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United States Department of Agriculture

Agricultural Research Service

Title: Plant N Capture in Pulse Driven Systems: Interactions Between Root Responses and Soil Processes

Authors
item James, Jeremy
item Richards, J - UNIV CAL/DAVIS

Submitted to: Journal of Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 20, 2005
Publication Date: February 24, 2006
Citation: James, J.J., Richards, J.H. 2006. Plant n capture in pulse driven systems: interactions between root responses and soil processes. Journal of Ecology. 94:765-777.

Interpretive Summary: Much research has demonstrated that soil inorganic nitrogen (N) concentration is a key factor limiting plant productivity in arid and semi-arid systems. Previous studies, however, have largely assumed soil N availability is constant in these systems. In arid ecosystems, however, N is mainly available to plants in brief pulses following precipitation events. During these events, water inputs stimulate microbial activity and breakdown of organic matter that accumulates during dry periods. In this study we investigated the major plant and soil mechanisms that influence the ability of a species to exploit N pulses through the season. 15N-labeled pulses were applied to two Atriplex species in early and mid spring. Sequential time harvests were used to quantify changes in root length, root N inflow rates, microbial biomass 15N, soil water content, and soil inorganic 15N pools. Plant N capture was greatest when pulses coincided with high root relative growth rates. Soil N supply rates did not limit plant N capture from pulses, partially due to high microbial nitrification rates and low microbial N immobilization rates. Instead, N capture was limited by N inflow rate per unit root length, which was strongly affected by plant N demand, soil water content, and total root length. Understanding how temporal variation in soil N availability interacts with plant and soil processes provides insight into mechanisms maintaining plant species diversity in arid and semi-arid systems.

Technical Abstract: Soil nitrogen (N) is often supplied in pulses in arid systems. While such temporal variation in N supply can alter plant N capture and growth, little is known about what mechanisms influence the ability of a species to exploit N pulses through the season. 15N-labeled pulses were applied to two Atriplex species in early and mid spring. Sequential time harvests were used to quantify changes in root length, root N inflow rates, microbial biomass 15N, soil water content, and soil inorganic 15N pools. Plant N capture was greatest when pulses coincided with high root relative growth rates. Path analysis suggested that soil N supply rates did not limit plant N capture from pulses, partially due to high nitrification rates and low N immobilization rates. Instead, N capture was limited by uptake capacity per unit root length, which was strongly affected by plant N demand, soil water content, and total root length. Understanding interactions between root responses, soil processes and pulse timing provides insight into mechanisms underlying competitive interactions and diversity maintenance in pulse-driven systems.

Last Modified: 9/23/2014
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