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Aims: There is still limited information about the dynamics of potassium (K) uptake and use over the growth cycle in cereals, but quantification of such relationships is necessary to model crop response to K and improve K fertiliser practice. This study examined the effects of varying K supply on K use efficiency, leaf gas exchange, root and shoot growth at successive stages of plant phenological development, and on seed yield in wheat ( Triticum aestivum L.). Methods: The study was conducted with a low-K loamy sand in a naturally-lit glasshouse. Six rates of soil K were applied as 15, 22.5, 30, 45, 75, 135 mg K kg −1, and six harvests were made to assess growth responses at different stages. Results: Tiller development, shoot dry weight, leaf photosynthesis and transpiration efficiency were closely related to soil K supply with time. Plants with 15 to 45 mg K kg −1 had lower root-to-shoot ratio than those supplied with 75 or 135 mg K kg −1. Plants showed maximal K accumulation in shoots prior to anthesis regardless of K rates, but K use efficiency differed during growth among the treatments. Adequate K supply enhanced seed yield by increasing ear numbers, single seed weight and harvest index. Conclusions: The rates of K supply affect K use efficiency, the root-to-shoot ratio and seed yield in wheat with a key feature of growth on a low-K sand as active K uptake during vegetative growth and subsequent reliance on K redistribution for reproductive growth. The poor adaptation of root growth to K deficiency may impair the plant’s ability for nutrient acquisition especially in water limited environment. [ABSTRACT FROM AUTHOR]

Aims: Roots need to be in good contact with the soil to take up water and nutrients. However, when the soil dries and roots shrink, air-filled gaps form at the root-soil interface. Do gaps actually limit the root water uptake, or do they form after water flow in soil is already limiting? Methods: Four white lupins were grown in cylinders of 20 cm height and 8 cm diameter. The dynamics of root and soil structure were recorded using X-ray CT at regular intervals during one drying/wetting cycle. Tensiometers were inserted at 5 and 18 cm depth to measure soil matric potential. Transpiration rate was monitored by continuously weighing the columns and gas exchange measurements. Results: Transpiration started to decrease at soil matric potential ψ between −5 kPa and −10 kPa. Air-filled gaps appeared along tap roots between ψ = −10 kPa and ψ = −20 kPa. As ψ decreased below −40 kPa, roots further shrank and gaps expanded to 0.1 to 0.35 mm. Gaps around lateral roots were smaller, but a higher resolution is required to estimate their size. Conclusions: Gaps formed after the transpiration rate decreased. We conclude that gaps are not the cause but a consequence of reduced water availability for lupins. [ABSTRACT FROM AUTHOR]

Immediate leaf functional responses to drought, such as stomatal closure and photosynthetic rate reduction, are already known from short-term studies. We tested the hypothesis that long-term acclimation of leaves to drought includes hydraulic and stomatal anatomical changes and that gas exchange and nitrogen allocation patterns are inevitably adjusted to the new structural status. 26 structural and functional traits in one sensitive cultivar (Simeto) and two drought resistant landraces (Ntopia Heraklion 184, Kontopouli 17) of field- grown wheat ( Triticum turgidum L. var. durum) were examined under four water shortage levels. Drought acclimation responses were more intense in Simeto than in the two landraces. In accordance to the working hypothesis, drought-acclimated leaves showed lower hydraulic conductance due to narrower vessels and higher stomatal and vein densities than the control leaves, resulting in a safe mode of water transfer and consumption which is essential for the survival in water limiting conditions.Irrespectively of genotype and water regime, significant correlations among structural (hydraulic characteristics, stomatal and vein patterns) and functional (gas exchange, nitrogen content) parameters were found, indicating the functional adjustment to the new structural status. The Principal Component Analysis showed that these structure-function interactions reflected the trade-off between growth and protection against water losses (Axis 1), as well as the competition between different sinks (carbon gain vs structural reinforcement and reproductive effort) in N allocation (Axis 2). Drought acclimation in wheat leaf is integrally processed by the coordination of structural and functional parameters in order to compensate for the adverse effects of water shortage. This structure-function network that regulates the transition from normal growth-mode to protection- mode, includes at least two important 'nodal points': xylem conducting efficiency (water entry) and stomatal function (water exit). This transition also includes the redirection of nitrogen resources to different sinks. [ABSTRACT FROM AUTHOR]

