The role of plant traits and their plasticity in determining community and ecosystem responses to alteration in nutrient availability

Background/Question/Methods

Plant traits likely play a large role in determining individual- and community-level responses to altered nutrient availability. Variation in an individual’s traits may be more important in the initial stages of nutrient addition experiments, while variation between species may be important during and after species reordering or immigration. Here we examined whether (a) species’ functional traits respond plastically to chronic nutrient alteration; (b) chronic nutrient additions alter community aggregated trait values; and (c) traits of species which are known to increase in abundance with nutrient additions differ from those of species which dominate under unaltered conditions. Nine functional traits (senesced, green, and emerging leaf numbers; height; total mass; leaf toughness; specific leaf area; leaf dry matter content; leaf thickness) were measured for fourteen plant species across the broad precipitation gradient of the North American Great Plains. Traits were measured after four years of chronic nutrient additions within a nutrient addition experiment, in which nitrogen, phosphorous, and potassium were added in all combinations (10 gm^-2 each). Species were chosen to represent both those which dominate each community under unaltered conditions and those which are known to increase in abundance after many years of chronic nutrient additions at each site. 

Results/Conclusions

In general, the species examined did not exhibit high levels of functional trait plasticity between control plots and plots with nutrients added. However, traits related to growth did vary significantly with nutrient additions for several species. Additionally, nutrient additions did not appear to influence any community aggregated trait values. The lack of response of community aggregated traits to nutrient additions was likely due to the limited variation of most species’ traits to nutrient additions and the absence of species reordering or immigration in these relatively short-term nutrient additions. Finally, we conducted a series of pair-wise comparisons to determine whether traits of species known to increase in abundance with nutrient additions differ from species which dominate under unaltered conditions at each site. Across all sites, species which dominated under altered conditions had shorter stature, lower leaf toughness, and greater SLA than species which dominate under ambient conditions. These traits could favor rapid invasion of nutrient rich sites and help maintain high densities under altered environmental conditions. Ultimately, species shifts with chronic nutrient additions will likely have major consequences for important ecosystem processes such as production, nutrient cycling, and resistance to herbivore outbreaks as a result of altered species functional trait values.