Investigations into the exploitation of heterogeneous soils by Lupinus albus L. and L. pilosus Murr. and the effect upon plant growth

In calcareous soils, genotypes of Lupinus albus L. generally grow poorly, resulting in stunted plants that often develop lime-induced chlorosis. In contrast, some genotypes of L. pilosus Murr. occur naturally in calcareous soils without developing any visible symptoms of stress. Some genotypic variation for tolerance to calcareous soil does exist in L. albus and the tolerance mechanisms need to be determined. The adaptation through root system morphological plasticity of L. albus and L. pilosus, to heterogeneous limed soil profiles (pH 7.8) containing either patches of acid (non-limed) soil, or vertically split between acid and limed soil, was investigated. When grown in the presence of patches of acid soil, L. albus had a 52% greater shoot dry weight and visibly greener leaves compared with plants grown in the homogeneous limed soil. Total root dry matter in the acid-soil patches was greater than in the control limed-soil patches. This was due to a four-fold increase in the cluster root mass, accounting for 95% of the root dry matter in the acid-soil patch. Although these cluster roots secreted no more citric acid per unit mass than those in the limed soil did, their greater mass resulted in a higher citrate concentration in the surrounding soil. L. pilosus responded to the patches of acid soil in a manner comparable with L. albus. When grown in the homogeneous limed soil, L. pilosus had a greater maximum net CO₂ assimilation rate (P_max) than L. albus, however, the P_max of both species increased after they had accessed a patch of acid soil. Differences were apparent between the L. albus genotypes grown in soil profiles split vertically into limed and acid soil. A genotype by soil interaction occurred in the partitioning between soils of the cluster roots. The genotype La 674 was comparable with L. pilosus and produced over 11% of its cluster roots in the limed soil, whereas the other genotypes produced only 1–3% of their cluster roots in the limed soil. These results indicate L. pilosus is better adapted to the limed soil than L. albus, but that both species respond to a heterogeneous soil by producing mainly cluster roots in an acid-soil patch. This revised version was published online in June 2006 with corrections to the Cover Date.     

Stress-induced changes in the root architecture of white lupin (Lupinus albus) in response to pH, bicarbonate, and calcium in liquid culture

Current agronomic cultivars of white lupin (Lupinus albus) are intolerant of calcareous or limed soils. In these soils, high pH, bicarbonate (HCO₃^?), and calcium (Ca) concentrations are the major chemical stresses to the root system. To determine the responses of the root system to these factors, evaluate root architecture, and compare genotypes for tolerance, a series of liquid culture experiments was completed using root chambers that allowed the study of the root system in two dimensions. Each stress condition caused changes in different parts of the root system and there was no generalised stress response. HCO₃^? (5 mM) had the greatest effect on cultivars intolerant of calcareous soil; it decreased the dry weight of the shoot and caused the highest percentage of tap root deaths. HCO₃^? also discriminated between short (determinate) and long (indeterminate) roots, as it decreased the number and density of the determinate roots only. Calcium (3 mM) affected all parts of the root system. The tap root was shortened and showed an increased tortuousness in its path compared with 1 mM Ca, although no plants suffered tap root death. The numbers and densities of the two lateral root forms were also decreased, as were the lengths of the indeterminate roots. Stress from alkaline pH (7.5) media caused a lower number and density of determinate lateral roots to be produced than at pH 6.5. The experiments demonstrated that each culture condition elicited a definable stress response. Stress conditions altered the root architecture of genotypes reported to be tolerant of calcareous soil less than in intolerant genotypes. Although soil is more complex than liquid culture, it is possible that in a calcareous or limed soil each stress condition examined may affect the overall stress of the plant, and increased tolerance may result from tolerance to a single stress.     

