Some Effects of Temperature and Substrate Content upon Respiration and the Carbon Balance of Field Beans (Vicia faba L.)

The effects of substrate content and temperature upon the productionof carbon dioxide in the dark were investigated in Vicia fabaand Sorghum vulgare, using the time courses for carbon dioxiderelease. No endogenous rhythms were found. With V. faba at highsubstrate contents, a steady rate of respiration was measuredat low temperatures, suggesting that the rate of respirationis limited by a third factor such as enzyme activity. This steadyrate eventually decreased rapidly. There was a first order rateof decrease with time at higher temperatures. Low substratecontents gave a complex decay. The rate of decrease of the rateof respiration was affected by the initial state of the plantsover the same range of rates. Reasons for this are discussed.The temperature sensitivity of respiration was investigated.The respiration of plants with high substrate contents had alower temperature sensitivity than those with low substratecontents. This was further investigated by measuring the stoichiometryof carbon dioxide production in the dark from total solublecarbohydrate (as hexose equivalent). It is likely that incompletehexose respiration, which occurs at high substrate contents,is less temperature sensitive than complete hexose respirationor the respiration of some other substrate. Vicia faba, Sorghum oulgare, carbon dioxide, respiration, temperature, substrate content     

Short- and Long-Term Inhibition of Respiratory Carbon Dioxide Efflux by Elevated Carbon Dioxide

Dark carbon dioxide efflux rates of recently fully expandedleaves and whole plants of Amaranthus hypochondriacus L., Glycinemax (L.) Merr., and Lycopersicon esculentum Mill. grown in controlledenvironments at 35 and 70 Pa carbon dioxide pressure were measuredat 35 and 70 Pa carbon dioxide pressure. Harvest data and whole-plant24-h carbon dioxide exchange were used to determine relativegrowth rates, net assimilation rates, leaf area ratios, andthe ratio of respiration to photosynthesis under the growthconditions. Biomass at a given time after planting was greaterat the higher carbon dioxide pressure in G. max and L. esculentum,but not the C₄ species, A. hypochondriacus. Relative growthrates for the same range of masses were not different betweencarbon dioxide treatments in the two C₃ species, because highernet assimilation rates at the higher carbon dioxide pressurewere offset by lower leaf area ratios. Whole plant carbon dioxideefflux rates per unit of mass were lower in plants grown andmeasured at the higher carbon dioxide pressure in both G. maxand L. esculentum, and were also smaller in relation to daytimenet carbon dioxide influx. Short-term responses of respirationrate to carbon dioxide pressure were found in all species, withcarbon dioxide efflux rates of leaves and whole plants lowerwhen measured at higher carbon dioxide pressure in almost allcases. Amaranthus hypochondriacus L., Glycine max L. Merr., Lycopersicon esculentum Mill., soybean, tomato, carbon dioxide, respiration, growth     

Responses of Respiration to Increases in Carbon Dioxide Concentration and Temperature in Three Soybean Cultivars

The purpose of this experiment was to determine how respirationof soybeans may respond to potential increases in atmosphericcarbon dioxide concentration and growth temperature. Three cultivarsof soybeans (Glycine max L. Merr.), from maturity groups 00,IV, and VIII, were grown at 370, 555 and 740cm³m^-3carbon dioxideconcentrations at 20/15, 25/20, and 31/26°C day/night temperatures.Rates of carbon dioxide efflux in the dark were measured forwhole plants several times during exponential growth. Thesemeasurements were made at the night temperature and the carbondioxide concentration at which the plants were grown. For thelowest and highest temperature treatments, the short term responseof respiration rate to measurement at the three growth carbondioxide concentrations was also determined. Elemental analysisof the tissue was used to estimate the growth conversion efficiency.This was combined with the observed relative growth rates toestimate growth respiration. Maintenance respiration was estimatedas the difference between growth respiration and total respiration.Respiration rates were generally sensitive to short term changesin the measurement carbon dioxide concentration for plants grownat the lowest, but not the highest carbon dioxide concentration.At all temperatures, growth at elevated carbon dioxide concentrationsdecreased total respiration measured at the growth concentration,with no significant differences among cultivars. Total respirationincreased very little with increasing growth temperature, despitean increase in relative growth rate. Growth respiration wasnot affected by carbon dioxide treatment at any temperature,but increased with temperature because of the increase in relativegrowth rate. Values calculated for maintenance respiration decreasedwith increasing carbon dioxide concentration and also decreasedwith increasing temperature. Calculated values of maintenancerespiration were sometimes zero or negative at the warmer temperatures.This suggests that respiration rates measured in the dark maynot have reflected average 24-h rates of energy use. The resultsindicate that increasing atmospheric carbon dioxide concentrationmay reduce respiration in soybeans, and respiration may be insensitiveto climate warming. Glycine max L. (Merr.); carbon dioxide; respiration; temperature; climate change     

