• Energy Research

Agro-wastes, such as crop residues, leaf litter, and sawdust, are major contributors to global greenhouse gas emissions, and consequently a major concern for climate change. Nowadays, mushroom cultivation has appeared as an emerging agribusiness that helps in the sustainable management of agro-wastes. However, partial utilization of agro-wastes by mushrooms results in the generation of a significant quantity of spent mushroom substrates (SMS) that have continued to become an environmental problem. In particular, Shiitake (Lentinula edodes Berk.) mushrooms can be grown on different types of agro-wastes and also generate a considerable amount of SMS. Therefore, this study investigates the biotransformation of SMS obtained after Shiitake mushroom cultivation into biogas and attendant utilization of slurry digestate (SD) in tomato (Solanum lycopersicum L.) crop fertilization. Biogas production experiments were conducted anaerobically using four treatments of SMS, i.e., 0% (control), 25, 50, and 75% inoculated with a proportional amount of cow dung (CD) as inoculum. The results on biogas production revealed that SMS 50% treatment yielded the highest biogas volume (8834 mL or 11.93 mL/g of organic carbon) and methane contents (61%) along with maximum reduction of physicochemical and proximate parameters of slurry. Furthermore, the biogas digestate from 50% treatment further helped to increase the seed germination (93.25%), seedling length (9.2 cm), seedling root length (4.19 cm), plant height (53.10 cm), chlorophyll content (3.38 mg/g), total yield (1.86 kg/plant), flavonoids (5.06 mg/g), phenolics (2.78 mg/g), and tannin (3.40 mg/g) contents of tomato significantly (p < 0.05) in the 10% loading rate. The findings of this study suggest sustainable upcycling of SMS inspired by a circular economy approach through synergistic production of bioenergy and secondary fruit crops, which could potentially contribute to minimize the carbon footprints of the mushroom production sector.

In arid ecosystems, lack of vegetation and nutrients can negatively impact soil carbon (C) content. In the current study, our goals were to assess soil C stocks to a depth of 50 cm in an arid ecosystem (Wadi Al-Sharaea, Saudi Arabia) and determine their relation to different vegetation cover. To address our research objective, a total of 102 quadrate (randomly selected) were established along the desert wadi. Soil samples were collected to a depth of 50 cm with 5 cm interval, then Soil Bulk Density (SBD, g/cm3), Soil Organic C Content (SOC, g C/kg), and stocks (kg C/m2) were estimated. Both soil mechanical and chemical analyses were conducted for a composite soil sample. Study sites were categorized based on their visual vegetation cover (VC) percentage (%) into three major groups: 1) scarce vegetation cover (VC less than 25%); 2) medium vegetation cover (VC is higher than 25% and less than 75%); and lastly 3) dense vegetation cover (VC is higher than 75%). Soils were characterized by higher sand content (48.2%, both fine and coarse compiled) than silt (36.7 ± 1.64%) or clay (10.1 ± 1.28%). There were significant differences among soil Calcium (Ca) and Potassium (K) content (p < 0.05), while those plant communities with medium vegetation cover showed the highest soil content of Ca and K (1.7 ± 0.24 and 0.2 ± 0.03 meq/l, respectively). Plant communities with dense vegetation cover had the lowest SBD (1.96 ± 0.03 g/cm3) and the highest SOC stocks (14.9 ± 2.1 kg C/m2). Moreover, our data analyses indicated that SBD and SOC content had strong and negative correlation, where soils with dense vegetation cover had the most significant correlation (R2 = 0.95). Our results recommend that soil carbon stocks to a depth of 50 cm based on different vegetation cover of arid ecosystems should be implemented on global soil carbon budget to better elucidate factors controlling SOC content at the regional and global scales.

Lead contamination is among the most significant threats to the environment. The phytoextraction approach uses plants that can tolerate and accumulate metals in their tissues. Lately, biofuel plants have been recommended to be suitable for remediation and implementation of potentially toxic elements (PTEs)-polluted soil. This research assessed the Pb phytoremediation potential of three Sorghum bicolor [red cultivar (S1), white cultivar (S2) and shahla cultivar (S3)]. A pot experiment with five treatments (0, 100, 200, 400 and 800 mg Pb/kg soil) was carried out to assess the potential possibility of using these cultivars to remediate the soil of Pb. The potential possibility of using these plants to phytoremediate the soil of Pb was also assessed. The results emphasized that all the examined cultivars could attain growth to maturity in high Pb spiked soil. However, Pb influenced morphological and chlorophyll contents, especially in plants grown in soil amended with 800 mg/kg. The S1 cultivar had the most significant reduction in total chlorophyll with an average of 72%, followed by the S2 and S3 cultivars (65% and 58% reduction, respectively). The highest Pb content in root (110.0, 177.6 and 198.9 mg/kg, respectively) and in-plant shoot (83.9, 103.6 and 99.0 mg/kg, respectively) were detected by sorghum (S1, S2 and S3, respectively) grown in soil enriched by 800 mg/kg of Pb. From the calculated results of the contamination indices, contamination factor (CF), translocation factor (TF), plant uptake (UT) and tolerance index (TI), none of the investigated cultivars were considered Pb hyperaccumulators, but all were identified as particularly ideal for phytostabilization.

AbstractCoastal ecosystems are characterized by high content of soil carbon storage; however, they experience severe land conversions in the past decades. The current study aims to examine how different land use/land cover (LU/LC) impact carbon stock in coastal ecosystem along Jazan coast, Saudi Arabia. In this study, impacts of LU/LC on carbon stocks in the coastal zone of Jazan, Saudi Arabia in 2009, 2013, and 2021 were assessed. Also, the LU/LC dynamics were evaluated using data provided by the land use dynamic model. The carbon stocks were modelled based on LU/LC using the InVEST program. Our study results showed that the decrease in mangroves from 2013 to 2021 reflects the high atmospheric emissions of carbon dioxide (CO2). Also, the increase in built-up areas might negatively impact total carbon stock. The estimated carbon stocks for the coastal zone of Jazan biome were 7279027.42 Mg C in 2009 (1Mg = 106 g). It decreased to 2827817.84 Mg C in 2013, with a total loss of − 4450675.40 Mg C, and an average of annual loss of − 1,112,669 Mg C in the study period with net value of − 461240790.53 US$. On the other hand, the total estimated carbon stock was increased from 2013 to 2021 with a 3772968.31 Mg C in 2021 (a total gain 944840.87 Mg C). Based on the current findings, we recommend that land-use-policy makers and environmental government agencies should implement conservation policies to reduce land use change at Jazan coastal ecosystems.