Plant Physiological Ecology
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Box 9E. 1 Continued FIGURE 2. The C–S–R triangle model (Grime 1979). The strategies at the three corners are C, competiti- winning species; S, stress-tolerating s- cies; R,ruderalspecies. Particular species can engage in any mixture of these three primary strategies, and the m- ture is described by their position within the triangle. comment briefly on some other dimensions that Grime’s (1977) triangle (Fig. 2) (see also Sects. 6. 1 are not yet so well understood. and 6. 3 of Chapter 7 on growth and allocation) is a two-dimensional scheme. A C―S axis (Com- tition-winning species to Stress-tolerating spe- Leaf Economics Spectrum cies) reflects adaptation to favorable vs. unfavorable sites for plant growth, and an R- Five traits that are coordinated across species are axis (Ruderal species) reflects adaptation to leaf mass per area (LMA), leaf life-span, leaf N disturbance. concentration, and potential photosynthesis and dark respiration on a mass basis. In the five-trait Trait-Dimensions space,79%ofallvariation worldwideliesalonga single main axis (Fig. 33 of Chapter 2A on photo- A recent trend in plant strategy thinking has synthesis; Wright et al. 2004). Species with low been trait-dimensions, that is, spectra of varia- LMA tend to have short leaf life-spans, high leaf tion with respect to measurable traits. Compared nutrient concentrations, and high potential rates of mass-based photosynthesis. These species with category schemes, such as Raunkiaer’s, trait occur at the ‘‘quick-return’’ end of the leaf e- dimensions have the merit of capturing cont- nomics spectrum.
fully developed meniscus in a cylindrical pore of radius, say 1:5 "m, would have a pressure drop across it of 1.0 MPa; the pressure, P, in the water would therefore be 0.1 MPa if refer enced to normal atmospheric pressure, or 0.9 MPa absolute pressure (given that standard atmospheric pressure is approximately 0.1 MPa). This reasoning also pertains to pores that are not cylindrical. It is the radius of curvature of the meniscus that determines the pressure difference across the meniscus, and this
carbonic anhydrase is important for minimizing it (Gillon & Yakir 2000). Evidence for an important role for the area of chlor oplasts bordering intercellular spaces as a determi nant of gm stems from a positive relationship with this parameter per unit leaf area (Evans & Loreto 2000). Data about a similar parameter, chloroplast area per leaf area, are more widely available and vary by an order of magnitude among species (Table 1) which is likely associated with gm. There General Characteristics
efficiency of photosynthesis and yield of C3 parents. The complex ity of anatomy and biochemistry of the C4 plants, however, is such, that these crosses have not pro duced any useful progeny (Brown & Bouton 1993). Since molecular techniques have become available which allow silencing and over expression of specific genes in specific cells, attempts have been made to reduce the activity of glycine decarboxylase, the key enzyme in photorespiration, in mesophyll cells of C3 plants and over express
fixation during the night that are similar in magnitude as those during the day, when the CO2 supply from the water is very low (Fig. 53). The aerial leaves of Isoetes howellii, in contrast to the submerged leaves of the same plants, do not show a diurnal fluctuation in the concentration of malic acid. Why would an aquatic plant have a similar photosynthetic pathway as is common in species from arid habitats? CAM in Isoetes is considered an adaptation to very low levels of CO2 in the water,
copyright Elsevier Science, Ltd.). respective growth temperatures; however, complete homeostasis is uncommon. Acclimation can play an important role in weakening positive feedback through the warming respiration atmospheric CO2 concentration connection (Atkin & Tjoelker 2003). Acclimation of leaf respiration to temperature is lar ger in conifers than in broad leaved species (Tjoelker et al. 1999); other than that, there are no major sys tematic differences in the degree of acclimation among