A Comparison of the Rate of Maintenance Respiration in Some Crop Legumes and Tobacco Determined by Three Methods

Carbon exchange was measured on whole plants of field bean,lucerne, chick pea, kidney bean, pea and tobacco. The maintenance respiration rate was measured in three ways:(i) by allowing the CO₂ efflux to decay in prolonged darknessto an asymptotic value which was then taken to be the maintenancevalue (the dark decay method); (ii) by plotting the dark CO₂efflux as a function of the net CO₂ uptake over a range of irradiancesand taking maintenance as the dark CO₂ efflux when the net CO₂uptake was zero (the dynamic method); and (iii) by plottingthe total CO₂ uptake as a function of the growth rate and takingmaintenance respiration as the CO₂ efflux when the growth ratewas zero (the zero growth rate method). The range of valuesfor the maintenance coefficient over all species was from 1.6to 2.1 per cent of the dry weight per day, 1.8 to 2.1 per centand 2.7 to 2.9 per cent as determined by these three methodsrespectively. There was a linear relationship, common to allspecies, between the maintenance respiration rate (dark decaymethod) and dry weight, total nitrogen and the organic nitrogencontent. The growth coefficient (0.69±0.01) was the samefor field bean, chick pea and lucerne and was unaffected bythe method of estimation. It was concluded that the dark decay method provided the bestestimate of the minimal maintenance requirements in the plantsstudied. Vicia faba L., Medicago sativa L., Cicer arientinum L., Phaseolus vulgaris L., Pisum sativum L., Nicotiana tobacum L., field bean, lucerne, chick pea, kidney bean, pea, tobacco, respiration, maintenance, growth, nitrogen content     

The Effect of Ethylene on Quantitative and Qualitative Aspects of Respiration During the Breaking of Dormancy of Spergula arvensis L. Seeds

The effect of ethylene on quantitative and qualitative aspectsof respiration in Spergula arvensis L. seeds was studied. Oxygenconsumption and CO₂ evolution from seeds increased 60 h afteraddition of ethylene to the dry seed; these increases were consideredto be a function of the number of seeds that were germination,rather than a direct effect of ethylene. The respiratory quotient(RQ) on day 1 (0.5) was lower than on subsequent days, indicatingan absence of anaerobic processes in the early stages of germinationand the use of a different respiratory substrate to that oxidizedon days 2–4. Measurements of C₄/C₁ ratios showed thatethylene did not break dormancy by initiating a switch fromthe Embden-Meyerhof-Parnas pathway (EMPP) to the pentose phosphatepathway (PPP). On the contrary, some evidence was obtained fora switch from the PPP to the EMPP after 3–6 h in pre-imbibedand non pre-imbibed seeds treated with ethylene. Spergula arvensis L., seed germination, ethylene, respiration, Embden-Meyerhof-Parnas pathway, pentose phosphate pathway, respiratory quotient     

Carbon Loss from the Roots of Forage Rape (Brassica napus L.) Seedlings Following Pulse-labelling with 14CO2

