Effects of soil compaction on root elongation and anatomy of different cereal plant species

Soil compaction affects pore structure and thereby plant root growth. Elongation and anatomy of seedling roots of wheat (Triticum aestivum), barley (Hordeum vulgare), rye (Secale cereale), triticale (Triticosecale Wittmack) and maize (Zea mays) grown in uncompacted bulk field (U) and compacted headland (C) Orthic Luvisol developed from loess of the same field were compared. The seedlings were grown in a growth chamber for 7 days, in cores with undisturbed silt loam taken from 5 to 10 cm depths at compacted and uncompacted sites. Transverse root sections were taken from 25 to 30 mm behind the apex following imbedding in resin. Areas of cortex and vascular cylinder in the sections were determined using the Zeiss LSM Image Examiner. Total root length was smaller in C compared with U by, approximately, 50% for barley to 79% for triticale. Anatomical responses of the roots to soil compaction were related to the general shape of roots (circular or flattened), likely induced by the shape of pores. In the circular roots of wheat, rye and maize the primary anatomical response to soil compaction were the invaginations and associated cell deformation in the cortex. This was mostly pronounced in maize, with greater inherent root diameter. However, in the flattened roots of barley and triticale deformation of root cells was observed both in the cortex and vascular cylinder with less pronounced invaginations. Depending on plant species, the area of cortex and/or vascular cylinder decreased or increased in response to soil compaction. Total cross section area of roots increased in C compared to U among the small-grain cereals, from 9.5 in wheat to 132% in rye, while no differences could be detected in maize. The results indicate that the root elongation and anatomy exhibit considerable plasticity in response to soil compaction and strength of the local environment around the roots.