Summary: Global nocturnal temperatures are rising more rapidly than daytime temperatures and have a large effect on crop productivity. In particular, stomatal conductance at night (g_sn) is surprisingly poorly understood and has not been investigated despite constituting a significant proportion of overall canopy water loss. Here, we present the results of 3 yr of field data using 12 spring Triticum aestivum genotypes which were grown in NW Mexico and subjected to an artificial increase in night‐time temperatures of 2°C. Under nocturnal heating, grain yields decreased (1.9% per 1°C) without significant changes in daytime leaf‐level physiological responses. Under warmer nights, there were significant differences in the magnitude and decrease in g_sn, values of which were between 9 and 33% of daytime rates while respiration appeared to acclimate to higher temperatures. Decreases in grain yield were genotype‐specific; genotypes categorised as heat tolerant demonstrated some of the greatest declines in yield in response to warmer nights. We conclude the essential components of nocturnal heat tolerance in wheat are uncoupled from resilience to daytime temperatures, raising fundamental questions for physiological breeding. Furthermore, this study discusses key physiological traits such as pollen viability, root depth and irrigation type may also play a role in genotype‐specific nocturnal heat tolerance.

Tropical dry forests (TDF) are one of the most widely distributed tropical land‐cover types in Mexico, but their regional‐to‐global contribution to the carbon and water cycles is still highly uncertain. We measured CO₂ and water vapor fluxes between the ecosystem and atmosphere using the eddy covariance technique from 2016 to 2018 in an old‐growth TDF in northwestern Mexico. First, we investigated the magnitude and seasonality of evapotranspiration (ET), net ecosystem production (NEP) and its contributing fluxes, gross ecosystem production (GEP), and ecosystem respiration (Reco). Second, we explored the main environmental factors controlling carbon and water fluxes as well as tested if this ecosystem acted as a net carbon source or sink. During the study period, all precipitation entering the ecosystem went back to the atmosphere through ET (738.9 ±58.26 mm y⁻¹). Ecosystem respiration (2203.16 ±244.2 g C m⁻² y⁻¹) was consistently larger than GEP (1975.32 ±295.52 g C m⁻² y⁻¹), determining an annual NEP (−227.6 ±59.4 g C m⁻² y⁻¹) that resulted in net annual carbon losses. This forest maintained its water use efficiency (WUE; GEP/ET) across years (2.53–3.24), but water availability constrained light use and maximum carbon assimilation rates. Our results render relevance to the feedback between soil water content and net radiation as the main environmental variables controlling ecosystem fluxes in this old‐growth TDF.

An experiment was carried out to evaluate the effect of increased temperature on roots and leaf water and osmotic potential, osmotic adjustment (OA) and transpiration on Triticum durum L. (CIRNO C2008 variety) during growth (seedling growth), tillering and heading phenophases. Wheat was sown under field conditions at the Experimental Technology Transfer Center (CETT-910), as a representative wheat crop area from the Yaqui Valley, Sonora México. Thermal radiators were placed at 1.20 m from the crop canopy. Treatments included warmed plots (2 °C) and ambient canopy temperature with five replicates. Temperature treatment was controlled using a (proportional, integrative, derivative) feedback control system on plots covering a circular area of r = 1.5 m. Results indicated a significant decrease in the osmotic potential of roots and leaves for the warmed plots. Water potential, under warming treatment, also experienced a significant reduction and a potential gradient was observed in both, roots and leaves, while the phenophases were delayed. Such results demonstrate that, under warmer conditions, plants increase water absorption for cooling. Hence, transpiration experienced a significant increase under warming in all phenophases that was related to the low root and leaf water potential. CIRNO C2008 also experienced OA in all phenophases with glycine betaine as the osmolyte with major contribution.

