Abstract
The moisture-conserving effect of straw mulch-based no-tillage (SMNT) is expected to increase fertile spikes and grain yield in environments with rainfall less than 200 mm. However, the mechanisms underlying the positive effect of SMNT on wheat tillering are not fully elucidated. A split-plot experiment was designed to investigate the combined effects of SMNT and cultivars on tillering of dryland wheat grown under both dry and favorable climates. Application of SMNT to a cultivar with 1–2 tillers exploited both tillering and kernel-number plasticity, increasing the mean grain yield by 20.5%. This increase was attributed primarily to an increased first-tiller emergence rate resulting from increased N uptake, leaf N content, and N remobilization from tillers to their grain. The second and third tillers, as transient sinks, contributed to the tiller survival rate, which depends on tiller leaf number. The increased total N uptake by SMNT also increased the dry mass yield of tillers and the C:N ratio, reducing the asymmetric competition between main stem and tillers. Owing to these beneficial effects, reduced mitogen-activated protein kinase (MAPK) and abscisic acid signals were observed under SMNT, whereas indole-3-acetic acid (IAA) signals and genes involved in DNA replication and mismatch repair were increased. These signals activated three critical transcription factors (the calmodulin-binding transcription activator, GRAS domain, and cysteine-2/histidine-2 family) and further increased rapid drought response and tiller maintenance after stem extension. Phenylpropanoid biosynthesis, sphingolipid biosynthesis, and galactose metabolism were most relevant to increased tillering under SMNT because of their critical role in drought response and lignin biosynthesis. Our results suggest that straw mulch-based no-tillage activates rapid drought response and improved wheat tillering by coordinating root N uptake, N remobilization, and asymmetric competition between main stem and tillers.
