Effects of root pruning on competitive ability and water use efficiency in winter wheat

This study was conducted to assess the effect of root system size and vertical distribution on competitive ability and water use efficiency (WUE) by root pruning at the stem elongation stage. The field experiments were carried out from 2004 to 2005 and 2005 to 2006 in the Loess Plateau regions, China. Root pruning succeeded in reducing root dry weight in the upper soil (0–20 cm soil layer), resulting in diminished total root weight in root pruned wheat (p < 0.05). Root pruning restrained stomatal conductance and transpiration of wheat at the stem elongation stage. However, both stomatal conductance and transpiration in root pruned plants were higher than those in control plants at the anthesis and grain filling stages. Root pruned wheat plants had a higher photosynthetic and lower root respiration rate than wheat plants in the control plot at the anthesis and grain filling stages, which resulted in a higher proportion of photosynthate being allocated to the shoots and an increased harvest index. Competitive ability was investigated using de Wit replacement series. There were no significant differences in shoot dry weight and grain yield between root pruned and control plots, but the root pruned wheat was less productive and had a lower relative yield compared with the control in the mixture field. The relative spike number of root pruned wheat decreased significantly in the mixture plots. Root pruned wheat had significantly higher dry mass per stem than control in the monoculture plot. In the mixture plot, the dry mass per stem of root pruned wheat tended to decrease with increase in plant density of the control wheat. The differences between root pruned and control wheat plants mentioned above showed that the competitive ability of root pruned wheat was lower than that of control wheat in mixture plots. It is an important result in this study that root pruning lowered water consumption significantly and improved the WUE of winter wheat. In conclusion, the current study showed that root pruning improved the WUE of winter wheat significantly by lowering the root biomass in the upper soil layer, which further demonstrated the speculation from different wheat cultivars that breeding of wheat varieties has unknowingly increased WUE and harvest index by reducing the root system size in the upper soil layer.