Microclimate, Canopy Structure and Photosynthesis in Canopies of Three Contrasting Temperate Forage Grasses: II. Microclimate and Canopy Structure

Profiles of shortwave radiation, net radiation and temperaturewere measured in swards of three grasses of contrasting structureLolium perenne cv. S24, L. perenne cv. Reveille and Festucaarundinacea cv. S170. Measurements were also made of the reflectionof shortwave radiation, leaf water potential and stomatal resistance.Differences in canopy structure influenced the absorption andreflection of radiation by the varieties. The absorption ofnet radiation and its influence on air temperature inside thecanopy was shown to vary with canopy structure. Calculationsshowed that diurnal changes in the reflection and transmissionof light (400–700 nm) would have little effect on canopyphotosynthesis. No clear relationship between leaf extensionrate, temperature and leaf water potential could be established,although decreases in water potential did appear to reduce thepotential response of leaf extension rate to temperature.     

Microclimate, Canopy Structure and Photosynthesis in Canopies of Three Contrasting Temperate Forage Grasses: III. Canopy Photosynthesis, Individual Leaf Photosynthesis and the Distribution of Current Assimilate

The rates of canopy and individual leaf photosynthesis and ¹⁴Cdistribution for three temperate forage grasses Lolium perennecv. S24, L. perenne cv. Reveille and Festuc'a arundinacea cv.SI70 were determined in the field during a summer growth period.Canopy photosynthesis declined as the growth period progressed,reflecting a decline in the photosynthetic capacity of successiveyoungest fully expanded leaves. The decline in the maximum photosyntheticcapacity of the canopies was correlated with a decline in theirquantum efficiencies at low irradiance. Changes in canopy structureresulted in changes in canopy net photosynthesis and dark respiration.No clear relationships between changes in the environment andchanges in canopy net photosynthesis and dark respiration wereestablished. The relative distributions of ¹⁴C in the shootsof the varieties gave a good indication of the amount of drymatter per ground area in the varieties.     

Canopy Photosynthesis and Crop Growth Rate of Eight Temperate Forage Grasses

The rates of canopy and individual leaf photosynthesis, ratesof growth of shoots and roots, and the extinction coefficientfor light of eight temperate forage grasses were determinedin the field during early autumn. Canopy gross photosynthesiswas calculated as net photosynthesis plus dark respiration adjustedfor temperature using a Q₁₀ = 2. The relationships between canopygross photosynthesis and light intensity were hyperbolic, andthe initial slopes of these curves indicated that light wasbeing utilized efficiently at low light intensities. The initialslope depended on the distribution of light in the canopy andthe quantum efficiency of the individual leaves. The maximumrate of canopy gross photosynthesis reflected the maximum rateof individual leaf photosynthesis. Although the maximum rateof canopy gross photosynthesis was correlated with crop growthrate, there was no significant relationship between daily grossphotosynthesis and crop growth rate. Indeed, daily gross photosynthesisvaried by only 22 per cent, whereas the daily growth of shootsand roots varied by 120 per cent. This poor correlation is influencedby a negative correlation (P < 0.01) between the maximumrate of canopy gross photosynthesis and the initial slope ofthe curve relating canopy gross photosynthesis and light intensity.Difficulties in the interpretation of measurements of dark respirationappeared to confound attempts to relate daily net photosynthesisto crop growth rate, individual leaf photosynthesis, and theextinction coefficient for light.     

Microclimate, Photosynthesis and Growth of Lucerne (Medicago sativa L.). II. Canopy Structure and Growth

The growth of lucerne var. Europe was examined in the fieldduring 1976. The annual dry matter production of unirrigatedlucerne during 1976, with no nitrogen fertilizer application,was 82.5 per cent greater than unirrigated S.24 perennial ryegrass,with a nitrogen application of 384 kg ha^–1. The mean aboveground growth rate of lucerne was 7.3 g DM m^–2 day^–1between March and early June, of which stem material contributeda maximum of 76.5 per cent. Significant losses of leaves andstems occurred from the end of April, indicating a loss of potentialforage material. Nitrogen analyses of the above ground crop suggested that in56 days lucerne yielded 10.7 per cent more nitrogen than didS.24 annually with a nitrogen fertilizer addition of 280 kgha^–1. Between 13 and 57 per cent of the daily photosynthate is translocatedbelow ground. Medicago sativaL, lucerne, dry matter production, canopy structure, nitrogen analyses     

