Disparity in 90Sr and 137Cs uptake in Alpine plants: phylogenetic effect and Ca and K availability

Background and aims

Uptake of ⁹⁰Sr and ¹³⁷Cs in plants varies widely between soil types and between plant species. It is now recognized that the radionuclide uptake in plants is more influenced by site-specific and plant-specific parameters rather than the bulk radionuclide concentration in soil. We hypothesized that the stress which Alpine plants experience because of the short growing season may enhance the phylogenetic effect on the ¹³⁷Cs and ⁹⁰Sr transfer factors as well as the dependency of the uptake by plant to the concentrations of exchangeable Ca and K of soils.

Methods

We carried out a field study on the ⁹⁰Sr and ¹³⁷Cs uptake by 11 species of Alpine plants growing on 6 undisturbed and geochemically different soils in the Alpine valley of Piora, Switzerland.

Results

Results show that a strong correlation exists between the log TF and the log of exchangeable Ca or K of the soils.

Conclusions

Cs uptake by Phleum rhaeticum (Poales) and Alchemilla xanthochlora (Rosales) is more sensitive to the amount of exchangeable K in the soil than the corresponding uptake by other orders. Moreover, the ⁹⁰Sr results indicate a phylogenetic effect between Non-Eudicot and Eudicots: the order Poales (Phleum rhaeticum) concentrating much less ⁹⁰Sr than Eudicots do.     

Preferential use of root litter compared to leaf litter by beech seedlings and soil microorganisms

Background and aims

Litter decomposition is regulated by e.g. substrate quality and environmental factors, particularly water availability. The partitioning of nutrients released from litter between vegetation and soil microorganisms may, therefore, be affected by changing climate. This study aimed to elucidate the impact of litter type and drought on the fate of litter-derived N in beech seedlings and soil microbes.

Methods

We quantified ¹⁵N recovery rates in plant and soil N pools by adding ¹⁵N-labelled leaf and/or root litter under controlled conditions.

Results

Root litter was favoured over leaf litter for N acquisition by beech seedlings and soil microorganisms. Drought reduced ¹⁵N recovery from litter in seedlings thereby affecting root N nutrition. ¹⁵N accumulated in seedlings in different sinks depending on litter type.

Conclusions

Root turnover appears to influence (a) N availability in the soil for plants and soil microbes and (b) N acquisition and retention despite a presumably extremely dynamic turnover of microbial biomass. Compared to soil microorganisms, beech seedlings represent a very minor short-term N sink, despite a potentially high N residence time. Furthermore, soil microbes constitute a significant N pool that can be released in the long term and, thus, may become available for N nutrition of plants.     

Mg and Ca root uptake and vertical transfer in soils assessed by an in situ ecosystem-scale multi-isotopic (26Mg & 44Ca) tracing experiment in a beech stand (Breuil-Chenue, France)

Background and aims

The sustainability of forest ecosystems may be at stake especially in forests on base-poor soils due to reduced nutrient deposition and intensified silvicultural practices. Understanding nutrient availability and cycling is therefore essential to manage forest soil fertility. This study aims to assess in a beech plot Mg and Ca vertical transfer in soil and root uptake using an isotopic tracing experiment.

Methods

A simulated rainfall containing a small amount (960 g?Mg.ha^?1; 530 g Ca.ha^?1) of highly enriched ²⁶Mg and ⁴⁴Ca was sprayed on the forest floor of a 35-yr-old beech plot. The isotopic composition of fine roots and of the soil exchangeable Mg and Ca pool was monitored during 1 year. A pool and flux model (IsoMod) was developed to predict the labeling of the soil and vertical transfer of tracers.

Results

Tracers (⁴⁴Ca and ²⁶Mg) were immediately retained in the thin litter layer. During the following year, Mg and to a lesser extent Ca were progressively released. After 1 year, the exchangeable Mg and Ca pools of the upper mineral layer (0–5 cm) were strongly labeled (~660?‰, representing ~55 % of the tracer input and ~370?‰, ~41 % of the tracer input respectively). A significant proportion (~8 % ²⁶Mg, ~2 % ⁴⁴Ca) of tracer was leached through the soil, below 10 cm. This amount was much larger than what was predicted using a simple mixing model. The Ca and Mg isotopic composition of fine roots at all depths was close or lower than that of exchangeable Ca and Mg respectively.