mmonia (NH) fluxes between beech leaves ( Fagus sylvatica) and the atmosphere were investigated in a 90-year-old forest canopy and related to leaf nitrogen (N) pools and glutamine synthetase (GS) activities. The stomatal ammonia compensation point, χ, was measured by both a twig cuvette and bioassay techniques involving measurements of pH and ammonium (NH) concentration in the leaf apoplastic solution. The χ determined on the basis of the gas exchange measurements followed a seasonal variation with early-season peaks during leaf expansion (9.6 nmol NH mol air) and late-season peaks during leaf senescence (7.3 nmol NH mol air). In the mid-season, the χ of mature green leaves was much lower (around 3 nmol NH mol air) and dropped below the NH concentration in the ambient atmosphere. For comparison, χ obtained by the apoplastic bioassay were 7.0, 3.7 and 6.4 nmol NH mol air in early-, mid-, and late -season, thus agreeing reasonably well with χ values derived from the gas exchange measurements. Potential NH emission fluxes during early and late season were 1.31 and 0.51 nmol m leaf surface area s, respectively, while leaves were a sink for NH during mid-season. During leaf establishment and senescence, both apoplastic and bulk tissue NH concentrations were relatively high coinciding with low activities of glutamine synthetase, which is a key enzyme in leaf N metabolism. In conclusion, the exchange of NH between beech leaves and the atmosphere followed a seasonal variation with NH emission peaks being related to N mobilization during early leaf establishment and remobilization during late leaf senescence. [ABSTRACT FROM AUTHOR]

Indigenous broadleaf plantations are increasingly developing as a prospective silvicultural management approach for substituting in place of large pure conifer plantations in subtropical China. However, little information is known about the effects of tree species conversion on soil-atmosphere greenhouse gas (GHG) exchanges. Four adjacent monospecific plantations were selected in subtropical China to examine the effects of tree species on soil-atmosphere exchanges of NO, CH and CO. One coniferous plantation was composed of Pinus massoniana (PM), and the three broadleaf plantations were Castanopsis hystrix (CH), Michelia macclurei (MM) and Mytilaria laosensis (ML). We found that mean soil NO and CO emissions in the PM plantation were 4.34 μg N m h and 43.25 mg C m h, respectively, lower than those in the broadleaf plantations (>5.25 μg N m h and >56.38 mg C m h). The PM plantation soil had higher mean CH uptake (39.03 μg C m h) than the broadleaf plantation soils (<32.67 μg C m h). Variations in soil NO emissions among tree species could be primarily explained by the differences in litter C:N ratio and soil total N stock. Differences in soil CH uptake among tree species could be mostly attributed to the differences in mean soil CO flux and water filled pore space (WFPS). Litter C:N ratio could largely account for variations in soil CO emissions among tree species. This study confirms that there is no GHG benefit of converting PM plantation to broadleaf plantations in subtropical China. Therefore, the future strategy of tree species selection for substituting in place of large coniferous plantations in subtropical China needs to consider the potential effects of tree species on soil-atmosphere GHG exchanges. [ABSTRACT FROM AUTHOR]

The banana ( Musa sp.) plant is one of the largest monocotyledoneous terrestrial herbaceous plants in the world. The measurement of transpiration (Tr) for a whole banana plant is always difficult to perform due to its size. However, the sap flow (SF) of the plant has been successfully measured by using the thermal dissipation probe (TDP) or ‘Granier’ method in the corm of the banana plant (Lu et al. J Exp Bot 53:1771–1779, ). The present study aimed to validate their method using a sizable number of banana plants in a greenhouse in Israel. The SF data was compared to the gravimetric measurement of transpiration. The lag time of SF behind Tr was also analyzed. Results showed that the daily SF agreed with the daily Tr when the effective radius for sap flow in the corm was taken as 0.63 R, where R is the radius of the corm. The SF lagged 45 min behind the Tr from 0630 to 1040 hours. Whereas the Tr was not statistically ( P>0.05) different from the SF between 1330 and 1700 hours. The reduction in water capacity of banana plant due to SF lag was about 10.5% of the daily Tr, and it recovered gradually in the afternoon. Using more plants can reduce the measurement error of the TDP method. The measured daily SF can be considered as an accurate estimation of the daily Tr for banana plant. [ABSTRACT FROM AUTHOR]

