Effects of soil compaction and light on growth of Quercus pyrenaica Willd. (Fagaceae) seedlings

Soil compaction and light availability influence plant growth via different mechanisms. In general, soil compaction has a direct effect on roots, whereas light affects leaves and stems. Although plants in nature are exposed to variable levels of soil compaction and light, no study on the potential mutual interactions of these limiting factors in woody plants has to the authors' knowledge been reported to date. The aim of this work was therefore to elucidate the effects of soil compaction and light availability on growth and biomass allocation in the deciduous oak Quercus pyrenaica. To this end, a study was conducted at two light levels (viz. 3% and 100% of incident light, designated as low-light and high-light, respectively) under a wide range of soil compaction (0.02-3 MPa as penetration resistance) in a greenhouse. Total biomass was found to be positively affected by both light and soil compaction. There was marginally significant interaction between the effects of the two factors on total biomass, which was positively affected by soil compaction only under high-light conditions. Soil compaction had a strong, negative effect on the length of the main root; thus, at maximum soil compaction, such a length was roughly one-half that observed at lower compaction levels. Also, the specific root length of main root (root length to root mass ratio) was reduced by roughly one-half in highly compacted soils. These results suggest that an unfavourable combination of soil compaction and light availability may have severely adverse effects on woody plant performance in drought periods since plants with short roots can hardly access water at deep soil levels. The strength of this effect may be modulated by light availability