affected by high nighttime temperature and negatively affected by high daytime temperature and combined high day and night temperature. Increased leaf area mainly contributed to increased biomass production in high nighttime temperature; higher nighttime respiration (RN) drove reductions in biomass in combined high daytime and nighttime temperature; and decreased leaf area and AN and increased RN drove reductions in biomass under high daytime temperature alone. AN was not impacted by high nighttime temperature, while decreased under high daytime temperature and increased with combined high daytime and nighttime temperature. Adjustments in leaf traits contributed to increases in AN in combined high daytime and nighttime temperature, and increased photorespiration and respiration contributed to reductions in AN under high daytime temperature. Overall, early season vegetative growth of cotton exhibited differential responses to high daytime and nighttime temperatures.

Empirical Models of Respiration and Net Ecosystem Productivity and Their Applications in a Subtropical Coniferous Plantation in China

Net ecosystem exchange (NEE), solar radiation (including photosynthetically active radiation PAR), and meteorological parameters were measured in a subtropical coniferous plantation in China during 2013–2016. Applying the PAR balance principle at a canopy level and analyzing the observation data, an empirical model of respiration (Re, EMRe) considering 3-factor and 2-factor situations was developed and tested for all sky conditions. Generally, the respiration simulations were in reasonable agreement with the observations for the hourly, monthly, and annual sums of respiration. For example, using 3-factor and 2-factor models, the estimated annual sums of daytime and nighttime respiration in 2013–2016 overestimated that which was observed by about 31% and 26%, respectively. Further applications of EMRe and an empirical model of gross primary production (GPP, EMGPP) developed previously at this site, and an empirical model of net ecosystem productivity (NEP, EMNEP) using 3-factor and 2-factor models were obtained (NEP = GPP-Re) and evaluated for all sky conditions. Generally, the simulations of the hourly, monthly, and annual sums of NEP showed reasonable performances. The estimated NEP values overestimated the observations by 22% and 27% for the hourly sums in 2013–2016 when using the 3-factor and 2-factor models, respectively, and 7% and 12% for annual sums in 2013–2015 (2016 data were not used as the CO2 flux measurements had some problems in the 2016 summer). The NEP estimations were evidently improved when more factors (e.g., dark respiration) influencing Re were considered in the daytime respiration compared to those without considering these factors. To simplify the numerous and complicated CO2 processes in the simulations of Re and NEP, the PAR energy method was applied to capture and describe its main processes and energy interactions. The PAR energy method was suitable for studying the energy relationships associated with CO2 processes and developing empirical models for the simulations of GPP, Re, and NEP. These models were useful tools to investigate the multiple interactions and mechanisms between CO2, other atmospheric compositions, and PAR. Thus, the energy method is suggested to be applied to carbon balance.

Genotypic variation in growth, single leaf physiology, and acclimation potential of thylakoid processes in cotton exposed to high temperature extremes

The cotton crop already experiences yield-limiting high temperatures during the growing season, which are predicted to worsen in a changing climate. This makes the identification of heat tolerant cultivars that can acclimate to high temperature conditions a necessity. The objective of this study was to assess the effects of growth temperature and genotype on plant growth, single-leaf physiology, and thermotolerance of thylakoid processes for cotton exposed to optimal and supra-optimal temperature conditions. A diverse collection of cotton cultivars was selected based on previously documented differences in thylakoid-specific thermotolerance, and they were exposed to optimal (30/20 C) and two supra-optimal growth temperatures (35/25 and 40/30 °C). There was a significant interaction between genotype (G) and growth temperature (T) for all growth measures (leaf area, mainstem node production, and plant dry weight), photosynthetic rates, nighttime respiration and stomatal conductance, and thermotolerance of photosystem II. Greater relative growth (plant dry matter) under high temperature was strongly and positively correlated with leaf area and strongly and negatively correlated with nighttime respiration and stomatal conductance. In contrast, photosynthetic parameters were not significantly associated with genotypic variation in growth-specific thermotolerance. Thermotolerance of the thylakoid reactions was not consistently associated with more thermotolerant growth. We conclude that genotypes with heat tolerant vegetative growth have higher relative leaf area and lower relative values for nocturnal respiration and stomatal conductance under high temperature conditions.