American elm ( Ulmus americana) seedlings were either non-inoculated or inoculated with Hebeloma crustuliniforme, Laccaria bicolor and a mixture of the two fungi to study the effects of ectomycorrhizal associations on seedling responses to soil compaction and salinity. The seedlings were grown in the greenhouse in pots containing non-compacted (0.4 g cm−3 bulk density) and compacted (0.6 g cm−3 bulk density) soil and subjected to 60 mM NaCl or 0 mM NaCl (control) treatments for 3 weeks. All three fungal inocula had similar effects on the responses of elm seedlings to soil compaction and salt treatment. In non-compacted soil, ectomycorrhizal fungi reduced plant dry weights, root hydraulic conductance, but did not affect leaf hydraulic conductance and net photosynthesis. When treated with 60 mM NaCl, ectomycorrhizal seedlings had several-fold lower leaf concentrations of Na+ compared with the non-inoculated plants. Soil compaction reduced Na+ leaf concentrations in non-ectomycorrhizal plants and decreased dry weights, gas exchange and root hydraulic conductance. However, in ectomycorrhizal plants, soil compaction had little effect on the leaf Na+ concentrations and on other measured growth and physiological parameters. Our results demonstrated that ECM associations could be highly beneficial to plants growing in sites with compacted soil such as urban areas. [ABSTRACT FROM AUTHOR]

Irrigation effects were investigated on an 8-year-old olive ( Olea europaea L., cv. Cobrançosa) commercial orchard located in northeast Portugal. Trees were subjected to a rainfed control (T0) and three treatments (T1, T2, T3) that received a seasonal water amount equivalent to 30%, 60% and 100% of the estimated local evaporative demand by a drip irrigation system. Irrigation increases the photosynthetic activity of olive trees, in association with increases in water status, and reduces the midday and afternoon depression in gas exchange. The closely association between photosynthetic rate ( A) and stomatal conductance ( g s) revealed that the decline in net photosynthesis over the course of the day was largely a consequence of stomatal limitation. However, the ratio of intercellular to atmospheric CO2 concentration increased markedly from morning to midday in non-irrigated plants, in spite of lower g s, suggesting that non-stomatal limitations of photosynthesis also occur when environmental conditions become more stressful. The occurrence of perturbations at chloroplastic level in rainfed plants was demonstrated by a lower maximum photochemical efficiency of photosystem II during the afternoon. Chlorophyll fluorescence measurements also revealed the occurrence of a dynamic photoinhibition in irrigated trees, mainly in T2 and T3, which seemed to be effective in protecting the photosynthetic apparatus from photodamage. Irrigation enhances antioxidant protection and decreases the oxidative damage at leaf level. Leaves grown under rainfed conditions revealed symptoms of oxidative stress, like the reduction (14%) in chlorophyll concentration and the increased levels (57%) of lipid peroxidation. We also found that the scavenging function of superoxide dismutase was impaired in rainfed plants. In contrast, the low thiobarbituric acid reactive substances concentration in T3 indicates that irrigation enhances the repairing mechanisms and decreases the oxidative damage by lipid peroxidation. Accordingly, leaves in T3 treatment had high levels of –SH compounds and the highest antioxidant potential. Meanwhile, the finding that guaiacol peroxidase activity increased in rainfed plants, associated with the appearance of oxidative damage, suggests that this enzyme has no major antioxidative function in olive. [ABSTRACT FROM AUTHOR]

