Shoot Relative Growth Rate Research Articles

Impact of Suboptimal Temperature on Growth, Photosynthesis, Leaf Pigments and Carbohydrates of Domestic and High-altitude Wild Lycopersicon Species

The impact of near-optimal (25/20 degrees C) and suboptimal (16/14 degrees C) day/night temperatures on growth, photosynthesis, pigment composition and carbohydrate content was compared between domestic and high-altitude wild Lycopersicon species. When related to the relative shoot growth rate (RSGR) measured at optimal temperature, genotypes of the domestic tomato (L. esculentum (L.) Mill. cv. Abunda and cv. Large Red Cherry (LRC) showed a stronger inhibition of RSGR at suboptimal temperature than the high-altitude wild species L. peruvianum Mill. LA 385 and L. hirsutum Humb. & Bonpl. LA 1777. The initiation rare of new leaves was 2.1-fold faster in all species at 25/20 degrees C than at 16/14 degrees C. In contrast to the other genotypes, the leaf area of suboptimally grown Abunda plants was 28 % smaller than the area of leaves that were fully expanded at optimal temperature. In all species, specific leaf area (SLA) at 16/14 degrees C was 17-26 % lower than at 25/20 degrees C. The percentage of leaf dry matter increased in response to growth ar suboptimal temperature. This increase was higher in L. esculentum genotype Abunda (99 %) than in genotype LRC (38 %), and the wild species L. peruvianum (50 %) and L. hirsutum (38 %), which could be attributed to inter- and intra-specific differences in starch accumulation of 16/14 degrees C-grown leaves. Only in both L. esculentum genotypes, net photosynthetic rate at growth irradiance (A(225)) and at light saturation (A(sat)) was 14 to 30 % lower in leaves grown and measured at suboptimal temperature, compared with leaves grown and measured at optimal temperature (25 degrees C). Chlorophyll (Chl) a fluorescence measurements indicated that the decrease of A225 in leaves of suboptimally grown L. esculentum plants was paralleled by a decrease in the quantum yield of photosystem II electron transport (Phi(PSII)), which could be mainly attributed to a decrease in the photochemical quenching component (q(P)). In all species, the nonphotochemical quenching component (NPQ) was 2 to 4-fold higher at 16/14 degrees C. Growth temperature hardly affected Chi content on a leaf area basis, whereas the content of xanthophyll cycle pigments (violaxanthin + antheraxanthin + zeaxanthin) on a Chi basis was ca. 1.5-fold higher in 16/14 degrees C-grown leaves. The epoxidation state of the xanthophyll cycle pool was only slightly lower in suboptimal leaves due to the moderate growth irradiance.

Effects of elevated atmospheric CO(2) on phenology, growth and crown structure of Scots pine (Pinus sylvestris) seedlings after two years of exposure in the field.

Three-year-old Scots pine (Pinus sylvestris L.) seedlings were grown for two years in the ground in open-top chambers supplied with either an ambient or elevated (ambient + 400 &mgr;mol mol(-1)) CO(2) concentration. Phenological observations and measurements of height and stem diameter growth, absolute and relative growth rates, starch and soluble carbohydrate concentrations of the needles, and crown structure and needle properties were made at frequent intervals throughout the two growing seasons. Elevated CO(2) significantly advanced the date of bud burst in both years. The increase in total needle area in response to elevated CO(2) was accounted for by longer shoots and an increase in individual needle area in the first year, and by an increase in the number and length of shoots in the second year. Stem diameter and tree height were enhanced more by the elevated CO(2) treatment in the first year than in the second, indicating a decreased effect of CO(2) on growth over time. This was confirmed by a study of absolute and relative growth rates of leader shoots. During the first growing season of CO(2) enrichment, mean weekly relative growth rates over the growing season (RGR(m)) were significantly enhanced. During the second year, RGR(m) in ambient CO(2) closely matched that in elevated CO(2).

