Total Shoot Biomass Research Articles

Radiation use efficiency and leaf CO 2 exchange for diverse C 4 grasses

Biomass accumulation of different grass species can be quantified by leaf area index (LAI) development, the Beer–Lambert light interception function, and a species-specific radiation-use efficiency (RUE). The object of this field study was to compare RUE values and leaf CO 2 exchange rates (CER) for four C 4 grasses. Biomass, LAI, and fraction of photosynthetically active radiation (PAR) intercepted were measured during three growing seasons. CER was measured on several dates and at several positions in the canopies. Switchgrass ( Panicum virgatum L.) had the greatest RUE whereas sideoats grama [ Bouteloua curtipendula (Michaux) Torrey] had the lowest. Big bluestem ( Andropogon gerardii Vitman) and eastern gamagrass [ Tripsacum dactyloides (L.) L.] values were intermediate. The two species with the greatest differences in RUE, switchgrass and sideoats grama, had similar relative amounts partitioned to roots. Likewise differences among species in the accumulation of soil carbon showed trends similar to total shoot biomass production. The light extinction coefficients ( k) of switchgrass, big bluestem, and eastern gamagrass were smaller than for sideoats grama, implying that light was more effectively scattered down into the leaf canopy of the first three grasses. Whole canopy CER values were calculated with a stratified canopy approach, using LAI values, the Beer–Lambert formula with appropriate extinction coefficients, and CER light response curves. Differences among species in RUE were similar to these values for estimated whole-canopy CER divided by the fraction of light that was intercepted. High LAI along with low k contributed to higher RUE in switchgrass, in spite of lower values for single-leaf CER.

Investigation of Factors Determining Genotypic Differences in Seed Yield of Non‐irrigated and Irrigated Chickpeas Using a Physiological Model of Yield Determination

Physiological attributes determining yield, both under drought and under irrigated conditions, of some advanced chickpea lines of recent origin were investigated over two seasons using a physiological model. Total shoot biomass, grain yield, and vegetative (Dv) and reproductive (Dr) durations were measured and the crop growth rates (C) and the rate of partitioning to seed (p) were estimated. The contribution of model parameters to variations in grain yield were determined by path analysis, and the relationships of the yield determinants with seed yield were obtained by regression techniques. The model was found to be suitable for chickpea, and when the parameters were fitted the model explained 98% of the variation. Irrigation enhanced Dr and C. While C was the major single yield determinant, the combination of C and p in non‐irrigated environments explained most of the grain yield variation. Dv and Dr exhibited a negative relationship while C and p exhibited a positive relationship under drought stress and a negative relationship in the irrigated environment. There were indications of the existence of an optimum Dv for maximum C among the genotypes, suggesting the need to select for optimum duration genotypes. As high values for p and C in severe drought stress and Dr and C in the irrigated environments are advantageous for high yield, separate breeding strategies are needed for different soil water environments.

An experimental field study of the cost of reproduction in Plantago major L.

Plantago major is a variable species that occupies a wide range of open habitats with a herbaceous canopy. Previous studies have shown that individuals from habitats where the canopy is kept short by mowing have a higher reproductive allocation than individuals from habitats with a tall canopy. The present study was conducted to determine whether or not the cost of reproduction differed between these two habitats. Fifteen half-sibling families, selected from a range of habitats differing in canopy height, were grown in the laboratory. Reproduction was controlled experimentally by photoperiod manipulations, and vegetative and reproductive plants of each family were transplanted to either a mown (short canopy) or unmown (tall canopy) grass sward in the fall of the first year. Number of leaves, length and width of largest leaf, and capsule production were monitored over the next 18 months. Total shoot biomass was determined at the end of this period. Cost of reproduction was assessed in three ways, by i) comparing the subsequent performance of vegetative and reproductive individuals, ii) calculating the phenotypic correlation between reproductive output in the first year of growth and subsequent performance using only those individuals that reproduced in the first year, and iii) calculating the above correlations at the among family level. Regardless of method used, cost of reproduction was smaller in the mown than in the unmown plots, suggesting that differences in cost among habitats may be involved in selecting for different allocation patterns.

