Effects of dust on forest tree health in Zagros oak forests

Potential distribution of Biscogniauxia mediterranea and Obolarina persica causal agents of oak charcoal disease in Iran's Zagros forests

In Iran, native oak species are under threat from episodes of Charcoal Disease, a decline syndrome driven by abiotic stressors (e.g. drought, elevated temperature) and biotic components, Biscogniauxia mediterranea (De Not.) Kuntze and Obolarina persica (M. Mirabolfathy). The outbreak is still ongoing and the country's largest ever recorded. Still, the factors driving its' epidemiology in time and space are poorly known and such knowledge is urgently needed to develop strategies to counteract the adverse effects. In this study, we developed a generic framework based on experimental, machine-learning algorithms and spatial analyses for landscape-level prediction of oak charcoal disease outbreaks. Extensive field surveys were conducted during 2013-2015 in eight provinces (more than 50 unique counties) in the Zagros ecoregion. Pathogenic fungi were isolated and characterized through morphological and molecular approaches, and their pathogenicity was assessed under controlled water stress regimes in the greenhouse. Further, we evaluated a set of 29 bioclimatic, environmental, and host layers in modeling for disease incidence data using four well-known machine learning algorithms including the Generalized Linear Model, Gradient Boosting Model, Random Forest model (RF), and Multivariate Adaptive Regression Splines implemented in MaxEnt software. Model validation statistics [Area Under the Curve (AUC), True Skill Statistics (TSS)], and Kappa index were used to evaluate the accuracy of each model. Models with a TSS above 0.65 were used to prepare an ensemble model. The results showed that among the different climate variables, precipitation and temperature (Bio18, Bio7, Bio8, and bio9) in the case of O. persica and similarly, gsl (growing season length TREELIM, highlighting the warming climate and the endophytic/pathogenic nature of the fungus) and precipitation in case of B. mediterranea are the most important influencing variables in disease modeling, while near-surface wind speed (sfcwind) is the least important variant. The RF algorithm generates the most robust predictions (ROC of 0.95; TSS of 0.77 and 0.79 for MP and OP, respectively). Theoretical analysis shows that the ensemble model (ROC of 0.95 and 0.96; TSS = 0.79 and 0.81 for MP and OP, respectively), can efficiently be used in the prediction of the charcoal disease spatiotemporal distribution. The oak mortality varied ranging from 2 to 14%. Wood-boring beetles association with diseased trees was determined at 20%. Results showed that water deficiency is a crucial component of the oak decline phenomenon in Iran. The Northern Zagros forests (Ilam, Lorestan, and Kermanshah provinces) along with the southern Zagros forests (Fars and Kohgilouyeh va-Boyer Ahmad provinces) among others are the most endangered areas of potential future pandemics of charcoal disease. Our findings will significantly improve our understanding of the current situation of the disease to pave the way against pathogenic agents in Iran.

The cellular consequences of particulate matter pollutants in plants: Safeguarding the harmonious integration of structure and function

Particulate matter (PM) pollution is one of the pressing environmental concerns confronting human civilization in the face of the Anthropocene era. Plants are continuously exposed to an accelerating PM, threatening their growth and productivity. Although plants and plant-based infrastructures can potentially reduce ambient air pollutants, PM still affects them morphologically, anatomically, and physiologically. This review comprehensively summarizes an up-to-date review of plant-PM interaction among different functional plant groups, PM deposition and penetration through aboveground and belowground plant parts, and plants' cellular strategies. Upon exposure, PM represses lipid desaturases, eventually leading to modification of cell wall and membrane and altering cell fluidity; consequently, plants can sense the pollutants and, thus, adapt different cellular strategies. The PM also causes a reduction in the photosynthetically active radiation. The study demonstrated that plants reduce stomatal density to avoid PM uptake and increase stomatal index to compensate for decreased gaseous exchange efficiency and transpiration rates. Furthermore, genes and gene sets associated with photosynthesis, glycolysis, gluconeogenesis, and the TCA cycle were dramatically lowered by PM stress. Several transcription factors, including MYB, C2H2, C3H, G2-like, and WRKY were induced, and metabolites such as proline and soluble sugar were accumulated to increase resistance against stressors. In addition, enzymatic and non-enzymatic antioxidants were also accumulated to scavenge the PM-induced reactive oxygen species (ROS). Taken together, this review provides an insight into plants' underlying cellular mechanisms and gene regulatory networks in response to the PM to determine strategies to preserve their structural and functional blend in the face of particulate pollution. The study concludes by recommending that future research should precisely focus on plants' response to short- and long-term PM exposure.

