Fig. 5. Causal models based on d-sep analysis (Shipley, 2000). Model 1 states that soil compaction affects directly and independently different variables: root morphology and
anatomy; plant physiology and plant growth. This model was rejected (P = 0.021). The model 2 states that soil compaction affects directly root variables: root morphology and
anatomy but not plant physiology and plant growth, which is independent of the changes in root characteristics. This model was also rejected (P = 0.014). Model 3 considers
that soil compaction produces changes in root traits that have consequences on plant physiology and growth. Model 3 was accepted (P = 0.777). The numbers near the arrows
indicate the standardized path coefficients of each relationship. Dashed and red lines indicate a negative relationship; continuous and black lines indicate positive relationship.
SRL, specific root length; , leaf water potential. The colours represent different types of variables: soil compaction (brown), physiology (blue), root anatomy (light green),
root structure (red) and plant growth (black). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)