Effects of Purple Nutsedge (Cyperus rotundus) on Tomato (Lycopersicon esculentum) and Bell Pepper (Capsicum annuum) Vegetative Growth and Fruit Yield

Additive series experiments were conducted under greenhouse conditions to determine the effect of season-long interference of different initial population densities of purple nutsedge on the shoot dry weight and fruit yield of tomato and bell pepper. Purple nutsedge densities up to 200 plants/m2linearly reduced shoot dry weight at flowering and fruit yield of both crops as weed density increased. Both variables were directly correlated, and for each percentage unit of tomato shoot dry weight loss at flowering, fruit yield was reduced 1.24 units, whereas for bell pepper this relationship was 1 to 2.01. Total shoot and tuber biomass of purple nutsedge increased as density increased. The presence of either crop caused a decline in the total shoot dry weight accumulation of purple nutsedge, with tomato producing a higher degree of loss than bell pepper to the weed. Fruit yield losses due to purple nutsedge interference reached 44% for tomato and 32% for bell pepper.

Tree Growth in Potting Media Made with De-inked Paper Sludge

De-inked paper sludge from a newsprint mill was evaluated as a substitute for softwood bark in container media. Whips, 1.2 m tall, of `October Glory' red maple (Acer rubrum L.), European birch (Betula pendula Roth), and `Royalty' crabapple (Malus L.) were planted in 15-L plastic pots that contained potting media amended with 0%, 20%, 40%, 60%, 80%, or 90% paper sludge and 80%, 60%, 40%, 20%, 0%, or 0%, respectively, bark (by volume). All media contained 10% sand. After 22 weeks, plant heights, trunk diameters, and shoot dry weights were determined. Initial pH of media increased as the amount of paper sludge in the media increased, with the 90% sludge mix having pH 7.2. Paper sludge had a low initial CEC. Physical properties of all sludge-amended media were suitable for tree growth, but media containing 80% or more paper sludge shrank in volume by 10% to 12% by the end of the study. All maple and crabapple trees grown in all sludge-amended media grew as well as those in 80% bark (control mix). In fact, maple and crabapples trees in 40% sludge produced at least 10% and 36% more total shoot biomass, respectively, than trees in 80% bark. Although birch trees grown in 40% or 60% paper sludge grew as well as control plants, those grown in 80% or more sludge were at least 11% shorter and produced 24% less total shoot biomass (leaves, stems, and trunk dry weight) than control trees. These results demonstrated that de-inked paper sludge was a worthy substitute for up to 40% of the bark in a container medium for the three species tested.

Biological N 2-fixation by three tropical forage legumes and its transfer to Brachiaria humidicola in mixed swards

A study was conducted (a) to determine the biological N 2-fixation (BNF) by three tropical pasture legumes ( Centrosema pubescens, Stylosanthes hamata and Pueraria phaseoloides) grown in monoculture and associated with the grass Brachiaria humidicola; and (b) to assess the potential transfer of fixed N from the legume to the companion grass. To calculate the proportion of N in the legume derived from air, the 15N isotope dilution technique was used. The fertilizer (ammonium sulfate 10% enriched with 15N) was applied in seven split doses during the growing season. Aboveground biomass of the grass and the legumes in monocrop and in mixture were determined twice a year, after 3 months of regrowth, and samples were analyzed for total N and 15N. Over the two evaluation periods, the association B. humidicola/C. pubescens was the most stable, with a proportion of 20–30% of the legume in the mixture. As the sole crop, B. humidicola had the highest production of shoot biomass (972 g m −2) among all treatments during the first regrowth period (middle of the rainy season). Total shoot biomass in the associations ranged from 574 ( B. humidicola/C. pubescens) to 807 g m −2 ( B. humidicola/S. hamata). Dry matter production for the second evaluation (end of the rainy season) showed the same trend, but lower yields were obtained due to soil drying conditions. The N content in the shoot biomass was always higher in the legumes than in grass. However, B. humidicola in monoculture showed the highest total N accumulation (18.1 g m −2) due to its higher growth rate. Legumes in monocrop had a very significant proportion of N derived from BNF (47–69%), with C. pubescens as the better N 2-fixing legume (51–69%). A higher contribution from BNF also was observed in the legumes when mixed with the grass (57–76%). No clear transfer of N from the legume to the companion grass was observed, since the 15N in B. humidicola was always higher in the mixed swards. This grass appeared to have a different pattern of N uptake, obtaining a very significant amount of unlabeled N from outside the marked plots.

