Effect of Temperature on the Growth and Development of Tomato Fruits

Tomato fruits ripened 95, 65, 46 and 42 d after flower openingwhen plants were grown under controlled environmental conditionsat 14, 18, 22 and 26 °C, respectively. A similar responseto temperature was observed when the temperature of individualtrusses was modified while the plants were grown at 20 °C.These data were used to develop a thermal time model for fruitmaturation. However, when buds/fruits were heated at differentstages in their development, the thermal time model proved tobe a poor predictor of the time of ripening. Fruits were moresensitive to elevated temperature in their later stages of maturation.Temperature also affected the rates of fruit growth in volume;these could be adequately described using a Gompertz function.Low temperatures reduced absolute volume growth rates and delayedthe time at which the absolute growth rate became maximal. However,the response of fruit growth to temperature differed when onlythe temperature of the fruits was modified. There was a tendencytowards small parthenocarpic fruits at both high (26 °C)and low (14 °C) temperature regimes which, combined withlow flower numbers and poor fruit set at 26 °C, resultedin low fruit yields. Temperature also affected the shoot drymatter content and partitioning. Copyright 2001 Annals of BotanyCompany Tomato, Lycopersicon esculentum, fruit, growth, ripening, temperature, temperature stress, parthenocarpy     

Effect of Temperature on Interception and Conversion of Solar Radiation by Stands of Groundnut

Stands of groundnut were grown in controlled environment glasshousesat air temperatures of 19, 22, 25, 28, and 31°C. Leaf areaindex (L) increased with rise of temperature, and after 85 dwas about 10-fold larger at 31°C than 19°C. Over mostof the range of temperature, both L and fractional interceptionof solar radiation (f) were functions of thermal time accumulatedfrom sowing (above a base of 10°C). In this respect, theywere tightly coupled to developmental rate at the main apex.In one experiment, only 38% of seeds emerged at 22°C and21% at 19°C, compared with more than 70% at 25°C and31°C, but the low population density was compensated byfaster leaf expansion by each plant (at 22°C only) and agreater fraction of solar radiation intercepted by unit leafarea. The amount of solar radiation intercepted by stands increasedwith rise in temperature, but the greatest differences betweentreatments occurred before the canopies achieved complete groundcover (i.e.f>0.9) and the relative effect of a rise in temperaturediminished the longer the duration of growth. The dry matterproduced for unit solar radiation intercepted was not stronglyaffected by temperature between 22°C and 31°C, wherethe mean was 2.1 g MJ^–1; the value at 19°C was uncertainsince the stands were sparse throughout the experiment. After85 d, the stand at 31°C had produced eight times the drymatter of that at 19°C—a difference caused mainlyby the effect of temperature on the rates of development andexpansion. Key words: Dry matter production, groundnut, radiation interception, temperature, thermal time, roses     

Bean Leaf Expansion in Relation to Temperature

When dwarf Phaseolus vulgaris plants were grown in a controlledenvironment at 20, 25, 30, and 35° C, expansion of the primaryleaves occurred in two phases with an intermediate lag. Varyingrates and duration of expansion were involved, leading to greatestfinal areas at the two intermediate temperatures. Dry weightsof the leaves and leaf areas were similary influenced by temperature,except that the initial rates of increase continued for a longerperiod for weights than for areas. The rates of cell divisionand final numbers of cells were similar from 25 to 35° C,but both were decreased at 20° C. Final cell sizes were,on the other hand, decreased only at the highest temperature.The time trends of cell expansion varied greatly with temperature. Leaf expansion is discussed as a possible consequence of substratesupply, which may be determined by temperature in a number ofways. Cell division and cell expansion are not considered tobe joint direct determinants of leaf expansion. Temperatureinfluences division, with two consequences; the rate interactswith substrate supply to determine size of cells, and finalcell number affects potential leaf area. Cell size is regardedas being secondary to numbers of cells and total material available,although some factors can vary cell size independently of substrate,e.g. water status. An important control of leaf growth, until the attainment ofabout half the final area, may be exercised by way of the leaf.Subsequently, intra-plant competition is likely to dominate.     

