Night Respiration Research Articles

Higher Grain-Filling Rate in Inferior Spikelets of Tolerant Rice Genotype Offset Grain Yield Loss under Post-Anthesis High Night Temperatures

Increased nighttime respiratory losses decrease the amount of photoassimilates available for plant growth and yield. We hypothesized that the increased respiratory carbon loss under high night temperatures (HNT) could be compensated for by increased photosynthesis during the day following HNT exposure. Two rice genotypes, Vandana (HNT-sensitive) and Nagina 22 (HNT-tolerant), were exposed to HNT (4 °C above the control) from flowering to physiological maturity. They were assessed for alterations in the carbon balance of the source (flag leaf) and its subsequent impact on grain filling dynamics and the quality of spatially differentiated sinks (superior and inferior spikelets). Both genotypes exhibited significantly higher night respiration rates. However, only Nagina 22 compensated for the high respiration rates with an increased photosynthetic rate, resulting in a steady production of total dry matter under HNT. Nagina 22 also recorded a higher grain-filling rate, particularly at 5 and 10 d after flowering, with 1.5- and 4.0-fold increases in the translocation of 14C sugars to the superior and inferior spikelets, respectively. The ratio of photosynthetic rate to respiratory rate on a leaf area basis was negatively correlated with spikelet sterility, resulting in a higher filled spikelet number and grain weight per plant, particularly for inferior grains in Nagina 22. Grain quality parameters such as head rice recovery, high-density grains, and gelatinization temperature were maintained in Nagina 22. An increase in the rheological properties of rice flour starch in Nagina 22 under HNT indicated the stability of starch and its ability to reorganize during the cooling process of product formation. Thus, our study showed that sink adjustments between superior and inferior spikelets favored the growth of inferior spikelets, which helped to offset the reduction in grain weight under HNT in the tolerant genotype Nagina 22.

Leaf day respiration involves multiple carbon sources and depends on previous dark metabolism.

Day respiration (Rd) is the metabolic, nonphotorespiratory process by which illuminated leaves liberate CO2 during photosynthesis. Rd is used routinely in photosynthetic models and is thus critical for calculations. However, metabolic details associated with Rd are poorly known, and this can be problematic to predict how Rd changes with environmental conditions and relates to night respiration. It is often assumed that day respiratory CO2 release just reflects 'ordinary' catabolism (glycolysis and Krebs 'cycle'). Here, we carried out a pulse-chase experiment, whereby a 13CO2 pulse in the light was followed by a chase period in darkness and then in the light. We took advantage of nontargeted, isotope-assisted metabolomics to determine non-'ordinary' metabolism, detect carbon remobilisationand compare light and dark 13C utilisation. We found that several concurrent metabolic pathways ('ordinary' catabolism, oxidative pentose phosphates pathway, amino acid production, nucleotide biosynthesisand secondary metabolism) took place in the light and participated in net CO2 efflux associated with day respiration. Flux reconstruction from metabolomics leads to an underestimation of Rd, further suggesting the contribution of a variety of CO2-evolving processes. Also, the cornerstone of the Krebs 'cycle', citrate, is synthetised de novo from photosynthates mostly in darkness, and remobilised or synthesised from stored material in the light. Collectively, our data provides direct evidence that leaf day respiration (i) involves several CO2-producing reactions and (ii) is fed by different carbon sources, including stored carbon disconnected from current photosynthates.

Breath of green life: Reduction in plant day and night respiration under elevated CO2.

Breath of green life: Reduction in plant day and night respiration under elevated CO2.

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.

