Nutrient enrichment and soil conditions drive productivity in the large-statured invasive grass Arundo donax

• Effects of abiotic factors on giant reed (Arundo donax) growth were evaluated.
• Nitrogen and organic soils had the strongest effect on biomass production.
• Nitrogen addition shifted allocation to belowground rhizomes.
• Arundo management must consider human-altered environmental conditions.

Introduction of the large-statured, invasive grass Arundo donax has negatively affected riparian ecosystems in Mediterranean-type climates and tropical regions worldwide. Control programs in large watersheds have been largely ineffective in reducing populations because of Arundo's ability to recolonize after flooding and human induced changes to resource availability that facilitates growth. In a greenhouse study, we evaluated the relative effects of nitrogen, soil type, soil moisture, and light availability on Arundo growth. All treatments significantly influenced plant growth, but nitrogen addition and soils with organic materials had the strongest positive effect on above- and belowground biomass production. Ratios of above- to belowground growth were relatively stable across soil types and moisture levels, but allocation to belowground structures was significantly increased by nitrogen addition and full sunlight. Our results imply that control and management programs should address the human-altered nutrient and soil conditions associated with agricultural and urban watersheds that may facilitate dispersal, establishment, and growth of Arundo and other invasive plants.