Energetic Costs of Tissue Construction in Yellow-poplar and White Oak Trees Exposed to Long-term CO2Enrichment

Two methods were used to estimate construction costs for leaves,stems, branches and woody roots of yellow-poplar (LiriodendrontulipiferaL.) trees grown at ambient (35 Pa) and elevated (65Pa) CO₂for 2.7 years and trees of white oak (Quercus albaL.)grown at these same CO₂partial pressures for 4 years. Samplecombustion in a bomb calorimeter combined with measurementsof ash and nitrogen content provided the primary method of estimatingtissue construction costs (W_G; g glucose g^-1dry mass). Thesevalues were compared with a second, simpler method in whichcost estimates were derived from tissue ash, carbon and nitrogencontent (V_G). Estimates of W_Gwere lower for leaves, branchesand roots of yellow-poplar and for leaves of white oak grownat elevated compared with ambient CO₂partial pressures. TheseCO₂-induced differences in W_Granged from 3.7% in yellow-poplarroots to 2.1% in white oak leaves. Only in the case of yellow-poplarleaves, however, were differences in V_Gobserved between CO₂treatments.Leaf V_Gwas 1.46 g glucose g^-1dry mass in ambient-grown treescompared with 1.41 g glucose g^-1dry mass for CO₂-enriched trees.Although paired-estimates of W_Gand V_Gclustered about a 1:1 linefor leaves and branches, estimates of V_Gwere consistently lowerthan W_Gfor stems and roots. Construction costs per unit leafarea were 95 g glucose m^-2for yellow-poplar trees grown at ambientCO₂and 106 g glucose m^-2for trees grown at elevated CO₂partialpressures. No differences in area-based construction costs wereobserved for white oak. Whole-plant energy content was 1220g glucose per tree in ambient-grown white oak compared with2840 g glucose per tree for those grown at elevated CO₂partialpressures. These differences were driven largely by CO₂-inducedchanges in total biomass. We conclude that while constructioncosts were lower at elevated CO₂partial pressures, the magnitudeof this response argues against an increased efficiency of carbonuse in the growth processes of trees exposed to CO₂enrichment. Bomb calorimeter; construction costs; elevated CO₂; energy allocation; global change; growth respiration; heat of combustion; respiration; Liriodendron tulipifera; Quercus alba     

Studies on the Movement of Water Through Apple Trees

Resistances to the flow of water through young potted appletrees were estimated by measuring the transpiration rate oftrees with and without root systems. Root system resistanceswere obtained by difference. Whole-plant resistances were ofthe order 10 x 10¹³ Pa s m^–3 and there was some evidencethat root resistances (R_r) varied with transpiration rate; theratio R_r:R_x (where R_x is resistance to water flow in the stemsystem) altered from 2:1 at relatively high transpiration ratesto 1:1 at lower rates. The trunk of a 9-year-old orchard tree (trunk diameter {smalltilde}7 cm, height {small tilde}2.5 m) was cut under water andestimates of the flow resistances in this tree were obtained.These were much lower than the resistances to flow in the pottedtrees. Capacitance (defined as the change in stored water content perunit change in plant water potential) values were calculatedfor the small trees and the large tree from measurements ofweight and water potential changes after the trees were removedfrom water. They were very similar on a weight basis (approx.2.0 x 10^–8 kg kg^–1 Pa^–1). Leaf capacitancevalues ({small tilde}1 x 10^–8 kg Pa^–1 m^–2)were also obtained. Stomatal conductances decreased with water potential and increasedwith short-wave radiation, but the relationships were not definitive.Estimates of boundary layer conductance in a greenhouse (verylow wind speeds) were of the same order ({small tilde}5 mm s^–1)as values obtained previously.     

CO2 efflux, CO2 concentration and photosynthetic refixation in stems of Eucalyptus globulus (Labill.)

