Physiological and Ecological Studies in the Analysis of Plant Environment: X. An Analysis, of the Effects of Seasonal Variation in Daylight and Temperature on the Growth of Helianthus annuus in the Vegetative Phase

To determine on a quantitative and mathematical basis the effectsof seasonal changes in the levels of daylight and temperatureon vegetative growth and development in two years pot experimentsin the open were carried out at successive weekly intervalsbetween May and September. So as to minimize errors arisingfrom ontogenetic drifts the procedure adopted was to sow atintervals of a few days throughout the season batches of potswith seed of Helianthus annuus and to select pots containingplants of a standard morphological status for the start of eachweekly experiment. At the beginning and end of the week halfthe pots were harvested, the plants divided into root, stem,and leaf, the leaf area estimated, and the dry weights determined.The diurnal changes in air temperature were continuously recordedwhile the amount of daylight, excluding infra-red and ultravioletradiation, was measured with a specially constructed integratingrecorder. From the biological data for each week twelve variables werecalculated, namely the relative growth rates of both the wholeplant and the individual parts, the proportion by dry weightof the individual parts (root-, stem-, and leaf-weight ratios),the ratio of leaf area to total plant weight (leaf-area ratio),the rate of leaf expansion, the ratio of leaf area to leaf weight,and the net assimilation rate on the criteria of leaf area andweight. The main independent variables considered were the meanweekly temperature, the mean daily maximum minus the mean nightlyminimum temperature, the total amount of light per week, andthe time of year when the individual experiment was undertaken. Multiple regression analyses showed that (i) save for the stem-weightratio the data for the two years could be pooled, (ii) the fluctuationin diurnal temperature was of little account, (iii) transformationof the light data to either logarithms or square roots did notimprove the fit and (iv) for some of the dependent variables,e.g. leaf-area ratio, the ‘time of year’ effectwas significant but could be eliminated if the equation wasmodified to predict the value at the end of the week, giventhe initial value and the light and temperature data. The final series of multiple regressions revealed that (i) theleaf-weight ratio is not controlled by either the amount oflight or mean temperature, (ii) the relative growth rate ofthe root and the root-weight ratio are positively linked onlywith temperature, (iii) the rate of leaf growth either in areaor weight together with the net assimilation rate (area basis)are positively dependent on light alone, (iv) the net assimilationrate (weight basis) and the relative growth rates of the wholeplant and the stem are directly and positively correlated withboth temperature and light, and (v) the leaf-area ratio, theratio of leaf area to leaf weight and the stem-weight ratioare depressed by increasing light but augmented by rising temperature.In the individual regressions for net assimilation rate (areaand weight), the relative growth rates of the whole plant, stemand leaf weight, and the ratios of stem weight and leaf areato leaf weight the percentage variation accounted for rangedfrom 47 to as high as 91 per cent. The implication of these findings in relation to experimentsin controlled environmental chambers are discussed.     

A Comparison of the Rates of Growth and Photosynthesis in First-Year Seedlings of Four Provenances of Pinus contorta Dougl

The results of four experiments are reported in which the parametersof growth were examined in first-year seedlings of Pinus contortaDougl. raised from seed of four different geographic origins(provenances). Highly significant differences in net photosynthesis were shownbetween provenances over a wide range of light intensities,in plants of both 12 and 19 weeks of age, when measurement wasmade at a temperature of 20 ?C. Provenances with a high netrate of photosynthesis also had a high rate of dark respiration,consequently provenance differences in gross photosyntheticrate paralleled those in net photosynthetic rate. Leaf-weightratios (i.e. the ratios of leaf weight: plant weight) also differedsignificantly between provenances, and there was an over-allnegative correlation between rates of photosynthesis and leaf-weightratios. Differences in relative growth-rate (RGR) result fromdifferences in the component variables, photosynthetic rate,and leaf-weight ratio. As the values of these two parameterswere negatively correlated in the experiment, the RGRs of thefour provenances differed little during the mid-seasonal periodof growth. It was not possible, despite precise measurementsof dry-weight increment made on plants grown in nutrient solution,to show inter-provenance differences in RGR which were statisticallysignificant during the mid-seasonal period. Marked inter-provenance differences occurred in the length ofgrowing season, as measured by the time interval between germinationand terminal bud formation, and these differences were associatedwith differences in seedling height. They were not, at leastwithin the time period examined, associated with differencesin seedling weight, and the significance of this fact is discussedin terms of productivity studies for forest tree species.     