Conclusions

An in situ ecosystem-scale ²⁶Mg and ⁴⁴Ca isotopic tracing experiment was successfully carried out. Tracers were at first strongly retained in the litter layer, then progressively transferred to soil horizons below. Nutrient cycling of Mg and Ca were proven to be very different. Mg had a higher mobility in the soil than Ca, and nutrient uptake sources were proven to be different.     

Prediction of leaf nitrogen from early season samples and development of field sampling protocols for nitrogen management in Almond (Prunus dulcis [Mill.] DA Webb)

Background and aim

Protocols for leaf sampling in deciduous tree crops are commonly executed too late in the season and do not adequately consider field variability to be effectively used to guide N management. The goal of this study was to develop improved sampling strategies to optimize nitrogen management in deciduous tree crops.

Method

Leaf nutrient concentration from individual trees in four mature commercial orchards was collected (n =1148) for three consecutive seasons to develop nitrogen prediction models and to estimate the distribution of N values in orchards in July. Spatial variance analysis was used to determine optimal sampling strategies.

Results

Leaf nitrogen concentration in summer can be predicted (r²?=?0.9) from the leaf N and B concentration in spring with the sum of K, Ca, and Mg equivalents. Mean field leaf nutrient concentration can be obtained by collecting one pooled sample per management zone composed of 30 trees each of which are at least 30 m apart. Using these methods the percentage of trees with leaf N above the recommended July critical value can be predicted accurately.

Conclusions

Optimized methods for sample collection and models to predict mid-season leaf N from early season samples can be used to improve N management in deciduous tree crops.     

Minor contribution of leaf litter to N nutrition of beech (Fagus sylvatica) seedlings in a mountainous beech forest of Southern Germany

Aims

Our aims were to characterize the fate of leaf-litter-derived nitrogen in the plant-soil-microbe system of a temperate beech forest of Southern Germany and to identify its importance for N nutrition of beech seedlings.

Methods

¹⁵N-labelled leaf litter was traced in situ into abiotic and biotic N pools in mineral soil as well as into beech seedlings and mycorrhizal root tips over three growing seasons.

Results

There was a rapid transfer of ¹⁵N into the mineral soil already 21 days after tracer application with soil microbial biomass initially representing the dominant litter-N sink. However, ¹⁵N recovery in non-extractable soil N pools strongly increased over time and subsequently became the dominant ¹⁵N sink. Recovery in plant biomass accounted for only 0.025 % of ¹⁵N excess after 876 days. After three growing seasons, ¹⁵N excess recovery was characterized by the following sequence: non-extractable soil N?>>?extractable soil N including microbial biomass?>>?plant biomass?>?ectomycorrhizal root tips.

Conclusions

After quick vertical dislocation and cycling through microbial N pools, there was a rapid stabilization of leaf-litter-derived N in non-extractable N pools of the mineral soil. Very low ¹⁵N recovery in beech seedlings suggests a high importance of other N sources such as root litter for N nutrition of beech understorey.     

Contribution of 15N-labelled leaf litter to N turnover, nitrous oxide emissions and N sequestration in a beech forest during eleven years

Aims

Decomposition of leaf litterfall plays a major role for nitrogen (N) dynamics in soils. However, little is known as to which extent beech leaf litter contributes to N turnover and nitrous oxide (N₂O) emissions within one decade after litterfall.

Methods

In 1997, we exchanged recently fallen leaf litter by ¹⁵N-labelled litter in a beech stand (Fagus sylvatica) at the Solling, Germany. Measurements were conducted 2–3 and 10–11 years after litter exchange.

Results

Two years after litter exchange, 92 % of added ¹⁵N was recovered in the surface 10 cm of the soil. The labelled N was primarily found in the upper part of the F layer of the moder type humus. Eleven years after litter exchange, 73 % of the added ¹⁵N was lost and the remaining 27 % was mainly recovered in the lower part of the F layer indicating N sequestration. The remaining leaf litter N was subject to measurable N mineralisation (2–3 % of litter N) and N₂O production (0.02 %). Between 0.3 % (eleventh year) and 0.6 % (second year) of total annual N₂O emissions were attributed to beech leaf litter of a single year.

