Translocation of Nutrients in N-limited, Non-Nodulated Pea Plants

Abstract

Pea ( Pisum sativum L., cv. Marma) was grown in solution culture with nitrate-N added to initially N-starved seedlings at relative rates (RA) of 0.06 and 0.12 day -1 . The relative growth rates (RGR; dry matter) of whole plants closely matched RA over the harvest interval, 25 to 29 days after sowing. Relative increment rates of C, N, K, P, Sand Ca matched RGR in root tissue, whereas relative increment rates of K, P, S and Ca appeared to be less correlated to RGR in shoots. Xylem sap was collected from cut stems (2cm above the root-shoot transition), either when exuding freely or when applying pressure to the root system. Estimates of translocation of N, C, K, P, and S were based on their abundance in xylem sap relative to Ca and on their tissue increment rates. The N gain in shoots was 13 and 36% of the N translocated to the shoot in the RA 0.06 and 0.12d -1 cultures, respectively, and data for K, P, and S generally fell within this range. These data indicate substantial cycling of N, as well as K, P, and S, when the external N source is growth-limiting. Shoot and root growth in plants growing under long-term N limitation appears uncorrelated to the flux of N per se to these organs.