Quality of supplementary LED lighting effects on growth and photosynthesis of two different Lactuca recombinant inbred lines (RILs) grown in a tropical greenhouse

LED lamps with various combinations of red (R) and blue (B) wavelengths were used to supplement sunlight for the growth of a heat-resistant (HR) and heat-sensitive (HS) recombinant inbred lines (RIL) of lettuce. The RB-LED ratios were 100R:0B (0B), 92R:8B (8B), 84R:16B (16B), and 76R:24B (24B) with an equal PPFD of 100 μmol m^?2 s^?1. The greatest leaf expansion rates were observed at 8B for both genotypes. All HR-RILs had similar values of growth parameters and specific leaf area (SLA). However, higher values of growth parameters were observed in HS-RIL with 0B, 8B, and 16B than that under 24B and sunlight. Furthermore, HS-RIL had higher SLA under 0B compared to other conditions. Photosynthetic light-use efficiency and maximal oxygen evolution rate were the lowest under 8B for both genotypes. The quality of LED lighting, if provided, seemed to implicate genotype dependence, probably as a result of their different sensitivities to heat stress.

     

Influence of Arbuscular Mycorrhiza and Phosphorus Supply on Polyamine Content, Growth and Photosynthesis of Plantago lanceolata

A greenhouse pot experiment with different phosphorus supply was conducted to study growth, photosynthesis and free polyamine (PA) content in Plantago lanceolata L. plants in relation to arbuscular mycorrhizal (AM) colonization. Inoculum of Glomus fasciculatum (BEG 53) was used. Inoculated plants had high colonization intensities which were related to the P supply. Non-mycorrhizal (NM) plants showed a typical yield response curve for P availability. Dry masses of mycorrhizal (M) plants were higher at the lowest soil P content than those of NM plants, but the opposite was found at the highest P supply. P contents in M plants were always higher. There were no differences in chlorophyll (Chl) concentrations (except the lowest soil P content) and ratios of variable to maximum Chl fluorescence (Fv/Fm) values between M and NM plants, whereas M plants had higher ratios of leaf area to fresh mass (A/f.m.) at low soil P contents and they had significantly higher CO₂ fixation capacities per unit leaf area. Free putrescine (Put), spermidine (Spd) and spermine (Spm) contents in NM plants were usually highest at the lowest P supply. The ratios of Put/(Spd+Spm) were identical in M and NM leaves. They were significantly higher, however, in NM roots at the two low P doses. It is concluded, that a P nutritional status might exist, below which PA concentrations and ratio are increased drastically, possibly indicating P deficiency or a certain state of plant development with a higher demand for AM symbiosis. This revised version was published online in July 2006 with corrections to the Cover Date.     

Combination of Red and Blue Lights Improved the Growth and Development of Eggplant (Solanum melongena L.) Seedlings by Regulating Photosynthesis

