The impact of leaf anatomy and drought on foliar water uptake and whole plant rehydration
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Dix Biology Honors Thesis.pdf
Fog and low lying clouds can impact ecosystems through increases in water inputs, changes in microclimate and direct impacts on plant water cycling. The interception of cloud water by vegetation leads to an increase in precipitation inputs resulting in increases in soil moisture content. Fog also directly impacts evapotranspiration via a reduction in evaporative demand. The absorption of fog directly by leaf surfaces (i.e. foliar uptake) alters plant water relations via an increase in water storage or relaxation of the tension in the xylem. Foliar uptake may therefore be an essential water source to plants that are experiencing both extended periods of drought and periods of fog or cloud immersion. Foliar uptake capacity has been measured in a number of different species although variation in the degree of rehydration is substantial and the reason for such variation has not been investigated. To determine whether leaf anatomy affects variation in foliar uptake, I completed a comparative survey of 16 species of plants in 13 different families. I quantified foliar uptake capacity and measured cuticle thickness, mesophyll thickness, hydrenchyma thickness, and overall leaf thickness. All species demonstrated a capacity for foliar uptake. I observed a four fold variation in foliar uptake capacity between species. I found a significant negative correlation between the capacity for foliar uptake and average leaf thickness. In contrast, foliar uptake capacity was not correlated with any other anatomical measures. I then performed a greenhouse experiment with Jatropha curcas to investigate whether foliar uptake capacity is affected by exposure to drought. Heat ratio sap flow sensors, which detect reversals in the transpiration stream of plants, were placed on plants that underwent drought and well watered conditions. Following a three or five day period of drought, all plants were placed in experimental fog chambers for a 24 hour period to examine patterns of transpiration and foliar uptake. In addition, water potential and relative water content of leaves were measured before and after the fogging event. I concluded from this experiment that plants under drought stress take up more water through their leaves than well watered plants. These results indicate that changes that occur to leaf cells during drought in Jatropha curcas alter their ability to absorb fog water.
Franklin and Marshall College Archives, Undergraduate Honors Thesis 2014
- F&M Theses Collection