Evidence of a plant genetic basis for maize roots impacting soil organic matter mineralization


 66.37 (61.03-71.81)0.53 (0.5-0.56) CRM, cumulative root-derived C mineralized; SOMC, cumulative soil organic matter C mineralized; SBM, shoot biomass; RBM, root biomass; RL, root length; ARD, average root diameter; SRL, specific root length; BM-RS, root-to-shoot biomass ratio. 

Table S2.

Stepwise multiple linear regression to explain soil organic matter C mineralization under combined maize genotypes (lines and hybrids) and maize lines alone. Only the variables in the model that explain a significant (P < 0.05) amount of variance or additional variance in soil organic matter C mineralization are presented. No variable could significantly explain the variance in soil organic matter C mineralization in the hybrids alone. Table S4. Genome-wide association mapping results for nine root traits in the DTMA panel of maize inbred lines. A positive or negative value indicates that the minor, or major allele, respectively, was favorable for enhanced trait performance. Bold words indicate the two candidate genes we identify with the regulation and active release of root exudates into the rhizosphere. Ice binding, homoiothermy, response to freezing, hsp binding MAF -Minor allele frequency; MLM-Mixed linear model; a The exact physical position of the SNP can be inferred from marker's name, for example, S1_82702920: chromosome 1; 82,702,920 bp; CRM, cumulative root-derived C mineralized; SOMC, cumulative soil organic matter C mineralized; SBM, shoot biomass; RBM, root biomass; Stover, total plant biomass (root and shoot biomass); RL, root length; ARD, average root diameter; SRL, specific root length; BM-RS, root-to-shoot biomass ratio. 

Table S5 .Figure S1a .

 S5S1a Figure S1a. Pearson correlation analysis of C mineralization in soil and plant traits for maize hybrids (a). SBM, shoot biomass; RBM, root biomass; Stover, total plant biomass (root and shoot biomass); RL, root length; ARD, average root diameter; SRL, specific root length; BM_RS, root-to-shoot biomass ratio; CRM, cumulative root-derived C mineralized; SOMC, cumulative soil organic matter C mineralized. Boxed squares show significant (P < 0.05) correlations. 


Figure S1b .

 S1b Figure S1b. Pearson correlation analysis of C mineralization in soil and plant traits for maize lines (b). SBM, shoot biomass; RBM, root biomass; Stover, total plant biomass (root and shoot biomass); RL, root length; ARD, average root diameter; SRL, specific root length; BM_RS, root-to-shoot biomass ratio; CRM, cumulative root-derived C mineralized; SOMC, cumulative soil organic matter C mineralized. Boxed squares show significant (P < 0.05) correlations. 


Figure S2 .

 S2 Figure S2. Distribution of 199,755 genotyping-by-sequencing markers in the maize genome (A), the colour key with marker densities indicates the number of markers within a window size of 1 Mb. Principal component analysis of the 97 genotypes (B). Principal components were calculated with TASSEL. 


Figure S3 .

 S3 Figure S3. A heatmap of the kinship matrix of the 97 DTMA maize association panel accessions calculated from 199,755 SNPs used in the GWAS suggests moderate levels of relatedness among the 97 lines. 




  


Table S1 .

 S1 Clustering of maize genotypes based on the measured phenotypes. Values are cluster means. Values in parentheses show range of variation within the cluster. Values in Bold indicates the best mean performance of lines among the clusters for specific trait. 


	Cluster	# of genotypes	SOMC (µg C g -1 soil)	CRM (µg C g -1 soil)	SBM (g)	RBM (g)	RL (m)	ARD (mm)	SRL (m g -1 root biomass)	BM-RS
	I	42	17.97 (17.68-18.72)	19.06 (14.84-21.96)	0.40 (0.34-0.51)	0.20 (0.17-0.26)	15.53 (13.39-18.03)	0.51 (0.48-0.52)	80.07 (71.91-86.93)	0.51 (0.48-0.54)
	II	24	18.08 (17.15-19.00)	21.34 (16.61-31.77)	0.42 (0.34-0.51)	0.23 (0.17-0.26)	15.80 (13.39-18.03)	0.51 (0.48-0.52)	73.14 (71.91-86.93)	0.54 (0.48-0.54)
	III	2	18.28 (18.16-18.40)	12.76 (12.19-13.32)	0.21 (0.19-0.22)	0.10 (0.09-0.11)	9.27 (8.68-9.86)	0.49 (0.48-0.5)	116.04 (111.04-121.04)	0.46 (0.45-0.47)
	IV	11	18.60 (17.71-19.14)	17.13 (15.62-19.55)	0.33 (0.29-0.38)	0.18 (0.15-0.21)	13.54 (12.09-15.47)	0.52 (0.51-0.53)	79.18 (68.54-84.95)	0.53 (0.48-0.58)
	V	16	18.90 (17.58-19.43)	16.11 (13.06-19.12)	0.30 (0.23-0.34)	0.15 (0.12-0.17)	13.05 (11.5-14.43)	0.49 (0.48-0.51)	87.07 (77.06-96.06)	0.51 (0.48-0.53)
	VI	10	18.07 (17.48-18.79)	22.18 (18.49-27.34)	0.54 (0.47-0.66)	0.29 (0.27-0.34)	16.10 (13.88-17.41)	0.53 (0.51-0.55)		