From minute to day: Ecophysiological response of phytoplankton to fluctuating light exposure during vertical mixing

AbstractUnderwater light is a highly dynamic resource for phytoplankton. Fluctuating light influences photosynthesis, respiration, biosynthesis, and growth at different timescales, but the interplay of these processes is not well‐understood. Subsamples of a phytoplankton community from the turbid, well‐mixed lake TaiHu (China) were either vertically moved through different mixing depths or incubated at fixed depths of matching daily light supply. Growth, photosynthetic electron transport rates, net oxygen production, and night respiration were measured for 9 days. Production was investigated during cyclic mixing, throughout the day, and among days of different integral light intensities. Electron transport rates were higher during vertical mixing and increased with mixing depth, therefore mixing phytoplankton better exploited short periods of surface illumination. On the other hand, light‐stimulation of oxygen consumption and photoperiod shortening increased the compensation light intensities for daily production and growth. The communities kept at the surface and sub‐surface were photoinhibited; their net oxygen production declined and compensation light intensity increased in the afternoon. There was no sign of afternoon depression of net oxygen production in mixing phytoplankton which metabolized photosynthetic products in periodic phases of low light in deeper layers. Mixing phytoplankton produced more oxygen during increasing light intensities and respired more at decreasing light intensities, decreasing net oxygen production during the day. This cyclic post‐illumination enhancement of respiration seemed to be hardwired to fluctuating light, regardless of mixing depth and uncoupled from night respiration rates. Photosynthesis and respiration seemed more tightly connected under fluctuating than constant light.

High night temperature during maize post‐flowering increases night respiration and reduces photosynthesis, growth and kernel number

AbstractIn the last years globally, daily night‐time low temperatures have increased more than twice compared with maximum temperatures. There is little evidence about maize growth and yield responses to high night temperature (HNT) under field conditions. In this study, we aimed to (i) evaluate the effect of HNT during post‐flowering on kernel number (KN), crop growth rate expressed in chronological days and thermal units (CGRDand CGRTU, respectively), radiation use efficiency (RUE), night respiration (Rn), net photosynthesis (Amax), chlorophyll fluorescence and cell membrane stability (CMS), and (ii) identify associations among the measured physiological traits. Two hybrids (Te, temperate; and St, subtropical) were exposed to two thermal conditions from R1 + 2d to R1 + 16d: (i) HNT from 1900 to 0700 h, and (ii) ambient night temperature (ANT). The HNT resulted in reductions in KN (8%), CGRD(11%), and CGRTU(19%), with non‐significant changes in kernel weight and grain yield. Reductions in KN were better explained by drops in CGRTUthan in CGRD. Under HNT, Amax significantly decreased (p < 0.05; 17%, among experiments and hybrids) with insignificant changes in CMS and chlorophyll fluorescence. HNT caused a larger effect on Rn in Te (+40%) than in St. We found a strong negative relationship between Rn and Amax, indicating that high Rn might exhibit an indirect effect on Amax, altering carbon balance and growth.

Review on Plant Physiology and Crop Modeling for the Response of Rice Crop to Climate Change

Climate change impacts the sustainability of agriculture. Physiological processes are very essential for improving crop modeling. The objective of this paper was to assess the integrated effects of crop modeling and crop physiology on the response of rice crop to climate change. Some models have weakness and this weakness rectified by better understanding of physiological features which is correlated to the growth and development of the plant. Process-based dynamic crop models are able to estimate a range of crop response to the environment and to assess the biophysical effects of future climate scenarios on growth and yield. Crop modelling has the potential to enable society to assess the efficacy of G × E technologies to mitigate and adapt crop production systems to climate change. An advanced integration of crop modeling and crop physiology will enable a gene-to-farm design of resilient and sustainable crop production systems under a changing climate at regional-to-global scales. High night temperature increases carbon loss from night respiration and reduces the activity of source–sink enzymes resulting in lower biomass, poor grain filling, and reduced grain weight of rice. ORYZA and CERES-Rice models are the most familiar physiological based rice models currently used for rice crop modeling studies. Interaction between plant physiology and modeling is essential to improving the existing models, for creating new models, and for improving predictions on crop responses to climate changes and variability. Keywords: Crop modeling, Physiology, climate change, crop response, Rice DOI: 10.7176/JNSR/13-4-01 Publication date: February 28 th 2022