Functional Analysis of the Genotypic Differences in Response of Pea (<i>Pisum sativum</i> L.) to Calcareous-Induced Iron Deficiency

Lime-induced iron chlorosis is a major nutritional disorder causing severe plant growth and yield reduction in the calcareous soils of Tunisia. The understanding the behavior of key metabolic functions of peas on calcareous soils, the identification of useful traits of tolerance, and the exploration of the genotypic differences in response to this constraint remain the most efficient approaches due to their coast, environmental benefits, and sustainability. For this purpose, a greenhouse experiment was conducted on three pea genotypes (Alexandra: Alex, Douce de provence: DP, and Merveille de Kelvedon: MK) cultivated on calcareous soil (Fe-deficient) and fertile soil (control). Plant growth, SPAD index, iron nutrition and distribution, photosynthesis, and antioxidant enzymes were deeply analyzed to discriminate genotypic differences. Calcareous-induced iron deficiency reduced SPAD index, plant growth, net photosynthesis, and tissue Fe content against a significant stimulation of the oxidative stress indicators, H₂O₂ and Malondialdehyde (MDA). Moreover, we reported a significant induction of SOD and CAT activity in shoots and roots of the Alexandra genotype. Fe use efficiency increased on calcareous soil and clearly discriminated the studied genotypes. Alexandra genotype was found to be the most tolerant to lime-induced iron chlorosis. This genotype protects its tissues against oxidative stress by stimulating enzyme activities (SOD and CAT) and develops significant efficiency of Fe uptake, translocation to shoots and use when cultivated on calcareous soil.     

The effect of soil moisture on the tolerance of Lupinus pilosus genotypes to a calcareous soil

Commercial narrow-leafed lupins (Lupinus angustifolius L.) grown on calcareous soils commonly display chlorotic symptoms resembling Fe deficiency. The severity of chlorosis increases with concurrent increases in soil moisture content. Our research has indicated that the rough-seeded lupin species, Lupinus pilosus Murr., has a range of adaptation to calcareous soils, from tolerant to intolerant. A pot experiment was conducted comparing a tolerant, a moderately tolerant and a moderately intolerant genotype of L. pilosus. Plants were grown for 35 days in a calcareous soil (50% CaCO₃) at three moisture contents (80%, 100% and 120% of field capacity); the growth was compared with that on a fertile black cracking clay control soil at 70% of field capacity. Visual chlorosis score, chlorophyll meter readings, number of leaves and shoot dry weights were recorded at 14, 21, 28 and 35 days after sowing. Concentrations of chlorophyll, active Fe and nutrients in the youngest fully expanded leaves were also measured. Results showed that increased soil moisture increased the severity of chlorotic symptoms (increased chlorosis score) in all genotypes. The tolerant genotype showed significantly less symptoms than other genotypes at all moisture contents. All genotypes were able to recover from chlorosis symptoms at 80% moisture in the calcareous soil. Chlorosis score negatively correlated with chlorophyll meter readings, chlorophyll concentration and foliar active and total Fe, and Mn concentrations. Visual chlorosis score appeared to be a cost effective, accurate and efficient method enabling classification of the tolerance of genotypes. The chlorotic symptoms were likely to be due to HCO₃ ^- induced nutrient deficiencies or a direct effect of HCO₃ ^- on chlorophyll synthesis. This study indicates that the most probable mechanism of tolerance is related to an ability to prevent uptake of HCO₃ ^- or efficiently sequester it once inside the root which prevents increases in internal pH and transport to the shoots.     

Iron accumulation in seed of common bean

The effect of soil and genotype on iron concentration [Fe] in common bean (Phaseolus vulgaris L.) seed was studied in the greenhouse. Liming an acid soil increased soil pH from 6.0 to 7.3 but had no effect on seed [Fe] of three bean genotypes (Voyager, T39, UI911) from the Middle American gene pool in North Dakota. However, liming decreased seed-manganese concentration [Mn]. The influence of FeEDDHA on Fe accumulation in seed of the three bean genotypes, grown on acid (pH=6.0) and naturally calcareous (pH=8.2) soils, was also studied in North Dakota. Seed from the acid soil contained 25% higher [Fe] than seed from the calcareous soil. FeEDDHA increased seed [Fe] only on the calcareous soil, but reduced seed [Mn] on both soils. Voyager seed, characterized by a relatively low [Fe] in the seed coat, had a higher seed [Fe] than the other two genotypes. The hypothesis that high seed [Fe] is characterized by a low seed-coat [Fe] was next investigated. Voyager, T39 and 10 diverse Latin American genotypes from the Middle American gene pool were grown on a soil (pH=7.0) with Andic properties in Mexico in the presence and absence of FeEDTA. FeEDTA increased seed [Fe]. Seed of Voyager and a Mexican genotype (Bayo 400) had the highest seed [Fe]. However, Bayo 400, unlike Voyager, contained a high percentage of its seed Fe in the seed coat. Consequently, a high seed [Fe] genotype does not necessarily have a low seed-coat [Fe]. Both soil and genotype affect Fe accumulation in bean seed.     

