Tolerance of ozone and drought in common waterhemp (Amaranthus tuberculatus)

ABSTRACT

Biological invasions in established cropping systems impact biodiversity and agricultural sustainability. Under conditions of multi-year drought and elevated tropospheric ozone (O₃), several Amaranthus species have recently become problematic weeds in California. We examined responses of common waterhemp (A. tuberculatus) to 12-h mean O₃ exposures of 4, 59, or 114 nmol O₃ mol air⁻¹, with two levels of irrigation, 33% (deficit irrigation, DI) or 100% (well-watered, WW) of field capacity. Daytime stomatal conductance (g_s) was reduced by O₃ but not by DI. Nocturnal g_s was uncommonly large but unaffected by either treatment. Plant productivity was not affected by O₃ or DI. Leaf mass per unit area and root mass per unit leaf area were reduced by O₃ but not by DI. Tolerance of this species to O₃ and deficit irrigation may increase its competitiveness with crops. High night-time water loss may reduce water availability for competing crops. The competitiveness of common waterhemp may increase, as climate change creates conditions that are adverse to major crops.

KEYWORDS:

• Air pollution
• climate change invasive species
• vegetation management
• weeds

Acknowledgments

The authors thank H-B. Vu for skilled assistance in making measurements. Mention of commercial products is for scientific information and does not constitute endorsement. The authors declare no conflict of interest.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the U.S. Department of Agriculture, Forest Service [Cooperative Agreement Order AG-04T0-P-13-0052];Harvey Scholarship [Jordan Assistantship];University of California at Riverside [Research Allocation Process].