Alternative oxidase 1a and 1d enable metabolic flexibility during Ala catabolism in Arabidopsis.

Ala is a central metabolite in leaf cells whose abundance is related to pyruvate (Pyr) metabolism and nocturnal respiration rates. Exposure of Arabidopsis (Arabidopsis thaliana) leaf disks to certain exogenous amino acids including Ala led to substantial increases in nighttime respiration rates as well as increases in alternative oxidase (AOX) 1d transcript and protein levels. During Ala treatment, AOX1d accumulation, but not AOX1a accumulation, was dependent upon the catabolism of Ala. Complete loss of AOX expression in aox1a aox1d leaf disks did not significantly affect oxygen consumption rates (OCR) under Ala treatment, indicating that AOX capacity per se was not essential for respiratory stimulation by Ala. Rather, Ala treatments caused induction of select antioxidant mechanisms in leaf disks, including a large increase of the ascorbate pool, which was substantially more oxidized in aox1a aox1d leaf disks. Furthermore, we observed differences in the accumulation of a sequence of TCA cycle intermediates from Pyr to 2-oxoglutarate (2-OG) in wild type (WT) upon Ala treatment that did not occur in aox1a aox1d leaf disks. The results indicate that AOX induction during enhanced Ala catabolism in leaves mediates mitochondrial redox status, allowing greater metabolic flexibility in mitochondrial organic acid metabolism.

Teaching NeuroImages: Sleep-related periodic breathing in acquired central sleep apnea

A 68-year-old man complained of the subtle onset of postural instability. A detailed investigation revealed the presence of ataxia with pulling to the right, right face and contralateral (left) trunk and limb hypoesthesia, slight dysphagia, right eyelid ptosis, and enophthalmos (figure, A) caused by medullary infarct (figure, B) (Wallenberg syndrome). Due to snoring, the patient underwent polysomnography, which showed central sleep apnea with Biot breathing ataxia (figure, C). Biot periodic breathing is an irregular, gasping respiration caused by respiratory pacemaker lesions, observed in comatose patients with bulbar damage.1 Here, Biot breathing presented in the context of central sleep apnea.2 Medullary breathing control circuit lesions impair autonomic respiration, which is critical for nighttime respiration.

One‐year‐long evaluation of non‐rainfall water available to soil biocrusts in the Negev Highlands

AbstractSoil biocrusts abound in deserts, but yet little agreement exists regarding their water sources. Most researchers regard non‐rainfall water (NRW), particularly dew as an important water source for soil biocrusts, but nevertheless, evidence from the Negev suggests that following the nocturnal soil heat efflux, NRW is drastically reduced. The possible contribution of NRW to 3‐ to 5‐mm‐tall lichens, which are less impacted by the warm nocturnal surface temperatures, poses an additional challenge. For this end, NRW obtained by cloths attached to the soil surface and cloths located at a 5‐mm height above ground were measured, accompanied by periodic temperature measurements. As for the cyanobacteria and the 1‐mm‐tall lichens, NRW did not reach the necessary threshold required for the performance of net photosynthesis by cyanobacterial (0.1 mm) or chlorolichens (0.05 mm) but was occasionally reached at 5‐mm height above ground. Nevertheless, when the average amount obtained at 1‐mm intervals (mimicking the length of the lichen thallus) along the 5‐mm height was calculated, it either fell below the necessary threshold or was too low during daytime to compensate for the carbon loss during nighttime respiration. The apparent incapability of NRW to provide sufficient water to sustain the 3‐ to 5‐mm‐tall lichens in the Negev Highlands is supported by the confinement of these lichens to north‐facing rock terraces (ledges), where they may benefit from additional water through runoff. One may therefore conclude that NRW may not be regarded as a meaningful water source for the Negev biocrusts, whether composed of cyanobacteria or of 1‐ to 5‐mm‐tall lichens.