Conclusions

Most of the annual N₂O emissions (1.33–1.54 kg N ha^?1 yr^?1) were probably derived from older soil N pools.     

Influence of the spatial layout of vegetation on the stability of slopes

Background and aims

Plant nutrient uptake is affected by environmental stress, but how plants respond to cation-nutrient stress is poorly understood. We assessed the impact of varying degrees of cation-nutrient stress on cation uptake in an experimental plant-mineral system.

Methods

Column experiments, with red pine (Pinus resinosa Ait.) seedlings growing in sand/mineral mixtures, were conducted for up to 9 months. The Ca and K were supplied from both minerals and nutrient solutions with varying Ca and K concentrations.

Results

Cation nutrient stress had little impact on carbon allocation after 9 months of plant growth and K was the limiting nutrient for biomass production. Measurement of Ca/Sr and K/Rb ratios allowed independent estimation of dissolution incongruency and discrimination against Sr and Rb during cation uptake processes. The fraction of K in biomass from biotite increased with decreasing K supply from nutrient solutions. The mineral anorthite was consistently the major source of Ca, regardless of nutrient treatment.

Conclusions

Red pine seedlings exploited more mineral K in response to more severe K deficiency. This did not occur for Ca since Ca was not limiting plant growth. Plant discrimination factors must be carefully considered to accurately identify nutrient sources using cation tracers.     

Influence of serpentine abundance on the vertical distribution of available elements in soils

Background and Aim

Biotic and abiotic factors contribute in shaping the distribution through the soil profile of elements released by mineral weathering; among them, leaching and biocycling dominate in temperate environments. We evaluated if the intensity of leaching and biocycling of nutrients can be modulated by element deficiencies linked to the abundance of serpentine in the soil parent material, i.e. if the most deficient elements are more efficiently retained.

Methods

We selected twelve poorly developed soils from Northern Italian beech stands, with variable amounts of serpentinites in the parent material, and determined total and exchangeable Ca, Mg and K, as well as an index of abundance of serpentine minerals.

Results

The total element content depended on the abundance of serpentines, while only exchangeable Mg was related to the parent material. The vertical trend of Ca and K indicated the role of biocycling in all soils, but the relative availability of Ca (ratio between exchangeable and total content) was much higher in the top horizons of serpentine-rich soils.

Conclusions

The different element availability among soils suggested that the vertical distribution of available elements was linked to the parent material and that losses were limited in serpentine-rich soils, probably because plants take up the deficient elements as soon as they are released from litter and thus limit their leaching in deeper soil horizons.     

Fungal community composition shifts along a leaf degradation gradient in a European beech forest

Aims

The fungal communities in living and decomposed leaves of European Beech (Fagus sylvatica) were compared to identify the phyllosphere fungi involved in litter decomposition at a site in Bavaria, Germany.

Methods

New primers were designed to cover a broad range of fungal ribosomal DNA sequence diversity. Following ‘environmental PCR’, clone libraries from each of five samples of living leaves (surface-sterilized and untreated), freshly fallen, initially and highly decomposed leaves, were screened using RFLP fingerprinting.

Results

Statistical analysis (ANOSIM) revealed that the fungal communities colonizing living (a) and initially decomposed leaves (c) significantly differed between each other and from freshly fallen (b) and highly decomposed leaves (d). Fungal assemblages of a and d were statistically indistinguishable from each other and from the endophyllous fungal community in living leaves.

Conclusions

The results showed that endophyllous fungi play a role throughout the whole decomposition process of beech leaf litter. Therefore, clarification of the life cycle of certain endophytic and/or soil fungi may only be achieved by considering both phyllosphere and soil habitats.     

Influence of potassium and sodium nutrition on leaf area components in Eucalyptus grandis trees

Background and Aims

Recent studies showed a positive tree response to Na addition in K-depleted tropical soils. Our study aimed to gain insight into the effects of K and Na fertilizations on leaf area components for a widely planted tree species.

Methods

Leaf expansion rates, as well as nutrient, polyol and soluble sugar concentrations, were measured from emergence to abscission of tagged leaves in 1-year-old Eucalyptus grandis plantations. Leaf cell size and water status parameters were compared 1 and 2 months after leaf emergence in plots with KCl application (+K), NaCl application (+Na) and control plots (C).

