Adsorption of Strontium onto Adaxial and Abaxial Cuticle of Photinia serrulata Leaf

The adsorption-desorption behavior of chlorothalonil in the cuticles of apple and red jujube

The distribution fate of chlorothalonil (CHT) in the environment (soil and water) and fruits is controlled by the capacity of cuticles to adsorb and desorb CHT, which directly affects the safety of both the environment and fruits. Batch experiments were conducted to reveal the adsorption-desorption behaviors of CHT in the cuticles of apple and red jujube. The adsorption kinetics showed that both physisorption and chemisorption occurred during the adsorption process. Furthermore, the isothermal adsorption of CHT in the fruit cuticles followed the Freundlich model. The thermodynamic parameters (ΔG ≤ -26.16 kJ/mol, ΔH ≥ 31.05 kJ/mol, ΔS ≥ 0.20 kJ/(mol K) showed that the whole CHT adsorption process was spontaneous, and the hydrophobic interaction was predominant. The CHT adsorption capacity of the apple cuticle was higher than that of the red jujube cuticle, potentially due to the significantly higher alkanes content of apples than that of red jujubes. An appropriate ionic strength (0.01 moL/L) could induce a higher adsorption capacity. In addition, the desorption kinetics were shown to conform to a Quasi-first-order model, meaning that not all the adsorbed CHT could be easily desorbed. The desorption ratios in apple and red jujube cuticles were 41.38% and 35.64%, respectively. The results of Fourier-transformed infrared spectroscopy and X-ray photoelectron spectroscopy further confirmed that CHT could be adsorbed and retained in the fruit cuticles. Investigating the adsorption-desorption behavior of CHT in the apple and red jujube cuticles allowed to determine the ratio of its final distribution in the fruits and environment, providing a theoretical basis to evaluate the risk of residue pesticide.

New Process for the Sulfonation of Algal/PEI Biosorbent for Enhancing Sr(II) Removal from Aqueous Solutions-Application to Seawater

Sulfonic resins are highly efficient cation exchangers widely used for metal removal from aqueous solutions. Herein, a new sulfonation process is designed for the sulfonation of algal/PEI composite (A*PEI, by reaction with 2-propylene-1-sulfonic acid and hydroxylamine-O-sulfonic acid). The new sulfonated functionalized sorbent (SA*PEI) is successfully tested in batch systems for strontium recovery first in synthetic solutions before investigating with multi-component solutions and final validation with seawater samples. The chemical modification of A*PEI triples the sorption capacity for Sr(II) at pH 4 with a removal rate of up to 7% and 58% for A*PEI and SA*PEI, respectively (with SD: 0.67 g L^-1). FTIR shows the strong contribution of sulfonate groups for the functionalized sorbent (in addition to amine and carboxylic groups from the support). The sorption is endothermic (increase in sorption with temperature). The sulfonation improves thermal stability and slightly enhances textural properties. This may explain the fast kinetics (which are controlled by the pseudo-first-order rate equation). The sulfonated sorbent shows a remarkable preference for Sr(II) over competitor mono-, di-, and tri-valent metal cations. Sorption properties are weakly influenced by the excess of NaCl; this can explain the outstanding sorption properties in the treatment of seawater samples. In addition, the sulfonated sorbent shows excellent stability at recycling (for at least 5 cycles), with a loss in capacity of around 2.2%. These preliminary results show the remarkable efficiency of the sorbent for Sr(II) removal from complex solutions (this could open perspectives for the treatment of contaminated seawater samples).

Effects of periodic drought with severe exhaust exposure on particle retention capacity and physiological responses of Photinia × fraseri Dress

