Sequential Harvests Research Articles

Restoration of drastically eroded land using coal fly ash and poultry biosolid

A 3-year field study was conducted at a 12 ha soil-borrow area adjacent to the Columbia Metropolitan Airport, South Carolina to investigate the restorative effects of co-application of coal fly ash (FA) and a poultry biosolid (PB). FA was applied at 0, 22, 280, 560 and 1120 Mg (tonne) ha −1, and PB at 5 and 10 Mg ha −1. The area was seeded with erosion-control species Atlantic Coastal panic grass ( Panicum amarum var amarum L.), sericea ( Lespedeza cuneata var. appalow [Dumont] G. Don.) and weeping love grass ( Eragrostis curvula Wolf.). Plant biomass and elemental composition were analyzed in sequential harvests. Soil and groundwater quality characteristics including pH, EC and elemental composition were also monitored throughout the study. In addition, the effect of amendments on the water holding capacity and bulk density of the soil was investigated. Amendment addition significantly increased plant biomass production by a maximum of 26% using 1120 Mg ha −1 FA and 10 Mg ha −1 PB. Application of the highest rate of FA significantly increased the plant tissue concentrations of Mn, As, Se and B. Soil pH was initially increased from 4.6 to 6.1 by amendments. Soil salinity was increased in the initial year only. Amended soils had higher concentrations of Ca, Mg, P and K, higher organic matter content and water holding capacity than unamended soil. Concentrations of plant-essential trace elements (B, Cu and Zn) that were marginally deficient in the unamended eroded soil increased to within typical soil concentrations following amendment with FA and PB. Groundwater quality was unaffected throughout the study. The co-application of FA and PB successfully promoted the revegetation of the eroded borrow area with no apparent adverse environmental side effects.

Spatial and temporal distribution of sucrose synthase in the radish hypocotyl in relation to thickening growth.

Sucrose synthase (SuSy) is a key enzyme in the development of storage root of radish. Clarification of its spatial and temporal expression during the thickening growth of radish hypocotyl, which later develops into storage root, was carried out immunologically using light microscopy. Sequential harvests at 3, 7, 11 and 13 d after sowing (DAS) were performed on two radish cultivars having different sink capacity. A very low level of SuSy was observed 3 DAS for both cultivars. White Cherrish (WC; strong storage root) showed the maximum level of SuSy between 7 and 11 DAS with increased cell development (thickening), while in Kosena (K; low storage root) the level remained high after 13 d of growth. A high level of SuSy was found in companion cells, which was consistent with previous observations, but SuSy was also found in the xylem parenchyma and in some cortical cells. The level of SuSy differed according to the localization and depended highly on cell development. Both cell division and cell enlargement were stimulated in WC compared with K. The role of SuSy during thickening growth of radish hypocotyl is discussed in terms of utilizing photosynthates.

Growth dynamics and mycorrhizas of Norway spruce ( Picea abies) seedlings in relation to boron supply

The effects of three boron levels on the growth dynamics and ectomycorrhizas of seedlings of Norway spruce [Picea abies (L.) Karst.] were studied in a growth room experiment. The seedlings were grown in forest humus mixed with quartz sand for 16 weeks. The B treatment was applied in the nutrient solution. Stem height, dry weight, number of root tips, mycorrhizas as well as B and N concentrations in the seedlings were monitored in sequential harvests. By the last harvest, in week 16, needle B concentrations were 6.6 mg kg–1 at the lowest B level and 17.5 mg kg–1 and 26.5 mg kg–1 at the two higher levels. Boron slightly increased the stem height and the total dry weight, but did not affect N content of the seedlings. Low internal B reduced the number of root tips and mycorrhizas as well as mycorrhizal percentage and root dry weight, which indicates the importance of B for root growth in Norway spruce seedlings. The seedlings grown with adequate internal B had more root tips than those receiving the two lower B treatments as early as week 9, when needle B concentrations at the lowest B supply were 16.0–17.3 mg kg–1, which has previously been considered a sufficient B level. Therefore, the critical needle B concentrations should perhaps be re-examined.