Results

K and Na applications enhanced tree leaf area by increasing both leaf longevity and the mean area of individual leaves. Higher cell turgor in treatments +K and +Na than in the C treatment resulting from higher concentrations of osmotica contributed to increasing both palisade cell diameters and the size of fully expanded leaves.

Conclusions

Intermediate total tree leaf area in treatment +Na compared to treatments C and +K might result from the capacity of Na to substitute K in osmoregulatory functions, whereas it seemed unable to accomplish other important K functions that contribute to delaying leaf senescence.     

Positive feedbacks between decomposition and soil nitrogen availability along fertility gradients

Background and aims

We determined the relationship between site N supply and decomposition rates with respect to controls exerted by environment, litter chemistry, and fungal colonization.

Methods

Two reciprocal transplant decomposition experiments were established, one in each of two long-term experiments in oak woodlands in Minnesota, USA: a fire frequency/vegetation gradient, along which soil N availability varies markedly, and a long-term N fertilization experiment. Both experiments used native Quercus ellipsoidalis E.J. Hill and Andropogon gerardii Vitman leaf litter and either root litter or wooden dowels.

Results

Leaf litter decay rates generally increased with soil N availability in both experiments while belowground litter decayed more slowly with increasing soil N. Litter chemistry differed among litter types, and these differences had significant effects on belowground (but not aboveground) decay rates and on aboveground litter N dynamics during decomposition. Fungal colonization of detritus was positively correlated with soil fertility and decay rates.

Conclusions

Higher soil fertility associated with low fire frequency was associated with greater leaf litter production, higher rates of fungal colonization of detritus, more rapid leaf litter decomposition rates, and greater N release in the root litter, all of which likely enhance soil fertility. During decomposition, both greater mass loss and litter N release provide mechanisms through which the plant and decomposer communities provide positive feedbacks to soil fertility as ultimately driven by decreasing fire frequency in N-limited soils and vice versa.     

Variability of stomatal conductance, leaf anatomy, and seasonal leaf wettability of young and adult European beech leaves along a vertical canopy gradient

This study assessed the variation of leaf anatomy, chlorophyll content index (CCI), maximal stomatal conductance (g _s ^max ) and leaf wettability within the canopy of an adult European beech tree (Fagus sylvatica L.) and for beech saplings placed along the vertical gradient in the canopy. At the top canopy level (CL_28m) of the adult beech, CCI and leaf anatomy reflected higher light stress, while g _s ^max increased with height, reflecting the importance of gas exchange in the upper canopy layer. Leaf wettability, measured as drop contact angle, decreased from 85.5°?±?1.6° (summer) to 57.5°?±?2.8° (autumn) at CL_28m of the adult tree. At CL_22m, adult beech leaves seemed to be better optimized for photosynthesis than the CL_28m leaves because of a large leaf thickness with less protective and impregnated substances, and a higher CCI. The beech saplings, in contrast, did not adapt their stomatal characteristics and leaf anatomy according to the same strategy as the adult beech leaves. Consequently, care is needed when scaling up experimental results from seedlings to adult trees.     

Use of foliar Ca/Sr discrimination and <Superscript>87</Superscript>Sr/<Superscript>86</Superscript>Sr ratios to determine soil Ca sources to sugar maple foliage in a northern hardwood forest

