Background: Light is a primary factor for plant growth and fruit development, and exogenous ABA also plays an essential role in metabolism of plants. Previous studies have documented that low light [LL] led to the adverse changes in morphology and physiology of cherry tomato, while exogenous ABA has been proven to be effective in improving plant tolerance to abiotic stresses. However, few works have explored the effects of exogenous ABA on the vegetative growth and quality formation of cherry tomato under [LL]. In the present study, the combined effect of [LL] and exogenous ABA on the plant growth and fruit quality of cherry tomato were investigated. Methods: Three levels of exogenous ABA (Control (CK), 0 mu M; A1, 38 mu M; A2, 76 mu M) were set under two light regimes, including normal light intensity (100%, [NL]) and low light intensity (50%, [LL]). Results: The results showed that [LL] increased plant height but decreased stem diameter and total soluble solids (TSS); conversely, reduced plant height and elevated stem diameter were found in the plants treated with exogenous ABA. Under [LL], A1 (38 mu M) decreased leaf gas exchange, WUEleaf, as well as WUEi, whereas A2 (76 mu M) enhanced the WUEi of plant without effect on net photosynthetic rate (An), transpiration rate and WUEleaf. Moreover, A2 (76 mu M) significantly elevated TSS and fruit firmness (FM) without compromising fruit yield. Conclusion: The study demonstrated that higher levels of exogenous ABA promote plant growth, leaf gas exchange, water use efficiency, and fruit quality in cherry tomato under [LL].

Ozone (O3) pollution is a major environmental stressor affecting forest productivity, yet species-specific responses in carbohydrate allocation and their effects on root architectures remain poorly understood. In this study, we investigated carbohydrate allocation, carbon (C) and nitrogen (N) balance, and root traits of three urban greening tree species (Celtis sinensis, Quercus acutissima, and Quercus nuttallii) across five O3 levels. Results showed that C. sinensis with high O3 tolerance maintained relatively stable total leaf C and N contents, while leaf non-structural carbohydrates (NSCs) pools increased, primarily due to starch accumulation; in contrast, the two less tolerant Quercus species exhibited increased starch and NSC contents in roots. Furthermore, root length of C. sinensis was greater than Quercus species but was inhibited by O3 stress, whereas other key root traits, such as specific root length (SRL), specific root area (SRA), and root tissue density (RTD), showed significant fluctuations under elevated O3 concentrations. Regression analyses suggested that in Q. acutissima and Q. nuttallii, SRL and SRA positively correlated with leaf soluble sugar contents and stem C/N ratio, but negatively correlated with leaf and stem N content, implying that excessive N availability may constrain root development by increasing nitrogen assimilation costs. These findings showed that species-specific patterns of carbohydrate allocation among tree organs can potentially determine trees’ O3 tolerance, underscoring the crucial role of carbohydrate allocation strategies and C/N stoichiometry in shaping root plasticity under O3 stress, and offering practical implications for tree species selection under atmospheric pollution.

Extreme heat and elevated ozone (O3) significantly affect plant growth and secondary metabolism, including biogenic volatile organic compound (BVOC) emissions. However, the impact of the extreme heat events (EHs) on the O3-induced BVOC emissions remains unclear. Here, Quercus nuttallii(an isoprene emitter) and Q. acutissima (a monoterpene emitter) were exposed to five O3 treatments for three months and subjected to a two-week EH. The emission rates of isoprene and monoterpenes, their synthesis capacities, and reactive oxygen species (ROS) levels were determined to investigate how heat stress modulates O3 effects. Both BVOC types showed a hormetic response to O3, with low doses of O3 stimulating emissions and high doses suppressing them. Isoprene (Hedges'g = 2.91) and monoterpene (Hedges'g = 2.52) emission rates were inhibited by short-term EH across the five O3 treatments. However, isoprene emission rates generally recovered during the post-EH period, except under the highest O3 exposure (NF80). EH also shifted isoprene's response to O3 from being synthesis-driven to ROS-driven. Although the monoterpene emission rate response to O3 was driven by synthesis capacity in the pre-EH period, this response became less explainable by either factor post-EH. These findings emphasize the profound effects of EH on the BVOC response to O3, providing crucial insights for predicting regional BVOC emissions under future climate scenarios.