Effect of Night Temperature on Photosynthesis, Transpiration, and Growth of Spray Carnations

Spray carnation plants were grown for several weeks under an8 h day/16 h night regime at temperatures of approximately 21°C by day and 6, 17, or 30 °C by night. Subsequently,the rates of photosynthesis and transpiration at 20 °C weresimilar. This contrasts with evidence published for some otherspecies. Night temperature had only a slight effect on the plant's growthrate. Leaf area ratios were also similar between treatmentsand for two intervals covering a 5 week period. At the highnight temperature flowers were initiated sooner and there werefewer side shoots per plant than at the lower temperatures. The implications of these results for the optimization of theclimatic environment are discussed briefly, and the resultsare compared with those reported for other species.     

The effect of root temperature on rose plants in relation to air temperature

Rose plants (Rosa hybrida ‘Sonia’=‘Sweet Promise’) were grown in heated (minimum night temperature 17°C), and unheated greenhouses with or without root heating to 21°C. These trials covered 6 growth cycles extending over two winter seasons. In the heated greenhouse, root heating did not increase yield, flower quality or plant development. In the unheated greenhouse, root-heated plants grew as well as those in the air-heated greenhouse as long as the air temperature did not fall below 6°C. When minimum night temperatures fell below 6°C, growth, yield and quality were reduced, irrespective of root temperature. Daytime plant water relations were studied in plants growing at 6 different root temperatures in the unheated greenhouse. Leaf resistance to water diffusion was lowest at optimal root temperature. Total leaf water potential was not significantly affected by root temperature.     

The Effect of Temperature on Growth and Development of Echinochloa Millets

Accumulation of dry weight and leaf plus stem area were measuredin Echinochloa utilis and E. frumentacea grown at temperatureregimes from 15/10°C to 33/28°C (day/night). Tilleringand height were recorded in addition to leaf number which wassubsequently used as a developmental index. In both species shoot dry weight increased with temperatureup to 33/28°C; the increase in relative growth rate (RGR)was negligible above 27/22°C. Below 27/22°C the RGRof E. frumentacea decreased sharply and at 15/10°C it madeno effective growth. At low temperatures the RGR of E. frumentaceawas lower than that of E. utilis due to slow leaf area expansion,and in particular smaller individual leaves. E. frumentaceatillered more than E. utilis. Plant development was retardedat low temperatures but was not as responsive to temperatureas dry weight and leaf area. The different responses to temperatureof the two species were described in equations suitable forinclusion in predictive growth models. Echinochloa spp., millet, growth, development, temperature, relative growth rate     

Effect of Temperature on Net Assimilation Rate

Net assimilation rates and other growth attributes were comparedfor rape, sunflower, and maize plants growing widely spacedat temperatures of 10°, 16°, 22°, 28°, and 34°C, in light of 3, 000 f.c. intensity. The optimum temperature for net assimilation rate lay between20° and 30° C, and was lowest for rape and highest formaize. The temperature coefficient of the net assimilation ratewas lower than that of the relative growth-rate, especiallyin rape and sunflower, corresponding to an increase in leaf-arearatio with in temperature. This arose to an increase in leaf-arearatio with rise in temperature. This mcrease arose through changeinleafarea/leaf weight; temperature had little effect on leafweight/plant weight. In moderate to warm conditions the net assimilation rate variedlittle with temperature: by only± 10 per cent between12° and 30° C for rape, and 23° and 36° C formaize. This agrees with observations in natural climates whichsuggest that temperature is generally less important than lightin controlling net assimilation rates, except in cool climates.In natural climates, as in these controlled climates, relativegrowth-rate is more temperature-dependent.     