In spite of the importance of respiration in forest carbon budgets,the mechanisms by which physiological factors control stem respirationare unclear. An experiment was set up in a Eucalyptus globulusplantation in central Portugal with monoculture stands of 5-year-oldand 10-year-old trees. CO₂ efflux from stems under shaded andunshaded conditions, as well as the concentration of CO₂ dissolvedin sap [CO₂^*], stem temperature, and sap flow were measuredwith the objective of improving our understanding of the factorscontrolling CO₂ release from stems of E. globulus. CO₂ effluxwas consistently higher in 5-year-old, compared with 10-year-old,stems, averaging 3.4 versus 1.3 µmol m^–2 s^–1,respectively. Temperature and [CO₂^*] both had important, andsimilar, influences on the rate of CO₂ efflux from the stems,but neither explained the difference in the magnitude of CO₂efflux between trees of different age and size. No relationshipwas found between efflux and sap flow, and efflux was independentof tree volume, suggesting the presence of substantial barriersto the diffusion of CO₂ from the xylem to the atmosphere inthis species. The rate of corticular photosynthesis was thesame in trees of both ages and only reduced CO₂ efflux by 7%,probably due to the low irradiance at the stem surface belowthe canopy. The younger trees were growing at a much fasterrate than the older trees. The difference between CO₂ effluxfrom the younger and older stems appears to have resulted froma difference in growth respiration rather than a differencein the rate of diffusion of xylem-transported CO₂. Key words: Eucalyptus globulus, refixation, stem respiration Received 19 May 2008; Revised 14 September 2008 Accepted 8 October 2008     

Stem Diameter Growth of Scots Pine Trees after Increased Mechanical Load in the Crown during Dormancy and (or) Growth

A field experiment with a 2 x2 factorial block design (W_xS_x)was conducted in northern Sweden where the mechanical loadsin the crowns of sixteen 2.5m high Scots pine (Pinus sylvestrisL.)trees were increased during one winter (W₁, dormant period)and (or) summer (S₁, growth period). Trees treated were loadedwith five 2kg bags hung over mid-crown branches close to thestem, i.e. 10kg per tree. After treatment, all trees were leftto grow untreated for one additional year. Trees were then cutat ground level and annual ring widths for the last 5 yearswere measured on stem discs taken at 1, 5, 10, 15, 20, 30 and50% of tree height. Differences between treatments were analysedwith two-way factorial ANOVA. Accumulated treatment responsewas positive for winter loading (W₁S_x) at all levels, and statisticallysignificant at 1, 15 and 20% of tree height. Summer loading(W_xS₁) had positive effects at the lowest and middle parts ofthe stem, and negative in between. No statistically significanttwo-way interaction (W xS) was observed. Results support thehypothesis that Scots pine trees can retain information aboutmechanical forces acting on their stems during winter, and respondto this during the following growth period. The results alsosuggest that stem form of trees in boreal forests may be stronglyaffected by winter conditions. Stem form; mechanical perturbation; Scots pine; Pinus sylvestris; dendrometer; diameter; growth; dormancy; thigmomorphogenesis; wind; sway     

Atmospheric ozone affects carbohydrate allocation and winter hardiness of Pinus halepensis (Mill.)

Fumigation of 2 year-old Aleppo pine (Pinus halepensis Mill.)trees with episodes of O₃ (up to 120 nl l^– as comparedto 25 nl l^–) throughout two summer seasons produces tallerplants with greater stem diameters but reduced root:shoot ratios.Both light and electron microscopy of current year needles carriedout at mid-summer reveal extensive accumulations of starch,particularly in the endodermis, and crushing of the phloem sievecells. Parallel measurements of starch levels also reveal anon-mobilizable component. All these features probably indicatethat episodes of high summer O₃ detrimentally affect the normalability of Aleppo pines to withstand severe water stress andthis may account for their reduced vitality in Mediterraneanregions. By autumn, however, the amounts of starch are similarto those in low O₃-grown trees and no evidence of the phloemsieve tube crushing remain although plastids do show increasednum bers of plastoglobull. Similar summer high level O₃-fumigatedneedles also show enhanced winter hardiness in the autumn whichis unusual for conifers. Key words: Pinus halepensis, Aleppo pine, amyloplasts, ozone, plastoglobuli, starch     

Above- and Below-ground Production of Young Scots Pine (Pinus sylvestris L.) Trees after Three Years of Growth in the Field under Elevated CO2