To better understand the effects of ground-level ozone (O3) on nutrients and stoichiometry in different plant organs, urban tree species Celtis sinensis, Cyclocarya paliurus, Quercus acutissima, and Quercus nuttallii were subjected to a constant exposure to charcoal-filtered air (CF), nonfiltered air (NF), or NF + 40, 60, or 80 nmol O3 mol–1 (NF40, NF60, and NF80) starting early in the summer of the growing season. At the end of summer, net CO2 assimilation rate (A), stomatal conductance (gs), leaf mass per area (LMA), and/or leaf greenness (SPAD) either were not significantly affected by elevated O3 or were even higher in some cases during the summer compared with the CF or NF controls. LMA was significantly lower in autumn only after the highest O3 exposures. Compared to NF, NF40 caused a large increase in gs across species in late summer and more K and Mn in stems. At the end of the growing season, nutrient status and stoichiometric ratios in different organs were variously altered under O3 stress; many changes were large and often species-specific. Across O3 treatments, LMA was primarily associated with C and Mg levels in leaves and Ca levels in leaves and stems. NF40 enriched K, P, Fe, and Mn in stems, relative to NF, and NF60 enhanced Ca in leaves relative to CF and NF40. Moreover, NF resulted in a higher Ca/Mg ratio in leaves of Q. acutissima only, relative to the other O3 regimes. Interestingly, across species, O3 stress led to different nutrient modifications in different organs (stems + branches vs leaves). Thus, ambient and/or elevated O3 exposures can alter the dynamics and distribution of nutrients and disrupt stoichiometry in different organs in a species-specific manner. Changes in stoichiometry reflect an important defense mechanism in plants under O3, and O3 pollution adds more risk to ecological stoichiometries in urban areas.

Urban trees possess different capacities to mitigate ozone (O3) pollution through stomatal uptake. Stomatal closure protects trees from oxidative damage but limits their growth. To date, it is unclear how plant hydraulic function affect stomatal behaviour and determine O3 resistance. We assessed gas exchange and hydraulic traits in three subtropical urban tree species, Celtis sinensis, Quercus acutissima, and Q. nuttallii, under nonfiltered ambient air (NF) and elevated O3 (NF60). NF60 decreased photosynthetic rate (An) and stomatal conductance (gs) only in Q. acutissima and Q. nuttallii. Maintained An in C. sinensis suggested high O3 resistance and was attributed to higher leaf capacitance at the full turgor. However, this species exhibited a reduced stomatal sensitivity to vapour pressure deficit and an increased minimal gs under NF60. Such stomatal dysfunction did not decrease intrinsic water use efficiency (WUE) due to a tight coupling of An and gs. Conversely, Q. acutissima and Q. nuttallii showed maintained stomatal sensitivity and increased WUE, primarily correlated with gs and leaf water relations, including relative water content and osmotic potential at turgor loss point. Our findings highlight a trade-off between O3 resistance and stomatal functionality, with efficient stomatal control reducing the risk of hydraulic failure under combined stresses.

Surface ozone (O3) 3 ) poses a significant threat to urban vegetation health, and assessing the O3 3 risk across woody species is of vital importance for maintaining the health of urban infrastructure. In the present study, Jarvis-type stomatal conductance model was parameterized for ten urban species in northern China. Incorporating the effects of time of day and diurnal O3 3 concentration significantly enhanced the model performance. For different plant functional types (greening trees, greening shrubs, and orchard-grown trees), three parameterizations were established to estimate stomatal O3 3 uptake (POD1, 1 , phytotoxic O3 3 dose over an hourly threshold of 1 nmol m- 2 s-1).-1 ). The differences in POD1 1 between greening trees and shrubs were primarily due to the difference in their stomatal sensitivity to light. Orchard-grown trees displayed the lowest O3 3 removal capacity (lowest value of POD1) 1 ) because of their shorter growing season despite of high stomatal conductance. These results indicated that plant phenology and light responsiveness determined stomatal O3 3 uptake, and the three parameterizations developed here could be applicable to various urban species in northern regions. Among climatic factors for O3 3 risk assessment, O3 3 concentration was the most important factor determining annual variation of POD1, 1 , which was primarily driven by air temperature. However, when O3 3 pollution decreased, O3 3 concentration exhibited less dependence on temperature and more dependence on light. These findings provide crucial insights for urban policy-makers and environmental scientists aiming to mitigate O3 3 pollution effects and enhance urban vegetation health.

