(1) What is the relationship between stomatal responses and the rate of photosynthesis? The COa flux density and stomatal conductance are closely correlated, but there is not a simple causal link between them. This relationship is complex, and depends on both parallel but independent responses to light of stomata and photosynthesis, and indirect response of stomata mediated by photosynthesis. This indirect response occurs through CO2 depletion in the air spaces of the mesophyll and stomatal response to CO2- No evidence was found in favour of the proposed effect of photosynthesis on stomata through an unknown messenger. (2) What is the nature of the interaction between stomatal responses to humidity and temperature? The hypothesis that these responses are brought about by a single response to relative humidity at the leaf surface was tested, and shown to be incompatible with the responses of Hedera helix. It is suggested that the most appropriate variable for expressing humidity is, in this context, the water vapour deficit at the leaf surface. (3) What is the role of the boundary layer in the control of stomatal opening? Real world and simulation experiments were used to show that responses to bulk air vapour and COa mol fractions are both dependent on stomatal responses to CO2 and humidity. It is also shown that a feedforward response to humidity requires feedback through another variable for stability under natural conditions. Response to wind speed is due to changes in humidity and CO2 mol fraction at the leaf surface. (4) Are our current knowledge, and the resulting models, good enough for predicting short-term stomatal responses to changes in the environment? The need for a careful analysis of simulation models is stressed. Ball's empirical model of stomatal conductance was analysed. The original interpretation was found to be flawed, and a new one was proposed. The new interpretation views the model as a description of the relationship between COj flux rate and stomatal conductance, rather than of stomatal conductance alone. It is shown that this model is useful for describing the behaviour of the intercellular COj concentration. The model, was tested against data from the experiments. It was found that the responses to temperature and humidity are not treated in a satisfactory way. The response of the model to other variables is realistic. A modification to the model is described and tested. It is concluded that the model is a good starting point for the development of simulation models to be used as submodels in canopy and regional models.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:640561 |
| Date | January 1991 |
| Creators | Aphalo, Pedro Jose |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/14758 |
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