The Hidden Costs of Nighttime Warming on Yields
2020; Elsevier BV; Volume: 25; Issue: 7 Linguagem: Inglês
10.1016/j.tplants.2020.02.003
ISSN1878-4372
AutoresWalid Sadok, S. V. Krishna Jagadish,
Tópico(s)Climate change impacts on agriculture
ResumoNighttime warming is reducing crop yields worldwide, threatening global food security.This phenomenon is more complex than may be assumed, likely to involve interaction between two driving forces: nighttime temperature and evaporative demand.The two conspire to limit carbon availability for yield and end-use quality traits while decreasing water use efficiency, potentially enhancing vulnerability to droughts.An ecophysiological framework is proposed as a guide to implement future research efforts to mitigate yield declines.Such efforts should integrate physiology with crop modeling, breeding, and management to identify sustainable pathways for mitigation as climate change intensifies. Nighttime warming poses a threat to global food security as it is driving yield declines worldwide, but our understanding of the physiological basis of this phenomenon remains very limited. Furthermore, it is often assumed that such declines are driven solely by increases in nighttime temperature (TNight). Here we argue that, in addition to temperature, increases in nighttime evaporative demand may 'conspire' to penalize yields and end-use quality traits. We propose an ecophysiological framework outlining the possible mechanistic basis of such declines in yield and quality. We suggest ways to use the proposed framework as a guide to future efforts aimed at alleviating productivity losses by integrating crop ecophysiology with modeling, breeding, and management. Nighttime warming poses a threat to global food security as it is driving yield declines worldwide, but our understanding of the physiological basis of this phenomenon remains very limited. Furthermore, it is often assumed that such declines are driven solely by increases in nighttime temperature (TNight). Here we argue that, in addition to temperature, increases in nighttime evaporative demand may 'conspire' to penalize yields and end-use quality traits. We propose an ecophysiological framework outlining the possible mechanistic basis of such declines in yield and quality. We suggest ways to use the proposed framework as a guide to future efforts aimed at alleviating productivity losses by integrating crop ecophysiology with modeling, breeding, and management. One of the most ubiquitous effects of anthropogenic climate change (see Glossary) is the increase in global temperature, an observation that led to the coining of the term 'global warming' by Wallace Broeker in the 1970s [1.Broecker W.S. Climatic change: are we on the brink of a pronounced global warming?.Science. 1975; 189: 460-463Crossref PubMed Scopus (189) Google Scholar]. In the case of crops, it could be argued that this terminology is alarmingly adequate. An overwhelming majority of reports have shown that heat stress due to increases in temperature are driving global yield declines of major crops more than any other environmental stressors [2.Deryng D. et al.Global crop yield response to extreme heat stress under multiple climate change futures.Environ. Res. Lett. 2014; 9034011Crossref Scopus (393) Google Scholar, 3.Tack J. et al.Disaggregating sorghum yield reductions under warming scenarios exposes narrow genetic diversity in US breeding programs.Proc. Natl. Acad. Sci. U. S. A. 2017; 114: 9296-9301Crossref PubMed Scopus (55) Google Scholar, 4.Zhao C. et al.Temperature increase reduces global yields of major crops in four independent estimates.Proc. Natl. Acad. Sci. U. S. A. 2017; 114: 9326-9331Crossref PubMed Scopus (863) Google Scholar, 5.Ortiz-Bobea A. et al.Unpacking the climatic drivers of US agricultural yields.Environ. Res. Lett. 2019; 14064003Crossref Scopus (57) Google Scholar]. Understandably, this has resulted in major international efforts to better understand the mechanisms of heat stress in crops and initiate global initiatives to mitigate its negative effects on crop productivity (e.g., see reviews in [6.Ortiz R. et al.Climate change: can wheat beat the heat?.Agric. Ecosyst. Environ. 