The Response of Muskmelon Growth and Development to Microclimate Modification by Shelterbelts

The relationships between shelterbelt (tree windbreak)-induced microclimate and muskmelon (Cucumis melo L.) growth and development were investigated at the Univ. of Nebraska-Lincoln Agricultural Research and Development Center near Mead, Nebr., during the 1992 and 1993 growing seasons. Wind speed, wind direction, air and soil temperatures, relative humidity, and soil moisture were monitored in both sheltered and nonsheltered areas. Plant growth parameters (plant height, vine length, plant dry weight, and leaf area) were measured at various stages of development. Shelterbelts provided improved growing conditions for muskmelon transplants. Direct wind damage and duration of higher wind speeds were reduced 47% to 56% in sheltered areas. Air temperatures in sheltered areas were slightly higher during daytime and slightly lower at night, and significantly so early in the growing season. Relative humidity was increased significantly in sheltered areas in 1992 and, while higher in 1993, the difference was nonsignificant. Soil moisture content was not affected significantly by wind protection. Sheltered plants exhibited earlier development and faster growth. The first female flower appeared 2 days earlier in sheltered areas in both years. The first fruit set, as indicated by fruit swelling and retention on the vine, occurred 6 days earlier and matured 5 and 6 days earlier in sheltered areas in 1992 and 1993, respectively. Leaf areas and dry-matter accumulation of sheltered plants were greater than those of exposed plants. The shoot relative growth rate of sheltered plants increased earlier in the growing season, but decreased slightly later in the growing season. The earlier development and faster growth of sheltered plants were related mainly to the reduction of wind speed, higher total accumulated air temperatures during the daylight hours (sum of daily average daytime air temperatures based on hourly averages), and higher soil temperature in sheltered areas. Total yields were not affected significantly in either year; however, early yields were significantly greater in sheltered areas in 1993. If earlier maturity and increased yield are possible in large sheltered fields, this practice would provide an economic benefit to producers.

Differential response of domestic and wild Lycopersicon species to chilling under low light: growth, carbohydrate content, photosynthesis and the xanthophyll cycle

The response of five Lycopersicon species to 14 days moderate chilling at 10°C under low light (75 μmol m−2 s−1) and subsequent recovery was examined by measurements on relative shoot growth rate, leaf dry matter and carbohydrate content, CO2‐exchange and pigment composition. In addition, the susceptibility to dark chilling and temperature dependence of chloroplast electron transport were analyzed by Chl a fluorescence measurements. During 7 days of recovery at 25/20°C subsequent to chilling, the domestic tomato Lycopersiconesculentum (L.) Mill. cv. Abunda exhibited a small capacity for shoot regrowth (39%) compared to the low‐altitude wild species L. pimpinellifolium (Jusl.) Mill. PI187002 (82%) and three wild species originating from high altitude: L. peruvianum Mill. LA 385 (92%), L. hirsutum Humb. & Bonpl. LA 1777 (67%) and L. chilense Dunn. LA 1970 (71%). The inter‐specific differences in chilling sensitivity at the chloroplast level, analyzed by the decline of the maximum rate of induced Chl fluorescence rise (FR) after 40 h at 0°C and the temperature at which qP reached the value 0.5, correlated in general well with the measured differences at whole plant level, measured by the post‐chilling regrowth capacity. Chilling resulted in a larger increase in leaf dry matter content in L. esculentum (45%) and L. pimpinellifolium (37%) compared to the high‐altitude species (13–16%), which could be attributed to a stronger accumulation of both soluble sugars and starch in mature leaves of the domestic and low‐altitude species. Photosynthetic and dark respiration rates during chilling could not account for this difference. The recovery of photosynthesis was better in the high‐altitude species. Chl content per unit leaf area decreased more throughout the experiment in the domestic and low‐altitude species (63–73%) than in their relatives from high altitude (8–29%). In response to chilling, the domestic and low‐altitude species showed an increase in the total xanthophyll cycle pool on Chl basis, whereas the de‐epoxidation state of the xanthophyll cycle increased in the high‐altitude wild species. Both responses resulted in increased zeaxanthin levels in chilled leaves of all Lycopersicon species.

Effects of Storage Temperature on Carbohydrate Content and Seedling Quality of Cabbage Plug Seedlings.