Photosynthesis of six barley genotypes as affected by water stress

The effect of water stress on plant water status and net photosynthetic gas exchange (PN) in six barley genotypes (Hordeum vulgare L.) differing in productivity and drought tolerance was studied in a controlled growth chamber. Osmotic adjustment (OA), PN, stomatal conductance (gs), and the ratio intercellular/ambient. CO2 concentration (Ci/Ca) were evaluated at four different levels of soil water availability, corresponding to 75, 35, 25 and 15 % of total available water. Variability in OA capacity was observed between genotypes: the drought tolerant genotypes Albacete and Alpha showed higher OA than drought susceptible genotypes Express and Mogador. The genotype Albacete exhibited also higher PN than the others at low water potential (Ψ). The ratios of PN/gs and Ci/Ca showed that differences in photosynthetic inhibition between genotypes at low Ψ were probably due to nonstomatal effects. In Tichedrett, a landrace genotype with a very extensive root development, OA was not observed, however, it exhibited a capacity to maintain its photosynthetic activity under water stress.     

Transgenic barley (Hordeum vulgare L.) expressing the wheat aluminium resistance gene (TaALMT1) shows enhanced phosphorus nutrition and grain production when grown on an acid soil

Barley ( Hordeum vulgare L.), genetically modified with the Al³⁺ resistance gene of wheat ( TaALMT1 ), was compared with a non-transformed sibling line when grown on an acidic and highly phosphate-fixing ferrosol supplied with a range of phosphorus concentrations. In short-term pot trials (26 days), transgenic barley expressing TaALMT1 (GP-ALMT1) was more efficient than a non-transformed sibling line (GP) at taking up phosphorus on acid soil, but the genotypes did not differ when the soil was limed. Differences in phosphorus uptake efficiency on acid soil could be attributed not only to the differential effects of aluminium toxicity on root growth between the genotypes, but also to differences in phosphorus uptake per unit root length. Although GP-ALMT1 out-performed GP on acid soil, it was still not as efficient at taking up phosphorus as plants grown on limed soil. GP-ALMT1 plants grown in acid soil possessed substantially smaller rhizosheaths than those grown in limed soil, suggesting that root hairs were shorter. This is a probable reason for the lower phosphorus uptake efficiency. When grown to maturity in large pots, GP-ALMT1 plants produced more than twice the grain as GP plants grown on acid soil and 80% of the grain produced by limed controls. Expression of TaALMT1 in barley was not associated with a penalty in either total shoot or grain production in the absence of Al³⁺, with both genotypes showing equivalent yields in limed soil. These findings demonstrate that an important crop species can be genetically engineered to successfully increase grain production on an acid soil.     

Photosynthesis of six barley genotypes as affected by water stress

The effect of water stress on plant water status and net photosynthetic gas exchange (PN) in six barley genotypes (Hordeum vulgare L.) differing in productivity and drought tolerance was studied in a controlled growth chamber. Osmotic adjustment (OA), PN, stomatal conductance (gs), and the ratio intercellular/ambient. CO2 concentration (Ci/Ca) were evaluated at four different levels of soil water availability, corresponding to 75, 35, 25 and 15 % of total available water. Variability in OA capacity was observed between genotypes: the drought tolerant genotypes Albacete and Alpha showed higher OA than drought susceptible genotypes Express and Mogador. The genotype Albacete exhibited also higher PN than the others at low water potential (Ψ). The ratios of PN/gs and Ci/Ca showed that differences in photosynthetic inhibition between genotypes at low Ψ were probably due to nonstomatal effects. In Tichedrett, a landrace genotype with a very extensive root development, OA was not observed, however, it exhibited a capacity to maintain its photosynthetic activity under water stress. This revised version was published online in June 2006 with corrections to the Cover Date.     

