Seasonal variations in plant nitrogen relations and photosynthesis along a grassland to shrubland gradient in Owens Valley, California

Abstract

Community composition in semi-arid ecosystems has largely been explained by water availability; however, nitrogen is a common limiting nutrient, and may be an important control on plant function and carbon uptake. We investigated nitrogen relations and photosynthesis of several dominant species at shallow groundwater sites in Owens Valley, California. We measured soil nitrogen (N) availability, leaf N and isotopes, water isotopes, and gas exchange of dominant shrub species Atriplex torreyi and Ericameria nauseosa and grass species Distichlis spicata throughout the summer season in three sites that had similar watertable depths, but that varied in community composition and N availability. Surface soil inorganic N was greatest at the grassland site and declined from June to September at all sites. Leaf N declined throughout the season in all species, and was correlated with soil inorganic N. Photosynthesis of A. torreyi remained relatively constant throughout the season. In contrast, D. spicata and E. nauseosa experienced seasonal declines in photosynthesis at sites with greater inorganic N availability. Leaf N was significantly correlated with photosynthesis in D. spicata across all sites and measurement periods. Controls on N cycling are likely to be an important determinant of photosynthesis of D. spicata in this region.

Groundwater use by native plants in response to changes in precipitation in an intermountain basin

“…nauseosa, in contrast to S. vermiculatus, maintained relatively constant J p and J m throughout the study period, despite large differences in soil water availability. This pattern is consistent with research from regions where winter precipitation dominates (Donovan and Ehleringer, 1994;Ehleringer et al, 1991;Flanagan et al, 1992;Goedhart et al, 2010), indicating that this species also appears to function similarly under a wide range of precipitation regimes across the western U.S. Unlike the shrubs, D. spicata and S. airoides had highly significant J responses to natural seasonal and experimentally controlled soil water availability, suggesting that both species acquire water with roots that are concentrated in upper soil layers.…”

“…Much less is known about herbaceous phreatophyte species. However, the grass Distichlis spicata is reported to use rainrecharged soil water in greater proportions than co-occurring woody phreatophytes in an arid basin with shallow groundwater but lacking summer monsoon precipitation (Goedhart et al, 2010;Pataki et al, 2008).…”

Response of dominant grass and shrub species to water manipulation: an ecophysiological basis for shrub invasion in a Chihuahuan Desert Grassland

“…Black grama exhibited a signiWcant positive relationship between N leaf and A max , whereas mesquite did not. Goedhart et al (2010) obtained similar results, suggesting fundamental diVerences in grass versus shrub N relations. Moreover, the range of variation in mesquite N leaf was narrower than that in black grama, and the highest levels of grass N leaf approximated the lowest levels of mesquite N leaf .…”

Leaf nitrogen is closely coupled to phenophases in a desert shrub ecosystem in China

“…Leaf N is strongly correlated with the rate of photosynthesis in the leaf. A shortage of leaf N may limit plant growth, as most of leaf N is invested in photosynthetic enzymes (Reich et al, 1997;Goedhart et al, 2010). SLA is also closely related to photosynthetic nitrogen use efficiency (NUE) (Schieving and Poorter, 1999).…”