Effects of Constant and Variable Nitrogen Supply on Sunflower (Helianthus annuus L.) Leaf Cell Number and Size

The effects of nitrogen (N) availability on cell number andcell size, and the contribution of these determinants to thefinal area of fully expanded leaves of sunflower (Helianthusannuus L.) were investigated in glasshouse experiments. Plantswere given a high (N =315 ppm) or low (N=21 ppm) N supply andwere transferred between N levels at different developmentalstages (5 to 60% of final size) of target leaves. The dynamicsof cell number in unemerged (< 0.01 m in length) leaves ofplants growing at high and low levels of N supply were alsofollowed. Maximum leaf area (LA_max) was strongly (up to two-fold)and significantly modified by N availability and the timingof transfer between N supplies, through effects on leaf expansionrate. Rate of cell production was significantly (P<0.05)reduced in unemerged target leaves under N stress, but therewas no evidence of a change in primordium size or in the durationof the leaf differentiation–emergence phase. In fullyexpanded leaves, number of cells per leaf (N_cell), leaf areaper cell (LA_cell) and cell area (A_cell) were significantly reducedby N stress. WhileLA_cell and A_cellresponded to changeover treatmentsirrespective of leaf size, significant (P<0.05) changes inN_cellonly occurred when the changeover occurred before the leafreached approx. 10% of LA_max. There were no differential effectsof N on numbers of epidermal vs. mesophyll cells. The resultsshow that the effects of N on leaf size are largely due to effectson cell production in the unemerged leaf and on both cell productionand expansion during the first phase of expansion of the emergedleaf. During the rest of the expansion period N mainly affectsthe expansion of existing cells. Cell area plasticity permitteda response to changes in N supply even at advanced stages ofleaf expansion. Increased cell expansion can compensate forlow N_cellif N stress is relieved early in the expansion of emergedleaves, but in later phases N_cellsets a limit to this response.Copyright 1999 Annals of Botany Company Helianthus annuus, leaf expansion, leaf cell number, leaf cell size, nitrogen, leaf growth, sunflower.     

中国亚热带常绿阔叶林优势种及常见种的水热分布类群

 利用目前国际上比较常用的植被—气候相关分析的气候指标,如Kira的温暖指数和寒冷指数,徐文铎的湿润指数,Penman的可能蒸散和干燥度指标,Thornthwaite的潜在可能蒸散和水分指数,Holdridge生命地带分类系统指标以及气温和降水等单一气候因子,综合对中国亚热带常绿阔叶林优势种及常见种进行TWINSPAN分类和DCA排序,可将植物种分为8个水热分布类群,较好地反映出优势种及常见种沿热量和水分梯度的分布格局。并总结了这8个水热分布类群的气候指标范围。这8个类群是：Ⅰ高温湿润型,Ⅱ高中温湿润型,Ⅲ低中温湿润型,Ⅳ高低温中湿型,Ⅴ低低温中湿型,Ⅵ低温半湿润型,Ⅶ高低温低湿型,Ⅷ低低温低湿型     

Growth Response of a Chrysanthemum Crop to the Environment. III, Effects of Radiation and Temperature on Dry Matter Partitioning and Photosynthesis

