University of Arizona Tucson, Arizona, United States
Background/Question/Methods
Elevated soil nitrogen (N) resulting from pollution, fertilizer, and woody encroachment in grasslands enhances invasion pressures from weedy plant species. Sawdust, sucrose, and other labile carbon (C) sources can be used as a soil amendment to combat the growth of exotic invasive plants by immobilizing soil N. However, studies that investigate how to optimize the impact of C addition for weed control have differed widely across previous research.
We first conducted a systematic review of 83 publications to ascertain the gaps in experimental methods and guide future studies. Using hierarchical mixed-effects meta-analytic models, we then synthesized 655 responses from native plants and 486 responses from exotic plants from a total of 47 publications to quantify the overall effect of C addition. We explored possible explanations for variation in effect, such as differing study conditions and how C was applied.
Results/Conclusions
Overall, C addition significantly decreased exotic plant abundance, but did not significantly affect native plant abundance. A C application rate of at least 210 g C m-2 y-1 decreased exotic plant abundance, but a rate of 2110-3000 g C m-2 y-1 was required to significantly increase native plant abundance. Carbon addition was most effective in the western USA and southeastern Australia, and when used to suppress exotic grasses (annual or perennial) and annual forbs. Furthermore, both sawdust and sucrose applied alone solicited a significant decrease in exotic plant abundance. However, this decrease was no longer significant after one year. The majority of papers (63%) did not include any cost information.
When there is a nearby and inexpensive source of C available, C addition can be used to control invasive exotic grasses and annual forbs in semiarid and arid regions of North America and Australia. In contrast to other weed control measures, especially herbicide, C addition does not significantly harm native perennial plants. Future studies should implement longer-term monitoring, establish larger plots, and include cost analysis to improve guidance for land managers.
