typically written from a biophysicist’s or a molecular plant physiologist’s point of view (Horton and Bowyer, Chlorophyll fluorescence analysis has become one of 1990; Krause and Weis, 1991; Govindjee, 1995). The aim the most powerful and widely used techniques avail- of this review is to provide a simple, practical guide to able to plant physiologists and ecophysiologists. This chlorophyll fluorescence for those beginners who are review aims to provide an introduction for the novice interested in applying the technique in both field and into the methodology and applications of chlorophyll laboratory situations. Whilst the principles behind the fluorescence. After a brief introduction into the theor- measurements will be discussed briefly, the emphasis will etical background of the technique, the methodology be on the applications and limitations of this technique and some of the technical pitfalls that can be encoun- in plant ecophysiology. tered are explained. A selection of examples is then used to illustrate the types of information that fluorescence can provide. The basis of chlorophyll fluorescence measurements

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Chlorophyll fluorescence—a practical guide

We discuss the physical and enzymatic bases of carbone isotope discrimination during photosynthesis, noting how knowledge of discrimination can be used to provide additional insight into photosynthetic metabolism and the environmental influences on that process

Carbon Isotope Discrimination and Photosynthesis

In the last decade, our understanding of the processes underlying plant response to drought, at the molecular and whole-plant levels, has rapidly progressed. Here, we review that progress. We draw attention to the perception and signalling processes (chemical and hydraulic) of water deficits. Knowledge of these processes is essential for a holistic understanding of plant resistance to stress, which is needed to improve crop management and breeding techniques. Hundreds of genes that are induced under drought have been identified. A range of tools, from gene expression patterns to the use of transgenic plants, is being used to study the specific function of these genes and their role in plant acclimation or adaptation to water deficit. However, because plant responses to stress are complex, the functions of many of the genes are still unknown. Many of the traits that explain plant adaptation to drought - such as phenology, root size and depth, hydraulic conductivity and the storage of reserves - are those associated with plant development and structure, and are constitutive rather than stress induced. But a large part of plant resistance to drought is the ability to get rid of excess radiation, a concomitant stress under natural conditions. The nature of the mechanisms responsible for leaf photoprotection, especially those related to thermal dissipation, and oxidative stress are being actively researched. The new tools that operate at molecular, plant and ecosystem levels are revolutionising our understanding of plant response to drought, and our ability to monitor it. Techniques such as genome-wide tools, proteomics, stable isotopes and thermal or fluorescence imaging may allow the genotype-phenotype gap to be bridged, which is essential for faster progress in stress biology research.

Understanding plant responses to drought — from genes to the whole plant

Contents

 Summary 1

I. What is FACE? 2
II. Materials and methods 2
III. Photosynthetic carbon uptake 3
IV. Acclimation of photosynthesis 6
V. Growth, above-ground production and yield 8
VI. So, what have we learned? 10

 Acknowledgements 11


 References 11


Appendix 1. References included in the database for meta-analyses  14


 Appendix 2. Results of the meta-analysis of FACE effects 18



Summary
Free-air CO2 enrichment (FACE) experiments allow study of the effects of elevated [CO2] on plants and ecosystems grown under natural conditions without enclosure. Data from 120 primary, peer-reviewed articles describing physiology and production in the 12 large-scale FACE experiments (475–600 ppm) were collected and summarized using meta-analytic techniques. The results confirm some results from previous chamber experiments: light-saturated carbon uptake, diurnal C assimilation, growth and above-ground production increased, while specific leaf area and stomatal conductance decreased in elevated [CO2]. There were differences in FACE. Trees were more responsive than herbaceous species to elevated [CO2]. Grain crop yields increased far less than anticipated from prior enclosure studies. The broad direction of change in photosynthesis and production in elevated [CO2] may be similar in FACE and enclosure studies, but there are major quantitative differences: trees were more responsive than other functional types; C4 species showed little response; and the reduction in plant nitrogen was small and largely accounted for by decreased Rubisco. The results from this review may provide the most plausible estimates of how plants in their native environments and field-grown crops will respond to rising atmospheric [CO2]; but even with FACE there are limitations, which are also discussed.

What have we learned from 15 years of free-air CO2 enrichment (FACE)? A meta-analytic review of the responses of photosynthesis, canopy properties and plant production to rising CO2.

I. CONTEXT * The Ecosystem Concept * Earth's Climate System * Geology and Soils * II. MECHANISMS * Terrestrial Water and Energy Balance * Carbon Input to Terrestrial Ecosystems * Terrestrial Production Processes * Terrestrial Decomposition * Terrestrial Plant Nutrient Use * Terrestrial Nutrient Cycling * Aquatic Carbon and Nutrient Cycling * Trophic Dynamics * Community Effects on Ecosystem Processes * III. PATTERNS * Temporal Dynamics * Landscape Heterogeneity and Ecosystem Dynamics * IV. INTEGRATION * Global Biogeochemical Cycles * Managing and Sustaining Ecosystem * Abbreviations * Glossary * References