Estimation of the optimal leaf area index (LAI) of an eggplant canopy based on the relationship between the nighttime respiration and daytime photosynthesis of the lowermost leaves

• Optimal leaf area index (LAI opt ) of eggplant was estimated based on carbon balance. • Night respiration (Σ R n ) and day photosynthesis (Σ A ) of lower leaves were correlated. • LAI opt can change considerably depending on solar radiation. • LAI should be maintained lower in winter and higher in summer. In year-round horticultural fruit production, proper management of the leaf area index (LAI) is important to improve fruit yields. This study investigated the optimal LAI (LAI opt ) of an eggplant canopy based on the daily incoming solar radiation (Σ S out ) and the carbon balance of the lowermost leaves. A simple analytical LAI opt model was developed by combining the Beer–Lambert law and a linear relationship between nighttime respiration (Σ R n ) and daytime net photosynthesis (Σ A ). Model parameters were derived from measurements (i.e., measurements of Σ R n and Σ A , the light-photosynthesis curve, and light extinction within the canopy). Σ R n and Σ A were linearly correlated ( R 2 = 0.67) for the lowermost leaves but not for the uppermost leaves ( R 2 = 0.13); the light-photosynthesis curves of the uppermost and lowermost leaves did not differ much under low-light conditions but differed considerably under high-light conditions; and the extinction coefficient of light was estimated to be 0.93. Using the obtained model parameters and publicly available Σ S out data, LAI opt was simulated. The simulation revealed that the LAI opt of an eggplant canopy can vary considerably depending on Σ S out ; a tenfold increase in Σ S out (3.0 to 30 MJ m −2 ) corresponded to a threefold increase in LAI opt (1.2 to 3.7 m 2 m −2 ). The developed model will be useful for obtaining estimates of LAI opt in year-round horticultural fruit production.

Spatial Patterns and Magnitudes of Agriculturally Pertinent Climate Indicators across Agroecosystems in Türkiye

Abstract This research utilized NASA–Prediction of Worldwide Energy Resource (POWER) datasets to quantify and map long-term annual and growing-season mean maximum, minimum, and mean air temperatures (Tmax, Tmin, and Tavg); diurnal temperature range (DTR); growing degree-days (thermal unit) (GDD); seasonal total precipitation; mean daily precipitation; incoming shortwave radiation Rs; relative humidity (RH); wind speed u2; saturation and actual vapor pressures (es and ea); vapor pressure deficit (VPD); grass- and alfalfa-reference evapotranspiration (ETo and ETr); and aridity index (AI) over the nine agricultural zones of Türkiye (Turkey). In addition to the latitudinal influence, the influence of continentality and oceanity effects and physiographic features were evident in the spatial patterns of all climate indicators. Tmin was the most spatially variable indicator at both scales, which can have significant impact on nighttime respiration, potentially reducing agroecosystem productivity. At the annual scale, climate indicators that showed coefficient of variation (CV) greater than 0.20 were GDD, Tavg, VPD, AI, and ea. Growing-season mean indicators with CV > 0.20 were GDD, AI, VPD, total precipitation, mean daily precipitation, and ea. The Rs showed the least spatial variability at both scales. Annual-scale mean CV (0.21) was 7% greater than that the growing season (0.19). To the best of our knowledge, the analyses, information, and resources presented here are the first to quantify agricultural-zone-specific climate indicators during the growing season in Türkiye and are invaluable for decision-making on issues at the intersection of meteorology, agriculture, water resources, and hydrology.

