Table 1.

Summary of the investigated 15 traits in this study.

Classification	Trait	Abbreviations	Units	Trait measurements
RM-related traits	Primary root length	PRL	cm	Measured with a ruler
	Total root length	TRL	cm	Analyzed by WinRHIZO
	Total root surface area	TSA	cm2	Analyzed by WinRHIZO
	Total root volume	TRV	cm3	Analyzed by WinRHIZO
	Total root number	TRN	number	Analyzed by WinRHIZO
	Root dry weight	RDW	g	Dried and weighted using a balance (1/1,000 g)
	Root-shoot ratio in dry weight	RSRD	g/g	RDW/SDW
NUE-related traits	Shoot dry weight	SDW	g	Dried and weighted using a balance (1/100 g)
	Total dry weight	TDW	g	RDW + SDW
	Shoot N concentration	SNC	mg/g	Smartchem 200 automatic analyzer
	Root N concentration	RNC	mg/g	Smartchem 200 automatic analyzer
	Shoot N uptake	SNU	mg	SNC × SDW
	Root N uptake	RNU	mg	RNC × RDW
	Total N uptake	TNU	mg	RNU + SNC
	N utilization efficiency	NUtE	g/mg	TDW/TNU