During two intensive field campaigns in summer and autumn 2004 nitrogen (N2O, NO/NO2) and carbon (CO2, CH4) trace gas exchange between soil and the atmosphere was measured in a sessile oak ( Quercus petraea (Matt.) Liebl.) forest in Hungary. The climate can be described as continental temperate. Fluxes were measured with a fully automatic measuring system allowing for high temporal resolution. Mean N2O emission rates were 1.5 µg N m−2 h−1 in summer and 3.4 µg N m−2 h−1 in autumn, respectively. Also mean NO emission rates were higher in autumn (8.4 µg N m−2 h−1) as compared to summer (6.0 µg N m−2 h−1). However, as NO2 deposition rates continuously exceeded NO emission rates (−9.7 µg N m−2 h−1 in summer and −18.3 µg N m−2 h−1 in autumn), the forest soil always acted as a net NO x sink. The mean value of CO2 fluxes showed only little seasonal differences between summer (81.1 mg C m−2 h−1) and autumn (74.2 mg C m−2 h−1) measurements, likewise CH4uptake (summer: −52.6 µg C m−2 h−1; autumn: −56.5 µg C m−2 h−1). In addition, the microbial soil processes net/gross N mineralization, net/gross nitrification and heterotrophic soil respiration as well as inorganic soil nitrogen concentrations and N2O/CH4 soil air concentrations in different soil depths were determined. The respiratory quotient (ΔCO2 resp ΔO) for the uppermost mineral soil, which is needed for the calculation of gross nitrification via the Barometric Process Separation (BaPS) technique, was 0.8978 ± 0.008. The mean value of gross nitrification rates showed only little seasonal differences between summer (0.99 µg N kg−1 SDW d−1) and autumn measurements (0.89 µg N kg−1 SDW d−1). Gross rates of N mineralization were highest in the organic layer (20.1–137.9 µg N kg−1 SDW d−1) and significantly lower in the uppermost mineral layer (1.3–2.9 µg N kg−1 SDW d−1). Only for the organic layer seasonality in gross N mineralization rates could be demonstrated, with highest mean values in autumn, most likely caused by fresh litter decomposition. Gross mineralization rates of the organic layer were positively correlated with N2O emissions and negatively correlated with CH4 uptake, whereas soil CO2 emissions were positively correlated with heterotrophic respiration in the uppermost mineral soil layer. The most important abiotic factor influencing C and N trace gas fluxes was soil moisture, while the influence of soil temperature on trace gas exchange rates was high only in autumn. [ABSTRACT FROM AUTHOR]

Lotus corniculatus L. and Lotus glaber Mill. are warm-season legume species adapted to many kinds of environmental stress, including flooding conditions, whereas other popular forage legumes, like alfalfa or white clover, cannot thrive. This study evaluates the relationship between root aerenchyma, water relations and leaf gas exchange and the differential tolerance to soil flooding of L. corniculatus and L. glaber. Adult plants of these species, established independently in grasslands mesocosms, were subjected to 40 days of early spring flooding at a water depth of 6 cm. Both species presented constitutive aerenchyma tissue in the roots. Under flooding conditions, this parameter was 26.2% in L. glaber and 15.3% in L. corniculatus. In addition, flooded plants of L. glaber presented a leaf biomass 47.5% higher above water while L. corniculatus showed a leaf biomass 59.6% lower in the same layer, in comparison to control plants. Flooded plants of L. glaber maintained the stomatal conductance ( g s) and transpiration rate ( E) for 25 days, although these parameters reduce slightly to 40–60% in comparison to controls after 40 days of flooding. In this species, a reduction in photosynthesis ( A) in flooding conditions was detected only on the last day of measurement. In L. corniculatus, the same parameters ( g s, E and A) were affected by flooding since day 18 of treatment, and values reached 25–40% in comparison to control plants after 40 days of flooding. Flooding did not affect above-ground biomass in L. glaber; while in L. corniculatus, above-ground biomass was 35% lower than in control plants. Our results confirmed that L. glaber is more able to cope with flooding stress than L. corniculatus, even in the presence of natural competitors. On the whole, this experiment provides information that can aid in the identification of anatomical and physiological parameters associated with flood-tolerance in this forage legume species, with economic potential for the agricultural areas subject to periodic flooding. [ABSTRACT FROM AUTHOR]