Effects of Elevated CO2 Concentrations on 13C Fractionation during Photosynthesis, Post-Photosynthesis and Night Respiration in Mangrove Saplings Avicennia marina and Rhizophora stylosa

Carbon fractionation (Δ13C) is well documented for various plants functional types. Yet, specific studies on Δ13C on mangroves are particularly rare although they have a key role in coastal carbon (C) cycling. In this study, we investigated the 13C exchanges between leaves and the atmosphere and between the main plant’s organs in two common mangroves species, Avicennia marina and Rhizophora stylosa subjected to two different CO2 concentrations. Two-years-old saplings were grown in mesocosms during one year under 400 ppm and 800 ppm of CO2. At the end of the experiment, the isotopic value of the night-respired CO2 was measured on six individuals for each species and CO2 treatment. Then, 60 saplings were harvested to measure the organs δ13C values, and, finally, carbon fractionation (Δ13C) during photosynthesis, post-photosynthesis and apparent Δ13C during night respiration were calculated. Results indicated that elevated CO2 reduced Δ13C during photosynthesis by 13% and during night respiration by 20%. Alongside, within-plant Δ13C was twice higher in the saplings grown under elevated CO2 concentrations. These results showed that ongoing and future increases in atmospheric CO2 concentrations have the potential to modify the δ13C values of mangrove trees. These results could have important implications in Blue Carbon sciences, and particularly in the comprehension of future carbon cycling in coastal wetlands, mangroves being an essential link in terrestrial and marine food webs along tropical and subtropical coastlines.

Narrowing Diurnal Temperature Amplitude Alters Carbon Tradeoff and Reduces Growth in C4 Crop Sorghum.

Effect of diurnal temperature amplitude on carbon tradeoff (photosynthesis vs. respiration) and growth are not well documented in C4 crops, especially under changing temperatures of light (daytime) and dark (nighttime) phases in 24 h of a day. Fluctuations in daytime and nighttime temperatures due to climate change narrows diurnal temperature amplitude which can alter circadian rhythms in plant, thus influence the ability of plants to cope with temperature changes and cause contradictory responses in carbon tradeoff, particularly in night respiration during dark phase, and growth. Sorghum [Sorghum bicolor (L.) Moench] is a key C4 cereal crop grown in high temperature challenging agro-climatic regions. Hence, it is important to understand its response to diurnal temperature amplitude. This is the first systematic investigation using controlled environmental facility to monitor the response of sorghum to different diurnal temperature amplitudes with same mean temperature. Two sorghum hybrids (DK 53 and DK 28E) were grown under optimum (27°C) and high (35°C) mean temperatures with three different diurnal temperature amplitudes (2, 10, and 18°C) accomplished by modulating daytime and nighttime temperatures [optimum daytime and nighttime temperatures (ODNT): 28/26, 32/22, and 36/18°C and high daytime and nighttime temperatures (HDNT): 36/34, 40/30, and 44/26°C]. After exposure to different temperature conditions, total soluble sugars, starch, total leaf area and biomass were reduced, while night respiration and specific leaf area were increased with narrowing of diurnal temperature amplitude (18 to 2°C) of HDNT followed by ODNT. However, there was no influence on photosynthesis across different ODNT and HDNT. Contradiction in response of foliar gas exchange and growth suggests higher contribution of night respiration for maintenance rather than growth with narrowing of diurnal temperature amplitude of ODNT and HDNT. Results imply that diurnal temperature amplitude has immense impact on the carbon tradeoff and growth, regardless of hybrid variation. Hence, diurnal temperature amplitude and night respiration should be considered while quantifying response and screening for high temperature tolerance in sorghum genotypes and comprehensive understanding of dark phase mechanisms which are coupled with stress response can further strengthen screening procedures.

Reduction in seed set upon exposure to high night temperature during flowering in maize.

