K00 1800

Fig. 5.3 Daily course of CO2 uptake (JCO2), intercellular CO2 concentration (pco ), leaf temperature (Tl), air temperature (TA) and solar irradiance (L) for a plant of Pitcairnia integrifolia in Trinidad and photograph of a plant with the head of the porometer attached, which was used for measurements. (Lüttge et al. 1986)

uptake and rehydration as well as possible repair mechanisms may restore photosynthetic capacity.

The phenomenon of reduced gas exchange during the hottest time of the day is called midday-depression. It is very frequent among trees, shrubs and herbs in hot

Fig. 5.3 (Continued)

and arid regions (Schulze et al. 1974, 1975a,b; Tenhunen et al. 1980, 1981, 1984; Pathre et al. 1998) and also frequently observed among trees in savannas and cerrados (Sect. 10.1.2.3, Figs. 10.10-10.13). The midday-depression may be smaller or larger. Gas exchange may be totally absent during this time by full stomatal closure. Moreover, recovery in the afternoon, as shown for example in Fig. 5.3, may be expressed to different extents and with increasing drought it may not occur at all. Usually nocturnal rehydration may provide more effective recovery but this as well will be reduced as drought becomes increasingly severe.

In addition to mechanisms of stress tolerance, there are also means of stress avoidance. P. integrifolia for example may roll its leaves, exposing only the lower abaxial surface to the sun. This surface is densely covered by silvery trichomes. Bromeliad trichomes have evolved for absorption of water and nutrients (Sect. 6.4). The trichomes of P. integrifolia are non-absorbent and composed of dead cells which effectively reflect the light. Compared to white paper (100% reflectance) the reflectance of the abaxial leaf surface with scales was found to be 46.5% but only 19.8% when the scales were removed. As an alternative role of the non-absorbent bromeliad trichomes functioning as a water repellent has been discussed rather than reflection of excessive light and reduction of photoinhibition (Pierce et al. 2001).

5.2.2.2 CAM: Escape from the Dilemma Desiccation or Starvation

Choosing between limiting the effects of any one stress represents a daily "damage limitation exercise" such that plants with C3-photosynthesis face the dilemma of desiccation or starvation, when under water stressed conditions. With the midday-depression, the strategy is to try to avoid desiccation by stomatal closure at the expense of CO2-supply for photosynthesis. Desiccation is always more rapid and is the more immediate danger than starvation. One escape from this dilemma is provided by the evolution of crassulacean acid metabolism (CAM) (Box 5.1), where CO2 is fixed during the night, when water-vapour pressure saturation deficit of the atmosphere is much lower than during the day, and hence stomatal opening has a smaller effect on the water budget of the plants. The CO2 fixed is stored in chemical form of organic acids mainly as malic acid, remobilized again during the day and made available for photosynthesis, so that the plants can utilize the light energy of solar irradiance for CO2-assimilation behind closed stomata.

Fig. 5.4 Phylogenetic tree of plant families with Crassulacean acid metabolism

This mode of photosynthesis was first discovered in plants of the genus Kalan-choe (see Sect. 2.5), which belong to the family of the Crassulaceae, and hence the name. However, it has evolved independently several times, i.e. polyphyletically, since there are CAM-performing taxa on almost all branches of the phylogenetic tree of vascular plants (Fig. 5.4). Among the plants of the thornbush-succulent forests many are CAM-plants, i.e. the cacti in the new world (Figs. 3.11B and 3.13), the succulent Euphorbiaceae in the old world, the Didieraceae (Fig. 3.12) and many of the rosette plants in the Bromeliaceae (which may cover the whole floor of neotropical dry forests like the rosettes of Bromelia humilis in Fig. 3.10A), Agavaceae and Liliaceae, to name the major ones.

However, CAM may not only operate in the simple day-night fashion described above. In fact it provides an enormous range of plasticity in form and function, allowing responses to environmental conditions to be optimised (see also Sect. 2.5). The best way of describing these options is by reference to the four phases of CAM according to the nomenclature introduced by Osmond (1978; see Box 5.1). Phase I represents nocturnal stomatal opening with CO2-uptake, fixation and storage as malic acid, whereas during phase III daytime stomatal closure with CO2-remobilization and assimilation occurs. Phases II and IV are transitional phases in the early morning and in the afternoon. Phase IV often plays an important role, because when CAM plants are well watered it may be quite extensive. Then CAM plants take up CO2 directly from the atmosphere and assimilate it directly by the C3-mode of photosynthesis via RuBISCO. This can make a major contribution to their productivity.