In order to understand how radiata pines respond to declining supply of soil-water in agroforestry systems, we monitored water potential in xylem (ψ x ), osmotic potential (ψ) and relative water content ( q) for fascicles at pre-dawn and at mid-day for 3-year-old trees that were raised from either seedlings (Seedling) or from tissue culture (TC3 and TC4), and grown either alone (Control) or over lucerne ( Medicago sativa) pasture (Lucerne). Water relations at dawn were mostly similar for all the pines, except late in the season when ψ was lower, bulk turgor pressure ( P), deduced as the difference between ψ x and ψ, was higher, for TC3 than for the other two pines. At mid-day, Seedling often had higher ψ x and ψ, but because of its poor osmotic adjustment ( OA) had lower P, than either TC3 or TC4. The cell walls were more elastic in Seedling with modulus of elasticity ( e) of 6.5 MPa compared with 8.1 MPa for both TC3 and TC4, while loss of turgor was estimated to occur at ψ x of −1.45 MPa for Seedling, −1.38 MPa for TC3 and −1.35 MPa for TC4. All trees irrespective of their origin had higher ψ x , P, CO2 assimilation ( A), and stomatal conductance ( g s ), but lower ψ, in Control than in Lucerne in which the soil profile was consistently drier. The trends in ψ x , ψ, q and A did not reflect the known differences in dry weight of trees, P was in the order TC3 > TC4 > Seedling, consistent with previously reported tree weights. Both TC3 and TC4 had higher P, due to their larger OA, than Seedling, although the latter had higher A. Thus ψ x and A that are routinely measured may not always adequately explain differences in growth amongst pines; it is advisable that ψ be determined to allow deductions of P be made when using water relations to analyse plant growth. [ABSTRACT FROM AUTHOR]

There have been no studies of the effect of take-all on leaf gas-exchange rates, despite the fact that take-all severely restricts plant water and nutrient uptake, which results in significant biomass and grain yield reduction. Here we describe the effect of inoculation with Gaeumannomyces graminis (Sacc.) var. tritici (Ggt) on carbon assimilation rate (A) and biomass production of wheat plants grown under two water regimes. We show that the impact of Ggt inoculation on plant growth and leaf A may be through reduced photosynthetic capacity of the leaves and not water stress per se. The nature of this reduced photosynthetic capacity remains uncertain but may involve nutrient deficiency and different enzymes produced by the fungus. In each of the 3 years the experiment was conducted, Ggt significantly reduced A, i.e. at anthesis by 18% in 2000, 15% in 2001, and 12% in 2002. In agreement with other field studies, Ggt reduced tiller number and production of all plant components, mostly root dry mass and grain mass per plant. Highly significant negative correlations were found between disease rating and A in all years, showing that at disease ratings equal or higher than 3 (on a scale from 1 to 4) A could practically be zero. While A decreased, intercellular CO2 concentration increased or did not change, and stomatal conductance was relatively high. In addition, A was more reduced under high than under low soil moisture content. These results support the idea that water stress per se did not contribute to the observed reduction of A. The mechanism of photosynthetic capacity reduction due to the Ggt root-rotting fungus is of interest as it may lead to the molecular mechanisms of plant resistance and ultimately to the development of take-all resistant plants. [ABSTRACT FROM AUTHOR]

Growth, gas exchange and water relations have been studied on hydroponically grown peach (cv. Armking) plants, grafted on GF677 (Arm/GF) and Mr.S.2/5 (Arm/MrS), exposed to 0, 40, 80 and 120 mM NaCl concentration, over a four-week period. Plant performance was also evaluated during a subsequent four-week period of relief from stress, by supplying the plants with a complete nutrient solution. Salinity stress reduced growth and net assimilation rate to a greater extent in Arm/GF than in Arm/MrS plants. Salt-induced water stress was more severe in Arm/GF than Arm/MrS leaves, and particularly during the first two weeks of treatment. On the other hand, leaf osmotic potential at full turgor (ΨπFT) of salt-treated Arm/MrS received a markedly greater contribution from Na+ and Cl- than salt-treated Arm/GF plants. By contrast, divalent cations and K+ made a substantially greater contribution to leaf ΨπFT of salt-treated Arm/GF than to the corresponding ΨπFT of Arm/MrS plants. Salinity stress markedly altered leaf carbohydrate composition and led to a preferential accumulation of sorbitol, independent on the scion/rootstock combination. Salt-treated Arm/GF but not Arm/MrS plants stored most of the Na+ and Cl- loaded in the shoot, into basal (old) leaves. The rootstock ability to control the accumulation of salt in the scion leaves during the salinity stress, determined striking differences in the recovery of photosynthetic performances, during the relief period. A full recovery of A and gs was detected in both 40 and 80 mM salt-treated Arm/GF leaves, but only in 40 mM salt-treated Arm/MrS, at the end of the relief treatment. These data indicate a greater efficiency of GF677 than Mr.S.2/5 in protecting peach plants from the deleterious effects of NaCl stress. [ABSTRACT FROM AUTHOR]

