32P uptake and transport to shoots in Pinuus serotina seedlings under aerobic and hypoxic growth conditions

We examined the effects o long-term hypoxic growth conditions on net uptake and transport of P to shoots of pond Pine (Pinus serotina Michx.), a moderately flood-tolerant southern pine. Seedlings were grown under aerobic orhypoxic solution conditions for 4–5 weeks in continuously flowing solution culture containing 100 μM P. Short – and long-term ³²P. experiments were then concluded with intact seedlings to determine rates of ³²P influx, efflux and net transport to the shoot. Shoot fresh weight/root fresh weight ratios were significantly higher under hypoxic gorwth conditions, reflecting the larger reduction in root growth than shoot growth, despite extensive aerechyma formation in roots. Estimates for the unidirectional influx of ³²P in aerobic and hypoxic seedlings were 1.43 and 3.20 μmol P (g_FW root)_?1 h_?1, respectively. However, ³²P accumulation between the two treatments became similar within 8 h, suggesting that efflux was also higer in seedlings from the hypoxic treatment. Indeed in a separate experiment, hypoxic growth conditions increased efflux by over 60%. Transport of ³²P to shoots was significantly reduced under hypoxic growth conditions, despite higher root P concentrations and lower shoot P concentrations. After 48 h, ³²P accumulation in roots was similar between the two treatments. Yet total accumulation of seedling ³²P decrcased by 31% under the hypoxic treatment, largely because of reduced transport of ³²p to the shoot. The lower accumulation of ³² by shoots of seedlings in the hypoxic treatment may be the result of a direct inhibition on the transport process in O²-defident tissues, but could also reflect a slower turnover or labeling of the ool available for transport. Indeed, the percentage of total ³²P in. roots present in the soluble P. (or transportable form of P) was about 33% lower in seedlings from the hypoxic treatment, probably reflecting increased assimilation into organic compounds as well as chelation with iron. Our results suggest that P transport to the shoots of acclimated seedlings may be more sensitive to hypoxic solution conditions than influx at the root Plasmalemma.     

Zinc Extraction potential of two common crop plants,Nicotiana tabacum and Zea mays

White spruce [Picea glauca (Moench) Voss] seedlings were inoculated with Hebeloma crustuliniforme and treated with 25 mM NaCl to examine the effects of salinized soil and mycorrhizae on root hydraulic conductance and growth. Mycorrhizal seedlings had significantly greater shoot and root dry weights, number of lateral branches and chlorophyll content than non-mycorrhizal seedlings. Salt treatment reduced seedling growth in both non-mycorrhizal and mycorrhizal seedlings. However, needles of salt-treated mycorrhizal seedlings had several-fold higher needle chlorophyll content than that in non-mycorrhizal seedlings treated with salt. Mycorrhizae increased N and P concentrations in seedlings. Na levels in shoots and roots of salt-treated mycorrhizal seedlings were significantly lower and root hydraulic conductance was several-fold higher than in non-mycorrhizal seedlings. A reduction of about 50% in root hydraulic conductance of mycorrhizal seedlings was observed after removal of the fungal hyphal sheath. Transpiration and root respiration rates were reduced by salt treatments in both groups of seedlings compared with the controls, however, both transpiration and respiration rates of salt-treated mycorrhizal seedlings were as high as those in the non-mycorrhizal seedlings that had not been subjected to salt treatment. The reduction of shoot Na uptake while increasing N and P absorption and maintaining high transpiration rates and root hydraulic conductance may be important resistance mechanisms in ectomycorrhizal plants growing in salinized soil.     

Carbon dioxide assimilation and growth of red spruce (Picea rubens Sarg.) seedlings in response to ozone,precipitation chemistry,and soil type

