The efficiency of crop production is defined in thermodynamic terms as the ratio of energy output (carbohydrate) to energy input (solar radiation). Temperature and water supply are the main climatic constraints on efficiency. Over most of Britain, the radiation and thermal climates are uniform and rainfall is the main discriminant of yield between regions. Total production of dry matter by barley, potatoes, sugar beet, and apples is strongly correlated with intercepted radiation and these crops form carbohydrate at about 1.4 g per MJ solar energy, equivalent to 2.4% efficiency. Crop growth in Britain may therefore be analysed in terms of ( a ) the amount of light intercepted during the growing season and ( b ) the efficiency with which intercepted light is used. The amount intercepted depends on the seasonal distribution of leaf area which, in turn, depends on temperature and soil water supply. These variables are discussed in terms of the rate and duration of development phases. A factorial analysis of efficiency shows that the major arable crops in Britain intercept only about 40 % of annual solar radiation and their efficiency for supplying energy through economic yield is only about 0.3%. Some of the factors responsible for this figure are well understood and some are immutable. More work is needed to identify the factors responsible for the large differences between average commercial and record yields.

Climate and the efficiency of crop production in Britain

What determines the number and size of the seeds produced by a plant? How often should it reproduce them? How often should a plant produce them? Why and how are seeds dispersed, and what are the implications for the diversity and composition of vegetation? These are just some of the questions tackled in this wide-ranging review of the role of seeds in the ecology of plants. The authors bring together information on the ecological aspects of seed biology, starting with a consideration of reproductive strategies in seed plants and progressing through the life cycle, covering seed maturation, dispersal, storage in the soil, dormancy, germination, seedling establishment, and regeneration in the field. The text encompasses a wide range of concepts of general relevance to plant ecology, reflecting the central role that the study of seed ecology has played in elucidating many fundamental aspects of plant community function.

The ecology of seeds

Phenotypic plasticity is an important element in the response repertoire of plants (25). It may be manifested as changes in organ (e.g. leaf) morphology as well as in patterns of biomass distribution. Morphological plasticity throughout growth is possible because plant development is modular in form (77, 184, 185). Growth results from the reiteration of basic morphological subunits produced by meristems. Because meristems may develop into either reproductive or vegetative structures, patterns of biomass distribution reflect developmental decisions (121, 172, 180). In this essay, we review data suggesting that at least in certain cases, architectural constraints affect the range of morphological plasticity that can be expressed. Because carbon is frequently viewed as a critical currency of allocation (76, 165), we focus on how these constraints influence assimilate (i.e. carbon) production and utilization. We postulate that when these constraints are present, plants consist not only of morphological subunits (185) but, as Adams (4) first suggested, of physiological subunits as well. We call these integrated physiological units (IPUs) and propose that they are made up of identifiable arrays of morphological subunits that together function as relatively autonomous structures with respect to the assimilation, distribution, and utilization of carbon. If such units of physiological integration exist,

Morphogenetic constraints on patterns of carbon distribution in plants

Constraints on patterns of carbon distribution in plants

Publisher Summary This chapter emphasizes the measurement of plant water potential following the realization of the importance of atmospheric demand in determining plant water deficits. The total water potential concept determines the movement of water through the soil-plant-atmosphere continuum in response to gradients in water potential and of the soil, plant, and atmospheric factors that influence the development of water deficits in plants. A water deficit occurs whenever water loss exceeds absorption. The use of total water potential as the best single indicator of plant water status has its limitations while attempting to understand the effect of water deficits on the various physiological processes involved in plant growth. The chapter discusses the effects of water deficits on crop growth, crop development, and crop yield. The differences in response of plants grown under controlled conditions and in the field are discussed. Some difficulties in extrapolating from controlled environments to the field are presented in the chapter.

R. K. Scott

Papers

Barley and its Environment. V. Stability of Grain Weight

Barley and its Environment. III. Carbon Budget of the Stand

Barley and its Environment. IV. Sources of Assimilate for the Grain

Barley and its Environment: VI. Growth and Development in Relation to Yield

Barley and its Environment. I. Theory and Practice