Soil cations influence bryophyte susceptibility to bisulfite

The hypothesis that metal ions absorbed by bryophytes from the underlying soil may ameliorate adverse effects of SO2 was investigated in the terricolous moss species Pleurozium schreberi (Brid.) Mitt. and Rhytidiadelphus triquetrus (Hedw.) Warnst. Dilute sodium bisulfite solutions (equivalent to dissolved SO2) were applied to shoots isolated from soil or in contact with artificial substrata. Marked inhibition of net photosynthesis was observed within 2 h of treatment with 0.3 mM bisulfite in both mosses. Progressive recovery of net photosynthesis occurred 2-8 h after bisulfite treatment, although the extent of this depended on the concentration and pH of the solution. When R. triquetrus and P. schreberi were grown on artificial substrata (calcareous, acid-mineral or acid-organic) with weekly bisulfite applications, the only significant effect was poorer growth of P. schreberi receiving bisulfite on the calcareous and acid-organic substrata. In both species, growth on the calcareous substratum led to increased concentrations of exchangeable Ca2+, whereas exchangeable Fe3+ concentrations increased following growth on the acid-mineral soil. In another experiment the two mosses were pre-treated with either Ca2+ or Fe3+ before incubation with bisulfite. In P. schreberi, the depression of net photosynthetic rate caused by bisulfite was ameliorated from 33 to 64% of the control by pre-treatment with Fe3+, but it was unaffected by Ca2+ pre-treatment. In R. triquetrus, the amelioration caused by Fe3+ pre-treatment was from 16 to 60% of the control, but pre-treatment with Ca2+ gave a greater amelioration, to 75% of the control value. The responses are discussed in terms of soil preferences of the mosses and possible underlying bisulfite amelioration mechanisms.     

Screening rough-seeded lupins (Lupinus pilosus Murr. and Lupinus atlanticus Glads.) for tolerance to calcareous soils

Soil- and solution-based screening methods were used to identify interspecific and intraspecific variation in lupins for tolerance to calcareous soils. Plants were grown for 21 days in a calcareous soil (pH 8.2; 50% CaCO₃; moisture content 90% of field capacity) for soil-based screening and in nutrient solution containing 15 mM KHCO₃ for solution-based screening. Chlorosis as an indicator of tolerance was recorded. Lupinus pilosus Murr. had the most tolerant genotypes and had the greatest range of intraspecific variation. Most genotypes of Lupinus atlanticus Glads. and Lupinus angustifolius L. were moderately intolerant, although two genotypes of L. atlanticus appeared to be tolerant. Lupinus albus L. had moderately tolerant to moderately intolerant genotypes, whilst the single genotypes of Lupinus cosentinii Guss. and Lupinus digitatus Forsk. appeared tolerant. In a field study six genotypes of L. pilosus identified in the soil-based screening as differing in their tolerance to the calcareous soil were grown on comparable calcareous (pH 8.3; topsoil 3% CaCO₃, subsoil 13% CaCO₃) and non-calcareous (pH 7.3) soils within a paddock. Chlorosis and nutrient concentrations in the youngest leaves were measured 53 days after sowing, whilst grain yield was estimated at harvest. Despite the soil containing a much lower CaCO₃ content than used in the screening method, the field study confirmed that moderately intolerant to intolerant genotypes had lower relative grain yields than more tolerant genotypes. Chlorosis rankings of the genotypes were correlated between field and the screening studies. It is suggested that the incorporation of genes conferring tolerance to calcareous soils into high yielding, agronomically suitable genotypes of L. pilosus should be an important objective in a lupin breeding program for calcareous soils.     