The photosynthesis, photomorphogenesis, and photoperiod processes in plants are regulated according to light intensity and quality. The aim of this study was to investigate the effects of different light qualities on eggplant seedlings and determine the best light quality for growth. The seedlings of eggplant cultivar ‘Jingqiejingang’ were grown under light-emitting diodes (LEDs): white (W, the control), red (R), blue (B), and different ratios of B/R lights (B/R = 1/1, B/R = 1/3, B/R = 1/6, B/R = 1/9). The growth parameters, leaf morphology, photosynthetic performance, chlorophyll fluorescence, and the carbon and nitrogen metabolism in the leaves of eggplant seedlings under different LED light treatments were studied. The results showed that the plant height, leaf development, and photosynthetic characteristics were inhibited by red light but elevated by blue light compared with the control. Conversely, the contents of chlorophyll a, chlorophyll b, and carotenoids were all increased by red light, while decreased by blue light significantly. In addition, the contents of carbohydrates and the activities of nitrogen assimilation enzymes were not or little changed by the monochromatic blue and red light. The combined light of red and blue were more beneficial for growth than the monochromatic light, especially B/R = 1/3 light. Under B/R = 1/3 light, the parameter values of plant growth, leaf development, photosynthetic pigments and characteristics, and carbon and nitrogen metabolism were all maximum. Taken together, combined application lights of red and blue are good practice for the cultivation of eggplant seedlings, and LED B/R = 1/3 light was optimum.

     

Some Effects of Alternating Temperature on the Growth of French Bean Plants

In the main experiment described plant dry weight and leaf area,relative growth-rate, net assimilation rate (on an area basis),leaf-weight ratio and leafarea ratio were studied for plantsgrown under a range of temperature régimes and in 12-hourdays. Comparisons under conditions where the mean temperaturewas the same showed that final dry weight and leaf area weregreatest at constant temperature and least where the temperaturefluctuated about the mean value. These findings are discussedin relation to the concept of thermoperiodism, and in relationto the significant effects of day and night temperature uponthe development of leaf area.     

Control of ascorbic acid synthesis and accumulation and glutathione by the incident light red/far red ratio in Phaseolus vulgaris leaves

The effects of red/far red (R/FR) ratios on leaf ascorbate (AA) and glutathione (GSH) accumulation were examined in common bean (Phaseolus vulgaris L.). Growth under low R/FR ratios resulted in a “shade” phenotype and much lower leaf AA and GSH contents than high (R/FR) ratios. Photosynthesis rates were unaffected by changes in the R/FR ratio but leaf respiration rates, pyridine nucleotide pools and antioxidant enzyme activities were decreased under the low R/FR regime. The GSH pool changed slowly in response to altered R/FR ratios but leaf ascorbate acclimated over a single photoperiod. We conclude that light quality signals, particularly R/FR ratios, are important regulators of antioxidant synthesis and accumulation. These acclimatory changes are an early response to changing light environment.     

The Effects of Light Intensity and Carbon Dioxide Concentration on the Growth of Chrysanthemum morifolium cv. Bright Golden Anne

Rooted cuttings were grown in controlled-environment cabinetsat daily visible light totals of 31, 63, 125, and 250 J cm^–28-h day^–1 and carbon dioxide concentrations of 325 and600 ppm. The experiment was repeated on another occasion withthe inclusion of a further carbon dioxide level of 900 ppm.A 5-h tungsten night break was used in the first week to delayflower initiation The plants in the various treatment combinationswere sampled by frequent small harvests for leaf area and freshand dry weights of leaf, stem, root, and flower, and also forvarious morphological features. Other growth measures were obtainedby manipulation of the primary data, including the fitting ofprogress curves. Plants were respaced at intervals to minimizemutual shading. There was an increase in total dry-matter production with increasinglight and carbon dioxide, with a small positive interactionbetween them. Plants in one experiment had a somewhat higherunit leaf rate and a lower leaf-area ratio, the latter beingdue to a slightly smaller leaf-weight ratio. The effects ofadditional carbon dioxide were largely accounted for by increasedphotosynthesis. Although there were substantial differencesin specific leaf area between treatment combinations withineach experiment, the leaf-weight ratio was little altered inthe period of vegetative growth. The inverse relationship betweenspecific leaf area and unit leaf rate showed a very similartrend for all combinations of light and carbon dioxide concentration.Leaf area was a linear function of absolute leaf water contentfor all treatment combinations within an experiment, but therewas a small significant difference between occasions. Flower development was extremely delayed in the lowest lightlevel and substantially delayed at the next higher level. Thenumber of leaves below the flower decreased with increasinglight level Flower weight increased with increasing light above63 J cm^–2 8-h day^–1 and with increasing carbon dioxideconcentration, there being a positive interaction between them The initial weight and leaf area of cuttings differed for thetwo experiments, and although the results on the two occasionswere in the same direction, their magnitudes were different.Some of the discrepancy was eliminated by expressing the variousgrowth measures as functions of plant dry weight, but therewas evidently a difference in the potential for growth of thetwo batches of cuttings. The plants which were initially smallerhad a higher average unit leaf rate which, due to a higher leafwater content, was not offset by a lower leaf area ratio.     