Scots pine (Pinus sylvestris L.) seedlings were grown for 3years in the ground in open top chambers and exposed to twoconcentrations of atmospheric CO₂(ambient or ambient + 400 µmol mol^-1) without addition of nutrients and water. Biomassproduction (above-ground and below-ground) and allocation, aswell as canopy structure and tissue nitrogen concentrationsand contents, were examined by destructive harvest after 3 years.Elevated CO₂increased total biomass production by 55%, reducedneedle area and needle mass as indicated, respectively, by lowerleaf area ratio and leaf mass ratio. A relatively smaller totalneedle area was produced in relation to fine roots under elevatedCO₂. The proportion of dry matter in roots was increased byelevated CO₂, as indicated by increased root-to-shoot ratioand root mass ratio. Within the root system, there was a significantshift in the allocation towards fine roots. Root litter constituteda much higher fraction of fine roots in trees grown in the elevatedCO₂than in those grown in ambient CO₂. Growth at elevated CO₂causeda significant decline in nitrogen concentration only in theneedles, while nitrogen content significantly increased in branchesand fine roots (with diameter less than 1 mm). There were nochanges in crown structure (branch number and needle area distribution).Based upon measurements of growth made throughout the 3 years,the greatest increase in biomass under elevated CO₂took placemainly at the beginning of the experiment, when trees grownin elevated CO₂had higher relative growth rates than those grownunder ambient CO₂; these differences disappeared with time.Symptoms of acclimation of trees to growth in the elevated CO₂treatmentwere observed and are discussed. Copyright 2000 Annals of BotanyCompany Elevated CO₂, Pinus sylvestris, biomass production, allocation, fine roots, root litter, crown structure, nitrogen, C/N ratio     

Water content, hydraulic conductivity, and ice formation in winter stems of Pinus contorta: a TDR case study

Stem water content, ice fraction, and losses in xylem conductivity were monitored from November 1996 to October 1997 in an even-aged stand of Pinus contorta (lodgepole pine) near Potlatch, Idaho, USA. A time domain reflectometry (TDR) probe was used to continuously monitor stem water contents and ice fractions. Stem sapwood water contents measured with TDR were not different from water contents measured gravimetrically. The liquid water content of stems ranged from 0.70 m³ m^-3 to 0.20 m³ m^-3 associated with freezing and thawing of the wood tissue. Ice fraction of the stem varied from 0-75% during the winter suggesting liquid water was always present even at ambient temperatures below -20°C. Shoot xylem tensions decreased through the winter to a minimum of ca. -1.4 MPa in February then increased to -0.4 MPa in May. Shoot xylem tensions decreased during the growing season reaching -1.7 MPa by September. Annually, low shoot water potentials were not correlated to decreases in stem hydraulic conductivity. Xylem conductivity decreased due to cavitation through the winter and was 70% of summer values by March. Decreases in xylem conductivity were correlated to low shoot water potentials and cumulative freezing and thawing events within the xylem. Xylem conductivity increased to pre-winter values by May and no reductions in xylem conductivity were observed during the growing season.     

Floodwater Oxygen Content, Ethylene Production and Lenticel Hypertrophy in Flooded Mango (Mangifera indica L.) Trees

A system was developed to test the effects of floodwater O₂concentration on ethylene evolution and stem lenticel hypertrophy,and the effects of exogenous ethylene on stem lenticel hypertrophyin mango (Mangifera indica L.) trees. Dissolved O₂ concentrationsof 1–7x10^–9 m³ m^–3 generally resulted in hypertrophyof stem lenticels within about 6 d of flooding, whereas floodwaterO₂ concentrations of 13–15 x 10^–9 m³ m^–3 delayedhypertrophy until about day 9. After 14d of flooding, therewere more than twice the number of hypertrophied lenticels pertree with floodwater O₂ concentrations of 1–7 x 10^–9m³ m^–3 than with floodwater O₂ concentrations of 15 x10^–9 m³ m^–3. Ethylene evolution from stem tissueimmediately above the floodline increased 4- to 8-fold in treesexposed to floodwater O₂ concentrations of 1–2 x 10^–9m³ m^–3, increased 2-fold for trees exposed to floodwaterO₂ concentrations of 6–7 x 10^–9 m³ m^–3, butremained constant with floodwater O₂ concentrations of 13–15x 10^–9 m³ m^–3. Plants maintained in highly oxygenatedfloodwater (13–15 x 10^–9 m³ m^–3), and givenexogenous ethylene developed many hypertrophied lenticels, whereasplants in highly oxygenated water and not given ethylene developedfewer or nohypertrophied lenticels. These data suggest thatethylene plays a role in promotion of stem lenticel hypertrophyin flooded mango trees, and that floodwater dissolved oxygenconcentration can regulate stem lenticel hypertrophy and ethyleneevolution in this species. Key words: Flooding, hypoxia, hypertrophic cell swelling     

