Soil compaction effects on growth and root traits of tobacco depend on light, water regime and mechanical stress

Soil compaction can strongly affect plant performance as many other stress factors. In nature, many combinations of different stress factors may be found. We expect that the effects of soil compaction may be different depending of the occurrence of other stress. This has not been fully investigated; most studies have included only one stress factor together with soil compaction. In this study, we combine soil compaction with the interaction of shade, low water availability and mechanical stress. We use as a model system tobacco plants (Nicotiana tabacum), in which the effects of the combination of these factors in a greenhouse experiment were studied on their growth, biomass allocation, root morphology and anatomy. Soil compaction effects on growth and root traits depended strongly on the other factors. In unstressed conditions, plant growth increased with compaction up to 1.4 g cm−3 bulk density and then declined. However, at low water and under mechanical stress plant growth declined monotonically with compaction, while under shade, soil compaction had no effect on growth. Soil compaction reduced fine root proportion in all treatments except in shade condition, while it increased root diameter and xylem area only under mechanical stress. These results indicate that analyses of soil compaction effects on plant performance should take the levels of other stress factors into account. More generally, they illustrate the difficulty of interpreting effects of a given stress factor on plants as these effects tend to interact with presence of other stressors.