Fatty acids, starch and biomass of Scots pine needles and roots in open-air ozone exposure

Scots pine (Pinus sylvestris L.) seedlings were fumigated with 1.2–1.5 x ambient ozone (cumulative exposure) over 2 seasons in an open-air experiment. Starch and fatty acid concentrations were analyzed in needle and root tissue in the summer, autumn and early winter. Seedling growth was determined by measuring the height of the stem and the total shoot and root biomass. Significant decreases in growth were found in exposed seedlings, even though visible symptoms were lacking. Almost significant reductions in needle and root starch concentrations were found. In the ozone treated foliage, significant increases in myristic acid (14∶0) were detected, but the major fatty acids remained unchanged. Fatty acid ratios showed that the degree of unsaturation decreased in treated needles in the summer. In the roots of ozone treated seedlings, changes in fatty acids were different from those in the foliage. Decreases of the main root fatty acids (16∶0, 18∶0, 18∶1, 18:2, 18∶3) were detected in the summer. These results show that Scots pine is susceptible to enhanced levels of ozone. If the tropospheric ozone levels continue to increase it may have deleterious effects on Scots pine forests in Finland.

Does Gulf Stream Position Affect Vegetation Dynamics in Western Europe?

It is widely accepted that the climate enjoyed by maritime western Europe is strongly affected by the warming influence of the North Atlantic Gulf Stream. Until recently, however, little account has been taken of the fact that the latitudinal position of the Gulf Stream varies continuously. In theory, such displacements could generate year-toyear variation in crop yields and in the productivity and relative abundance of component species in natural vegetation. Here we test this hypothesis by examining the productivity of above-ground vegetation, monitored annually in permanent plots at Bibury (Gloucestershire, southern England) over the period 1966-1993, in relation to changes in latitudinal position of the Gulf Stream. The long-term field experiment on the road verges at Bibury (Yemm and Willis 1962, Willis 1972, 1988) has recently provided an unforeseen opportunity to examine year-to-year variations in species composition in permanent plots experiencing a standardized management regime (late autumn mowing). We examined inter-annual variation in mean total shoot biomass in each of the main Bibury species in relation to a Gulf Stream northerliness index (see legend to Table 1). Total productivity of above-ground vegetation was positively correlated with Gulf Stream northerliness (Fig. la). Annual species were negatively correlated with northerliness during certain periods, biennials showed no clear relations, and perennial species were positively correlated. Shoot biomass was positively correlated with northward displacement of the Gulf Stream in 10 species, showed a negative relation in three other species, and had no consistent effect on the remaining 10. Different species showed significant correlations with Gulf Stream movements at different times of the year (e.g. Fig. lb), and some species showed correlations with movements in the preceding year or in the year before that. Table 1 classifies the Bibury species according to response to Gulf Stream northerliness, life history and ecology (ecological data from Grime et al. 1988). Species favoured by northerly tracks include robust, perennial grasses (Bromopsis erect, Dactylis glomerata, Elytrigia repens and Festuca rubra). At Bibury, and across Western Europe, these grow rapidly in early spring and are major contributors to community biomass. The similarly responsive dicotyledons (Achillea millefolium, Gahum verum, Knautia arvensis, Plantago lanceolata and Vicia sativa) have relatively later phenologies and fairly deep root systems. Species declining in biomass with Gulf Stream northerliness (Anisantha sterilis, Galium aparine and Urtica dioica) are more heterogeneous ecologically, but are either annuals and/or have field distributions associated with damp or shaded locations where water relations may be important (Grime et al. 1988). The circumstantial evidence is that variation in Gulf Stream position is associated with changes in the relative abundance of components of the vegetation. Because these differ in phenology and rooting depth, moisture supply appears to be implicated, though the precise mechanism is unclear. Large-scale changes in atmospheric circulation are known to affect both the position of the Gulf Stream and the weather in the United Kingdom. However, it has been suggested by Taylor and Stephens (1980) that displacement of the Gulf Stream may directly influence the movement of cyclones across the North Atlantic and hence affect the frequency of anticyclones to the west of the UK (Taylor 1995a). Clearly, both of these actors may affect rainfall patterns. To test this assertion, we examined relations between Bibury weather and Gulf Stream position (see legend to Fig. 1). The relation for local atmospheric pressure appears in Fig. lc, showing that high pressure is clearly related to northward displacement. Analyses also confirm, as expected, that high pressure is associated with higher mean temperatures, more sunshine hours, and lower rainfall. We conclude (a) that the overall productivity of Bibury vegetation and the performance of certain individual spe-

