Contribution of physiological and morphological plant traits to a species' competitive ability at high and low nitrogen supply

Why do inherently fast-growing species from productive habitats generally have a higher rate of biomass production in short-term low-nitrogen experiments than slow-growing species from unproductive habitats, whereas the opposite is found in long-term experiments? Is this mainly due to inherent differences in biomass allocation, leaf characteristics or the plants' physiology? To analyse these questions we grew five monocotyledonous species from productive and unproductive habitats in a climate chamber at both high and low nitrogen supply. Nitrate was supplied exponentially, enabling us to compare inherent differences in morphological and physiological traits between the species, without any interference due to differences in the species' ability to take up nutrients. At high nitrogen supply, we found major inherent differences in specific leaf area and nitrogen productivity, i.e. daily biomass increment per unit plant nitrogen, where-as there were only small differences in net assimilation rate, i.e. daily biomass increment per unit leaf area, and biomass partitioning. We propose that the higher specific leaf area and nitrogen productivity of inherently fast-growing species are the key factors explaining their high abundance in productive habitats compared with inherently slow-growing ones. At low nitrogen supply, the net assimilation rate was decreased to a similar extent for all species, compared with that at high nitrogen supply. The nitrogen productivity of the inherentlyfast-growing species decreased with decreasing nitrogen supply, whereas that of the inherently slow-growing species remained constant. There were no inherent differences in nitrogen productivity in this treatment. At this low nitrogen supply, the inherently fast-growing species invested relatively more biomass in their roots that the slow-growing ones did. The inherently fast-growing species still had a higher specific leaf area at low nitrogen supply, but the difference between species was less than that at high nitrogen supply. Based on the present results and our optimization model for carbon and nitrogen allocation (Van der Werf et al. 1993a), we propose that the relatively large investment in root biomass of fast-growing species is the key factor explaining their higher biomass production in short-term experiments. We also propose that in the long run the competitive ability of the slow-growing species will increase due to a lower turnover rate of biomass. It is concluded that the plant's physiology (net assimilation rate and nitrogen productivity), only plays a minor role in the species' competitive ability in low-nitrogen environments.     

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.     

Effects of nitrogen supply on the anatomy and chemical composition of leaves of four grass species belonging to the genus Poa, as determined by image-processing analysis and pyrolysis–mass spectrometry

Previous experiments have shown that the anatomy and chemical composition of leaves of inherently fast- and slow-growing grass species, grown at non-limiting nitrogen supply, differ systematically. The present experiment was carried out to investigate whether these differences persist when the plants are grown at an intermediate or a very low nitrogen supply. To this end, the inherently fast-growing Poa annua L. and Poa trivialis L., and the inherently slow-growing Poa compressa L. and Poa pratensis (L.) Schreb. were grown hydroponically at three levels of nitrate supply: at optimum (RGR_max) and at relative addition rates of 100 and 50 mmol N (mol N)^?1 d^?1 (RAR₁₀₀ and RAR₅₀), respectively. As expected, at the lowest N supply, the potentially fast-growing species grew at the same rate as the inherently slow-growing ones. Similarly, the differences in leaf area ratio (LAR, leaf area:total dry mass), specific leaf area (SLA, leaf arear:leaf dry mass) and leaf mass ratio (LMR, leaf dry mass:total dry mass) disappeared. Under optimal conditions, the fast-growing species differed from the slow-growing ones in that they had a higher N concentration. There were no significant differences in C concentration. With decreasing N supply, the total N concentration decreased and the differences between the species disappeared. The total C concentration increased for the fast-growing species and decreased for the slow-growing ones, i.e. the small, but insignificant, difference in C concentration between the species at RGR_max increased with decreasing N supply. The chemical composition of the leaves at low N supply, analysed in more detail by pyrolysis–mass spectrometry, showed an increase in the relative amounts of guaiacyl lignin, cellulose and hemicellulose, whereas those of syringyl lignin and protein decreased. The anatomy and morphology of the leaves of the four grass species differing in RGR_max were analysed by image-processing analysis. The proportion of the total volume occupied by mesophyll plus intercellular spaces and epidermis did not correlate with the amount of leaf mass per unit leaf area (specific leaf mass, SLM) at different N supply. The higher SLM at low N supply was caused partly by a high proportion of non-veinal sclerenchymatic cells per cross-section and partly by the smaller volume of epidermal cells. We conclude that the decrease in relative growth rate (and increase in SLM) at decreasing N supply is partly due to chemical and anatomical changes. The differences between the fast- and slow-growing grass species at an optimum nutrient supply diminished when plants were growing at a limiting nitrogen supply.     