Conversely, water stress may become so severe that even CAM plants face the dilemma of desiccation or starvation. Then, stomata may be closed even during the night, and CAM represents an option for survival by recycling CO2 internally. The CO2 evolved nocturnally during respiratory metabolism is refixed and stored as malic acid; the day-time remobilization and reassimilation, using solar radiation, recycles carbohydrate reserves for the subsequent night (Box 5.1). Under severe drought stress cacti, for instance, keep stomata closed continuously for many months (see also Sect. 8.2.3.2.1). By CO2-recycling they do not gain carbon, but very little is lost and solar energy can be used to maintain metabolism and remain competent until water is available again. At the same time, with totally closed stomata, the plants lose only a little water via cuticular transpiration. Water storage tissues in cacti and other succulents also provide reserves and help to overcome drought periods.

In a drought deciduous forest in western Mexico, Lerdau et al. (1992) studied the performance of the arborescent cactus Opuntia excelsea. In the dry season, when trees had shed their leaves, the cactus had a competitive advantage, as there was no light limitation. However, a factor associated with plant size, possibly water status, limited carbon gain during the dry season. Larger individuals were able to utilize water stored in their trunks and main branches (see also Sect. 8.2.3.2.1). Light availability in the forest understorey constrained CO2-assimilation of the cactus in the wet season.

Daytime CO2-remobilization from nocturnally stored organic acids behind closed stomata also participates in controlling photoinhibition which would be amplified

Box 5.1 Crassulacean acid metabolism (CAM)

In CAM plants there are two ways of primary CO2 fixation, namely via the enzymes phosphoenolpruvate-carboxylase (PEPC) and ribulosebisphosphate-carboxylase oxygenase (RuBISCO). In its typical performance CAM has four phases (Osmond 1978):

Nocturnal dark fixation of CO2 via PEPC generating malic acid, which is translocated into the vacuole by proton pumps (H+-ATPase and H+-pyrophosphatase - PP; ase - transporting protons) and an inward rectifying malate anion channel (transporting malate2-) at the tonoplast.

A transition phase in the early morning, after light energy becomes available, with primary CO2 fixation partially via PEPC and RuBISCO, respectively.

Efflux of non-dissociated malic acid from the vacuole, malate decarboxyla-tion and refixation of the CO2 via RuBISCO behind closed stomata.

Opening of stomata in the afternoon, when nocturnally accumulated malic acid is consumed, and primary CO2 fixation via RuBISCO.

CAM may play a role as a water-conserving mechanism at different levels of drought stress.

• In the typical performance dominating nocturnal CO2 uptake reduces tran-spirational loss of water related to CO2 acquired and thus increases water-use efficiency, because the evaporative demand on leaves with open stomata is smaller in the dark than in the light.

• At increased drought stress first phase IV and then also phase II are eliminated, and stomata remain closed for the whole light period, further restricting transpirational loss of water.

• At still more severe drought, stomata may also be partially or totally closed during the dark period. In this situation the CO2 fixed nocturnally for the accumulation of malic acid partially or totally may come from internal sources, i.e. mainly respiration (CO2 recycling). This further reduces transpirational loss of water but also limits carbon acquisition.

The scheme of CAM (►) shows the key reactions in metabolism. With PYR pyruvate; PEP phosphoenolpyruvate; OAA oxaloacetate; MAL malate; P; inorganic phosphate; [CH2 O] carbohydrate and transport across the tonoplast: with MC malate transporter; the H+-ATPase and H+-PP;ase, and passive malic acid efflux.

Net CO2 exchange by the CAM-plant Kalanchoe daigremontiana (►►) with increasing drought stress: o—o well-watered; +---+ low and •—• high drought stress. Phases I to IV are indicated. Phase II and IV CO2 exchange is expressed only in the well-watered plant; onset of phase I CO2 exchange is delayed in the severely stressed plant (Smith and Luttge 1985).

Box 5.1 (Continued)

when internal CO2-levels at high irradiance were low as in the midday depression of C3-plants (Sect. 5.2.2.1) (Osmond 1982; Adams and Osmond 1988; Griffiths 1989). In fact, internal CO2-levels (pCo2) behind closed stomata during the light period of CAM may be very high and reach up to a few percent (Cockburn et al. 1979; Kluge et al. 1981; see Lüttge 1987, 2002). However, in correlation with the internal CO2-concentrating mechanism of organic acid remobilization from the vacuoles and the

Fig. 5.5 Chlorophyll-fluorescence variables (see Box 4.6 for explanation) in Clusia minor in the C3

phase IV,-phase III).