The effects of storage temperature on plant growth and carbohydrate content during low-temperature storage and on photosynthesis and growth of transplants after the end of storage were studied in cabbage plug seedlings. Plants were stored in the dark for 14 d at 5, 10 and 15°C. Fresh weight in shoots increased as storage temperature increased but dry weight decreased slightly, which reduced the dry matter ratio in shoots. Starch concentration in leaves decreased remarkably during the first 4 d in storage, regardless of storage temperature. Sugar concentrations in leaves decreased at 10 and 15°C, due mainly to the reduction in dry matter ratio. Concentrations at 5°C, however, increased transiently and remained higher than at the other temperatures. The effects of storage temperature on photosynthesis and shoot relative growth rate of transplants after the end of storage were comparatively smaller than the effects on plant growth and carbohydrate content during storage. These results indicate that storage temperature affects succulent growth during storage by etiolation and this is related to reducing accumulated starch.

Potassium efficiency and dynamics in the rhizosphere of wheat, maize, and sugar beet evaluated by a mechanistic model

Potassium (K) efficiency and its depletion in the rhizosphere of summer wheat (Triticum aestivum L. cv. Planet), maize (Zea mays L. cv. Pirat), and sugar beet (Beta vulgaris L. cv. Orbis) was studied in a pot culture experiment with Anglberg sandy clay loam soil from Bavaria, Germany having 50 μM K (K1), 140 μMK (K2), and 1,700 μM K (K3) in soil solution. Soil and plant parameters were determined to evaluate nutrient uptake model NST 3.0 which takes into account contribution of root hairs. Sugar beet produced maximum dry matter yield at 50 μM K in soil solution. Increasing level of K did not affect dry matter yield, while K content of plants increased three times. Wheat and maize dry matter yield increased by 60 and 30%, respectively, with increase in soil solution K to 140 μM suggesting that sugar beet had higher K efficiency than wheat and maize. Sugar beet had the lowest root/shoot ratio but highest relative shoot growth rate resulting in 3.2 and 2 times higher shoot demand on root than wheat and maize, respectively. On the other hand sugar beet had four times higher K influx at 50 uM K in soil solution than wheat and maize. Thus, the higher K efficiency of sugar beet was because of higher K influx. Nutrient uptake model calculations showed that initial soil solution K concentration of 50 uM at the root surface decreased to as low as 2.7 uM for sugar beet compared to 9.3 uM for maize and 13 uM for wheat alter 11 days of uptake. According to these calculations the higher influx of sugar beet was due to its capability to decrease the K concentration at the root surface to a lower value thereby increasing the concentration gradient and so the transport to the root surface. Mathematically modeled soil and plant parameters satisfactorily predicted K influx, however at Kt level model over predicted K influx for wheat and maize and under predicted for sugar beet. Sensitivity analysis demonstrated that at K1 level CLi was the most sensitive factor increasing K influx in wheat, maize, and sugar beet. Increasing Imax increased K influx in wheat and maize, but did not help increasing K influx in sugar beet.

Seedling Growth of Intermountain Perennial and Weedy Annual Grasses

Squirreltail [Elymus elymoides (Raf.) Swezey] is a native cool-season grass that has been observed to invade rangelands dominated by the weedy annual grasses, cheatgrass (Bromus tectorum L.) and medusahead wildrye [Taeniatherum caput-medusae (L.) (Nevski]. Our objective was to determine if growth characteristics could account for this squirreltail trait. We used growth analysis to examine differences in seedling growth and tissue allocation of 5 squirreltail entries, 2 long-lived perennial grasses ('Goldar' bluebunch wheatgrass [Pseudoroegneria spicata (Pursh) A. Love] and 'Hycrest' crested wheatgrass [Agropyron desertorum (Fisch. ex Link) Schult. X A. cristatum (L.) Gaertn.]), cheatgrass, and medusahead wildrye. We monitored the 9 entries in a greenhouse for mean relative growth rate, net assimilation rate, leaf area ratio, specific leaf area, leaf weight ratio, root relative growth rate, specific root length, root-to-shoot dry-mass ratio, and root length-to-leaf area ratio beginning 10 days after sowing at 9 destructive harvests at 3-day intervals. Cheatgrass had high relative growth rate for both shoot and root. Only medusahead wildrye equalled the shoot relative growth rate of cheatgrass, and only Hycrest equalled its root relative growth rate. Cheatgrass seedlings were larger than squirreltail seedlings by 2 to 3 weeks after emergence. Few differences were detected among perennials and medusahead wildrye. Cheatgrass displayed the highest leaf area ratio and specific leaf area of the 9 entries but was similar to medusahead wildrye and Red Deer River squirreltail for specific root length. Growth characteristics cannot account for squirreltail's observed ability to invade annual grass stands. However, the combination of high specific leaf area and specific root length in squirreltail germplasm, as found in cheatgrass, may enhance squirreltail survival under competition with annual grasses, especially medusahead wildrye.