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

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

Isolation and Characterization of Dinitrogen-Fixing Bacteria from the Rhizosphere of Temperate Cereals and Forage Grasses

N₂(C₂H₂)-fixing bacteria were isolated from the rhizosphere of various cereals and forage grasses grown in the greenhouse and from the rhizosphere of field-grown wheat in Sweden. All 46 isolates from the greenhouse plants lost their nitrogenase activity during purification. By imposing a stronger selection pressure, we obtained pure isolates with nitrogenase activity from field-grown wheat. Some isolates were identified as Enterobacter agglomerans and Bacillus polymyxa, but several bacteria of uncertain taxonomy also occurred. One of the isolates grew and reduced acetylene only in the presence of other bacteria or certain vitamins. Species of Azotobacter or Azospirillum could not be isolated from the rhizosphere of any of the cereals and forage grasses studied.     

Arthropod Abundance,Canopy Structure,and Microclimate in a Bornean Lowland Tropical Rain Forest1

This study applies a novel, vertically stratified fogging protocol to document arthropod abundance, density, and biomass across a vertical gradient in a primary, lowland dipterocarp forest canopy in Borneo. We fogged arthropods at 5 m vertical intervals and 20 m horizontal intervals along six full‐canopy transects and measured leaf surface areas along the same transects. The results show that arthropod biomass in the aboveground regions was 23.6 kg/ha, the abundance was 23.9 million individuals/ha, and the density on leaf surfaces was 280 individuals/m² leaf area. All three numbers are five to ten times higher than estimated by previous surveys of tropical lowland rain forest canopies using mass‐collection techniques. Arthropod abundance and biomass were analyzed in relation to canopy structure, composition, vapor pressure deficit (VPD), photosynthetic photon flux density (PPFD), and height. Using stepwise regression we found that 13 of 14 arthropod groups had significant positive relationships with one‐sided leaf area, 11 had significant negative relationships with VPD, 3 had significant relationships with height, and none showed positive relationships with light. Classifying the 14 taxa based on their responses to leaf area and VPD created three groups that corresponded roughly to the biology of these taxa. This study suggests that the biomass and abundance, and perhaps therefore—by extrapolation—the biodiversity, of tropical canopy arthropods may be very much higher than previously estimated.     

The Effects of Temperature upon Seed Development in Three Species of Forage Grasses

The effects of three temperature regimes, 25°C day/20°Cnight, 20°C day/15°C night and 15°C day/10°Cnight upon seed development in S.22 Italian ryegrass, S.24 perennialryegrass, S.215 meadow fescue and a Swiss ecotype of meadowfescue were investigated. The largest ovaries and largest seedswere obtained from the 15/10°C environment and floret fertilitywas greatest at 20/15°C. The largest seed weight per inflorescencewas at 20/15°C, except for the Swiss ecotype of meadow fescuewhere it was greatest at 15/10°C. The percentage germinationwas highest from those seeds developed at 25/20°C and thiswas particularly marked at germination temperatures of 13–20°C.There was a low rate of germination of seeds from the 15/10°Ctreatment, but they produced seedlings with the largest dryweights. It is concluded that year to year temperature differenceswill affect the yield and quality of seed crops of forage grasses.     