This work evaluates the experimental warming effects on phenology and grain yield components of wheat in the Yaqui Valley, Sonora, México, using CIRNO C2008 variety fromTriticum durumL., as a model during the cropping cycle of 2016–2017 (December to April). Infrared radiators were deployed to induce experimental warming by 2 °C above ambient crop canopy temperature, in a temperature free-air controlled enhancement system. Temperature was controlled by infrared temperature sensors placed in eight plots which covered a circle ofr= 1.5 m starting five days after germination until harvest. The warming treatment caused a reduction of phenophases occurrence starting at the stem extension phenophase. Such phenological responses generated a significant biological cycle reduction of 14 days. Despite this delay, CIRNO C2008 completed its biological cycle adequately. However, plant height under the warming treatment was reduced significantly and differences were particularly observed at the final phenophases of the vegetative cycle. Plant height correlated negatively with spikes length, spikes mass, and number of filled grains. Warming also reduced grain yield in 33%. The warming treatment caused a stress intensity (SI = 1-yield warming/yield control) of 39.4% and 33.2% in biomass and grain yield, respectively. The differences in stress intensities between biomass and grain yield were based on plant height reduction. Grain mass was not affected, demonstrating the crop capability for remobilization and adequate distribution of elaborated substances for the spikes under warming conditions.

Soil respiration (R_S) is an important component of the C cycle because it contributes significant CO₂ emissions to the atmosphere that result from metabolism and respiration of its autotrophic and heterotrophic components. However, the relative importance of different biophysical controls that drive the variability of this flux and their influence along forest succession pathways is still unknown. We incorporate multiyear R_S, ecosystem flux and meteorological measurements in old-growth (OG), mid-secondary (MS) and early-secondary (ES) tropical dry forests (TDFs) with the goal of assessing the temporal variation of R_S and identifying the biophysical controls at each site by applying structural equation models (SEM). Along forest succession, R_S followed the pattern of precipitation events; we identified by the end of the wet season that R_S was sustained by a longer period at OG, while in MS and ES, R_S decreased according to the soil moisture availability. According to SEM, soil moisture and soil temperature exert an effect on the variability of R_S in all sites. However, we found that R_S was also controlled by the vapor pressure deficit at MS and gross primary production at OG and ES. Our results suggest that seasonality has a different impact on R_S along forest succession in TDFs found in northwestern Mexico and highlights the relevance of considering additional biophysical controls of R_S for a better understanding this critical process of the C cycle.

Global night-time temperatures are increasing and correlate with a decline in crop yield. Various aspects of nocturnal physiology in plants are understudied, one of which is the independent influence on daytime processes. Twelve elite wheat genotypes were field grown in plots with artificially increased night-time temperatures (+ 2°C). The stomatal conductance on the adaxial and abaxial leaf sides were measured during the morning and the night, and stomatal morphological traits were assessed during the same period of plant growth. To determine whether an increase in early daytime stomatal conductance provides a growth and/or yield advantage under high temperature, the biomass (Bm), grain number (Gn), thousand-grain weight (TGW), and grain yield (Yld) were measured. Genotypes exhibiting the highest early daytime stomatal conductance also showed higher Bm, Gn, and Yld. An increase of 19% in early daytime stomatal conductance led to a Yld increase of 86 and 65 gm-2, in heated and control conditions respectively, translating to 43 and 35% Yld enhancement. Irrespective of the environment, the adaxial leaf side showed the highest diurnal and nocturnal conductance, mirroring direct stomatal aperture (SA) measurements. The high night-time temperature treatment increased daytime stomatal conductance but reduced nocturnal conductance. SA varied with growing conditions; in the morning, plants under high night-time temperatures showed larger SA than those from the control independently of the leaf side, conversely, the opposite trend was observed in the night. Stomata on the adaxial leaf side showed higher density and larger size. Results from this study show that early daytime conductance increased productivity in hot-irrigated environments studied here. Previous studies showed that high pre-dawn conductance improves morning photosynthesis, and here we find that high nocturnal temperatures increased early morning conductance but reduced night-time conductance and this may be a factor that contributed to minimize Yld losses.