Seasonal variation in biomass, morphometric parameters and production of seagrasses in the lagoon of Venice

Results of a year long study on the biomass dynamics and production of three seagrass species (i.e. Zostera marina L., Zostera noltii Hornem., and Cymodocea nodosa (Ucria) Asher.) recorded in the lagoon of Venice are presented in this paper. Seagrasses showed different biomass trends and reproductive phenology. Cymodocea nodosa, in spite of its shorter growing period, exhibited the greatest maximum (∼7.6 kg fwt m −2) and mean (∼4.0 kg fwt m −2) standing crops, on an annual basis. The biomass was significantly lower in Z. noltii (maximum: 5.4 kg fwt m −2, mean: 2.6 kg fwt m −2), whereas, Z. marina showed intermediate values (maximum: 6.3 kg fwt m −2, mean: 3.1 kg fwt m −2). On average, the biomass of shoots in Z. marina and Z. noltii was twice as high as that of roots–rhizomes, whereas, the biomasses of Cymodocea roots–rhizomes and shoots were similar. This latter species, of sub-tropical origins, showed a below-ground biomass 3–4 times higher than shoot biomass in winter. The daily length increase (DLI) of shoots and rhizomes of Z. marina, derived from marking techniques, on an annual basis was 3.6±1.2 cm d −1 (maximum: 5.7 cm d −1) and 0.16±0.07 cm d −1 (maximum: 0.28 cm d −1), respectively. The per cent relative growth rate (%RGR) of shoots ranged from 1.1% to 4.5% (mean: 1.87%). The plastochrone interval was 12.4±3.1 days and the mean leaf age 48±16 days. The net production of Z. marina was estimated to be ca. 15 kg fwt m −2 y −1, for above-ground parts, and 5.9 kg fwt m −2 y −1, for roots–rhizomes, accounting for a total carbon production of ca. 1093 g C m −2 y −1. On an annual basis, the net production of Z. marina was estimated to be ca. 0.8 million tonnes, on a fresh weight basis, whereas, the total seagrass production could be higher than 2 million tonnes.

Effects of excluding goat herbivory on Acacia tortilis woodland around pastoralist settlements in northwest Kenya

Abstract Browsing by goats is considered to cause poor tree regeneration and reduced tree growth around settlements throughout the arid zones of sub-Saharan Africa. This study investigated whether excluding goats from Acacia tortilis woodlands increased tree regeneration, current season's shoot growth rates and browse production over a period of 52 months between 1986 and 1990. The study also investigated the effects of climatic variability on tree growth and browse production. Excluding goat herbivory provided no advantage over continuous browsing for juvenile A. tortilis . Trees on the unbrowsed and on browsed transects increased by 22.2 (standard error [SE] ± 0.53) cm·yr −1 and 25.0 (SE ± 0.58) cm·yr −1 , respectively. Fewer but longer shoots were produced by trees on the unbrowsed transects, while trees on the browsed transects invested more in shorter shoots. Net total browse production was lower on unbrowsed (1.73 [standard deviation (SD) ± 4.3] t·ha −1 ·yr −1 ) than on the browsed (3.03 [SD ± 3.6] t·ha −1 ·yr −1 ) transects. Biomass production on unbrowsed and browsed transects was closely correlated with rainfall and presumably soil moisture during wet seasons. Relative growth rates (RGR) of current season's shoots in the two treatments did not differ, implying goat herbivory at moderate stocking density (i.e. 13.0 tropical livestock units [TLU]·km −2 ) stimulated shoot growth. RGR remained positive except on the browsed transects during 1990, a dry year. Goat browsing pressure was moderate. Total biomass loss on unbrowsed transects was 15.5 %·yr −1 compared with 27.7 %·yr −1 on the browsed transects. These findings do not support the notion that goats always destroy young trees around settlements. Goat herbivory at moderate intensity stimulated shoot productivity. However, the results should not be used to generalize all conditions throughout sub-Saharan Africa, let alone the arid zones of northern Kenya. Rather, there is a need to emphasize individual case studies that ultimately can be used for managing degraded woodlands near pastoralist settlements.