(Haag-Kerwer 1994)

related high rates of CO2-reduction, high internal oxygen concentrations also build up, i.e. close to 40% or twice the atmospheric O2-concentration (Luttge 2002). Thus, other protective mechanisms of energy dissipation (Sects. 4.1.4 and 4.1.6) must also be active.

Experiments measuring chlorophyll fluorescence in the neotropical facultative CAM-tree Clusia minor, which can perform both CAM and C3-photosynthesis (Sect. 6.6.2.3), have shown that photoinhibition, if it occurs, is most likely to be observed during phase IV of CAM, when stomata are open and plants fix CO2 via RuBISCO rather than in phase III. Light response characteristics of chlorophyll-fluorescence variables (see Box 4.6) in phases II and IV were similar to those observed with C. minor in the C3-state and very different to those of phase III of CAM (Haag-Kerwer 1994; Fig. 5.5).

When nocturnal accumulation of malic acid occurs from recycled CO2 alone (= 100% recycling), this is an extreme case. However, stomata may only be partially closed during the night and malic acid accumulation may be due to both recycled CO2 and CO2-uptake from the atmosphere. Since the stoichiometry of CO2-fixed to malic acid formed is unity, recycling can be calculated in absolute terms as malic acid accumulated minus CO2 taken up or in relative terms (% recycling) as malic acid accumulated minus CO2 taken up 100 malic acid accumulated

The degree of recycling may then depend on the severity of drought stress. This is illustrated in Fig. 5.6 by a study of Aechmea aquilega and its higher altitude coun-

500 1000 1500 2000 2500 Annual Precipitation (mm)

Fig. 5.6 Net nocturnal CO2 uptake from the atmosphere and internal CO2 recycling of Aechmea (A. aquilega at the three lower altitudes and A. fendleri at the highest altitude) in relation to altitude and precipitation in Trinidad. (After data of Griffiths et al. 1986)

500 1000 1500 2000 2500 Annual Precipitation (mm)

Fig. 5.6 Net nocturnal CO2 uptake from the atmosphere and internal CO2 recycling of Aechmea (A. aquilega at the three lower altitudes and A. fendleri at the highest altitude) in relation to altitude and precipitation in Trinidad. (After data of Griffiths et al. 1986)

terpart Aechmea fendleri along a gradient of altitude and precipitation in Trinidad. A. aquilega grows both terrestrially and epiphytically from very dry deciduous thornbush-forests to quite wet forests, and A. fendleri is epiphytic in wet forests. Figure 5.6 shows that with increasing altitude and precipitation total CO2-uptake by the Aechmeas increased and relative CO2-recycling decreased considerably.

References

Adams WW, Osmond CB (1988) Internal CO2 supply during photosynthesis of sun and shade grown CAM plants in relation to photoinhibition. Plant Physiol 86:117-123 Affek HP, Yakir D (2002) Protection by isoprene against singlet oxygen in leaves. Plant Physiol 129:269-277

Brodribb TJ, Holbrook NM (2003) Changes in leaf hydraulic conductance during leaf shedding in seasonally dry tropical forest. New Phytol 158:295-303 Brodribb TJ, Holbrook NM (2004) Diurnal depression of leaf hydraulic conductance in a tropical tree species. Plant Cell Environ 27:820-827 Brodribb TJ, Holbrook NM (2005) Leaf physiology does not predict leaf habit; examples from tropical dry forest. Trees 19:290-295 Brodribb TJ, Holbrook NM, Gutiérrez MV (2002) Hydraulic and photosynthetic co-ordination in seasonally dry tropical forest trees. Plant Cell Environ 25:1435-1444 Brodribb TJ, Holbrook NM, Edwards EJ, Gutiérrez MV (2003) Relations between stomatal closure, leaf turgor and xylem vulnerability in eight tropical dry forest trees. Plant Cell Environ 26:443-450

Choat B, Ball MC, Luly JG, Holtum JAM (2005) Hydraulic architecture of deciduous and evergreen dry forest tree species from north-eastern Australia. Trees 19:305-311 Cockburn W, Ting IP, Sternberg LO (1979) Relationships between stomatal behaviour and the internal carbon dioxide concentrations in crassulacean acid metabolism plants. Plant Physiol 63:1029-1032