Vegetative crops of chrysanthemum were grown for 5 or 6 weekperiods in daylit assimilation chambers. Crop responses to differentradiation levels and temperatures were analysed into effectson dry matter partitioning, specific leaf area, leaf photosynthesisand canopy light interception. The percentage of newly formed dry matter partitioned to theleaves was almost constant, although with increasing radiationor decreasing temperature, a greater percentage of dry matterwas partitioned to stem tissue at the expense of root tissue.There was a positive correlation between the percentage of drymatter in shoot material and the overall carbon: dry matterratio. Canopy photosynthesis was analysed assuming identical behaviourfor all leaves in the crop. Leaf photochemical efficiency wasonly slightly affected by crop environment. The rate of grossphotosynthesis per unit leaf area at light saturation, P_A (max),increased with increasing radiation integral, but the same parameterexpressed per unit leaf dry matter, P_w (max) was almost unaffectedby growth radiation. In contrast, P_A (max) was hardly affectedby temperature but P_w (max) increased with increasing growthtemperature. This was because specific leaf area decreased withdecreasing temperature and increased with decreasing radiation.There was a positive correlation between canopy respirationintegral and photosynthesis integral, and despite a four-foldchange in crop mass during the experiments, the maintenancecomponent of canopy respiration remained small and constant. Canopy extinction coefficient showed no consistent variationwith radiation integral but was negatively correlated with temperature.This decrease in the efficiency of the canopy at interceptingradiation exactly cancelled the increase in specific carbonassimilation rate that occurred with increasing growth temperature,giving a growth rate depending solely on the incident lightlevel. Chrysanthemum, dry matter partitioning, photosynthesis, specific leaf area     

浙江舟山群岛山茶所在群落物种组成及多样性

以山茶Camellia japonica 所在的阔叶林和灌丛群落为研究对象,通过典型样地调查,对物种组成及多样性进行研究。结果表明,8 个植物群落共调查到维管束植物147 种,隶属于65 科118 属;地理成分多样,热带成分大于温带、亚热带成分,表现为亚热带向暖温带过渡的性质,同时反映出群落所在生境热量条件相对优越。山茶所在的阔叶林群落中,乔木层的丰富度和Shannon-Wiener 指数与演替趋势呈明显的负相关关系,处于岛屿较高海拔的灌丛和疏林,其灌木层和藤本层的丰富度和Shannon-Wiener 指数大于阔叶林;受相应群落乔木层的优势种红楠Machilus thunbergii、青冈Cyclobalanopsis glauca 或台湾蚊母树Distylium gracile 以及更新层的舟山新木姜子Neolitsea sericea 优势突出影响,乔木层与更新层的Pielou 指数波动幅度较大。     

The Greenhouse Effect: Acclimation of Tomato Plants Growing in High CO2, Photosynthesis and Ribulose-1, 5-Bisphosphate Carboxylase Protein

Tomato plants were grown in solution culture in a controlledenvironment at 20 ?C with a 12 h photoperiod of 400 µmolquanta m^–2 s^–1 PAR with either normal ambient CO₂,approximately 340 vpm, or with 1000 vpm CO₂. The short- andlong-term effects of CO₂ enrichment on photosynthesis were determinedtogether with the levels of ribulose-1, 5-bisphosphate carboxylase(RuBPco) E.C. 4.1.1.39 [EC] protein and activity throughout leafdevelopment of the unshaded 5th leaf above the cotyledons. Thehigh CO₂ concentration during growth did not appreciably affectthe rate of leaf expansion or final leaf area but did increasethe fresh weight per unit area of leaf. With short-term CO₂enrichment, i.e. only during the photosynthesis measurements,the light-saturated photosynthetic rate (P_max) of young leavesdid not increase while those reaching full expansion more thandoubled their net rate of CO₂ fixation. However, with longerterm CO₂ enrichment, i.e. growing the crop in high CO₂, theplants did not maintain this photosynthetic gain. While theCO₂ concentration during growth did not affect the peak in P_maxmeasured in 300 vpm CO₂ or P_max in 1000 vpm CO₂, RuBPco proteinor its activity, the subsequent ontogenetic decline in theseparameters was greatly accelerated by the high CO₂ treatment.Compared with plants grown in normal ambient CO₂ the high CO₂grown leaves, when almost fully expanded, contained only approximatelyhalf as much RuBPco protein and P_max in 300 vpm CO₂ and P_maxin1000 vpm CO₂ were similarly reduced. The loss of RuBPco proteinmay be a major factor associated with the accelerated fall inP_max since it was close to that predicted from the amount andkinetics of RuBPco assuming RuBP saturation. In the oldest leavesexamined grown in high CO₂ additional factors may be limitingphotosynthesis since RuBPco kinetics marginally overestimatedP_max in 300 vpm CO₂ and the initial slope of photosynthesisin response to intercellular CO₂ was also less than expectedfrom the extractable RuBPco. Key words: Lycopersicon esculentum (Mill.) cv. Findon Cross, CO₂ enrichment, acclimation to high CO₂, photosynthesis, RuBPco protein and activity     