Direct foliar acquisition of desert dust phosphorus fertilizes forest trees despite reducing photosynthesis

Phosphorus (P) availability to forest trees is often limited by local soil conditions that increase its fixation to soil minerals. In certain regions, atmospheric-P inputs can compensate for low soil-P availability. Among atmospheric-P sources, desert dust is the most dominant. However, the effects of desert dust on P nutrition and its uptake mechanisms by forest trees are currently unknown. We hypothesized that forest trees that naturally grow on P-poor soils or soils with high soil-P fixation capacity can acquire P from desert dust deposited on their leaves via direct foliar uptake, bypassing the soil, thus promoting tree growth and productivity. We performed a controlled greenhouse experiment with three forest tree species: Palestine Oak (Quercus calliprinos) and Carob (Ceratonia siliqua), native to the NE edge of the Saharan desert, and Brazilian peppertree (Schinus terebinthifolius), native to the Atlantic Forest in Brazil, which is located on the western part of the trans-Atlantic Saharan dust route. To simulate natural dust deposition events, the trees had desert dust applied directly upon their foliage and were monitored for growth and final biomass, P levels, leaf surface pH and the rate of photosynthesis. The dust treatment increased the P concentration significantly by 33-37% in Ceratonia and Schinus trees. On the other hand, trees that received the dust displayed a 17-58% reduction in biomass, probably related to particle coverage of the leaf surface that inhibited photosynthesis by 17-30%. Overall, our findings show that direct P uptake from desert dust can be an alternative P uptake pathway for multiple tree species under P-deficient conditions, with implications for forest trees' P economy.

A review of common natural disasters as analogs for asteroid impact effects and cascading hazards

Modern civilization has no collective experience with possible wide-ranging effects from a medium-sized asteroid impactor. Currently, modeling efforts that predict initial effects from a meteor impact or airburst provide needed information for initial preparation and evacuation plans, but longer-term cascading hazards are not typically considered. However, more common natural disasters, such as volcanic eruptions, earthquakes, wildfires, dust storms, and hurricanes, are likely analogs that can provide the scope and scale of these potential effects. These events, especially the larger events with cascading effects, are key for understanding the scope and complexity of mitigation, relief, and recovery efforts for a medium-sized asteroid impact event. This paper reviews the initial and cascading effects of these natural hazards, describes the state of the art for modeling these hazards, and discusses the relevance of these hazards to expected long-term effects of an asteroid impact. Emergency managers, resource managers and planners, and research scientists involved in mitigation and recovery efforts would likely derive significant benefit from a framework linking multiple hazard models to provide a seamless sequence of related forecasts.

Transcriptome Analysis of Persian Oak (Quercus brantii L.) Decline Using RNA-seq Technology

Since the late 1980s, the oak decline has affected the Zagros oak forests in western Iran. Persian oak (Quercus brantii L.) the most important tree species of these forests has been damaged more than any other plant species. In the present study, the RNA sequencing technique was used for the first time to identify key genes and molecular mechanisms involved in Persian oak decline. The RNA was extracted from the leaves of healthy and declined oak trees, and sequenced using the Illumina HiSeq 2500 platform (2 × 150 bp paired-end reads). De novo transcriptome assembly of Persian oak revealed 56,743 unigenes and 6049 differentially expressed genes (DEGs) between declined and control samples. The results of gene ontology analysis showed that most of the DEGs involved in oak decline belong to the group of stress-responsive genes. In general, oak decline samples showed significant reductions in gene expression associated with "photosynthesis and storage of sugar" and "protein synthesis and related processes." Additionally, DEGs related to the starch degradation pathway were up-regulated, whereas DEGs associated with acetate-mevalonate (MVA), biosynthesis of lignin, and lignases pathways were down-regulated. The present study's findings can be an effective step in identifying the genes involved in oak decline and deciphering the relationship between this phenomenon and biotic and abiotic stresses.