High temperature reduces crop production; however, little is known about the effects of high night temperature (HNT) on the development of male and female reproductive organs, pollination, kernel formation and grain yield in maize (Zea mays L.). Therefore, a temperature-controlled experiment was carried out using heat-sensitive maize hybrid and including three temperature treatments of 32/22°C (day/night; control), 32/26°C and 32/30°C during 14 consecutive days encompassing the flowering stage. When exposed to 30°C night temperature, grain yield and kernel number reduced by 23.8 and 25.1%, respectively, compared with the control. The decrease in grain yield was mainly because of the lower kernel number rather than change in kernel weight under HNT exposure around flowering. No significant differences in grain yield and kernel number were found between 22 and 26°C night temperatures. HNT had no significant effects on the onset of flowering time and anthesis-silking interval but significantly reduced time period of pollen shedding duration and pollen viability, and increased leaf night respiration. Different from high daytime temperature, HNT had no lasting effects on daytime leaf photosynthesis, biomass production and assimilate transportation. From the perspective of source-flow-sink relationship, the unchanged source and flow capacities during daytime are supposed to alleviate the adverse effects on sink strength caused by HNT compared with daytime heat stress. These new findings commendably filled the knowledge gaps concerning heat stress in maize.

Carbon balance and source-sink metabolic changes in winter wheat exposed to high night-time temperature.

Carbon loss under high night-time temperature (HNT) leads to significant reduction in wheat yield. Growth chamber studies were carried out using six winter wheat genotypes, to unravel postheading HNT (23°C)-induced alterations in carbon balance, source-sink metabolic changes, yield, and yield-related traits compared with control (15°C) conditions. Four of the six tested genotypes recorded a significant increase in night respiration after 4days of HNT exposure, with all the cultivars regulating carbon loss and demonstrating different degree of acclimation to extended HNT exposure. Metabolite profiling indicated carbohydrate metabolism in spikes and activation of the TriCarboxylic Acid (TCA) cycle in leaves as important pathways operating under HNT exposure. A significant increase in sugars, sugar-alcohols, and phosphate in spikes of the tolerant genotype (Tascosa) indicated osmolytes and membrane protective mechanisms acting against HNT damage. Enhanced night respiration under HNT resulted in higher accumulation of TCA cycle intermediates like isocitrate and fumarate in leaves of the susceptible genotype (TX86A5606). Lower grain number due to lesser productive spikes and reduced grain weight due to shorter grain-filling duration determined HNT-induced yield loss in winter wheat. Traits and mechanisms identified will help catalyze the development of physiological and metabolic markers for breeding HNT-tolerant wheat.

Leaf growth rate and nitrogen content determine respiratory costs during leaf expansion in grapevines

Respiration processes are well recognized as fundamental for the plant carbon balance, but little attention has been paid to the relationships among respiration rates, environment and genetic variability. This can be of particular interest to understand the differences in net carbon balances in crops as grapevines. Night respiration (Rn ) and its associated growth (Rg ) and maintenance (Rm ) components were evaluated during leaf expansion in two grapevine cultivars (Tempranillo cv. and Garnacha cv.) that differ in their plant growth pattern and carbon balance. Simultaneously, leaf traits as leaf mass area, nitrogen (N) and carbon (C) content were evaluated in order to relate to the respiratory processes and the leaf growth. The results showed the differences in respiration rates associated with the leaf expansion pattern. Tempranillo developed leaves with higher leaf area and lower dry weight per leaf unit than Garnacha. Although differences between cultivars were observed in terms of growth costs in expanding leaves, the maintenance costs were similar for both cultivars. Also, a significant linear regression was found between respiration rates and N content in expanding and mature leaves. The results indicate that differences in structure and nitrogen content of expanding leaves may lead to respiratory differences between cultivars. These results also demonstrate the importance of respiratory cost components in carbon balance calculations in grapevines.