Microclimate, Photosynthesis and Growth of Lucerne (Medicago sativa L.). I. Microclimate and Photosynthesis

Measurements of microclimate and photosynthesis of lucerne var.Europe were made in the field during the spring of 1976. Themaximum rate of canopy gross photosynthesis (14.3 g CO₂ m^–2h^–1, I = ) was 2.5 times greater than that of S 24 perennialryegrass at the same LAI. This difference was due to differencesin individual leaf photosynthesis. The photosynthetic rate ofthe youngest fully expanded leaf of lucerne remained constantthroughout the experimental period at 3.6 g CO₂ m^–2 h^–1(300 W m^–2). Measurements of soil water potential profiles indicated thatlucerne extracted water from the soil to a depth of at least800 mm, with a region of maximum uptake between 400 and 600mm. This capability, with a moderate mean leaf resistance of460 s m^–1, conferred a high assimilation efficiency onlucerne, with a mean water use efficiency of 34 g H₂O lost pergram of carbohydrate assimilated, compared with 200 g H₂O pergram of carbohydrate for S 24. Medicago sativa L, lucerne, photosynthesis, assimilation efficiency     

The Water Relations of Young Olive Trees in a Mediterranean Winter: Measurements of Evaporation from Leaves and Water Conduction in Wood

We report measurements of evaporation rate, leaf resistanceto evaporation and water conduction in the stems of young olivetrees (Olea europea L.) growing in Messina, Italy, during thewinter and early spring. We have measured what Zimmermann calls‘leaf specific conductivity’ (LSC) of stem segmentsexcised from olive trees. The LSC is a measure of the specifichydraulic conductivity of stem segments normalized per unitarea of leaves supplied by the stem segment rather than perunit area of sapwood cross-sectional area. We find that theLSC's of primary stems were the largest followed in magnitudeby the LSC's of secondary stems and tertiary stems. Under winterand early spring conditions the maximum evaporative flux fromCoratina and Nocellara varieties of olive trees is about 2.6x 10^–5 kg 8^–1 m^–2. From this and the LSC measurementswe calculate that the pressure gradients needed to maintainthis rate of evaporation in the steady state is 65 kPa m^–1in primary stems, 170 kPa m^–1 in secondary stems and 560kPa m^–1 in tertiary stems. Olive, Olea europea L, evaporation, leaf specific conductivity, hydraulic conductivity, leaf resistance     

Xylem Hydraulic Characteristics, Water Relations and Wood Anatomy of the Resurrection PlantMyrothamnus flabellifoliusWelw.

Myrothamnus flabellifoliusWelw. is a desiccation-tolerant (‘resurrection’)plant with a woody stem. Xylem vessels are narrow (14 µmmean diameter) and perforation plates are reticulate. This leadsto specific and leaf specific hydraulic conductivities thatare amongst the lowest recorded for angiosperms (k_s0.87 kg m^-1MPa^-1s^-1;k_l3.28x10^-5kg m^-1MPa^-1s^-1, stem diameter 3 mm). Hydraulic conductivitiesdecrease with increasing pressure gradient. Transpiration ratesin well watered plants were moderate to low, generating xylemwater potentials of -1 to -2 MPa. Acoustic emissions indicatedextensive cavitation events that were initiated at xylem waterpotentials of -2 to -3 MPa. The desiccation-tolerant natureof the tissue permits this species to survive this interruptionof the water supply. On rewatering the roots pressures thatwere developed were low (2.4 kPa). However capillary forceswere demonstrated to be adequate to account for the refillingof xylem vessels and re-establishment of hydraulic continuityeven when water was under a tension of -8 kPa. During dehydrationand rehydration cycles stems showed considerable shrinking andswelling. Unusual knob-like structures of unknown chemical compositionwere observed on the outer surface of xylem vessels. These maybe related to the ability of the stem to withstand the mechanicalstresses associated with this shrinkage and swelling.Copyright1998 Annals of Botany Company cavitation, desiccation, hydraulic conductivity, refilling, resurrection plant, root pressure, xylem anatomy,Myrothamnus flabellifolius     