The influence of R:FR ratio on the growth, photosynthesis and rooting ability of Terminalia spinosa Engl. and Triplochiton scleroxylon K. Schum

Stockplants of the tropical hardwoods Terminalia spinosa Engl, and Triplochiton scleroxylon K. Schum were grown in a controlled environment under red:far-red (R:FR) ratios ranging from 0.5-3.1. In both species, rates of shoot height increment were higher (P < 0.05) under the low R:FR ratios as a result of increased internode elongation. In Terminalia spinosa , specific leaf area (SLA) was also significantly higher under lower R:FR ratios, values ranging from 175 to 210 cm² g^-1 in the 3.1 and 0.9 treatments respectively. No effect of R:FR ratio on SLA was recorded in Triplochiton scleroxylon. Pre-severance photo-synthetic rate, stomatal conductance and water-use efficiency were increased under the higher R:FR ratios in Terminalia spinosa , rates of photosynthesis ranging between 2.68-4.59 μmol m^-2 s^-1 in the 0.5 and 3.1 R:FR treatments respectively. Gas exchange rates of Triplochiton scleroxylon were unaffected by R:FR treatment. These contrasting responses to variation in R:FR ratio were associated with differences in rooting ability. In Terminalia spinosa , significantly higher percentage rooting was recorded in the cuttings from the 3.1 R:FR treatment than from 0.5, with values of 93.7% and 77.5% recorded respectively. R:FR ratio also affected rooting percentages of Triplochiton scleroxylon , but in this case, higher rooting percentages were recorded in the lower R:FR ratios, values ranging from 31.1–54.1% in the 3.0 and 0.5 R.FR treatments respectively. This difference in rooting response is attributed to the contrasting effects of R:FR ratio on the leaf and stem morphology of the two species. The implications of these results for stockplant management are discussed.     

Studies in the Nutrition of Apple Rootstocks: III. Effects of Level of Magnesium Nutrition on Growth, Form and Mineral Composition

One-year rooted shoots of apple M. VII rootstock were grownfor a single season by spraying their roots continuously withnutrient solutions containing <3, 10, 45, and 135 ppm Mg.These treatments respectively produced plants with a severeMg deficiency (Mg₍₀₎), a mild deficiency (Mg₍₁₎), normal foliageand growth (Mg₍₂₎), and a high level of Mg (Mg₍₃₎). The effectof Mg nutrition on the leaves can explain most of the observedeffects on vegetative growth. Depression of growth of Mg₍₁₎)plants was not detected until late in the season although necrosis,typical of Mg deficiency, occurred on the lower leaves by mid-July.This loss of photosynthetic area of leaf was to a large extentcompensated for by increased efficiency of the remaining greenleaves; as the deficiency symptoms progressed, the loss of leaf,and therefore of carbohydrate production, predominated and totalgrowth was affected. The form of the plant was little altered. Symptoms were apparent on leaves of severely deficient Mg₍₀₎plants by late June, and reductions in growth and modificationsin form by August. The poor root systems and thin shoots arelargely attributed to loss of leaf rather than to the low Mgconcentration in these organs. No symptoms of toxicity developed on the Mg₍₃₎ plants althoughby the end of the season the total dry weights were less thanthose of the Mg₍₂₎ controls, and the plants also produced thickershoots. Plant dry weight, and more especially Mg uptake, increasedfrom Mg₍₀₎ to Mg₍₂₎ but above this level the gradient of Mguptake in relation to supply was less steep. The excess Mg takenup at the Mg(j) level led to the relatively lower weights ofthese plants. Much of the excess Mg accumulated in the leaves,especially in the older ones. Mg moved from, or accumulatedin, the lower leaves of the shoot according to the level ofMg supplied to the plants. Thus the shoot apex tended towardsnormality both in the concentration of Mg and in its growth. In general, growth of the plant, and of individual componentparts, governed the uptake of elements other than Mg, althoughmore K, Ca, and Mn and less Fe per unit of plant dry weightaccumulated at the lower levels of Mg than at the higher levels.     