Azolla cover significantly decreased CH4 but not N2O emissions from flooding rice paddy to atmosphere

ABSTRACTAzolla (Azolla filiculoides) is a common aquatic fern that has been used successfully as a dual crop with lowland rice. It grows rapidly and has the ability to fix N2 for rice paddy. However, its ecological significance especially on greenhouse gases emissions remains unclear. To investigate the effect of azolla cover on methane (CH4) and nitrous oxide (N2O) emissions from rice paddy, a pot experiment with two treatments, control (rice plant only) and azolla cover (rice plus azolla covering on the flooding water), was carried out in Tsuruoka, Yamagata, Japan, in 2016. The results showed that the rice growth parameters, like shoot height, maximum and productive tiller numbers, and plant biomass were not significantly different between the two treatments. Dual cropping of azolla with rice significantly suppressed CH4 emissions, likely due to an increase in dissolved oxygen concentration and redox potential at the soil-water interface between flooding water and soil surface. There were significant (P < 0.05) positive correlations between CH4 flux and night respiration (CO2 emissions) between the two treatments. The cumulated CH4 emissions during the growth period until 106 days after transplanting (DAT) was significantly lower at 36.2 g C m−2 from azolla cover treatment than that from control treatment pot at 55.4 g C m−2. A prolonged nonsignificant N2O emission under the azolla cover treatment after the initial highest peak at 15 DAT was recorded due to denitrification of the nitrate in initial soil. No further N2O emissions were recorded thereafter from both treatments. Azolla cover did not affect N2O emissions from both treatments.

Forage rice varieties Fukuhibiki and Tachisuzuka emit larger CH4 than edible rice Haenuki

ABSTRACTTo determine methane (CH4) emission differences between edible and forage rice cultivars, we conducted a pot experiment in Yamagata, Japan to grow edible rice Haenuki, and forage rice Fukuhibiki (for feed rice) and Tachisuzuka (for whole-crop silage (WCS) rice) under similar soil and meteorological conditions. The total amounts of N, P, and K fertilizers applied for Fukuhibiki and Tachisuzuka were 1.7, 1.3, and 1.3 times, respectively, higher than those of Haenuki. CH4 fluxes, and rice plant night respirations were measured once weekly or fortnightly. As per the results, for the whole growth period, shoot height, maximum and productive tiller numbers, and plant biomass were significantly different among the three rice varieties. The rice growth period for Haenuki and Fukuhibiki was 107 days after transplanting (DAT), while that for Tachisuzuka was 135 DAT. The highest peak of CH4 flux occurred around the heading stage for the three varieties. Consistently significant (P < 0.05) or obvious (P < 0.1) positive correlations between CH4 flux and night respiration among the varieties were observed from 9 weeks after rice transplanting to harvest, indicating that much of the CH4 flux was from newly produced root exudates and plant debris through plant photosynthesis. The cumulated CH4 emissions during the same growth period, 106 DAT, from Haenuki, Fukuhibiki, and Tachisuzuka were 55.36, 77.46, and 78.40 g C m−2, respectively. Additionally, Tachisuzuka emitted 25.11 g C m−2 more CH4 between 106–134 DAT. The final cumulated CH4 emissions from Fukuhibiki and Tachisuzuka were 39.9% and 87.0% higher than that from Haenuki, respectively, throughout their growth period.

High day–night transition temperature alters nocturnal starch metabolism in rice (Oryza sativa L.)

Transitory starch plays a vital role in maintenance respiration as its degradation products provide substrate for the night respiration. A study was conducted with two contrasting rice cultivars: Vandana (high night temperature susceptible) and Nagina 22 (high night temperature tolerant) by subjecting them to increase in transition temperature from anthesis to physiological maturity. Night respiration on plant area basis increased by 35% in Vandana at 5 days after anthesis but was unaffected in tolerant cultivar. A simultaneous 18% decrease in starch content was observed in the susceptible cultivar. An analysis of the starch-metabolizing enzymes showed that activity of β-amylase increased markedly in Vandana whereas both β and α-amylase decreased in Nagina 22 following high day to night transition temperature exposure. The level of starch breakdown product, maltose, increased in the susceptible cultivar but glucose levels declined in both the cultivars. Concurrently, expression of chloroplastic isoforms α-amylase OsAMY1, OsAMY2 and β-amylase OsBAM2 increased in Vandana. A lower accumulation of dry matter was recorded in the susceptible than the tolerant cultivar. Our study elucidated the regulatory role of transitory starch in supporting the high day to night transition temperature-induced night-time respiration which is mediated by the increased activity of β-amylase through enhanced expression of OsBAM2 in flag leaves of susceptible cultivar.