2008; 126: 46-58Crossref Scopus (472) Google Scholar,7.Reynolds M.P. et al.An integrated approach to maintaining cereal productivity under climate change.Glob. Food. Sec. 2016; 8: 9-18Crossref Scopus (75) Google Scholar]). A comparatively less known dimension to this warming effect consists in yield declines that are specifically attributed to increases in minimal (i.e., nighttime) temperatures. This effect is the result of an asymmetric increase in the warming trends whereby global TNight values are rising at a rate that is 1.4 times that of daytime temperatures [8.Peng S. et al.Rice yields decline with higher night temperature from global warming.Proc. Natl. Acad. Sci. U. 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For wheat for instance, in experiments integrating field-based infrastructure with cyber-physical systems, it was found that for every 1°C increase in TNight during the seed-fill period, yield declines averaged 6% among winter wheat cultivars that are widely grown in the US Great Plains [15.Hein N.T. et al.Integrating field-based heat tents and cyber-physical system technology to phenotype high night-time temperature impact on winter wheat.Plant Methods. 2019; 1541Crossref PubMed Scopus (18) Google Scholar]. Similarly, about 4–7% reduction in yield per 1°C increase in TNight was observed for field-grown spring wheat and rice, with treatments imposed during flowering and seed-fill stages [13.García G.A. et al.High night temperatures during grain number determination reduce wheat and barley grain yield: a field study.Glob. Change Biol. 2015; 21: 4153-4164Crossref PubMed Scopus (85) Google Scholar,14.García G.A. et al.Post-anthesis warm nights reduce grain weight in field-grown wheat and barley.Field Crop Res. 2016; 195: 50-59Crossref Scopus (64) Google Scholar,18.Lyman N.B. et al.Neglecting rice milling yield and quality underestimates economic losses from high-temperature stress.PLoS One. 2013; 8e72157Crossref PubMed Scopus (130) Google Scholar]. An even less known component of nighttime warming is mediated by increases in nighttime atmospheric vapor pressure deficit (VPD). This effect is now well‐documented for daytime conditions, where continent-wide historic increases in VPD have been reported and projected to further increase over the next decades [19.Ficklin D.L. Novick K.A. Historic and projected changes in vapor pressure deficit suggest a continental-scale drying of the United States atmosphere.J. Geophys. Res. 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Manag. 2019; 448: 445-456Crossref Scopus (22) Google Scholar, 32.Groh J. et al.Quantification and prediction of nighttime evapotranspiration for two distinct grassland ecosystems.Water Resour. Res. 2019; 55: 2961-2975Crossref Scopus (23) Google Scholar]. While VPDNight values are substantially (e.g., one order of magnitude) lower than those during the day (typically averaging 1–3 kPa daily), reports point to an increasing frequency of events of much higher average night VPD values. In some extreme cases, these could fall within the daytime range, under an array of environments from tropical to arid and Mediterranean, particularly the summer, a period that is in the growing season of many field crops [25.Alvarado-Barrientos M.S. et al.Nighttime transpiration in a seasonally dry tropical montane cloud forest environment.Trees. 2015; 29: 259-274Crossref Scopus (31) Google Scholar,26.Si J. et al.Nighttime sap flow and its driving forces for Populus euphratica in a desert riparian forest, northwest China.J. Arid Land. 2015; 7: 665-674Crossref Scopus (12) Google Scholar,28.O'Keefe K. Nippert J.B. Drivers of nocturnal water flux in a tallgrass prairie.Funct. Ecol. 2018; 32: 1155-1167Crossref Scopus (20) Google Scholar,29.Yu T. et al.Depressed hydraulic redistribution of roots more by stem refilling than by nocturnal transpiration for Populus euphratica Oliv. in situ measurement.Ecol. Evol. 2018; 8: 2607-2616Crossref PubMed Scopus (32) Google Scholar,31.Di N. et al.Diurnal and nocturnal transpiration behaviors and their responses to groundwater-table fluctuations and meteorological factors of Populus tomentosa in the North China Plain.For. Ecol. Manag. 