Developmental Physiology of Sugar-beet: IV. EFFECTS OF GROWTH SUBSTANCES AND DIFFERENTIAL ROOT AND SHOOT TEMPERATURES ON SUBSEQUENT GROWTH

The effects of three growth substances, viz. indol-3yl-aceticacid (IAA), gibberellic acid (GA₃), and kinetin (KIN), and differentialshoot and root temperatures on growth of sugar-beet (Beta vulgarisL.) plants have been studied. IAA, GA₃, and KIN were applied in aqueous lanolin at differentconcentrations (50 ppm to 5000 ppm) to decapitated sugar-beetplants at the eight-leaf stage, one group also having alternateleaves removed. The growth substances significantly increasedthe dry weights of the plants when all the leaves were present,which was mainly explained by the large increase in roots. Thegrowth substances probably stimulated cambial activity and hencethe mobilization of substrates resulting in a bigger root whena relatively large leaf area existed. The failure of the plantsto respond to treatments following the removal of alternateleaves suggests that under such conditions the growth substanceshave hardly any major effect on the production of substrates;rather they influence growth by regulating the movement of substratesby altering the ‘sink strength’ if the supply ofsubstrates is not limiting. It could also be that the rootsproduce sufficient growth substances to maintain half the leavesat maximum expansion and maximum photosynthesis. Treatment withgrowth substances would therefore have little effect. When allthe leaves were present, they are limited by insufficient growthsubstances. All combinations of root and shoot temperatures of 17 and 25°C were imposed on plants decapitated at the eight-leafstage, one group also having each alternate leaf removed. Leaf8 expanded most at shoot and root temperature of 25 °C whereasother leaves had the largest areas at shoot and root temperatureof 17 °. When all the leaves were present root growth wasmaximal at shoot temperature of 17°C and root temperatureof 25 °C, but when alternate leaves were removed maximumroot growth occurred at shoot and root temperatures of 25 °C.Generally, a higher concentration of soluble carbohydrates wasfound in the roots and leaves when either the shoot or rootor both were kept at 17 °C. Concentrations of nitrogen,phosphorus, and potassium in different organs were less at 17°C than at higher shoot or root temperatures and decreasedwith age.     

Thermal tolerance ofStypocaulon scoparium (Phaeophyta,Sphacelariales) from eastern and western shores of the North Atlantic Ocean

Isolates ofStypocaulon scoparium Kütz. were collected from the Gulf of St. Lawrence, Canada and compared in culture to isolates collected from the Atlantic and Mediterranean coasts of Europe. The Canadian isolates grew at temperatures ranging from −2° C up to 22° C, with maximum rates of growth at 10–15° C; in trials lasting 3 months they survived the lowest temperatures but died at 22 or 25° C. In contrast, for the European isolates, maximum growth occurred between 10 and 27° C, and they died only after several months at 30 or 33° C. At the low end of the temperature range, European plants suffered damage or died at 5° C. Only the northernmost isolate, from Brittany, could both survive at 0° C and remain undamaged at 5° C in short days. All European isolates died at −2° C. Geographic distributions and the different thermal responses suggest that the eastern and western Atlantic populations are two different entities, the European plants being possibly of Tethyan origin, and the Canadian plants being possibly of north Pacific origin. The former would then have occupied the north Atlantic for thelongest time, which may partly explain the occurrence of ecotypic variation among these isolates.     

Effects of Low Temperature on Growth and Nutrient Accumulation in Rye (Secale cereale) and Wheat (Triticum aestivum)