Summary The influence of ozone, mist chemistry, rain chemistry, and soil type on CO₂ assimilation and growth of red spruce (Picea rubens Sarg.) seedlings was investigated over a 4-month period under controlled laboratory and glasshouse conditions. Growth was evaluated through interval estimates of aboveground relative growth rates (RGR) and the partitioning of biomass components at harvest to root, stem, and needle fractions. Precipitation chemistry treatments and O₃ exposure dynamics were based on reported characteristics of air chemistry and/or deposition in high-elevation forests of eastern North America. The two soils were collected from Camels Hump in the Green Mountains of Vermont and Acadia National Park on the Maine coast. Soil from Acadia had higher organic content, higher levels of extractable base cations, and lower levels of extractable aluminum and heavy metals. The only treatment variables that consistently influenced the growth of P. rubens were soil type and rain chemistry. In comparison with seedlings grown in soil from Acadia National Park, those grown in Camels Hump soil had significantly less needle (27%), stem (33%), and root (26%) biomass at harvest and statistically lower aboveground RGR within 2 months after initiation of the treatments. Seedlings grown in Camels Hump soil had significantly higher levels of aluminum (6.5X), copper (1.4X), and nickel (2.7X) in new needle tissue. The only influence of precipitation chemistry on the growth of P. rubens was a pattern of greater root and shoot biomass in seedlings experiencing the more acidic rain treatments. Interactive effects among the main treatment variables (e.g., acidic mist and O₃, acidic rain and soil type) on seedling growth were not notable. Rates of CO₂ assimilation and transpiration on a per gram needle dry weight basis [mol·g^-1·s^-1] were not influenced by any of the main treatment variables or their interaction. Because neither soil type nor precipitation chemistry influenced the efficiency of CO₂ assimilation per gram dry weight of needle tissue, the physiological mechanism underlying the growth response of P. rubens is attributed to a change in either whole-plant allocation of carbon resources or a direct toxic effect in the rhizosphere on root growth.     

Compensatory Changes in the Partitioning of Dry Matter in Relation to Nitrogen Uptake and Optimal Variations in Growth

Equations are derived relating relative growth rate (RGR) toroot:shoot ratio, root length, nitrogen inflow rate, leaf area,photosynthesis and carbon and nitrogen concentrations in theplant. The extents to which changes in specific root lengthand root: shoot ratio can compensate for the effects of lowN availability upon RGR are examined. Such responses could haveseveral compensatory functions: maximizing RGR; maintaininggrowth in which the activities of root and shoot limit RGR equally;and maximizing the efficiency of increase in RGR. Growth, nitrogen, carbon, dry matter, partitioning, root:shoot ratio, relative growth rate     

Maintenance of 32P uptake and transport in Pinus serotina seedlings under hypoxic growth conditions

In the present study, we examined the effects of long- and short-term hypoxia on net uptake and transport of phosphorus to shoots of pond pine (Pinus serotina Michx.), a moderately flood-tolerant southern pine, and the influence aerenchyma formation might have in maintenance of P uptake and transport. Seedlings were grown under aerobic (250 μM O₂) or hypoxic (≤50 μM O₂) solution conditions for 5.3 weeks in continuously flowing solution culture containing 100 μM P. Intact seedlings were then labeled with ³²P for up to 24 h to determine how short- and long-term hypoxic solution conditions affected rates of unidirectional influx and the accumulation of ³²P in roots and shoots. Seedlings in the long-term hypoxic treatment were grown for 5.3 weeks in hypoxic solution and also labeled in hypoxic uptake solution. The short-term hypoxic treatments included a 24-h hypoxic pretreatment followed by time in labeled hypoxic uptake solution for seedlings grown under aerobic or hypoxic conditions; in the latter case, diffusion of atmospheric O₂ entry into stem and root collar lenticels was blocked, thus removing any influence that aerenchyma formation might have had on enhancing O₂ concentrations of root tissue. Although unidirectional influx rates of ³²P in roots of seedlings grown under long-term hypoxic conditions were 1.4 times those of aerobically grown seedlings, accumulation of ³²P in roots was similar after 24 h in labeled uptake solution. These results suggest that ³²P efflux was also higher under hypoxic conditions. Higher shoot/root fresh weight ratios and lower shoot P concentrations in seedlings grown under hypoxic solution conditions suggest that the “shoot P demand” per unit root should be high. Yet accumulation of ³²P in shoots was reduced by 50% after 24 h in hypoxic uptake solution. Both short-term hypoxic treatments decreased accumulation of ³²P in roots by more than 50%. Short-term hypoxia decreased shoot accumulation in seedlings grown under aerobic and hypoxic conditions by 84 and 50%. respectively. Short- and long-term hypoxic conditions increased the percentage of root ³²P in the nucleic acid and chelated-P pools, resulting in a significantly smaller percentage of ³²P in the soluble inorganic phosphate (p_i) pool, the pool available for transport to the shoot. However, a reduction in pool size or in labeling of the pool available for transport cannot fully account for the large reduction in accumulation of ³²P in shoots, particularly in the short-term hypoxic treatment of aerobically grown seedlings. Our results suggest that both influx and transport of ³²P to shoots of pond pine seedlings are O₂-dependent processes, and that the transport of ³²P to shoots may be more sensitive to hypoxic solution conditions than influx at the cortical and epidermal plasmalemma, with aerenchyma formation supporting a substantial amount of both ³²P uptake and transport.     

