TITLE:
Responses of bioenergy sorghum cell wall metabolism to agronomic practices
AUTHORS:
Jason P. Wight, Frank M. Hons, Godson O. Osuji
KEYWORDS:
Peroxidase Enzymology; Free Solution Isoelectric Focusing; Lignin and Cellulose; Biochemical Mechanism of Crop Rotation
JOURNAL NAME:
Advances in Biological Chemistry,
Vol.4 No.1,
February
27,
2014
ABSTRACT: Maximum
lignocellulose yield of biomass sorghum [Sorghum
bicolor L. (Moench.)] is hampered by complex biological phenomena related
to rotation, nitrogen (N) fertilization, soil tillage, and excessive biomass
removal. The biochemical basis of the effects of agronomic practices on sorghum
production was studied by the enzymology of the active peroxidase (EC
1.11.1.7) isoenzymes that synthesize lignin. All studied practices altered the
peroxidase pI values. Control sorghum without rotation and without N
fertilization had the most inhibited peroxidase with very low maximum
velocity (Vmax) value (3.10 mmol·min﹣1), and very low lignin (857 kg·ha﹣1)
yield, which could decrease soil organic carbon possibly leading to adverse
changes in soil chemistry. Corn-sorghum rotations with and without N
fertilization increased the Vmax values of peroxidase and lignin and cellulose
yields. Rotated sorghum subjected to 50% residue return (the percentage of crop
residue was returned to the plot immediately after grinding at harvest) and 280
kg·ha﹣1 N fertilization possessed very active peroxidase (Vmax
value 66.4 mmole·min﹣1) and the highest lignin (1387 kg·ha﹣1)
yield. The 25% residue return rate without N fertilization induced high lignin
(1125 kg·ha﹣1) and cellulose (11,961 kg·ha﹣1) but the 25%
residue return rate with 280 kg·ha﹣1 N fertilization induced lower
lignin (1046 kg·ha﹣1) yield. Continuously cropped sorghum treated
with 336 kg·N·ha﹣1 produced active peroxidase that shared
competitive inhibition relationship with the peroxidase of the 84 kg·N·ha﹣1 treatment. Ridge tillage combined with 280 kg·ha﹣1 N fertilization
under continuous sorghum resulted in inhibited peroxidase possessing low Vmax
value (13.0 μmole·min﹣1). Changing to conventional tillage combined
with 280 kg·ha﹣1 N fertilization relieved the inhibition and
increased the Vmax value to 23.7 mmol·min﹣1. These biological
anomalies of sorghum cell wall related to agronomic practices originated
from doubly inhibited sorghum peroxidases. This understanding may guide the
choice of sustainable agronomic practices for maximizing lignocellulose
yields for the bioenergy industry while protecting the environment.