Physiological ecology of Salix nigra in disturbed riparian environments

The strategies and mechanisms involved in growth and physiological responses of Salix nigra Marshall to environmental stresses were studied in field, laboratory and greenhouse studies. A large-scale restoration project was conducted on an eroded streambank at Little Topashaw Creek, MS, using S. nigra cuttings. Moisture availability (deficit, excess) in the sediment, as mediated by sediment texture and depth to the prevailing water table was a major factor governing survival. Higher survival rates were found in cuttings at low elevation plots with intermediate soil texture. Cuttings that had been soaked in water prior to planting had higher rates of survival compared to unsoaked cuttings. The effects of high oxygen content in a soaking treatment included early growth advantages in roots and shoots of cuttings in a greenhouse study. This was the first study that addressed this question in the published literature. Project managers at restoration sites, who are trying to promote the rapid establishment of willow cuttings on the streambank, can use highly oxygenated water for soaking to increase the probability of survival. The resprouting response of S. nigra following shoot removal was investigated in two greenhouse studies. Partial shoot removal resulted in a rapid recovery of photosynthetic surface area. Osmotic adjustment was reported in roots and shoots as a mechanism to reduce negative effects from soil moisture stress. Both drought and periodic flooded treatments exhibited higher total ethanol soluble carbohydrates (TESC) in roots and shoots compared to a well-watered control. S. nigra exhibited greater sensitivity to drought compared to periodic flooded treatment. Combined stresses of shoot removal and soil moisture stress indicated a greater chance of plant injury than either stress alone. Mobilization of NSC reserves for shoot growth, with a concurrent reduction in root biomass was found in response to both shade and shoot removal treatments. NSC reserves were not completely mobilized in response to shoot removal. The presented findings increase our understanding of the physiological and growth strategies utilized by a wetland plant that is well adapted for survival in highly disturbed environments.