Salinity tolerance in Hordeum vulgare : ion concentrations in root cells of cultivars differing in salt tolerance

The tolerance of 24 genotypes of barley was assessed by estimating their survival in saline conditions either in a glasshouse or in a controlled environment cabinet. Two cultivars, sensitive Triumph and resistant Gerbel, were picked for further study, which involved sequential harvesting of plants grown in a range of salinities. After about one month in 200 mol m_3 sodium chloride, the sodium concentration in the roots and shoots of the sensitive Triumph was about 1.5 times that in the roots of resistant Gerbel. The addition of Na to the root medium reduced the potassium transport to the shoot in Triumph to a much greater extent than in Gerbel, so the K:Na ratio of Gerbel was twice that for Triumph, when averaged over all treatments and harvests. The sodium, potassium and chloride concentrations within the major subcellular compartments of the cortical cells of roots of Triumph and Gerbel were determined by X-ray microanalysis following freeze-substitution and dry-sectioning. The mean cytoplasmic sodium concentration (245 molm_3 analysed volume) in Triumph grown in 200 molm_3 NaCl for 15 d was almost 1.4 times greater than that in the resistant Gerbel: the potassium concentration in Gerbel showed a lower reduction than did that of Triumph. Another major difference between the two cultivars was the higher concentrations of sodium and chloride in the cell walls of Triumph than Gerbel: the sodium concentration in the cortical cell walls of the salt-sensitive cultivar was about 1.75 times that in the more salt-resistant cultivar. The exchange capacity of the cell walls of Gerbel was greater than that of Triumph. We hypothesise that ion transport to the shoot reflects cytosolic ion concentrations, with a more sensitive cultivar having a higher sodium concentration in its cytoplasm than a more resistant variety. It is noteworthy that the difference in the K:Na ratio between the shoots of Gerbel and Triumph after 15 days of exposure to 200 mol m_3 NaCl was similar to the difference in their symplastic K:Na ratios.

Codified Morphological Stage for Predicting Digestibility of Italian Ryegrass during the Spring Cycle

A precise prediction of changes in digestibility of grasses during the growth cycle would allow targeting of harvests to desired levels of nutritive composition to meet specific animal requirements. In this study, regression analysis was used to formulate and test prediction equations for organic matter digestibility (OMD) of standing crops of Italian ryegrass (Lolium multiflorum Lam.) with codified morphological stage, canopy age, growing degree days (GDD), and N fertilization as independent variables. The field study was conducted for 7 yr with six Italian ryegrass cultivars, diversified for ploidy and earliness, grown in the western Po Valley (Italy). Nitrogen fertilizer was applied at various rates as top dressing. Sequential harvesting from early vegetative to full flowering provided herbage samples varying in age and stage of development. The 0–400 classification system that was used to evaluate the morphological stage included four primary stages: vegetative, elongation, inflorescence emergence, and flowering. The OMD decreased from 928 to 576 g kg−1 OM, as the herbage aged. All cultivars responded in the same way during the whole growth cycle. Morphological stage was a better predictor of OMD than GDD or age in days, with a higher r2 (0.88) and a lower root mean square error (28.0 g kg−1 OM). Nitrogen fertilization slightly decreased digestibility. The developed equation tested on an independent set of farm scale data showed that this codified morphological stage system can provide a rapid and easy estimate of Italian ryegrass digestibility in the field.

672 Modelling Nutrient Use by Tree Crops, Development of a Computer-based Fertilization Program

The aim of this research was to determine the seasonal patterns of N demand and uptake in mature almond trees and to use this information to develop an integrated computer model to guide fertilization management. To this end sequential whole tree excavations were conducted at 5 stages during a 15-month period. At each harvest date, five entire mature trees were excavated and partitioned into leaves, root, trunks, and branches. Samples were then analyzed for total nutrient content and differences in nutrient content between sequential harvests, which represents tree nutrient demand and tree nutrient uptake. Infromation on seasonal N uptake dynamics and total yearly N demand has now been integrated into a user-friendly interactive computer program that can be used to optimize N fertilizer management. The details of this program will be discussed. In summary, the determination of N fluxes in almond demonstrates that the majority of N uptake and demand occurs from late February through to early September and that the primary demand for N is for nut fill and nut development. N demands can therefore be predicted by estimating yield and can be applied during the periods of greatest N uptake from the soil which occurs during nut development. By timing N applications with periods of greatest demand, and matching N application rates with crop load we provide growers with a tool that will encourage maximum efficiency of use of N fertilizers. Maximum efficiency of use will result in a minimization of N loss from the orchard system.