Why do fast- and slow-growing grass species differ so little in their rate of root respiration,considering the large differences in rate of growth and ion uptake?

Herbaceous plants grown with free access to nutrients exhibit inherent differences in maximum relative growth rate (RGR) and rate of nutrient uptake. Measured rates of root respiration are higher in fast-growing species than in slow-growing ones. Fast-growing herbaceous species, however, exhibit lower rates of respiration than would be expected from their high rates of growth and nitrate uptake. We investigated why the difference in root O₂ uptake between fast- and slow-growing species is relatively small. Inhibition of respiration by the build-up of CO₂ in closed cuvettes, diurnal variation in respiration rates or an increasing ratio of respiratory CO₂ release to O₂ uptake (RQ) with increasing RGR failed to explain the relatively low root respiration rates in fast-growing grasses. Furthermore, differences in alternative pathway activity can at most only partly explain why the difference in root respiration between fast- and slow-growing grasses is relatively small. Although specific respiratory costs for maintenance of biomass are slightly higher in the fast-growing Dactylis glomerata L. than those in the slow-growing Festuca ovina L., they account for 50% of total root respiration in both species. The specific respiratory costs for ion uptake in the fast-growing grass are one-third of those in the slow-growing grass [0·41 versus 1·22 mol O₂ mol (NO₃^–)^–1]. We conclude that this is the major cause of the relatively low rates of root respiration in fast-growing grasses.     

Photosynthetic responses to variable light: a comparison of species from contrasting habitats

Photosynthetic responses to variable light were compared for species from habitats differing in light availability and dynamics. Plants were grown under the same controlled conditions and were analysed for the kinetics of photosynthetic induction when photon flux density (PFD) was increased from 25 to 800 mol m^-2s^-1. Gas exchange techniques were used to analyse the two principal components of induction, opening of stomata and activation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). On average, 90% of the final photosynthetic rate was attained after 7 min for obligate shade plants (two species), 18 min for fast-growing sun plants (seven species from productive habitats) and 32 min for slow-growing sun plants (nine species from unproductive habitats). The rapidity of response of the shade plants was explained by stomata remaining more open in the low-light period prior to induction. This was also observed in two species of deciduous trees, which therefore resembled shade plants rather than other fast-growing sun plants. The slow response of the slow-growing sun plants was the result of lower rates of both Rubisco activation and stomatal opening, the latter being more important for the final phase of induction. The lower rate of Rubisco activation was confirmed by direct, enzymatic measurements of representative plants. With increasing leaf age, the rate of stomatal opening appeared to decrease but the rate of Rubisco activation was largely conserved. Representative species were also compared with respect to the efficiency of using light-flecks relative to continuously high light. The shade plants and the slow-growing sun plants had a higher efficiency than the fast-growing sun plants. This could be related to the presence of a higher electron transport capacity relative to carboxylation capacity in the former group, which seems to be associated with their lower photosynthetic capacities. Representative species were also compared with respect to the ability to maintain the various induction components through periods of low light. Generally, the fast-growing sun plants were less able than the other two categories to maintain the rapidly reversible component. Thus, although the rate of induction appears to be related to the ecology of the plant, other aspects of photosynthetic dynamics, such as the efficiency of using lightflecks and the ability to maintain the rapidly reversible component, seem rather to be inversely related to the photosynthetic capacity.     