Cunningham SC (2004) Stomatal sensitivity to vapour pressure deficit of temperate and tropical evergreen rainforest trees of Australia. Trees 18:399-407 Diaz M, Granadillo E (2005) The significance of episodic rains for reproductive phenology and productivity of trees in semiarid regions of north-western Venezuela. Trees 19:336-348 Dünisch O, Montóia VR, Bauch J (2003) Dendrochronological investigations on Swietenia macro-

phylla King and Cedrela odorata L. (Melicaceae) in the central Amazon. Trees 17:244-250 Engelbrecht BMJ, Kursar TA (2003) Comparative drought-resistance of seedlings of 28 species of co-occurring tropical woody plants. Oecologia 136:383-393 Engelbrecht BMJ, Wright SJ, Steven D de (2002) Survival and ecophysiology of tree seedlings during El Niño drought in a tropical moist forest in Panama. J Trop Ecol 18:569-579 Engelbrecht BMJ, Kursar TA, Tyree MT (2005) Drought effects on seedling survival in a tropical moist forest. Trees 19:312-321 Griffiths H (1989) Carbon dioxide concentrating mechanisms and the evolution of CAM in vascular epiphytes. In: Lüttge U (ed) Vascular plants as epiphytes: evolution and ecophysiology. Ecological studies, vol 76. Springer, Berlin Heidelberg New York, pp 42-86 Griffiths H, Lüttge U, Stimmel K-H, Crook CE, Griffiths NM, Smith JAC (1986) Comparative ecophysiology of CAM and C3 bromeliads. III. Environmental influences on CO2 assimilation and transpiration. Plant Cell Environ 9:385-393 Haag-Kerwer A (1994) Photosynthetische Plastizität bei Clusia und Oedematopus. Dr. rer.-nat.-Thesis, Darmstadt)

Holbrook NM, Franco AC (2005) From wet to dry: tropical trees in relation to water availability. Trees 19:280-281

Kluge M, Böhlke C, Queiroz O (1981) Crassulacean acid metabolism (CAM) in Kalanchoe. Changes in intracellular CO2 concentration during continuous light or darkness. Planta 152:87-92

Lerdau MT, Keller M (1997) Controls on isoprene emission from trees in a subtropical dry forest.

Plant Cell Environ 20:569-578 Lerdau MT, Holbrook NM, Mooney HA, Rich PM, Whitbeck JL (1992) Seasonal patterns of acid fluctuations and resource storage in the arborescent cactus Opuntia excelsea in relation to light availability and size. Oecologia 92:166-171 Lüttge U (1987) Carbon dioxide and water demand: crassulacean acid metabolism (CAM) a versatile ecological adaptation exemplifying the need for integration in ecophysiological work. New Phytol 106:593-629 Lüttge U (2002) CO2-concentrating: consequences in crassulacean acid metabolism. J Exp Bot 53:2131-2142

Lüttge U, Klauke B, Griffiths H, Smith JAC, Stimmel K-H (1986) Comparative ecophysiology of CAM and C3 bromeliads. V. Gas exchange and leaf structure of the C3 bromeliad Pitcairnia integrifolia. Plant Cell Environ 9:411-419 Meinzer FC, Goldstein G, Holbrook NM, Jackson P, Cavellier J (1993) Stomatal and environmental control of transpiration in a lowland tropical forest tree. Plant Cell Environ 16:429-436 Meinzer FC, Andrade JL, Goldstein G, Holbrook NM, Cavelier J, Wright SJ (1999) Partitioning of soil water among canopy trees in a seasonally dry tropical forest. Oecologia 121:293-301 Murali KS, Sukumar R (1993) Leaf flushing phenology and herbivory in a tropical dry deciduous forest, southern India. Oecologia 94:114-119 Nieuwstadt MGL van, Sheil D (2005) Drought, fire and the survival in a Borneo rain forest. J Ecol 93:191-201

Osmond CB (1978) Crassulacean acid metabolism: a curiosity in context. Annu Rev Plant Physiol 29:379-414

Osmond CB (1982) Carbon cycling and stability of the photosynthetic apparatus in CAM. In: Ting IP, Gibbs M (eds) Crassulacean acid metabolism. American Society of Plant Physiologists, Rockville, pp 112-127