Intraspecific variability and maternal effects in the response to nutrient addition in Chenopodium album

Intrapopulational variability in the response to nutrient addition was studied in plants of the widespread annual weedChenopodium album L. Five seed "families" (each the progeny of a single individual) were selected at random from a natural population, and the germinated seeds were grown for two generations with either a high or a low nutrient supply. Sequential harvests were performed in which we measured plant height, total biomass, leaf area, root/shoot ratios, and reproductive characteristics for each plant. The data were analysed with two- or three-way analysis of variance. The response to nutrient treatments varied among families and depended on both the particular trait considered and the stage of development. Maternal environment affected plant growth especially when the offspring was grown at low nutrient levels. Seed germination varied significantly according to both the maternal and the grand-maternal nutrient environment. The results show a high plasticity in the response to nutrient levels and the persistence of environmental effects for more than one generation.Key words: Chenopodium album, nutrients, maternal effects, phenotypic plasticity.

Muskmelon (Cucumis melo L.) fruit ripening and postharvest quality after a preharvest spray of aminoethoxyvinylglycine

Abstract Aminoethoxyvinylglycine (AVG) at 60, 130, or 260 mg l −1 was applied to plots of ‘Primo’ and ‘Mission’ muskmelon 18 or 12 days prior to harvest. Melons were harvested twice from each plot and quality attributes evaluated at harvest or after cold storage. Melons harvested from plots sprayed with AVG had lower rates of ethylene production at harvest and after cold storage than melons harvested from control plots. Melon ethylene production after storage varied inversely with AVG application rate and was consistently lower when AVG was applied 7 days after full net. No difference was observed in flesh firmness, soluble solids, fresh mass or incidence of decay at harvest or after storage in melons harvested from plots sprayed with AVG. Uniformity of melon maturity within a plot was not enhanced by AVG, and plots treated with AVG required sequential harvests similar to control plots. Applications of 260 mg l −1 of AVG did, however, delay initial development of an abscission zone. Plots sprayed with 130 or 260 mg l −1 AVG developed a dose- related, leaf chlorosis readily visible 4 days after spraying. Plants with leaf chlorosis were rated equal in vigor to plants without leaf chlorosis.

Outcome of scalp donor sites in 450 consecutive pediatric burn patients.

The scalp is a useful and reliable donor site in pediatric burn patients that can be multiply harvested with minimal morbidity. Healing complications, however, may include alopecia and chronic folliculitis. To investigate scalp donor-site morbidity, a consecutive series of 2478 pediatric burn patients treated over a 10-year period were reviewed. A total of 450 of these patients had scalp donor sites for wound closure. Percent of total body surface area burned was 46+/-23 percent (mean+/-standard deviation), and the mean number of sequential scalp donor-site harvests was 2.2+/-2 (range, 1 to 10) with mean intervals between harvesting of 6+/-0.6 days. Ten patients (2.2 percent) had related complications. Eight patients developed scalp folliculitis, with Staphylococcus sp as the predominant organism (80 percent). Two patients were managed successfully with wound care alone; the other six patients required surgical debridement and split-thickness skin grafting to achieve wound healing. These eight patients developed varying degrees of alopecia. Two patients developed alopecia without previous folliculitis. Six patients required reconstructive surgery, which consisted of primary closure (3), staged excision (1), and tissue expansion (2). A number of variables were examined to determine any differences in the group that had complications compared with the group of patients that did not. No differences in age, sex, race, burn type, burn size, septic episodes, time to wound closure, or number of times the scalp was harvested were detected. Healed second-degree burns to the scalp that were subsequently taken as donor sites seemed to be a risk factor (p < 0.05) for folliculitis and alopecia. Our study confirms that scalp donor sites are reliable with low morbidity. Complications include alopecia and chronic folliculitis that can be avoided by meticulous technique and avoidance of previously burned areas.