The loss of organic material from the roots of forage rape (Brassicanapus L.,) was studied by pulse-labelling 25-d-old non-sterilesand-grown plants with ¹⁴CO₂. The distribution of ¹⁴C withinthe plant was measured at 0, 6 and 13 d after labelling whilst¹⁴ C accumulating in the root-zone was measured at more frequentintervals. The rates of ¹⁴C release into the rhizosphere, andloss of ¹⁴CO₂ from the rhizosphere were also determined. Thesedata were used to estimate the accumulative loss of ¹⁴C fromroots and loss respiratory ¹⁴CO₂ from both roots and associatedmicro-organisms. Approximately 17-19% of fixed ¹⁴CO₂ was translocatedto the roots over 2 weeks, of which 30-34% was released intothe rhizosphere, and 23-24% was respired by the roots as ¹⁴CO₂. Of the ¹⁴C released into the rhizosphere, between 35-51%was assimilated and respired by rhizosphere micro-organisms.Copyright1993, 1999 Academic Press Brassica napus L., carbon loss, carbon partitioning, microbial nutrition, microbial respiration, forage rape, pulse-labelling, rhizodeposition, root respiration, sand culture     

Changes in Adenosine Pyrophosphates in Cantaloupe Fruit Ripening Normally and after Treatment with Ethylene

During the climacteric rise in respiration of cantaloupe fruit(Cucumis melo L., var. reticulatus Naud.) the concentrationper gramme fresh weight of adenosine triphosphate (ATP) increasedand that of adenosine diphosphate (ADP) did not change; thusa net synthesis of adenosine pyrophosphate occurs during therespiratory climacteric. A net synthesis of protein which wasobserved was positively correlated with the concentration ofATP. Ethylene treatment stimulated a climacteric-like rise inthe respiration and in the rate of ripening in fruit harvestedat 9 to 32 days after anthesis. The ratio ATP/ADP increasedin fruit ripened with ethylene only when harvested 20 days ormore after anthesis.     

Rates of Respiration and of Increase in Structural Dry Matter in Young Wheat, Ryegrass and Maize Plants in Relation to Temperature, to Water Stress and to Their Sugar Content

A method to determine the rate of conversion of reserve materialsinto structural dry matter in living, whole plants is presented.It is based on a brief measurement of plant respiration. Therate of increase in structural dry matter and of decrease ofreserve materials is calculated by subtracting the maintenancerespiration component from the total respiration. The remainder,the growth respiration rate, is multiplied by a factor thatis derived from the biochemical composition of the structuraldry matter formed. This method is applied to determine the relations of the rateof conversion of reserve material into structural dry matterto temperature, water stress and the level of reserve carbohydratesin plants of three species. The weakest part of the method is in the determination of therate of maintenance respiration. Consequences of different assumptionsconcerning the rate of adjustment of this respiration componentto modified environmental conditions are discussed. Lolium perenne L, Triticum aestivum L, Zea mays L, ryegrass, wheat, maize, respiration, maintenance respiration, water stress, sugar content, structured dry matter     

The Growth and Carbon Economy of Selection Lines of Lolium perenne cv. S23 with Differing Rates of Dark Respiration: 2. Grown as Young Plants from Seed

Young plants of two selection lines of Lolium perenne cv. S23with ‘fast’ and ‘slow’ rates of ‘maturetissue’ respiration were individually grown from seed,together with plants of S23, their common parent, in 9.2 cmpots in a controlled environment at 20/15 °C day/night temperatures. No significant differences were found between the genotypesin leaf extension and tiller production during this early stageof their growth. They did differ however, by an average of 26%,in the rate of dark respiration of fully expanded leaf laminae.The use of a simple model demonstrated that such a differencein respiration could alone account for the different rates ofdry matter production shown by the selection lines when grownas young crops from seed. Possible penalties of ‘slow’respiration are also considered. Lolium perenne L., ryegrass, respiration, maintenance respiration, stimulated swards, leaf growth, tiller production, carbon economy     

Effects of Prolonged Darkness on the Sensitivity of Leaf Respiration to Carbon Dioxide Concentration in C3and C4Species