Rye (Secale cereale cv. Rheidol) and wheat (Triticum aestivumcv. Mardler) were grown at shoot/root temperatures of 20/20°C (warm grown, WG plants), 8/8 °C (cold grown, CG plants)and 20/8 °C (differential grown, DG plants). Plants fromcontrasting growth temperature regimes were standardized andcompared using a developmental timescale based on accumulatedthermal time (°C d) at the shoot meristem. Accumulationof dry matter, nitrogen and potassium were exponential overthe time period studied (150–550 °C d). In rye, therates of plant dry matter and f. wt accumulation were linearlyrelated to the temperature of the shoot meristem. However, inwheat, although the rates of plant dry matter and f. wt accumulationwere temperature dependent, the linear relationship with shootmeristem temperature was weaker than in rye. The shoot/rootratio of rye was stable irrespective of growth temperature treatment,but the shoot/root ratio of wheat varied with growth temperaturetreatment. The shoot/root ratio of DG wheat was 50% greaterthan WG wheat. In both cereals, nutrient concentrations anddry matter content tended to be greater in organs exposed directlyto low temperatures. The mean specific absorption rates of nutrientswere calculated for the whole period studied for each species/temperaturecombination and were positively correlated with both plant shoot/rootratio and relative growth rate. The data suggest that nutrientuptake rates were influenced primarily by plant demand, withno indication of specific nutrient limitations at low temperatures. Nutrient accumulation, relative growth rate (RGR), rye, Secale cereale cv. Rheidol, temperature, thermal time, Triticum aestivum cv. Mardler, wheat     

Shoot--root Plasticity and Episodic Growth in Red Pine Seedlings

Red pine seedlings of a half-sib seed source were grown in growthchambers under thermoperiodic regimes of 30/20 °C, 25/15°C and 20/10 °C day/night temperatures. Classical growthanalyses based on weekly harvests of leaves, stem and rootswere employed to study the first 3 to 15 weeks of seedling development.Leaf and root growth were inversely related and episodic. Significantshort term surges in growth of either organ were effective inreversing periodic imbalances that occurred, thus maintaininga long term dry weight equilibrium between above and below groundseedling parts. Adaptive plasticity in the leaf-root balanceat different temperatures gave plants grown at 25/15 °Ca larger proportion of leaves relative to roots and a greatersize compared to seedlings grown under other regimes. Episodicfluctuations in leaf and root growth occurred simultaneouslywith depressions in net assimilation rate. Apparently, balancedgrowth is maintained at an assimilatory cost to the plant, periodic‘corrections’ of shoot—root imbalances requiringcarbohydrate conversion and energy expenditure. Pinus resinosa Ait., red pine, episodic growth, shoot—root balance, plasticity, net assimilation rate, growth analysis     

Differential responses of Arabidopsis ecotypes to cold, chilling and freezing temperatures

Arabidopsis plants show an increase in freezing tolerance in response to exposure to low nonfreezing temperatures, a phenomenon known as cold acclimation. In the present study, we evaluated the physiological and morphological responses of various Arabidopsis ecotypes to continuous growth under chilling (14°C) and cold (6°C) temperatures and evaluated their basal freezing tolerance levels. Seedlings of Arabidopsis plants were extremely sensitive to low growth temperatures: the hypocotyls and petioles were much longer and the angles of the second pair of true leaves were much greater in plants grown at 14°C than in those grown at 22°C, whereas just intermediate responses were observed under the cold temperature of 6°C. Flowering time was also markedly delayed at low growth temperatures and, interestingly, lower growth temperatures were accompanied by longer inflorescences. Other marked responses to low temperatures were changes in pigmentation, which appeared to be both ecotype specific and temperature dependent and resulted in various visual phenotypes such as chlorosis, necrosis or enhanced accumulation of anthocyanins. The observed decreases in chlorophyll contents and accumulation of anthocyanins were much more prominent in plants grown at 6°C than in those grown at 14°C. Among the various ecotypes tested, Mt‐0 plants markedly accumulated the highest levels of anthocyanins upon growth at 6°C. Freezing tolerance examination revealed that among 10 ecotypes tested, only C24 plants were significantly more sensitive to subzero temperatures. In conclusion, Arabidopsis ecotypes responded differentially to cold (6°C), chilling (14°C) and freezing temperatures, with specific ecotypes being more sensitive in particular traits to each low temperature.     