Neotropical savannas are exposed to recurrent dry periods of varied duration, and forage grasses must be able to cope with such temporal stresses to maintain productive pastures. This study compared leaf water relations and net photosynthesis under drought of five perennial Brachiaria species: the tufted B. brizantha (CIAT 6780), the semi-stoloniferous B. decumbens (CIAT 606) and B. mutica, and the stoloniferous B. humidicola (CIAT 679) and B. dictyoneura (CIAT 6133). Plants of the five grasses were grown in large pots and subjected to drought by suspending watering until first wilting symptoms (14 days for B. brizantha, B. decumbens and B. mutica, and 29 days for B. humidicola and B. dictyoneura). Afterwards, they were re-watered and a second soil dry cycle was imposed. Time trends in leaf water potential (Ψl), relative water content (RWC), osmotic potential at full turgor (Ψ0100), stomatal conductance (Gs) and net photosynthesis (A) of stressed (DT) plants were compared to those of well-irrigated (CT) plants. Predawn Ψl in DT plants decreased to a minimum of -1.5 and -2.0 MPa in B. brizantha and B. mutica, compared to -2.5 to -3.0 MPa in B. decumbens, B. humidicola and B. dictyoneura. RWC decreased up to 50% in B. brizantha, compared to 75% in the other species. In B. humidicola, B. dictyoneura and in a lesser extent, B. decumbens, leaves of DT plants adjusted osmotically, by an apparent accumulation of nutrient solutes, at a rather constant ratio of turgid to dry weight of the tissue. Calculated osmotic adjustment ranged between 0.38 (B. decumbens) to 0.87 MPa (B. humidicola). This adjustment in Ψ0100 was in some cases maintained 7 days after re-watering. In B. brizantha and B. mutica, Gs and A were significantly affected by drought, with maximum reduction percentages at the second drought period of 65 and 80%, respectively. The corresponding reduction in B. decumbens was 53 and 55%, respectively; whereas in B. humidicola and B. dictyoneura Gs and A were reduced less than 20%. In all species, re-watering allowed for the water relations (except Ψ0100) and photosynthetic activity of leaves of DT plants to reach values comparable to those of CT plants. Results are discussed in term of root morphology and soil water extraction pattern, as well as leaf traits that may contribute to withstand drought under moderate soil water stress. [ABSTRACT FROM AUTHOR]

Drainage of waterlogged sites has been part of the normal forestry practice in Fennoscandia, the Baltic countries, the British Isles and in some parts of Russia since the early 20th century, and currently, about 15 million hectares of peatlands and other wetlands have been drained for forestry purposes. The rate of forest clear-felling on drained peatlands will undergo a rapid increase in the near future, when a large number of these forests approach their regeneration age. A small-scale pilot survey was performed at two nutrient-rich and old peatland drainage areas in southern Finland to study if forest clear-felling has significant impacts on the exchange of nitrous oxide (N2O) and methane (CH4) between soil and atmosphere. The average N2O emissions from the two drainage areas during three growing seasons following clear-felling were 945 and 246 μg m-2 d-1. The corresponding CH4 fluxes were -0.07 and -0.52 mg m-2 d-1. Clear-felling had impacts on the environmental factors known to affect the N2O and CH4 fluxes of peatlands, i.e. clear-felling raised the water table level and increased the peat temperature. However, no substantial changes in the fluxes of CH4 following clear-felling were observed. The results concerning N2O indicated a potential for increased emissions following clear-felling of drained peatland forests, but further studies are needed for a critical evaluation of the impacts of clear-felling on the fluxes of CH4 and N2O. [ABSTRACT FROM AUTHOR]