Dose-dependent toxicity of polyethylene microplastics (PE-MPs) on physiological and biochemical response of blackgram and its associated rhizospheric soil properties

Microplastic contamination in terrestrial ecosystem is emerging as a global threat due to rapid production of plastic waste and its mismanagement. It affects all living organisms including plants. Hence, the current study aims at understanding the effect of polyethylene microplastics (PE-MPs) at different concentrations (0, 0.25, 0.50, 0.75, and 1.00% w/w) on the plant growth and yield attributes. With blackgram as a test crop, results revealed that a maximum reduction in physiological traits like photosynthetic rate; chlorophyll a, b; and total chlorophyll by 5, 14, 10, and 13% at flowering stage; and an increase in biochemical traits like ascorbic acid, malondialdehyde, proline, superoxide dismutase, and catalase by 11, 29.7, 16, 22, and 30% during vegetative stage was observed with 1% PE-MP application. Moreover, a reduction in growth and yield attributes was also observed with increasing concentration of microplastics. Additionally, application of 1% PE-MPs decreased the soil bulk density, available phosphorus, and potassium, whereas the EC, organic carbon, microbial biomass carbon, NO3-N, and NH4-N significantly increased. Moreover, the presence of PE-MPs in soil also had a significant influence on the soil enzyme activities. Metagenomic analysis (16 s) reveals that at genus level, Bacillus (19%) was predominant in control, while in 1% PE-MPs, Rubrobacter (28%) genus was dominant. Microvirga was found exclusively in T5, while the relative abundance of Gemmatimonas declined from T1 to T5. This study thus confirms that microplastics exert a dose-dependent effect on soil and plant characteristics.

Unveiling the effect of microplastics on agricultural crops - a review

Microplastics (MPs), ever since they were identified as a potential and widely distributed persistent contaminant, the number of studies highlighting their impacts on various terrestrial ecosystems have been increasing. Recently, the effect of MPs on the agricultural ecosystem has gained momentum. Hence, the present review examines the impact of microplastics on agricultural crop systems and the mechanism underlying its toxicity. The current review revealed that most of the studies were conducted at a laboratory scale and under controlled conditions. Additionally, it was observed that polystyrene (PS) followed by polyethylene (PE) are the most studied polymer type, while the most studied plants are wheat and maize. Hitherto, literature studies suggest that the microplastics' influence on plant growth can be negative or sometimes neutral; while in some cases it exerts a hormetic effect which depends on other factors determining plant growth. Notably, the main mechanisms through which microplastics influence plant growth are mechanical damage, alteration of soil properties, or by leaching of additives. Overall, with burgeoning research interest in this aspect, the current review has significant implications for the toxicity of MPs on plants and throws light on the need to develop novel guidelines toward the sustainable use of plastics in agricultural sector. However, realistic field-level studies and estimating the MPs concentration at various region are essential to develop remediation approaches. Future studies should also focus on translocation and accumulation of micron sized MPs in edible portion of crops and their effect on food safety.

Effect of ozone stress on crop productivity: A threat to food security

Tropospheric ozone (O3), the most important phytotoxic air pollutant, can deteriorate crop quality and productivity. Notably, satellite and ground-level observations-based multimodel simulations demonstrate that the present and future predicted O3 exposures could threaten food security. Hence, the present study aims at reviewing the phytotoxicity caused by O3 pollution, which threatens the food security. The present review encompasses three major aspects; wherein the past and prevailing O3 concentrations in various regions were compiled at first, followed by discussing the physiological, biochemical and yield responses of economically important crop species, and considering the potential of O3 protectants to alleviate O3-induced phytotoxicity. Finally, the empirical data reported in the literature were quantitatively analysed to show that O3 causes detrimental effect on physiological traits, photosynthetic pigments, growth and yield attributes. The review on prevailing O3 concentrations over various regions, where economically important crop are grown, and their negative impact would support policy makers to implement air pollution regulations and the scientific community to develop countermeasures against O3 phytotoxicity for maintaining food security.

Response of rice (Oryza sativa L.) cultivars to elevated ozone stress

The plant response to elevated ozone stress reveals inter-species and intra-species disparity. Ozone-induced crop yield loss is predicted to increase in the future, posing a threat to the world economy. This study aims to evaluate the cultivar specific variation in rice exposed to elevated ozone. Fifteen short-duration rice cultivars were exposed to 50 ppb ozone for 30 days at reproductive stage. The physiological, biochemical, growth and yield traits of all test cultivars were significantly affected in response to elevated ozone. On an average, ozone stress decreased the tiller number by 22.52%, number of effective tillers by 30.43%, 1000 grain weight by 0.62% and straw weight by 23.83% over control. Spikelet sterility increased by 19.26% and linear multiregression 3D model significantly fits the spikelet sterility and photosynthetic traits with the R² of 0.74 under elevated ozone. Principal Component Analysis with total variance of 57.5% categorized 15 rice cultivars into four major groups, i.e., ozone sensitive (MDU6, TRY(R)2 and ASD16), moderately ozone sensitive (ASD18, ADT43, and MDU5), moderately ozone tolerant (ADT37, ADT(R)45, TPS5, Anna(R)4, PMK(R)3, and ADT(R)48), and ozone tolerant (CO51, CO47, and ADT36). This study indicates that the different responses of rice cultivars to elevated ozone stress through a change in plant physiology, biochemical, growth, and yield traits and the results directed to provide scientific information on plant adaptations to ozone stress and helps in efforts to search ozone tolerant gene for plant breeding.