Poster: Root Biology

Abs # 534: Effects of root architecture on whole root respiration of contrasting common bean (Phaseolus vulgaris L.) genotypes in relation to phosphorus availability

Presenter:	Ho, Melissa D., mdho@psu.edu
Authors	Ho, Melissa D. (A)   Liao, Hong  (B)   Lynch, Jonathan P (C)
Affiliations:	(A): Intercollege Program in Plant Physiology, Penn State University (B): Laboratory of Plant Nutritional Genetics and Root Biology Center, South China Agricultural University (C): Department of Horticulture, Penn State University

Low phosphorus availability typically increases root biomass allocation, which presumably enhances phosphorus acquisition, but also results in decreased plant growth rates due to reduced growth of photosynthetic tissue. Low P availability increases the fraction of the daily carbon budget used in root respiration in common bean. P-efficient bean genotypes have lower rates of whole root respiration than P-inefficient genotypes. As a result P-efficient genotypes are able to maintain greater root biomass allocation without increasing overall root carbon costs. The objective of this study was to examine the importance of genotypic differences in root architecture for whole root system carbon costs, particularly in low P environments. Plants were grown in an Al-P buffered nutrient solution at high and low P. Growth, maintenance, and ion uptake respiration rates of individual root types were determined over time. Shoot and root biomass and P content were also determined. Root construction costs did not differ greatly between genotypes or among different root types, but were affected by P availability. Maintenance and ion uptake respiration rates differed significantly among root types and between the two genotypes under high and low P. Root types that had a higher specific root length (m g^-1), such as adventitious roots, had higher respiratory costs per unit dry weight, but lower respiratory costs per unit length. The respiratory costs for all root types were almost always lower for the P-efficient genotype compared with the P-inefficient genotype, particularly under low P. Thus, the P-efficient genotype was able to maintain a larger root biomass and root length under low P, even though its whole root system carbon cost was lower relative to the P-inefficient genotype.