Use of the Plastochron Index to Evaluate Effects of Light, Temperature and Nitrogen on Growth of Soya Bean (Glycine max L. Merr.)

The plastochron index (PI) has been compared with leaf growthand biomass accumulation in young soya bean plants of severalcultivars that were grown in controlled environments with differentirradiance levels and durations, temperatures, and nitrogen(N) regimes. Increasing the photoperiod from 10 to 16 h day^–1 increasedthe plastochron rate (PR) and the proportion of axillary growth.Doubling the photosynthetic photon flux density (PPFD) to 1000µmol m^–2S^–1, increased PR and the proportionof roots to total plant weight, but decreased the proportionof stems plus petioles to total. In a series of experiments,the plants were grown in an 8 h photoperiod at constant temperaturesof 17, 20, 26 or 32 °C. As temperature increased, PR increased,but the duration of leaf expansion decreased. Leaves were largestat 20 and progressively smaller at 26, 32 and 17 °C. Biomasswas greatest for a given PI at 20 °C and decreased in theorder of 26, 32, and 17 °C. The proportion of axillary growthalso was greatest at 20 °C. When plants were grown in a15 h photoperiod at temperatures from 17.1 to 26.6 °C, leafsize continued to increase up to the highest temperature. At17 °C, the PR in the 15 h photoperiod (PPFD 390 µmol;m^–2S^–1) was about threefold greater than in 8 h(500 µmol m^–2 S^–1); biomass accumulation perday was about fivefold greater. Increasing N from 3 to 36 mMincreased PR about 10 per cent, altered biomass partitioningamong plant parts, and increased the biomass of the plants.The NO₂ form of N markedly stimulated axillary growth as comparedwith the NH₄⁺ form. Environment or cultivar had little influenceon the duration of leaf expansion in terms of PI. Cultivarsdid not differ consistently in biomass production and allocationin the different environments. Glycine max (L.) Merrill, soybean, soya bean, plastochron index, leaf development, growth analysis, partitioning, light, nitrogen, temperature     

Leaf movement of bush bean: a biometeorological perspective

 Leaf movements of bush bean plants were studied at the relatively low photon flux density of 0.2 mmol/m² per s, and air temperatures of 25° and 35° C in a growth chamber. A beta-ray gauge system was used to monitor continuously pulvinus water status and bending. Leaf angles were below the horizontal and were linearly related to the soil water content (R≥−0.91 at 25° C and R≥−0.93 at 35° C). The beta-ray transmission maxima coincided with the stem temperature minima in darkness and vice versa when brightness prevailed as the growth chamber temperature varied with the photoperiod. Leaf angle increased linearly with increased beta-ray transmission. The Q₁₀ temperature coefficient, a measure of the metabolic energy requirement for leaf movement between 25° and 35° C was estimated at 1.8, and the corresponding mean Arrhenius constant at 423 kJ/mol for bush bean. Received: 19 July 1996 / Accepted: 9 September 1996     

Growth Reductions of Rice at Low Root Temperature: Decreases in Nutrient Uptake and Development of Chlorosis

The physiological mechanisms for growth reductions of rice atlow root temperatures were investigated in detail via time coursesin nutrient status of several cultivars. During short-term exposureto low temperature, i.e. between 0–2.5 d with roots at10°C, leaf extension rates were reduced approximately 80%-95%in all cultivars. In contrast, relative growth rates of shootson a dry weight basis were often even greater for plants withroots at 10°C relative to 30°C. During long-term growthat low root temperatures, i.e. between 2.5–10 d, relativegrowth rates of shoots were reduced, chlorosis developed andcultivar differences were observed which were consistent withfield observations of cold-tolerant and cold-intolerant cultivars. The results indicate that decreases in nutrient concentrationsin plants could not account for growth reductions during short-termexposure to low root temperatures. However, it is possible thatthey are responsible for most of the growth reductions and chlorosislater than 2.5 d. The latter suggestion is not proven unequivocallybut is supported by: (i) similar results when plants were transferredto CaSO⁴ solutions at 30°C in terms of growth, nutrientdecreases with time and chlorosi (ii) N and sometimes P concentrationsfalling below critical levels for rice and (iii) lower nutrientuptakes and concentrations, particularly of N, in a cold-intolerantthan a cold-tolerant cultivar. Key words: Root temperature, growth, rice, nutrient uptake     