Assimilation,respiration and allocation of carbon inPlantago major as affected by atmospheric CO2 levels

The response ofPlantago major ssp,pleiosperma plants, grown on nutrient solution in a climate chamber, to a doubling of the ambient atmospheric CO₂ concentration was investigated. Total dry matter production was increased by 30% after 3 weeks of exposure, due to a transient stimulation of the relative growth rate (RGR) during the first 10 days. Thereafter RGR returned to the level of control plants. Photosynthesis, expressed per unit leaf area, was stimulated during the first two weeks of the experiment, thereafter it dropped and nearly reached the level of the control plants. Root respiration was not affected by increased atmospheric CO₂ levels, whereas shoot, dark respiration was stimulated throughout the experimental period. Dry matter allocation over leaves stems and roots was not affected by the CO₂ level. SLA was reduced by 10%, which can partly be explained by an increased dry matter content of the leaves. Both in the early and later stages of the experiment, shoot respiration accounted for a larger part of the carbon budget in plants grown at elevated atmospheric CO₂. Shifts in the total carbon budget were mainly due to the effects on shoot respiration. Leaf growth accounted for nearly 50% of the C budget at all stages of the experiment and in both treatments.Abbreviations LAR leaf area ratio - LWR leaf weight ratio - RGR relative growth rate - R/S root to shoot ratio - RWR root weight ratio - SLA specific leaf area - SWR stem weight ratio     

Storage and mobilization of nonstructural carbohydrates and biomass development of beech seedlings (Fagus sylvatica L .) under different light regimes

 Beech seedlings were grown under 8%, 13%, 23% and 100% relative light intensity for 2 years after germination. Starch, sucrose and monosaccharides from the bark and wood parenchyma of shoots and roots were analyzed during the course of the second year. The annual allocation pattern of starch revealed five successive phases: starch disintegration in November (1) was paralleled by high monosaccharide concentrations in the shoot cortex (≤ 33.4 mg/g DW). Seedlings of all light variants reached maximum sucrose concentrations (≤ 82.8 mg/g DW) during starch disintegration in January (2) that coincided with decreased monosaccharide contents. Up to mid-April, resynthesis of starch (3) occurred in most shaded and unshaded seedlings. In May, starch was converted into monosaccharides in all storage tissues (4). Seedlings grown under 13% light intensity showed de novo synthesis of starch (5) 4 weeks after bud burst. These seedlings reached 98% maximum starch storage capacity of the shoot and 89% of the root in July. In mid-October, the maximum starch concentration of the roots increased with light intensity, and this corresponded with an increase of lateral root growth. The variation of shoot and root dry weight was closely related to the content of nonstructural carbohydrates during the second year. The shift of shoot growth to the first half of the growing season and the suppression of lateral root growth during the second half is assumed to be a strategy of young beech to survive under light limiting conditions. Received: 22 May 1997 / Accepted: 10 October 1997     

