Table 1 Results of the linear mixed models (LMM)

	Variable	Air pollution	Emitter exposure	Herbivory phase	Air pollution x Emitter exposure	Air Pollution x Herbivory phase	Emitter exposure x Herbivory phase
	Bark damage area	NS	F = 11.62 p = 0.002**	NA	NS	NA
Photosynthetic traits	A_N	F = 3.387 p = 0.031*	F = 4.326 p = 0.046*	F = 3.343 p = 0.066†	NS	F = 2.180 p = 0.094†	NS
Photosynthetic traits	G_S	F = 3.202 p = 0.037*	NS	NS	NS	F = 2.317 p = 0.079†	NS
VOC emission rate	MT	F = 2.653 p = 0.066†	NS	F = 17.932 p < 0.001***	NS	NS	NS
	oMT	F = 3.007 p = 0.046*	NS	F = 27.565 p < 0.001***	NS	F = 5.846 p < 0.001***	NS
	SQT	NS	NS	F = 4.066 p = 0.046*	NS	F = 3.864 p = 0.011*	NS
	GLV	F = 5.541 p = 0.001**	NS	NS	NS	NS	NS
	BZ	F = 8.969 p < 0.001***	NS	NS	NS	F = 2.675 p = 0.051†	NS
	ONI	F = 14.971 p < 0.001***	NS	NS	NS	NS	NS
	TOTAL	F = 3.864 p = 0.019*	NS	F = 16.928 p < 0.001***	NS	NS	NS
Damage-based VOC emission increase	MT	NS	NS	NA	NS	NA
	oMT	NS	NS		NS
	SQT	NS	NS		NS
	GLV	NS	F = 4.926 p = 0.038*		NS
	BZ	NS	NS		NS
	ONI	NS	F = 4.563 p = 0.054†		NS
	TOTAL	NS	F = 3.315 p = 0.074†		NS

The tests were performed on bark damage area, net photosynthesis rate (A_N), stomatal conductance rate (G_S), VOC emission rates and damage area-based increases in VOC emissions. Fixed factors were air pollution (O₃ enrichment, diesel exhaust enrichment, combination of O₃ and diesel exhaust enrichment as well as ambient air), emitter exposure (damaged and control), herbivory phase (phase 1 = pre-herbivory, phase 2 = post-herbivory) and their two-way interactions. p < 0.001 ***, p < 0.01 **, p < 0.05 *, p < 0.1 †. Herbivory phase did not apply to damage area and damage-based VOC emission increase. NA, data not available. NS, models not significant.
MT non-oxygenated monoterpenes, oMT oxygenated monoterpenes, SQT sesquiterpenes, GLVgreen-leaf volatiles, BZ benzenoids, ONI other non-isoprenoids.

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