Production and nitrogen cycling in an ecosystem of Eragrostis curvula in semiarid Argentina. II. Nitrogen content and transfers

摘要

The major components of the nitrogen cycle were studied in an ecosystem of Eragwslis curvula (Schrad.) Nees, an extensively utilized forage grass in semiarid Argentina. We constructed an annual nitrogen budget for this ecosystem including data on plant, soil and atmosphere nitrogen concentration and pools, and estimates of nitrogen transfers between compartments. Most of the nitrogen in the plant-soil system was in the soil (annual average = 6400 kg ha"1 up to 1 m depth) since only 3.4% were in the plant at the time of maximum aboveground plant biomass. Roots of E. curvula contained most (> 83%) of the total plant nitrogen during the observation period. They appeared to be in a steady state since their annual nitrogen uptake (215.80 kg ha-1) was balanced by nitrogen looses through mortality (191.69 kg ha- yr1) and decomposition (223.51 kg ha-1 yr1). Root decomposition returned 95.5% of the total annual nitrogen input to the soil (231.54 kg ha-1). Annual circulation of nitrogen through the vegetation was a very small fraction (3.4%) of the total nitrogen content in the plant-soil system (annual average = 6536 kg ha"1). Nitrogen partitioning and transfers within this system are discussed in detail.