Ecophysiology of Arundo donax, an invasive energy feedstock

Background/Question/Methods

In recent years there has been some controversy surrounding the sustainable development of cellulosic biofuels.  One aspect that has received ecological critique is the fact a number of the plants selected as the more promising cellulosic feedstocks are reputed invasive plants.  Although numerous Federal and international scientific organizations have commented that cultivating invasive species will likely have subsequent negative effects on native biological diversity by inadvertently facilitating the introduction and spread of invasive species, development with invasive species continues.  Some of the controversy about the ecological consequences that these novel energy crops will have is in part associated with sparse information regarding the ecological thresholds exert an invasive plants’ competitive advantage. 

Arundo donax (Arundo) is an invasive grass species that is currently being developed for biofuel in eastern Washington and Oregon.  Although Arundo has invaded riparian areas around the world, little information is available regarding the ecological and physiological factors that limit the growth of this species.  A set of experiments were conducted to elucidate the ecophysiological characteristics which would likely facilitate the success of an Arundo invasion in areas adjacent to the biofuel farms, and also how these scenarios might change in accordance with climate change. In the present study, we evaluated Arundo growth and photosynthetic responses to salinity, water, light, and carbon dioxide under controlled environmental conditions.  Further, we compared Arundo’s responses to reported values of the dominant native plant community—cottonwood/willow—found in watersheds where Arundo are being cropped.

Results/Conclusions

Our results indicate that Arundo donax is highly tolerant of increased salinity; the salinity tolerance is evaluated to be at least four times greater than the native riparian species, exhibiting tolerances equal to salt cedar.  Additionally, Arundo is highly drought tolerant.  When water is available however Arundo would also have a competitive advantage, because it exhibited greater water use efficiencies per leaf area than the willow or cottonwood.  Arundo does however have greater leaf area index than the native species, consequently an Arundo stand transpires greater net quantities than the native riparian species.  The stress tolerance and greater resource use efficiency identified in our research suggest that Arundo is likely to have a significant competitive ecophysiological advantage over the dominant native plants.   Thus, by increasing propagule pressure through regional cultivation of Arundo as a biofuel feedstock the likelihood for an invasion is probable if not inevitable.