Document Type : Research Article
Authors
1 Department of Horticulture and Green Space, Faculty of Agriculture, Ferdowsi University of Mashhad
2 horticulture department, faculty of agriculture, ferdowsi university of mashhad
Abstract
Introduction
Urban agriculture is one of the basic characteristics of urban schematization, which helps to increase the quality of urban life via reducing the climate pollution, preserving and increasing biodiversity, as well as re-utilizing urban waste. Therefore, in recent years, urban agriculture has gained significant importance due to its economic, social and cultural benefits. However, studies have indicated that urban soils can contain high concentrations of certain infrequent elements such as lead and cadmium. These heavy metals can be distinguished from other pollutants because they cannot be bio-degraded; but they accumulate in living organisms and subsequently cause diseases and various disorders even in relatively lower concentrations. Plants, like other organisms, have defense mechanisms that are activated in stressful conditions. Thus, under stress, enzymatic antioxidant systems and non-enzymatic metabolites enhance, due to the production of reactive oxygen species. Peppermint plant (Mentha piperita L) has an essential oil with medicinal properties. High levels of heavy metals cause chlorosis and necrosis, increase the accumulation of reactive oxygen species (ROS) and oxidative stress in mint plants. The present study was conducted on a regional scale in order to investigate heavy metal pollution and determine their impacts on some physiological and biochemical traits as well as the concentration of Cd and Pb in peppermint plants grown in urban green spaces.
Material and methods
This study was conducted to assess the amount of heavy metal absorption and its effect on some biochemical properties of peppermint plant (Mentha piperita L.), in Mashhad city in 2021.The experiment was carried out as a factorial in the form of randomized complete block design in three replications. The first factor (location) were Faz4 Park (with high degree of contamination) and Nasim Park (with low degree of contamination). The second factor was the times of harvest (June15, July15 and August 15). At the time of every harvest fully developed leaves were collected to evaluate physiological and biochemical traits.
Results and discussion
The results of analysis of variance indicated that the effect of location was significant on all traits except for the yield of essential oil. Also, the effect of harvest time was significant on all traits except for peroxidase activity and the yield of essential oil. However, the interaction of location and harvest was significant only on phenol, flavonoid, proline, cadmium and lead concentration.
The results indicated that the ascorbate peroxidase, catalase and peroxidase activities were higher in Faz 4 Park. Moreover, the highest activities of ascorbate peroxidase, catalase and peroxidase were recorded in Faz 4 + first harvest. Heavy metals cause the production of reactive free radicals and also increase the activity of antioxidant enzymes. However, the chlorophyll a, b, carotenoid and total chlorophyll contents were higher in Nasim. Thus, the highest contents of Chla, Chlb, Chltotal and carotenoid were observed in Nasim + first harvest. The higher amount of chlorophyll and carotenoids in the first harvest is due to the optimal growth conditions such as day length and sunlight and ambient temperature. In addition total phenol, flavonoid, proline, Cd and Pb elements indicated a reducing trend in Faz 4 compared to Nasim Park in different harvest times, but the amount of these traits were higher in the first harvest than in the subsequent harvests. Increased amount of total phenol in the first harvest can be related to the high air temperature at the first harvest which caused stressful conditions in this stage. Proline production also improves under heavy metal stress in order to protect the plant against toxicity. Nevertheless, the percentage of essential oil showed an increasing trend via enhancing the absorption of Pb and Cd in Faz 4 compared to Nasim Park. The higher percentage of essential oil in Faz 4 can be due to the lower growth of leaves due to the presence of more heavy elements in this area. In general, despite the fact that only the concentration of Pb was higher than the world standard level in both parks, the contamination with Cd and Pb (especially Pb) was more in Faz 4 than in Nasim Park, which was a factor in diminishing the growth traits of peppermint plants. In a case of harvest times, the first harvest recorded better growth characteristics and higher absorption of heavy metals due to the higher strength of the plant, while in the third harvest, due to spending more energy for regrowth, it had lower growth characteristics and weaker absorption of Pb and Cd metals. It was cadmium.
Keywords
Main Subjects
)
Send comment about this article