Table 5.

Predictive power for the determination of water mass per area (WMA), relative water content (RWC), and leaf water potential (Ψ_leaf), from terahertz spectroscopy, including the root mean square error (RMSE), the R ², and the normalized RMSE (NRMSE), for individual leaves of each species (with minimum, mean [bold type], and maximum values reported), and using species‐specific relationships, and the all‐species relationship (Table 4; Figure 8)

Species code	Variable	RMSE (min‐mean‐max)	R 2 (min‐mean‐max)	NRMSE (min‐mean‐max)
Individual leaf‐level prediction
Arabidopsis thaliana	WMA	8.43–28.0–48.2	0.80–0.89–0.99	0.347–0.0942–0.123
	RWC	0.0254–0.0597–0.0981	0.80–0.89–0.99	0.0344–0.0940–0.123
	Ψleaf	0.0223–0.200–0.371	0.49–0.76–0.92	0.0762–0.130–0.235
Hedera canariensis	WMA	1.55–7.57–15.0	0.80–0.80–0.80	0.0199–0.104–0.193
	RWC	0.00670–0.0284–0.0553	0.80–0.80–0.80	0.0199–0.101–0.185
	Ψleaf	0.174–0.256–0.339	0.70–0.70–0.70	0.0665–0.112–0.170
Platanus racemosa	WMA	1.67–4.71–11.4	0.80–0.80–0.80	0.0410–0.0828–0.173
	RWC	0.0122–0.0246–0.0398	0.80–0.80–0.80	0.0411–0.0829–0.173
	Ψleaf	0.0680–0.170–0.225	0.70–0.70–0.70	0.0305–0.115–0.176
Species‐level prediction
Arabidopsis thaliana	WMA	58.7	0.74	0.136
	RWC	0.184	0.44	0.218
	Ψleaf	0.487	0.42	0.209
Hedera canariensis	WMA	28.9	0.32	0.182
	RWC	0.0935	0.45	0.164
	Ψleaf	0.703	0.57	0.202
Platanus racemosa	WMA	29.8	0.56	0.151
	RWC	0.0841	0.58	0.159
	Ψleaf	0.425	0.29	0.175
All‐species‐level prediction
All species	WMA	61.6	0.37	0.138
All species	RWC	0.151	0.56	0.159
All species	Ψleaf	0.700	0.42	0.201