In this experiment the effect of light intensity (photosynthetic photon flux density, PPFD) and cutting size (10 and 7 cm) was investigated during five weeks rooting of hibiscus (Hibiscus rosa-sinensis L. 'Adonicus Yellow'). The light regimes included three constant PPFD: 16, 76 and 151 mu mol m- 2 s- 1; and three changing PPFD after two weeks: 16 -* 76, 16 -* 151 and 76 -* 151 mu mol m- 2 s- 1. The light intensity has a dual effect, promoting photosynthesis and carbohydrate production, but also water loss through transpiration with the potential for desiccating the cutting. The treatments starting with 16 mu mol m- 2 s- 1 insufficiently supported the rooting process, illustrated by the lack shoot growth after two weeks. Within each treatment type (constant or changing PPFD) the root formation was linearly correlated to the total light integral for the propagation period (r2 = 0.835-1.000) for respective cutting size. The changing PPFD treatments showed the strongest response to increasing light integral with the [76 -* 151] treatment producing most roots for both cutting sizes, despite the constant 151 mu mol m- 2 s- 1 having the highest total light integral. This indicates that conserving water is of crucial importance before root emergence in the third week of rooting. The 7 cm cuttings produced more root biomass and had higher root:shoot ratio than the 10 cm cuttings. The 7 cm cuttings had higher rates of photosynthesis one week after rooting, probably due to higher sink demand from the growing roots and mobilised more soluble sugars from the leaves. The rooting process takes five weeks and does not demand high light, so the results are promising for moving propagation of hibiscus from the greenhouse to a vertical production system based on light emitting diodes (LEDs) to save production area for final production.

Greenhouse gas (GHG) emissions from rice paddies have gained widespread attention, and fertilization management can mitigate GHG emissions. Red paddy soils in southern China are characterized by phosphorus (P) deficiency, requiring fertilization management. In the present study, soils from a red paddy field were used in a pot experiment with 5 levels of P application (P1–P5: 0, 22.5, 45, 90, 113, 135 kg ha −1 , respectively) to investigate growth and yield of rice ( Oryza sativa L.) and carbon dioxide (CO 2 ) and methane (CH 4 ) emissions from soils. P application increased photosynthetic rate, tiller number, plant biomass and yield. All P treatments decreased CH 4 emission at the tillering stage but increased it at the filling and maturing stages, causing decreases in cumulative CH 4 emission under P1, P2, and P4. Cumulative CO 2 emission did not significantly differ among P0–P3 but increased by P4 and P5. Cumulative CO 2 and CH 4 emissions were positively correlated with plant height, implying that changes in plant structure such as aerenchyma might be attributable to GHG emissions. Overall, P application of 89 kg ha −1 was sufficient to reduce GHG emissions and enhance rice yield. These results provide a reference for adjusting P management in red paddy fields.

Potato is an important crop worldwide and threatened by various environmental stresses, including elevated ozone (e[O3]). Here, we conducted a meta-analysis to quantify the effect of e[O3] on potato plants and how it varies depending upon different experimental conditions. Regarding plant growth and biomass, e[O3] significantly decreased shoot biomass by 18

Studying the long-term effect of elevated atmospheric CO2 concentration (e[CO2]) on wheat (Triticum aestivum L.) over multiple generations has received increasing attention. Here, five wheat cultivars were grown under ambient CO2 concentration (a[CO2], 400 ppm) and e[CO2] (800 ppm), respectively, for three consecutive generations (G1 to G3) under two nitrogen (N) levels (1N and 2N). Compared to plants grown under a[CO2], e[CO2] increased shoot biomass and grain yield (GY) over three generations and the enhancement was greater in G3 than in G1. However, plant N concentration was lowered by e[CO2] and the reduction was not mitigated by higher N supply. The carbon (C) concentration significantly increased in leaf and stem but decreased in grain, indicating an inhibited C translocation to grain under e[CO2]. Most importantly, these negative impacts were exacerbated in G3. Concentrations of mineral nutrients in grain were significantly lowered by e[CO2] with larger reduction in G3 than in G1 in some micronutrients such as Zn, Cu and Fe. These findings suggest that long-term exposure to e[CO2] sustained the positive effects on plant growth and production but aggravated the reduction of grain quality over multiple generations. Among the five cultivars, 325Jimai showed the greatest increase in shoot biomass and GY, and a greater sink capacity compared with the other cultivars, indicating its potential for future breeding strategies.