Shoot Population Dynamics of Carex kobomugi on a Coastal Sand Dune in Relation to its Zonal Distribution

Shoot population dynamics of Carex kobomugi Ohwi, a rhizomatous perennial sedge with a guerilla-type growth form, dominating on Japanese coastal dunes, were examined to detect factors generating the zonal distribution pattern of the plant species. Relative growth rate of shoot (RGRS) and number of branching shoots formed by a mother shoot in a year (NBr) were measured in three populations occurring at three different distances from the shoreline. In 1992, Carex kobomugi shoots at the most inland site (90 m from the shoreline), where Imperata cylindrica var. koenigii dominated and soil-water salinity is always low, showed the lowest RGRS (0.0172 g g-1 day-1 from April to June and 0.00079 g g-1 day-1 in July) and the smallest NBr (1.3 shoots shoot-1 year–1 averaged for 3 years). Shoots of the species at the most seaward site (40 m from the shoreline), where the soil-water salinity is always higher than that of more inland sites, showed the highest RGRS (0.0228 g g-1 day-1 from April to June and 0.0093 g g-1 day-1 in July) and the largest NBr (2.5 shoots-1). However, Carex kobomugi population at the 40 m site had a high fraction of injured shoots (46% of total shoots sampled), which were recorded as shoots without any greenish above-ground part, and high mortality (0.34) due to temporal flooding of sea water caused by storms. In the intermediate site (70 m from the shoreline), Carex kobomugi had intermediateRGRS and NBr with low injury rate. The NBr value, however, showed a decreasing trend over the 3 years of observation, suggesting deteriorating effects of intraspecific competition on population dynamics. In the spring of the fourth year, shoots of Carex kobomugi at 70 m and 90 m from the shoreline produced 1.2 to 2.0 times higher number of buds per shoot than the 3-year-averaged NBrs. This suggests that some fractions of the buds were terminated or became dormant through intra- and/or inter-specific competition. The sparse distribution of Carex kobomugi at the 90 m site may be dictated by its competitive inferiority to Imperata cylindrica which has a denser root system and an aggressive growth form of a phalanx type.

Differential Inhibition of Shootvs.Root Growth at Low Temperature and its Relationship with Carbohydrate Accumulation in Different Wheat Cultivars

Abstract Shoot and root growth rate, carbohydrate accumulation (including fructan), reducing sugar content and dry matter percentage were measured in six wheat cultivars, ranging from winter to spring types, grown at either 5 or 25 °C. At 5 °C (compared with 25 °C), the relative growth rate (RGR) of shoots was similarly reduced in all cultivars, but the RGR of shoots was more affected in winter wheats. This difference resulted in smaller root:shoot ratios than in spring wheats, which also developed more first-order lateral roots. A direct relationship between carbohydrate accumulation at low temperatures and reduction in root growth was established. These results suggest that differential shoot vs. root growth inhibition at low temperature may play a key role in carbohydrate accumulation at chilling temperatures. This differential response might lead to improvements in survival at temperatures below 0 °C, regrowth during spring, and water and nutrient absorption at low temperatures.

The relative importance of sulfate availability in the growth of Spartina alterniflora and Spartina cynosuroides

The marsh cordgrass Spartina alterniflora Loisel. dominates temperate coastal marshes on the Atlantic coast of North America, and it is an aggressive invader in other coastal wetlands around the world. However, it also flourishes at much lower salinities, extending well into the mesohaline region of major estuaries such as Chesapeake Bay. This species survives even in oligohaline marshes, usually disappearing in the natural environment at salinities below about 2‰ The possibility that this distribution is related to sulfate limitation was investigated in a long-term greenhouse experiment. Sulfate uptake kinetics were first determined for S. alterniflora. The long-term growth response to four different concentrations of sulfate was then evaluated for S. alterniflora and for Spartina cynosuroides (L.) Roth, a low salinity species of overlapping distribution. Growth indices included the total number of leaves, total leaf length, and the relative growth rate of shoots and of whole plants. Spartina alterniflora responded positively to increasing sulfate concentration; however, S. cynosuroides did not exhibit a growth response. These results suggest that S. alterniflora distribution in oligohaline marshes is limited by sulfate supply, and that the plant may have an uncommonly high sulfate requirement.