2019; 448: 445-456Crossref Scopus (22) Google Scholar,33.Bazié H.R. et al.Temporal variations in transpiration of Vitellaria paradoxa in West African agroforestry parklands.Agrofor. Syst. 2018; 92: 1673-1686Crossref Scopus (8) Google Scholar,34.Zhao C. et al.Nighttime transpiration of Populus euphratica during different phenophases.J. For. Res. 2019; 30: 435-444Crossref Scopus (12) Google Scholar]. Recently, such increases in VPDNight have been related to decreases in ecosystem productivity independent from temperature [27.Nagano H. et al.Extremely dry environment down-regulates nighttime respiration of a black spruce forest in Interior Alaska.Agric. For. Meteorol. 2018; 249: 297-309Crossref Scopus (8) Google Scholar], leading to major alterations to ecosystem water balance [28.O'Keefe K. Nippert J.B. Drivers of nocturnal water flux in a tallgrass prairie.Funct. Ecol. 2018; 32: 1155-1167Crossref Scopus (20) Google Scholar,32.Groh J. et al.Quantification and prediction of nighttime evapotranspiration for two distinct grassland ecosystems.Water Resour. Res. 2019; 55: 2961-2975Crossref Scopus (23) Google Scholar]. However, the effects of VPDNight on crop physiology and productivity are typically not considered either separately or in interaction with increases in TNight. As a result, the ecophysiological basis of yield declines induced by nighttime warming remains poorly understood, a knowledge gap that urgently needs to be filled in the global effort to mitigate the impacts of climate change on crop productivity. Why are warmer nights causing crop yield decreases? The physiological mechanisms underlying yield decreases in response to TNight are complex, operating at different tissues, organs, and organizational levels. In vegetative tissues, the general operating principle enabling high TNight to result in yield penalties comprises losses in the amount of carbon directed toward plant and seed growth [14.García G.A. et al.Post-anthesis warm nights reduce grain weight in field-grown wheat and barley.Field Crop Res. 2016; 195: 50-59Crossref Scopus (64) Google Scholar,35.Atkin O.K. et al.Respiration as a percentage of daily photosynthesis in whole plants is homeostatic at moderate, but not high, growth temperatures.New Phytol. 2007; 174: 367-380Crossref PubMed Scopus (139) Google Scholar,36.Impa S.M. et al.Carbon balance and source–sink metabolic changes in winter wheat exposed to high night-time temperature.Plant Cell Environ. 2019; 42: 1233-1246Crossref PubMed Scopus (52) Google Scholar]. However, there are multiple groups of mechanisms that separately or together 'conspire' to result in carbon loss (Figure 1, Key Figure). One such group involves high TNight-induced increases in nighttime respiration [12.Bahuguna R.N. et al.Post-flowering night respiration and altered sink activity account for high night temperature-induced grain yield and quality loss in rice (Oryza sativa L.).Physiol. Plant. 2017; 159: 59-73Crossref PubMed Scopus (78) Google Scholar,37.Atkin O.K. Tjoelker M.G. Thermal acclimation and the dynamic response of plant respiration to temperature.Trends Plant Sci. 2003; 8: 343-351Abstract Full Text Full Text PDF PubMed Scopus (899) Google Scholar, 38.Atkin O.K. et al.The hot and the cold: unravelling the variable response of plant respiration to temperature.Funct. Plant Biol. 2005; 32: 87Crossref Scopus (356) Google Scholar, 39.Shi W. et al.Source–sink dynamics and proteomic reprogramming under elevated night temperature and their impact on rice yield and grain quality.New Phytol. 