Publisher Summary This chapter reviews the evidence for the pattern of growth decline with age and discusses the evidence for the mechanisms that may be responsible. It begins with an overview of the proposed mechanisms. The chapter also presents a framework for understanding the changes in stand productivity with age, because many of the proposed mechanisms are linked and affect carbon allocation. The available information on the importance of various mechanisms behind growth decline, in the context of the stand carbon cycle is presented. The common patterns of a decline in stand leaf area and leaf photosynthetic capacity suggest a new model of carbon balance with stand development. In this model, photosynthesis and above-ground dry-matter production increase with canopy development. After the forest reaches a maximum leaf area, photosynthesis and dry-matter production decline as leaf area, photosynthetic capacity, and photosynthesis also decline. The model assumes that allocation to respiration and below ground to roots and symbionts is a constant fraction of assimilation over the life of a forest stand.

Age-Related Decline in Forest Productivity: Pattern and Process

The growth of plants and crop stands, in terms of dry weight or carbon gain, has traditionally been measured by sampling, drying, weighing and chemical analysis of the dried material (Chapters 1 and 3). Direct measurement of carbon dioxide (CO2) uptake provides a complementary approach. Whilst harvesting methods are appropriate in assessing long-term changes, they are unsuitable when interest centres either on short-term carbon gain, i.e. intervals of days, hours or minutes, or on contributions made by individual organs, e.g. the flag leaves of cereals. Measurement of CO2 uptake provides an alternative and direct method of measuring carbon exchange, with important advantages: it is instantaneous and nondestructive. Furthermore it allows: measurement of the total carbon gain by a plant or stand; separation of the uptake by the different photosynthetic organs of a plant; and separation of photosynthetic gain from respiratory losses. In studying photosynthesis in vivo, measurements of O2 evolution, and of fluorescence and absorption spectroscopy, now provide valuable methods for interpreting limitations and efficiencies. However, only measurement of CO2 uptake can provide an unambiguous and direct measure of the net rate of photosynthetic carbon assimilation.

Measurement of CO2 assimilation by plants in the field and the laboratory

Effect of light, nutrient, cultivation time and salinity on lipid production of newly isolated strain of the green microalga, Botryococcus braunii KMITL 2.

Leaf-level morphological and structural adaptations to reduce water loss were examined in five olive (Olea europaea L.) tree cultivars (Arbequina, Blanqueta, Cobrancosa, Manzanilla and Negrinha) growing under field conditions with low water availability. Leaf measurements included leaf tissue thickness, stomatal density, leaf area, leaf mass per unit area, density of leaf tissue, relative water content, succulence, water saturation deficit, water content at saturation and cuticular transpiration rate. We found considerable genotypic differences among the cultivars. Negrinha, Manzanilla and Cobrancosa had more morphological and structural leaf adaptations to protect against water loss than the other cultivars. Manzanilla and Negrinha enhanced their sclerophylly by building parenchyma tissues and increasing protective structures like the upper cuticle and both the upper and lower epidermis. Cobrancosa exhibited good protection against water loss through high density of foliar tissue and by thick cuticle and trichome layers. Compared with the Negrinha, Manzanilla and Cobrancosa cultivars, Arbequina leaves had a thinner trichome layer, implying that the leaves were less protected against water loss; however, the development of smaller leaves may reduce water loss at the whole-plant level. Among cultivars, Blanqueta had the largest leaves and some anatomical traits that may lead to high water loss, especially from the adaxial surface. The mechanisms employed by the cultivars to cope with summer stress are discussed at the morpho-structural level.

Sclerophylly and leaf anatomical traits of five field-grown olive cultivars growing under drought conditions.

This study was conducted in Department of Horticulture, Faculty of Agriculture, University of Cukurova in 1999 and 2000. Watermelon (Citrullus lanatus (Thunb.) Matsum and Nakai) cultivar Crimson Tide was grafted onto 10 different rootstocks. Cucurbita moschata, Cucurbita maxima and Lagenaria siceraria were open pollinated cultivars, and Strong Tosa, Gold Tosa, P360 (Cucurbita maxima × Cucurbita moschata), Skopje, Emphasis, 216 and FRG (Lagenaria spp.) were hybrid cultivars. The ungrafted Crimson Tide watermelon cultivar was used as the control. Plants were grown under low tunnel conditions until the outdoor temperature was suitable (22-25°C) for watermelon growth. Our results showed that while survival rate was low (65%) in Cucurbita type rootstocks, it was high (95%) in Lagenaria type rootstocks. Grafted plants flowered about 10 days earlier and showed more vigorous vegetative growth than the control plants. Grafted plants had up to 148% higher fresh weights than control plants. Similarly, grafted plants showed 42-180% higher dry weight, 58-100% more leaves and larger leaf area as compared with the control. In total yield, Lagenaria type rootstocks produced a higher yield but Cucurbita type rootstocks produced a lower yield than the control. While control plants had 6.43 kg/m 2 yield, Lagenaria type rootstocks produced 27-106% higher yield than the control. In contrast, Cucurbita type rootstocks had 127-240% less yield than the control. This could be attributed to incompatibility of Cucurbita rootstocks because some of the plants died before harvest. The study showed that rootstock choices influence plant growth as well as yield and quality of scion fruit, suggesting an important consideration in the potential use of grafting applications in watermelon.

Effect of different rootstock on plant growth, yield and quality of watermelon

Techniques in Bioproductivity and Photosynthesis

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Techniques in Bioproductivity and Photosynthesis