No abstract

SUMMARYA study was made of photosynthesis and expression of crassulacean acid metabolism (CAM) in naturally exposed and shaded populations of Clusia minor L. during the transition from wet to dry season in Trinidad (mid-February to mid- April, 1990). At the start of the dry season, plants from exposed and shaded habitats showed a capacity for CAM either through the fixation of external or internal (respiratory) CO.^. Exposed plants showed continuous uptake of CO^ over 24 h although dark fixation accounted for only a small proportion of CO^ fixed over the day. The expression of CAM was considerably enhanced as the dry season progressed with substantial increases in the overnight accumulation of titratable acidity, particularly in leaves of exposed plants. This was accompanied by a reduction in day-time photosynthesis and an increase m dark fixation, with shaded plants showing only night-time fixation of CO,^. The magnitude of CAM in C. minor was substantial with a maximum AH" of 1410 mol m"'' measured in leaves from exposed branches. Both malic and citric acids were accumulated overnight. The highest citric.malic acid ratios were found in young leaves from exposed plants with 250 mol m~' * malic and 125 mol m'ĉ itric acid accumulated near the time of maximum CAM activity. Photosynthetic efficiency, measured as light responses of O^ evolution, also varied on a daily basis dependent on the incident photosynthetic photon flux density (PPFD). Apparent quantum yield and photosynthetic capacity showed marked reductions depending on the degree of exposure, suggesting that photoinhibitory responses are important under natural conditions. An analysis of three members of the Clusiaceae endemic to Trmidad showed that each had the capacity to induce CAM activity, despite being found in a narrow range of habitats which have higher rainfall than those of C. minor. However, despite the variable expression of CAM activity, carbon isotope composition suggested that when integrated throughout the year, carbon accumulation is predominantly mediated via the C^ pathway in all the species studied.

SUMMARYFive days after emergence radish {Raphanus sativus L. cv. Cherry Belle) plants were transferred to a phytotron at the GSF Munchen, where they were exposed in four large controlled climate chambers to two atmospheric concentrations of COj ('ambient', daily means of % 385 //mol mol'; elevated, daily means of « 765 //mol mol ') and two O3 regimes ('non-polluted' air, 24 h mean of 20 nmol mo! '; polluted air, 24 h mean of 73 nmol mol"'). Leaf gas-exchange measurements were made at intervals, and visible O3 damage, effects on growth, dry matter partitioning and mineral composition were assessed at a final whole-plant harvest after 27 d. In 'non-polluted air' CO2 enrichment resulted in a progressive stimulation in A^^^, whilst there was a decline in g^ which decreased E (i.e. improved WUE,). The extra carbon fixed in elevated CO2 stimulated growth of the root (-h hypocotyl) by 43 °o, but there was no significant effect on shoot growth or leaf area. Moreover, a decline in SLA and LAR in COj-enriched plants suggested that less dry matter was invested in leaf area expansion. Tissue concentrations of N, S, P, Mg and Ca were lower (particularly in the root+ hypocotyl) m elevated CO.,, indicating that total uptake of these nutrients was not affected by CO.,, and there was an increase in the C: N ratio in root (+ hypocotyl) tissue. In contrast, O3 depressed A^^^ (« 26 "o) and induced slight stomatal closure, with the result that WUEj declined. All plants exposed to 'polluted' air developed typical visible symptoms of O3 injury, and effects on carbon assimilation were reflected in reduced growth, with shoot growth maintained at the expense of the root. In addition, O,, increased the P and K concentration in shoot and root ( +hypocotyl) tissue, indicating enhanced uptake of these nutrients from the growth medium. However, there was no affect of O3 on tissue concentrations of N, S, Mg and Ca. Interactions between the gases were complex, and often subtle. In general, elevated COj counteracted (at least in part) the detrimental effects of phytotoxic concentrations of O3, whilst conversely, O.j reduced the impact of elevated CO^. Moreover, there were indications that cumulative changes in source: sink relations in 03-exposed plants may limit plant response to COj-enrichment to an even greater extent in the longterm. The future ecological significance of interactions between CO., and O3 are discussed.

U .M M A R YScanning electron microscopy was used to investigate tbe effects of O., fumigation (70 d of 240//g O., m''' for 6 h d^', during a 12 b pbotoperiod) on tbe condition of tbe epicuticular wax tbat fills atid surrounds tbe stomatal antecbamber of tbe needles of se\ en clones of" Norway spruce (Picea abies (L.) Karst.). Tbe rate of cbange of tbe physical structure of tbe wax differed between clones, but in all cases ()., accelerated tbe process on current and previous year's needles. Tbe cbange consisted of a transition from a crystalline array of fine tubes to an amorpbous, 'melted' layer witb no visible structure. Tbis resulted in a bigber frequency of stotnata occluded by ati apparetitly continuous plug. In four clones, ()., fumigation resulted in 70-80 "" of tbe stomata on previous year's needles being occluded, in contrast to 7-28 "" in cbarcoal-filtered air. F'ive of tbe clones sbowed a greater effect of O., on tbe wax of tbe previous year's needles tban on current needles. ^Vhe pbysiological consequences of sucb O.j-induced effects are discussed. Premature wax degradation induced by O., atid/or acid mist may bave contributed to tbe decline of spruce in bigb-altitude forests of continental Europe.

SUMMARYThree-year old Norway spruce [Picea abies (L.) Karst.] trees from two clones (4076 and 4102) of a medium altitude southern German provenance were transplanted in May 1986 into an acid brown earth soil. During the summers of 1987 and 1988 the trees were exposed in large-scale fumigation chambers (solardomes) to ozone at 100 or 20 nl r' (control). Acid (pH 3-6) or control mist (pH 5-5) was applied daily to trees, 'l^'he wettability of current and 1-year-old needles was assessed in November 1988 by measuring the contact angle of water droplets placed on needles, and the amount of surface wax was determined. The contact angle of water droplets on current and 1-year-old needles was significantly reduced by 100 nl T' PPB ozone and/or acid mist, indicating that the wettability had increased, but the combined effect of ozone and acid mist was no more than additive. Exposure to the pollutants resulted in a slight decrease in the quantity of surface wax, but the effect was not significant. Ozone and acid mist treatment also increased the projected area of needles relative to their dry weight. The possible involvement of such effects in forest decline are discussed.