Gas exchange, antioxidants and foliar injuries in saplings of a tropical woody species exposed to ozone

Changes in growth pattern and rhizospheric soil biochemical properties of a leguminous tree species Leucaena leucocephala under long-term exposure to elevated ozone

Increasing concentrations of ground-level ozone (O₃) exert significant impacts on the plants, but there is limited data for belowground processes. We studied the effects of long-term exposure of elevated O₃ (EO₃) on plant growth parameters (plant height and biomass) and biochemical parameters (nutrients, microbial biomass and enzymatic activities) of rhizospheric soil of leguminous tree species Leucaena leucocephala. L. leucocephala seedlings were grown under ambient O₃ (AO₃) and EO₃ (+20 ppb above ambient) under Free Air Ozone Concentration Enrichment (O₃-FACE) facility and changes in plant growth and their rhizospheric soil properties were studied during 6, 12, 18 and 24 months of EO₃ exposure. L. leucocephala showed significant reductions in shoot length, root biomass, shoot biomass, leaf biomass and total biomass during 12, 18 and 24 months of exposure to EO₃. Total nutrients in rhizospheric soil like carbon and phosphorus were significantly reduced after 24 months of EO₃ exposure. Most of the available nutrients showed significant reduction after 6, 12 and 24 months of EO₃ exposure. A significant decrease was apparent in microbial biomass carbon, nitrogen and phosphorus after 6, 12, 18 and 24 months of EO₃ treatment. Significant reductions were observed in extracellular enzymatic activities (dehydrogenase, alkaline phosphatase, β-glycosidase, fluorescein diacetate, arylsulfatase, cellulase and protease) of soil after 6, 12 and 24 months of EO₃ exposure. These results suggest that increasing O₃ concentrations will directly impact L. leucocephala growth as well as have indirect impact on the nutrient contents (C, N, and P), microbial biomass and extracellular enzymatic activities of rhizospheric soil of L. leucocephala. Our results suggest that continuous increase in O₃ concentrations will have serious implications for aboveground plant growth and belowground soil fertility in this region considered as O₃ hotspot.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03215-1.

Impact of chronic elevated ozone exposure on photosynthetic traits and anti-oxidative defense responses of Leucaena leucocephala (Lam.) de wit tree under field conditions

In this study, the impact of long term exposure of elevated ozone (+20 ppb above ambient) on photosynthetic traits and anti-oxidative defense system of Leucaena leucocephala, a tree of great economic importance, was studied in a Free Air Ozone Concentration Enrichment (O₃-FACE) facility at different time intervals (6, 12, 18, and 24 months). Results showed that net photosynthesis, photosynthetic pigments and lipid peroxidation were significantly reduced after 6, 12 and 24 months of exposure to elevated ozone (eO₃) whereas stomatal conductance and transpiration rate were significantly decreased after 12 months of exposure to eO₃. Antioxidant enzymatic activities (catalase, ascorbate peroxidase and glutathione reductase) were significantly increased after 12 months of exposure to eO_3. Ascorbate was increased significantly after 6 and 12 months of exposure to eO₃ while reduced glutathione content declined significantly after 6 and 24 months of exposure to eO₃. The study showed that there were several negative long lasting physiological and biochemical responses in Leucaena. The results provide evidence that Leucaena exhibited greater sensitivity to O₃ during initial exposure (up to 12 months) but showed moderate tolerance by the end of the 2nd year.

Applications of SERS in the Detection of Stress-Related Substances

A wide variety of biotic and abiotic stresses continually attack plants and animals, which adversely affect their growth, development, reproduction, and yield realization. To survive under stress conditions, highly sophisticated and efficient tolerance mechanisms have been evolved to adapt to stresses, which consist of the variation of effector molecules playing vital roles in physiological regulation. The development of a sensitive, facile, and rapid analytical methods for stress factors and effector molecules detection is significant for gaining deeper insight into the tolerance mechanisms. As a nondestructive analysis technique, surface-enhanced Raman spectroscopy (SERS) has unique advantages regarding its biosensing applications. It not only provides specific fingerprint spectra of the target molecules, conformation, and structure, but also has universal capacity for simultaneous detection and imaging of targets owing to the narrow width of the Raman vibrational bands. Herein, recent progress on biotic and abiotic stresses, tolerance mechanisms and effector molecules is summarized. Moreover, the development and promising future trends of SERS detection for stress-related substances combined with nanomaterials as substrates and SERS tags are discussed. This comprehensive and critical review might shed light on a new perspective for SERS applications.