Table S3 .

 S3 Mean, variance components and least significant difference (LSD) at 5% for nine traits for maize inbred lines in the DTMA association panel. 


		Traits	Mean	σ 2 G	σ 2 e	H 2	LSD0.05 CV (%)
	Variables Lines and hybrids RL ARD CRM	Model SOMC = 25.65 -0.49xRL SOM-C 18.09 CRM 19.14 SOMC = -0.88 + 38.35xARD 1.28* 25.46** SBM 0.39 0.01* SOMC = 16.20 + 0.12xCRM RBM 0.20 0.003*	12.22 89.52 0.01 0.003	0.18 0.36 0.64 0.64	R 2 2.89 0.161 11.22 0.127 0.16 0.058 0.09	8.06 49.44 26.49 27.59	P-value <0.0001 <0.0001 0.0003	RMSE 4.770 4.865 5.055
	RL, ARD	SOMC = 8.71 -0.42xRL + 31.76xARD RL 14.94 5.063**	9.74	0.51	0.245 4.40	20.88	<0.0001	4.534
	RL, CRM	SOMC = 25.24 + 0.27xCRM -0.82xRL ARD 0.51 0.0001* 0.001	0.41	0.406 0.04	6.19	<0.0001	4.024
	ARD, CRM RL, ARD, CRM Lines RL	SOMC = -1.55 + 0.10xCRM + 35.90xARD SOMC = 14.35 + 0.25xCRM -0.75xRL + 20.47xARD SRL 78.08 161.02** 367.41 0.47 BM_RS 0.52 0.002* 0.01 0.35 SOMC = 25.74 -0.50xRL Stover 0.60 0.02** 0.02 0.65	0.168 0.439 25.91 0.15 0.172 0.25	24.31 15.20 26.02	<0.0001 <0.0001 <0.0001	4.761 3.918 4.844
	ARD	SOMC = -5.66 + 47.96xARD			0.154		<0.0001	4.898
	CRM	SOMC = 16.09 + 0.12xCRM			0.055		0.0008	5.175
	RL, ARD	SOMC = 5.25 -0.42xRL + 38.51xARD			0.266		<0.0001	4.572
	RL, CRM	SOMC = 25.30 + 0.28xCRM -0.83xRL			0.416		<0.0001	4.078
	ARD, CRM	SOMC = -7.13 + 0.11xCRM + 46.82xARD		0.201		<0.0001	4.770
	RL, ARD, CRM	SOMC = 10.17 + 0.26xCRM -0.74xRL + 28.50xARD	0.466		<0.0001	3.909
	RL, root length (m); ARD, average root diameter (mm); CRM, cumulative root-derived C mineralized (µg C g -1 soil); SOMC, cumulative soil organic
	matter C mineralized (µg C g -1 soil), RMSE, root mean squared error				

σ 2 G, Genotypic variance; σ 2 e, residual error variance; H 2 , broad sense heritability; CRM, cumulative root-derived C mineralized; SOMC, cumulative soil organic matter C mineralized; SBM, shoot biomass; RBM, root biomass; Stover, total plant biomass (root and shoot biomass); RL, root length; ARD, average root diameter; SRL, specific root length; BM_RS, root-to-shoot biomass ratio. * and ** indicate significance at P<0.05 and P<0.01, respectively.
Manje Gowda, Jill E Cairns, Lumbani Mwafulirwa, Tim J Daniell, Christian Thierfelder, Eric Paterson, Elizabeth M Baggs
Evidence of a plant genetic basis for maize roots impacting soil organic matter mineralization