Field responses of grain sorghum to a salinity gradient

Grain sorghum is a potential crop for moderately saline areas, having been identified as fairly tolerant to salinity, and shown to contain intraspecific variability for that trait. The aim of this work was to describe the responses of grain sorghum to saline irrigation, assess the responses of a set of genotypes to salinity, and to analyze the relationships between several agronomic and physiological traits and salinity tolerance. In an experiment during three years, eleven public inbred lines and one cultivar were exposed to a salinity gradient (NaCl and CaCl 2, 1:1 w/w) created with a triple line source sprinkler system. The traits most affected by salinity were grain yield, number of grains per head, shoot dry weight (both grain and stover), harvest index, and leaf chloride, sodium, calcium, and potassium concentrations. Plant height, head length, and head number per plot were moderately affected by salinity, whereas flowering time, and total number of leaves per plant were unaffected. Two sets of three genotypes were identified with consistently contrasting responses to salinity across the three years. The differences in tolerance between these two groups were not associated with differences in total shoot biomass, but rather with different patterns of biomass partitioning under the most saline conditions. There were significant differences between the tolerant and susceptible genotypes in leaf chloride and potassium concentrations. The possible implications of the latter in the determination of the contrasting genotypic responses to salinity are discussed.

Effects of nitrogen, phosphorus and potassium fertilization on field performance ofDactylorhiza majalis

The effects of nitrogen, potassium and phosphorus fertilization on performance of Dactylorhiza majalis (Rchb.f.) Hunt & Summerh. were studied in a Juncus acutiflorus-dominated hayfield. Frequency, total shoot biomass and flowering incidence decreased as a result of both nitrogen and phosphorus application. Nutrient additions also affected yields of species showing positive and negative association with orchid performance. These changes were sufficient in explaining the nitrogen and phosphate response of orchid shoot biomass and extent of flowering. The most important competitors in this respect were Rumex acetosa and Holcus lanatus. The negative overall N- and P-effect on orchid frequency seemed to be independent of changes in the surrounding vegetation however. The relative importance of nutrient limitations and additions is discussed in relation to the species decline in frequency and to its reappearance in grasslands under restoration management with decreasing nutrient availability.

Influence of Phosphorus Fertility on Intra- and Interspecific Interference between Lettuce (Lactuca sativa) and Spiny Amaranth (Amaranthus spinosus)

Greenhouse studies were conducted to determine the effect of phosphorus (P) fertility on intra- and interspecific competition between lettuce and spiny amaranth for 4 wk after emergence. Total lettuce shoot biomass per pot and weight per plant increased 39 and 44% in response to increased P fertility, respectively. P fertility had no impact on growth of spiny amaranth. Total shoot biomass of spiny amaranth increased with increasing density from four to eight plants, however, lettuce did not. Total shoot biomass of both species increased as density increased from 4 to 16 plants. Spiny amaranth, but not lettuce, weight per plant decreased in response to intraspecific competition. Reciprocal yield analysis showed that spiny amaranth produced 2.4 times more biomass than lettuce when competing intraspecifically and four times more biomass under interspecific competition. Lettuce weight per plant was not affected. Relative yield analysis indicated that spiny amaranth was more competitive than lettuce regardless of P fertility. However, increased P fertility increased competitiveness of lettuce. Relative crowding coefficients indicated that spiny amaranth at the low density with low P fertility was 33 times more competitive than lettuce. Addition of P caused lettuce and spiny amaranth to be equally competitive at the lowest density; however, at the highest density, spiny amaranth was 4 tunes more competitive than lettuce regardless of additional P.

