Effects of soil penetration resistance on early response of Q. robur seedlings since germination.

Negative consequences of compaction may cause changes in soil characteristics and such conditions can influence negatively seedlings development. Plantlets may delay both germination and penetration of the soil surface by the radicle and the alterations in compacted soil may also affect plants rooting through variations in structural arrangement in attempt to avoid the mechanical obstacle. This work aimed to assess the early response to the soil compaction of Quercus robur seedlings during the first month and half after germination. The experiment was carried out in a nursery and the compaction was obtained by direct compression of the soil surface on the top of containers using a compression machine in laboratory. Three compaction levels were considered (low:<0.5 MPa, medium: 1 MPa, and high: 2MPa). We investigated the effect of soil compaction on morphological attributes of seedlings grown in plastic containers on above and below ground traits during the first month after germination. In particular, morphological traits of seedlings’ shoot and root system were analysed comparing the various degrees of compaction. Results showed significant differences in seedlings traits among treatments and a constraint effect of increasing levels of compaction on early seedlings growth. The effect was particularly detrimental on root system development, particularly on the development in depth (root system depth, main root length). This represents a critical factor for regeneration establishment. Our results suggest that compaction affects seedling root system growth since the first growth stages after germination, thus, it represents an additional critical factor for seedlings establishment, particularly in Mediterranean environments where the early growth is critical to overcome the dry season.