Dynamics of Carbon Photosynthetically Assimilated in Nodulated Soya Bean Plants under Steady-state Conditions 2. The Incorporation of 13C into Carbohydrates, Organic Acids, Amino Acids and some Storage Compounds

Nodulated soya bean (Glycine max L.) plants at the early floweringstage were allowed to assimilate ¹³CO₂ under steady-state conditions,with a constant ¹³C abundance, for 8 h in the light. The plantswere either harvested immediately or 2 d after the end of the¹³CO₂ feeding, divided into young leaves (including flower buds),mature leaves, stems+petioles, roots and nodules; the ¹³C abundancein soluble carbohydrates, organic acids, amino acids, starchand poly-ß-hydroxybutyric acid was determined witha gas chromatography-mass spectrometry. The rapid turnover of ¹³C in the sucrose pools observed in allorgans of the plants showed that sucrose was the principal materialin the translocation stream of primary products of photosynthesis.At the end of the ¹³CO₂ exposure, sucrose in the mature leavesas the major source organs and in the stems+petioles was labelledwith currently assimilated carbon to about 75 per cent, whereasa much higher labelling of sucrose was found in the roots andin the nodules. This suggests the existence of two or more compartmentedpools of sucrose in mature leaves and also in stems+petioles. The relative labelling patterns of individual organic acidsand amino acids were similar in various plant organs. However,the rapid turnover of succinate and glycine was characteristicof nodules. Treatment with a high concentration of nitrate inthe nutrient media increased the turnover rate of amino acidcarbon in shoot organs and roots, while it markedly decreasedthe labelling of amino acids in nodules. The cyclitols, exceptfor D-pinitol, were significantly labelled with assimilated¹³C in mature leaves, but in nodules, the labelling was verymuch less. In the nodules, which were actively fixing atmospheric nitrogen,a large proportion (80–90 per cent) of currently assimilatedcarbon was found as sucrose and starch at the end of the ¹³CO₂feeding. This was also true of the roots. On the other hand,in young growing leaves, the distribution of currently assimilatedcarbon into sucrose, starch and other soluble compounds wasmuch less. This suggests that a large amount of carbon assimilatedby and translocated to young leaves was used to make up structuralmaterials, mainly protein and cell wall polymers synthesis,during the light period. Glycine max L., soya bean, ¹³CO₂ assimilation, carbon metabolism in nodules     

Components of Growth and Dark Respiration of Kikuyu (Pennisetum clandestinum Chiov.) at Various Temperatures

Growth and dark respiration were measured in dense, miniatureswards of kikuyu grass grown at constant temperatures of 15,20, 25 and 30 °C. Total respiration over the first 12 hof darkness was very high and CO² efflux per unit surface areavaried from 2.4 to 3.9 g CO₂ m^–2 h^–1 at 15 and 30°C respectively. Such rates were consistent with the correspondinglyhigh net growth rates of 24 and 63 g d. wt m^–2 d^–1and the heavy yields of herbage. When plants were kept in thedark, CO₂ efflux subsequently declined rapidly to a lower, constantrate which was taken to be the maintenance respiration rate.The half-life of the declining phase of respiration averaged10.9 and 6.0 h at 15 and 30 °C respectively, and was curvilinearlyrelated to the specific maintenance respiration rate (m). Therapid decline in respiration was consistent with the low concentrationsof total soluble carbohydrate and starch in the herbage. Valuesof m for lamina and top growth increased with temperature witha Q₁₀ of 2.6 and 1.42 respectively, but m of stems alone wasnot affected by temperature. Using results from this study forkikuyu and from McCree (1974) for sorghum and white clover,it was noted that all three species have similar m when grownat temperatures which are near their respective optimums forgrowth. Kikuyu, Pennisetum clandestinum, growth, respiration, temperature     

C3 and CAM Photosynthetic Characteristics of the Submerged Aquatic Macrophyte Littorella uniflora: Regulation of Leaf Internal CO2 Supply in Response to Variation in Rooting Substrate Inorganic Carbon Concentration