Cultivar Differences in the Performance of Bean Seedlings at Suboptimal Temperatures

Growth analysis of plants raised under controlled environments(10–5, 12, 15, 18 and 20 °C, and 21 h photoperiod)was used to examine whether varietal differences in the minimumgermination temperature of four bean cultivars persist duringgrowth at suboptimal temperatures. A method to estimate theminimum vegetative growth temperature, based on axis relativegrowth rate, was developed. In order to compensate for ontogeneticdrift, the harvests were conducted at the same stage of developmentof the plants. Axis relative growth rates, reduction rates ofthe cotyledons and other growth parameters were calculated inorder to compare the cultivars. Cultivar ‘Marschall’showed better growth potential at 12 °C than the others,‘Pergousa‘ at 15 °C, and ‘Marschall’,‘Olsok’ and ‘Pergousa’ at 18 and 20°C. The effect of temperature on axis RGR was similar for‘Marschall’, ‘Olsok’ and ‘Pergousa’(Q₁₀ = 2·1) and more pronounced than for ‘Processor’(Q₁₀ = 1·3). Although there were significant differencesin the growth parameters among the cultivars within each temperatureused, the differences did not correspond with the differencesduring germination at low temperatures. The minimum vegetativegrowth temperature was close to 10 °C for all the cultivarstested. Phaseolus vulgaris L., beans, suboptimum temperature, growth analysis, minimum germination temperature, minimum vegetative growth temperature     

Transpiration and Photosynthesis in Soybean: EFFECTS OF TEMPERATURE AND VAPOUR PRESSURE DEFICIT

Continuous and simultaneous measurements of CO₂ exchange andtranspiration rates of whole soybean plants were made undercontrasting, controlled environmental conditions for periodsof up to 3 d. Daytime temperatures and vapour pressure deficits(VPD) were 27.5 °C/12 mb; 27.5 °C/5 mb; 22.5 °C/12mb, and 22.5 °C/5 mb. Night temperatures were 5°C lowerthan day temperatures and night VPD was 2.7 mb and 3.5 mb atthe higher and lower temperature respectively. The experimentalconditions were virtually the same as those under which theplants had been grown. Transpiration rates were higher at the higher VPD but were alsoinfluenced by temperature. At 12 mb VPD the rates were 16 percent lower at 22.5 °C than at 27.5 °C. Temperature hadno effect on the transpiration rate at 5 mb VPD. Photosynthesis rates were lower at 5 mb VPD than at 12 mb VPDat both temperatures: the difference was substantially greater(c. 70 per cent) at 22.5 °C. Under all treatments meso-phyllresistance (r'_m) appeared to have a major effect on the photosyntheticrate, and varied more than twofold between treatments. r'_m washighest in plants grown at 22.5 °C/5 mb VPD and lowest at27.5 °C/12 mb VPD.     

The Influence of Water Deficit on the Factors Controlling the Daily Pattern of Growth of Phaseolus Trifoliates