Phosphate Deficiency in Maize. I. Leaf Phosphate Status, Growth, Photosynthesis and Carbon Partitioning

Maize plants (Zea mays L.) were cultured with nutrient solutioncontaining 0.001 or 0.5 mM orthophosphate (Pi). Effects of lowphosphate (low-P) nutrition on growth, leaf phosphate status,photosynthesis, and carbon partitioning were investigated. Withlow-P treatment, the fresh weight of aerial parts decreasedby about 40% by 24 days after planting. Detailed studies ofthe effects of low-P treatment on the other characteristicsof maize leaves-were done using the middle part of the thirdleaf, counting from the base. Low-P treatment had almost noeffect on specific leaf weight or soluble protein content measured13 to 21 days after planting. Low-P treatment decreased Chicontent slightly (by 15% 19 days after planting). Twenty onedays after planting, low-P treatment had greatly decreased thelevels of leaf acid extractable Pi (by 77%) and photosynthesisrates (by 68%). The detrimental effects of low-P treatment onthe rates of photosynthesis and the amounts of acid extractablePi became progressively greater with time. There was a strongcorrelation between levels of leaf acid extractable Pi and ratesof photosynthesis. The minimum level of Pi necessary to sustainthe maximum photosynthesis rate was 0.6 mmol m^–2. Belowthis minimum content of Pi, the rate of photosynthesis decreasedsharply with decreasing Pi. To investigate the direct effectof Pi depletion on photosynthate partitioning at equivalentrates of photosynthesis, the rates in controls were reducedto almost the same as those in 18 or 19 day old low-P plants(about 50% of those in controls) by lowering light intensityand/ or ambient CO₂ concentration. The data clearly indicatesthat low-P treatment had a direct effect in lowering photosynthatepartitioning into starch. Starch mobilization during the nightwas also inhibited under low-P conditions. (Received January 7, 1991; Accepted March 5, 1991)     

A Tropical Freshwater Wetland: I. Structure,Growth, and Regeneration

Forested wetlands dominated by Terminalia carolinensis are endemic to Micronesia but common only on the island of Kosrae, Federated States of Micronesia. On Kosrae, these forests occur on Nansepsep, Inkosr, and Sonahnpil soil types, which differ in degree of flooding and soil saturation. We compared forest structure, growth, nutrition, and regeneration on two sites each on Nansepsep and Inkosr soils and one site on the much less common Sonahnpil soil type. Terminalia tree sizes were similar on all three soil types, but forests differed in total basal area, species of smaller trees, and total plant species diversity. Terminalia regeneration was found only on the Inkosr soil type, which had the highest water table levels. Other Terminalia species are relatively light demanding, and T. carolinensis exhibited similar characteristics. It is therefore likely that Terminalia requires periodic, but perhaps naturally rare, stand-replacing disturbances (e.g., typhoons) in order to maintain its dominance, except on the wettest sites, where competition from other species is reduced. Terminalia swamps in the Nansepsep soil type appeared to be at the greatest risk of conversion to other uses, but swamps on all three types may face greater pressure as Kosrae's population increases and the island's infrastructure becomes more developed.     

Effects of Nitrate Application on Amaranthus powellii Wats. : I. Changes in Photosynthesis, Growth Rates, and Leaf Area

Physiological effects of different nitrate applications were studied using the C₄ plant, Amaranthus powellii Wats. Plants were grown in a controlled environment chamber and watered daily with nutrient solutions containing 45, 10, 5, or 1 millimolar nitrate. Chloride and sulfate were used to keep the cation and phosphate concentrations constant. Total leaf nitrogen concentration, chlorophyll concentration, specific leaf mass, leaf area, relative growth rate, relative leaf growth rate, unit leaf rate (increase of dry mass per unit leaf area per day), net photosynthetic rate, and incident quantum yield decreased with decreasing nitrate concentration. The per cent decrease of unit leaf rate was similar to the decrease of light-saturated net photosynthetic rate; however, the decrease in relative growth rate was less than that of unit leaf rate because leaf area ratio (leaf area per unit dry mass) increased with decreasing nitrate concentration. Essential mineral concentrations per unit leaf area were about equal among all treatments. Leaf expansion, determined by stomatal density, decreased except for the 1 millimolar treatment which showed relatively more cell expansion but less cell division. Decreased nitrate application was correlated with higher osmotic potentials and lower pressure potentials (determined by pressure-volume curves), whereas leaf water potentials were equal among treatments. Even though total leaf area and shoot mass decreased with decreasing applied nitrate, the increase of the leaf area ratio may be related to selection for the highest possible growth rate.     