Stress indications in copper- and nickel-exposed Scots pine seedlings

Scots pine nursery seedlings were planted in pots, five seedlings per treatment, and placed in an experimental field at the University of Oulu in northern Finland at the beginning of June 1997. Copper and nickel sulphates were mixed with forest mineral soil before seedling planting. The metal levels ranged from 0 to 25 mg Ni kg(-1) dry soil and 0 to 50 mg Cu kg(-1) in dry soil and in combinations of both metals. Current year's needles for element analyses, EDS microanalyses, microscopy and glutathione and peroxidase activity analyses were collected from 1-5 seedlings per treatment in September. Seedling biomass in controls, Cu25 and Cu50 differed significantly from the Ni25Cu50 treatment. The root/shoot ratio was highest in the Ni5 treatment, indicating good root growth, though the roots were visibly healthier in the Cu25 treatment than in the Ni5 treatment. At higher Ni levels, the condition of roots deteriorated. The proportion of plasmolysed mesophyll cells was highest in the Ni25 treatment. Copper-treated seedlings did not suffer from Cu stress, because no severe injuries were seen in either the roots or the needles in Cu-exposed seedlings. The needle concentrations of Cu increased only slightly due to treatments. Ni accumulation in needles increased with increasing concentrations in soil. Needles of Cu-treated seedlings had less oxidized glutathione than those of Ni-treated seedlings, but the roots had higher, not significantly, peroxidase activity levels. Light-colored, swollen thylakoids were occasionally observed in the Ni25Cu50 treatment, indicating some interaction between Ni and Cu. Ni seemed to cause more oxidative stress to the seedlings than copper, which was manifested as a decreased GSH level and an increased proportion of GSSG in the Ni treatments. Copper together with nickel strongly decreased root growth, the root/shoot ratio being lowest in the Ni25Cu50 treatment.     

Effects of increasing saturation vapour pressure deficit on growth and ABA levels in black spruce and jack pine

 Plant responses to saturation vapour pressure deficit (SVPD) were studied by subjecting black spruce [Picea mariana (Mill) B.S.P.] and jack pine seedlings (Pinus banksiana Lamb.) to humid (0.3 – 0.8 kPa) or dry (2.0 – 2.5 kPa SVPD) regimes for 4 weeks using a computer-controlled environmental system to control diurnal variation in SVPD. Dry matter accumulation in needles was not altered by increasing SVPD. However, root growth declined by 60% which increased shoot to root ratio and reduced total seedling dry weight in both black spruce and jack pine. Relative growth rate of jack pine also declined to about half the rate of plants grown under humid conditions. In situ root marking studies showed that the decline in root growth of jack pine under the high SVPD was the result of reduced lateral root initiation, whereas root elongation was unaffected by humidity. A 4-week exposure to dry air increased abscisic acid (ABA) levels in needles, but not roots, of jack pine whereas ABA levels in black spruce were not altered. A short (3-day) exposure failed to increase needle ABA levels in either species. These results suggest that the responses of conifers to dry air were not the result of ABA accumulation. Received: 24 March 1996 / Accepted: 30 May 1996     

Effects of experimental warming on growth,biomass allocation,and needle chemistry of <Emphasis Type="Italic">Abies faxoniana</Emphasis> in even-aged monospecific stands

The response and adaption mechanisms of seedlings under long-term warming have remained largely unknown. In this study, we investigated the effects of warming for 6 years on growth, and needle carbon, nitrogen, chlorophyll, and carbohydrate levels in a coniferous tree species, Abies faxoniana. Seedlings were grown in even-aged monospecific stands under ambient and warming (ambient +2.2°C) temperature in climate control chambers. Warming caused statistically significant increases in the specific leaf area, leaf area ratio, root biomass, leaf biomass, branch biomass, stem biomass, and total mass of the seedlings, and reduced the root/shoot ratio. Warming also increased total chlorophyll concentrations, specific chlorophyll pigments, and Chlorophyll a/b ratios in both studied needle age classes. In addition, C/N ratios of current-year and 1-year-old needles increased by warming. In contrast, warming decreased the levels of N, sugar, cellulose, and starch in needles, while warming had no effect on the height, stem diameter, needle mass ratio, root mass ratio, and root/needle ratio. We conclude that warming increases branch growth and changes needle chemistry, which enhances the light capture potential of seedlings.     

Modulation of carbon and nitrogen allocation in Urtica dioica and Plantago major by elevated CO2: Impact of accumulation of nonstructural carbohydrates and ontogenetic drift