Comparison of Palaeobotanical Observations with Experimental Data on the Leaf Anatomy of Durmast Oak [Quercus petraea(Fagaceae)] in Response to Environmental Change

To test whether stomatal density measurements on oak leaf remainsare reliable tools for assessing palaeoatmospheric carbon dioxideconcentration [CO₂], under changing Late Miocene palaeoenvironmentalconditions, young seedings of oak (Quercus petraea,Liebl.) weregrown at elevatedvs.ambient atmospheric [CO₂] and at high humiditycombined with an increased air temperature. The leaf anatomyof the young oaks was compared with that of fossil leaves ofthe same species. In the experiments, stomatal density and stomatalindex were significantly decreased at elevated [CO₂] in comparisonto ambient [CO₂]. Elevated [CO₂] induced leaf cell expansionand reduced the intercellular air space by 35%. Leaf cell sizeor length were also stimulated at high air humidity and temperature.Regardless of a temperate or subtropical palaeoclimate, leafcell size in fossil oak was not enhanced, since neither epidermalcell density nor length of the stomatal apparatus changed. Theabsence of these effects may be attributed to the phenologicalresponse of trees to climatic changes that balanced temporalchanges in environmental variables to maintain leaf growth underoptimal and stable conditions.Quercus petraea,which evolvedunder recurring depletions in the palaeoatmospheric [CO₂], maypossess sufficient phenotypic plasticity to alter stomatal frequencyin hypostomatous leaves allowing high maximum stomatal conductanceand high assimilation rates during these phases of low [CO₂].Copyright1998 Annals of Botany Company Atmospheric CO₂, high humidity, elevated temperature,Quercus petraea,durmast oak, Late Miocene, palaeoclimates, leaf anatomy, stomatal density, stomatal index     

The Relation Between the Nitrogen Concentration and Photosynthetic Capacity of Potato (Solanum tuberosum L.) Leaves

Measurements of the rate of light-saturated photosynthesis (P_max)were made on terminal leaflets of potato plants growing in cropssupplied with 0, 3, 6, 12, 24 and 36 g N m^–2. Measurementswere made between 100 and 154 d after planting. Two types ofleaf were selected—the fourth leaf on the second-levelbranch (L₄, _B1) and the youngest terminal leaflet that was measurable(L_YM). Later, the total nitrogen concentration of each leaflet(N_L) was measured. A linear regression between P_max and N_L,common to both leaf positions, explained 68.5% of the totalvariation. With L₄, _B1 leaves there was a significant improvementin the proportion of variation explained when regressions withseparate intercepts and a common slope were fitted to individualfertilizer treatments. These results suggest that an increasingproportion of leaf nitrogen was not associated with the performanceof the photosynthetic system with increasing nitrogen supply.This separation between nitrogen treatments was not as clearfor L_YM leaves. Stomatal conductance to transfer of water vapourwas neither influenced by leaf position nor directly by nitrogensupply. Rather conductance declined in parallel with the declinein photosynthetic capacity. Solanum tuberosum, potato, nitrogen, photosynthesis, stomatal conductance, leaf     

The role of apical development around the time of leaf initiation in determining leaf width at maturity in wheat seedlings (Triticum aestivum L.) with impeded roots

