Morphological anatomical and physiological features and adaptations to environmental conditions

Water use

Leaves are arranged spirally around the stem in a dense rosette pattern (see Coppens d'Eeckenbrugge and Leal, Chapter 2, this volume). This shape and orientation channel light rains and dew to the base of the plant, making a significant contribution to the water economy of the plant (Ekern, 1965, 1968).

Large trichomes completely cover both adaxial and abaxial leaf surfaces (Fig. 5.7), and a highly cutinized upper epidermis and a multicelled hypodermis are two significant morphological and anatomical features of pineapple leaves that contribute to the plant's water economy (Krauss, 1930, 1949; see Coppens d'Eeckenbrugge and Leal, Chapter 2, this volume). There are 30-35 tri-chomes mm-2 on the abaxial leaf surface (Aubert, 1973), which cover strips of stomata located in furrows between ridges devoid of stomata (Fig. 5.7). There are relatively few stomata per unit leaf area (70-85 mm2) and the stomatal pore is small (Krauss, 1949; Bartholomew and Kadzimin, 1977).

The mature 'Smooth Cayenne' leaf cross-section can be up to 4 mm thick (Krauss, 1949), with approximately half the volume of the plant leaf occupied by a water-storage parenchyma. The balance of the leaf volume

Pineapple Leaves Sem

Fig. 5.7. Scanning electron micrographs (SEM) showing the large multicellular trichomes on the adaxial and abaxial surfaces of a 'Smooth Cayenne' pineapple leaf. Note that the trichomes are much more prominent on the abaxial surface. In the right-hand SEM, the trichomes have been removed from a section of the abaxial surface to show the rows of stomata located in furrows that parallel the longitudinal axis of the leaf. (Scanning electron micrographs of D. Bartholomew.)

Fig. 5.7. Scanning electron micrographs (SEM) showing the large multicellular trichomes on the adaxial and abaxial surfaces of a 'Smooth Cayenne' pineapple leaf. Note that the trichomes are much more prominent on the abaxial surface. In the right-hand SEM, the trichomes have been removed from a section of the abaxial surface to show the rows of stomata located in furrows that parallel the longitudinal axis of the leaf. (Scanning electron micrographs of D. Bartholomew.)

is chlorenchyma. This water-storage parenchyma functions as a reservoir of water, which is utilized during periods of drought. The depleted tissue is replenished after adequate rain (Krauss, 1949; Sanford, 1962).

As noted previously, these morphological and anatomical features result in low evapotranspiration (ET) (Ekern, 1965) and extreme tolerance to drought. Transpiration values of 1.3 mm day-1 on cloudy days and 2.7 mm day-1 on fine days, average 2.1 mm day-1, were obtained for 15-16-month-old fruiting pineapple plants (Shiroma, 1973). In a pot study in sandy soil, transpiration was maximum during the summer when temperature and solar radiation were highest (respectively about 27°C and 10-12 MJ m-2 day-1) (Shiroma, 1971); a low value of 0.4 mm day-1 was estimated during the coldest periods. Average ET values for 'Smooth Cayenne' pineapple in field experiments in Hawaii were 0.83 mm day-1 with a plant-trash mulch and 1.25 mm day-1 with plastic mulch (Ekern, 1965). For a leaf canopy formed by small plants (LAI = 4.2) during fruit development, daily maximum ET was 1.3 mm on cloudy days (irradiance = 10.7 MJ m-2) and 2.7 mm on a sunny day (irradiance = 16.6 MJ m-2), with an average of 2.1 mm day-1 (Shiroma, 1973). Measurements of ET made in Côte d'Ivoire (N'Guessan, 1985) showed that values decreased from 0.25 mm h-1 over a 10 h period 5-6 months after planting to 0.11 mm h-1 per 10 h period 7-10 months after planting. However, ET in Côte d'Ivoire can reach 4.5 mm day-1 when solar radiation is high (Combres and Perrier, 1976). With irrigation, ET averaged 3.0 mm day-1 over a 2-month period (Combres, 1979).

Drought

Despite the high resistance of pineapple to drought, effects of drought on plant morphology and growth are important. In a dry season, the width of young leaves, the rate of leaf emergence and the weight of successive 'D' leaves may be reduced (Py, 1965). In Hawaii, leaf elongation decreased when the soil moisture content declined below 30-35% (Ekern, 1964). During the dry season in Côte d'lvoire, water content was less and specific leaf area (SLA) (g m-2, fresh weight basis) was greater in unirrigated than in irrigated crops (E. Malezieux, unpublished results). The symptoms of drought develop slowly, the earliest being reduced growth and wilting of the older leaves (Swete Kelly and Bartholomew, 1993). With severe and prolonged drought, leaf colour changes from dark to pale green, then to pale yellow and finally to red. At the later stages, leaf margins curl downward, leaves lose their turgid-ity and become limp and growth stops (Py et al., 1987; Swete Kelly and Bartholomew, 1993).