Doubling the atmospheric CO² concentration from 350 to 700 μ1 1^?1 increased the relative growth rate (RGR) of hydroponically grown Urtica dioica L. and Plantago major ssp. pleiosperma Pilger only for the first 10–14 days. Previous experiments with P. major led to the conclusion that RGR did not respond in proportion to the rate of photosynthesis. The present paper is focussed on the analysis of the impact of changes in leaf morphology, dry matter partitioning, dry matter chemical composition and ontogenetic drift on this discrepancy. Soon after the start of the treatment, carbohydrate concentrations were higher at elevated CO²: a reaction that was largely due to starch accumulation. An increase in the percentage of leaf dry matter and decreases in the specific leaf area (SLA) and the shoot nitrogen concentration were correlated with an increase in the total nonstructural carbohydrate concentration (TNC). A combination of accumulation of soluble sugars and starch and ontogenetic drift explains the decrease in SLA at the elevated CO² level. A similar ontogenetic effect of elevated CO² was observed on the specific root length (SRL). Other variables such as shoot nitrogen concentration and percentage leaf dry matter were not affected by correction of data for TNC levels. The net diurnal fluctuation of the carbohydrate pool in P. major was equal for both CO² concentrations, indicating that the growth response to elevated CO² may be ruled by variables other than photosynthesis, as for instance sink strength. Elevated CO² did not greatly influence the partitioning of nitrogen between soluble and insoluble, reduced N and nitrate, nor the allocation of dry matter between leaf. stem and root. The finding that the root to shoot ratio (R/S) was not affected by elevated CO² implies that, in order to maintain a balanced activity between roots and shoot, no shift in partitioning of dry matter upon doubling of the atmospheric CO² concentration is required. Our data on R/S are in good agreement with the response of R/S to high CO² predicted by models based on such a theorem.     

Altered root growth and plant chemistry ofPinus sylvestris seedlings subjected to aluminum in nutrient solution

One-year-old Scots pine (Pinus sylvestris L.) seedlings were grown for 9 weeks in nutrient solutions containing 0, 0.5, 1, 2 and 4 mM aluminum nitrate (Al(NO3)3) at pH 4.2. Nine weeks exposure to Al significantly reduced total plant, shoot and root mass and caused a linear decline in proportional allocation of biomass to roots. Relative growth rate of roots declined to as low as zero. Aluminum treatment decreased calcium and magnesium uptake and increased Al content in roots and needles. After 3 weeks of exposure a 10–60% increase in total phenols in roots and a 20–40% increase in o-diphenols in roots and needles were noted. Roots affected by Al showed degeneration of meristematic cells, fewer cell divisions, deformation in cell walls and higher lignification and suberization. The majority of root apices were structurally similar to dormant roots, and a premature senescence of the entire root system was observed. Net photosynthetic rate after 6 weeks of treatment was negatively correlated with needle Al content and Al/Ca ratio (r < -0.9, P < 0.1). The results suggest that Scots pine may be more susceptible to Al than was expected based on previous experiments.     

The effect of an elevated atmospheric CO2 concentration on growth, photosynthesis and respiration of Plantago major

The effect of an elevated atmospheric CO₂ concentration on growth, photosynthesis and root respiration of Plantago major L. ssp. major L. was investigated. Plants were grown in a nutrient solution in growth chambers at 350 and 700 μl I⁻¹ CO₂ during 7 weeks. The total dry weight of the Co₂-enriched plants at the end of this period was 50% higher than that of control plants. However, the relative growth rate (RGR) was stimulated only during the first half of the growing period. The transient nature of the stimulation of the RGR was not likely to be due to end-product inhibition of photosynthesis. It is suggested that in P. major , a rosette plant, self-shading causes a decline in photosynthesis and results in an increase in the shoot: root ratio and a decrease in RGR. CO₂-enriched plants grow faster and cosequently suffer more from self-shading. Corrected for this ontogenetic drift, high CO₂ concentrations stimulated the RGR of P. major throughout the entire experiment.     

Nutrition and growth of coniferous seedlings at varied relative nitrogen addition rate