金叶银杏半同胞子代无性系的叶色和色素含量变化及呈色机制分析

对4月份至11月份金叶银杏‘万年金'( Ginkgo biloba ‘Wannianjin')32个半同胞子代无性系与亲本的叶色差异进行比较;比较了不同色系叶片的色素含量和比值及叶色参数(L*、a*和b*)的变化,分析了叶色参数与叶片色素含量的相关性;并观察了不同色系的叶绿体超微结构。结果表明：32个半同胞子代无性系可被分为金黄、浅黄、草绿和蓝绿4个色系。随时间推移,草绿和蓝绿色系叶片的总叶绿素( Chl)、叶绿素a( Chla)、叶绿素b( Chlb)和类胡萝卜素( Car)含量均呈“双峰型”变化趋势,Car/Chl和Car/Chla比值的变幅均较小;而金黄和浅黄色系叶片的上述色素含量呈“升高—降低—升高”变化趋势,Car/Chl和Car/Chla比值总体呈“迅速下降—相对稳定—缓慢升高”的变化趋势。各色系叶片的上述色素含量在夏季均不同程度下降,Car/Chlb比值变化差异较大,且金黄和浅黄色系的各色素含量均低于草绿和蓝绿色系。随时间推移,金黄和浅黄色系叶片的L*、a*和b*值以及草绿和蓝绿色系叶片的L*和b*值均先降低后升高,后2个色系的a*值则先升高后下降;并且,前2个色系的L*和b*值总体上显著高于后2个色系,而a*值则总体上低于后2个色系。金黄色系的Chla和Chl含量与L*和a*值显著负相关,而其Car/Chl和Car/Chla比值则与L*、a*和b*值显著或极显著正相关;浅黄色系的Chlb含量与a*值显著负相关,其Car/Chla比值与L*和b*值以及Car/Chlb比值与a*值均显著正相关;草绿色系的Chla含量与L*值显著负相关,其Car/Chla比值与L*和b*值以及Car/Chlb比值与a*值均显著正相关;这3个色系叶片的其余指标间以及蓝绿色系叶片的各指标间均无显著相关性。观察结果显示：金黄和浅黄色系的叶绿体基粒片层发育不健全,基粒片层可见但排列较疏松,且无明显垛叠,分布范围小而稀疏;蓝绿和草绿色系叶绿体的基粒类囊体垛叠层数均较多,基粒片层发达且排列紧致、整齐,分布范围大而稠密。综合分析结果表明：‘万年金'4个色系半同胞子代无性系叶片的呈色差异和叶色变化由多种因素控制,其中,Car/Chl和Car/Chla比值高且叶绿体基粒片层发育不健全是叶片呈黄色的主要原因。     

Growth and carbon economy of a fast-growing and a slow-growing grass species as dependent on nitrate supply