Differential chemical allocation and plant adaptation: A Py-MS Study of 24 species differing in relative growth rate

The chemical composition of leaves of 24 wild species differing in potential relative growth rate (RGR) was analysed by pyrolysis-mass spectrometry. The variation in RGR significantly correlated with differences in chemical composition: slow-growing species were richer in glucan-based polysaccharides and in C16:0 fatty acid, whereas fast growing ones contained more protein (other than those incorporated in cell walls) and chlorophyll, sterols and diglycerides. Other, apparently significant correlations, e.g. for pentose-based hemicellulose and for guaiacyl lignin appeared solely based on a group separation between mono- and dicotyledonous species.Considering the eleven monocotyledonous and thirteen dicotyledonous species separately, correlations were found in addition to the previously mentioned general ones. Within the group of the monocotyledons the low-RGR species were significantly enriched in pentose-based hemicellulose, ferulic acid and (hydroxy)proline-rich cell wall protein and nearly significant in guaiacyl and syringyl lignin, fast-growing species contained more potassium. Within the group of the dicotyledons slow-growing species were enriched in triterpenes and aliphatic wax esters.In general, the monocotyledons contained more cell wall material such as pentose-based hemicellulose, ferulic acid, glucans (including cellulose) and guaiacyl-lignin, and also more aliphatic wax esters, than the dicotyledons. The dicotyledons, on the other hand, contained somewhat more protein than the grasses.Per unit weight of cell wall, the amount of (hydroxy)proline- rich protein in low-RGR species was comparatively low. A higher investment of cell wall proteins to explain the low rate of photosynthesis per unit of leaf nitrogen of slow-growing species as suggested by Lambers and Poorter (1992), therefore, seems unlikely.Abbreviations HPRP (hydroxy)proline-rich protein(s) - LAR leaf area ratio - LWR leaf weight ratio - MVA multivariate analysis - NAR net assimilation rate - PC principal component - PNUE photosynthetic nitrogen use efficiency - PyGCMS pyrolysis-gas chromatography-mass spectrometry - PyMS pyrolysis mass spectrometry - RGR relative growth rate - SLA specific leaf area - SLM specific leaf mass     

Phenotypic plasticity in response to nitrate supply of an inherently fast-growing species from a fertile habitat and an inherently slow-growing species from an infertile habitat

The aim of the present study was to investigate possible differences in plasticity between a potentially fast-growing and a potentially slow-growing grass species. To this end, Holcus lanatus (L.) and Deschampsia flexuosa (L.) Trin., associated with fertile and infertile habitats, respectively, were grown in sand at eight nitrate concentrations. When plants obtained a fresh weight of approximately 5 g, biomass allocation, specific leaf area, the rate of net photosynthesis, the organic nitrogen concentration of various plant parts and the root weight at different soil depths were determined. There were linear relationships between the morphological and physiological features studied and the In-transformed nitrate concentration supplied, except for the specific leaf area and root nitrogen concentration of H. lanatus, which did not respond to the nitrate concentration. The root biomass of H. lanatus was invariably distributed over the soil layers than that of D. flexuosa. However, D. flexuosa allocated more root biomass to lower soil depths with decreasing nitrate concentration, in contrast to H. lanatus, which did not respond. The relative response to nitrate supply, i.e. the value of a character at a certain nitrate level relative to the value of that character at the highest nitrate supply, was used as a measure for plasticity. For a number of parameters (leaf area ratio, root weight ratio, root nitrogen concentration, vertical root biomass distribution and rate of net photosynthesis per unit leaf weight) the potentially slow-growing D. flexuosa exhibited a higher phenotypic plasticity than the potentially fast-growing H. lanatus. These findings are in disagreement with current literature. Possible explanations for this discrepancy are discussed in terms of differences in experimental approach as well as fundamental differences in specific traits between fast- and slow-growing grasses.     

