جستجوی مقالات مرتبط با کلیدواژه "آنزیم ها" در نشریات گروه "جنگلداری"

Drought significantly impacts plant growth and has become a critical global concern. Understanding how plants respond to drought is essential. Under arid conditions, forests are prone to experiencing various types of stress. Trees protect themselves from drought stress through both physical and chemical defenses. Physical defenses include increasing the density of structures like leaves, thorns, and hairs, while chemical defenses involve producing physiological responses that serve as protective barriers against environmental factors. Oaks are known for their resistance to drought and heat, which is attributed to their physiological responses during dry conditions. The reaction of the dominant species of Persian oak (Quercus brantii) in the Zagros forests to recent droughts suggests that this species is highly sensitive to these conditions. The response to drought stress in mature, multi-year-old trees differs from that of seedlings of the same species. Certain physiological mechanisms influence the internal changes in trees as they react to stress. Therefore, the objective of this study is to examine the effects of drought stress on the physiological traits of mature oak trees under both optimal and stressful natural conditions.

This research was conducted on multi-year-old Persian oak trees over two years (2020-2022) in the natural forest environment of the Fajr Safa agro-industrial complex, located 10 kilometers from Khorramabad city. The experiment followed a completely randomized block design with three levels of drought stress. Drought treatments included a severe drought treatment (where the soil was completely covered with white plastic to prevent any moisture from reaching it for two years), moderate soil moisture treatment (with irrigation every 10 days), and a control group. The statistical sample included 120 trees, divided into 30 trees for each treatment group. On September 10, 2022, at the end of the experiment, leaves were collected from each tree at a fixed height of two meters around the trunk, from all four cardinal directions, and were taken to the laboratory. By measuring fresh weight, turgid weight, and dry weight, the relative water content of the leaves was calculated. To further analyze physiological traits, the leaves were dried in an oven at 70°C for 72 hours and ground into a powder. The following were measured in trees across all three treatment groups: proline levels, soluble and insoluble sugars, enzyme activity (peroxidase, superoxide dismutase, and ascorbate oxidase), as well as the amounts of carotenoids, chlorophyll a, chlorophyll b, and total chlorophyll.

The analysis of variance results indicated that different treatment levels had a significant effect at the 0.05 level on the amounts of proline, relative water content of the leaves, and the activities of enzymes (peroxidase, superoxide dismutase, and ascorbate oxidase). However, no significant difference at the 0.05 level was observed between treatments regarding soluble sugars, insoluble sugars, and photosynthetic pigments (carotenoids, chlorophyll a, chlorophyll b, and total chlorophyll). Among the treatment levels, the relative water content of the leaves showed the most variation. As drought stress increased, the relative water content of the leaves decreased, while proline, soluble sugars, insoluble sugars, enzymes (superoxide dismutase, peroxidase, and ascorbate oxidase), and photosynthetic pigments (chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids) showed an increasing trend. The highest proline levels were found in the control group, with the lowest observed in the irrigated group. Relative water content, peroxidase, and superoxide dismutase activity were highest in the irrigated group. Under severe drought stress, levels of proline, soluble sugars, and insoluble sugars increased compared to the control group.

Based on the results of this study, mature oak trees tend to preserve carbohydrates and sugars under stress. This research highlights the adaptability of mature oak trees to both optimal conditions (comparing control with irrigated trees) and their resilience during dry periods (comparing control with stressed trees). The findings indicate that mature Persian oak trees can resist drought stress to some extent by increasing proline and antioxidant enzyme activity. Compared to previous studies, where seedlings showed greater vulnerability to changes in carbohydrates and soluble sugars under stress, mature trees seem to conserve their carbohydrates and sugars. These findings are highly relevant for forest management strategies and can inform forest specialists and stakeholders. Overall, the results suggest a strong relationship between drought stress responses and plant physiology. It can be concluded that the climatic conditions affecting Persian oak stands are critical and should be a major consideration for forest managers responsible for developing management programs for the western forests of the country.

