Combined application of organic fertilizer and alginic acid improves the stress resistance and quality of Astragalus mongolicus in saline-alkali land

Objectives Organic fertilizer and alginic acid have been proved of increasing the stress resistance of crop. We studied the combinations of organic fertilizer rates and alginic acid concentrations on improving the photosynthetic efficiency, stress resistance, yield, and medical quality of A. mongholicus in saline-alkali land.

Methods A field experiment with a two-factor-three-level complete design was conducted in saline-alkali land for two consecutive years, using seedlings of A. mongholicus as materials. The two factors were organic fertilizer and alginic acid, the three application levels of organic fertilizer were 0, 1200, and 2400 kg/hm² (denoted as O0, O1, and O2); and the three application concentration levels of alginic acid (A) were 0, 1, and 2 g/L (denoted as A0, A1, and A2). At 60 days after the rejuvenation of A. mongholicus, the leaf photosynthetic parameters, antioxidant enzyme activities, and osmoregulation substance contents were measured. And at 120 days, the yield, and the contentd of medicinal components and heavy metals in A. mongholicus roots were measured.

Results Compared with O0, O1 and O2 treatment increased the leaf P_n, T_r, and G_s in 2022 and 2023 by 13.6%−29.2%, 17.0%−32.3%, and 14.8%−21.2%, enhanced the activities of CAT, SOD, and POD by 10.4%−24.0%, 9.5%−13.5%, and 7.5%−29.5%, increased of soluble sugar, soluble protein, and proline contents by 11.0%−28.8%, 22.3%−94.3%, and 13.2%−61.4%, and increased the root yields by 3.8%−8.1%, the AIV contents by 7.4%−19.4% and C7G contents by 4.5%−22.7%, and decreased Pb, Cd, As, and Cu contents by 1.4%−16.0%, 5.0%−19.5%, 5.6%−9.7%, and 11.5%−35.2%, respectively (P<0.05). Compared with A0, A1 treatment significantly increased all the tested photosynthesis parameter values, the activities of antioxidant enzymes, and the contents of osmoregulation substances, significantly enhanced the root yields and medicinal component contents, and decreased Pb, Cd, As, Hg, and Cu contents by 12.0%−22.2%, 6.9%−17.1%, 7.5%−13.3%, 7.1%−18.9%, and 16.1%−21.9%, respectively. In both 2022 and 2023, O2A1 treatment was recorded the highest root yield (6887, and 7153 kg/hm²) while O0A2 treatment was recorded the lowest root yield (6065, and 6278 kg/hm²). Compared with O2A1 treatment, O1A1 increased AIV content by 5.1%−7.2% and C7G content by 5.3%−13.5%.

Conclusions Both organic fertilizer and alginic acid application showed obvious effect on increasing the stress resistance, root yield and the medicinal composition contents of A. mongholicus, due to the enhanced photosynthetic efficiencies and antioxidant enzyme activities. Satisfactory synergetic effect on yield and quality but low heavy metal content can be obtained at combination rate of organic fertilizer 1200 kg/hm² with 1.0 g/L of alginic acid to produce A. mongholicus in saline-alkali land.