Predicting responses of plant and global carbon balance to theincreasing concentration of carbon dioxide in the atmosphererequires an understanding of the response of plant respirationto carbon dioxide concentration ([CO₂]). Direct effects of thecarbon dioxide concentration at which rates of respiration ofplant tissue are measured are quite variable and their effectsremain controversial. One possible source of variation in responsivenessis the energy status of the tissue, which could influence thecontrol coefficients of enzymes, such as cytochrome-c oxidase,whose activity is sensitive to [CO₂]. In this study we comparedresponses of respiration rate to [CO₂] over the range of 60to 1000 µmol mol^-1in fully expanded leaves of four C₃andfour C₄herbaceous species. Responses were measured near themiddle of the normal 10 h dark period, and also after another24 h of darkness. On average, rates of respiration were reducedabout 70% by the prolonged dark period, and leaf dry mass perunit area decreased about 30%. In all species studied, the relativedecrease in respiration rate with increasing [CO₂] was largerafter prolonged darkness. In the C₃species, rates measured at1000 µmol mol^-1CO₂averaged 0.89 of those measured at 60µmol mol^-1in the middle of the normal dark period, and0.70-times when measured after prolonged darkness. In the C₄species,rates measured at 1000 µmol mol^-1CO₂averaged 0.79 of thoseat 60 µmol mol^-1CO₂in the middle of the normal dark period,and 0.51-times when measured after prolonged darkness. In threeof the C₃species and one of the C₄species, the decrease in theabsolute respiration rate between 60 and 1000 µmol mol^-1CO₂wasessentially the same in the middle of the normal night periodand after prolonged darkness. In the other species, the decreasein the absolute rate of respiration with increase in [CO₂] wassubstantially less after prolonged darkness than in the middleof the normal night period. These results indicated that increasingthe [CO₂] at the time of measurement decreased respiration inall species examined, and that this effect was relatively largerin tissues in which the respiration rate was substrate-limited.The larger relative effect of [CO₂] on respiration in tissuesafter prolonged darkness is evidence against a controlling roleof cytochrome-c oxidase in the direct effects of [CO₂] on respiration.Copyright 2001 Annals of Botany Company Carbon dioxide, respiration, Abutilon theophrasti(L.), Amaranthus retroflexus(L.),Amaranthus hypochondriacus (L.), Datura stramonium(L.), Helianthus annuus(L.), Solanum melongena(L.), Sorghum bicolor(L. Moench), Zea mays     

The Promoter of the Gene for Glutamine Synthetase from Rice Shows Organ-Specific and Substrate-Induced Expression in Transgenic Tobacco Plants

A 2-kb fragment from the 5'-flanking region of the RGS-28 gene,which encodes the cytosolic glutamine synthetase in Oryza sativaL., was fused to a ß-glucuronidase (GUS) reportergene and introduced into Nicotiana tabacum by Agrobacterium-mediatedtransformation. The promoter was predominantly active in theleaves of transgenic plants, as it is in authentic rice plants.The promoter also responded to externally applied ammonium ions.It is suggested that the cis-acting regulatory elements responsiblefor the recognition of the leaf as a site of synthesis and ofammonia, a substrate for glutamine synthetase, are located withina 2-kb region of the promoter. (Received October 15, 1990; Accepted January 11, 1991)     

Effects of Temperature and Light on the Carbon Budget of Young Cucumber Plants Studied by Steady-State Feeding with 14CO2

Shishido, Y., Challa, H. and Krupa, J. 1987. Effects of temperatureand light on the carbon budget of young cucumber plants studiedby steady-state feeding with ¹⁴CO°₂J. exp. Bot. 38: 1044–1054. The effect of temperature on the fate of ¹⁴C assimilated insteady-state by the expanding third leaf of cucumber seedlingswas studied at irradiances of either 30 or 75 W m^–2 (PAR)with a daylength of 8 h. The irradiance did not affect the relativedistribution of ¹⁴C assimilated by the source leaf between growth,respiration and export. In the range 15–30°C risesin temperature generally increased the proportion of carbonexported. The average rate of carbon exported during the nightwas about half the rate in the day. About 45% of the exportedcarbon was lost by respiration. The distribution pattern ofcarbon exported during the day differed considerably from thatof carbon exported during the night. The intensity of irradiance did not affect the proportion oflabelled carbon recovered from the roots. Thus the decreasedshoot/root ratio generally observed with increased irradianceis not directly controlled by carbohydrate supply. We found that the distribution patterns of exported ¹⁴C do notnecessarily represent the real carbon distribution, due to differencesin specific activity of imported carbon of individual organs.Consequently distribution patterns of ¹⁴C observed in experimentswith one source leaf have to be considered with caution. Key words: Carbon budget, ¹⁴C, ¹⁴C steady-state feeding, translocation, respiration, assimilate distribution, cucumber, temperature     

