14. The scatter plots in Fig. 4 show that the growth indices of plants generally decline with increasing TN and NH4 concentrations, significantly so for LLeaf versus both TN and NH4 in all the three layers (Fig. 4b, g), for DMLeaf with TN in the lower layer and with NH4 in the middle and lower layers (Fig. 4c, h), and for LRoot with both TN and NH4 in the middle layer (Fig. 4d, i).