Mycorrhizal dependency of micropropagated argan tree (Argania spinosa): I. Growth and biomass production

The influence of V.A. mycorrhization was studied on two clones of in-vitro micropropagated plantlets ofArgania spinosa, a slow-growing tree of great importance in agroforestry systems in the semi-arid and arid zones of southwestern Morocco. Inoculation increased total shoot length, stem girth and biomass of the plants, when cultivated in controlled conditions with a phosphorus fertilization of 31 mgP·kg−1 added to a substrate already containing 13.5 mg·kg−1 available P (Olsen). The positive effect increased with time and, after 6 months, the above-ground dry matter production was 5 to 6 times higher for inoculated plants. The Relative Mycorrhizal Dependency Index, calculated on total dry matter, reached 77–78% at the end of experiment. Calculated on above-ground dry matter, the R.M.D.I. was 81–83%, placing the argan tree among the plants most dependent on mycorrhizal symbiosis. The root/shoot ratio was markedly (40–50%) reduced by inoculation, demonstrating the higher efficiency of a mycorrhizal root system.

Growth responses of tomato plants to low concentrations of sulphur dioxide and nitrogen dioxide

Forty-five-day-old plants of Lycopersicon esculentum were exposed to 0.1 ppm SO 2, 0.2 ppm NO 2 and 0.1 ppm SO 2 + 0.2 ppm NO 2 for 4 h daily for 50 days. Plant height, number of leaves, total leaf area, total leaf biomass, total shoot biomass and total plant biomass were increased by these low dosages. When exposed to either NO 2 or SO 2 alone, relative growth rate, net assimilation rate, leaf production rate and specific leaf area increased initially but declined after exposure for longer times. Both SO 2 and NO 2 reduced root growth and resulted in a low root:shoot ratio. Number of leaves, total leaf area, total leaf biomass and leaf area duration increased up to 30 days of both SO 2 and NO 2 exposure, indicating that the tomato plants in response to SO 2 and NO 2 allocated a greater proportion of its photoassimilates for growth and development of photosynthetic organs. Chlorophyll concentration increased initially but declined after exposure for longer periods. Foliar N and SO 2− 4-S content increased in plants exposed to NO 2 and SO 2, respectively. P content was reduced following exposure to SO 2 and NO 2 alone or in combination. The study suggests that low dosages of pollutants are fertilizing the plants, promoting vegetative growth at the expense of reproductive growth.

Effects of season-long CO 2 enrichment on cereals. I. Growth performance and yield

Two cultivars each of spring wheat ( Triticum aestivum L., cultivars ‘Star’ and ‘Turbo’) and spring barley ( Hordeum vulgare L., cultivars ‘Alexis’ and ‘Arena’) were exposed throughout the growing season to ambient (384 p.p.m.) and above ambient CO 2 concentrations (471, 551, 624, 718 p.p.m.) in open-top chambers. Plant samples were taken four times during plant development and biomass partitioning into stem, leaves and ear was measured. Total above-ground biomass increased mainly in the CO 2 concentration range between 400–550 p.p.m. for wheat, and between 400–700 p.p.m. for barley. Stimulation of biomass was largely due to an increase in tillering rate. At the tiller level CO 2 enrichment revealed a decrease in leaf dry weight at anthesis stage, which was due to a reduction in leaf size (barley) and in leaf number (wheat). Specific leaf weight of the mature flag leaf was unaffected by CO 2. Stem biomass per tiller was temporarily (‘Star’, ‘Alexis’) or during the whole growth period (‘Turbo’, ‘Arena’) increased by CO 2 exposure, while ear dry weight was increased (barley) or even decreased (‘Star’). Except for the barley cultivar ‘Arena’, which showed a 84% increase in the number of grains per ear, the number of ears was almost entirely responsible for the increased grain yield among the CO 2 treatments. At the highest CO 2 concentration yield increase amounted to 19% and 27% for the two wheat cultivars, and 52% and 89% for the two barley cultivars in comparison with the ambient CO 2 level. Among all cultivars there was an inverse relationship between the total shoot biomass produced at ambient CO 2 conditions and the plant's response to the CO 2 enrichment. This indicates that the genetic potential of wheat unlike barley is highly adapted to present atmospheric CO 2 conditions and thus responsible for the small CO 2 effect on wheat.

