Changes in Crested Wheatgrass Root Exudation Caused by Flood, Drought, and Nutrient Stress

Abstract

Root exudates can chelate inorganic soil contaminants, change rhizosphere pH, and may increase degradation of organic contaminants by microbial cometabolism. Root‐zone stress may increase exudation and enhance phytoremediation. We studied the effects of low K+, high NH4+/NO3− ratio, drought, and flooding on the quantity and composition of exudates. Crested wheatgrass (Agropyron cristatum) was grown in Ottawa sand in sealed, flow‐through glass columns under axenic conditions for 70 d. Root exudates were collected and analyzed for total organic carbon (TOC) and organic acid content to compare treatment effects. Plants in the low K+ treatment exuded 60% more TOC per plant per day (p = 0.01) than the unstressed control. Drought stress increased cumulative TOC exuded per gram dry plant by 71% (p = 0.05). The flooded treatment increased TOC exuded per gram dry plant by 45%, although this was not statistically significant based on the two replicate plants in this treatment. Exudation from the high NH4+/NO3− ratio treatment was 10% less than the control. Exudation rates in this study ranged from 8 to 50% of rates in four other published studies. Gas chromatography‐mass spectrometry (GC–MS) analysis indicated that malic acid was the predominant organic acid exuded. Fumaric, malonic, succinic, and oxalic acids were also detected in the exudates of all treatments. These results demonstrate that nutrient and water stress have significant effects on the quantity and composition of root exudates. Cultural manipulations to induce stress may change the quantity of root exudates and thus increase the effectiveness of phytoremediation.

High aromatic ring-cleavage diversity in birch rhizosphere: PAH treatment-specific changes of I.E.3 group extradiol dioxygenases and 16S rRNA bacterial communities in soil

“…The pollution stress might affect the root exudate composition or even result in some form of plant-microbe interaction. Stress has been shown to affect root exudates of poplar (Populus tremula L) (Qin et al, 2007) and wheatgrass (Agropyroncristatum) (Henry et al, 2007). Bacterial products, such as lumichrome, are known to stimulate root respiration and thereby increase the availability of root exudates for bacteria (Phillips et al, 1999).…”

Stability of grassland soil C and N pools despite 25 years of an extreme climatic and disturbance regime

“…As discussed above, increases in precipitation and soil moisture often result in greater soil respiration due to increased microbial activity, potentially increasing C losses, but increased microbial activity can also increase C adsorption to clay particles, increasing C retention. Also, root exudation and turnover rates vary substantially among plant species [Grayston et al, 1997;Gill and Jackson, 2000] and in stressed versus nonstressed plants [Henry et al, 2007]. These factors may respond to environmental drivers and impact biogeochemical pools differently than root growth.…”

Microbial expression profiles in the rhizosphere of willows depend on soil contamination

“…In fact, plant biomass was not reduced in contaminated soils and leaf biomass even increased when willows were planted in contaminated soils. As suggested by Henry et al (2007), one way to improve phytoremediation would be by increasing plant stress levels through various manipulations (for example, soil nutrient and water content), in order to increase stimulation of the microbes in the rhizosphere.…”