d. Rhlzosphere oxidation. Some hydrophytic species (e.g. Nyssa 



; ~ aquatica, Myvica gale) are capable of transferring gaseous oxy- 



' gen from the root system Into soil pores immediately surrounding 



the roots. This adaptation prevents root deterioration and 

 maintains the rates of water and nutrient absorption under 

 anaerobic soil conditions. 



e. Ability for root growth in low oxygen tensions. Some species 

 -' (e.g. Ty-pha angusti folia, Juncus effusus) have the ability to 



maintain root growth under soil oxygen concentrations as low as 

 0.5 percent. Although prolonged (>1 year) exposure to soil 

 oxygen concentrations lower than 0.5 percent generally results 

 in the death of most individuals, this adaptation enables some 

 species to survive extended periods of anaerobic soil 

 conditions . 



f. Absence of alcohol dehydrogenase (ADH) activity. ADH is an 



~ enzyme associated with increased ethanol production. When the 

 enzyme is not functioning, ethanol production does not increase 

 significantly. Some hydrophytic species (e.g. Potenttlla 

 anserina. Polygonum amphibium) show only slight increases in ADH 

 activity under anaerobic soil conditions. Therefore, ethanol 

 production occurs at a slower rate in species that have low 

 concentrations of ADH. 



Reproductive adaptations 



5. Some plant species have reproductive features that enable them to 

 ^) become established and grow in saturated soil conditions. The following have 



been identified in the technical literature as reproductive adaptations that 



occur in hydrophytic species: 



a Prolong ed seed viability. Some plant species produce seeds that 

 -■ may remain viable for 20 years or more. Exposure of these seeds 

 to atmospheric oxygen usually triggers germination. Thus, 

 species (e.g., Taxodium distiahum) that grow in very wet areas 

 may produce seeds that germinate only during infrequent periods 

 when the soil is dewatered. NOTE: Many upland specves also 

 have prolonged seed viability, but the trigger mechamsm for 

 germination is not exposure to atmospherzc oxygen. 



some 



Seed germination under low oxygen concen trations. Seeds of 

 hydrophytic species germinate when submerged. This enables 

 germination during periods of early-spring inundation, which may 

 provide resulting seedlings a competitive advantage over species 

 whose seeds germinate only when exposed to atmospheric oxygen. 

 Fl ood-tolerant seedlings. Seedlings of some hydrophytic species 

 (e.g. Fraxinus pennsylvanioa) can survive moderate periods of 

 total or partial inundation. Seedlings of these species have a 

 competitive advantage over seedlings of flood-intolerant 

 species. 



)^ 



C7 