The sensitivity of isoprene emission rate (ISOrate) to ozone (O3) in plant suggests potentially large changes in future isoprene emissions, which will have important consequences for atmospheric chemistry. However, the interspecific variation of ISOrate sensitivity to O3 and its key drivers remain largely unknown. In this study, four urban greening tree species were exposed to two O3 treatments (charcoal-filtered air, CF; and non-filtered ambient air plus 60 ppb extra O3, EO3) in open-top chambers for one growing season. We aimed to compare the interspecific variation in O3 inhibitory effect on ISOrate and explore its physiological mechanism. EO3 decreased the ISOrate by on average 42.5 % across species. According to absolute effect size ranking, the highest ISOrate sensitivity to EO3 was observed in Salix matsudana, followed by Sophora japonica and hybrid poplar clone '546', while Quercus mongolica ISOrate was the least sensitive. Leaf anatomical structures differed in tree species but did not respond to EO3. Furthermore, the ISOrate sensitivity to O3 was driven by the concurrent effects of O3 on ISO synthesis ability (i.e., dimethylallyl diphosphate and isoprene synthase contents) and stomatal conductance. Overall, the mechanistic understanding grained from this study may promote the integrity of O3 effect into process-based ISO emission models.

Forest ecosystems cover a large area of the global land surface and are important carbon sinks. The water-carbon cycles of forests are prone to climate change, but uncertainties remain regarding the magnitude of water use efficiency (WUE) response to climate change and the underpinning mechanism driving WUE variation. We conducted a meta-analysis of the effects of elevated CO2 concentration (eCO2 ), drought and elevated temperature (eT) on the leaf- to plant-level WUE, covering 80 field studies and 95 tree species. The results showed that eCO2 increased leaf intrinsic and instantaneous WUE (WUEi, WUEt), whereas drought enhanced both leaf- and plant-level WUEs. eT increased WUEi but decreased carbon isotope-based WUE, possibly due to the influence of mesophyll conductance. Stimulated leaf-level WUE by drought showed a progressing trend with increasing latitude, while eCO2 -induced WUE enhancement showed decreasing trends after >40° N. These latitudinal gradients might influence the spatial pattern of climate and further drove WUE variation. Moreover, high leaf-level WUE under eCO2 and drought was accompanied by low leaf carbon contents. Such a trade-off between growth efficiency and defence suggests a potentially compromised tolerance to diseases and pests. These findings add important ecophysiological parameters into climate models to predict carbon-water cycles of forests.

Blue and red light are essential light signals used to regulate stomatal development and leaf structure. In the present study, stomatal and leaf traits that respond to blue and red light were studied at two light intensities (400 and 100 µmol m−2 s−1) in soybeans. The stomatal traits and leaf characteristics were determined. Furthermore, their contribution to the operational maximum stomatal conductance (gopmax) was evaluated using the rdacca.hp R package. With the light intensity significantly reduced, the stomatal size (SZ) under blue light did not change. Similarly, the decrease in light intensity did not influence the stomatal density (SD), specific leaf weight (SLW) or gopmax under red light. These results implied that the regulation of SD and SLW depended on blue light and that SZ was highly sensitive to red light. In addition, SLW was strongly correlated with SD. The SLW and SD had the highest contribution rates (19.43% and 19.5%, respectively) to gopmax, as compared with the other parameters. In conclusion, these results suggested that in long-term exposure to blue light, the enhancements in gopmax were primarily due to the synergistic promotion of SLW and SD.

Plant photosynthetic capacity directly determines crop yield. Light quality regulates photosynthetic capacity. This review discusses plant responses to far-red light from the phenotypic to the molecular level, focusing specifically on the improvement of photosynthetic capacity by adjustment of photosynthetic electron transport and the path of light energy. Far-red light can also regulate leaf angle and increase plant height and leaf area, via expression of associated genes, to capture more light energy. Thus, far-red light regulates plant morphology and photosynthetic capacity. Identifying the mechanism of this regulation may lead to increased crop yields.

Intensified drought stress threatens plant growth and productivity, while elevated CO2 (e[CO2]) alleviates the negative impact of drought stress on plants through alteration in water use and improvement in plant growth. In the terrestrial ecosystem, crops are particularly sensitive to drought and benefit from e[CO2]. To cope with the drier and CO2-enriched climate, plants have evolved various adaptive strategies. Water-dependent crops can benefit from e[CO2] but are species-dependent and depend on the intensities and durations of drought stress. In this chapter, we summarized drought impact on crops, crop performance under e[CO2], as well as their interactions in physiological, biochemical, and molecular levels.