Chloride accumulation and partitioning in Barley as affected by differential root and foliar salt absorption under saline sprinkler irrigation

Barley is a crop that has been classified as tolerant to soil salinity, but under sprinkler irrigation with saline water it can readily absorb salts through its leaves and develop injury. Experiments using a triple-line-source sprinkler system were conducted on barley between 1989 and 1991 to determine: (1) the specific effects of foliage wetting on the mass of different shoot components; (2) the relative contribution of root and foliar absorption processes to foliar Cl accumulation; and (3) the extent by which these processes affect Cl partitioning in the shoot at the end of the season. Some plants were covered with plastic during the irrigation process to prevent foliar wetting while others remained uncovered. Salinity affected the partitioning of dry matter in the shoots regardless of whether plants were covered during the irrigation process. The organs associated with reproduction, e.g., heads and peduncles, comprised a larger fraction of the total shoot biomass under high salinity than under low salinity, indicating that plants under salinity stress were able to redistribute their dry matter to favor reproductive growth. The Cl concentration of the young leaves sampled from uncovered plants was linearly related (i.e., r 2>0.71) to the Cl concentration of the irrigation water. Equivalent leaves from covered plants also contained a substantial amount of Cl but concentrations were weakly correlated (i.e., r 2<-0.41) with the concentration of Cl in the irrigation water. At low salinity, there were no differences in leaf Cl concentrations between covered and uncovered treatments. In young leaves, differences between these treatments progressively increased with increasing salinity, indicating that the relative contribution of Cl in the leaf from foliar absorbed salts increased with increasing Cl in the irrigation water. Only in the youngest leaves sampled at the end of the season from plants grown at high salinity was the Cl concentration in uncovered plants (foliar plus root-absorbed Cl) found to be more than twice that in covered plants (only root-absorbed Cl) indicating that most of the Cl in young leaves originated from foliar absorption. In addition, only in the youngest leaves (e.g., flag leaves) was the slope of the relationship between leaf-Cl concentration and Cl concentration of the sprinkling water of uncovered plants more than twice that of covered plants, also indicating that foliar-Cl absorption was more substantial than root-Cl absorption. At high salinity, the difference in leaf Cl concentration between covered and uncovered plants was maximum in the youngest leaf (flag leaf), but differences became progressively smaller with increasing leaf age until ultimately concentrations of chloride in leaves older than the flag leaf-2 were highest in covered plants. In older tissue, it was difficult to distinguish which process, foliar or root absorption, was most responsible for leaf-Cl accumulation. These processes may not be entirely independent of one another and much of the Cl in the oldest leaves of uncovered plants could have been derived from foliar sources during the first month of sprinkling, reaching maximal levels, and thereby restricting root-absorbed Cl. Furthermore, since these leaves at the end of the season are more injured and drier than those from covered plants, late-season sprinkler irrigations may have been responsible for leaching some of the Cl out of these necrotic leaves.

Seasonal changes in the pigments, carbohydrates and growth of red spruce as affected by exposure to ozone for two growing seasons

summaryThree‐year‐old red spruce seedlings were exposed to various concentrations of ozone, from 0.4 to 3 times ambient, for two consecutive growing seasons in open‐top chambers in Ithaca, NY, USA. Exposures, which varied with changes in daylength, were from 30 May to 14 December 1987 and 1 June to 1 December 1988. Seedling biomass, foliar pigments and carbohydrate content of roots and shoots were assessed once or twice per month. Tree biomass increased through the summer and declined slightly in late autumn, regardless of ozone treatment. Biomass and contents of sugar and starch of 1988 fixed growth declined linearly with exposure to increasing levels of ozone. Rates of decline in total shoot biomass and old shoot biomass increased linearly with exposure to increasing concentrations of ozone, but tree height was not affected. Seasonal means of starch content of roots decreased linearly with increasing doses of ozone, but in contrast seasonal mean sugar content and rate of sugar accumulation of roots increased linearly. Chlorophyll a and chlorophyll b contents were not affected by ozone.These data are consistent with the concept that ozone stress is cumulative, since effects on biomass and carbohydrate content of roots and shoots were not detected after the first year of exposure, but were detected after the second year of treatments. Furthermore, biomass was reduced by ozone only in tissues that were initiated during the first year of exposures and developed during the second year of exposures (1988 fixed growth).

