Regulated Lignin Structural Units and Soil Organic Carbon Content by Cowpea Peroxidase

Peroxidases participate in lignin biosynthesis, but there is no biochemical resolution between the structural units of lignin and soil organic carbon (SOC) contents. Black-eyed beans are staple high-protein foods for millions of at-risk populations in every continent. Its cultivation in semiarid zones could be leveraged to maximize SOC sequestration. Cowpea was treated with stoichiometric mixes of mineral nutrients. Peroxidase was electrophoretically purified from leaves, and assayed for o-dianisidine (guaiacyl units) and pyrogallol (p-hydroxyphenyl units) substrate specificities. Lignin, and SOC compositions were determined by gravimetry. Sulfate-treated cowpea produced the highest lignin (318.88 kg·ha-1) because the o-dianisidine maximum velocity (Vmax) value (0.36 µM·min-1·mg-1) was higher than that for the pyrogallol (0.08 µM·min-1·mg-1), but the SOC (64.75 kg·ha-1) was low due to the guaiacyl being higher than p-hydroxyphenyl units. Peroxidase Vmax value was low (0.12 µM·min-1·mg-1) for both substrates in the control cowpea, and accordingly lignin (268.44 kg·ha-1) and SOC (42.33 kg·ha-1) compositions were very low. The pyrogallol Vmax value (0.5 µM·min-1·mg-1) was lower than the o-dianisidine value (1.0 µM·min-1·mg-1) for KK-treated cowpea, and accordingly the lignin contents (227.4 kg·ha-1) possessed variable compositions of guaiacyl and p-hydroxyphenyl units, leading to very high SOC composition (214.56 kg·ha-1). The high SOC sequestration technology involving fertilization with stoichiometric mixes of mineral nutrients could enable limited resource farmers who cultivate cowpeas as cover crop in the Sahel to improve SOM while producing their staple crop.