A montane species treeline is defined by both temperature and drought effects on growth season length

Montane treelines are defined by a threshold low temperature. However, what are the dynamics when the snow-free summer growth season coincides with a 6-month seasonal drought? We tested this fundamental question by measuring tree growth and leaf activity across elevations in Mt Hermon (2814 m; in Israel and Syria), where oak trees (Quercus look and Quercus boissieri) form an observed treeline at 1900 m. While in theory, individuals can be established at higher elevations (minimum daily temperature >6.5 °C for >4 months even at the summit), soil drying and vapor pressure deficit in summer enforces growth cessation in August, leaving only 2-3 months for tree growth. At lower elevations, Q. look Kotschy is replaced by Quercus cerris L. (1300 m) and Quercus calliprinos Webb (1000 m) in accompanying Q. boissieri Reut., and growth season length (GSL) is longer due to an earlier start in April. Leaf gas exchange continues during autumn, but assimilates are no longer utilized in growth. Interestingly, the growth and activity of Q. boissieri were equivalent to that of each of the other three species across the ~1 km elevation gradient. A planting experiment at 2100 m showed that seedlings of the four oak species survived the cold winter and showed budding of leaves in summer, but wilted in August. Our unique mountain site in the Eastern Mediterranean introduces a new factor to the formation of treelines, involving a drought limitation on GSL. This site presents the elevation edge for each species and the southern distribution edge for both the endemic Q. look and the broad-range Q. cerris. With ongoing warming, Q. look and Q. boissieri are slowly expanding to higher elevations, while Q. cerris is at risk of future extirpation.

Effect of Dust Types on the Eco-Physiological Response of Three Tree Species Seedlings: Eucalyptus camaldulensis, Conocarpus erectus and Bombax ceiba

Dust is the collection of fine particles of solid matter, and it is a major issue of atmospheric pollution. Dust particles are becoming the major pollutants of the urban environment due to hyperbolic manufacturing and automobile pollution. These atmospheric pollutants are not only hazardous for human beings, but they also affect tree growth, particularly in urban environments. This study was designed to examine the changes in morphological and physiological traits of three tree species seedlings (Eucalyptus camaldulensis, Conocarpus erectus, and Bombax ceiba) in response to different dust types. In a pot experiment under controlled conditions, three-month-old seedlings of selected trees species were subjected to four treatments of dust: T1 = controlled; T2 = wood dust; T3 = soil dust; and T4 = carbon dust. During the whole experiment, 10 g/plant/dose was applied in 8 doses with a one-week interval. The results depicted that the growth was the maximum in T1 (control) and the minimum in T4 (carbon dust). In our findings, B. ceiba performed better under the same levels of dust pollution as compared with the other two tree species. The B. ceiba tree species proved to be the most tolerant to dust pollution by efficiently demolishing oxidative bursts by triggering SOD, POD, and CAT under different dust types compared to controlled conditions. Stomatal conductance, photosynthetic rate, and transpiration rate were negatively influenced in all three tree species in response to different dust applications. Based on the findings, among these three tree species, B. ceiba is recommended for dust polluted areas followed by E. camaldulensis and Conocarpus erectus due to their better performance and efficient dust-foraging potential.

Particulate Matter (PM) Adsorption and Leaf Characteristics of Ornamental Sweet Potato (Ipomoea batatas L.) Cultivars and Two Common Indoor Plants (Hedera helix L. and Epipremnum aureum Lindl. & Andre)

Particulate matter (PM) is a serious threat to human health, climate, and ecosystems. Furthermore, owing to the combined influence of indoor and outdoor particles, indoor PM can pose a greater threat than urban PM. Plants can help to reduce PM pollution by acting as biofilters. Plants with different leaf characteristics have varying capacities to capture PM. However, the PM mitigation effects of plants and their primary factors are unclear. In this study, we investigated the PM adsorption and leaf characteristics of five ornamental sweet potato (Ipomea batatas L.) cultivars and two common indoor plants (Hedera helix L. and Epipremnum aureum Lindl. & Andre) exposed to approximately 300 μg m−3 of fly ash particles to assess the factors influencing PM adsorption on leaves and to understand the effects of PM pollution on the leaf characteristics of plants. We analyzed the correlation between PM adsorption and photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (Tr), leaf area (LA), leaf width/length ratio (W/L), stomatal density (SD), and stomatal pore size (SP). A Pearson’s correlation analysis and a principal component analysis (PCA) were used to evaluate the effects of different leaf characteristics on PM adsorption. The analysis indicated that leaf gas exchange factors, such as Pn and Tr, and morphological factors, such as W/L and LA, were the primary parameters influencing PM adsorption in all cultivars and species tested. Pn, Tr, and W/L showed a positive correlation with PM accumulation, whereas LA was negatively correlated.

