Factors Controlling Denitrification in a Chihuahuan Desert Ecosystem

Denitrification may be an important pathway for N loss from desert ecosystems. Few studies, however, have investigated the factors limiting this process in a desert environment. A factorial experiment was conducted to determine the factors controlling denitrification in the northern Chihuahuan Desert. Specifically, we measured the response of denitrification to additions of water, C, N, and C + N. Soil cores were collected from four vegetation zones along an alluvial piedmont. Dry cores were subjected to five treatments: (i) water; (ii) water + NO 3 ; (iii) water + C; (iv) water + NO 3 + C; and (v) a control (no additions). When denitrification rates were averaged across vegetation zones and patch types (between or under vegetation), the following treatment effects were significantly different: water + NO 3 + C > > > water + NO 3 = water » water + C > control. These results indicate that denitrification at this site is limited by the availability of water. In wet soil cores, C additions immobilized available NO 3 and suppressed denitrification. When water + NO 3 + C was added (C/N = 22), however, denitrification was significantly greater than when water + NO 3 were added. This result indicates that C and N interact to control denitrification in wet desert soils. No evidence for an overall NO 3 limitation in moist cores was found. Surprisingly, denitrification rates in wet cores of nutrient‐poor desert soils (≈32.9 ng N cm −2 h −1 ) were similar to those measured in the nutrient‐rich soils of temperate and tropical forests. When extrapolated to an annual rate, denitrification for this site is 7.22 kg N ha −1 yr −1 . Extreme drying‐wetting cycles common in desert ecosystems may account for the high rates observed.