ARS | Publication request: Does hydraulic lift or nighttime transpiration facilitate nitrogen acquistion?

Submitted to: Plant and Soil Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 30, 2008
Publication Date: February 21, 2008
Citation: Snyder, K.A., James, J.J., Richards, J.H., Donovan, L.A. 2008. Does hydraulic lift or nighttime transpiration facilitate nitrogen acquistion?. Plant and Soil Journal. 306:159-166.

Interpretive Summary: This study investigates whether hydraulic lift by plants increases a plant's ability to capture nitrogen from the soil. We used greasewood (Sarcobatus vermiculatus) in Mono Lake, CA for this study. Hydraulic redistribution is the observed phenomenon where, at night when plant stomata are less open, plants passively redistribution water through their root system in response to differences in soil water availability near the plant's root zone, which become the driving gradient for water movement. Hydraulic lift is the specific case where water from deep wetter layers is redistributed to shallow soil layers. Since the bulk of soil nutrients are concentrated near the soil surface, it has been proposed that this behavior may facilitate nutrient uptake. We found no evidence to support this hypothesis for nitrogen uptake. The range of hydraulic lift we studied had no effect on nitrogen uptake. However, we did find that plants that transpired at night, relative to plants where we artificially suppressed nighttime transpiration had increased nitrogen uptake. Indicated that nighttime transpiration my facilitate nitrogen capture.

Technical Abstract: It has been proposed that plant species that hydraulically lift water to dry shallow soil layers should have improved nutrient relations. Yet, this idea has not been adequately tested. We choose ten Sarcobatus vermiculatus plants with different magnitudes of hydraulic lift to examine the hypothesis that the magnitude of lift will be positively related to the amount of nitrogen (N) uptake. A 15N tracer was injected in the 20-30 cm soil layer to determine plant 15N capture by shallow roots that exhibited hydraulic lift. Half of the plants were also placed in large humidified tents (i.e. ¿bagged¿) to suppress nighttime transpiration in an effort to increase hydraulic lift. All plants showed uptake of the 15N tracer, but contrary to our hypothesis the magnitude of hydraulic lift had no significant effect on the rate of N capture or the total amount of N captured over a 9 day period. Plants that were not bagged appeared to have greater 15N capture. The observed trend indicates that nighttime transpirational water loss may improve nutrient status.