Source decomposition of eddy-covariance CO2 flux measurements for evaluating a high-resolution urban CO2 emissions inventory

We present the comparison of source-partitioned CO2 flux measurements with a high-resolution urban CO2 emissions inventory (Hestia). Tower-based measurements of CO and 14C are used to partition net CO2 flux measurements into fossil and biogenic components. A flux footprint model is used to quantify spatial variation in flux measurements. We compare the daily cycle and spatial structure of Hestia and eddy-covariance derived fossil fuel CO2 emissions on a seasonal basis. Hestia inventory emissions exceed the eddy-covariance measured emissions by 0.36 µmol m−2 s−1 (3.2%) in the cold season and 0.62 µmol m−2 s−1 (9.1%) in the warm season. The daily cycle of fluxes in both products matches closely, with correlations in the hourly mean fluxes of 0.86 (cold season) and 0.93 (warm season). The spatially averaged fluxes also agree in each season and a persistent spatial pattern in the differences during both seasons that may suggest a bias related to residential heating emissions. In addition, in the cold season, the magnitudes of average daytime biological uptake and nighttime respiration at this flux site are approximately 15% and 27% of the mean fossil fuel CO2 emissions over the same time period, contradicting common assumptions of no significant biological CO2 exchange in northern cities during winter. This work demonstrates the effectiveness of using trace gas ratios to adapt eddy-covariance flux measurements in urban environments for disaggregating anthropogenic CO2 emissions and urban ecosystem fluxes at high spatial and temporal resolution.

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.

Effects of CO2 concentration and soil water content on short-term water-use efficiency at whole-plant level

Uncovering the variations of short-term water-use efficiency (WUEp) at whole-plant level in response to CO2 concentration (Ca) and soil water content (SWC) can improve the understanding of plant survival strategies under climate change. In this study, Platycladus orientalis saplings were cultured in simulated climate chambers.There were totally 15 treatments, including Ca of 400 (C400), 600 (C600) and 800 (C800) μmol·mol-1 and SWC of 35%-45% field water holding capacity (FC), 50%-60%FC, 60%-70%FC, 70%-80%FC and 95%-100%FC. The WUEp was measured by mini-lysimeters, weighting method, and static assimilation chamber. The results showed that both daytime (0.12-1.87 mol·h-1) and nighttime transpiration rates (0.01-0.16 mol·h-1) at whole-plant level reached the maximum at C400×70%-80%FC, while the whole-plant daytime net photosynthetic rate (2.12-22.10 mmol·h-1) reached the maximum at C800×70%-80%FC. In contrast, nighttime respiration rate (0.84-4.41 mmol·h-1) increased with increasing SWC, but decreased with increasing of Ca, reaching the maximum at C400×95%-100%FC. For WUEp (5.37-24.35 mmol·mol-1), it reached the maximum at C800×50%-60%FC, indicating that plants could use less water and fixed more carbon by adjusting adaptation strategies under high Ca and drought conditions. In addition, leaf instantaneous water-use efficiency was a good predictor of WUEP when the canopy structure was similar.

Field-grown soybean shows genotypic variation in physiological and seed composition responses to heat stress during seed development

An average temperature increase between 2.6 and 4.8 °C, along with more frequent extreme temperatures, will challenge crop productivity by the end of the century. To investigate genotypic variation in soybean response to elevated temperature, six soybean ( Glycine max ) genotypes were subjected to elevated air temperature of + 4.5 °C above ambient for 28 days in open-top field chambers. Gas exchange and chlorophyll fluorescence were measured before and during heating and yield as well as seed composition were evaluated at maturity. Results show that long-term elevated air temperature increased nighttime respiration, increased the maximum velocity of carboxylation by Rubisco, impacted seed protein concentration, and reduced seed oil concentration across genotypes. The genotypes in this study varied in temperature responses for photosynthetic CO 2 assimilation, stomatal conductance, photosystem II operating efficiency, quantum efficiency of CO 2 assimilation, and seed protein concentration at maturity. These diverse responses among genotypes to elevated air temperature during seed development in the field, reveal the potential for soybean heat tolerance to be improved through breeding and underlines the importance of identifying efficient selection strategies for stress-tolerant crops. • Six soybean genotypes were exposed to elevated air temperature in the field. • Several physiological responses to elevated temperature varied among genotypes. • Elevated temperature increased nighttime respiration across genotypes. • Elevated temperature reduced seed oil concentration across genotypes. • Seed protein concentration response to temperature varied among genotypes.

