Growth and Nitrogen Uptake by Agropyron desertorum and Pseudoroegneria spicata when Exposed to Nitrate Pulses of Different Duration

Abstract

Plant growth and nitrate uptake were measured for two Great Basin perennial grasses, Agropyron desertorum and Pseudoroegneria spicata, in sand-filled pots in either monoculture or mixed culture (2 plants/pot). All plants were supplied with the same initial amount of nitrate but delivered in five different pulse durations ranging from 0.5 to 72 h. The pulse duration was controlled by flushing the pots with water at different times after applying the nitrate pulse. The same concentration of nitrate was used in all pulse treatments. Increasing the pulse duration led to significantly increased plant biomass production for both species in both mono- and mixed cultures, and to reduced root/shoot biomass ratio. Biomass and root/shoot ratio were greater for Agropyron in mixed culture than in monoculture. To assess root nitrate uptake capacity, a 30-min tracer pulse was applied to all plants. Plants that had been exposed to longer pulses acquired significantly more nitrate than those that had been exposed to shorter pulses for both total plant acquisition and acquisition per unit root length. With greater root/shoot ratio than Pseudoroegneria, total nitrate acquisition by Agropyron was significantly greater at most pulse durations. Root nitrate uptake per unit mass was also greater for Agropyron than for Pseudoroegneria, indicating that Agropyron is more responsive to nitrate pulsing.