Effect of elevated atmospheric CO2 on mycorrhizal colonization, external mycorrhizal hyphal production and phosphorus inflow in Plantago lanceolata and Trifolium repens in association with the arbuscular mycorrhizal fungus Glomus mosseae

Abstract Plantago lanceolata and Trifolium repens were grown under ambient (400 μmol mol–1) and elevated (650 μmol mol–1) atmospheric CO2 conditions. Plants were inoculated with the arbuscular mycorrhizal fungus Glomus mosseae and given a phosphorus supply in the form of bonemeal. Six sequential harvests were taken in order to determine whether the effect of elevated CO2 on internal mycorrhizal colonization and external hyphal production was independent of the stimulatory effect of elevated CO2 on plant growth. At a given time, elevated CO2 increased the percentage of root length colonized (RLC), the total length of colonized root and the external mycorrhizal hyphal (EMH) density and decreased the ratio of EMH to total length of colonized root. When plant size was taken into account, the CO2 effect on RLC and total length of colonized root was greatly reduced (and only apparent for early harvests in T. repens) and the effects on the EMH parameters disappeared. Root tissue P concentration was unchanged at elevated CO2, but there was a decrease in shoot P at the later harvests. There was no direct effect of elevated CO2 on P inflow for the earlier period (&lt; 50 d) of the experiment. However, over the last period, there was a significant negative effect of elevated CO2 on P inflow for both species, independent of plant size. It is concluded that elevated CO2 had no direct effect on mycorrhizal colonization or external hyphal production, and that any observed effects on a time basis were due to faster growing plants at elevated CO2. However, for older plants, elevated CO2 had a direct negative effect on P inflow. This decrease in P inflow coincides with the observed decrease in shoot P concentration. This is discussed in terms of downregulation of photosynthesis often seen in elevated CO2 grown plants, and the potential for mycorrhizas (via external hyphal turnover) to alleviate the phenomenon. The direction for future research is highlighted, especially in relation to carbon flow to and storage in the soil.

Depletion of soil mineral N by roots of Cucumis sativus L. colonized or not by arbuscular mycorrhizal fungi

Two experiments were conducted where Cucumis sativus were grown in uncompartmented pots either alone or in symbiosis with Glomus intraradices Schenck and Smith (Experiment 1) or Glomus sp. (Experiment 2) in order to investigate if root colonization by arbuscular mycorrhizal (AM) fungi has an effect on depletion of the soil mineral N pool. All pots were gradually supplied with 31 mg NH4NO3-N kg-1 dry soil from 12–19 days after planting and an additional 50 mg (NH4)2SO4-N kg-1 dry soil (15N-labelled in Experiment 1) was supplied at 21 or 22 days after planting in Experiments 1 and 2, respectively. Dry weight of plant parts, total root length, mycorrhizal colonization rate and soil concentration of NH 4 + and NO 3 - were recorded at five sequential harvest events: 21, 24, 30, 35 and 42 days (Experiment 1) and 22, 25, 28, 31 and 35 days (Experiment 2) after planting. In Experiment 1, plants were also analysed for total content of N and 15N. The mycorrhizal colonization rate increased during time: from 25 to 40% in Experiment 1 and from 50 to 60% in Experiment 2. Plant dry matter accumulation was unaffected by mycorrhizal colonization, except in Experiment 1 where shoot dry weights were slightly increased and in Experiment 2 where root dry weights were slightly decreased compared to non-mycorrhizal control plants. The total root length was similar in the control and mycorrhizal treatments in Experiment 1, while it was decreased (20–30%) by mycorrhizal colonization in the last two harvest in Experiment 2. Mycorrhizal colonization affected the rate of depletion of soil mineral N in Experiment 1, where both NH 4 + and NO 3 - concentrations were markedly lower in the first two harvests, when plants were mycorrhizal. As the root length was similar in mycorrhizal and control treatments, this may indicate that the external AM hyphae contributed to the depletion of the soil mineral N pool. A similar pattern was observed in Experiment 2, although the effect was less pronounced. The 15N enrichment in mycorrhizal plants (Experiment 1) also indicated a faster NH 4 + uptake than in the non-mycorrhizal controls in the first two harvests after application of the 15N-labelled N source. However, the external hyphae and roots seemed to have access to the same N sources as the 15N enrichment and total N content were similar in mycorrhizal and control plants at the end of the experiment.

Patterns of defensive chemical production in wild parsnip seedlings (Apiaceae: Pastinaca sativa L.)

To ascertain patterns of allocation between growth and defense in seedlings, we measured plant biomass and the amount of six furanocoumarin defensive chemicals in wild parsnip roots and shoots (Apiaceae: Pastinaca sativa L.) in sequential harvests for sixty days following emergence and compared them to previous studies on mature plants. Furanocoumarins were present from the first day of emergence and were actively synthesized from the onset of seedling growth. Although initial amounts of each furanocoumarin species differed, they were produced at the same rate. Furanocoumarin production was not commensurate with biomass accretion, and fluctuations in concentration varied dramatically between roots and shoots. Concentrations of furanocoumarins in seedlings are far lower than in adult plants, perhaps because the selective regime of seedlings differs from that of mature plants, and inter-seedling competition favors investment in growth rather than defense.