Estimation of the Optimal Leaf Area Index (Lai) of an Eggplant Canopy Based on the Relationship between the Nighttime Respiration and Daytime Photosynthesis of the Lowermost Leaves

Estimation of the Optimal Leaf Area Index (Lai) of an Eggplant Canopy Based on the Relationship between the Nighttime Respiration and Daytime Photosynthesis of the Lowermost Leaves

Comparison of Embedded Sensor Data for Long-Term Care Residents Before and After Onset of the COVID-19 Pandemic

Older adults have experienced greater isolation and mental health concerns during the COVID-19 pandemic. In long-term care (LTC) settings, residents have been particularly impacted due to strict lockdown policies. Little is known about how these policies have impacted older adults. This study leveraged existing research with embedded sensors installed in LTC settings, and analyzed sensor data of residents (N=30) two months pre/post the onset of the U.S. COVID-19 pandemic (1/13/20 to 3/13/20, 03/14/20 to 5/13/20). Data from three sensors (bed sensors, depth sensors, and motion sensors) were analyzed for each resident using paired t-tests, which generated information on the resident’s pulse, respiration, sleep, gait, and motion in entering/exiting their front door, living rooms, bedrooms, and bathrooms. A 14.4% decrease was observed in front door motion in the two months post-onset of the pandemic, as well as a 2.4% increase in average nighttime respiration, and a 7.6% increase in nighttime bed restlessness. Over half of our sample (68%) had significant differences (p<0.05) in restlessness. These results highlight the potential impact of the COVID-19 pandemic and social distancing policies on older adults living in LTC. While it is not surprising that significant differences were found in the front door motion sensor, the bed sensor data can potentially shed light on how sleep was impacted during this time. As older adults experienced additional mental health concerns during this time, their normal sleep patterns could have been affected. Implications could help inform LTC staff, healthcare providers, and self-management of health approaches among older adults.

Dissolved Oxygen and pH Dynamics Coupled to Photosynthesis in Huntington Bay, Western Long Island Sound

Abstract--- With global warming and eutrophication prompting increases in hypoxia and acidification in the oceans, it is important to understand the relationship between pH and O2 in coastal waters. In Huntington Bay (HB), an estuarine extension of western Long Island Sound, a region subject to both hypoxia and eutrophic acidification, summertime pH and O2 are elevated in surface water during the day at the height of photosynthesis. The high pH (8.4 - 8.6) and O2 (10 - 16 mg L-1) water may be exported from HB into the adjacent Sound, mitigating conditions there. The effects of nighttime respiration, seasonal variations, and responses to episodic events such as storms remain to be determined.

Improving estimations of ecosystem respiration with asymmetric daytime and nighttime temperature sensitivity and relative humidity

Accurately quantifying ecosystem respiration (ER) is crucial for understanding the feedback between the terrestrial carbon (C) cycle and climate change. However, the current estimation of ER by partitioning net ecosystem exchange (NEE) meets a great challenge due to the response difference of daytime and nighttime respiration to temperature and the effects of air humidity. In this study, we modified daytime flux partitioning methods to estimate ER by integrating the different daytime and nighttime temperature sensitivities of ER (E0, day and E0, night, referred to as DT-E0) and then relative humidity (DT-RH) based on eddy covariance and isotopic data at three sites. Our results showed that diurnal and seasonal patterns of daytime ER derived from DT-E0 and DT-RH agreed well with isotopic data, but were considerably different from previous widely used methods (e.g., nighttime (NT) and daytime (DT) methods). The daily mean ER with DT-E0 was 6%∼18% less than those with NT and DT, suggesting that the difference between E0, night and E0, day greatly affects ER estimates. By adding RH, the difference in mean ER estimated by DT-RH and DT-E0 was largest in the dry period at CN-Qia, suggesting that the change in RH at dawn and dusk may significantly influence ER and E0 in the water-limited season. In addition, the magnitude of inhibition by light in the daytime ER from DT was less than that from DT-RH, especially in forest ecosystems, indicating the previous underestimation of light inhibition for ER. Our study highlights the crucial importance of diurnal variations in E0 and RH in accurately estimating ER, which may need to be incorporated into regional and global models to improve the assessment of global C budgets.