Principles of Terrestrial Ecosystem Ecology

The comparative phenotypic plasticity of 16 species of tropical rainforest shrubs (genus Psychotria, Rubiaceae) was investigated by growing plants in three light environments on Barro Colorado Island (BCI, Panama). The three light environments gave daily photon flux densities (PPFD) similar to the natural light gradient from shaded forest understory to small and large canopy gaps. Six of the species are principally found in gaps or forest edge environments, whereas the other ten species are principally found in shaded understories. Interactions between light treatment and species resulted in unpredictable mean phenotypic expression across light treatments. Shoot relative growth rates (RGR) were similar for understory and gap species in the low light treatment. Gap species had significantly greater shoot RGR in the intermediate light treatment than in the high light treatment. Mean plasticity was significantly lower for morphological variables when com- pared to physiological variables, while variation in plasticity was significantly greater for structural variables. Significant differences between gap and understory species were found in the plasticity of six out of the seven variables. The mean phenotypic plasticity of the seven variables was significantly greater for gap than for understory species. The high plasticity of gap species was consistent with the hypothesis that specialization in a more favorable environment increases plasticity. The species exhibited a wide range of leaf longevities, from four to 29 months, with gap species having, on average, shorter leaf life- span than understory species. Mean phenotypic plasticity decreased with increasing leaf longevity. Selection for greater plasticity may be stronger in the gap species because gaps exhibit a relatively predictable decrease in PPFD for which plasticity could be adaptive. While we have found a significant correlation between phenotypic plasticity and habitat affiliation, phylogeny (subgenus ascription) was not correlated with plasticity or with plant performance in any given PPFD treatment, reinforcing the hypothesis that phenotypic plas- ticity has evolved through natural selection in this diverse genus.

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Plastic Phenotypic Response to Light of 16 Congeneric Shrubs From a Panamanian Rainforest

INTRODUCTION .. . . . . .... ......... . . . . . . . . ....... ........ . ... .. ......... 421 LIGHT DYNAMICS IN CANOPIES 422 Theory . . . . . . . . . .. . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . ... . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422 Empirical Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . ....... . . . . . . . 424 PHOTOSYNTHESIS IN TRANSIENT LIGHT .. . ..... . . . . . . .. ........ .. . . . . . . . ...... .. . . ...... 425 Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425 Measurement of Transient Photosynthesis ...... . . . . . . ......... .. . .. . . . . . . . . . . . . . . . 427 Dynamics of CO2 Assimilation during Sunj1ecks . . . ... . .. ... . . .. . . . . . . . . .. .. ... 429 Limitation of Sunj1eck Use by the P hotosynthetic Induction Requirement ........ ..... 436 Modulation of Induction State in Natural Light Regimes . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . 440 ENVIRONMENTAL CONSTRAINTS ON SUNFLECK UTILIZATION . . . . . . ........ . . . 442 Temperature and Water Stress ..... .. . . . . . . . . . . . ..... . . ........ . . . . . . . . .... .... ... . .. 442 Ph otoinhibition during Sunflecks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . .. . ........ .... . . . . .. 443 CONCLUDING REMARKS 444

Sunflecks and photosynthesis in plant canopies

Plants assimilate carbon by one of three photosynthetic pathways, commonly called the C 3 , C 4 , and CAM pathways The C 4 photosynthetic pathway, found only among the angiosperms, represents a modification of C 3 metabolism that is most effective at low concentrations of CO 2  Today, C 4 plants are most common in hot, open ecosystems, and it is commonly felt that they evolved under these conditions However, high light and high temperature, by themselves, are not sufficient to favor the evolution of C 4 photosynthesis at atmospheric CO 2 levels significantly above the current ambient values A review of evidence suggests that C 4 plants evolved in response to a reduction in atmospheric CO 2 levels that began during the Cretaceous and continued until the Miocene

Climate change and the evolution of C4 photosynthesis

. In this review we relate the physiological significance of C4 photosynthesis to plant performance in nature. We begin with an examination of the physiological consequences of the C4 pathway on photosynthesis, then discuss the ecophysiological performance of C4 plants in contrasting environments. We then compare the performance of C3 and C4 plants when they occur together in similar habitats, and finally discuss the distribution of C4 photosynthesis with respect to the physical environment, phylogeny, and life form.

Comparative ecophysiology of C3 and C4 plants

The quantum yield for CO2 uptake was measured on a number of C3 and C4 monocot and dicot species. Under normal atmospheric conditions (330 microliters per liter CO2, 21% O2) and a leaf temperature of 30°C, the average quantum yields (moles CO2 per einstein) were as follows: 0.052 for C3 dicots, 0.053 for C3 grasses, 0.053 for NAD-malic enzyme type C4 dicots, 0.060 for NAD-malic enzyme type C4 grasses, 0.064 for phosphoenolpyruvate carboxykinase type C4 grasses, 0.061 for NADP-malic enzyme C4 dicots, and 0.065 for NADP-malic enzyme type C4 grasses. The quantum yield under normal atmospheric conditions was temperature dependent in C3 species, but apparently not in C4 species. Light and temperature conditions during growth appeared not to influence quantum yield. The significance of variation in the quantum yields of C4 plants was discussed in terms of CO2 leakage from the bundle sheath cells and suberization of apoplastic regions of the bundle sheath cells.

Robert W. Pearcy

Papers

Plastic Phenotypic Response to Light of 16 Congeneric Shrubs From a Panamanian Rainforest

Sunflecks and photosynthesis in plant canopies

Climate change and the evolution of C4 photosynthesis

Comparative ecophysiology of C3 and C4 plants

Variation in Quantum Yield for CO2 Uptake among C3 and C4 Plants