Cramer, MD , Verboom, GA , Hoffmann, V .
Nutrient availability regulates transpiration in Ehrharta calycina.
Transpiration driven mass-flow of water in soil facilitates movement of some nutrients to the root surface. Transpiration rate may thus be regulated by plant nutrient status. Seeds of Ehrharta calycina from ten sites across a rainfall gradient were collected and cultivated for 2 months in sand, after which some received slow-release fertilizer embedded in the rhizosphere (“interception”) while others received the same amount of nutrients from a point source screened with 2 Âµm mesh and not directly accessible to the roots (“mass-flow”). “Mass-flow” plants had on average lower (F=146.49; P<0.01) dry weights (2.60Â±0.22 g) than “interception” plants (6.08Â±0.39 g). The “mass-flow” plants thus experienced nutrient deprivation, as demonstrated by the lower tissue N contents. However, transpiration rates were higher (F=16.31; P<0.01) in “mass-flow” (10.01Â±0.48 mmol m-2 s-1) than in “interception” plants (6.25Â±0.15 mmol m-2 s-1). The transpiration rates were negatively correlated with the N content of the plants. The Î´15N value of the “mass-flow” plant tissue was less than that of the N source (slow release fertilizer, Î´15N=0.43), possibly as a consequence of isotope fractionation during mass-flow of nutrients to the root surface. The concentrations of N, P, K, Ca, Mg, Na, Mn, Fe, Cu, Zn and B in the leaf tissue were correlated with the concentrations of those nutrients in the fertilizer. “Mass-flow” plants had 1.6-fold higher transpiration rates and 1.4-fold higher tissue Ca, Na, Mn, Cu, and Zn than “interception” plants. Chemical speciation analysis showed that fertilizer Mg, Fe and P would be partially precipitated. Thus transpiration may partially determine uptake of soluble cations. Tissue N and K concentrations were similar between “mass-flow” and “interception” treatments. We concluded that transpiration rate was partially regulated by N availability and that mass-flow was increased when N was less available.
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1 - University of Cape Town, Botany, Private Bag X1, Rondebosch, Cape Town, 7701, South Africa
2 - University of Cape Town, Zoology, Private Bag X1, Rondebosch, Cape Town, 7701, South Africa
Presentation Type: Oral Paper:Papers for Topics
Location: Stevens 1/Hilton
Date: Tuesday, July 10th, 2007
Time: 9:15 AM