Minisymposium 1: Nutrient Biology

Abs # 11001: Root architecture effects 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, Jonthan 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

A common response to low phosphorus availability is increased biomass allocation to roots, which presumably enhances phosphorus acquisition. At the same time, an increased root:shoot ratio results in decreased growth rates due to a reduction in the carbon allocation to photosynthetic tissue. Common bean plants grown in low P utilize a larger fraction of net carbon assimilation for root respiration than plants grown in high P. P-efficient bean genotypes, which tend to exhibit more root shallowness, have lower rates of whole root respiration. As a result P-efficient genotypes are able to maintain a greater root biomass allocation without increasing overall root carbon costs, supporting the notion that root carbon costs are a primary limitation to plant growth in low P soils. The objective of this study was to examine the importance of root architecture for determining whole root system carbon costs, particularly in low P environments. Our hypothesis was that genotypic differences in specific root architecture traits account for the observed differences in whole root respiration rates between P-efficient and P-inefficient bean genotypes. Plants were grown in an Al-P buffered nutrient solution system at high P and low P in the greenhouse. Growth, maintenance and ion uptake respiration rates of individual root types (adventitious, basal, tap and lateral roots of each) were determined at weekly intervals for four weeks after transplanting. Plants were also harvested for shoot and root biomass and for P analysis. Growth respiration was determined from elemental analysis, maintenance respiration was determined using a Clark oxygen electrode, and ion uptake respiration was estimated from total plant N and biomass accumulation over time. P availability and root architecture had significant effects on whole root carbon allocation. Low P resulted in an increase in respiration costs for almost all root types of both genotypes. The respiration costs of root types most important for phosphorus acquisition, specifically adventitious and lateral roots, were almost always lower for the P-efficient genotype than for the P-inefficient genotype. As a result, the P-efficient genotype was able to maintain a larger root system that is more effective at phosphorus acquisition under low P.