Herbage yield, tiller number and root system activity after defoliation of prairie grass (Bromus catharticus Vahl)

The effects of defoliation upon root and shoot systems of prairie grass (Bromus catharticus Vahl) were examined in both field and pot studies. The varieties used were 78–32 (HY), a high‐yielding variety; 79–42 (LY), a low‐yielding variety; and the commercial variety Grasslands Matua. In the field, the presence of roots in early and late spring was estimated by measuring uptake of [32P]phosphate by roots; herbage yields and tiller numbers were recorded. In a pot study, root and shoot dry‐matter (DM) yields were analysed. In the field, roots were detected to a depth of 1·2 m. After defoliation to a height of 0·1 m, root presence decreased more than 50% at depths of 0·6 m for LY and 1·0 m for Matua in early spring and at several depths for each variety in late spring. After a second defoliation, the apparent growth rate of shoots decreased by 35% in relation to the first regrowth period. In pots, shoot DM and root DM of control plants (undefoliated) had the following allometric relationship of the form: In (shoot DM) = 0·61 + 1·14 ln (root DM) (r2= 0·81). After defoliation, compared with undefoliated controls, the relative growth rate of shoots and total herbage yields were higher, but root and stubble DM were lower in all three varieties. Pooled root DM means were 10·3 and 6·8 g plant−1 and pooled stubble DM means were 12·7 and 7·6 g plant−1 for control and defoliated plants respectively. HY produced heavier tillers than LY, pooled means being 0·94 and 0·53 g DM tiller−1 (field study) and 3·44 and 2·05 g DM tiller−1 (pot study) for HY and LY respectively. HY had 5–6 green leaves per tiller, whereas LY had 3–4. Developed green leaves were heavier in HY (58 g m−2) than in LY (48 g m−2). It is suggested that differences in both leaf parameters may be related to higher herbage yields for HY than LY.

Ammonium Tolerance and Carbohydrate Status in Maize Cultivars

Four maize (Zea maysL.) hybrids were grown hydroponically for 4 weeks with 20 mmammonium or nitrate as the sole nitrogen source. Dry matter production was strongly depressed by ammonium nutrition in the hybrid Helga relative to plants grown on nitrate, and moderately decreased in the hybrid Melina. Ammonium had no inhibitory effect on total yield in the other two hybrids (Ramses and DK 261). The relative growth rate (RGR) of roots and shoots of the sensitive hybrid Helga decreased significantly under ammonium nutrition during the first 2 weeks of the experiment, while at the end of the experiment nitrogen form had no effect on the RGR in any of the four hybrids. The strong reduction in RGR of Helga in the early seedling stage was correlated with the accumulation of twice the concentration of free ammonium in the shoot tissue relative to the other hybrids. Helga was therefore unable to sufficiently detoxify ammonia in the roots. Root concentrations of water soluble carbohydrates (WSC) in Helga and Melina in the early seedling stage did not differ under ammonium and nitrate nutrition. In contrast, Ramses and DK 261 both had elevated WSC concentrations in ammonium-fed roots. It is hypothesized that a sufficient supply of carbon skeletons for ammonium assimilation in the roots is required for maximum growth under high ammonium concentrations, and that there is genotypic variability in this physiological trait.