Correlations between allocation to foliar phosphorus fractions and maintenance of photosynthetic integrity in six mangrove populations as affected by chilling.

Chilling restrains the distribution of mangroves. We tested whether foliar phosphorus (P) fractions and gene expression are associated with cold tolerance in mangrove species. We exposed seedlings of six mangrove populations from different latitudes to favorable, chilling and recovery treatments, and measured their foliar P concentrations and fractions, photochemistry, nighttime respiration, and gene expression. A Kandelia obovata (KO; 26.45°N) population completely and a Bruguiera gymnorhiza (Guangxi) (BGG; 21.50°N) population partially (30%) survived chilling. Avicennia marina (24.29°N), and other B. gymnorhiza (26.66°N, 24.40°N, and 19.62°N) populations died after chilling. Photosystems of KO and photosystem I of BGG were least injured. During chilling, leaf P fractions, except nucleic acid P in three populations, declined and photoinhibition and nighttime respiration increased in all populations, with the greatest impact in B. gymnorhiza. Leaf nucleic acid P was positively correlated with photochemical efficiency during recovery and nighttime respiration across populations for each treatment. Relatively high concentrations of nucleic acid P and metabolite P were associated with stronger chilling tolerance in KO. Bruguiera gymnorhiza exhibited relatively low concentrations of organic P in favorable and chilling conditions, but its partially survived population showed stronger compensation in nucleic acid P and Pi concentrations and gene expression during recovery.

Joint CO2 Mole Fraction and Flux Analysis Confirms Missing Processes in CASA Terrestrial Carbon Uptake Over North America

AbstractTerrestrial biosphere models (TBMs) play a key role in the detection and attribution of carbon cycle processes at local to global scales and in projections of the coupled carbon‐climate system. TBM evaluation commonly involves direct comparison to eddy‐covariance flux measurements. We use atmospheric CO2 mole fraction ([CO2]) measured in situ from aircraft and tower, in addition to flux‐measurements from summer 2016 to evaluate the Carnegie‐Ames‐Stanford‐Approach (CASA) TBM. WRF‐Chem is used to simulate [CO2] using biogenic CO2 fluxes from a CASA parameter‐based ensemble and CarbonTracker version 2017 (CT2017) in addition to transport and CO2 boundary condition ensembles. The resulting “super ensemble” of modeled [CO2] demonstrates that the biosphere introduces the majority of uncertainty to the simulations. Both aircraft and tower [CO2] data show that the CASA ensemble net ecosystem exchange (NEE) of CO2 is biased high (NEE too positive) and identify the maximum light use efficiency Emax a key parameter that drives the spread of the CASA ensemble in summer 2016. These findings are verified with flux‐measurements. The direct comparison of the CASA flux ensemble with flux‐measurements confirms missing sink processes in CASA. Separating the daytime and nighttime flux, we discover that the underestimated net uptake results from missing sink processes that result in overestimation of respiration. NEE biases are smaller in the CT2017 posterior biogenic fluxes, which assimilate observed [CO2]. Flux tower analyses reveal an unrealistic overestimation of nighttime respiration in CT2017 which we attribute to limited flexibility in the inversion strategy.

Open Field Simulating Nocturnal Warming on Summer Maize Performance in the North China Plain