The Respiration of Mature Field Bean (Vicia faba L.) Leaves During Prolonged Darkness

Dark respiration in attached and detached mature leaves of thefield bean (Vicia faba L.) was studied whilst leaves experiencedup to 60 h of darkness. The results showed: (1) the initialrespiration rate to vary according to the irradiance duringthe previous photoperiod; (2) the dark respiration rate (perunit area) of attached leaves to be essentially constant duringa normal 12 h night although there was a rapid loss in leafd. wt during this time; (3) after 12 h, the respiration rateof attached leaves decayed to an asymptotic value at about 36h; (4) the respiration rate of leaves detached at the end ofthe photoperiod and maintained in the dark on deionised water,decayed only after 36 h of darkness; (5) there was no differencebetween the respiration rate of attached and detached leavesduring the normal 12 h night. It is concluded that the dark respiration of attached fieldbean leaves is intially related to the synthesis and translocationof sucrose in addition to maintenance. After about 36 h, whenthe rate of CO₂ efflux is more or less steady, the CO₂ effluxreflects the intensity of maintenance processes only. The maintenancerespiration rate (determined after 60 h in the dark) rangedfrom 062 to 151 mg CO₂ (g d. wt)^–1 h^–1 but wasrelatively unaffected by several applied treatments. Vicia faba L., field bean, respiration, maintenance, nitrate, non-structural carbohydrate, export     

Respiration and Mitochondrial Activity in Zea mays Roots As Affected by Osmotic Stress

Studies were made of metabolism in highly vacuolated and slightlyvacuolated Zea mays root tissue both during and after plasmolysis. Plasmolysis resulted in decreased respiration and carbon dioxideevolution from glucose and an increased sucrose synthesis. Inhibitionof respiration during plasmolysis in both the highly vacuolatedand slightly vacuolated tissue was not relieved by supply ofglucose, organic acids, or uncouplers of oxidative phosphorylation.Mitochondria isolated from plasmolysed tissue were tightly coupled,but activity in vitro was inhibited by exposure to a high negativeosmotic potential. It is suggested that low TCA cycle activityin vivo must be due either to inhibition of mitochondrial activityor to reduced flow of carbon through the glycolytic pathway. A low potential for TCA cycle activity after deplasmolysis issuggested, as addition of pyruvate stimulated carbon dioxideevolution but not oxygen uptake, which was severely decreased.This was presumably due to severe mitochondrial damage as shownby their activity in vitro. However, it is not clear whetherrespiration in vivo is rate limited by rapid leakage of metabolicintermediate (reported earlier) or by lysis of mitochondria. Deplasmolysis did not damage mitochondria from slightly vacuolatedtissue, a result which was consistent with respiratory measurementsmade in vivo. The data show that mitochondria in vacuolated tissue are damagedduring and after deplasmolysis and not before. It is suggestedthat lysis of mitochondria occurs in vivo as a result of a sharpincrease in the osmotic potential of the cell fluids.     

