Full Answer
Why do plants have more stomata on the lower surface?
If the stomata are present on the plant’s lower surface, they will be less exposed to the sun and more protected from the breeze. Transpiration is the loss of water through stomata, hence the lower surface has more stomata to prevent excessive water loss.
Why do lily pads have more stomata?
The lower surface of leaf has more number of stomata because if upper surface have more amount of stomata then more water will get lost due to transpiration as the upper surface is exposed to sunlight but lower surface do not get this much sunlight so more stomata is found there. Where are the stomata located on a lily pad?
What plants have stomata?
Stomata are present in the sporophyte generation of all land plant groups except liverworts. In vascular plants the number, size and distribution of stomata varies widely. Dicotyledons usually have more stomata on the lower surface of the leaves than the upper surface.
How does gas exchange rate affect plant stomata?
Overall, this indicates that leaves built for higher rates of gas exchange have smaller stomata and faster dynamic characteristics. With the aid of a stomatal control model, it is demonstrated that higher gop can potentially expose plants to larger tissue water potential gradients, and that faster stomatal response times can help offset this risk.
What determines the stomatal conductance of a plant?
Under favourable conditions of low evaporative demand and high light, the upper limit of the CO 2 assimilation rate is determined by the maximum operating stomatal conductance, gop (assuming the biochemical limitations to CO 2 assimilation rate are fixed). Under severe water deficits resulting from high evaporative demand and/or dry soil, plants rely upon full stomatal closure and a highly water-impermeable leaf cuticle to minimize water loss ( Hinckley et al ., 1980; McDowell et al ., 2008 ). Across plant taxa there is a wide range of operating and minimum stomatal conductances ( Jones, 1992; Schulze et al ., 1994; Körner, 1995 ). However, it is not known if maximum and minimum stomatal conductance typically scale with one another.
What is the operating conductance of a stomata?
The operating conductance gop is constrained by the maximum stomatal conductance, gmax, which in turn is determined by two physical attributes of stomata: (i) their size ( S) and (ii) their density ( D ), or number per unit area. A distinction is made between gmax and gop because gmax relates to stomata opened to their widest possible apertures (e.g. under 100% relative humidity and low ambient CO 2 concentration), whereas under typical operating conditions (<100% relative humidity and normal ambient CO 2 concentration) stomatal apertures will be less than fully open. It has been shown that across broad geological time scales and evolutionary lineages, higher gmax and gop are associated with smaller stomatal size and higher density, and that S is negatively correlated with D ( Hetherington and Woodward, 2003; Franks and Beerling, 2009 ). This relationship has also been found to apply within a single species across environmental gradients ( Franks et al ., 2009 ), and also across a group of six tree species of different genera ( Aasama et al ., 2001 ). Smaller stomata, due to their greater membrane surface area to volume ratio, may have faster response times compared with larger stomata, and this in combination with high stomatal density may allow the leaf to attain high gop rapidly under favourable conditions, and to reduce conductance rapidly when conditions are unfavourable. In such a system, the rate of stomatal response would be positively correlated with gop and negatively correlated with stomatal size. However, to date, these functional relationships have not been confirmed.
What does GMIN stand for in a leaf?
gmin (dawn), prior to morning light exposure; gop, at full stomatal opening under ideal conditions; gmin (day), following closure in response to leaf darkening at midday; gmin (abs), after leaf excision.
How does GOP affect stomatal response?
The correlation between gop and (d g /d t) max is consistent with selection for a stomatal control mechanism that minimizes exposure to excessive water potential gradients. With increasing gop, the plant is more exposed to potentially damaging water potential gradients arising from sudden changes in evaporation potential. Faster stomatal closure in response to these changes will reduce the risks associated with such exposure, including formation of air embolisms in the xylem. Stomatal response to light and VPD (or transpiration rate) have similar kinetics ( Grantz and Zeiger, 1986 ), so it may be useful to compare species on the basis of them having generally ‘faster’ or ‘slower’ stomatal mechanisms. In Fig. 9 the value of faster response times for plants with higher gop is illustrated. The simulations use the data and model in Franks (2006) for plants with different gas exchange and hydraulic capacities. It is shown that, for a step increase in VPD from 1 kPa to 1.5 kPa, plants operating with higher gop at 1 kPa VPD are exposed to higher leaf water potential gradients (ΔΨ leaf) immediately after the change, and may therefore benefit from a faster rate of reduction of stomatal conductance to the new steady rate at 1.5 kPa VPD.
What is the stomatal opening phase?
5A–E ). For each species, the stomatal opening phase was accompanied by an increase in CO 2 assimilation rate ( A) to a maximum steady-state value ( Aop ), although Aop was established prior to gop ( Fig. 5F–J ).
How many guard cell pairs are there in a stomatal complex?
Stomatal morphological parameters [guard cell length L (µm) and guard cell pair width W (µm)] were measured from images obtained from planar sections as the mean of 20 stomatal complexes (guard cell pairs) for each species. Stomatal size ( S) is reported as the product of L and W (µm 2 ).
Does stomatal conductance scale with one another?
However, it is not known if maximum and minimum stomatal conductance typically scale with one another. Commonly defined as the minimum stomatal conductance in darkness, gmin for a given leaf may differ on account of the time of day or other physiological circumstances.