High soil resistance to root penetration (measured as penetrometerresistance, R_s slows down leaf growth and reduces mature leafsize in wheat seedlings {Triticum aestivum L.). Underlying changesin the kinetics of cell partitioning and expansion and in thesize and organization of mature cells were reported in companionpapers (Beemster and Masle, 1996; Beemster et al., 1996). Inthe present study, the relationships between apex growth, primordiuminitiation and expansion were analysed for plants grown at contrastingR_s, focusing on a leaf whose whole development proceeded afterthe onset of root impedance (leaf 5). High R_s reduced the rates of apex and leaf development, butdid not appear to have immediate effects on the pattern of developmentof the newly initiated phytomers. During an initial short period,the rate of development of a leaf primordium and associatednode were related to plastochronic age, according to similarrelationships (slopes) at the two R_s. Effects on developmentalpatterns were first detected on phytomer radial expansion duringplastochron 2. The ontogenetic pattern of leaf elongation wasaffected later, during the next few plastochrons preceding leafemergence (‘post-primordial stage’). It is concludedthat a reduction in the number of formative divisions and inthe number of proliferative cells along the intercalary mer-istemreported earlier (Beemster and Masle, 1996; Beemster et al.,1996) is not related to the size of the apical dome at leafinitiation nor to the size and number of meristematic cellsinitially recruited to the leaf primordium, which were all unaffectedby R_s. Rather they are generated at the primordial and post-primordialstages. Key words: Wheat, apex development, leaf primodium development, mature leaf width, root impedance     

Long-time variations in leaf mass and area of Mediterranean evergreen broad-leaf and narrow-leaf maquis species

Morphological (dry mass, DM; surface area, LA; leaf mass per area, LMA), anatomical (leaf thickness, L), phenological (leaf life span, LL), and physiological (net photosynthetic rate, P _N) leaf traits of the evergreen species co-occurring in the Mediterranean maquis developing at Castelporziano (Rome) were tested. The correlation analysis indicated that LMA variation was tightly associated with LL variations: Cistus incanus and Arbutus unedo had a short LL (4±1, summer leaves, and 11±1 months, respectively) and low LMA (153±19 g m⁻²) values, Quercus ilex, Phillyrea latifolia, and Pistacia lentiscus high LMA (204±7 g m⁻²) and long LL (22±3 months), Erica arborea, Erica multiflora, and Rosmarinus officinalis a short LL (9±2 months) and an either high (213±29 g m⁻², R. officinalis and E. multiflora) or low (115±17 g m⁻², E. arborea) LMA. LMA values were significantly (p≤0.05) correlated with P _N (r≥0.68). In the tested species, LMA increased in response to the decrease of the total rainfall during the leaf expansion period. LMA variation was due to the unequal variation of DM and LA in the considered species. LMA is thus a good indicator of evergreen maquis species capability to respond to climate change, in particular to total rainfall decrease in the Mediterranean basin.     

Exogenous Auxin and N-1 -Naphthylphthalamic Acid Effects on Populus deltoides Xylogenesis

A method was developed for evaluating the empirical alterationof xylem vessel differentiation in the central leaf trace ofPopulus deltoides, a species that exhibits helical phyllotaxis.Effects of experimental treatments for a period of six plastochronswere evaluated by vessel parameter ratios = 2.P_T/ (P_T+1 + P_T–1),where P was either vessel number or mean transverse vessel areameasured at mid-intern ode at Leaf Plastochron Indices of T– 1, T, and T + 1. Excising leaf laminae reduced vesselnumber and mean vessel area in the associated central leaf traceby 50% and 70%, respectively, compared to unexcised laminaecontrols. Replacing excised laminae with a concentration seriesof exogenous indoleacetic acid (IAA) resulted in a 5% increaseper log mol m^–3 of IAA in the number of vessels differentiatingin the associated central leaf traces compared to excised controls.Mean vessel areas within these leaf traces were 50% of thoseof intact leaf traces. No significant effects of different concentrationsof exogenously applied IAA on mean vessel area could be demonstrated.A lanolin paste ring of N-1 -naphthylphthalamic acid (NPA),an auxin transport inhibitor, around the petioles of intactleaves reduced the number of differentiating vessels by 7% andmean vessel area by 29% per log mol m^–3 of NPA comparedto central leaf traces of leaves ringed with plain lanolin paste.The results suggest that NPA treatments may be used to distinguishexperimentally, at least in part, the cell division from thecell enlargement phases of primary xylogenesis within centralleaf traces of P. deltoides stems. Key words: Auxin transport, Vessel area, Vessel number     