The recycling of different paper and paperboard products can supply the major shortage of cellulosic raw materials needed for the production of pulp and paper, and it can be important from the economic and environmental point of view. Using recycled pulp in papermaking reduces the quality of the final paper. Therefore, the use of enzyme pre-treatment separately or combined sequences as well as pulp bleaching can be effective in improving the quality properties of the final paper obtained from recycled pulp. This research was conducted with the aim of investigating the effect of enzyme pre-treatment with cellulase and laccase sequence on the bleachability of the resulting pulp with hydrogen peroxide, and the quality of the final pulp after bleaching system were investigated.

At first, the mixture of waste newspaper and magazine papers were deinked using enzyme pre-treatment (combined sequence of cellulase and laccase) as well as conventional chemical method. Enzymatic pre-treatment was done as experimental treatments C1L1 (cellulase usage: 0.1% and duration time: 10 minutes; laccase usage: 20u and duration time: 120 minutes), C1L2 (cellulase usage: 0.1% and duration time: 10 minutes; laccase usage: 40u and duration time: 120 minutes), C2L1 (cellulase usage: 0.1% and duration time: 20 minutes; laccase usage: 20u and duration time: 120 minutes) and C2L2 (cellulase usage: 0.1% and duration time: 20 minutes; laccase usage: 40u and duration time: 120 minutes) under specific process conditions. Also, control pulp (without adding chemicals or enzymes) and chemically deinked pulp samples were also prepared and then bleaching of deinked pulp was accomplished using hydrogen peroxide bleaching system including 2% hydrogen peroxide, 2% sodium hydroxide, 2% sodium silicate, 0.2% DTPA chelating agent and 0.1% magnesium sulfate in separate plastic bags under process conditions of 10% consistency, 70°C temperature and 2 hours in a water bath. At the end, the optical and strength characteristics of the bleached pulp were evaluated.

The results of the evaluation of bleached pulp with hydrogen peroxide after deinking with conventional method and also cellulase and laccase enzyme pre-treatment sequences showed that the use of enzyme pre-treatment in deinking improves the overall performance of the hydrogen peroxide bleaching process and resulted in the papers with better optical and strength characteristics after bleaching compared to pulp pre-deinked by conventional chemical method. C2L2 and C2L1 pre-treatments in combined enzymatic treatments after bleaching with hydrogen peroxide led to an improvement in brightness by 11.12% (increase of about 5 units) and 9.5% (increase of about 4 units), respectively. In these pretreatments, the whiteness of the paper increased by 31.92% and 24.54% (an increase of about 9 and 6 units), respectively. Also, the yellowness of the paper decreased by 40.19% and 44.25%, respectively, and the opacity of the paper reduced by 37.74% and 23.97%, respectively. Also, in experimental runs of C2L1 and C2L2, the paper tensile index increased 29.17% and 35.64%, respectively (40.64 Nm/g and 38.7 Nm/g, respectively), breaking length enhanced by 64.42% and 99%, respectively (5.92 km and 4.89 km), and the paper burst index also increased by 70.85% and 92.37% (3.81 mN.m2/g and 4.29 kPa.m2/g), respectively. The tear indices of paper in these runs were determined on average about 6.82 mN.m2/g and 6.62 mN.m2/g, which are a little lower compared to the chemically deinked pulp after bleaching, but in the pretreatment with the combined sequence C2L1, the tear index of paper was almost equivalent to that of chemically deinked pulp.

Mixed office waste deinking by conventional chemical process, other than having higher chemical consumption and considerable emission of environmental pollutions, has relatively lower deinking efficiency. On the other hand, enzymatic deinking increases deinking efficiency even at reduced environmental pollutions, but it may reduce the strength properties of deinked pulp. At present paper, the physical and strength properties of mixed office waste enzymatic deinked pulps, selected from superior enzymatic treatments in terms of deinking efficiency using commercial cellulase enzyme from Aspergillus niger, were compared with the selected superior samples of chemical deinking treatments and the reference sample. The results showed that, the hand sheets of enzymatic deinked pulps, in comparison with chemical deinking, had lower caliper and bulk but without having significant differences with chemically deinked pulps in terms of the strength properties. As a result, because of its better deinking efficiency and also acceptable physical and strength properties, enzymatic deinking was recommended, as a proper substitute of conventional chemical deinking, for deinking of mixed office waste papers.