Calcium/strontium and ⁸⁷Sr/⁸⁶Sr ratios in foliage can be used to determine the relative importance of different soil sources of Ca to vegetation, if the discrimination of Ca/Sr by the plant between nutrient sources and foliage is known. We compared these tracers in the foliage of sugar maple (Acer saccharum) to the exchange fraction and acid leaches of soil horizons at six study sites in the White Mountains of New Hampshire, USA. In a previous study, sugar maple was shown to discriminate for Ca compared to Sr in foliage formation by a factor of 1.14 ± 0.12. After accounting for the predicted 14% shift in Ca/Sr, foliar Ca/Sr and ⁸⁷Sr/⁸⁶Sr ratios closely match the values in the Oie horizon at each study site across a 3.6-fold variation in foliar Ca/Sr ratios. Newly weathered cations, for which the Ca/Sr and ⁸⁷Sr/⁸⁶Sr ratios are estimated from acid leaches of soils, can be ruled out as a major Ca source to current foliage. Within sites, the ⁸⁷Sr/⁸⁶Sr ratio of the soil exchange pool in the Oa horizon and in the 0–10 cm and 10–20 cm increments of the mineral soil are similar to the Oie horizon and sugar maple foliar values, suggesting a common source of Sr in all of the actively cycling pools, but providing no help in distinguishing among them as sources to foliage. The Ca/Sr ratio in the soil exchange pool, however, decreases significantly with depth, and based on this variation, the exchange pool below the forest floor can be excluded as a major Ca source to the current sugar maple foliage. This study confirms that internal recycling of Ca between litter, organic soil horizons and vegetation dominate annual uptake of Ca in northern hardwood ecosystems. Refinement of our understanding of Ca and Sr uptake and allocation in trees allows improvement in the use of Ca/Sr and ⁸⁷Sr/⁸⁶Sr ratios to trace Ca sources to plants.     

A comparison between Ca and Sr cycling in forest ecosystems

In favourable conditions, the ⁸⁷Sr/⁸⁶Sr isotope ratios of the Sr delivered by rain and soil mineral weathering differ. Assuming that Ca and Sr behave similarly in forest ecosystems, several authors have used the ⁸⁷Sr/⁸⁶Sr variation in forest compartments to calculate the contribution of rain and mineral weathering to Ca fluxes and pools. However, there are a number of experimental reports showing that Ca and Sr may behave differently in the soil and in the plant. We have tested this Ca–Sr analogy in the field by measuring the variation of Sr and Ca concentrations, fluxes and pools in spruce, beech and maple stands on granite, sandstone and limestone. Results show that (1) variations of Ca and Sr concentrations are generally correlated at each level of the ecosystems. (2) In spruce on acid soils, a preferential uptake of Ca over Sr occurs (Aubure spruce Sr/Ca = 0.8×10⁻³; soil exchangeable Sr/Ca between 2 and 6×10⁻³). On calcareous soils, a preferential uptake of Sr over Ca by spruce may occur. (3) In spruce and beech on acid and calcareous soils, a preferential translocation of Ca over Sr from roots to leaves occurs ((Sr/Ca) in leaves was between 10 and 90% of that in roots). (4) The biological cycling of Ca and Sr leads to an enrichment of the upper soil layers in Ca and Sr. Compared to Sr, Ca accumulates in the upper layer of acid soils because Ca cycling through litterfall is favoured over Sr cycling, and possibly because of the selectivity of acid organic exchangers for Ca. This revised version was published online in June 2006 with corrections to the Cover Date.     

Causes of variation in mineral soil C content and turnover in differently managed beech dominated forests

Background and aims

Forest soils are important carbon stores and considered as net CO₂ sinks over decadal to centennial time scales. Intensive forest management is thought to reduce the carbon sequestration potential of forest soils. Here we study the effects of decades of forest management (as unmanaged forest, forest under selection cutting, forest under age class management) on the turnover of mineral associated soil organic matter (MOM) in German beech (Fagus sylvatica L.) dominated forests.

Methods

Radiocarbon contents were determined by accelerator mass spectrometry (AMS) in 79 Ah horizon MOM fractions of Cambisols (n?=?13), Luvisols (n?=?51) and Stagnosols (n?=?15). Mean residence times (MRTs) for soil organic carbon (SOC) were estimated with a 2-pool model using the litter input derived from a forest inventory.

Results

MOM fractions from Ah horizons contained 64?±?8.8 % of the bulk SOC. The radiocarbon content of MOM fractions in Ah horizons, expressed as Δ¹⁴C, ranged between ?2.8?‰ and 114?‰ for the three soil groups. Almost all samples contained a detectable proportion of ‘bomb’ carbon fixed from the atmosphere since 1963. Under the assumption that depending on the soil texture between 19 % and 24 % of the SOC from the labile pool is transferred to the stable SOC pool, the corresponding MRTs ranged between 72 and 723 years, with a median of 164 years.