The effect of FeEDDHA on the development of lime-chlorosis in two seedling populations ofEucalyptus obliqua L'Hérit

Summary The application of FeEDDHA to a calcareous soil significantly increased yield and alleviated severe lime-chlorosis in a genotype ofEucalyptus obliqua that is native to acidic soils. The alleviation of chlorosis brought about a significant decrease in the levels of P, Ca and K but an increase in the uptake of Fe in leaves. The total Fe content of foliage, however, was poorly coorelated with the occurrence of lime-chlorosis. It was concluded that the differential susceptibility ofE. obliqua to lime-chlorosis is related to interactions between Fe and Ca, as well as Fe and P, occurring during the absorption and translocation processes.     

Changes in root morphology of white lupin (Lupinus albus L.) and its adaptation to soils with heterogeneous alkaline/acid profiles

The ability of Lupinus albus L. to adapt to a heterogeneous soil profile containing acid subsoil below limed topsoil of the same type, and to utilize nutrients by significantly altering its root system structure, was investigated using specially constructed soil profile tubes. Plants grown in homogeneous acid profiles had the fastest growth while those grown in homogeneous limed-soil profiles showed the slowest growth and exhibited some chlorosis after 19 days. Limed topsoil combined with an acid subsoil profile initially retarded plant growth similar to that in a homogeneous limed soil. However, after 68 days significantly greater growth had occurred in the limed/acid soil treatment relative to the homogeneous limed soil, indicating plants had benefited from the acid subsoil stratum. Plants in the homogeneous limed soil profile had lower concentrations of P, Fe and Mn in shoots compared with those in heterogeneous soils. In contrast, the concentration of Ca increased by 74%, due mainly to an increase in the water-soluble Ca fraction. When grown in a heterogeneous limed/acid soil profile, concentrations of P, Ca, K, Mg, Fe, Mn and Zn in shoots were comparable to those grown in a soil with a homogeneous acid profile. Although total root production was lower in the homogeneous limed-soil profile compared to the acid-soil containing profiles, cluster root mass was maintained at a level comparable with that in acid soil. The roots in heterogeneous soil profiles exhibited extensive plasticity, demonstrating a root-type specific, morphological response to the soil conditions. Within the acid subsoil of a heterogeneous profile, there was a large increase in cluster root mass compared with non-cluster roots. The proliferation of cluster roots in acid soil below limed topsoil may enhance the plant's ability to exploit this soil and facilitate the cultivation of L. albus on limed soil. This revised version was published online in August 2006 with corrections to the Cover Date.     

The effects of nutrient supply,predominantly addition of iron,and rhizobial inoculation on the tolerance of Lupinus pilosus genotypes to a calcareous soil

Two glasshouse experiments were conducted to examine the effects of nutrient supply and rhizobial inoculation on the performance of Lupinus pilosus genotypes differing in tolerance to calcareous soils. In experiment 1, plants were grown for 84 days in a calcareous soil (50% CaCO₃; soil water content 90% of field capacity) at four nutrient treatments (no-added nutrients, added nutrients without Fe, added nutrients with soil applied FeEDDHA, added nutrients with foliar applied FeSO₄). In experiment 2, plants were grown for 28 days with supply of NH₄NO₃ without inoculation or inoculated with Bradyrhizobium sp. (Lupinus). Chlorosis in the youngest leaves was a good indicator of the relative tolerance of the genotypes to the calcareous soil in both experiments, except the treatment with FeEDDHA at 5 mg kg^–1 soil which was toxic to all genotypes. Chlorosis scores correlated with chlorophyll meter readings and chlorophyll concentrations. The foliar application of FeSO₄ did not fully alleviate chlorotic symptoms despite concentrations of active or total Fe in the youngest leaves being increased. Adding nutrients and chemical nitrogen did not change the severity of chlorosis or improve the growth of the plant. The nutrient supply did not alter the ranking of tolerance of genotypes to the calcareous soil. The results suggest that nutrient deficiency or poor nodulation was not a major cause of poor plant growth on calcareous soils and that bicarbonate may exert a direct effect on chlorophyll synthesis. The mechanism for tolerance is likely to be related to an ability to exclude bicarbonate or prevent its transport to the leaves.     

Incorporation of calcium into the soft tissues and calcareous corpuscles of larval Taenia taeniaeformis.