In previous experiments systematic differences have been found in the morphology, carbon economy and chemical composition of seedlings of inherently fast- and slow-growing plant species, grown at a non-limiting nutrient supply. In the present experiment it was investigated whether these differences persist when plants are grown at suboptimal nutrient supply rates. To this end, plants of the inherently fast-growing Holcus lanatus L. and the inherently slow-growing Deschampsia flexuosa (L.) Trin. were grown in sand at two levels of nitrate supply. Growth, photosynthesis, respiration and carbon and nitrogen content were studied over a period of 4 to 7 weeks. At low N-supply, the potentially fast-growing species still grew faster than the potentially slow-growing one. Similarly, differences in leaf area ratio (leaf area:total dry weight), specific leaf area (leaf area:leaf dry weight) and leaf weight ratio (leaf dry weight:total dry weight), as observed at high N-supply persisted at low N-availability. The only growth parameter for which a substantial Species × N-supply interaction was found was the net assimilation rate (increase in dry weight per unit leaf area and time). Rates of photosynthesis, shoot respiration and root respiration, expressed per unit leaf, shoot and root weight, respectively, were lower for the plants at low N-availability and higher for the fast-growing species. Species-specific variation in the daily carbon budget was mainly due to variation in carbon fixation. Lower values at low N were largely determined by both a lower C-gain of the leaves and a higher proportion of the daily gain spent in root respiration. Interspecific variation in C-content and dry weight:fresh weight ratio were similar at low and high N-supply. Total plant organic N decreased with decreasing N-supply, without differences between species. It is concluded that most of the parameters related to growth, C-economy and chemical composition differ between species and/or are affected by N-supply, but that differences between the two species at high N-availability persist at low N-supply.     

Controls Over Leaf Litter and Soil Nitrogen Fixation in Two Lowland Tropical Rain Forests

Global comparisons suggest that rates of N fixation in tropical rain forests may be among the highest on earth. However, data supporting this contention are rare, and the factors that regulate N fixation within the biome remain largely unknown. We conducted a full-factorial (N × P) fertilization experiment in two lowland tropical rain forests in Costa Rica to explore the effects of nutrient availability on rates of free-living N fixation in leaf litter and soil. P fertilization significantly increased N fixation rates in both leaf litter and soil, and the effect was dependent on sampling date. Fertilization with N did not affect rates of N fixation at any time. In addition, variation in N fixation rates measured in unfertilized plots at four sampling time points suggested seasonal variability in N fixation: leaf litter N fixation ranged from 0.36 kg/ha/yr in the dry season to 5.48 kg/ha/yr in the wet season. Soil N fixation showed similar patterns ranging from a dry season low of 0.26 kg/ha/yr to a wet season high of 2.71 kg/ha/yr. While the observed temporal variability suggests potential climatic control over free-living N fixation in these forests, data suggest that neither soil nor leaf litter moisture alone regulate N fixation rates. Instead, we hypothesize that a combination of ample C availability, low leaf litter N:P ratios, and high rainfall coincide during the latter portions of the rainy season and drive the highest free-living N fixation rates of the year.     

Baobab trees (Adansonia) in Madagascar use stored water to flush new leaves but not to support stomatal opening before the rainy season

Baobab trees (Adansonia, Bombacaceae) are widely thought to store water in their stems for use when water availability is low. We tested this hypothesis by assessing the role of stored water during the dry season in three baobab species in Madagascar. In the dry season, leaves are present only during and after leaf flush. We quantified the relative contributions of stem and soil water during this period through measures of stem water content, sap flow and stomatal conductance. Rates of sap flow at the base of the trunk were near zero, indicating that leaf flushing was almost entirely dependent on stem water. Stem water content declined by up to 12% during this period, yet stomatal conductance and branch sap flow rates remained very low. Stem water reserves were used to support new leaf growth and cuticular transpiration, but not to support stomatal opening before the rainy season. Stomatal opening coincided with the onset of sap flow at the base of the trunk and occurred only after significant rainfall.     

Relationship between leaf area index and yield in double-crop and full-season soybean systems