Phaseolus seedlings were grown in liquid culture under controlledtemperature and irradiance and measurements were made of dailyvariation in growth of the first trifoliate leaves. Leaf growthrate was significantly enhanced within a few hours of the startof the light period. Over a similar time, a small decrease inleaf turgor and an increase in cell wall plasticity were recorded.Slowly declining growth rates as the light period progressedmay have been caused by decreases in turgor during this time.When water availability to the leaves was restricted by growingthe plants for several days in nutrient solution maintainedat a low temperature (12°C), the daily pattern of growthof the trifoliates was changed quite markedly. Dark-growth rateswere slightly enhanced, while light-growth rates were significantlyreduced when compared to growth rates of plants well-suppliedwith water (roots at 20°C). Relative ‘plateau’growth rates of plants well-supplied (ww) with water or sufferinga restricted supply (ws) in the light (L) and in the dark (D)were as follows: ww L > ws D > ww D > ws L. In thelight, turgors of the two groups of plants were similar, suggestingthat the reduced growth rate of the cooled plants resulted froma change in cell wall structure and/or properties. Immediatelybefore the lights were switched on, plants grown with a restrictedwater supply showed relatively high turgors in the trifoliatesand these were presumably responsible for the enhanced growthrates at this time. Restriction of water availability may haveslightly increased the plasticity of cell walls and decreasedthe yield threshold for growth. The control of leaf growth inplants developing water deficit is discussed. Key words: Leaf growth turgor, Cell wall plasticity, Water deficit, Light     

Changes in the Distribution of 14C-Labelled Assimilates in Sugar-beet with Variation of Temperature

Plants were allowed to assimilate ¹⁴CO₂ for 30 min at 5, 15,25, and 35 °C. The changes in ¹⁴C content of a mature expandedleaf (Leaf 4), young apical leaves, and storage root, were sequentiallyfollowed over a subsequent period of 24 h in continuous light.In a second experiment plants were transferred after ¹⁴CO₂ assimilationto temperatures of 10, 18, 26, and 34 °C, and the partitionof ¹⁴C between the ethanol-soluble and ethanol-insoluble fractionsof the roots and leaves was followed over a period of 72 h. The specific activities of the apical leaves and of the storageroot increased to a maximum 2 h after labelling at 25 °C,4 h at 15 and 35 °C, and 6 h at 5 °C suggesting thatthe optimum temperature for translocation of photosynthate wasabout 25 °C. The ¹⁴C partition to ethanol-soluble and ethanol-insoluble fractionsof the roots and leaves was largely attained in. 9 h. Littlerepartition of ¹⁴C assimilate fractions occurred as a resultof temperature change or growth. Root ethanol-insoluble activity,however, did increase significantly over the 72-h period : possiblecauses of this slow incorporation and their relevance to themechanism of sugar storage are discussed.     

The influence of temperature and nitrogen source on growth and nitrogen uptake of two polar-desert species,Saxifraga caespitosa and Cerastium alpinum

Polar-desert plants experience low average air temperatures during their short growing season (4–8 °C mean July temperature). In addition, low availability of inorganic nitrogen in the soil may also limit plant growth. Our goals were to elucidate which N sources can be acquired by polar-desert plants, and how growth and N-uptake are affected by low growth temperatures. We compared rates of N-uptake and increases in mass and leaf area of two polar-desert species (Cerastium alpinum L. and Saxifraga caespitosa L.) over a period of 3 weeks when grown at two temperatures (6 °C vs. 15 °C) and supplied with either glycine, NH₄ ⁺ or NO₃ ⁻. At 15 °C, plants at least doubled their leaf area, whereas there was no change in leaf area at 6 °C. Measured mean N-uptake rates varied between 0.5 nmol g⁻¹ root DM s⁻¹ on glycine at 15 °C and 7.5 nmol g⁻¹ root DM s⁻¹ on NH₄ ⁺ at 15 °C. Uptake rates based upon increases in mass and tissue N concentrations showed that plants had a lower N-uptake rate at 6 °C, regardless of N source or species. We conclude that these polar-desert plants can use all three N sources to increase their leaf area and support flowering when grown at 15 °C. Based upon short-term (8 h) uptake experiments, we also conclude that the short-term capacity to take up inorganic or organic N is not reduced by low temperature (6 °C). However, net N-uptake integrated over a three-week period is severely reduced at 6 °C. This revised version was published online in June 2006 with corrections to the Cover Date.