Vegetable Plant Part Relationships. II. A Quantitative Hypothesis for Shoot/Storage Root Development

A simple quantitative formulation of the concept of the controlof partitioning of assimilated carbon by the behaviour of plantcomponents as competing sinks is developed. An equation, In s = + In r—t, relating shoot (s) and storage root (r) d. wts, and the lengthof growth period (t), is constructed by considering possiblefates of imported assimilates into different plant parts. Thevalues of the equations' parameters depend on the relative sinkactivities of the plant parts, tissue respiration rates andinitial weights of plant components. The equation closely fitteddata collected from a number of carrot and beet experimentsin which planting density had been varied. Estimates of shootand storage root maintenance respiration rates, derived fromthe parameter , were of the correct order of magnitude. Othersets of experimental data are also discussed in the light ofpredictions of the theory and possible uses and extensions ofthis approach to assimilate partitioning are briefly discussed. Daucus carota L., Beta vulgaris, carrot, red beet, partition of assimilated carbon, maintenance respiration, storage root     

Growth Rate, Photosynthesis and Respiration in Relation to Leaf Area Index

This work examined three possible explanations of growth rateresponses to leaf area index (LAI) in which growth rate perunit of ground area (crop growth rate, CGR) increased to a plateaurather than decreasing above an optimum LAI at which all lightwas intercepted. Single leaf photosynthetic measurements, andwhole plant 24 h photosynthesis and respiration measurementswere made for isolated plants and plants in stands using Amaranlhushybridus, Chenopodium album, and two cultivars of Glycine maxgrown at 500 and 1000 µimol m^–2 S^–1 photosyntheticphoton flux density at 25 °C. CGR, relative growth rate(RGR), and LAI were determined from 24 h carbon dioxide exchangeand leaf area and biomass measurements. Respiration increasedrelative to photosynthesis with crowding in A. hybridus andthere was an optimum LAI for CGR. In contrast, the ratio ofrespiration to photosynthesis was constant across plant arrangementin the other species and they had a plateau response of CGRto LAI. Neither increased leaf photosynthetic capacity at highLAI nor a large change in biomass compared to the change inLAI could account for the plateau responses. It was calculatedthat maintenance respiration per unit of biomass decreased withdecreasing RGR in C. album and G. max, but not A. hybridus,and accounted for the plateau response of CGR to LAI. Sincesimilar decreases in maintenance respiration per biomass atlow RGR have been reported for several other species, a constantratio of respiration to photosynthesis may occur in more speciesthan constant maintenance respiration per unit of biomass. Amaranlhus hybridus L., Chenopodium album L., Glycine max L Merr, soybean, photosynthesis, respiration, growth, leaf area index     

Effect of Drought on Metabolism and Partitioning of Carbon in Two Wheat Varieties Differing in Drought-tolerance

A model was constructed to describe the partitioning of carbonon the third and seventh day from anthesis for well-wateredand droughted plants of two wheat varieties (Triticum aestivumL. cv. Warigal and Condor). The glasshouse-grown plants weredetillered so that a simplified model could be derived for themain stem. The 9-d drought treatment, imposed just after anthesisduring the period of cell division in the grains, reduced grainyield by 18 per cent in Warigal and 30 per cent in Condor. Netcarbon fixation was up to 60 per cent higher in Warigal thanCondor towards the end of the drought period and this correlatedwith better osmotic adjustment in the flag leaf. Carbon partitioningbetween plant organs responded to water deficit more rapidlythan net carbon fixation. On day 3, carbon allocation to theroots of droughted plants was maintained in Condor and increasedby 14 per cent in Warigal, whereas carbon allocation to theear decreased in both varieties. However the roots did not competewell with the ear when the water deficit became more severe.Warigal accumulated 3 times more stem reserves than Condor underdrought. In the roots, the pattern of carbon allocation betweenrespiration and carbon accumulation changed soon after impositionof drought. Although total root respiration decreased underdrought it became more energy efficient, particularly for Warigal,as less respiration took place via the alternative pathway.On day 3, the larger carbon allocation to the roots and thelower root respiration accounted for the 4-times larger sugaraccumulation in droughted roots of Warigal compared with thoseof Condor. Osmotic adjustment in mature leaves and roots maybe of importance for the maintenance of vital processes andfor recovery after drought. Triticum aestivum L., wheat, drought, carbon, partitioning     

Respiratory and Carbohydrate Changes in Developing Pea (Pisum sativum L.) Seeds in Relation to their Ability to Withstand Desiccation

In the development of garden pea seeds (P. sativum L., cv. ‘KelvedonWonder’) the ability to withstand desiccation was foundto be preceded by a fall in respiration rate and seed moisturecontent, both of which followed a sharp decline in ethanol-solublesugars. When harvested seeds were kept in high humidity conditionsrespiration was found to decline even though the moisture contentwas maintained. The fall in respiration was always associatedwith a fall in the level of sugars. Further experiments showedthat the seeds whose respiration had fallen in humid storagecould be induced to respire more rapidly by the addition ofsucrose. It is suggested that seeds can only withstand rapid desiccationafter a decrease in physiological activity following a fallin the supply of respiratory substrate in the form of sugars.     