Short and Long Term Fluctuations of the Leaf Mass Per Area of Tomato Plants--Implications for Growth Models

The leaf mass per unit leaf area (LMA) is a key variable inmany growth models, since it is often used to predict leaf areaexpansion from leaf dry weight increase, orvice versa. Influencesof source-sink balance on leaf area, leaf dry weight, LMA, andleaf content in non-structural carbohydrates were investigatedin glasshouse tomato crops. The source-sink balance was manipulatedby artificial shading, CO₂enrichment or fruit removal usingdifferent tomato cultivars. Leaf area was hardly affected bycompetition for assimilates except under extreme conditions.In contrast, leaf dry weight, and consequently LMA, underwentlarge and rapid fluctuations in response to any factor thatchanged source and sink activities. A 60% reduction of photosyntheticallyactive radiation involved a 24% decrease in LMA after 10 d.Carbon dioxide enrichment and fruit removal induced about a45% and 15% increase in LMA, respectively, on plants with twofruiting trusses, but hardly affected LMA of producing plants.No significant cultivar effect could be identified. Changesin starch and soluble sugar content in leaves accounted foronly 29% of diurnal variations in LMA, suggesting regular fluctuationsof other components. We propose that structural LMA varies betweena maximum and a minimum value according to the ratio of assimilatesupply and demand during leaf development. Leaf area is independentof the supply of assimilates when the minimum structural LMAis realised. When the maximum structural LMA is attained, astorage pool of assimilates may accumulate in leaves duringperiods of high supply and low demand. We present a model includingthese hypotheses, which predicts structural and non-structuralLMA variations of plants with different source-sink ratios.Copyright1998 Annals of Botany Company Tomato,Lycopersicon esculentumMill., SLA, SLW, leaf growth, vegetative sink strength, assimilate competition, source-sink ratio, non-structural carbohydrate, models.     

Some Factors in Relation to Bulliform Cell Silicification in the Grass Leaf

The formation of discrete ‘tablets’ of hydratedsilica in the bulliform cells of the leaf blade was followedover a 16-day period in three species of the Gramineae representingdifferent habitats. Seedlings of Oryza sativa (rice) and Cynodondactylon (Bermuda Grass) were cultured under growth-cabinetconditions at levels of 50 and 500 ppm dissolved silica (SiO₂)in the nutrient solution. In addition, bulliform depositionwas studied in mature tiller leaves of Sieglingia decumbens(Heath Grass). Attached leaves, as well as those excised fromthe culm, were used. Initial stages of tablet formation were observed by the 2-dayharvest in the central and basal zones of the fully expandedseedling blades. Deposition did not occur at a stage when bulliformturgor changes might influence blade evolvement. At the 16-dayharvest, deposition was heaviest in the tip zone, and decreasedprogressively towards the base of the blade. In addition, proportionatelyhigher tablet counts (P = 0.05) generally were absent from theleaves grown at the higher silica level. This indicated a limitedavailability of deposition sites. These results are discussed in relation to (i) cellular maturation;(ii) internal leaf anatomy; (iii) leaf expansion; (iv) a basipetalsenescence gradient within the leaf blade. Certain of theseare considered to be possible limiting factors to silica depositionin the grass leaf.     

