PARENT SESSION
Oral Session # 45: Plant Ecology III: Plant - Water Relations I.
Presiding: R Giuliani
Wednesday, August 6. 8:00 AM to 11:30 AM, SITCC Meeting Room 200.
Seasonal nitrogen capture among coexisting desert plants is differentially affected by water and phosphorous availability.
James, Jeremy*,1, Richards, James1, 1 University of California Davis, Davis, California
ABSTRACT- In deserts water and nitrogen limit productivity and are mainly available to plants in brief pulses following rainfall. Consequently, the ability to rapidly increase N capture through morphological and physiological adjustments determines, in part, survival and competitive ability. While such responses are well-described, little is known about how the seasonal timing and magnitude of N pulses affect plant N acquisition or the extent limitations of other resources may alter plant response to an N pulse. We applied pulses of 15N labeled K15NO3 at two rates (low, 28 mg N m-2 or high, 5 g N m-2) three times during the growing season (Early, Mid, or Late Spring) to the three dominant species at our cold desert study site (two C3 shrubs, Sarcobatus vermiculatus and Chrysothamnus nauseosus and a C4 grass Distichlis spicata). We also manipulated soil water and phosphorous availability concurrently with these N pulses to determine if plant N capture during a pulse is affected by the availability of these resources. We quantified plant 15N capture, and soil and microbial N pools for each of the three pulse periods. All species increased N capture at higher rates of N addition. Relative to controls, the shrubs did not increase N capture following water addition during any pulse period but N capture in Distichlis increased 1.6 and 7-fold during the mid and late spring pulses. Chrysothamnus N capture increased 3-fold following P addition in the late spring pulse but did not increase N capture in the other species. These results suggest that N capture is not only significantly influenced by both the magnitude and timing of the N pulse but depends on the availability of other soil resources. Moreover, these results demonstrate that the ability these coexisting species to capture N may be differentially affected by soil water and P availability.
Key words: Desert, Nitrogen , Pulses