Effects of experimental warming on stomatal traits in leaves of maize (Zea may L.)

Abstract

We examined the warming effects on the stomatal frequency, stomatal aperture size and shape, and their spatial distribution pattern of maize (Zea may L.) leaves using a light microscope, an electron scanning microscope, and geostatistic techniques. A field manipulative experiment was conducted to elevate canopy temperature by 2.08°C, on average. We found that experimental warming had little effect on stomatal density, but significantly increased stomatal index due to the reduction in the number of epidermal cells under the warming treatment. Warming also significantly decreased stomatal aperture length and increased stomatal aperture width. As a result, warming significantly increased the average stomatal aperture area and stomatal aperture circumference. In addition, warming dramatically changed the stomatal spatial distribution pattern with a substantial increase in the average nearest neighbor distance between stomata on both adaxial and abaxial surfaces. The spatial distribution pattern of stomata was scale dependent with regular patterns at small scales and random patterns at larger scales on both leaf surfaces. Warming caused the stomatal distribution to become more regular on both leaf surfaces with smaller L(t) values (Ripley's K-function, L(t) is an expectation of zero for any value of t) in the warming plots than the control plots.

Keywords: Elevated temperature; Ripley's K-function; maize (Zea may L.); spatial distribution pattern; stomatal aperture size and shape; stomatal frequency.

Figure 1

Scanning electron micrographs (SEM) showed the characteristics of stomata and epidermal cells at the middle section of maize leaves grown in ambient (A–C) and elevated temperature (D–F). Note that shorter and wider stomatal pores were observed on both the adaxial surface (B) and abaxial surface (C) of maize leaves grown at elevated temperature than those of their counterparts (E and F) grown at ambient temperature. In addition, elevated temperature also increased the width of epidermal cells. Bars, 10 μm (A and D) and 40 μm (B, C, E, and F).

Figure 2

Point pattern analyses of stomata on the adaxial surface in leaf 1, leaf 2, and leaf 3 of maize plants grown at ambient temperature (A–C) and in leaf 1, leaf 2, and leaf 3 of maize plants grown at elevated temperature (D–F), respectively. The dotted lines give a 95% confidence envelope for complete spatial randomness. The data were given for three leaves from three ambient or warmed plots.

Figure 3

Point pattern analyses of stomata on the abaxial surface in leaf 1, leaf 2, and leaf 3 of maize plants grown at ambient temperature (A–C) and in leaf 1, leaf 2, and leaf 3 of maize plants grown at elevated temperature (D–F), respectively. The dotted lines give a 95% confidence envelope for complete spatial randomness. The data were given for three leaves from three ambient or warmed plots.

Figure 4

Stomatal conductance (A) and transpiration rate (B) of maize leaves grown under ambient temperature or elevated temperature. The data given are means ± standard deviation for five leaves from three ambient or warmed plots. Note that experimental warming significantly increased stomatal conductance (Gs) and transpiration rate (Tr) 163% and 81%, respectively.