Relationships between root and leaf responses
Comparing response to density in root and leaf allocation, we found an attenuated decrease in root allocation by density and an intensified decrease in leaf allocation from 50 d to 70 d in infertile soil, and with better soil conditions at 50 d (Wang et al. 2017). It implied a trade-off relationship between responses of the two modules. The mass accumulation of stem is important for its elongation and leaf positioning, thus determining plant competition advantage. Therefore the increment of root mass cannot be at the cost of stem mass but of leaf mass at vegetative stage, determining the negative relationship between responses of roots and leaves.
It is reported a positive relationship exists between below- and above-ground competition under fertilized condition (Cahill 1999). Inconsistent results may be caused by different methodologies in study systems. In competition studies, competition intensity and plant response were usually estimated by referring to plant above-ground performance only, regardless of below-ground performance (Cahill 1999, Gaucherand et al. 2006). However, in plasticity studies, we often considered root, leaf and stem traits respectively, which indeed differed substantially in response to neighbors. Further evidence for the relationship between above- and below-ground competitions can be provided by relevant studies via calculating responses of both above- and below-ground modules.