Conclusions

Our results indicate that the MOM fraction of Ah horizons from beech forests contained a high proportion of young carbon, but we did not find a significant decadal effect of forest management on the radiocarbon signature and related turnover times. Instead, both variables were controlled by clay contents and associated SOC concentrations (p?<?0.01). This underlines the importance of pedogenic properties for SOC turnover in the MOM fraction.     

The natural abundance of 15N in litter and soil profiles under six temperate tree species: N cycling depends on tree species traits and site fertility

Aims

We investigated the influence of tree species on the natural ¹⁵N abundance in forest stands under elevated ambient N deposition.

Methods

We analysed δ¹⁵N in litter, the forest floor and three mineral soil horizons along with ecosystem N status variables at six sites planted three decades ago with five European broadleaved tree species and Norway spruce.

Results

Litter δ¹⁵N and ¹⁵N enrichment factor (δ¹⁵N_litter–δ¹⁵N_soil) were positively correlated with N status based on soil and litter N pools, nitrification, subsoil nitrate concentration and forest growth. Tree species differences were also significant for these N variables and for the litter δ¹⁵N and enrichment factor. Litter from ash and sycamore maple with high N status and low fungal mycelia activity was enriched in ¹⁵N (+0.9 delta units) relative to other tree species (European beech, pedunculate oak, lime and Norway spruce) even though the latter species leached more nitrate.

Conclusions

The δ¹⁵N pattern reflected tree species related traits affecting the N cycling as well as site fertility and former land use, and possibly differences in N leaching. The tree species δ¹⁵N patterns reflected fractionation caused by uptake of N through mycorrhiza rather than due to nitrate leaching or other N transformation processes.     

Changes induced by the roots of Erica arborea L. to create a suitable environment in a soil developed from alkaline and fine-textured marine sediments

Background and aims

We report on the modifications induced by the roots of Erica arborea L. on a soil derived from alkaline and fine-textured marine sediments.

Methods

Physical, chemical, mineralogical and biochemical properties of bulk soil and of the rhizosphere of Erica were characterised to evaluate its role on soil development.

Results

Once the upper horizons had been decarbonated because of geomorphic and pedogenic processes, Erica colonised the soil and progressively modified it through the activity of roots. In the upper horizons, there was no difference between rhizosphere and bulk soil for pH, organic C and exchangeable Al and H. At depth, pH, organic C and exchangeable Al and H differed between rhizosphere and bulk soil. The weathering reactions induced by the Erica roots caused a relative quartz enrichment in the rhizosphere compared with the bulk soil. In the E, EB and Bw horizons, the microbial community of the rhizosphere appeared better adapted than in the underlying 2Bw horizons, where the rhizospheric microorganisms were poorly adapted as these horizons represented the boundary between acid and sub-alkaline soil environments.

Conclusions

The activity of Erica roots modified soil properties so to produce more favourable conditions for itself and the rhizosphere microflora.     

Effects of exotic and native tree leaf litter on soil properties of two contrasting sites in the Iberian Peninsula

Aims

We assessed the effects of native and exotic tree leaf litter on soil properties in two contrasting scenarios. The native Quercus robur and Pinus pinaster tree species coexist with the aliens Eucalyptus globulus and Acacia dealbata in acid soils of NW Spain. The native trees Fraxinus angustifolia and Ulmus minor coexist with the aliens Ailanthus altissima, Robinia pseudoacacia and Ulmus pumila in eutrophic basic riparian soils in Central Spain.

Methods

Four plastic trays per species were filled with homogenized top-soil of the site and covered with leaf litter. Before and after 9?months of incubation, litter mass, soil pH, organic matter, mineral and total N were measured. Available mineral N (NO ₃ ^? -N and NH ₄ ⁺ -N) was assessed every 2?months.

Results

Soil biological activity was higher in the basic than in the acid soil. Litter of the exotic trees tended to decompose less than litter of native species, probably due to the presence of secondary metabolites in the former. Soil pH, mineral and total N responded differently to different litter types, irrespective of their exotic or native origin (acid soil), or was similar across litter treatments (basic riparian soil). The similar response of the basic soil to the addition of different litter types may be due to the low contrast of litter quality between the species. E. globulus litter inhibitied soil microbial activity much more than the rest of the studied litter types, leading to a drastic impoverishment of N in soils.

