Two-year-old potted sweet chestnut seedlings were grown at 350 ppm CO^ and 700 ppm, day and night in eonstantly ventilated tunnels duting two full growing seasons, near Paris, Fiance (48° N, 2" E), Enrichment with CO, caused an unusual shoot growlh response. After the end of July, stetn elongation eeased in 62% of the COn enriehed plants as compared with 37% in the eontrol. The leaves of COi-enriched seedlings showed early senescence, indicated by ptetnature yellowing and a decrease in chlorophyll content. T'his was associated with nutrient dilution brought about by the rapid growth of these trees. The iticrease in total dry weight of the COi-enriehed seedlings was essentially the result of increase in the root dry weight (69%). Shoot weight decreased by 22% relative to the control. Total leaf area per enriched plant was 25% smaller than the control. This unusual pattetn of growth and cat"bon allocation of the COT treated Chestnut trees etnphasizes the concept of a response specificity within tiees to an increase of atmospheric CO^.

A mathematical model of the processes involved in carbon metabolism is described that predicts the influence of temperature on the growth of plants. The model assumes that the rate of production of dry matter depends both on the temperature and the level of nonstructural carbohydrate. The level of nonstructural carbohydrate is determined by the rates of photosynthesis, growth, and maintenance respiration. The model describes the rate of growth and dark respiration, and the levels of carbohydrate seen in vegetative growth of carnation and tomato. The model suggests that the growth of plants at low temperatures is limited by a shortage of respiratory energy, whereas at high temperatures growth is limited by the shortage ofcarbohydrate. Thermoperiodism, wherein a warm day and cool night results in faster growth than does constant temperature, is explained by the model as an increase in the level of nonstructural carbohydrate which promotes the rate of growth relative to the rate of maintenance respiration.Although temperature has a major influence on plant growth, attempts to predict the response are confounded by several phenomena. The heat sum or growing degree day concept (26) predicts the development of a crop growing in the field solely from the accumulation of heat units above a base temperature. A more complex temperature response of growth is seen under controlled, constant-temperature conditions. At 5 to 20°C, the rate of growth increases exponentially; at 20 to 30°C, it levels off; and above 30 to 35°C, the growth rate falls (9,19,27). This has been ascribed to inactivation of an enzyme crucial to growth metabolism both at high and low temperatures which modifies the usual exponential temperature dependence of an enzyme reaction rate (21). Neither model explains the nonadditive effect of fluctuating diurnal temperatures (27) or the influence of light and CO2 (4,9,19) on the growth response.At a constant temperature, the rate of plant growth is linearly related to the rate of photosynthesis (8,13,25). However, the temperature dependence of growth and photosynthesis is not the same. Photosynthesis increases with temperature in an asymptotic manner to a plateau above 15°C (5, 10), while the growth rate increases exponentially in this interval and falls rapidly at temperatures above 25°C (9,19,27). This divergence occurs because only some of the carbohydrate is used to promote growth and the rest is used to maintain the plant in the current state (15,18,20 experimentally from respiration due to growth by plotting the total dark respiration versus the growth rate (13, 23). Growth respiration and maintenance respiration increase exponentially up to 20°C (13, 18). Whereas growth starts to decrease above 25°C, maintenance keeps increasing. This concept accounts for the carbohydrate mass balance of plant metabolism; but, more information is required to explain why maintenance is promoted at higher temperatures and growth is not.In this report, Okhams razor is applied to derive the simplest model that predi...

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The rates of CO2 assimilation by potted spray carnation plants (cv. Cerise Royalette) were determined over a wide range of light intensities (45-450 W m~2 PAR), CO2 concentrations (200-3100 vpm), and leaf temperatures (5-35 °C). Assimilation rates varied with these factors in a way similar to the response of single leaves of other temperate crops, although the absolute values were lower. The optimal temperature for CO2 assimilation was between 5 and 10 °C at 45 W m~2 PAR but it increased progressively with increasing light intensity and CO2 concentration up to 27 °C at 450 W m~2 PAR and 3100 vpm CO2 as expressed by the equation 2\>pt = -6-47 + 2-336 In C + 0-031957 where C is CO 2 concentration in vpm and I is photosynthetically active radiation in W m~2. CO2 enrichment also increased stomatal resistance, especially at high light intensities.The influence of these results on optimalization of temperatures and CO2 concentrations for carnation crops subjected to daily light variation, and the discrepancy between optimal temperatures for growth and net photosynthesis, are discussed briefly.

SUMMARY The influence of irrigation with CO2‐enriched water on plant development and yield is reviewed. The reason for irrigation with CO2‐enriched water was – in most cases – to increase yield. The present evaluation considers results from over a hundred studies performed since the first experiment in 1866. Special emphasis is given to the comparison of 85 experiments made by Mitscherlich in 1910 with 358 irrigation experiments made in the last 80 years. In a statistical analysis of these experiments, the measured plant parameter (often growth and/or gas exchange rates) showed a highly significant mean increase of 2.9 % in plants irrigated with CO2‐enriched water as compared with control. Evidence of five mechanisms was found. The subterranean carbon dioxide concentration influences: (a) the rate of nitrification and hence of nitrogen availability; (b) the rate of weathering and pH, and hence the availability of other plant nutrients; (c) the CO2 uptake via roots into the transpiration stream, contributing to the rate of leaf photosynthesis; (d) the hormone levels in the plant; and (e) the rate of pesticide decomposition in soils. After examining the available evidence we found that (a) and (b) in some experiments are important to plant growth, since they change the physiochemical environment of the roots. On the other hand, while (c) could theoretically contribute up to 5% of plant carbon assimilation, it usually contributes less than 1 %, while (d) contributes most of the observed effects of CO2‐enriched water on plants. In addition, pesticide decomposition in soils can be delayed by supra‐ or sub‐optimal CO2 concentrations.