Effects of elevated O3 on physiological and biochemical responses in three kinds of trees native to subtropical forest in China during non-growing period

Numerous studies have documented the negative effects of ozone (O₃) on tree species in growing season, however, little is done in non-growing season. Three evergreen tree species, Phoebe bournei (Hemsl.) Yang (P. bournei), Machilus pauhoi Kanehira (M. pauhoi) and Taxus chinensis (Pilger) Rehd (T. chinensis), were exposed to non-filtered air, 100 nmol mol^-1 O₃ air (E1) and 150 nmol mol^-1 O₃ air (E2) in open-top chambers in subtropical China. In the entire period of experiment, O₃ fumigation decreased net photosynthesis rate (Pn) through stomatal limitation during the transition period from growing to non-growing season (TGN), and through non-stomatal limitation during the period of non-growing season (NGS) in all species tested. Meanwhile, O₃ fumigation reduced and delayed the resilience of Pn in all species tested during the transition period from non-growing to growing season (TNG). O₃ fumigation significantly decreased chlorophyll contents during NGS, whereas no obvious injury symptoms were observed till the end of experiment. O₃ fumigation induced increases in levels of malondialdehyde, superoxide dismutase, total phenolics and reduced ascorbic acid, and changes in four plant endogenous hormones as well in all species tested during NGS. During NGS, E1 and E2 reduced Pn by an average of 80.11% in P. bournei, 94.56% in M. pauhoi and 12.57% in T. chinensis, indicating that the O₃ sensitivity was in an order of M. pauhoi > P. bournei > T. chinensis. Overall, O₃ fumigation inhibited carbon fixation in all species tested during NGS. Furthermore, O₃-induced physiological activities also consumed the dry matter. All these suggested that elevated O₃, which is likely to come true during NGS in the future, will adversely affect the accumulation of dry matter and the resilience of Pn during TNG in evergreen tree species, and further inhibit their growth and development in the upcoming growing season.

Ozone affects leaf physiology and causes injury to foliage of native tree species from the tropical Atlantic Forest of southern Brazil

In southern Brazil, the recent increase in tropospheric ozone (O₃) concentrations poses an additional threat to the biodiverse but endangered and fragmented remnants of the Atlantic Forest. Given the mostly unknown sensitivity of tropical species to oxidative stress, the principal objective of this study was to determine whether the current O₃ levels in the Metropolitan Region of Campinas (MRC), downwind of São Paulo, affect the native vegetation of forest remnants. Foliar responses to O₃ of three tree species typical of the MRC forests were investigated using indoor chamber exposure experiments under controlled conditions and a field survey. Exposure to 70ppb O₃ reduced assimilation and leaf conductance but increased respiration in Astronium graveolens while gas exchange in Croton floribundus was little affected. Both A. graveolens and Piptadenia gonoacantha developed characteristic O₃-induced injury in the foliage, similar to visible symptoms observed in >30% of trees assessed in the MRC, while C. floribundus remained asymptomatic. The underlying structural symptoms in both O₃-exposed and field samples were indicative of oxidative burst, hypersensitive responses, accelerated cell senescence and, primarily in field samples, interaction with photo-oxidative stress. The markers of O₃ stress were thus mostly similar to those observed in other regions of the world. Further research is needed, to estimate the proportion of sensitive forest species, the O₃ impact on tree growth and stand stability and to detect O₃ hot spots where woody species in the Atlantic Forest are mostly affected.

Ozone exposure- and flux-based response relationships with photosynthesis, leaf morphology and biomass in two poplar clones

Poplar clones 546 (P. deltoides cv. '55/56'×P. deltoides cv. 'Imperial') and 107 (P. euramericana cv. '74/76') were exposed to five ozone concentrations in 15 open-top chambers (OTCs). Both ozone exposure (AOT40, Accumulation Over a Threshold hourly ozone concentration of 40ppb) and flux-based (POD₇, Phytotoxic Ozone Dose above an hourly flux threshold of 7nmol O₃ m^-2 PLA (projected leaf area) s^-1) response relationships were established with photosynthesis, leaf morphology and biomass variables. Increases in both metrics showed significant negative relationships with light-saturated photosynthesis rate, chlorophyll content, leaf mass per area, actual photochemical efficiency of PSII in the light and root biomass but not with stomatal conductance (g_s), leaf and stem biomass. Ozone had a greater impact on belowground than on aboveground biomass. The ranking of these indicators from higher to lower sensitivity to ozone was: photosynthetic parameters, morphological index, and biomass. Clone 546 had a higher sensitivity to ozone than clone 107. The coefficients of determination (R²) were similar between exposure- and flux-based dose-response relationships for each variable. The critical levels (CLs) for a 5% reduction in total biomass for the two poplar clones were 14.8ppmh for AOT40 and 9.8mmol O₃ m^-2 PLA for POD₇. In comparison, equivalent reduction occurred at much lower values in photosynthetic parameters (4ppmh for AOT40 and 3mmol O₃ m^-2 PLA for POD₇) and LMA (5.8ppmh for AOT40 and 4mmol O₃ m^-2 PLA for POD₇). While in recent decades different CLs have been proposed for several plant receptors especially in Europe, studies focusing on both flux-based dose-response relationships and CLs are still scarce in Asia. This study is therefore valuable for regional O₃ risk assessment in Asia.