The effects of drought are reversible and, when water again becomes available, the leaves rehydrate and normal growth resumes. Leaves not yet fully expanded resume their growth. Leaf width rapidly increases, resulting in a constriction at the point where elongation resumed (Py et al., 1987). Such leaves generally develop spines on the margins at the point where growth was restricted. Symptoms of water stress may appear more rapidly where soil waterholding capacity is low, if rooting depth is restricted or if the root system has been damaged by pests or disease (Swete Kelly and Bartholomew, 1993).

Temperature

Leaf and plant temperatures of this relatively non-transpiring crop reach values that are detrimental, perhaps even lethal, to meso-phytic crops. The temperature of horizontal leaves of 6-month-old 'Smooth Cayenne' plants reached 48°C between 1 and 3 p.m. in Hawaii (Aubert and Bartholomew, 1973). The difference between the leaf middle and base reached 18°C and the maximum difference between leaf and air temperatures was 18.6°C at 1 p.m. Such extreme leaf temperatures caused no permanent harm, but their specific effects on physiological processes have not been studied. As discussed previously, the effects of temperature on stomatal conductance are significant.

The effect of temperature on growth is quite complicated. The morphology of 'Smooth Cayenne' plants is markedly affected by temperature. Optimum nutrition in environments having a controlled night temperature greater than about 25°C and in warm, humid, low-altitude climates near the equator produces plants with numerous, wide, flaccid leaves (Fig. 5.8; Py et al., 1987; Bartholomew and Malezieux, 1994). Conversely, in controlled environments with cool night temperatures (Friend, 1981) and in cooler climates, leaves are erect, straight, rigid, shorter and fewer in number (Fig. 5.8; Py et al., 1987; Bartholomew and Malezieux, 1994). In Hawaii, leaves of plants grown in high, cool elevations are shorter and more rigid than those on plants grown at lower elevations.

Indices such as SLA (leaf area per unit of leaf dry mass, m2 kg-1) and leaf area ratio (LAR) (leaf area per unit of total plant dry mass, m2 kg-1) allow the effects of temperature on plant morphology to be quantified and extend our ability to predict the effects of environment on vegetative growth.

Whole-vegetative-plant SLAs over time were consistently lower for plants grown at night temperatures of 18, 22 and 26°C than for those grown at 30°C (Fig. 5.9). The lowest SLA was about 3.8 m2 kg-1 dry weight at a day/night temperature of 22/18°C (Bartholomew, 1982). SLA declines gradually as plant mass and age increase (Fig. 5.9), especially at the cooler night temperatures, so comparisons of SLA between plants in different environments must be made using plants having approximately the same mass.

Growth slows when night temperatures are cool, and a lower SLA at such temperatures will further reduce the rate of increase in LAI and prolong the time required to reach full canopy closure and complete interception of available light. Thus, the rate of leaf area expansion will probably decrease more rapidly as night temperature decreases than would be predicted just on the basis of the effects of temperature on leaf elongation. Mitigating this effect of cool temperature, at

Bartholomew And Malezieux
Fig. 5.8. Effects of warm (30°C) and cool (22°C) night temperatures on the leaf orientation of 'Smooth Cayenne' pineapple. The plants were grown for 5 months at the indicated temperatures. (Photo of D. Bartholomew.)

Fig. 5.9. Effects of day and night temperature (°C) on the specific leaf area (SLA) (m2 kg-1 dry weight) of the green leaf tissue of 'Smooth Cayenne' pineapple grown in controlled environments. Pineapple crowns were started in a 26/22°C day/night temperature environment and transferred to the various temperatures 100 days after planting. Notice the gradual decrease in SLA with increasing time after planting. At a given harvest date, larger plants generally had a lower SLA than did smaller plants. Plants harvested after 400 or more days had produced fruit at night temperatures of 18 and 22°C while plants at warmer night temperatures remained vegetative. Data points are means of total green leaf area (white and pale green basal tissue removed) and dry weight for two plants. (Redrawn from Bartholomew and Malezieux, 1994.)