A comparison of the development and metabolic activity of mycorrhizas formed by arbuscular mycorrhizal fungi from different genera on two tropical forage legumes

Two glasshouse experiments were done to assess the development and metabolic activity of mycorrhizas formed by isolates of arbuscular mycorrhizal fungi (AMF) from three different genera, Acaulospora, Gigaspora and Glomus on either Pueraria phaseoloides L. or Desmodium ovalifolium L. plants. The second of the two experiments included three levels of a localised phosphate source in the pots. Alkaline phosphatase (ALP), stained histochemically in the intra-radical mycelium (IRM) of AMF over sequential harvests, did not provide a direct marker for the efficiency of AMF in mobilising phosphorus (P) for plant growth and development. The ability of the extra-radical mycelium (ERM) to scavenge a localised phosphate source, determined by its extraction from buried 35-μm mesh pouches, was dependent on the species of AMF tested. This work indicates that AMF from different genera have unique patterns of mycelial development when forming mycorrhizas with tropical hosts in the presence of a localised phosphate source. AMF also appear to have different mechanisms for the control of P transfer, within the mycelium, to the host. The significance of the architecture of the ERM is discussed as well as the localisation of ALP in the IRM in determining the efficiency of AMF in terms of P accumulation in planta and subsequent growth of plants.

The effects of simulated spring goose grazing on the growth rate and protein content of Phleum pratense leaves.

The effects of simulated goose grazing on Phleum pratense plants were tested in an Iceland hayfield during the spring goose staging period (19 April-11 May 1997). Plants in an area exclosed from the influence of grazing and the nutrient effects of goose faeces were subject to the removal of the youngest lamina once, three and four times during this period. Clipping three and four times resulted in 25-41% increases in cumulative elongation of youngest laminae compared with unclipped plants. Total cumulative lamina growth of entire plants showed no significant difference between unclipped plants and those clipped three and four times, hence no overcompensation occurred. Sequential clipping elevated the protein content of the youngest laminae from 20% to 27-33%, whereas there was no change amongst shoots clipped only once. Because geese only consume the youngest lamina of each Phleum plant, measurements from this experiment showed that regular physical removal of growing biomass doubled the biomass of preferred tissue available to geese and increased the potential protein intake 3.5 times at experimental clipping frequencies similar to levels of sequential harvesting observed amongst staging geese compared to less frequent harvesting. These increases were achieved without any fertilising effects of goose faeces implicated in such effects in previous studies.

Dynamics of nitrogen remobilization in defoliated Phleum pratense and Festuca pratensis under short and long photoperiods

The impact of photoperiod on the rate and magnitude of N remobilization relative to uptake of inorganic N during the recovery of shoot growth after a severe defoliation was compared over 18 days in two temperate grass species, timothy (Phleum pratense L. cv. Bodin) and meadow fescue (Festuca pratensis Huds. cv. Salten). Plants were grown in flowing solution culture with N supplied as 20 mM NH4NO3 and pre‐treated by extending the 11 h photosynthetically significant light period either by 1 h (short‐day or SD plants) or 7 h (long‐day or LD plants) of very low light intensity, during the 10 days prior to defoliation. Following a single severe defoliation, 15N‐labelled NH4+ or NH4++ NO3− was supplied over a 20‐day recovery period under the same SD and LD conditions. Changes in the relative contributions of remobilized N and newly acquired mineral N to shoot regrowth were assessed by sequential harvests. Both absolute and relative rates of N remobilization from root and stubble fractions were higher in LD than SD plants of both species, with the enhancement more acute but of shorter duration in timothy than fescue. Remobilized N was the predominant source of N for shoot regrowth in all treatments between days 0 and 8 after cutting; on average more so for fescue than timothy, because the presence of NO3− reduced the proportional contribution of remobilized N to the regrowth of timothy but not of fescue. Net uptake of mineral N began to recover between days 4 and 6 after cutting, with NO3− uptake restarting 1 or 2 days earlier than NH4+ uptake, even when NH4+ was the only form of N supply. LD timothy plants supplied solely with NH4+ were slowest to resume uptake of mineral N. Supplying NO3− in addition to NH4+ after defoliation promoted shoot regrowth rate but not remobilization of N. Rates of regrowth (shoot dry weight production per plant) were not correlated with rates of N remobilization from stubble either over the short‐term (days 0–8) or longer term (days 0–18), interpreted as evidence against a causal dependence of regrowth rate on N remobilization under these conditions. The results are discussed in relation to hypotheses for source/sink‐driven rates of N remobilization and their interactions with mineral N uptake following defoliation.