Leaf dynamics and shoot phenology of eleven warm-temperate evergreen broad-leaved trees near their northern limit in central Japan

Dynamic features of shoot phenology including leaf emergence and leaf fall, and leaf life span for eleven evergreen broad-leaved tree species were investigated in a warm-temperate rain forest in Mount Kiyosumi, central Japan. All species had periodic leaf emergence or flushing pattern, and were classified into two types; single and multiple flush and only one species, Eurya japonica, represented the latter type and the rest had single flush in spring. The single flush type can further be subdivided into two groups according to their duration of shoot growth; short and long flush. Seasonal patterns of leaf fall were categorized into four; unimodal, bimodal, broad unimodal, and multimodal type though they were not fixed pattern. The leaf emergence and leaf fall patterns were correlated for the eleven species, and five phenological types were categorized. Four of them were the single flush types, i.e., short flush of leaf emergence with unimodal leaffall (SSU) type of Castanopsis sieboldii and Quercus salicina, short flush with bimodal leaf fall (SSB) type of Quercus acuta, Machilus thunbergii, Neolitsea sericea, and Cinnamomum japonicum, long flush with bimodal leaffall (SLB) type of Myrsine seguinii, and long flush with broad unimodal leaffall (SLR) type of Symplocos prunifolia, Cleyera japonica, and Illicium anisatum. The multiple flush type is only one species, Eurya japonica, and it had multimodal leaffall pattern (MM type). The phenological pattern varied in relation to leaf life span, leaf size, and tree habit. Leaf life span ranged from 1.1 to 5.8 yr. The short flush species or SSU and SSB types were all canopy or subcanopy trees, and the former had short and the latter had long leaf life spans. The long flush species were all microphyllous small trees, and SLB type had a relatively long leaf life span in understory, SLR type had a long leaf life span in understory or in open habitat and/or forest gap as a pioneer tree. MM type had a long leaf life span and colonizing species in open habitat but they can survive in understory as well. The phenological attributes of evergreen trees were well corresponded to the ecological guild of the tree in both forest structure and successional stage, and were also constrained by phylogenetic groups.     

Effects of N2O narcosis on breathing and effort sensations during exercise and inspiratory resistive loading

Fothergill, D. M., and N. A. Carlson. Effects ofN₂O narcosis on breathing andeffort sensations during exercise and inspiratory resistive loading.J. Appl. Physiol. 81(4):1562-1571, 1996.The influence of nitrous oxide(N₂O) narcosis on the responses toexercise and inspiratory resistive loading was studied in thirteen maleUS Navy divers. Each diver performed an incremental bicycle exercisetest at 1 ATA to volitional exhaustion while breathing a 23%N₂O gas mixture and a nonnarcoticgas of the same PO₂, density, andviscosity. The same gas mixtures were used during four subsequent30-min steady-state submaximal exercise trials in which the subjectsbreathed the mixtures both with and without an inspiratory resistance(5.5 vs. 1.1 cmH₂O ^· s ^· l¹at 1 l/s). Throughout each test, subjective ratings of respiratory effort (RE), leg exertion, and narcosis were obtained with acategory-ratio scale. The level of narcosis was rated between slightand moderate for the N₂O mixturebut showed great individual variation. Perceived leg exertion and thetime to exhaustion were not significantly different with the twobreathing mixtures. Heart rate was unaffected by the gas mixture andinspiratory resistance at rest and during steady-state exercise but wassignificantly lower with the N₂O mixture during incremental exercise (P < 0.05). Despite significant increases in inspiratory occlusionpressure (13%; P < 0.05),esophageal pressure (12%; P < 0.001), expired minute ventilation (4%;P < 0.01), and the work rate ofbreathing (15%; P < 0.001) when the subjects breathed the N₂O mixture,RE during both steady-state and incremental exercise was 25% lowerwith the narcotic gas than with the nonnarcotic mixture(P < 0.05). We conclude that the narcotic-mediated changes in ventilation, heart rate, and RE induced by23% N₂O are not of sufficientmagnitude to influence exercise tolerance at surface pressure.Furthermore, the load-compensating respiratory reflexes responsible formaintaining ventilation during resistive breathing are not depressed byN₂O narcosis.

