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 similar to 1.4 Mg m(-3)), moderate (BD similar to 1.6 Mg m(-3)), and high (BD similar to 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.

Automated summary

Soil compaction severely restricts root growth, while genotype and nitrogen application have less impact. Nitrogen application can mitigate the adverse effect of high compaction on root volume density. Different genotypes show varied responses to high compaction and nitrogen stress.