Effects of Water, Nitrogen and Competition on Growth, Yield and Yield Components of Field-grown Tepary Bean

SummaryThe effects of water and nitrogen on growth, yield and yield components of tepary bean (Phaseolus acutifolius) were evaluated at Tucson, Arizona in 1987 and the effects of water and intercrop competition with Sonoran panicgrass (Panicum sonorum) in 1988. Total shoot biornass and reproductive yield were significantly reduced by lack of water in both seasons. Addition of nitrogen had no significant effect on total shoot biomass or reproductive yield in 1987. Intercrop competition significantly reduced total shoot biomass and reproductive yield of tepary bean in 1988. Yield component responses varied slightly depending on treatment and year.

Growth and yield responses of rice to carbon dioxide concentration

SUMMARYRice plants (Oryza salivaL., cv. IR30) were grown in paddy culture in outdoor, naturally sunlit, controlled-environment, plant growth chambers at Gainesville, Florida, USA, in 1987. The rice plants were exposed throughout the season to subambient (160 and 250), ambient (330) or superambient (500, 660, 900 μmol CO2/mol air) CO2concentrations. Total shoot biomass, root biomass, tillering, and final grain yield increased with increasing CO2concentration, thegreatest increase occurring between the 160 and 500 μmol CO2/mol air treatments. Early in the growing season, root:shoot biomass ratio increased with increasing CO2concentration; although the ratio decreased during the growing season, net assimilation rate increased with increasingCO2concentration and decreased during the growing season. Differences in biomass and lamina area among CO2treatments were largely due to corresponding differences in tillering response. The number of panicles/plant was almost entirely responsible for differences in final grain yield among CO2treatments. Doubling the CO2 concentration from 330 to 660 μmol CO2/mol air resulted in a 32 % increase in grain yield. These results suggest that important changes in the growth and yield of rice may be expected in the future as the CO2concentration of the earth's atmosphere continues to rise.

ATMOSPHERIC CO2 ENRICHMENT OF TOMATO AND STRAWBERRY PLANTS UNDER FIELD PRODUCTION CONDITIONS

A technique was developed for controlled micro-release of CO2 into the leaf canopy of strawberry and tomato plants under field production conditions; The leaf canopy atmosphere of tomato plants was enriched to 500 and 1200 ppm CO2 with release rates of 60 and 300 l/h·30 m of row respectively. After 60 days of enrichment for 6 h each day beginning at fruit set, the total shoot biomass and yield was increased 41% and 25 % respectively for the high CO2 release rate. Strawberry leaf canopies did not show increased CO levels with CO2 enrichment except under ventilated2 row-covers where the atmospheric CO2 level was increased to 1500 ppm CO2. Although the total biomass was increased 39% this did not translate into increased yields perhaps due to excessive temperatures under the row covers.

The effects of nutrient additions on mixtures of Typha latifolia L. and Typha domingensis pers. along a water-depth gradient

Over a 2-year period, nutrients (N, P and K) were added to mixtures of Typha latifolia L. and T. domingensis Pers. growing across a water-depth gradient in order to determine: (1) the relationship between nutrient limitation and water depth; (2) the differential effect of nutrient addition on species performance. In addition, sediment characteristics were determined for untreated mixtures, monocultures and bare sediment. Additions of nutrients resulted in a rapid increase in total shoot density compared to controls. Increases in total shoot biomass, however, occurred gradually over time in response to nutrient additions. Nutrients enhanced T. latifolia in shallow to medium depths while T. domingensis was enhanced in medium to deep waters. Compared to bare sediment, pH was not affected by the presence of either species. Redox potential, however, was increased by T. domingensis in medium depths while unaffected by T. latifolia. Coupled with the observation that T. domingensis is capable of growing in deeper water than T. latifolia, the E h data suggest that T. domingensis may have a greater capacity to aerate its roots and rhizosphere. Sediment ammonium concentrations were reduced by c. 90–95% by plant growth while potassium was reduced by c. 35–55%. Phosphate was unchanged compared to bare sediment. These results suggest that sediment nitrogen was the most limiting nutrient.