Remobilized old‐leaf nitrogen predominates for spring growth in two temperate grasses

Abstract

Summary The importance of N derived from internal remobilization and root uptake to growth in spring is reported here for the perennial grasses Festuca rubra and Agrostis capillaris derived from seminatural grasslands in Scotland, UK. Plants grown in sand culture, received 15N‐enriched nutrient solution during the first year of growth and nutrient solution with N at natural abundance during the subsequent spring and summer when destructive harvests were taken. Labelled N was recovered in new growth of overwintering tillers and new tillers. Remobilized N contributed 70% and 82% for F. rubra and A. capillaris, respectively, to the total N in new above‐ground growth in early spring, declining to 34% and 45%, respectively, by mid June. Species showed similar patterns of remobilization on a new growth biomass basis. The root system did not remobilize N to support new above‐ground growth. Labelled N was derived from senescing leaves present on overwintering tillers. Net balances of labelled N suggest that N was translocated between tillers; reproductive tillers acted as sinks, vegetative tillers as the source of N. Initial growth in spring is largely independent of N uptake from the soil, provided that overwintering leaves are present on the plants.