     

The Effect of Temperature on Leaf Appearance in Rice

Temperature is the principal environmental determinant of cropleaf appearance. The objective of this study is to analyse whetherthere are different effects of day temperature (T_D) and nighttemperature (T_N) on main-stem leaf appearance in rice (OryzasativaL.). Plants of 12 rice cultivars were grown at five constant temperatures(22, 24, 26, 28 and 32 °C) and four diurnally fluctuatingtemperatures (T_D/T_N: 26 /22, 30 /22, 22 /26 and 22 /30 °C)with a constant photoperiod of 12hd^-1. The leaf appearance onthe main stem was measured. A constant change in leaf appearance rate was observed duringontogeny. The relation between the number of emerged leavesand days from seedling emergence was described by a power-lawequation with only one cultivar-specific parameter. Values forthis parameter were estimated for the five constant temperaturetreatments, and the relation between this parameter and temperaturewas quantified by a nonlinear model. Leaf appearance for thefour fluctuating temperature treatments could be accuratelypredicted on the basis of these relations in each cultivar.This indicated that there were no specific effects ofT_DandT_Nonleaf appearance in rice, in contrast with phenological developmentto flowering. The optimum temperature for leaf development wasfound to be substantially higher than for development to flowering. The final main-stem leaf number differed with diurnal temperatureconditions. When a diurnal temperature delayed flowering, itincreased the leaf number as well. This might explain whyT_DandT_Nhada different effect on development to flowering but not on leafdevelopment. Oryza sativa; rice; leaf appearance; leaf number; day and night temperature     

Factors Affecting the Prolongation of NMR Relaxation Times of Water Protons in Leaves of Woody Plants Affected by Formation of Insect Galls

Changes in NMR relaxation times (T₁) of water protons and watercontents of leaves of woody plants affected by formation ofinsect galls were studied in Machilus, Zelkova and Cinnamomumparasitized with a gall-midge, an aphid and two different Triozinepsyllids, respectively. The presence of galls in Machilus leavesincreased both T₁ and water contents in the galled leaf tissues,while such tissues in Zelkova showed only increases in T₁. Similartrends for both parameters were also observed in gall-bearingleaf tissues of Machilus and Cinnamomum, with galls caused bytwo different psyllids. It seems that it is the particular characteristicsof leaf tissues of the host plant that determine whether thesystemic effect of the presence of galls is reflected both inT₁ and in water content, or only in T₁. Histologic features,including the presence of tannins in and leakage of electrolytesfrom these materials, were compared with those of normal (ungalled)leaves to determine possible causative factors involved in theprolongation of T₁ relaxation times that were associated withthe presence of insect galls. The eco-physiological implicationof tannins with respect to the host-parasite relationship isalso discussed. (Received October 27, 1989; Accepted April 24, 1990)     

Nitrogen Fixation in the Canopy of Temperate Forest Trees: A Re-examination

¹⁵N₂ studies and acetylene reduction assays of leaves and shootsof Douglas fir and other forest trees do not confirm previousreports that extensive nitrogen fixation occurs on leaf surfacesand it is concluded that the importance of nitrogen fixationin the canopy of forest trees has been exaggerated. The presenceof nitrogen-fixing bacteria on the leaves of trees is confirmed,however, and they have been identified as Enterobacter agglomerans,Clostridium butyricum and Bacillus sp. Their distribution onleaves is fortuitous since dead oak leaves and artificial leavesbecome colonized to the same extent as living oak leaves. nitrogen fixation, acetylene reduction, Enterobacter agglomerans, Clostridium butyricum, Bacillus sp, Douglas fir, Pseudotsuga menziensii, larch, Larix x oak, Quercus petraea.     

The Remobilization of Nitrogen Related to Leaf Growth and Senescence in Rice Plants (Oryza sativa L.)