Photosynthesis and biochemical responses to elevated O3 in Plantago major and Sonchus oleraceus growing in a lowland habitat of northern China

A field experiment was carried out to compare the responses to ozone (O₃) in two common herbaceous plant species, Plantago major L. and Sonchus oleraceus L., by building open-top growth chambers in situ to simulate O₃ stress (+O₃, 85±5ppb, 9hr/day for 30days) in a lowland habitat in Inner Mongolia, Northern China. Responses to O₃ of gas exchange, chlorophyll a fluorescence, leaf pigment content, antioxidant capability, soluble protein content, membrane lipid peroxidation and dark respiration (R_d) were analyzed. Results showed that elevated O₃ exposure significantly reduced the light-saturated net photosynthesis (P_Nsat), stomatal conductance (g_s) and transpiration rate (E) in both species. Although non-significant interactive effect between species and O₃ on P_Nsat was analyzed, the reduction in P_Nsat in S. oleraceus might be due primarily to the higher fraction of close PSII reaction centers and impaired activities of plant mesophyll cells as evidences by decreased maximum efficiency of PSII photochemistry after dark adapted state (F_v/F_m) and unchanged intercellular CO₂ concentration (C_i). Besides, biochemical analysis showed that S. oleraceus had lower antioxidant ability compared to P. major. As a result, S. oleraceus was damaged to the larger extent in terms of lipid peroxidation and visible O₃ injury, indicating that S. oleraceus was more sensitive to O₃ than P. major. Our results indicated that wild herbaceous plant species growing in a lowland habitat in sandy grassland were sensitive to O₃ stress and S. oleraceus can be considered as one of the bio-indicators for high O₃ concentration in semi-arid grassland of northern China.

Ozone stomatal flux and O3 concentration-based metrics for Astronium graveolens Jacq., a Brazilian native forest tree species

The current levels of surface ozone (O3) are high enough to negatively affect trees in large regions of São Paulo State, southeastern Brazil, where standards for the protection of vegetation against the adverse effects of O3 do not exist. We evaluated three O3 metrics - phytotoxic ozone dose (POD), accumulated ozone exposure over the threshold of 40 ppb h (AOT40), and the sum of all hourly average concentrations (SUM00) - for the Brazilian native tropical tree species Astronium graveolens Jacq. We used the DO3SE (Deposition of Ozone for Stomatal Exchange) model and calculated PODY for different thresholds (from 0 to 6 mmol O3 m(-2) PLA s(-1)), evaluating the model's performance through the relationship between measured and modelled conductance. The response parameters were: visible foliar injury, considered as incidence (% injured plants), severity (% injured leaves in relation to the number of leaves on injured plants), and leaf abscission. The model performance was suitable and significant (R(2) = 0.58; p < 0.001). POD0 was better correlated to incidence and leaf abscission, and SUM00 was better correlated to severity. The highest values of O3 concentration-based metrics (AOT40 and SUM00) did not coincide with those of POD0. Further investigation may improve the model and contribute to the proposition of a national standard for the protection of native species.

Responses of a tropical tree species to ozone: visible leaf injury, growth, and lipid peroxidation

The Brazilian native tree species Astronium graveolens was indicated as sensitive to ozone in a fumigation experiment. Thus, the objective of this study was to evaluate how sensitive A. graveolens is to ozone under realistic conditions in the field. Eighteen saplings were exposed to ozone in a contaminated area and in a greenhouse with filtered air during two exposure periods of approximately 63 days each (March-May 2012 and September-October 2012). Leaf injury was analyzed by means of its incidence and severity, the leaf injury index (LII) and the progression of leaf abscission. These variables were monitored weekly, whereas growth and lipid peroxidation were monitored monthly. Plants exposed to ozone showed significant growth decrease and visible leaf injury increase, but lipid peroxidation and leaf abscission remained unchanged. These results indicated that plants subjected to ozone possibly diverted energy from growth to the production of antioxidants necessary to cope with ozone-induced oxidative stress.

Is guava phenolic metabolism influenced by elevated atmospheric CO2?