2013; 197: 825-837Crossref PubMed Scopus (151) Google Scholar], leading to decreases in the amount of photoassimilates available for plant growth and yield. In grapevine (Vitis vinifera), for instance, increasing TNight from 25°C to 35°C resulted in increased leaf respiratory carbon losses reflected by decreases in nonstructural carbohydrates by 0.025 and 0.041 mg g−1 dry weight, respectively, relative to the control treatment of 15°C [40.Tombesi S. et al.Relationship among night temperature, carbohydrate translocation and inhibition of grapevine leaf photosynthesis.Environ. Exp. Bot. 2019; 157: 293-298Crossref Scopus (15) Google Scholar]. Such losses are consistent with metabolite profiling studies in wheat and rice, which revealed an increase in tricarboxylic acid (TCA) cycle intermediates in leaves exposed to high TNight, supporting increased respiration in the photosynthesizing tissue [36.Impa S.M. et al.Carbon balance and source–sink metabolic changes in winter wheat exposed to high night-time temperature.Plant Cell Environ. 2019; 42: 1233-1246Crossref PubMed Scopus (52) Google Scholar,41.Glaubitz U. et al.High night temperature strongly impacts TCA cycle, amino acid and polyamine biosynthetic pathways in rice in a sensitivity-dependent manner.J. Exp. Bot. 2015; 66: 6385-6397Crossref PubMed Scopus (49) Google Scholar]. Another group of mechanisms reflect the direct effects of higher TNight on carbon availability by depressing photosynthesis-dependent processes (Figure 1). In this regard, recent reports indicate that inhibitory effects may arise from faster rates of leaf senescence [16.Lesjak J. Calderini D.F. Increased night temperature negatively affects grain yield, biomass and grain number in Chilean quinoa.Front. Plant Sci. 2017; 8: 352Crossref PubMed Scopus (38) Google Scholar], as a consequence of deactivation of several key chloroplastic stroma enzymes during the night [40.Tombesi S. et al.Relationship among night temperature, carbohydrate translocation and inhibition of grapevine leaf photosynthesis.Environ. Exp. Bot. 2019; 157: 293-298Crossref Scopus (15) Google Scholar,42.Sakuraba Y. et al.Delayed degradation of chlorophylls and photosynthetic proteins in Arabidopsis autophagy mutants during stress-induced leaf yellowing.J. Exp. Bot. 2014; 65: 3915-3925Crossref PubMed Scopus (58) Google Scholar]. This situation could lead to yield penalties by reducing the duration of effective light interception by the crop, and/or reducing the duration of the functional 'stay-green' window that is critical to sustain seed fill. In addition, although limited, preliminary evidence points to a role of higher TNight in downregulating photosynthesis the following day, presumably through a mechanism of feedback inhibition arising from overaccumulation of carbohydrates in the leaves [40.Tombesi S. et al.Relationship among night temperature, carbohydrate translocation and inhibition of grapevine leaf photosynthesis.Environ. Exp. Bot. 2019; 157: 293-298Crossref Scopus (15) Google Scholar]. Consistently with this, high TNight stress imposed at either the pre- or post-flowering stage impacted yields negatively, although the post-flowering treatment generated the highest yield penalty [12.Bahuguna R.N. et al.Post-flowering night respiration and altered sink activity account for high night temperature-induced grain yield and quality loss in rice (Oryza sativa L.).Physiol. Plant. 2017; 159: 59-73Crossref PubMed Scopus (78) Google Scholar,36.Impa S.M. et al.Carbon balance and source–sink metabolic changes in winter wheat exposed to high night-time temperature.Plant Cell Environ. 2019; 42: 1233-1246Crossref PubMed Scopus (52) Google Scholar,39.Shi W. et al.Source–sink dynamics and proteomic reprogramming under elevated night temperature and their impact on rice yield and grain quality.New Phytol. 