Understanding nutrient cycling in drylands is critical for promoting productivity in arid regions that cover 41% of Earth’s terrestrial surface. In mesic systems, plants have shown preferences for taking up different forms of nitrogen, possibly contributing to niche partitioning among those species. However, the effects of N form on resource partitioning in dryland systems has rarely been investigated among non-agricultural plants. Furthermore, there is little information available on the rate at which 15N tracers move from roots to leaves, an important parameter for tracer movement studies in plant-soil systems. We compared rates of movement of labeled nitrogen from roots to leaves in three native plant species from New Mexico. We collected 15 individuals each of Bouteloua eriopoda (C4 grass), Achnatherum hymenoides (C3 grass), and Gutierrezia sarothrae (C3 forb) and grew them in the greenhouse for two months. We added 15N-isotopically enriched nitrate, ammonium (inorganic substrates), or glutamate (organic substrate) to the roots and collected leaf tissue in subsequent days to track uptake and rates of movement from roots to leaves.
Results/Conclusions
We found that within 24 hours, leaves of all species became significantly enriched compared to natural abundance values. 15N transport was highest overall in plants of B. eriopoda, which also showed the greatest differences between substrates, with nitrate showing the greatest movement. G. sarothrae plants had the lowest transport rate from roots to leaves for any substrate, which could be due to differences in growth habit, functional group or plant condition. Overall, glutamate tended to be the slowest substrate to move in all three species. These results indicate that if N is present near the roots, it’s highly likely that these plants will take up at least a fraction and transport it to the leaves within 48 hours. The data also show that these plants may have slight preferences for N form but are capable of taking up all of them, and thus there is not strong evidence of niche partitioning in these three species.