Elevated CO2 concentration (e[CO2]) alleviates the impact of drought stress on plants where abscisic acid (ABA) is involved. To explore the mechanisms by which tomato plants respond to short-term osmotic stress, Solanum lycopersicum cv. Ailsa Craig (AC), a transgenic line overproducing ABA (sp5), and an ABA-deficient mutant (flacca) were hydroponically grown under ambient CO2 (400 ppm) and e[CO2] (800 ppm) and then exposed to 10% or 15% (w/v) polyethylene glycol (PEG) 6000 for 24 h before transferring to PEG-free nutrient solution for 24 h. Under non-stress condition, e[CO2] decreased root hydraulic conductance (Kroot), which was overridden by high endogenous ABA in sp5 through increasing specific leaf area and root branching intensity. Basically, e[CO2] improved stress resistance through enhanced water status. PEG stress decreased stomatal conductance and osmotic potential in AC but these effects were less pronounced in sp5, which exhibited a stronger osmotic adjustment (OA) and improved plant fitness. A greater flexibility of hydraulic system and a reduced sensitivity of Kroot to ABA might confer sp5 a great ability to recover from PEG stress. On the contrary, high stomatal density, size and pore aperture of flacca rendered plants suffering severe stress. Moreover, the premise that PEG stress could mimic soil water deficit was the sufficient achievement of OA. Our results indicate that e[CO2] and high endogenous ABA level could improve osmotic stress resistance in tomato plants via osmotic and hydraulic adjustments.

Drought stress often occurs concurrently with heat stress, yet the interacting effect of high vapor pressure deficit (VPD) and soil drying on the physiology of potato plants remains poorly understood. This study aimed to investigate the physiological and growth responses of potatoes to progressive soil drying under varied VPDs. Potato plants were grown either in four separate climate-controlled greenhouse cells with different VPD levels (viz., 0.70, 1.06, 1.40, and 2.12 kPa, respectively) or under a rainout shelter in the field. The VPD of each greenhouse cell was caused by two air temperature levels (23 and 30 °C) combined with two relative humidity levels (50 and 70%), and the VPD of the field was natural conditions. Irrigation treatments were commenced three or four weeks after planting in greenhouse cells or fields, respectively. The results indicated that soil water deficits limited leaf gas exchange and shoot dry matter (DMshoot) of plants while increasing the concentration of abscisic acid (ABA) in the leaf and xylem, as well as water use efficiency (WUE) across all VPD levels. High VPD decreased stomatal conductance (gs) but increased transpiration rate (Tr). High VPD increased the threshold of soil water for Tr began to decrease, while the soil water threshold for gs depended on temperature due to the varied ABA response to temperature. High VPD decreased leaf water potential, leaf area, and DMshoot, which exacerbated the inhibition of soil drying to plant growth. Across the well-watered plants in both experiments, negative linear relationships of gs and WUE to VPD and positive linear relations between Tr and VPD were found. The results provide some novel information for developing mechanistic models simulating crop WUE and improving irrigation scheduling in future arid climates.

Leaf veins constitute the transport network for water and photosynthetic assimilates in vascular plants. The class III homeodomain-leucine zipper (HD-Zip III) gene family is central to the regulation of vascular development. In this research, we performed an overall analysis of the HD-Zip III genes in soybean (Glycine max L. Merr.). Our analysis included the phylogeny, conservation domains and cis-elements in the promoters of these genes. We used the quantitative reverse transcription-polymerase chain reaction to characterize the expression patterns of HD-Zip III genes in leaf vein development and analyze the effects of exogenous hormone treatments. In this study, twelve HD-Zip III genes were identified from the soybean genome and named. All soybean HD-Zip III proteins contained four highly conserved domains. GmHB15-L-1 transcripts showed steadily increasing accumulation during all stages of leaf vein development and were highly expressed in cambium cells. GmREV-L-1 and GmHB14-L-2 had nearly identical expression patterns in soybean leaf vein tissues. GmREV-L-1 and GmHB14-L-2 transcripts remained at stable high levels at all xylem developmental stages. GmREV-L-1 and GmHB14-L-2 were expressed at high levels in the vascular cambium and xylem cells. Overall, GmHB15-L-1 may be an essential regulator that is responsible for the formation or maintenance of soybean vein cambial cells. GmREV-L-1 and GmHB14-L-2 were correlated with xylem differentiation in soybean leaf veins. This study will pave the way for identifying the molecular mechanism of leaf vein development.