Urban plants are regarded as an effective agent to control particulate matter (PM) pollution by absorbing PM. Repeated PM and drought stress in urban areas often cause morphological and physiological damage to plants, resulting in lower ecological benefits. Nevertheless, knowledge in PM retention capability, morphology and physiology of plants under repeated stress and cross stress has been barely available. In order to investigate changes in these aspects under repeated stress, we applied periodic drought with severe exhaust exposure on Photinia × fraseri Dress (a common urban tree species with strong PM retention ability). The study was carried out in a six-period scenario, with a duration of 10 days for each period: initial value (R0), initial stress period (S1), initial recovery period (R1) second stress period (S2), second recovery period (R2) and final stress period (S3). The results are as follows: In terms of periodic factor, PM retention of tail gas stress group (P) and cross stress group (PD) in S2 decreased by 10.00 μg/cm² and 12.60 μg/cm² respectively compared with those during S1 (p > 0.05). During S3, the total amount of PM on leaf surface in both P and PD demonstrated a significant decrease (p < 0.05). The retention capacity of P. fraseri may be dramatically limited under multi-period stress. In this experiment, we attribute the decrease of PM retention to the morphological changes (shedding of mature leaves, smaller leaf area and thinner wax layer) and physiological responses (an increase in gas exchange) under multi-period stress. In terms of cross-stress factor, the total retained PM on leaf surface in PD was higher than that in P, especially during S3, and the interaction between drought and PM reached a significant level (p < 0.01, η² = 0.808), which indicated that drought reduced the loss of dust under PM stress. Changes in morphology and gas exchange indicated that the mechanisms for the high dust retention rate on the leaf surface of PD group varied in the three stress periods. In addition, except the chlorophyll relative value, the alleviated accumulation of MDA and intense production of soluble sugar with PD showed favorable responses to disturbance compared with those in P under the repeated stress. Therefore, we infer that, under multi-period stress of drought and tail gas, P. fraseri may better maintain PM retention ability and resistance than under single stress.

Cuticular conductance of adaxial and abaxial leaf surfaces and its relation to minimum leaf surface conductance

Cuticular conductance to water (g_cw ) is difficult to quantify for stomatous surfaces due to the complexity of separating cuticular and stomatal transpiration, and additional complications arise for determining adaxial and abaxial g_cw . This has led to the neglect of g_cw as a separate parameter in most common gas exchange measurements. Here, we describe a simple technique to simultaneously estimate adaxial and abaxial values of g_cw , tested in two amphistomatous plant species. What we term the 'Red-Light method' is used to estimate g_cw from gas exchange measurements and a known CO₂ concentration inside the leaf during photosynthetic induction under red light. We provide an easy-to-use web application to assist with the calculation of g_cw . While adaxial and abaxial g_cw varies significantly between leaves of the same species we found that the ratio of adaxial/abaxial g_cw (γ_n ) is stable within a plant species. This has implications for use of generic values of g_cw when analysing gas exchange data. The Red-Light method can be used to estimate total cuticular conductance (g_cw-T ) accurately with the most common setup of gas exchange instruments, i.e. a chamber mixing the adaxial and abaxial gases, allowing for a wide application of this technique.

The distribution and retained amount of benzo[a]pyrene at the micro-zones of mangrove leaf cuticles: Results from a novel analytical method

Plant leaf cuticles play a critical role in the accumulation and transport of atmospheric polycyclic aromatic hydrocarbons (PAHs). The relationship between the distribution and retained amount of PAHs on the leaf cuticles and the leaves micro-zone structures is still unclear. In this study, a confocal microscopic fluorescence spectral analysis (CMFSA) system with a spatial resolution of 200 nm was established as a direct and noninvasive means to determine the microscopic distribution and quantify the retained amount of benzo[a]pyrene (B[a]P) at Aegiceras corniculatum (Ac), Kandelia obovata (Ko) and Avicennia marina (Am) leaf cuticle micro-zones (0.096 mm²). The linear ranges for the established method were 10-1900 ng spot^-1 for Ac, 15-1700 ng spot^-1 for Ko and 30-1800 ng spot^-1 for Am, and the detection limits were 0.06 ng spot^-1 for Ac, 0.06 ng spot^-1 for Ko and 0.07 ng spot^-1 for Am. Notably, B[a]P formed clusters and unevenly distributed at the leaf cuticles. On the adaxial cuticles, B[a]P was mainly accumulated unevenly along the epidermis cell wall, and it was also distinctively distributed in the secretory cells around salt glands for Ac and Am. On the abaxial leaf cuticles, B[a]P was concentrated in the salt glands and stomata apart from being unevenly distributed in the epidermis cell wall. Moreover, the amount of B[a]P retained presented a negative correlation with the polarity of leaf cuticles, which resulted in the amount of B[a]P retained on the adaxial leaf cuticles being significantly higher than that on abaxial leaf cuticles. Our results provide a potential in situ method for investigating the distribution and retained amount of PAHs at plant leaf surface micro-zones, which would contribute to further studying and understanding the mechanism of migration and transformation of PAHs by plant leaves from a microscopic perspective.