Growth and δ13C Responses to Increasing Atmospheric Carbon Dioxide Concentrations for Several Crop Species

Abstract The responses of plant growth and carbon isotope discrimination (Δ) to elevated atmospheric CO2 concentrations for several crop species (lettuce: Lactuca sativa L.; corn: Zea mays L. var. P3540; wheat: Triticum aestivum L. var Haruyutaka; and soybean: Glycine max (L). Merr. var. Kitamusume) were investigated. Shoot relative growth rate was used to indicate plant growth, and δ13C value of leaf materials in corn (C4 species) was used to calculate Δ for C3 species. Plant growth was stimulated by enriched CO2, while Δ remained almost constant as CO2 concentration changed. Δ showed interspecific difference, and the plant species of larger Δ had larger relative growth rates. Relative growth rates of the plants of larger Δ were stimulated by CO2 enrichment more than those of the plants of smaller Δ. We propose that plant Δ could be a possible parameter to assess the interspecific difference of plant response to the increasing atmospheric CO2 concentrations.

The Relationship between Growth and Development of Vegetative Shoots in Genotypes of Tall Fescue (Festuca arundinacea Schreb.)

In perennial grasses, shoot growth consists of: (a) the increase in the number of tillers (tillering), and (b) the increase in the size of tillers; while shoot development can be represented by an allometric relationship between these two components. This study examined how genetic differences in the developmental process of a shoot influence the various components of vegetative growth in 16 genotypes of a perennial grass, Festuca arundinacea Schreb. A negative correlation between the relative tillering rate (Rtil) and relative growth rate of single tillers (RGRtil) showed that the genotypes can be classified into two categories: genotypes producing few large tillers, and those producing many small tillers. The relative growth rate of the whole shoot (RGRshoot) correlated positively with RGRtil (r = 0·69**), but not with Rtil (r = 0·24). Root d. wt and the accumulation rate of nonstructural carbohydrate correlated negatively with Rtil and positively with RGRtil in spite of the absence of any apparent correlations with RGRshoot. These results demonstrate that: (1) the shoot developmental process has marked effects on various components of vegetative growth, and (2) the production of few large tillers results in higher carbon availability within a plant than the production of many small tillers.

Diurnal variations in growth rate and growth substrate levels of spinach (Spinacia oleracea L.) under nitrogen‐limiting conditions

ABSTRACTSpinach plants were grown in hydroponic culture provided with variable limiting amounts of N. During a complete diurnal cycle, growth of the root and shoot parts, as well as levels of soluble and insoluble sugars and of free amino acids, were monitored. No clear relationship could be detected between the level of N feeding and the levels of free sugars and amino acids. Analysis of variance revealed that the variances in the relative growth rates of plant root and shoot could be correlated with the levels of sugars and amino acids. Root amino acid concentration could be correlated with shoot amino acid concentration and root sugar concentration. No relationship was found between the variances in root and shoot free sugar concentrations.

Reduction in phosphoribulokinase activity by antisense RNA in transgenic tobacco: effect on CO2 assimilation and growth in low irradiance

SummaryTo quantify the importance of the Calvin cycle enzyme phosphoribulokinase (PRK) in photosynthesis and to perturb photosynthesis without large direct reductions in leaf protein content, tobacco plants (Nicotiana tabacum L.) were transformed with an inverted cDNA encoding tobacco PRK. A population of plants expressing antisense RNA and a range of PRK activities from wild‐type to less than 5% of wild‐type were obtained. CO2 assimilation under the growing conditions (330 µmol photons m−2 sec−1, 350 µbar CO2, 25°C) was not inhibited until more than 85% of PRK activity had been removed. With reduction in PRK activity of between 85 and 95%, assimilation rates and amounts of chlorophyll compared with wild‐type were reduced by up to half. Decreased absorption of light by leaves with less chlorophyll accounte0d for only a small part of the reduction in assimilation rate. When PRK activity was below 15% of wild‐type, amounts of ribulose‐5‐phosphate, ribose‐5‐phosphate, ATP and fructose‐6‐phosphate were 1.5‐ to fivefold higher and levels of ribulose‐1,5‐bisphosphate, 3‐phosphoglyceric acid and ADP 1.5‐ to fourfold lower than in wild‐type. It is estimated that these changes maintained flux through PRK to realise the assimilation rates observed. A possible shift of control within the Calvin cycle towards fructose‐1,6‐bisphosphatase in plants with low PRK is discussed. Amounts of hexoses and starch in particular were reduced in plants expressing the lowest PRK activities; amounts of sucrose were little affected. Lower CO2 assimilation in plants with low PRK activity correlated with reduced relative growth rate of shoots and delayed flowering, but there was no effect on specific leaf area. It is concluded that (i) in wild‐type plants grown in constant low light, PRK has a flux‐control coefficient for CO2 assimilation of zero, and that even when amounts of PRK are reduced 20‐fold relative to wild‐type, altered amounts of metabolites compensate for much of the reduction in PRK protein; (ii) in plants where there is a 95% reduction in amounts of PRK, photosynthesis was reduced twofold without large changes in leaf protein content or leaf geometry.