Sodium and Chloride Sensitivity in Alfalfa (Medicago sativa L.): Growth,Photosynthesis, and Tissue Ion Regulation in Contrasting Genotypes

Alfalfa (Medicago sativa L.) is a moderately salt-tolerant plant. This study was conducted to evaluate responses of two contrasting alfalfa genotypes (OMA-84-salt sensitive and OMA-285-salt-tolerant) to components (Na⁺, and/or Cl^?) of salt stress. Alfalfa genotypes were exposed to Na⁺???salts (without chloride), Cl^????salts (without sodium), and NaCl (sodium chloride) stresses with two concentrations (30 and 150 mM). The treatments, involving macronutrients, with the same osmotic potentials, were taken as control. Salt stress, irrespective of type and intensity, caused a significant reduction in plant biomass, physiological (net photosynthetic rate, photosystem II efficiency, chlorophyll fluorescence, water use efficiency, maximum yield of primary photochemistry, and electron transport rate), and shoot mineral (calcium, magnesium, phosphorus, and potassium) contents compared to control; however, this reduction was in the order of NaCl (150 mM)?>?Na⁺ (150 mM)?>?Cl^? (150 mM). The alfalfa genotype OMA-285 sustained growth under both types of salt stresses than the genotype OMA-84 due to less accumulation of Na⁺ and Cl^? ions, maintenance of higher K⁺/Na⁺ ratio, and better photosynthetic activities. In conclusion, salt stress caused a significant reduction in alfalfa growth, this reduction was more under NaCl stress and the effect was mainly additive. The alfalfa genotype OMA-285 sustained growth under salt stresses than the genotype OMA-84 due to ionic homeostasis. However, the tested genotypes were more sensitive to Na⁺ toxicity than the Cl^? toxicity, and the contrasting genotypes differed in tissue tolerance of high Na⁺ and Cl^?. Further research is needed to evaluate tissue tolerance in a diverse and large group of alfalfa genotypes to elucidate the general salt tolerance mechanism in alfalfa.

     

Sodium Absorption and Distribution in Forage Grasses of Different Potassium Status

The absorption and distribution of sodium were examined in threegrasses grown in flowing solution culture with different suppliesof potassium. There were marked differences between the speciesin the rate of absorption by their roots, timothy absorbingat a much slower rate than either ryegrass or cocksfoot. Inall species, the rate of Na absorption was greatest when therewas a maintained supply of K and/or when the K contents of theplants were high. Transport of Na from roots to shoots of timothywas restricted; it was less restricted in the other speciesand large proportions of the Na moved from roots to shoots whenK was not supplied to the plants. Sodium transported from theroots accumulated in old leaves and not in the younger leaves.When K was no longer supplied, the growth of ryegrass was maintainedin the plants previously grown with Na plus K; Na supplied insteadof K, however, did not maintain growth. Cocksfoot grown withNa grew less well than when grown without Na when plants wereno longer supplied with K; the growth of timothy was unaffectedby Na. Dactylis glomerata L., Lolium perenne L., Phleum pratense L., cocksfoot, ryegrass, timothy, absorption of ions, distribution of ions, potassium, sodium     

群体中叶片光合能力的分布及其对群体光合作用的影响

利用数学变分原理分析了群体中叶片光合能力对环境适应和有限氮资源利用的最优分布。叶片光合能力呈现与光强相同的负指数衰减分布时,“群体的光合速率和对氮的利用率最高;叶片对环境光强适应的优越性随群体消光系数和叶面积指数增加而增加。由此推导了叶片光合能力最优分布下的群体光合模型。     

