Elevated CO sub(2) and nutrient addition after soil N cycling and N trace gas fluxes with early season wet-up in a California annual grassland

• Published in: Biogeochemistry Vol. 37; no. 2; pp. 89 - 109
• Main Authors: Hungate, Bruce A, Lund, Christopher P, Pearson, Holly L, CHAPIN, FSTUART
• Format: Journal Article
• Language: English
• Published: 01.05.1997
• Subjects: USA, California
• ISSN: 0168-2563; 1573-515X
• DOI: 10.1023/A:1005747123463

We examined the effects of growth carbon dioxide (CO sub(2))concentration and soil nutrient availability on nitrogen (N)transformations and N trace gas fluxes in California grasslandmicrocosms during early-season wet-up, a time when rates of Ntransformation and N trace gas flux are high. After plant senescenceand summer drought, we simulated the first fall rains and examined Ncycling. Growth at elevated CO sub(2) increased root productionand root carbon:nitrogen ratio. Under nutrient enrichment, elevatedCO sub(2) increased microbial N immobilization during wet-up,leading to a 43% reduction in gross nitrification anda 55% reduction in NO emission from soil. ElevatedCO sub(2) increased microbial N immobilization at ambientnutrients, but did not alter nitrification or NO emission. ElevatedCO sub(2) did not alter soil emission of N sub(2)O ateither nutrient level. Addition of NPK fertilizer (1:1:1) stimulatedN mineralization and nitrification, leading to increased N sub(2)Oand NO emission from soil. The results of our study support a mechanisticmodel in which elevated CO sub(2) alters soil N cycling and NOemission: increased root production and increased C:N ratio in elevatedCO sub(2) stimulate N immobilization, thereby decreasingnitrification and associated NO emission when nutrients are abundant.This model is consistent with our basic understanding of how C availabilityinfluences soil N cycling and thus may apply to many terrestrial ecosystems.