Effects of Chemical Fertilizer Reduction Combined with Biochar on the Content of Related Substances and Enzyme Activity of NO Synthesis and AsA-GSH Cycle in Tobacco Leaves

Purpose To study the mitigation mechanism of reduced chemical fertilizer application combined with biochar on continuous cropping obstacles in tobacco, especially the effects on the enzymes and non-enzymatic substances methyl jasmonate (MeJA), S-nitrosothiols (SNOs), and so on in the nitrogen sources and (AsA-GSH) cycle of tobacco plants.

Methods Using Yunyan 87 as the test material, five fertilizer applications and biochar additions per plant were set, including fertilizer 30 g (T₁), fertilizer 30 g+biochar 300 g (T₂), fertilizer 45 g (T₃); fertilizer 45 g+biochar 300 g (T₄), fertilizer 60 g (T₅). The effects of different treatments on the antioxidant system of tobacco were analyzed by measuring the contents of non-enzyme antioxidants and related enzyme activities in AsA-GSH cycle system, as well as the contents of MeJA and SNOs.

Results 1) In T₅ treatment, the nitrate reductase activity and nitric oxide (NO) content in tobacco leaves were 244.01 IU/L and 150.05 μmol/g, respectively; in contrast, T₂ treatment significantly reduced by 15.50% and 17.53%, respectively. 2) In T₅ treatment, SNOs content and S-nitrosoglutathione reductase (GSNOR) activity were 114.76 pg/mL and 147.42 IU/L, respectively; in contrast, T₂ and T₄ treatments significantly increased SNOs content by 9.72% and 17.78%, respectively, and significantly decreased GSNOR activity by 31.93% and 39.00%, respectively. 3) In T₅ treatment, levels of AsA, GSH, ascorbate peroxidase, glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), and MeJA in tobacco leaves were 266.04 μg/g, 75.03 ng/L, 66.14 ng/L, 162.77 ng/L, 17.66 ng/L, and 36.85 nmol/L, respectively; in contrast, T₂ and T₄ treatments significantly increased GR activity by 88.34% and 123.14%, respectively, and significantly increased MeJA levels by 6.90% and 17.26%, respectively.

Conclusion Reduced fertilizer application combined with biochar can decrease NO content in tobacco leaves under stress conditions. NO can regulate SNOs content, GSNOR activity, AsA-GSH cycle-related substances and enzyme activity, and synthesis of MeJA, to maintain redox balance, mitigate stress responses from continuous cropping obstacles and enhance tobacco resistance.