Effect of enhanced atmospheric CO2 on mycorrhizal colonization by Glomus mosseae in Plantago lanceolata and Trifolium repens

Plantago lanceolata L. and Trifolium repens L. were grown for 16 wk in ambient (360 μmol mol−1) and elevated (610 μmol mol−1) atmospheric CO2. Plants were inoculated with the arbuscular mycorrhizal (AM) fungus Glomus mosseae (Nicol. &amp; Gerd.) Gerdemann &amp; Trappe and given a phosphorus supply in the form of bonemeal, which would not be immediately available to the plants. Seven sequential harvests were taken to determine whether the effect of elevated CO2 on mycorrhizal colonization was independent of the effect of CO2 on plant growth. Plant growth analysis showed that both species grew faster in elevated CO2 and that P. lanceolata had increased carbon allocation towards the roots. Elevated CO2 did not affect the percentage of root length colonized (RLC); although total colonized root length was greater, when plant size was taken into account this effect disappeared. This finding was also true for root length colonized by arbuscules. No CO2 effect was found on hyphal density (colonization intensity) in roots. The P content of plants was increased at elevated CO2, although both shoot and root tissue P concentration were unchanged. This was again as a result of bigger plants at elevated CO2. Phosphorus inflow was unaffected by CO2 concentrations. It is concluded that there is no direct permanent effect of elevated CO2 on mycorrhizal functioning, as internal mycorrhizal development and the mycorrhizal P uptake mechanism are unaffected. The importance of sequential harvests in experiments is discussed. The direction for future research is highlighted, especially in relation to C storage in the soil.

The role of mycorrhiza in determining the response of Plantago lanceolata to CO2 enrichment

Plantago lanceolata L. was grown for 104 d with (M) or without (NM) arbuscular mycorrhizal colonization under conditions of ambient (CAMB=350 μl l−1) and elevated (CELEV=540 μl l−1) CO2. Sequential harvests (H) were taken at 41 (H1), 76 (H2) and 104 d (H3) to determine the time‐course of mycorrhizal influence on the response of the plant to CO2 enrichment. Total yields of M plants were greater than those of NM from H2 onwards. Plants in the MELEV treatment were significantly larger than those in the MAMB at 104 d. There were significant but much smaller differences in yield between NMELEV and NMAMB. The differences in total yield arose through impact of CELEV on both shoots and roots. Total root length was greater in MELEV than in MAMB only at H3, but total length of mycorrhizal root was greater at H2 and H3. The percentages of root length colonized and that occupied by arbuscules and vesicles were greater in MELEV than in MAMB at the last two harvests, indicating increased sequestration of carbon in internal fungal structures. Though extraradical hyphal lengths were greater in MELEV than in MAMB at H2 and H3, the differences were not significant. Phosphorus inflow and P content of M plants were higher than those of NM plants at H2 and H3, and were higher in MELEV than in MAMB at H3. anova revealed no significant interactions between CO2 and mycorrhizal treatment.The results are discussed in relation to carbon sequestration in mycorrhizal systems and likely impacts of CO2 enrichment on P. lanceolata grown under field conditions. The importance of sequential harvesting for realistic determination of responses to CO2 is stressed.

Structure and function of the ectomycorrhizal association between Paxillus involutus and Betula pendula. II. Metabolic changes during mycorrhiza formation

Seedlings of Betula pendula Roth. were grown in the presence of Paxillus involutus (Batsch) Fr., and metabolic changes during mycorrhiza formation were examined by measuring organic acid and amino acid pools and related enzyme activities, following sequential harvests. Glutamine, aspartate and asparagine pools were always lower in infected roots than in non‐infected roots, especially during Hartig net initiation and formation. Glutamate concentration was similar in both tissues. Citrate and malate were the two major organic acids detected and their concentrations were equal in infected and non‐infected roots. Aspartate aminotransferase, glutamine synthetase, NAD‐dependent malate dehydrogenase and glucose‐6‐phosphate dehydrogenase activities were higher in infected roots than non‐infected roots. For all enzymes revealed on polyacrylamide gels, both root and fungal isoforms were present in infected roots. Quantitative changes in enzyme capacities and metabolite pools indicated that mycorrhiza formation caused a re‐arrangement of the main metabolic pathways during the very early stages following contact, which might be related to the structural changes.