The relationships between CO₂ concentrating mechanisms, photosyntheticefficiency and inorganic carbon supply have been investigatedfor the aquatic macrophyte Littorella uniflora. Plants wereobtained from Esthwaite Water or a local reservoir, with thelatter plants transplanted into a range of sediment types toalter CO₂ supply around the roots. Free CO₂ in sediment-interstitial-waterranged from 1–01 mol m^–3 (Esthwaite), 0.79 mol m^–3(peat), 0.32 mol m^–3 (silt) and 0–17 mol m^–3(sand), with plants maintained under PAR of 40 µmol m^–2s^–1. A comparison of gross morphology of plants maintained underthese conditions showed that the peat-grown plants with highsediment CO₂ had larger leaf fresh weight (0–69 g) andtotal surface area (223 cm² g^–1 fr. wt. including lacunalsurface area) than the sand-grown plants (0.21 g and 196 cm²g^–1 fr. wt. respectively). Root fresh weights were similarfor all treatments. In contrast, leaf internal CO₂ concentration[CO₂], was highest in the sand-grown plants (2–69 molm^–3, corresponding to 6.5% CO₂ in air) and lowest inthe Esthwaite plants (1–08 mol m^–3). Expressionof CAM in transplants was also greatest in the low CO₂ regime,with H⁺ (measured as dawn-dusk titratable acidity) of 50µmolg^– fr. wt., similar to Esthwaite plants in natural sediment.Assuming typical CAM stoichiometry, decarboxylation of malatecould account largely for the measured [CO₂]₁ and would makea major contribution to daytime CO₂ fixation in vivo. A range of leaf sections (0–2, 1–0, 5–0 and17–0 mm) was used to evaluate diffusion limitation andto select a suitable size for comparative studies of photosyntheticO₂ evolution. The longer leaf sections (17.0 mm), which weresealed and included the leaf tip, were diffusion-limited witha linear response to incremental addition of CO₂ and 1–0mol m^–3 exogenous CO₂ was required to saturate photosynthesis.Shorter leaf sections were less diffusion-limited, with thegreatest photosynthetic capacity (36 µmol O₂ g^–1 fr. wt. h^–1) obtainedfrom the 1.0 mm size and were not infiltrated by the incubatingmedium. Comparative studies with 1.0 mm sections from plants grown inthe different sediment types revealed that the photosyntheticcapacity of the sand-grown plants was greatest (45 µmolO₂ g^–1 fr. wt. h^–1) with a K_0.5 of 80 mmol m^–3.In terms of light response, saturation of photosynthesis intissue slices occurred at 850–1000 µmol m^–2s^–1 although light compensation points (6–11 µmolm^–2s^–1) and chlorophyll a: b ratios (1.3) were low.While CO₂ and PAR responses were obtained using varying numbersof sections with a constant fresh weight, the relationshipsbetween photosynthetic capacity and CO₂ supply or PAR were maintainedwhen the data were expressed on a chlorophyll basis. It is concludedthat under low PAR, CO₂ concentrating mechanisms interact inintact plants to maintain saturating CO₂ levels within leaflacunae, although the responses of the various components ofCO₂ supply to PAR require further investigation. Key words: Key words-Uttorella uniflora, internal CO₂ concentration, crassulacean acid metabolism, root inorganic carbon supply, CO₂ concentrating mechanism     

Modelling the Seasonal Nitrogen Partitioning in Young Sycamore (Acer pseudoplatanus) Trees in Relation to Nitrogen Supply

A model of nitrogen partitioning during the seasonal growthof sycamore (Acer pseudoplatanus) seedlings was developed andtested against data from trees grown with two contrasting levelsof nitrogen supply. The model considered each tissue type (roots,trunk, stems and leaves) as sources and sinks for nitrogen andused flow equations to simulate the dynamics of nitrogen partitioningduring a growing season, with increases in tissue dry matteras driving force variables. Withdrawal of nitrogen from leavesduring senescence was allocated back to other tissues assuminga linear decrease in leaf mass. The model was fitted to data from trees grown in sand culturewith 6·0 molN m^-3 (high N) supplied with the irrigation.Model parameters thus determined were used to predict nitrogenpartitioning in trees grown with 1·0 molN m^-3 (low N)in the same year, and for trees from both treatments given eitherhigh or low N during a second year. The model accurately predictedthe nitrogen content of roots and leaves and gave small errorsin the amount of nitrogen partitioned to stems. In contrast,the nitrogen content of the trunks were over-estimated due toa failure to simulate the decreased in nitrogen content foundat the start of the growing season. The ability of the modelto simulate nitrogen partitioning by changes in tissue dry matterin trees of varying size and nitrogen status is discussed andpossible modifications to model partitioning of trunk nitrogenmore accurately suggested.Copyright 1993, 1999 Academic Press Modelling, nitrogen partitioning, ¹⁵N supply, Acer pseudoplatanus (sycamore), young seedlings     