-♦- 22/18 ❖ -A— 30/18 -O- 34/18 22/22 -tr- 26/22 -O- 30/26 30/30 34/30

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Days after treatment

least to some degree, is the fact that plants growing in cooler environments have a higher net assimilation rate, which would offset to some degree the benefit imparted by a more rapid rate of leaf expansion that would occur in warm environments. Thus, dry-matter gain by plants in cooler environments may be as high as that which occurs in warmer environments, where leaves expand more rapidly. Unfortunately, simultaneous changes in other climatic factors as temperature changes, possible differences in the growth rate of 'Smooth Cayenne' clones and differences in quality of management make it very difficult to compare productivity across environments having different temperature regimes.

Consistent with the effect of temperature on SLA, LAR values for the 'Smooth Cayenne' clone 'Champaka F-153' also generally increased with increasing night temperature (Fig. 5.10) and decreased with increasing plant age. An increase in LAR was also observed for plants grown in the field as elevation decreased and average temperature increased (Fleisch, 1988). The SLA and LAR, both on a dry-mass basis, were related to average air temperature (T) by the equations:

where SLA is expressed in cm2 g-1 and T in °C. The relatively low R2 values for equations (4) and (5) are assumed to be due, at least in part, to the decrease in SLA and LAR with increasing plant mass and age.

In contrast to many crops (Biscoe and Gallagher, 1977) and regardless of the air temperature, the leaves of the pineapple mother plant persist at least into the first ratoon in Hawaii, a period of more than 24 months. However, the functionality of pineapple leaves of various ages has not been adequately determined.

Both the 'Smooth Cayenne' pineapple leaf and stem are important storage organs and can accumulate large quantities of starch.

22/18 34/18 26/22 -0- 30/22 -O- 30/26 30/30 34/30

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Days after treatment

Fig. 5.10. Effects of day and night temperature (°C) on the leaf area ratio (m2 of leaf kg-1 dry weight of plant) of 'Smooth Cayenne' pineapple grown in controlled environments. Pineapple crowns were started in a 26/22°C day/night temperature environment and transferred to the various temperatures 100 days after planting. Data are means for two plants. (Redrawn from Bartholomew and Malezieux, 1994.)

The stem of a crown at the time of fruit maturation can contain more than 20% starch on a dry basis. Stem fresh weight increases slowly during the first months after planting and during this time, starch and dry matter content initially decline and remain at about 10-12% for several to many months - about 9-11 months in Hawaii (Pineapple Research Institute of Hawaii, personal communication). In Hawaii, dry-matter content and stem starch then begin to increase and stem dry-matter content can reach 30% (Fig. 5.11) and starch can exceed 60%, dry basis, at the time of flower induction (Bartholomew and Paull, 1986). At a plant population density of 4.3 plants m-2, at 458 days after planting when flowering was forced, stem starch accumulation reached about 325 g m-2 of ground area (Pineapple Research Institute of Hawaii, personal communication). About 90 days later, starch mass per unit of ground area exceeded 800 g m-2. In environments warmer than Hawaii, there may be no increase in stem dry-matter content until vegetative growth is interrupted by forced induction. Data for controlled conditions showed that, at night temperatures of 26 or

30°C, plants had lower dry-matter content and little starch in the stem, while plants grown at night temperatures of 18 and 22°C had significant amounts of starch (Bartholomew and Paull, 1986). Plant dry-matter and starch content are believed to be especially important after floral induction (see Bartholomew et al., Chapter 8, this volume).

While stem starch levels at the time of floral induction can be as high as 60% in Hawaii, starch levels do not reach 20% at the time of forcing in Côte d'Ivoire, where temperatures are higher. Forcing occurs much sooner after planting in Côte d'Ivoire than in Hawaii, because suckers are the primary source of planting material and vegetative growth is more rapid in the warm environment. Because the LAR increases as night or average temperature or both increase, large differences exist between statistical models of vegetative growth developed in Hawaii (Fleisch, 1988; Zhang, 1992) and in Côte d'Ivoire (Malézieux, 1991).

Leaf dry-matter content also gradually increases with time during vegetative and early reproductive growth (Fig. 5.11) and,

Leaf Dry Matter Content Over Time

Fig. 5.11. Dry-matter content of 'Smooth Cayenne' pineapple stem (SDM) and leaves (LDM) from 3 months after planting in December 1 932 until after plant-crop fruit harvest in July 1934. The arrows indicate the approximate time of natural induction of flowering and of fruit harvest. (Redrawn from King, 1935.)