Effect of nitrogen supply on growth,allocation and gas exchange characteristics of two perennial grasses from inland dunes

Summary We studied the effects of nitrogen supply on growth, allocation, and gas exchange characteristics of two perennial grasses of dry, nutrient-poor inland dunes: Corynephorus canescens (L.) Beauv. and Agrostis vinealis Schreber. C. canescens invests more biomass in leaves and less in roots, but has less leaf area and more root length per unit plant weight than A. vinealis. A. vinealis invests more nitrogen per unit leaf weight, but less per unit leaf area, despite a similar relative nitrogen investment in leaves and plant nitrogen concentration. Between-species differences in the rate of net photosynthesis, transpiration and shoot respiration are positively related to leaf nitrogen content per unit leaf area. The rate of net photosynthesis per unit plant weight is higher for A. vinealis at both levels of nitrogen supply, due to differences in leaf area ratio (LAR), and despite the reverse differences in the rate of net photosynthesis per unit leaf area. The water use efficiency of the two species is similar and increases significantly with an increase in nitrogen supply. The photosynthetic nitrogen use efficiency on the other hand is not affected by nitrogen supply, while at both low and high nitrogen supply A. vinealis has a 10% higher photosynthetic nitrogen use efficiency than C. canescens.     

Relationship between leaf nitrogen and photosynthetic rate for three NAD-ME and three NADP-ME C4 grasses

Theoretical considerations have suggested that there may be differences in photosynthetic nitrogen use efficiency (PNUE) among plants that use different biochemical variants of C(4) photosynthesis. To test this hypothesis we examined the leaf nitrogen content and photosynthetic rates of six grass species (three of C(4) subtype NAD-ME and three of C(4) subtype NADP-ME) grown over a wide range of nitrogen supply. While there were significant differences among the species in various traits, there were no consistent differences between the C(4) subtypes in either leaf nitrogen content at a given level of nitrogen supply or in the leaf nitrogen-photosynthesis relationship. We suggest that species-level variation in photosynthetic nitrogen use efficiency among C(4) species is large enough to mask any differences that may be due to C(4) subtype.     

Respiratory energy requirements of roots vary with the potential growth rate of a plant species

The rates of growth, net rate of nitrate uptake and root respiration of 24 wild species were compared under conditions of optimum nutrient supply. The relative growth rate (RGR)of the roots of these species varied between 110 and 370 mg g^-1 day^-1 and the net rate of nitrate uptake between 1 and 7 mmol (g root dry weight)^-1 day^-1. The rate of root respiration was positively correlated with the RGR of the roots. Root respiration was also calculated from the measured rate of growth and nitrate uptake, using previously determined values for the costs of maintenance, growth and ion uptake of two slow-growing species. The calculated rate of respiration was slightly lower than the measured one for slow-growing species, but twice as high as measured rates for rapid-growing species. This discrepancy was not due to a relatively smaller electron flow through the alternative pathway and, consequently, a more efficient ATP production in the fast-growing species. Neither could variation in specific costs for root growth or maintenance explain these differences. Therefore, we conclude that fast-growing species have lower specific respiratory costs for ion uptake than slow-growing ones. Due partly to these lower specific costs of nutrient uptake, the fraction of respiration that rapid-growing species spend on anion uptake is lower than that of slow-growing species, in spite of the much higher rate of ion uptake of the fast-growing ones.     

Photosynthesis, biomass partitioning and peroxisomicine A1 production of Karwinskia species in response to nitrogen supply

Species of the genus Karwinskia are medicinal woody plants producing secondary metabolites (anthracenones, peroxisomicine A₁) with antitumour effects. We investigated the photosynthetic and growth characteristics of Karwinskia parvifolia Zucc. and Karwinskia humboldtiana Rose plants grown at two rates of nitrogen supply. There were significant differences in growth, CO₂ exchange (photosynthesis, respiration), chlorophyll and nitrogen concentration between plants grown at high nitrogen supply (HN) and low nitrogen supply (LN). At HN, the plants of both species grew faster than those cultivated at LN. Rates of photosynthesis, leaf respiration and root respiration, quantum yield, the concentration of chlorophylls ( a, b, a + b ), specific leaf area, leaf mass ratio and peroxisomicine A₁ concentration were higher in plants grown at HN. The species-specific difference in the daily carbon budget was mainly due to variation in rates of carbon fixation. K. parvifolia responded more strongly to the nitrogen treatment than K. humboldtiana , in terms of growth, as well as with respect to photosynthesis and peroxisomicine A₁ concentration.     