Interaction between mild NaCl salinity and sublethal SO 2 pollution on wheat Triticum aestivum cultivar ‘Wilgoyne’ (Ciano/Gallo). I. Responses of stomatal conductance, photosynthesis, growth and assimilate partitioning

Wheat ( Triticum aestivum cultivar ‘Wilgoyne’ (Ciano/Gallo)) plants were exposed to a factorial combination of two levels of salinity (control and 50 mM NaCl), and three levels of SO 2 (<10 (ambient), 231, and 441 nl 1 −1) in fumigation chambers with rain-exclusioon tops for 4 h per dayfor up to 51 days. The objective was to investigate whether mild salinity stress could decrease the sensitivity of plant growth to sublethal SO 2 stress. Exposure to 441 nl 1 −1 SO 2 significantly decreased CO 2 stomatal conductance, net photosynthesis rate, and at the end of experiment, chlorophyll concentrations in the youngest fully expanded (YFE) leaves. Inhibition of hotosynthesis by 441 nl 1 −1 SO 2 fumigation resulted in a change in assimilate allocation in favour of shoot growth, leading to an increase in shoot to root ratio. Exposure to 441, but not 231 nl 1 −1 SO 2 significantly decreased plant dry weight and relative growth rate (RGR) of both root and shoot. 50 mM NaCl treatment first decreased shoot growth, resulting in a decrease in shoot to root ratio, but later a significant decrease in root growth developed, probably owing to limited assimilate supply from the shoot, and resulted in an increase in shoot to root ratio. There was generally no significant interaction between SO 2 fumigation and NaCl salinity on net photosynthesis rate and leaf chlorophyll concentration. However, CO 2 stomatal conductance in the YFE leaves of 50 mM NaCl-treated and SO 2-fumigated plants recovered more quickly after the completion of fumigation than the non-saline and SO 2-fumigated plants. 50 mM NaCl alinity and 441 nl 1 −1 SO 2 fumigation had an antagonistic interaction on both shoot and root dry weight. Exposure to 231 nl 1 −1 SO 2 increased the shoot to root ratio in plants with 50 mM NaCl. No significant interaction between SO 2 fumigatio and 50 mM NaCl was observed on the RGR of both shoot and root. The results showed that 50 mM NaCl salinity did not provide ann effective protection against SO 2 uptake in the leaves by increasing stomatal resistance during SO 2 fumigation. Other physiological mechanisms could be involved in the antagonistic interaction between 50 mM NaCl salinity and 441 nl 1 −1 SO 2 fumigation on plant growth.

Relative importance of soil phosphorus to the growth of wiregrass (Aristida armata) compared with other grasses common to the mulga shrublands of Queensland

The influence of phosphorus (P) applied to mulga topsoil on the growth of Aristida amata, Cenclirus ciliaris, Digitaria ammophila, and Thyridolepis mitchelliana was examined in2 glasshouse trials, to test the hypothesis that the invasion of A. amata into mulga shrublands may result from a superior ability to exploit and utilise soil P compared to the other grasses.Growth of all grasses was poor without added P, and all grasses produced large growth responses to added P. In contrast to the other native grasses, A. armata required as much added P as the exotic C. ciliaris to achieve maximum growth. The ability of the grasses to grow without added P was related more to an ability to absorb P than to differences in internal requirements. With no P added, T. mitchelliana had the highest P absorption rate (�g P/g root.day), followed by A. amata, C. ciliaris, and D. ammophila. Adding P reversed this order. Cenchrus ciliaris and D. ammophila had the highest relative growth rates of shoots during early growth stages, especially with P added. Although A amata had a greater ability than C. ciliaris to access and utilise soil P at low P concentrations, there was no evidence that it was superior to the other native grasses.