Parry MAJ, Andralojc PJ, Khan S, Lea PJ, Keys AJ (2002) Rubisco activity: effects of drought stress. Ann Bot 89:833-839 Pathre U, Sinha AK, Shirke PA, Sane PV (1998) Factors determining the midday depression of photosynthesis in trees under monsoon climate.Trees 12:472-481 Peñuelas J, Llusia J, Asensio D, Munné-Bosch S (2005) Linking isoprene with plant thermotoler-

ance, antioxidants and monoterpene emissions. Plant Cell Environ 28:278-286 Phillips N, Bond BJ, Ryan MG (2001) Gas exchange and hydraulic properties in the crowns of two tree species in a Panamanian moist forest. Trees 15:123-130 Pierce S, Maxwell K, Griffiths H, Winter K (2001) Hydrophobic trichome layers and epicuticular wax powders in Bromeliaceae. Am J Bot 88:1371-1389 Rascher U, Bobich EG, Lin GH, Walter A, Morris T, Naumann M, Nichol CJ, Pierce D, Bil K, Kudeyarov V, Berry JA (2004) Functional diversity of photosynthesis during drought in a model tropical rainforest - the contributions of leaf area, photosynthetic electron transport and stomatal conductance to reduction in net ecosystem carbon exchange. Plant Cell Environ 27:1239-1256

Rentería LY, Jaramillo VJ, Martínez-Yrézar A, Pérez-Jiménez A (2005) Nitrogen and phosphorus resorption in trees of a Mexican tropical dry forest. Trees 19:431-441 Schulze E-D, Lange OL, Evenari M, Kappen L, Buschbom U (1974) The role of air humidity and leaf temperature in controlling stomatal resistance of Prunus armeniaca L. under desert conditions. I. A simulation of the daily course of stomatal resistance. Oecologia 17:159-170 Schulze E-D, Lange OL, Evenari M, Kappen L, Buschbom U (1975a) The role of air humidity and leaf temperature in controlling stomatal resistance of Prunus armeniaca L. under desert conditions. III. The effect on water use efficiency. Oecologia 19:303-314 Schulze E-D, Lange OL, Kappen L, Evenari M, Buschbom U (1975b) The role of air humidity and leaf temperature in controlling stomatal resistance of Prunus armeniaca L. under desert conditions. II. The significance of leaf water status and internal carbon dioxide concentration. Oecologia 18:219-233

Sharkey TD, Yeh SS (2001) Isoprene emission from plants. Annu Rev Plant Physiol Plant Mol Biol 52:407-436

Smith JAC, Luttge U (1985) Day-night changes in leaf water relations associated with the rhythm of crassulacean acid metabolism in Kalanchoe daigremontiana. Planta 163:272-282 Sobrado MA (1993) Trade-off between water transport efficiency and leaf life-span in a tropical forest. Oecologia 96:19-23 Sobrado MA (1995) Seasonal differences in nitrogen storage in deciduous and evergreen species of a tropical dry forest. Biol Plant 37:291-295 Sobrado MA (2003) Hydraulic characteristics and leaf water use efficiency in trees from tropical montane habitats. Trees 17:400-406 Tenhunen JD, Lange OL, Braun M, Meyer A, Losch R, Pereira JS (1980) Midday stomatal closure in Arbutus unedo leaves in a natural macchia under simulated habitat conditions in an environmental chamber. Oecologia 47:365-367 Tenhunen JD, Lange OL, Braun M (1981) Midday stomatal closure in mediterranean type scle-rophylls under simulated habitat conditions in an environmental chamber. II. Effect of the complex of leaf temperature and air humidity on gas exchange of Arbutus unedo and Quercus ilex. Oecologia 50:5-11

Tenhunen JD, Lange OL, Gebel J, Beyschlag W, Weber JA (1984) Changes in photosynthetic capacity, carboxylation efficiency, and CO2-compensation point associated with midday stom-atal closure and midday depression of net CO2 exchange of leaves of Quercus suber. Planta 162:193-203

Tyree MT, Vargas G, Engelbrecht BMJ, Kursar TA (2002) Drought until death do us part: a case study of the desiccation-tolerance of a tropical moist forest seedling-tree, Licania platypus (Hemsl.) Fritsch. J Exp Bot 53:2239-2247 Tyree MT, Engelbrecht BMJ, Vargas G, Kursar TA (2003) Desiccation tolerance of five tropical seedlings in Panama. Relationship to a field assessment of drought performance. Plant Physiol 132:1439-1447

Wilkinson MJ, Owen SM, Possell M, Hartwell J, Gould P, Hall A, Vickers C, Hewitt CN (2006) Circadian control of isoprene emissions from oil palm (Elaeis guineensis). Plant J 47:960-968 Worbes M (1999) Annual growth rings, rainfall-dependent growth and long-term growth patterns of tropical trees from the Caparo Forst Reserve in Venezuela. J Ecol 87:391-403

Chapter 6

Was this article helpful?

0 0
Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

Get My Free Ebook


Post a comment