3种禾草苗期生长和水分利用对土壤水分变化的反应

采用5种不同的水分处理,于室内生长箱内盆栽条件下对引种禾草柳枝稷(Panicum virgatum)、乡土禾草白羊草(Bothriochloa ischaemum)和栽培禾草谷子(Setaria italica)等苗期根冠生长和水分利用特征进行了比较分析.结果显示:(1)充分供水下3种禾草的苗期生物量和蒸腾效率均显著高于其它4种水分处理,而高水与低水处理下各自的根冠比无显著差异;(2)各水分处理下谷子苗期总生物量、蒸腾效率和耗水量均显著大于白羊草和柳枝稷;(3)在5种水分处理下,苗期根冠比谷子均最小,柳枝稷最大;(4)低降复水后,3种禾草生物量和蒸腾效率较低水处理分别显著提高16.7%-98.7%和28.2%-118.2%,显示出补偿效应,以白羊草增幅最大.结果表明,白羊草、谷子和柳枝稷在不同土壤水分处理下的苗期生物量、根冠分配比例以及水分利用效率差异反映了野生种、栽培种和引进种禾草苗期对半干旱环境条件水分生态适应性的异同.     

Phytostabilization of Acidic Soils with Heavy Metal Contamination Using Three Forage Grasses in Combination with Organic and Inorganic Amendments

Two experiments were conducted to investigate the effects of organic and inorganic amendments on metal stabilization and the potential of three forage grasses, i.e., Pennisetum americanum × Pennisetum, Euchlaena mexicana, and Sorghum dochna, for phytostabilization of acidic heavy metal-contaminated soils. The three grasses died 5 days after transplanting into the contaminated soils. Organic fertilizer (pig slurry and plant ash) only or combined with lime, NPK fertilizer, and sewage sludge resulted in adequate grass growth in the contaminated soils through a significant increase in the soil pH, N, P, K, and organic matter contents, and a decrease in the metal concentrations. The shoot biomass of P. americanum×P. purpureum and S. dochna was 1.92 and 2.00 times higher than that of E. Mexicana. The solubility of Cd, Pb, and Zn strongly depends on organic matter, while the solubility of Cu strongly depends on both soil organic matter and pH. The concentrations of Cd, Pb, and Zn in plant shoots growing in soil with a mixed amendment were significantly lower than plants growing in soil amended with an organic fertilizer only, whereas the Cu concentrations in plant shoots exhibited the opposite trend. The results indicated that 5% organic fertilizer only or combined with 5% sewage sludge were appropriate amendments and S. dochna and P. americanum × Pennisetum are suitable plants for phytostabilization of acidic heavy metal-polluted soils.     

A Canopy Photosynthesis Model for the Dynamics of Size Structure and Self-thinning in Plant Populations

A dynamic model for growth and mortality of individual plantsin a stand was developed, based on the process of canopy photosynthesis,and assuming an allometric relationship between plant heightand weight, i.e. allocation growth pattern of plant height andstem diameter. Functions G(t, x), for the mean growth rate ofindividuals of size x at time t, and M(t,x), for the mortalityrate of individuals of size x at time t, were developed fromthis model and used in simulations. The dynamics of size structurewere simulated, combining the continuity equation model, a simpleversion of the diffusion model, with these functions. Simulationsreproduced several well-documented phenomena: (1) size variabilityin terms of coefficient of variation and skewness of plant weightincreases at first with stand development and then stabilisesor decreases with an onset of intensive self-thinning; (2) duringthe course of self-thinning, there is a power relationship betweendensity and biomass per unit ground area, irrespective of theinitial density and of the allocation-growth pattern in termsof the allometric parameter relating plant height and weight.The following were further shown by simulation: (a) competitionbetween individuals in a crowded stand is never completely one-sidedbut always asymmetrically two-sided, even though competitionis only for light; (b) plants of ‘height-growth’type exhibit a greater asymmetry in competition than plantsof ‘diameter-growth’ type, (c) the effect of competitionon the growth of individuals in a crowded stand converges toa stationary state, even when the stand structure still changesgreatly. All of these theoretical results can explain recentempirical results obtained from several natural plant communities.Finally, a new, general functional form for G(t, x) in a crowdedstand is proposed based on these theoretical results, insteadof a priori or empirical growth and competition functions. Canopy photosynthesis, competition mode, continuity equation, self-thinning, simulation, size distribution     

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.