Soil Compaction Affects Root Growth and Gene Expression of Major N-Assimilating Enzymes in Wheat

A strong soil is averse to root growth and development, affecting the soil–plant-water-nutrient dynamics. The purpose of this study is to know the primary effect of compaction on roots and subsequently the gene expressions of the major N-assimilating enzymes in the plant, which may differ and act as an indicator of soil compaction. To test the hypothesis, a pot experiment was conducted with three soil compaction levels: no (bulk density: BD ~ 1.4 Mg m−3), moderate (BD ~ 1.6 Mg m−3), and high (BD ~ 1.8 Mg m−3) compaction; two nitrogen doses: @150 kg N ha−1 (+ N) and no N application (− N); and two wheat genotypes: Choti Lerma (low N-responsive) and HD-2967 (high N-responsive). Wheat was grown for 7 weeks in pots in a phytotron. Compaction severely restricted root growth, while genotype and N-doses had no effect. Higher compaction reduced root length density (RLD) of Choti Lerma by 25–41%. In the HD-2967 genotype, compaction had no impact on RLD with + N but reduced with − N (13–25%; p < 0.05). N application reduced the adverse effect of high compaction on root volume density (RVD) in Choti Lerma compared to 28% (p < 0.05) reduction without N. Gene expression of N-assimilating enzymes varied in two contrasting genotypes. Under N-limiting (− N) condition, gene expressions related to N assimilation increased in HD-2967 with higher soil compaction, whereas after upregulation to moderate compaction, gene expression was downregulated in Choti Lerma. With adequate N supply, gene expressions were regulated in HD-2967, indicating greater N-response by the genotype even at higher soil compaction. Genotype role was found to be greater in adjusting compaction and N-stress. Soil compaction has a role in transferring the signal for regulation of gene expression, especially concerning N assimilation, and opens an arena of research.