亚热带杉木和马尾松群落土壤系统呼吸及其影响因子

 亚热带杉木(Cunninghamia lanceolata)和马尾松(Pinus massoniana)在我国森林资源中占有十分重要的地位, 研究它们的土壤与表层凋落物的呼吸有助于了解它们的碳源汇时空分布格局及碳循环过程的关键驱动因子。采用Li-Cor 6400-09连接到Li-6400便携式CO2/H2O分析系统测定湖南两种针叶林群落(2007年1月至12月)的土壤呼吸及其相关根生物量和土壤水热因子。研究结果表明: 杉木和马尾松群落中土壤呼吸的季节变化显著, 在季节动态上的趋势相似, 都呈不规则曲线格局, 全年土壤呼吸速率平均值分别为186.9 mg CO₂•m^–2•h^–1和242.4 mg CO₂•m^–2•h^–1。从1月开始, 两种群落的土壤呼吸速率由最小值33.9 mg CO₂•m^–2•h^–1和38.6 mg CO₂•m^–2•h^–1随着气温的升高而升高, 杉木群落到7月底达到全年中最大值326.3 mg CO₂•m^–2•h^–1, 而马尾松群落到8月中旬达到最大值467.3 mg CO₂•m^–2•h^–1, 土壤呼吸的季节变化与土壤温度呈显著的指数相关, 土壤温度可以分别解释土壤呼吸变化的91.7%和78.0%, 和土壤含水量呈二次方程关系, 土壤含水量可以解释土壤呼吸变化的5.4%和8.4%。由土壤呼吸与土壤温度拟合的指数方程计算Q₁₀值, 杉木和马尾松群落中全年土壤呼吸的Q₁₀值分别为2.26和2.13, Q₁₀值随着温度升高逐渐减小。两种群落土壤呼吸的差异主要受群落植被的根生物量、群落的凋落物量的影响。     

Autunmal sedimentation of Microcystis spp. as result of an increase in carbohydrate ballast at reduced temperature

Autumnal sedimentation of the Microcystis population was studiedin Lake Nieuwe Meer (Amsterdam, The Netherlands). In summer,Microcystis formed a high percentage of the total phytoplanktonin the water column, but a low percentage in sedimentation traps.The reverse was found during September and October, with a highpercentage in the sedimentation traps, but a low percentagein the water column. The decrease in the numbers of Microcystiscolonies coincided with a decrease in waler temperature. Inexperiment with a strain of Mirocystis, isolated from Lake NieuweMeer, the percentage of total colonies that were sinking increasedin a few days to 100% after a shift from 20C to 15.3, 13.0or 10.5C. The gas vesicle volume in the cells remained constantduring the incubations. Sinking of the colonies resulted froman increased glycogen content. Calculation of carbon (C) flowsduring the first 2 days of the incubation at reduced temperatureshowed that the glycogen accumulation was the result of a muchlower rate of protein synthesis during the light period at thelower temperatures. Although the photosynthetic rate itselfdecreased at reduced temperature, it resulted in more fixedCO₂ being stored as glucose. Because the respiratory rate alsodecreased (with an almost similar decrease to that of photosynthesis),glycogen accumulated at lower temperatures. It was calculatedthat after an incubation period of-I week at reduced temperature,the rate of photosynthesis had decreased by 10.1% of the valueat 20C per 1C, while the rate of respiration had decreasedonly 1.8%. It is proposed that there is a feedback mechanismin which an increasing concentration of glycogen inhibits photosynthesisand stimulates respiration.