The contribution of roots and shoots to whole plant nitrate reduction in fast- and slow-growing grass species

The hypothesis was tested that slow-growing grass species perform a greater proportion of total plant NO3- reduction in their roots than do fast-growing grasses. Eight grass species were selected that differed in maximum relative growth rate (RGR) and net NO3- uptake rate (NNUR). Plants were grown with free access to nutrients in hydroponics under controlled-environment conditions. The site of in vivo NO3- reduction was assessed by combining in vivo NO3- reductase activity (NRA) assays with biomass allocation data, and by analysing the NO3- to amino acid ratio of xylem sap. In vivo NRA of roots and shoots increased significantly with increasing NNUR and RGR. The proportion of total plant NO3- reduction that occurs in roots was found to be independent of RGR and NNUR, with the shoot being the predominant site of NO3- reduction in all species. The theoretical maximum proportion of whole plant nitrogen assimilation that could take place in the roots was calculated using information on root respiration rates, RGR, NNUR, and specific respiratory costs associated with growth, maintenance and ion uptake. The calculated maximum proportion that the roots can contribute to total plant NO3- reduction was 0.37 and 0.23 for the fast-growing Dactylis glomerata L. and the slow-growing Festuca ovina L., respectively. These results indicate that slow-growing grass species perform a similar proportion of total plant NO3- reduction in their roots to that exhibited by fast-growing grasses. Shoots appear to be the predominant site of whole plant NO3- reduction in both fast- and slow-growing grasses when plants are grown with free access to nutrients.     

Photosynthetic performance and resource utilization of two mangrove species coexisting in a hypersaline scrub forest

In a hypersaline mangrove scrub forest in northern Florida, coexisting trees of Laguncularia racemosa and Avicennia germinans were either fertilized with nitrogen or phosphorus, or not fertilized (controls). We aimed to test whether nutrient additions differentially altered photosynthetic performance and resource utilization in these two species. In control trees, photosynthetic rates were higher in L. racemosa than A. germinans. However, leaf nitrogen concentrations were higher in A. germinans than L. racemosa. Avicennia germinans responded to fertilization with nitrogen by increasing leaf nitrogen concentrations and rates of photosynthesis such that they were equivalent to photosynthesis in L. racemosa. Laguncularia racemosa did not show a response to nitrogen additions. Neither species showed strong responses to phosphorus fertilization. Avicennia germinans had high photosynthetic water-use efficiency (photosynthesis/transpiration), but low photosynthetic nitrogen-use efficiency (photosynthesis/leaf nitrogen). In contrast, L. racemosa had comparatively low photosynthetic water use efficiency and high photosynthetic nitrogen use efficiency. Leaf level characteristics lead us to hypothesize that coexistence of A. germinans and L. racemosa should occur where nitrogen levels are low and salinity is moderate, or at least moderate for some period of the year.     

Nodulation of acacia species by fast- and slow-growing tropical strains of Rhizobium

Thirteen Acacia species were classified into three groups according to effective nodulation response patterns with fast- and slow-growing tropical strains of Rhizobium. The first group nodulated effectively with slow-growing, cowpea-type Rhizobium strains; the second, with fast-growing Rhizobium strains; and the third, with both fast- and slow-growing Rhizobium strains. The Rhizobium requirements of the Acacia species of the second group were similar to those of Leucaena leucocephala.     