2013; 197: 825-837Crossref PubMed Scopus (151) Google Scholar,43.Peraudeau S. et al.Increase in night temperature in rice enhances respiration rate without significant impact on biomass accumulation.Field Crop Res. 2015; 171: 67-78Crossref Scopus (32) Google Scholar]. There is evidence, however, that early imposition of high TNight stress could have a stronger impact on crop development than may be assumed. In wheat, it was found that seedlings exposed to an increase in TNight from 20°C to 30°C for 21 days after planting with daytime T maintained at 30°C resulted in a reduction in total leaf area by up to 60% among 11 spring wheat cultivars from south Australia, Mexico, and France [44.Schoppach R. Sadok W. Transpiration sensitivities to evaporative demand and leaf areas vary with night and day warming regimes among wheat genotypes.Funct. Plant Biol. 2013; 40: 708-718Crossref Scopus (23) Google Scholar]. Importantly, such effects were exhibited only by the European cultivars, indicating a potential to breed against penalties arising from restricted leaf growth. Furthermore, findings point to negative effects arising from high TNight reducing the rates of carbohydrate translocation from leaves to sink organs [40.Tombesi S. et al.Relationship among night temperature, carbohydrate translocation and inhibition of grapevine leaf photosynthesis.Environ. Exp. Bot. 2019; 157: 293-298Crossref Scopus (15) Google Scholar], suggesting a role of high TNight stress on phloem loading/unloading processes (Figure 1). A final mechanism links increases in TNight to potential impacts on daytime water use, although evidence for this is much more limited [44.Schoppach R. Sadok W. Transpiration sensitivities to evaporative demand and leaf areas vary with night and day warming regimes among wheat genotypes.Funct. Plant Biol. 2013; 40: 708-718Crossref Scopus (23) Google Scholar]. In this case, exposing the same 11 previously mentioned wheat cultivars to increasing TNight during seedling stages generally led to a higher daytime transpiration rate (TR) concomitant with decreases in leaf area, suggesting significant decrease in water use efficiency (WUE). The authors of [44.Schoppach R. Sadok W. Transpiration sensitivities to evaporative demand and leaf areas vary with night and day warming regimes among wheat genotypes.Funct. Plant Biol. 2013; 40: 708-718Crossref Scopus (23) Google Scholar] hypothesized that TNight treatments could have altered plant hydraulic conductance by promoting aquaporin activity while negatively impacting photosynthesis, leading to reduced biomass accumulation and leaf area. Besides reducing carbon availability and its rate of translocation to seeds, increases in TNight induce yield losses through direct impacts on complex reproductive and seed maturity processes, resulting in not only quantitative grain losses (Figure 1) but also effects on grain quality and composition (Figure 2). One mechanism that enables yield penalties through high TNight operates by lowering seed set as a result of poor pollination. This effect has been shown to be mediated by increased accumulation of reactive oxygen species (ROS) leading to increased membrane damage, ultimately leading to lower pollen viability [45.Prasad P.V.V. Djanaguiraman M. High night temperature decreases leaf photosynthesis and pollen function in grain sorghum.Funct. Plant Biol. 2011; 38: 993Crossref PubMed Scopus (89) Google Scholar,46.Luria G. et al.Direct analysis of pollen fitness by flow cytometry: implications for pollen response to stress.Plant J. 2019; 98: 942-952Crossref PubMed Scopus (28) Google Scholar]. However, as is the case with leaves, damage from high TNight during the reproductive stage also extends to triggering significantly higher rates of respiration in reproductive tissues [17.Loka D.A. Oosterhuis D.M. Effect of high night temperatures on cotton respiration, ATP levels and carbohydrate content.Environ. Exp. Bot. 2010; 68: 258-263Crossref Scopus (69) Google Scholar]. Particularly during seed fill, this process penalizes yields by decreasing the amount of carbon available for starch production and accumulation, consequently leading to lower seed mass [14.García G.A. et al.Post-anthesis warm nights reduce grain weight in field-grown wheat and barley.Field Crop Res. 2016; 195: 50-59Crossref Scopus (64) Google Scholar] (Figure 1). In wheat, recent developments indicate that this process has major implications for not only seed size but also its composition (Figure 2). For instance, in wheat spikes, high TNight strongly interferes with carbohydrate metabolism, leading to increased accumulation of sugars, sugar alcohols, and phosphate in seeds concomitant with an increase in the accumulation of starch degradation enzymes (e.g., isoamylase III, alpha-amylase, beta-amylase [47.Impa S.M. et al.High night temperature induced changes in grain starch metabolism alters starch, protein and lipid accumulation in winter wheat.Plant Cell Environ. 