Larval Taenia taeniaeformis in vivo accumulates 45Ca2+ in soft tissues and calcareous corpuscles. Radioactivity was demonstrable in the corpuscles six months after a single dose of 45Ca2+ was administered to the host by means of a stomach tube. Ca2+ also was taken up by isolated larvae. Accumulation in vitro was more rapid then in vivo and was correlated with the external Ca2+ concentration. Temperature variation, oxygen availability, and metabolic inhibitors had little effect on the Ca2+ uptake, indicating that active transport of Ca2+ is unlikely in this parasite. Variations in the external Pi concentrations had no effect on Ca2+ accumulation or on its distribution. Addition of 5% CO2 increased the uptake of Ca2+ by the calcareous corpuscles under anaerobic conditions. Radioactivity from NaH14CO3 also was accumulated in soft tissues and corpuscles of T. taeniaeformis. Assuming that the 14C taken up by the corpuscles was in the form of 14CO3(2-), the ratio of Ca2+ to CO3(2-) accumulation in the corpuscles approximates the ratio of these constituents in dolomite: CaMg(CO3)2.     

Expression levels of genes involved in metal homeostasis,physiological adaptation,and growth characteristics of rice (Oryza sativa L.) genotypes under Fe and/or Al toxicity

Acid sulphate soil contains high amounts of iron (Fe) and aluminum (Al), and their contamination has been reported as major problems, especially in rainfed and irrigated lowland paddy fields. Rice is sensitive to Fe and Al grown in acid soil (pH < 5.5), leading to growth inhibition and grain yield loss. The objective of this study was to evaluate Fe and/or Al uptake, translocation, physiological adaptation, metal toxicity, and growth inhibition in rice genotypes grown in acid soil. Fe and Al in the root tissues of all rice genotypes were enriched depending on the exogenous application of either Fe or Al in the soil solution, leading to root growth inhibition, especially in the KDML105 genotype. Expression level of OsYSL1 in KDML105 was increased in relation to metal uptake into root tissues, whereas OsVIT2 was downregulated, leading to Fe (50.3 mg g⁻¹ DW or 13.1 folds over the control) and Al (4.8 mg g⁻¹ DW or 2.2 folds over the control) translocation to leaf tissues. Consequently, leaf greenness (SPAD), net photosynthetic rate (P_n), stomatal conductance (g_s), and transpiration rate (E) in the leaf tissues of genotype KDML105 under Fe + Al toxicity significantly declined by 28.4%, 35.3%, 55.6%, and 51.6% over the control, respectively. In Azucena (AZU; Fe/Al tolerant), there was a rapid uptake of Fe and Al by OsYSL1 expression in the root tissues, but a limited secretion into vacuole organelles by OsVIT2, leading to a maintenance of low level of toxicity driven by an enhanced accumulation of glutathione together with downregulation of OsGR expression level. In addition, Fe and Al restrictions in the root tissues of genotype RD35 were evident; therefore, crop stress index (CSI) of Fe + Al–treated plants was the maximum, leading to an inhibition of g_s (53.6% over the control) and E (49.0% over the control). Consequently, free proline, total phenolic compounds, and ascorbic acid in the leaf tissues of rice under Fe + Al toxicity significantly increased by 3.2, 1.2, and 1.5 folds over the control, respectively, indicating their functions in non-enzymatic antioxidant defense. Moreover, physiological parameters including leaf temperature (T_leaf) increment, high level of CSI (>0.6), SPAD reduction, photon yield of PSII (Φ_PSII) diminution, P_n, g_s, and E inhibition in rice genotype IR64 (Fe/Al-sensitive) under Fe + Al treatment were clearly demonstrated as good indicators of metal-induced toxicity. Our results on Fe- and/or Al-tolerant screening to find out the candidate genotypes will contribute to present screening and breeding efforts, which in turn help increase rice production in the Fe/Al-contaminated acid soil under lowland conditions.