Dynamics of Carbon Photosynthetically Assimilated in Nodulated Soya Bean Plants under Steady-state Conditions 1. Development and Application of 13CO2 Assimilation System at a Constant 13C Abundance

A long-term, steady-state ¹³CO₂ assimilation system at a constantCO₂ concentration with a constant ¹³C abundance was designedand applied to quantitative investigations on the allocationof photoassimilated carbon in nodulated soya bean (Glycine maxL.) plants. The CO₂ concentration in the assimilation chamberand its ¹³C abundance were maintained constant with relativevariances of less than ±0.5 per cent during an 8-h assimilationperiod. At the termination of 8-h ¹³CO₂ assimilation by plantsat early flowering stage, the currently assimilated carbon relativeto total tissue carbon (measured by the degree of isotopic saturation)were for young leaves (including flower buds), 13.9 per cent;mature leaves, 15.7 per cent; stems+petioles, 5.9 per cent;roots, 5.4 per cent and nodules, 6.9 per cent, 48 h after theend of the ¹³CO₂ assimilation period, they were 12.3, 7.5, 7.4,6.8 and 6.1 per cent, respectively. The treatment with a highconcentration of nitrate in the nutrient media significantlydecreased the allocation of ¹³C into nodules. Experiments on¹³CO₂ assimilation by plants at the pod-filling stage were alsoconducted. Labelling by ¹³C was weaker than at the early floweringstage, but an intense accumulation of ¹³C into reproductiveorgans was observed. Glycine max L., nodulated soya bean plants, ¹³CO₂ assimilation, carbon dynamics     

Measuring the Canopy Net Photosynthesis of Glasshouse Crops

A null balance method is described for measuring net photosynthesisof mature canopies of cucumber and other protected crops overperiods of 10 min in a single-span glasshouse (c. 9m x 18m inarea). Accuracy of control of the CO₂ concentration in the greenhouseatmosphere is within ±10 vpm of the normal ambient level(c. 350 vpm). The amounts of CO₂ used in canopy net photosynthesisare measured with linear mass flowmeters accurate to within±0.80g. The total errors incurred in measuring canopynet photosynthesis at an ambient CO₂ level are estimated tobe of the order of ± 1·2% in bright light (350W m^–2, PAR)and ±3·6% in dull light (100W m^–2, PAR). Measurements of the rates of net photosynthesis of a maturecanopy of a cucumber crop were made at near-ambient CO₂ concentrationsover a range (0–350 W m^–2) of natural light fluxdensities. A model of light absorption and photosynthesis applicableto row crops was used to obtain a net photosynthesis versuslight response curve for the cucumber crop. At a light fluxdensity of 350 W m^–2 the fitted value of canopy net photosynthesiswas 2.65 mg CO₂ m^–2s^–1 (equivalent to over 95 kgCO₂ ha^–1h^–1). The results are discussed in relationto the need for CO₂ supplements to avoid depletion in both ventilatedand unventilated glasshouses during late spring and summer. Key words: Glasshouse crops, cucumber, measurement, canopy photosynthesis, light, CO₂     

ASPECTS OF THE LIFE CYCLE, POPULATION DYNAMICS,GROWTH AND SECONDARY PRODUCTION OF THE EDIBLE SNAIL HELIX LUCORUM LINNAEUS, 1758 (GASTROPODA, PULMONATA) IN GREECE