Fig. 5.11. Dry-matter content of 'Smooth Cayenne' pineapple stem (SDM) and leaves (LDM) from 3 months after planting in December 1 932 until after plant-crop fruit harvest in July 1934. The arrows indicate the approximate time of natural induction of flowering and of fruit harvest. (Redrawn from King, 1935.)

though such changes are relatively small, when total storage per unit of land area is computed, the accumulation is significant. In an unpublished study conducted in Hawaii (Pineapple Research Institute of Hawaii, personal communication), the starch content of leaves sampled early in the morning averaged about 0.25% for the first 400 days after planting. Starch then gradually increased to 1.27% at 570 days after planting (120 days after forcing). At that time, plants had accumulated an average of 254 g m-2, land-area basis, of starch in leaves. Both stem and leaf starch declined sharply after floral induction, presumably as reserves were drawn upon to support fruit and sucker growth. In tropical environments, little starch is accumulated in plant tissues by the time of forcing, so growth of fruit and propagules such as suckers, is dependent on current photosynthesis. In these environments, propagule development is delayed until after the fruit is harvested.

Changes in plant dry-matter content and partitioning with changing root temperature at ambient air temperature were similar to the effects of temperature observed in controlled environments. Leaf dry-matter content decreased from 16.5 to 12% as the root temperature increased from 15 to 30°C

(Ravoof, 1973). Also, as root temperature increased, the percentage of dry matter allocated to leaves increased from 77 to 80%, while that allocated to stem decreased from 17 to 13% (Ravoof, 1973). Plant LAR probably increased as root temperature increased.

Light interception

The spectral properties of the adaxial surface of pineapple leaves over the wavelength range from 520 to 750 nm were not significantly different from those of wheat, olive, orange and peach (N'Guessan, 1985). However, pineapple leaves have very low reflectances in the infrared region with minima at 1440 and 1990 nm (water peaks). Despite reflectances in the visible range comparable to those of mesophytes, much of the radiant energy falling on a pineapple plant is entrapped by multiple reflections within the rosette leaf array (Ekern, 1965). As a consequence, the total reflectance of the canopy is low (Ekern, 1965), resulting in canopy albedos that ranged from 0.14 to 0.16 for canopies ranging in age from 1 to 16 months (Shiroma, 1973; Combres, 1983). There was no significant variation in albedo with canopy height (N'Guessan, 1986).

Estimated canopy light extinction coefficients for pineapple are typical of canopies with a relatively erect leaf orientation. Extinction coefficients (k) of 0.56-0.59 were calculated for 'Smooth Cayenne' pineapple in Hawaii (Fleisch, 1988; Zhang, 1992), resulting in 95% light interception at an LAI of about 5.0. Extinction coefficients for meso-phytic crops typically range from 0.4 for erectophile canopies to 0.8 or greater for planophile ones (Russell et al., 1989). A significantly lower k of 0.29 was found for pineapple in Côte d'Ivoire by measuring total radiation interception of pineapple crops with a somewhat wider row spacing (Malézieux, 1991). Low k values account in part for the ability of pineapple to sustain very high LAIs.

Photoperiod and irradiance

The data on the effects of photoperiod and irradiance are sparse and few useful generalizations can be made from them. Also, changes in these parameters in natural environments are often confounded with temperature. At low light, seedling leaf lengths decreased as the PPF increased from 100 to 325 ^mol m-2 s-1 (Aromose, 1989). Average leaf length was greater in 16 than in 8 or 24 h photoperiods (Aromose, 1989). At an average PPF of 400 ^mol m-2 s-1, the length of the longest leaf of plants grown for 692 days in controlled conditions increased as pho-toperiod increased from 6 to 10 h, was unchanged at 12 h and declined sharply at 16 h (Friend and Lydon, 1979). The width of the longest leaf increased continuously with increasing photoperiod while leaf thickness (g cm-2, fresh weight basis) declined (Friend and Lydon, 1979).

In natural environments, leaves of plants grown in low irradiance are long, erect and dark green, while those of plants grown in very high irradiance become red or even yellow (Py et al., 1987). Physical damage and death, typically referred to as sunburn, due to high irradiance was reported in India (Srivastava and Singh, 1971). Connelly (1969) found that average 'D'-leaf length was 52 cm in full sun, 55 cm in 25% shade and 50 cm in 50% shade.

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Responses

  • Tom
    What is adaptation featire of pineapple?
    3 years ago
  • sonja
    What is the storage organ for pineapple?
    2 years ago

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