Table 1.

Organic acid release from roots of Cryptomeria japonica (μmol g^–1 day^–1 _FW), Pinus thunbergii (μmol g^–1 day^–1 _FW), and Populus tremula (μmol g^–1 _DW) after exposition to Al³⁺ (according to Qin et al., 2007; Hirano et al., 2012).

Tree species	Al3+ concen-tration (μM)	Citrate	Malate	Oxalate
Cryptomeria japonica	0	0.08a	0.10a	0.14a
	100	0.39	0.14	0.49
	500	0.41	0.14	0.75
	1000	0.38	0.13	0.70
	P valueb	ns	ns	*
Pinus thunbergii	0	0.03a	0.03a	0.47
	100	0.10	0.03a	1.08
	500	0.10	0.03a	2.93
	1000	0.11	0.03a	4.04
	P value	*	ns	**
Populus tremula	0	0.0a	0.0a	0.1
	50	0.8	0.0a	4.5
	100	1.9	0.0a	3.9
	200	18.4	0.0a	5.6
	500	20.5	0.0a	25.7
	1000	20.3	0.0a	18.8
	P value	***	ns	***

^aBelow detection limit.

^bANOVA: ***P < 0.001, **P < 0.01, *P < 0.05; ns, not significant.