Carbon, nitrogen, and hydrogen isotope ratios in creekside trees in western Kansas

Three species of creekside trees were monitored weekly during the 2007 and 2008 growing seasons. The 2007 growing season was wet early, but became drier as the season progressed. In contrast, the 2008 growing season was dry early, but became wetter as the season progressed. Creekside trees were measured to determine effects of changing water regimes on leaf-level processes. Lonicera tatarica plants were compared to Morus alba and Celtis occidentalis trees. Leaves were monitored for changes in stomatal conductance, transpiration, δ13C, δ15N, δD, leaf temperature, and heat losses via latent, sensible, and radiative pathways. δD of creek water was more similar to ground water than to rain water, but the creek was partially influenced by summer rains. δD of bulk leaf material was significantly higher in individuals of C. occidentalis compared to the other species, consistent with source water coming from shallower soil layers. Despite decreasing water levels, none of these tree species showed signs of water stress. There were no significant differences between species in stomatal conductance or transpiration. Leaf δ13C was significantly lower in individuals of L. tatarica compared to the other species. Differences in δ13C were attributed to a lower carboxylation capacity, consistent with lower leaf nitrogen content in L. tatarica plants. Leaf δ15N was significantly lower in individuals of L. tatarica compared to the other species, consistent with uptake of a different N source. Two of the three sites appeared to be affected by inorganic N from fertilizer run-off. Evidence is presented that these species acquired water and nitrogen from different sources, resulting from differences in root uptake patterns.

Research highlights▶ Leaf δD was higher in C. occidentalis, consistent with water uptake from shallower soil. ▶ There were no differences between species in stomatal conductance or transpiration. ▶ Leaf δ13C was lower in L. tatarica, consistent with lower leaf nitrogen content. ▶ Leaf δ15N was lower in L. tatarica plants, consistent with a different N source. ▶ Water and nitrogen uptake differences resulted from differences in root uptake.