Nutrient and productivity relations of the dune grasses Ammophila arenaria and Elymus mollis

Summary A comparative study of blade photosynthesis and nitrogen use efficiency was made on the dune grasses Ammophila arenaria and Elymus mollis. In the laboratory, an open system gas analysis apparatus was used to examine the gas exchange characteristics of blades as influenced by nitrogen supply. Plants were grown under near-ambient coastal conditions in a greenhouse near Bodega Bay, California, and given either high or low supplies of nitrogen in an otherwise complete nutrient solution. In the field, ¹⁴CO₂ uptake techniques were employed to measure the seasonal patterns of blade photosynthesis of plants growing in situ at Point Reyes National Seashore. Blades used in the lab and field studies were analyzed for total nitrogen content, thus allowing for calculations of photosynthetic nitrogen use efficiency (CO₂ fixed/unit of blade N.).Under laboratory conditions, the introduced Ammophila developed higher rates of light-saturated photosynthesis than the native Elymus, especially under the nitrogenlimited growth regime. Higher rates of photosynthesis and lower concentrations of blade N resulted in a significantly greater nitrogen use efficiency for Ammophila regardless of nutrient treatment. Low N availability induced qualitatively similar physiological responses in both species, including reductions in maximum net photosynthesis, mesophyll conductance, leaf conductance, dark respiration, and blade nitrogen content, and an increase in the CO₂ compensation point.Although the photosynthetic rates of Ammophila blades were higher in the lab, those of Elymus blades were consistently higher in the field. This could have resulted from differential effects of drought on the two species (i.e. Ammophila may have been more sensitive) or a higher photosynthetic capacity in Elymus that reflected the greater (1.2–1.5 X) nitrogen content of its blades. However, the nitrogen use efficiency of Ammophila blades was greater than that of Elymus throughout most of the sampling year, despite lower average rates of field photosynthesis.The results indicated that rates of photosynthesis perunit of blade area do not account for the greater aboveground productivity of Ammophila stands along the Pacific coast of North America. Instead, efficient nitrogen use in photosynthesis maycomplement other structural and physiological traits and thereby enhance long-term carbon gain in Ammophila relative to Elymus.     

Do slow-growing species and nutrient-stressed plants respond relatively strongly to elevated CO2?

Mainly based on a simulation model, Lloyd & Farquhar (1996 ; Functional Ecology, 10, 4–32) predict that inherently slow-growing species and nutrient-stressed plants show a relatively strong growth response to an increased atmospheric CO₂ concentration. Compiling published experiments, I conclude that these predictions are not supported by the available data. On average, inherently fast-growing species are stimulated proportionately more in biomass than slow-growing species and plants grown at a high nutrient supply respond more strongly than nutrient-stressed plants.     

Carbon and nitrogen economy of 24 wild species differing in relative growth rate

The relation between interspecific variation in relative growth rate and carbon and nitrogen economy was investigated. Twentyfour wild species were grown in a growth chamber with a nonlimiting nutrient supply and growth, whole plant photosynthesis, shoot respiration, and root respiration were determined. No correlation was found between the relative growth rate of these species and their rate of photosynthesis expressed on a leaf area basis. There was a positive correlation, however, with the rate of photosynthesis expressed per unit leaf dry weight. Also the rates of shoot and root respiration per unit dry weight correlated positively with relative growth rate. Due to a higher ratio between leaf area and plant weight (leaf area ratio) fast growing species were able to fix relatively more carbon per unit plant weight and used proportionally less of the total amount of assimilates in respiration. Fast growing species had a higher total organic nitrogen concentration per unit plant weight, allocated more nitrogen to the leaves and had a higher photosynthetic nitrogen-use efficiency, i.e. a higher rate of photosynthesis per unit organic nitrogen in the leaves. Consequently, their nitrogen productivity, the growth rate per unit organic nitrogen in the plant and per day, was higher compared with that of slow growing species.     