2020; 43: 431-447Crossref PubMed Scopus (30) Google Scholar]). While such responses are likely to serve the purpose of meeting higher respiratory demand, the accumulation of such compounds may enable protection of membrane integrity against high TNight damage [36.Impa S.M. et al.Carbon balance and source–sink metabolic changes in winter wheat exposed to high night-time temperature.Plant Cell Environ. 2019; 42: 1233-1246Crossref PubMed Scopus (52) Google Scholar]. Similarly, in field-grown rice, TNight-driven reductions in grain yield extend to poor grain quality and increased chalkiness [12.Bahuguna R.N. et al.Post-flowering night respiration and altered sink activity account for high night temperature-induced grain yield and quality loss in rice (Oryza sativa L.).Physiol. Plant. 2017; 159: 59-73Crossref PubMed Scopus (78) Google Scholar,18.Lyman N.B. et al.Neglecting rice milling yield and quality underestimates economic losses from high-temperature stress.PLoS One. 2013; 8e72157Crossref PubMed Scopus (130) Google Scholar] as a result of a reduction in major starch-synthesizing enzymes leading to symptoms illustrated in Figure 2. In the case of wheat, however, the decrease in starch concentration driven by carbon losses due to increasing nighttime respiration led to greater accumulation of protein and lipids [36.Impa S.M. et al.Carbon balance and source–sink metabolic changes in winter wheat exposed to high night-time temperature.Plant Cell Environ. 2019; 42: 1233-1246Crossref PubMed Scopus (52) Google Scholar], but such gains – particularly in protein – were not enough to compensate for the incurred yield penalties. Importantly, genotypic differences in these traits have been reported, suggesting the possibility to breed directly for seed composition tolerance to high TNight stress (Figure 2). Such impacts on grain composition are likely to further aggravate the negative economic impacts resulting from a decrease in yield per se by lowering end-use product quality [12.Bahuguna R.N. et al.Post-flowering night respiration and altered sink activity account for high night temperature-induced grain yield and quality loss in rice (Oryza sativa L.).Physiol. Plant. 2017; 159: 59-73Crossref PubMed Scopus (78) Google Scholar,18.Lyman N.B. et al.Neglecting rice milling yield and quality underestimates economic losses from high-temperature stress.PLoS One. 2013; 8e72157Crossref PubMed Scopus (130) Google Scholar]. For instance, lower amounts of starch may complicate starch-based processes that are key to the breadmaking, biofuel, and beer industries. Compared with TNight stress, the effects of higher VPDNight on crop physiology, development, and productivity are much less understood. There is, however, a strong agreement in the literature that higher VPDNight would result in non-negligible levels of crop water losses through increases in nighttime TR (TRNight; Figure 1). Depending on the species and the environment, this loss could amount to 5–50% of daytime water use. This has been reported for several key grain and fruit crops, including wheat [48.Rawson H.M. Clarke J.M. Nocturnal transpiration in wheat.Aust. J. Plant Physiol. 1988; 15: 397-406Google Scholar, 49.Balota M. et al.Morphological and physiological traits associated with canopy temperature depression in three closely related wheat lines.Crop Sci. 2008; 48: 1897Crossref Scopus (71) Google Scholar, 50.Schoppach R. et al.Genotype-dependent influence of night-time vapour pressure deficit on night-time transpiration and daytime gas exchange in wheat.Funct. 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