Tomato is an important vegetable that is highly sensitive to drought (DR) stress which impairs the development of tomato seedlings. Recently, melatonin (ME) has emerged as a nontoxic, regulatory biomolecule that regulates plant growth and enhances the DR tolerance mechanism in plants. The present study was conducted to examine the defensive role of ME in photosynthesis, root architecture, and the antioxidant enzymes’ activities of tomato seedlings subjected to DR stress. Our results indicated that DR stress strongly suppressed growth and biomass production, inhibited photosynthesis, negatively affected root morphology, and reduced photosynthetic pigments in tomato seedlings. Per contra, soluble sugars, proline, and ROS (reactive oxygen species) were suggested to be improved in seedlings under DR stress. Conversely, ME (100 µM) pretreatment improved the detrimental-effect of DR by restoring chlorophyll content, root architecture, gas exchange parameters and plant growth attributes compared with DR-group only. Moreover, ME supplementation also mitigated the antioxidant enzymes [APX (ascorbate peroxidase), CAT (catalase), DHAR (dehydroascorbate reductase), GST (glutathione S-transferase), GR (glutathione reductase), MDHAR (monodehydroascorbate reductase), POD (peroxidase), and SOD (superoxide dismutase)], non-enzymatic antioxidant [AsA (ascorbate), DHA (dehydroascorbic acid), GSH (glutathione), and GSSG, (oxidized glutathione)] activities, reduced oxidative damage [EL (electrolyte leakage), H2O2 (hydrogen peroxide), MDA (malondialdehyde), and O2•− (superoxide ion)] and osmoregulation (soluble sugars and proline) of tomato seedlings, by regulating gene expression for SOD, CAT, APX, GR, POD, GST, DHAR, and MDHAR. These findings determine that ME pretreatment could efficiently improve the seedlings growth, root characteristics, leaf photosynthesis and antioxidant machinery under DR stress and thereby increasing the seedlings’ adaptability to DR stress.

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Organic amendments (animal manure and biochar) to agricultural soils may enhance soil organic carbon (SOC) contents, improve soil fertility and crop productivity but also contribute to global warming through nitrous oxide (N 2 O) emission. However, the effects of organic amendments on N 2 O emissions from agricultural soils seem variable among numerous research studies and remains uncertain. Here, eighty-five publications (peer-reviewed) were selected to perform a meta-analysis study. The results of this meta-analysis study show that the application of animal manure enhanced N 2 O emissions by 17.7%, whereas, biochar amendment significantly mitigated N 2 O emissions by 19.7%. Moreover, coarse textured soils increased [lnRR = 182.6%, 95% confidence interval (CI) = 151.4%, 217.7%] N 2 O emission after animal manure, in contrast, N 2 O emission mitigated by 7.0% from coarse textured soils after biochar amendment. In addition, this study found that 121-320 kg N ha − 1 and ⩽ 30 T ha − 1 application rates of animal manure and biochar mitigated N 2 O emissions by 72.3% and 22.5%, respectively. Soil pH also played a vital role in regulating the N 2 O emissions after organic amendments. Furthermore, > 10 soil C: N ratios increased N 2 O emissions by 121.4% and 27.6% after animal and biochar amendments, respectively. Overall, animal manure C: N ratios significantly enhanced N 2 O emissions, while, biochar C: N ratio had not shown any effect on N 2 O emissions. Overall, average N 2 O emission factors (EFs) for animal manure and biochar amendments were 0.46% and − 0.08%, respectively. Thus, the results of this meta-analysis study provide scientific evidence about how organic amendments such as animal manure and biochar regulating the N 2 O emission from agricultural soils.

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