     

Productivity differences among loblolly pine genotypes are independent of individual-tree biomass partitioning and growth efficiency

Genetic differences in individual-tree biomass partitioning, growth efficiency, and stem relative growth rate (RGR) could confer intraspecific productivity differences and might strongly influence forest ecosystem carbon storage. We examined the relationship between genotype productivity (stem volume), whole-tree biomass partitioning, growth efficiency (stem wood production per unit leaf area), and stem RGR among nine different loblolly pine (Pinus taeda L.) genotypes from three different genetic groups of contrasting inherent genetic homogeneity: three open-pollinated (half-sib) families, three mass-control pollinated (full-sib) families, and three clonal varieties. We hypothesized that genotype productivity would be positively associated with increased partitioning to stem wood relative to other plant parts, higher stem RGR, and enhanced growth efficiency. After 3 years under plantation conditions, genotypes showed significant differences in stem volume, percent stem wood, percent branch wood, and partitioning to fine roots, yet no differences in stem RGR or growth efficiency. Furthermore, genotypic differences in stem volume were independent of genotypic differences in biomass partitioning, and overall, we found no evidence to support the hypothesized relationships. Even so, the observed variation in biomass partitioning has implications for forest C sequestration as genotypes which partition more biomass to long-lived biomass pools such as stems, may sequester more C. Moreover, the lack of a genetic relationship between stem volume and belowground partitioning suggests that highly productive genotypes may be planted without compromising belowground C storage.     

Effects of liming on rhizosphere chemistry and growth of fine roots and of shoots of sessile oak (Quercus petraea)

Soil acidification can be detrimental to root growth and nutrient uptake, and liming may alleviate such acidification. In the following study, seedlings of sessile oak (Quercus petraea Liebl. M.) were grown in rhizotrons and subjected to liming (L) or gypsum (G) treatments and compared with the control (C). In order to study and interpret the impact of these calcium rich treatments on fine root development and tree growth, the following parameters were assessed: fine root biomass, fine root length, seedling development (height, diameter, leaves), seedling biomass, nutrient content of roots and seedlings, bulk soil and soil solution chemistry and rhizosphere soil chemistry. The results show that liming increased bulk soil pH, exchangeable Mg, Ca and the Ca/Al molar ratio, and decreased exchangeable Al, mainly in the A-horizon. Gypsum had a similar but smaller impact on exchangeable Al, Ca, H⁺ and the Ca/Al molar ratio in the A-horizon, but reacted with depth, so that exchangeable Mn, Mg and Ca were increased in the B-horizon. In the rhizosphere, the general pattern was determined by the treatment effects of the bulk soil. Most elements were more concentrated in the rhizosphere than in bulk soil, except for Ca which was less concentrated after liming or gypsum application. In the B-horizon rhizosphere pH was increased by the treatments (L > G,C) close to the root tips. Furthermore, the length of the zone with a positive root-induced pH increase was greater for the limed roots as compared with both the other treatments. Fine root growth was stimulated by liming (L > G,C) both in terms of biomass and length, whereas specific root length was not obviously affected apart from the indication of some stimulation after liming at the beginning. The live:dead ratio of fine roots was significantly higher in the limed rhizotrons as compared to the control (G not assessed), indicating lower mortality (higher longevity). Shoot growth showed greater lime-induced stimulation (L > G,C) as compared to root growth. As a result the shoot:root ratio was higher in the limed rhizotrons than in the control (L > G,C). Liming induced a higher allocation of P, S, Mg, Ca and K to the leaves, stem and twigs. Gypsum showed similar effects, but was only significant for S. Liming increased the foliar Ca/Al ratio by both increasing foliar Ca and decreasing foliar Al, whereas gypsum did not clearly improve foliar nutrition. This study suggests that a moderate application of lime can be successful in stimulating seedling growth, but that gypsum had no effect on seedling growth. It can be concluded that this lime-induced growth stimulation is directly related to the improved soil fertility status, and the alleviation of Al toxicity and acid stress, resulting in better foliar nutrition. The impact of liming on fine roots, as a consequence, was not limited to a stimulation of the total amount of fine roots, but also improved the root uptake performance. This revised version was published online in June 2006 with corrections to the Cover Date.     