Climate changes show asymmetrical warming, and warming is typically greater at night than during the day. To understand how nocturnal warming (NW) affects the performance of maize (Zea mays L.), an open-field experiment with a free air temperature increase (FATI) facility was conducted for three seasons during 2014 to 2016 at Luancheng eco-agro-experimental station on the North China Plain (NCP). Three nocturnal warming scenarios were set up: the entire growing period (T1, from V4 to maturity), only the vegetative stages (T2, from V4 to a week presilking) and the reproductive stages (T3, from a week presilking to R6). The treatment without NW was the control. Maize lodged seriously in 2015 due to heavy rainfall combined with strong winds, and the experiment failed. The results from 2014 and 2016 were analyzed in this study. During the experimental duration, the average nocturnal temperature was increased by approximately 3.6 and 3.3 °C at 150 cm height and 2.0 and 1.7 °C at the soil surface during the vegetative stages. The corresponding increases were 2.1 and 2.5 °C and 0.7 and 1.2 °C at the soil surface during the reproductive stages in 2014 and 2016, respectively, as compared with that of the CK treatment. NW during the whole growth period significantly decreased maize yield for the two seasons. Treatment T2 had a smaller impact on maize yield than T1 and T3. The silking stage was delayed by 2 days in 2014 and 2016 under T1. As a result, presilking duration and VT-R1 interval were prolonged by 1–2 days; and the postsilking duration were shortened by 1–3 days under T1. The soil moisture in the warmed plots was slightly lower than that in the control plots in the 2014 and during the stages before the earlier grain-filling stages in 2016, but NW decreased soil water content greatly at the later grain-filling stages in 2016, which caused the fast green leaf senescence and exacerbated the negative effects of NW on maize yield. NW for the whole growth duration (T1) significantly decreased seed weight and harvest index. NW increased leaf nighttime respiration rate in both seasons. No significant effects of NW on ear leaf net photosynthesis, leaf area, and specific leaf weight at early grain-filling stage were observed, irrespective of the warming stage and season. The results suggested that reproductive stages were more sensitive to NW compared to vegetative stages under the growing conditions of NCP. The negative effects of NW were worsened in dry seasons. The reduction in maize yield with nocturnal warming was driven by the reduction in the aboveground carbon allocation from shoot to grain during postanthesis stage.

357 Daridorexant Does Not Impair Respiratory Function in Patients with Mild/Moderate Obstructive Sleep Apnea Irrespective of Severity

Abstract Introduction Daridorexant is a dual orexin receptor antagonist developed for the treatment of insomnia. The effect of the highest phase-3 dose of 50 mg daridorexant on nighttime respiratory function was evaluated in patients with mild/moderate obstructive sleep apnea (OSA). This study showed that repeated doses of daridorexant had no clinically meaningful effect on nighttime respiration (i.e., apnea-hypopnea index [AHI] and peripheral oxygen saturation [SpO2]). In the same study, other relevant respiratory endpoints were evaluated. Methods In this randomized, double-blind, placebo-controlled, two-period, crossover study, daridorexant or placebo was administered in each period once daily for 5 consecutive nights to 28 patients. Treatment differences (daridorexant – placebo) for total number and mean/longest duration of apneas and hypopneas as well as mean and lowest SpO2 during apnea/hypopnea events in Night 5 were explored using linear mixed-effects modeling. Treatment differences for the above-mentioned endpoints versus AHI during TST at baseline (i.e., OSA severity) was analyzed by linear regression using least square approach. Results Of 28 patients enrolled, 25 completed the study and were included in the analysis (n=15/10 with mild/moderate OSA; mean [standard deviation, SD] AHI: 16.3 events/h [8.2]). Compared to placebo, daridorexant increased mean duration of TST and accordingly to a not statistically significant extent the mean number of apneas + hypopneas by 16.4 events (n=103 versus 86.2; 90% confidence interval [CI]: -0.4–33.2]) without difference in mean [SD] AHI between daridorexant (15.1 events/h [7.9] and placebo (14.2 [7.7]). No treatment difference was detected for mean (0.0 sec [-2.6–2.7]) or longest (0.8 sec [-8.9–10.5]) duration of apneas nor for mean (0.2 sec [-2.2–2.5]) or longest (8.3 sec [6.4–23.1]) duration of hypopneas. No treatment difference was observed for mean (0.3% [-0.2–2.1]) and lowest (0.9% [0.3–2.1]) SpO2 during apnea/hypopnea events. Treatment differences for any of the evaluated endpoints did not significantly correlate with AHI at baseline as a marker of OSA severity (r2 ≤ 0.09). Conclusion Daridorexant can safely be administered to patients with mild/moderate OSA as treatment differences for respiratory-related endpoints were not of statistical significance and independent of disease severity in the studied population. Support (if any) Funded by Idorsia Pharmaceuticals Ltd.