Seedlings of Psidium guajava cv. Pedro Sato were distributed into four open-top chambers: two with ambient CO(2) (∼390 ppm) and two with elevated CO(2) (∼780 ppm). Monthly, five individuals of each chamber were collected, separated into root, stem and leaves and immediately frozen in liquid nitrogen. Chemical parameters were analyzed to investigate how guava invests the surplus carbon. For all classes of phenolic compounds analyzed only tannins showed significant increase in plants at elevated CO(2) after 90 days. There was no significant difference in dry biomass, but the leaves showed high accumulation of starch under elevated CO(2). Results suggest that elevated CO(2) seems to be favorable to seedlings of P. guajava, due to accumulation of starch and tannins, the latter being an important anti-herbivore substance.

The guava tree as bioindicator during the process of fuel replacement of an oil refinery

This study was performed to verify whether the exchange of the fuel used in the boilers of a crude oil refinery located in Cubatão (SE Brazil) would result in alterations on gas exchange, growth and leaf injuries in saplings of Psidium guajava 'Paluma'. The purpose of the refinery was to reduce the SO2 emission, but using natural gas as fuel could increase the concentrations of O3 precursors in the atmosphere. Thus a biomonitoring was performed with a native species sensitive to O3. The plants were exposed in five areas (CM1, CM5, CEPEMA, Centro, and RP) at different distances to the refinery, both before and after the fuel exchange. We performed six exposures under environmental conditions, with length of ca. 90 days each. With the utilization of natural gas, the saplings presented reductions in carbon assimilation rate under saturating light conditions (Asat, μmolCO2m(-2)s(-1)) and the stomatal conductance (gs, molH2Om(-2)s(-1)), and increase in height, number of leaves, and dry mass of leaves and shoots. There were also reductions in root dry mass and in the root/shoot ratio. The saplings also presented O3-induced leaf injuries. The responses of P. guajava 'Paluma' were altered after the fuel exchange as a result of a new combination of pollutants in the atmosphere. The fuel exchange has not resulted in environmental benefit to the surrounding forest; it has only altered the contamination profile of the region.

Critical analysis of the potential of Ipomoea nil'Scarlet O'Hara' for ozone biomonitoring in the sub-tropics

This study aimed to analyze critically the potential of Ipomoea nil'Scarlet O'Hara' for O(3) biomonitoring in the sub-tropics. Four field experiments (one in each season of 2006) were carried out in a location of the city of São Paulo mainly polluted by O(3). Each experiment started with 50 plants, and lasted 28 days. Sub-lots of five plants were taken at intervals between three or four days long. Groups of four plants were also exposed in closed chambers to filtered air or to 40, 50 or 80 ppb of O(3) for three consecutive hours a day for six days. The percentage of leaf injury (interveinal chloroses and necroses), the concentrations of ascorbic acid (AA) and the activity of superoxide dismutase (SOD) and peroxidases (POD) were determined in the 5th, 6th and 7th oldest leaves on the main stem of the plants taken in all experiments. Visible injury occurred in the plants from all experiments. Seasonality in the antioxidant responses observed in plants grown under field conditions was associated with meteorological variables and ozone concentrations five days before leaf analyses. The highest levels of antioxidants occurred during the spring. The percentage of leaf injury was explained (R(2) = 0.97, p < 0.01) by the reduction in the levels of AA and activity of POD five days before the leaf analyses and by the reduction in the levels of particulate matter, and enhancement of temperature and global radiation 10 days before this same day. Although I. nil may be employed for qualitative O(3) biomonitoring, its efficiency for quantitative biomonitoring in the sub-tropics may be compromised, depending on how intense the oxidative power of the environment is.

Responses of native broadleaved woody species to elevated ozone in subtropical China

To assess ozone sensitivity of subtropical broadleaved tree species and explore possible underlying mechanisms, six evergreen and two deciduous native species were exposed to either charcoal-filtered air or elevated O(3) (E-O(3), ∼150ppb) for one growing season. Initial visible symptoms in deciduous species appeared much earlier than those in evergreen species. The species which first showed visible symptoms also had the largest reductions in biomass. E-O(3) induced significant decreases in photosynthesis rate, chlorophyll content and antioxidant capacity but a significant increase in malondialdehyde content in two deciduous species and two evergreen species (Cinnamomum camphora and Cyclobalanopsis glauca). Except C. glauca, however, E-O(3) had no significant effects on stomatal conductance (g(s)), total phenols and ascorbate contents. Difference in O(3) sensitivity among all species was strongly attributed to specific leaf mass rather than g(s). It suggests that some subtropical tree species will be threatened by rising O(3) concentrations in the near future.