Thermotolerant wheat cultivar (Triticum aestivum L. var. WR544) response to ozone, EDU, and particulate matter interactive exposure

The present study was conducted to assess the response of thermotolerant wheat cultivar (Triticum aestivum L. var. WR544) to individual and combination of ambient ground level ozone (AO₃) and particulate matter (PM) air pollutants with ethylene diurea (EDU) used as an ozone stress mitigator. The four treatment combinations to which wheat cultivars were exposed are T1 (AO₃ + PM), T2 (EDU + PM), T3 (AO₃-PM), and T4 (EDU-PM). The effect of different treatments on morphological (foliar ozone injury, leaf area, shoot height, number of leaves, and total biomass), biochemical (leaf extract pH, electrical conductivity, relative water content, total chlorophyll, ascorbic acid content), nutritional (leaf carbohydrate content and leaf protein content), and yield (biological yield, economic yield, and harvest index) attributes of the cultivar were monitored. The plants under T1 experienced 20-30% foliar ozone injury and recorded lowest economic yield (0.58 g/plant). Plants under T2 and T3 showed visible foliar ozone injury range between 0 and 5% whereas plants under T4 exhibited negligible ozone injuries. EDU-treated plants without PM deposition (T4) exhibited better morphology, leaf protein content, leaf carbohydrate content, biological and economic yield as compared to T1-, T2-, and T3-treated plants but EDU was only partially effective. Despite being a thermotolerant variety, WR544 gets adversely affected by the individual and combined exposure of AO₃ and PM air pollutants. These result findings highlighted the need for more detailed study of air quality impact on the thermotolerant cultivars of other key crops to individual and combined air pollutants.

Vegetation response to changes in temperature, rainfall, and dust in arid environments

Climate change is responsible for changes in the world's vegetation. This study was aimed to investigate the effect of long-term variations in the air temperature, precipitation, and dust concentration on normalized difference vegetation index (NDVI) variations in the spring, summer, and growing season over arid regions of Iran. The results showed that the precipitation had a positive association with the NDVI in the spring and growing seasons (β > + 0.28; P < 0.05), while air temperature had a negative relationship with the NDVI changes in these seasons (β > - 0.34; P = 0.013). Our results also showed a negative relationship between the accumulated dust concentration (ADC) and NDVI in the spring (β = - 0.23; P = 0.09) and growing seasons (β = - 0.24; P = 0.003). Spatially, the strongest linkage between NDVI and climatic variables was observed in about two-thirds of the study region. In total, our findings indicate that the use of dust concentration, air temperature, and precipitation helps us to make a more accurate approach for evaluating the impacts of climate change on vegetation variations in the arid environments.

The Complex Issue of Urban Trees—Stress Factor Accumulation and Ecological Service Possibilities

This review paper is the first that summarizes many aspects of the ecological role of trees in urban landscapes while considering their growth conditions. Research Highlights are: (i) Plant growth conditions in cities are worsening due to high urbanization rates and new stress factors; (ii) Urban trees are capable of alleviating the stress factors they are exposed to; (iii) The size and vitality of trees is related to the ecological services they can provide. Our review shows, in a clear way, that the phenomenon of human-related environmental degradation, which generates urban tree stress, can be effectively alleviated by the presence of trees. The first section reviews concerns related to urban environment degradation and its influence on trees. Intense urbanization affects the environment of plants, raising the mortality rate of urban trees. The second part deals with the dieback of city trees, its causes and scale. The average life expectancy of urban trees is relatively low and depends on factors such as the specific location, proper care and community involvement, among others. The third part concerns the ecological and economic advantages of trees in the city structure. Trees affect citizen safety and health, but also improve the soil and air environment. Finally, we present the drawbacks of tree planting and discuss if they are caused by the tree itself or rather by improper tree management. We collect the latest reports on the complicated state of urban trees, presenting new insights on the complex issue of trees situated in cities, struggling with stress factors. These stressors have evolved over the decades and emphasize the importance of tree presence in the city structure.