Initial growth and root surface properties of dicotyledonous plants in structurally intact field soil and compacted headland soil

Abstract

The root surface physicochemical properties affect the ratio and uptake of cations by plants and are influenced by environmental threats. In this study, we examine the effect of soil compaction on the root surface properties and growth of dicotyledonous plants including Fabaceae: lupine, pea, soybean and Brassicaceae: mustard and rape. Undisturbed samples from a Haplic Luvisol derived from loess were taken in cores at 5–15 cm depth from a structurally intact area in the centre of a field (reference R) vs. repeatedly and intensively compacted headland area of the same field (compacted C). The soil dry bulk densities were 1.29 and 1.61 Mg m−3, respectively. Plants were grown in these soil cores for 11 days in a controlled environment chamber. Based on the curves of potentiometric titration, the cation exchange capacity (CEC), the total negative charge (Qtot) and the acid strength of the surface groups responsible for surface charging were determined. The apparent surface area (S) was calculated using the adsorption of water vapour method. Soil compaction resulted in a reduced fraction of strongly acidic groups (pKapp<5.5) in rape and mustard and increased in soybean and pea. The CEC of roots response to soil compaction increased in pea and soybean (by 6.1 and 22.8%, respectively) and decreased in mustard and rape (by 10.5 and 22.9%, respectively). In lupine roots, the number of the surface groups and CEC were not significantly influenced by soil compaction. The S decreased from R to C in lupine and pea (by 32.8 and 20.8%, respectively) and increased in soybean, mustard, and rape (by 10.3, 44.1, and 38.3%, respectively). Fourier-transform infrared (FTIR) spectroscopy was used to describe the chemical composition and structure of plant roots. Soil compaction caused an increase and a decrease of the pectin carboxylic groups in the Fabaceae and Brassicaceae species, respectively. The peaks of lignin and cellulose decreased mostly in the lupine grown under C. Cluster analysis grouped the obtained FTIR spectra in two clusters for the Fabaceae and Brassicaceae species with a higher heterogeneity between the roots from R and C for the former. Among the five dicotyledonous plants used in this study, the lowest relative reduction in root length was recorded for lupine with the thickest roots. Based on results of the surface physicochemical properties and root and shoot growth, incorporating lupine in crop rotation seems to be most reasonable to improve plant growth conditions in compacted headland soil.