Biochar effects on phenotypic characteristics of wild and sickle Medicago truncatula genotypes

Pyrogenic biochar materials are being considered as a soil amendment in multiple contexts around the world. However, there is limited knowledge about the interaction of biochar with root and nodule development in legumes. A greenhouse study was conducted to evaluate the effect of biochars of differing sources on two Medicago truncatula (clover) genotypes wild (w) and sickle (skl) (an ethylene insensitive mutant). Biochars of two biomass feedstocks (corn stover and switchgrass) and two pyrolytic processes (slow and fast pyrolysis) were used to evaluate the two genotypes for plant growth, root nodulation, and root morphology. Biochar treatments at a 1 % (10 g kg(-1) soil) application rate increased nodule formation and plant biomass across all genotypes. Corn stover fast pyrolysis biochar induced a higher degree of nodulation. Fast pyrolysis process biochars resulted in greater shoot dry weight for both genotypes compared to control. Shoot dry weight was less in plants treated with corn stover slow pyrolysis biochar compared to other biochars. Biochar stimulated nodule formation in both w and skl genotypes compared to controls. Biochar increased root length of higher and lower order lateral roots (0-1 mm and 1-2 mm diameter). There was a significant genotype x biochar treatment interaction for root length in the 1-2 mm diameter root class. Overall a positive effect of biochar was observed on plant growth, root nodulation, and root morphology of two Medicago truncatula genotypes. Biochars of different biomass feedstock and pyrolytic processes resulted in differences in root morphology and plant growth. The increase in nodule numbers resulting from biochar additions appears to be independent of the mechanism causing the increase in nodule numbers in the skl mutant. Differences in genotype response to biochar highlight the need to consider plant genetic composition as well as biochar type when evaluating potential for crop response to biochar soil amendments.