Elevated carbon dioxide ameliorates the effects of ozone on photosynthesis and growth: species respond similarly regardless of photosynthetic pathway or plant functional group.

Due to their different physiological effects, elevated carbon dioxide and elevated ozone might have interactive impacts on plants, and differentially so on plants differing in photosynthetic pathway and growth rate. To test several hypotheses related to these issues, we examined the physiological, morphological and growth responses of six perennial species grown at various atmospheric concentrations of carbon dioxide and ozone. The species involved (two C3 trees: Populus tremuloides Michx., Quercus rubra L.; two C3 grasses: Agropyron smithii Rybd., Koeleria cristata L.; two C4 grasses: Bouteloua curtipendula Michx., Schizachyrium scoparium Michx.) differed in growth form, stomatal conductance and photosynthetic pathway. In situ photosynthesis, relative growth rate (RGR) and its determinants (leaf area ratio, specific leaf area, leaf weight ratio and root weight ratio) were determined via sequential harvests of seedlings that were grown in all combinations of 366 or 672 μmol mol-1 CO2 and 3 or 95 nmol mol-1 O3 over a 101-d period. Elevated CO2 had minimal effect on either photosynthesis or RGR. By contrast, RGR for all six species was lower in high O3 concentrations at ambient CO2 , significantly so in A. smithii and P. tremuloides. Five of the six species also exhibited reductions in in situ photosynthesis at ambient CO2 in high-O3 -grown compared with low-O3 -grown plants. For all species, these O3 -induced reductions in RGR and photosynthesis were absent in the elevated CO2 environment. Root weight ratio was significantly reduced by elevated O3 in A. smithii and P. tremuloides in ambient but not elevated CO2 . Species with high stomatal conductance were the most susceptible to oxidant injury, while those with low stomatal conductance, such as the C4 species and Q. rubra, were not as detrimentally affected by O3 . Elevated levels of CO2 will reduce stomatal conductance and O3 uptake, and might therefore reduce the potential for oxidant damage. However, there was a stronger relationship of the percent reduction in whole-plant mass due to O3 , related to the ratio of photosynthesis to stomatal conductance. In general, results of this study of six functionally diverse plant species suggest that O3 pollution effects on carbon balance and growth are likely to be ameliorated by elevated concentrations of atmospheric CO2 .

Drying of surface soil decreased Lupinus angustifolius root length and manganese uptake in a split-root experiment

In a glasshouse, a split-root experiment was used to determine the ability oflupins (Lupinus angustifolius L.) to take up manganese(Mn) from dry soil either when young or at mid-flowering of the primarybranches. Three soil-watering regimes (maintained at field capacity,maintained below wilting point, and alternating from field capacity to wellbelow wilting point) were imposed after taproots had grown through topsoil andinto a nutrient solution below. Four sequential harvests (11, 22, 37, and 49days after sowing) were taken to determine the effect of soil drying on lupingrowth, Mn uptake, and soil-extractable Mn.Soil drying early in the lupin plant's life stopped the growth of lateralroots in the soil and slowed the growth of roots grown in subsoil solution andthe growth of lupin tops. Soil drying decreased uptake of Mn in the tops to13% of that under continuous wet soil conditions. Of the 13%,most (11%) was taken up while the soil was drying. Soil re-wettingenabled the plants to resume uptake of Mn and soil re-drying (just beforeanthesis) decreased the Mn concentration in the lupin stems to 4·8µg/g, whereas stems of lupins grown in the wet and dry soilscontained 10·3 and 3·3 µg/g, respectively. Easilyreducible and plant-available soil Mn were not affected by soil wetting anddrying treatments.This study confirms that the uptake of Mn by lupin may be severely restrictedby drying of surface soil at both the beginning and the end of the lupinplant's life. The decrease in root length rather than the chemical form of Mn restricted Mn uptake.