Post-flowering night respiration and altered sink activity account for high night temperature-induced grain yield and quality loss in rice (Oryza sativa L.).

High night temperature (HNT) is a major constraint to sustaining global rice production under future climate. Physiological and biochemical mechanisms were elucidated for HNT-induced grain yield and quality loss in rice. Contrasting rice cultivars (N22, tolerant; Gharib, susceptible; IR64, high yielding with superior grain quality) were tested under control (23°C) and HNT (29°C) using unique field-based tents from panicle initiation till physiological maturity. HNT affected 1000 grain weight, grain yield, grain chalk and amylose content in Gharib and IR64. HNT increased night respiration (Rn) accounted for higher carbon losses during post-flowering phase. Gharib and IR64 recorded 16 and 9% yield reduction with a 63 and 35% increase in average post-flowering Rn under HNT, respectively. HNT altered sugar accumulation in the rachis and spikelets across the cultivars with Gharib and IR64 recording higher sugar accumulation in the rachis. HNT reduced panicle starch content in Gharib (22%) and IR64 (11%) at physiological maturity, but not in the tolerant N22. At the enzymatic level, HNT reduced sink strength with lower cell wall invertase and sucrose synthase activity in Gharib and IR64, which affected starch accumulation in the developing grain, thereby reducing grain weight and quality. Interestingly, N22 recorded lower Rn-mediated carbon losses and minimum impact on sink strength under HNT. Mechanistic responses identified will facilitate crop models to precisely estimate HNT-induced damage under future warming scenarios.

Diurnal temperature amplitude alters physiological and growth response of maize (Zea mays L.) during the vegetative stage

Global climate models predict increase in mean daily temperature to be mainly driven by rapid increase in nighttime temperature compared to daytime temperature, leading to narrowing diurnal temperature amplitude. Higher day and night temperatures induce significant negative impact on growth and development of different crops. However, limited studies have focused on quantifying impacts associated with different diurnal temperature amplitudes maintaining the same daily mean temperature. The main objectives were to (i) quantify the impact of diurnal temperature amplitudes on the carbon balance of the plant (photosynthesis versus night respiration rate) and (ii) evaluate the significance of variable day and night temperature with a common mean on the carbohydrate composition and overall plant growth. A maize hybrid (DKC47-27RIB) was grown in controlled environments at two mean daily temperatures (30°C and 35°C) with three different combinations of day and night temperatures resulting in diurnal temperature amplitudes of 2°C, 10°C and 18°C. After 42days of temperature treatments, lower diurnal temperature amplitude led to a linear increase in night respiration and a linear decrease in total sugars, non-reducing sugars, starch concentrations, plant height, total leaf area and total biomass accumulation. However, there was no significant change in photosynthetic rate among the treatment combinations, while photochemical efficiency (Fv/Fm) and chlorophyll index decreased only with diurnal temperature amplitude of 18°C and 2°C, respectively. A significant negative relationship was found between night respiration and total biomass accumulation (R2=0.73; P<0.01), total leaf area (R2=0.82; P<0.01), specific leaf area (R2=0.21; P<0.01), non-reducing sugars (R2=0.50; P<0.01) and starch concentrations (R2=0.50; P<0.01). The results imply that narrowing diurnal temperature amplitude as a result of higher night temperature is the major driver of the negative impact on vegetative growth in maize.

Balance between carbon gain and loss under long-term drought: impacts on foliar respiration and photosynthesis in Quercus ilex L.