The growth of two provenances of Pinus sylvestris L. were compared with two provenances of Picea abies (L.) Karst. and with Pinus contorta Dougl. when grown in solution cultures with low nutrient concentrations. Nitrogen was added at different exponentially increasing rates, and the other nutrients were added at a rate high enough to ensure free access of them to the seedlings. During an initial period of the culture (a lag phase), when the internal nutrient status was changing from optimum to the level of the treatment, deficiency symptoms appeared. The needles yellowed and the root/shoot ratio increased. The initial phase was followed by a period of exponential growth and steady-state nutrition. The needles turned green again, and the root/shoot ratio stabilized at a level characteristic of the treatment. These patterns were the same as previously reported for other tree species. The relative growth rate during exponential growth was numerically closely equal to the relative nitrogen addition rate. The maximum relative growth rates were about 6 to 7.5% dry weight increase day^-1. This is a much lower maximum than for broad-leaved species (about 20 to 30% day^-1) under similar growth conditions. The internal nitrogen concentrations of the seedlings and the relative growth rates were stable during the exponential period. Close linear relationships were found between these parameters and the relative addition rate up to maximum growth. During steady state the relative growth rates of the different plant parts were equal. However, there were large differences between genotypes in absolute root growth rate at the same seedling size because of differences in root/shoot ratio. Lodgepole pine had the highest root growth rate, whereas that of Norway spruce, especially the southern provenance, was remarkably low. Yet, Norway spruce had a high ability to utilize available nutrients. In treatments with free nutrient access, growth allocation to the shoot had a high priority in all genotypes, but there was still a marked tendency for luxury uptake of nutrients. Nitrogen productivity (growth rate per unit of nitrogen) was lower than in broadleaved species and highest in lodgepole pine. The relevance of the dynamic factors, i.e. maximum relative growth rate, nutrient uptake rate, nitrogen productivity, growth allocation and root growth rate, are discussed with regard to conifer characteristics and selection value.     

Recovery of Norway spruce (Picea abies) seedlings from repeated drought as affected by boron nutrition

The effects of two boron (B) levels on growth, shoot water potential, gas exchange and nutrient accumulation in Norway spruce [Picea abies (L.) Karst.] seedlings were studied in a growth room experiment lasting 22 weeks which included well-watered control seedlings and seedlings exposed to one (8 days) or two (6+8 days) periods of drought and a rewatering period (8 days) at the end of the experiment. The effects of B and drought were monitored during drought and recovery. Needle B concentrations were 6 mg kg^–1 (–B treatment) and 34 mg kg^–1 (+B treatment) at the end of the experiment. The –B seedlings showed visible symptoms of damage in the upper shoot after repeated drought and had reduced height growth, root dry mass, allocation of biomass to roots and formation of root tips and mycorrhizas and reduced needle P, Ca, and Mg concentrations and contents. In contrast, ¹⁵N uptake, shoot water potential and gas exchange were not markedly affected by B. It can be concluded that the visible symptoms of damage at low B were probably related to reduced B transport due to repeated drought. In contrast, the effects of low B on growth, particularly of the roots, and on nutrient uptake can be regarded as early effects which occur before any influence on shoot water potential or gas exchange. The positive effects of B on root biomass and nutrient accumulation are of particular importance regarding the establishment of young seedlings in the field.     

Nutritional and root development factors affecting growth of tissue culture plantlets of loblolly pine

Tissue culture plantlets of loblolly pine ( Pinus taeda L.) were compared to seedlings to quantify growth and developmental differences. The two plant types were grown in containers in a greenhouse and sampled periodically for twenty weeks. Dry weights and nitrogen and phosphorus concentrations of the shoots and roots were determined every two weeks.
During the twenty weeks in the greenhouse, seedlings grew to a greater size than the plantlets, but the relative rates of growth were approximately equal. Plantlets had significantly lower concentrations of nitrogen and phosphorus per g of shoot dry weight. Seedlings were much more efficient at nutrient uptake per g of dry weight of root. Plantlets had thick, unbranched roots, which were inefficient at nitrogen and phosphorus uptake. Nutrient uptake based on an index of root surface area was equal in the plantlets and seedlings.
The main differences between plantlets and seedlings apparently were related to root system morphology rather than physiological processes. The uptake of nutrients showed the greatest difference between the plant types.     

Comparative greenhouse study of Eucalyptus grandis in vitro plantlets and half-sib seedlings,II. Dry matter accumulation and relative distribution

In vitro directly micropropagated plantlets from three selected five-year-old Eucalyptus grandis Hill ex. Maiden hybrids were compared to their related half-sib seedlings for growth and growth pattern parameters under greenhouse conditions used for operational seedling production. The oven dry weights were determined from stem, leaf, and root samples collected every 40 days for four times. Relative growth rate, net assimilation rates and shoot:root ratio were calculated. Survival was 98% and 95% for plantlets and seedlings, respectively. Significant differences were observed between parents in terms of shoot and root dry weights and their ratios with similar ranking among plantlets and seedlings, suggesting genetic control over these traits. Plantlets started with significantly higher root: shoot ratios and stem, leaf, root, and total dry weight. Although seedlings had higher relative growth and net assimilation rates, all the initial differences decreased sharply over time.     