Polyamine concentrations in four Poa species, differing in their maximum relative growth rate, grown with free access to nitrate and at limiting nitrate supply

Polyamines are thought to play a role in the control of inherent or environmentally-induced growth rates of plants. To test this contention, we grew plants of four grass species, the inherently fast-growing Poa annua L. and Poa trivialis L. and the inherently slow-growing Poa compressa L. and Poa pratensis (L.) Schreb., at three levels of nitrate supply. Firstly, plants were compared when grown with free access to nitrate, allowing the plants to grow at their maximum relative growth rate (RGR_max). Secondly, we compared the plants when grown with relative nitrate addition rates of 100 and 50 mmol N (mol N)^–1 day^–1 (RAR₁₀₀ and RAR₅₀, respectively).The freely-occurring polyamines, spermine, spermidine and putrescine, were separated from their conjugates; the latter were further subdivided into a TCA-soluble and a TCA-insoluble fraction. Each of the three fractions responded differently to the nitrate supply. Under nitrogen limitation, the total concentration of polyamines (free and bound ones together) decreased in both leaves and roots of all Poa species, whereas that in the stem remained more or less the same. These effects were to a large extent determined by the free polyamines. For the conjugates there was more differentiation, both between plant organ and among polyamine structures. A positive correlation between the RGR, LAR (leaf area per plant mass), SLA (leaf area per leaf mass), LMR (leaf mass per plant mass) and SMR (stem mass per plant mass) with the polyamine concentration was found. The RMR (root mass per plant mass) showed a negative one. No significant differences were found between the inherently fast- and slow-growing grass species.The (putrescine)/(spermine + spermidine) ratio in the leaves increased with decreasing nitrate supply, which is associated with a decrease in leaf expansion, accounting for a decrease in LAR and SLA. For the roots, this ratio tended to decrease with decreasing nitrate supply, whereas for the stems the results were somewhat more variable.We found no evidence for a crucial role of polyamines in the determination of inherent variation of growth in spite of a positive correlation of especially the free polyamines with growth parameters.     

内蒙古浑善达克沙地97种植物的光合生理特征(英文)

 报告了内蒙古浑善达克沙地不同生境下97种不同科、属植物的光合速率、蒸腾速率和水分利用效率特征。结果表明：猪毛菜（Salsola collina）、沙米（Agriophyllum pungens）、黑沙蒿（Artemisia ordosica）、狗尾草（Setaria viridis）、柠条（Caragana microphylla）等具有C4光合碳同化途径或具固氮能力的植物种具有较高的光合能力,其净光合速率大于30 μmol CO2·m-2·s-1, 而大部分具C3途径和无固氮能力的植物种的净光合速率较低,为1.29～10 μmol CO2·m-2·s-1;71%的植物种蒸腾速率集中在2～10 mmol H2O·m-2·s-1。所选出的高光效植物种在当地植被恢复与重建过程中应有很高利用价值。C4植物种占所测植物种的1/5左右,主要分布于固定沙丘上,且随着生境土壤湿度的增大其与C3植物种的光合速率差异逐渐缩小。在3种生境条件下,灌木和草本植物的光合速率和蒸腾速率顺序为：低湿地> 滩地 > 固定沙丘(p<0.01),而乔木为固定沙丘>滩地 (p<0.01) 。不同功能型植物的气体交换特征随生境的不同而异, 在固定沙丘上, 草本的蒸腾速率最高,乔木的水分利用率最高,三者光合速率相差不大。     

Chemical composition of 24 wild species differing in relative growth rate

The chemical composition of 24 plant species which showed a three-fold range in potential growth rate was investigated. The carbon content of whole plants was lower for fast-growing species than for slow-growing ones. Fast-growing species accumulated more organic N-compounds, organic acids and minerals, whereas slow-growing species accumulated more (hemi)cellulose, insoluble sugars and lignin. No correlations with relative growth rate were found for soluble phenolics, soluble sugars and lipids. The costs to construct 1 g of plant biomass were rather similar for fast- and slow-growing species, both when expressed as C needed for C-skeletons, as glucose to provide ATP and NAD(P)H, and as total glucose costs. Therefore, we conclude that, despite the differences in chemical composition between fast- and slow-growing species, variation in the costs of synthesis of whole plant biomass cannot explain interspecific variation in relative growth rate of herbaceous species.