This paper examines the biology and ecology of Helix lucorumL. which lives in mainland Greece, as well as its growth andsecondary production. A demographic study revealed that (a)3 cohorts exist at any time during the year (when adults ofall generations belong to the same cohort) (b) egg-laying andhatching occur during the months of July and August respectively,(c) the most rapid growth takes place during spring. Study ofH. lucorum genitalia in relation to age showed that the snailsaxe sexually mature 3 years after hatching, when the largestdiameter of their shell (D) is equal to or greater than 35 mm Von Bertallanffy's method suggests that Helix lucorum may liveup to 14 years or more in order to reach its possible maximumsize (48.80 mm) The study of relative growth of D in relation to P_s (peristomesurface) of Helix lucorum shows that D grows faster than P_swhen D12.50 mm; juveniles change their growth rate when theirD arrives at 22.05 mm, and growth becomes slower when adultsarrive at 36.27 mm Annual secondary production calculated by the size frequencymethod gave a mean annual density of 3.39 individuals per m²,a mean annual crop (biomass) of 4.04 g-m^–2 and an annualproduction (P) of 5.02 g · m^–2. The annual turnoverratio (P//b) is equal to 1.24 (Received 23 June 1987;     

Frequency and Time-Domain Dielectric Measurements of Stem Water Content in the Arborescent Palm, Sabal palmetto

Two methods for monitoring stem water content in the arborescentpalm, Sabal palmetto by determining its dielectric constantwerecompared. The first approach used an oscillating circuit whosefrequency (40 to 70 kHz) was determined by a parallel-platecapacitor that sandwiched a portion of the stem. The secondtechnique was based on measurement of the velocity of an electromagneticpulse (frequency range of 500 kHz and 1 GHz) propagating withina wave-guide embedded in the stem (Time-Domain Reflectometry,TDR). There was basic agreement in the apparent dielectric constantas determined by the two techniques; both resulted in valuesof approximately 90 when the plant was fully hydrated, fallingto values near 50 when water was withheld for one week. The capacitance technique was non-invasive, but was influencedby temperature fluctuations, and we were unable to calibrateit accurately against stem volumetric water content. Insertionof TDR probes did not lead to tissue damage and determinationof an empirical relationship to volumetric water content allowedquantitative estimates of stem water content. Sensitivity ofTDR to small changes in stem water content was restricted bythe fact that attenuation of the pulse within the stem necessitatedthe use of short (0·125 m) wave guides. Despite this,during periods of high transpiration (>10kg plant^–1d^–1) bi-hourly changes in stemmoisture content were detectable. Key words: Dielectric constant, Sabal palmetto, stem capacitance, time-domain reflectometry, water storage     

千烟洲红壤丘陵区人工针叶林土壤CH4排放通量

 CH₄在温室效应中起着重要作用,为估算中亚热带CH₄的源汇现状,评价森林生态系统对温室效应的影响,采用静态箱-气相色谱法研究了千烟洲红壤丘陵区人工针叶林的土壤CH₄ 排放通量特征及水热因子对其的影响。对2004年9月～2005年12月期间的观测结果分析表明 ：千烟洲人工针叶林土壤总体表现为大气CH₄的吸收汇,原状林地土壤(Forest soil)情况下,CH₄通量的变化为7.67～-67.17μg&;#8226;m^-2&;#8226;h^-1,平均为-15.53μg&;#8226;m^-2&;#8226;h^-1;无凋落物处理(Litter-free)情况下,CH₄通量的变化是9.31～-90.36 μg&;#8226;m^-2&;#8226;h^-1,平均为-16.53μg&;#8226;m^-2&;#8226;h^-1。 二者对土壤CH₄的吸收表现出明显的季节变化规律,秋>夏>冬>春,但无凋落物处理CH₄变化幅度较原状林地土壤大,无凋落物处理吸收高峰出现在10月,最低值出现在翌年3月,原状林地土壤则分别在9月和翌年2月,均提前1个月。对土壤CH₄吸收通量与温度和湿度的相关分析表明： 无论是原状林地土壤还是无凋落物处理情况下,土壤CH₄通量都与地下5 cm的温度和湿度相关性最高。偏相关分析反映了不同季节水热配置对土壤吸收CH₄通量的影响：冬季为12月～翌年2月,温度起主要作用;雨季3～6月,温度作用为主,随着温度的升高而升高,水分作用微弱;7～8月,CH₄吸收通量随着湿度的降低而增加,但高温限制了CH₄的吸收;秋季（9～11月）水热配置适宜,CH₄通量达到高峰值。总之,CH₄吸收通量随着温度的升高和 湿度的降低而增大,但温度过高会抑制其吸收。