Interactive effects of inorganic phosphate nutrition and carbon dioxide enrichment on assimilate partitioning in barley roots

The combined effects of inorganic phosphate (Pi) insufficiency and CO₂ enrichment on metabolite levels and carbon partitioning were studied using roots of 9-, 13- and 17-day-old barley seedlings (Hordeum vulgare L. cv. Brant). Plants were grown from seed in controlled environment chambers providing 36 ± 1 Pa (ambient) or 100 ± 2 Pa (elevated) CO₂ and either 1.0 mM (Pi sufficient) or 0.05 mM (Pi insufficient) Pi. When values were combined for both Pi treatments, plants grown under enhanced CO₂ showed increased root dry matter, adenylates (ATP + ADP), glutamine and non- structural carbohydrates other than starch. In contrast with shoots, enhanced CO₂ partially reversed the inhibition of root dry matter formation imposed by Pi insufficiency. The Pi-insufficient treatment also increased sucrose, glucose and fructose levels in barley roots. The Pi and CO₂ treatments were additive, so that the highest soluble carbohydrate levels were observed in roots of Pi-insufficient plants from the elevated CO₂ treatment. Pi limitation decreased dry matter formation, acid-extractable Pi, nitrate, hexose-phosphates, glutamate, glutamine and acid invertase activity of barley roots in plants grown in both ambient and elevated CO₂. Adenylate levels in roots were unaffected by the moderate Pi insufficiency described here. Thus, the reduced hexose-phosphate levels of Pi-insufficient roots were not likely to be the result of low adenylate concentrations. The above results suggest that the capacity of barley roots to utilize carbohydrates from the shoot is inadequate under both Pi-insufficient and CO₂-enriched treatments. In addition, the Pi and CO₂ treatments used here alter the nitrogen metabolism of barley roots. These findings further emphasize the importance of avoiding nutrient stress during CO₂ enrichment experiments.     

Modelling of the responses to nitrogen availability of two Plantago species grown at a range of exponential nutrient addition rates

Abstract. Plantago major ssp. major and P. lanceolata were grown in solution culture with exponential nutrient addition rates. Compared with P. lanceolata, P. major major showed a higher shoot weight ratio (SWR, fraction of plant dry weight in the shoot) and a higher net assimilation rate (NAR, expressed on a leaf dry weight basis) at equal plant (PNC) and shoot (SNC) nitrogen concentration, respectively. No difference was observed in shoot nitrogen ratio (SNR, fraction of plant nitrogen in the shoot) against PNC between the two species. The effect of these differences in matter partitioning and NAR on plant growth was examined by using a growth model. The model assumed (1) that the SWR and SNR are a linear function of PNC and (2) that the NAR is a rectangular hyperbolic function of SNC. Curvilinear relationships were observed between relative growth rate (RGR) and PNC. P. major major had a higher RGR at equal PNC and, thus, a higher nitrogen productivity (NP) than P. lanceolata. Steady-stale exponential growth was simulated for different nitrogen availability in the environment. P. major major had a higher RGR over the whole range of nitrogen availability but the difference attenuated with decreasing availability of nitrogen. The simulation also showed P. lanccolata having higher plasticity in the shoot/root ratio, which resulted from its higher variability in PNC.     

Effect of a strong cold storage induced desiccation on metabolic solutes,stock quality and regrowth,in seedlings of two oak species

Bare-root seedlings of pedunculate oak (Quercus robur L.) and northern red oak (Quercus rubra L.) were lifted in January and stored at 1.8°C, at 82% relative humidity, until their fresh weight declined by 33%. Root growth potential (RGP), fine root electrolyte leakage (REL), fine root water content (RWC), shoot tip water content (SWC), starch and metabolic solute contents in root and shoot, were measured just after lifting and after treatment. Survival of treated seedlings was also assessed in a field trial. RWC, SWC, REL, RGP were dramatically affected by desiccation during cold storage. In both species, root soluble carbohydrate level, inositol level and isocitrate level increased, whereas root starch level and shoot soluble carbohydrate level decreased. In northern red oak, treated seedlings had higher root contents of soluble carbohydrates, inositol and proline than in pedunculate oak. Moreover, treatment induced proline accumulation only in northern red oak roots. These differences could explain why field survival of treated seedlings was significantly better in northern red oak than in pedunculate oak.