Terrestrial carbon exchange is a key process of the global carbon cycle consisting of a delicate balance between photosynthetic carbon uptake and respiratory release. We have, however, a limited understanding how long-term decreases in precipitation induced by climate change affect the boundaries and mechanisms of photosynthesis and respiration. We examined the seasonality of photosynthetic and respiratory traits and evaluated the adaptive mechanism of the foliar carbon balance of Quercus ilex L. experiencing a long-term rainfall-exclusion experiment. Day respiration (Rd) but not night respiration (Rn) was generally higher in the drought treatment leading to an increased Rd/Rn ratio. The limitation of mesophyll conductance (gm) on photosynthesis was generally stronger than stomatal limitation (gs) in the drought treatment, reflected in a lower gm/gs ratio. The peak photosynthetic activity in the drought treatment occurred in an atypical favourable summer in parallel with lower Rd/Rn and higher gm/gs ratios. The plant carbon balance was thus strongly improved through: (i) higher photosynthetic rates induced by gm; and (ii) decreased carbon losses mediated by Rd. Interestingly, photosynthetic potentials (Vc,max, Jmax, and TPU) were not affected by the drought treatment, suggesting a dampening effect on the biochemical level in the long term. In summary, the trees experiencing a 14-year-long drought treatment adapted through higher plasticity in photosynthetic and respiratory traits, so that eventually the atypical favourable growth period was exploited more efficiently.

The dark side of algae cultivation: Characterizing night biomass loss in three photosynthetic algae, Chlorella sorokiniana, Nannochloropsis salina and Picochlorum sp.

Night biomass loss in photosynthetic algae is an essential parameter that is often overlooked when modeling or optimizing biomass productivities. Night respiration acts as a tax on daily biomass gains and has not been well characterized in the context of biomass production for biofuels. We examined the night biomass loss in three algae strains that may have potential for commercial biomass production (Nannochloropsis salina — CCMP1776, Chlorella sorokiniana — DOE1412, and Picochlorum sp. LANL-WT). Biomass losses were monitored by ash free dry weight (AFDWmgL−1) and optical density (OD750) on a thermal-gradient incubator. Specific night biomass loss rates were highly variable (ranging from −0.006 to −0.59day−1), species-specific, and dependent on both culture growth phase prior to the dark period and night pond temperature. In general, the fraction of biomass lost over a 10h dark period, which ranged from ca. 1 to 22% in our experiments, was positively correlated with temperature and declined as the culture transitioned from late exponential to linear to late linear phase. The dynamics of biomass loss should be taken into consideration in algae strain selection, are critical in predictive modeling of biomass production based on geographic location, and can influence the net productivity of photosynthetic cultures used for bio-based fuels or products.

Differential response of rice plants to high night temperatures imposed at varying developmental phases

Increasing night temperatures can reduce growth and yield of rice plants, but limited information is available on the comparative effects of high night temperature (HNT) treatment at different growth stages on growth and physiological responses of rice. We conducted a study in controlled-environment chambers to determine the growth and physiological responses and spikelet differentiation of rice cultivars to HNT treatment at different growth stages. Plants were exposed to two temperatures: 30/21°C (low) and 30/25°C (high) day/night temperatures. At the end of the vegetative period, plants grown in the low (LNT) and high (HNT) night temperatures were further subdivided and plants were exposed to different temperature treatments in the reproductive growth period. Photosynthesis, night respiration rates, and plant growth parameters were measured at various stages. High night temperature had no significant effects on the growth of rice cultivars during the vegetative phase. Maximum photosynthesis at the vegetative phase was not significantly affected, but plant dark respiration increased (within the 14–20% range). Genotypic variation in dark respiration was observed at later growth stages. Rice plants that received HNT at the early reproductive stage had the lowest number of spikelets per panicle, presenting a 35.9% of degenerated spikelets, significantly higher than those observed in other treatment times. This study shows that the response of rice cultivars to HNT varies with time of treatment and that the occurrence of HNT during the reproductive period provided supportive evidence on how HNT might reduce yield by increasing plant’s dark respiration rate and spikelet degeneration (which consequently reduced sink size), thus, decreasing biomass production.