Previous research indicates a correlation between leaf area index (LAI) and yield of full-season soybean [Glycine max (L.) Merrill], which is a single crop planted early in the season. Leaf area index values of at least 3.5-4.0 in the reproductive stages are required for maximum potential yield. It is unknown how yields of double-crop soybean, which is planted late into harvested small grain fields, respond to changes in leaf area index. We hypothesized that double-crop soybean would be more sensitive to defoliation than full-season soybean. This study used linear and linear plateau models to describe the yield response of full-season and double-crop soybean to reductions in leaf area index through manual defoliation, and evaluated the yield response of double-crop soybean to reductions in leaf area index through natural insect defoliation. From 15 manual defoliation experiments over 3 yr, significant linear decreases in yield occurred in both full-season and double-crop soybean when leaf area index values were below 3.5-4.0 by developmental stages R4 to R5, whereas yields usually reached a plateau at higher leaf area index levels. Average yield loss was 769 +/- 319 kg ha(-1) for each unit decrease in leaf area index below the plateau; average maximum yield was 3,484 +/- 735 kg ha(-1). From eight field experiments over 2 yr, insect defoliators had no effect on double-crop soybean yield; leaf area index levels were above 4.0 by the developmental stage when leaf area index estimates were taken (R3 to R6). Therefore, double-crop soybean that maintains leaf area index values above the 3.5-4.0 critical level by mid-reproductive developmental stages can tolerate defoliating pests.     

Growth of bean and tomato plants as affected by root absorbed growth substances and atmospheric carbon dioxide

Summary Bean and tomato plants were grown in solution culture root media containing pre-determined concentrations of gibberellin A₃ (GA), 1-naphthaleneacetic acid (NAA), N⁶-benzyladenine (BA), (2-chloroethyl)trimethylammonium chloride (CCC), and at atmospheric levels of 300 and 1000 ppm of CO₂. Net assimilation rates (NAR), relative growth rates (RGR), leaf area ratios (LAR), root to top dry weight ratios (R/T) and changes in dry weight, size, and form of each organ were recorded.Gibberellin had no effect on RGR of either plant species but increased the NAR of tomatoes at 1000 ppm CO₂. Total dry weight was only slightly affected by GA but root growth and R/T were markedly depressed. CCC had no effect on NAR, but decreased RCR and LAR. Root growth of beans and R/T in both plants were promoted by CCC. NAR and RGR were strongly inhibited by BA and NAA. Inhibition of stem and leaf growth by CCC and NAA was greater than that for roots; thus, R/T ratios were increased. Root branching was promoted by NAA.High (1000 ppm), compared to the low (300 ppm), atmospheric levels of CO₂ generally promoted root growth and produced an increase in the R/T, both in the absence and presence of chemical treatment. The multiplicity of effects of the rootabsorbed chemical growth substances and CO₂ on growth and photosynthesis is discussed.Journal article No 3883 of the Michigan Agricultural Experiment Station.NATO Fellow, University of Pisa, Italy.     

Phenology and nutrition of miombo woodland trees in Zambia

Seasonality in nitrogen (N) and phosphorus (P) concentration in soil and shoots of five Brachystegia-Julbernardia (miombo) woodland trees was studied from September 1991 to March 1993 at two regrowth miombo sites in central Zambia. Shoot growth started in the dry season (September–November) and lasted until April during the 1991/92 season but had virtually ceased by January 1993 during the 1992/93 season. The shoot growing season was associated with low foliar N/P ratios. These ratios were much lower (<5) during the 1991/92 season than in the 1992/93 season (12–15). The increase in foliar N/P ratios after the shoot growing season was caused by a sharp drop in foliar P concentration, apparently due to reabsorption before leaf fall. There were no annual variations in biomass N concentration in contrast to P. During the 1992/93 growing season P concentrations in foliage and wood were a quarter and a third, respectively, of the 1991/ 92 levels. Since the short shoot growing season observed during the 1992/93 season is typical of savanna woodland trees in southern Africa, the high biomass P concentration and longer growing season in 1991/92 season were exceptional and may have been related to reduced competition by shallow rooting herbaceous plants caused by the severe drought of that season.     