Conclusion

Litter of exotic N-fixing trees (A. dealbata and R. pseudoacacia) did not increase soil N pools because of the inhibition of microbial activity by secondary compounds. Therefore, secondary metabolites of the litter played a major role explaining exotic litter impact on soil properties.     

A simple model for estimating Ni availability and leaf Ni accumulation for the Ni-hyperaccumulator Leptoplax emarginata

Aims

The aim of the present study was to predict kinetics of both Ni concentration in soil solution and leaf Ni mass for the Ni-hyperaccumulator Leptoplax emarginata cultivated on a fertilized and Ni-contaminated sandy topsoil.

Methods

The 0-D (independent of space) one-site rate-limited desorption model proposed by Ingwersen et al. (J Environ Qual 35:2055–2065, 2006) was modified. The plant sink term of the model was approximated by the biophysical equation which assumes that the leaf nickel mass is equal to the triple product of the Intact Plant Transpiration Stream Concentration Factor for Ni IPTSCF_Ni (xylem:solution Ni concentration ratio), Ni concentration in solution and the volume of transpired water. The model input variables were the constant mean IPTSCF_Ni value, determined from independent leaf Ni accumulation kinetics, and the exponential law fitting the transpiration rate kinetics. Using the best calibration, the model was validated and a sensitivity analysis was carried out thereafter. Models were formulated as sets of ordinary differential equation systems which were solved using the fourth-order Runge–Kutta method.

Results

The best model calibration was the joint parameter optimization: the two parameters of the Freundlich Ni adsorption isotherm and of the Ni desorption rate coefficient are obtained using the kinetics of Ni concentrations in the soil solutions for the reference unplanted Ni-contaminated topsoils. The model was validated reasonably well for both Ni concentration in soil solution and leaf Ni mass.

Conclusions

The joint parameter optimization of the two parameters of the Freundlich nickel sorption isotherm and of the Ni desorption rate was successful whereas the Freundlich batch Ni sorption isotherm dramatically overestimated Ni sorption. This joint approach is therefore recommended for any plant metal uptake model. The 0-D one-site rate-limited desorption model linked to a biophysical coupled Ni and water uptake model reasonably validated the kinetics of both Ni concentration in solution and leaf Ni mass. This promising simplified model for predicting both metal concentration in solution and leaf metal mass for metal needs further validations in culture chambers and further improvements in order to use it in the field as a one-dimensional model, taking into account soil moisture dynamics.     

Mapping and genomic targeting of the major leaf shape gene (L) in Upland cotton (Gossypium hirsutum L.)

Key message

A major leaf shape locus (L) was mapped with molecular markers and genomically targeted to a small region in the D-genome of cotton. By using expression analysis and candidate gene mapping, two LMI1 -like genes are identified as possible candidates for leaf shape trait in cotton.

Abstract

Leaf shape in cotton is an important trait that influences yield, flowering rates, disease resistance, lint trash, and the efficacy of foliar chemical application. The leaves of okra leaf cotton display a significantly enhanced lobing pattern, as well as ectopic outgrowths along the lobe margins when compared with normal leaf cotton. These phenotypes are the hallmark characteristics of mutations in various known modifiers of leaf shape that culminate in the mis/over-expression of Class I KNOX genes. To better understand the molecular and genetic processes underlying leaf shape in cotton, a normal leaf accession (PI607650) was crossed to an okra leaf breeding line (NC05AZ21). An F₂ population of 236 individuals confirmed the incompletely dominant single gene nature of the okra leaf shape trait in Gossypium hirsutum L. Molecular mapping with simple sequence repeat markers localized the leaf shape gene to 5.4 cM interval in the distal region of the short arm of chromosome 15. Orthologous mapping of the closely linked markers with the sequenced diploid D-genome (Gossypium raimondii) tentatively resolved the leaf shape locus to a small genomic region. RT-PCR-based expression analysis and candidate gene mapping indicated that the okra leaf shape gene (L ^o ) in cotton might be an upstream regulator of Class I KNOX genes. The linked molecular markers and delineated genomic region in the sequenced diploid D-genome will assist in the future high-resolution mapping and map-based cloning of the leaf shape gene in cotton.