Rice plants (Oryzae sativa L.) grown in a nutrient solutionwere fed with (¹⁵NH₄)₂SO₄ during the 5 days of their young panicleformation. At the end of that time in the youngest leaf blade, which hadstarted to emerge during the labelling, absorbed-nitrogen accountedfor 37% of the increased nitrogen of the tissue; in the nextdeveloping leaf blade it accounted for 55%. Thus, remobilized-nitrogenoriginating from older patrs of the plant made up 63 and 45%,respectively, of their total nitrogen. The important contributionof the remobilized-nitrogen to the development of a leaf isevident. The remobilization of nitrogen in the 12th leaf blade on themain stem was examined in detail after labelling during itsdeveloping stage. The ¹⁵N level started to decrease soon afterthe end of the labelling period and continued to decrease untilfull senescence, although the total nitrogen in the same leafincreased until just after its complete expansion, suggestingthat even a young leaf plays a role as a supplier of remobilized-nitrogen. During the rapid decrease in the total nitrogen after its peakat full expansion of the leaf, the actual proportion of labelledabsorbed nitrogen remained nearly the same, indicating thatinflux of new nitrogen into a senescing leaf is very limited. (Received March 13, 1981; Accepted July 13, 1981)     

Nitrate Supply and the Biophysics of Leaf Growth in Salix viminalis

The influence of nitrogen on leaf area development and the biophysicsof leaf growth was studied using clonal plants of the shrubwillow, Salix viminalis grown with either optimal (High N) orsub-optimal (Low N) supplies of nitrate. Leaf growth rate andfinal leaf size were reduced in the sub-optimal treatment andthe data suggest that in young rapidly growing leaves, thiswas primarily due to changes in cell wall properties, sincecell wall extensibility (% plasticity) was reduced in the LowN plants. The biophysical regulation of leaf cell expansion also differedwith nitrogen treatment as leaves aged. In the High N leaves,leaf cell turgor pressure (P) increased with age whilst in theLow N leaves P declined with age, again suggesting that foryoung leaves, cell wall plasticity limited expansion in theLow N plants. Measurements of cell wall properties showed thatcell wall elasticity (%E) was not influenced by nitrogen treatmentand remained constant regardless of leaf age. Key words: Salix, cell wall extensibility, nitrogen nutrition, biophysics of leaf growth     

Responses of N2 Fixation-linked Respiration to Host-plant Energy Status in White Clover Acclimated to a Controlled Environment

Ryle, G. J. A., Powell, C. E. and Gordon, A. J. 1988. Responsesof N₂ fixation-linked respiration to host-plant energy statusin white clover acclimated to a controlled environment.—J.exp. Bot. 39: 879–887. Single plants of white clover, acclimated to a controlled environmentand dependent for nitrogen on N₂ fixation in their root nodules,were darkened, defoliated or exposed to enhanced CO₂ levelsto establish the quantitative relationships between the photosynthesisof the host plant and the N₂ fixation metabolism of root nodules. The nodule respiration associated with N₂ fixation (FLR) declinedrapidly to 10–15% of its normal rate following plant darkeningearly in the photoperiod. Darkening at progressively later intervalsduring the photoperiod demonstrated a positive, apparently linearrelationship between duration of illumination and total FLRduring the photoperiod and the following night period. Completeor partial defoliation reduced FLR according to the leaf arearemoved: again, there was a strong positive correlation betweencurrent rate of photosynthesis, whether of defoliated or undefoliatedplants and the FLR of root nodules. Doubling the current rateof photosynthesis, by enhancing CO₂ levels around the shoots,promoted FLR within 1–2 h when plants were stressed bylack of light. However, enhanced CO₂ levels increased FLR onlyslowly over a period of several hours in plants entrained tothe normal growing conditions. It is concluded that, in these plants acclimated to a uniformand favourable controlled environment, the supply and utilizationof photosynthetic assimilate in N₂ fixation was finely balancedand quantitatively linked during a single diurnal period andthat nodule functioning was not depressed by lack of energysubstrate. Key words: White clover, N₂ fixation, photosynthesis.