Nitrogen fixation and nutrient uptake by two chickpea genotypes cultivated in sandy soils of Egypt

A field experiment was conducted to compare local chickpea (Giza 2) and its recently developed cultivar L₃. The two genotypes were examined for biological dinitrogen fixation and P uptake as enhanced by inoculation withRhizobium (Rh) and/or arbuscular mycorrhiza (AM). Significant increase in dry mass was obtained by biological inoculation. Soil chemical and physical properties have a significant effect on the ability of the two genotypes to fix nitrogen on their P uptake and N content. Growth of the local genotype (G₂) was pronounced in sandy loam soil as compared with the sandy one.     

Growth response to subsurface soil acidity of wheat genotypes differing in aluminium tolerance

Subsurface soil acidity coupled with high levels of toxic Al is a major limiting factor in wheat production in many areas of the world. This study examined the effect of subsurface soil acidity on the growth and yield of two near-isogenic wheat genotypes differing in Al tolerance at a single genetic locus in reconstructed soil columns. In one experiment, plants were grown in columns with limed topsoil and limed or acidic subsurface soils, and received water only to the subsurface soil at a late part of the growth period. While shoot dry weight, ear number and grain yield of Al-tolerant genotype (ET8) were not affected by subsurface soil acidity, liming subsurface soil increased shoot weight and grain yield of Al-sensitive genotype (ES8) by 60% and ear number by 32%. Similarly, root length density of ET8 was the same in the limed and acidic subsurface soils, while the root length density of ES8 in the acidic subsurface soil was only half of that in the limed subsurface soil. In another experiment, plants were grown with limed topsoil and acidic subsurface soil under two watering regimes. Both genotypes supplied with water throughout the soil column produced almost twice the dry weight of those receiving water only in the subsurface soil. The tolerant genotype ET8 had shoot biomass and grain yield one-third higher than ES8 when supplied with water throughout the whole column, and had yield 11% higher when receiving water in the subsurface soil only. The tolerant genotype ET8 produced more than five times the root length in the acidic subsurface soil compared to ES8. Irrespective of watering regime, the amount of water added to maintain field capacity of the soil was up to 2-fold higher under ET8 than under ES8. The results suggest that the genotypic variation in growth and yield of wheat grown with subsurface soil acidity results from the difference in root proliferation in the subsurface soil and hence in utilizing nutrient and water reserves in the subsurface soil layer.     

磷高效利用野生大麦基因型筛选及其根际土壤无机磷组分特征

通过土培盆栽试验,研究了16份野生大麦种质资源在相同供磷水平下磷素吸收利用的基因型差异,探讨磷高效野生大麦根际土壤无机磷组分特征.结果表明：拔节期和扬花期磷素干物质生产效率（CV=11.6%、12.4%）、成熟期磷素籽粒生产效率（CV=13.7%）基因型间差异较大.不同生育时期磷高效基因型IS-22-30和IS-22-25生物量、磷积累量和磷素干物质生产效率均显著高于低效基因型IS-07-07,且高效基因型的籽粒产量分别是低效基因型的3.10和3.20倍.不施磷、施磷30 mg·kg^-1条件下,不同磷素利用效率野生大麦根际土壤有效磷和水溶性磷含量均显著低于非根际土壤,且高效基因型较低效基因型根际土壤水溶性磷亏缺量更大.根际与非根际土壤无机磷组分含量为Ca₁₀-P＞O-P＞Fe-P＞Al-P＞Ca₂-P＞Ca₈-P.在拔节期和扬花期,施磷30 mg·kg^-1条件下,磷高效基因型根际土壤Ca₈-P含量显著高于低效基因型,而Ca₂-P含量显著低于低效基因型;不施磷条件下,高效基因型根际土壤Ca₂-P和Ca₈-P含量均显著高于低效基因型,且根际土壤Ca₁₀-P均减少.施磷30 mg·kg^-1条件下,根际土壤Fe-P和O-P含量均表现为高效基因型显著高于低效基因型,Al-P含量则呈现相反的趋势;不施磷条件下,高效基因型根际土壤Al-P、Fe-P和O-P含量均显著低于低效基因型.低磷胁迫下,高效基因型活化吸收Ca₂-P、Al-P的能力强于低效基因型.