Studies in the Nutrition of Apple Rootstocks: II. Effects of Concentration of Iron in the Nutrient Solution on Growth and Chlorophyll Content

Rooted one-year shoots were grown for one season by sprayingtheir roots with nutrient solution. Iron supplied as Fe-EDTAat four concentrations resulted in plants which were respectively(a) severely chlorotic, (b) mildly chlorotic, (c) dark greenand healthy (controls), and (d) dark green but with slight reductionin growth. Severely deficient plants showed 40–70 per cent reductionsin growth as measured by fresh weight, shoot length, diameterincrease, leaf area, net assimilation and relative growth-rates.Dry weights were reduced 70–80 per cent and of the totaldry-weight increment a greater proportion remained in the leaves,which had a lower dry weight and higher water content per unitarea. However, because the initial old stem formed a greaterproportion of the total dry weight, the leaf area ratio remainedabout 11 per cent lower than in the controls. Severely deficientplants had, per unit of chlorophyll, a higher dry-weight increaseand net assimilation rate than the controls. Mild deficiency caused 10–20 per cent reductions in growthand net assimilation rate; the leaf area ratio was normal. Possible mechanisms of the effects of low iron supply are discussed,while the small growth reduction at the highest Fe-EDTA concentrationis attributed to chelate toxicity     

不同光质对桑树幼苗生长和光合特性的影响

光质可影响植物光合特性、形态以及生理过程。本试验研究了不同光质(白光W、红光R、红蓝混合光RB、蓝光B)对桑树植株生长、形态和光合作用的影响。结果表明:与白光对照相比,红光、蓝光和红蓝混合光处理下植株的生长、干物质积累受到抑制;红光处理下植株的株高、叶面积显著高于白光、红蓝混合光、蓝光处理;而白光、红蓝混合光、蓝光处理下植株的LMA、叶绿素a/b比值、可溶性蛋白含量、蔗糖、淀粉含量和叶片总N含量显著高于红光处理;红蓝混合光处理下植株的Pn、Gs、ΦPSⅡ与白光处理相近,红光、蓝光处理下植株的Pn、ΦPSⅡ低于白光、红蓝混合光处理,同时红光、红蓝混合光、蓝光处理下植株的抗氧化酶活性高于白光处理,而MDA含量低于白光处理;红光处理下植株的叶片厚度、栅栏组织和海绵组织厚度显著小于白光处理。因此,一定比例的红蓝混合光可以使桑树植株的生长、光合特性、生理特征和叶片解剖结构与白光下生长植株相近,并减少单质红光、单质蓝光对植株生长发育的不利影响。     

Does the direct effect of atmospheric CO2 concentration on leaf respiration vary with temperature? Responses in two species of Plantago that differ in relative growth rate

The objective of this study was to investigate the direct effect of elevated atmospheric CO2 concentrations on leaf respiration in darkness (R) over a broad range of measurement temperatures. Our aim was to further elucidate the underlying mechanism(s) of the often-reported inhibition of leaf R by a doubling of the atmospheric CO2 concentration. Experiments were conducted using two species of Plantago that differed in maximum relative growth rate (fast-growing Plantago lanceolata L. and the slow-growing P. euryphylla Briggs, Carolin & Pulley). Rates of leaf respiration (R) were measured at atmospheric CO2 concentrations ranging from 75 to 2000 &mgr;mol mol-1 at temperatures from 12 to 42 degrees C. R was measured as CO2 release with a portable gas exchange system with infrared gas analysers. Our hypothesis was that the changes in temperature alter the flux coefficient (i.e. the extent to which changes in potential enzyme activity has an effect on the rate of a reaction) of enzymes potentially affected by CO2. Initial analysis of our results suggested that R was inhibited by elevated CO2 in both species, with the apparent degree of inhibition being greatest at low temperature. Moreover, the apparent degree of inhibition following a doubling of atmospheric CO2 concentration from 350 to 700 &mgr;mol mol-1 was similar to that reported by several previous studies (approximately 14% and 26% for P. lanceolata and P. euryphylla, respectively) at a temperature equal to the mean of the previous studies. However, subsequent correction for diffusion leaks of CO2 across the gas exchange's cuvette gaskets revealed that no significant inhibition had occurred in either species, at any temperature. The inhibitory effect of elevated CO2 on leaf respiratory CO2 release reported by previous studies may therefore have been overestimated.