Physiological characterization of recombinant inbred lines of barley with contrasting levels of carbon isotope discrimination

Background and Aims

Carbon isotope discrimination (Δ¹³C) in C₃ plants used as an indirect measure of water-use efficiency (WUE) provides a tool for selecting crops with high WUE under dry environments.

Methods

We evaluated the physiology and Δ¹³C of a set of 8 F₅ recombinant inbred lines (RILs) with contrasting levels of leaf Δ¹³C derived from two parents, ‘W89001002003’ (low Δ¹³C) and ‘I60049’ (high Δ¹³C) of six-row barley (Hordeum vulgare L.) in a greenhouse and under field conditions in three locations (Lacombe, Vegreville and Castor). In the greenhouse experiment, seven days of water deficit was imposed at the stem elongation stage followed by re-watering to pre-deficit level.

Results

A significant negative relationship between WUE and leaf Δ¹³C was observed. Under water-deficit conditions, both photosynthetic rate (A) and stomatal conductance (g _s ) were significantly reduced with a strong positive correlation (r = 0.89) between the two, and the variation in g _s was proportionally greater than A. The low leaf-Δ¹³C RIL ‘147’ maintained the highest A and g _s among ten genotypes (RILs and parents) under water-deficit conditions. Leaf Δ¹³C was positively correlated with biomass and grain yield in the field trials. Multivariate analysis of leaf Δ¹³C, harvest index and plant height discriminated genotypes into three clusters: drought sensitive, drought tolerant and an intermediate type.

Conclusions

The study suggests that it is possible to select low Δ¹³C lines such as RIL ‘147’, which is able to maintain or produce high yields under low moisture conditions on the Canadian Prairies     

Decomposition of lupine seeds and seedlings as N fertilizer in organic vegetable production

Aims

We investigated the response of the perennial grass Molinia caerulea (L.) Moench to combined effects of fertilization (N, P) and drought events. We hypothesized that N fertilization increases, and drought decreases productivity, but that N addition strengthens negative effects caused by drought.

Methods

Within a full-factorial 2-year greenhouse experiment we measured biomass productivity and allocation, tissue nutrient concentrations and nitrogen allocation patterns using ¹⁵N as a tracer.

Results

N fertilization caused a strong increase in productivity, but effects of drought were almost insignificant. However, we found strongly interrelated, non-additive effects of fertilization and drought, expressed by a strong increase of necrotic tissue. Dead aboveground biomass showed the highest values for N and ¹⁵N.

Conclusions

Accelerated productivity of aboveground tissue under N fertilization resulted in increased evaporative demands and thus higher drought susceptibility. In addition ¹⁵N allocation patterns showed that fertilization-drought treatments disenabled plants’ control of their N allocation. Molinia was unable to withdraw leaf N during the dieback of aboveground tissue. Due to the lack of an adaptive strategy to the combined effects of fertilization and drought, increasing summer drought may weaken the competitive performance of species with traits comparable to those of Molinia in N-fertilized environments.     

Nitrogen use efficiencies of spring barley grown under varying nitrogen conditions in the field and growth chamber

Background and Aims

Nitrogen-use efficiency (NUE) of cereals needs to be improved by nitrogen (N) management, traditional plant breeding methods and/or biotechnology, while maintaining or, optimally, increasing crop yields. The aims of this study were to compare spring-barley genotypes grown on different nitrogen levels in field and growth-chamber conditions to determine the effects on N uptake (NUpE) and N utilization efficiency (NUtE) and ultimately, NUE.

Methods

Morphological characteristics, seed yield and metabolite levels of 12 spring barley (Hordeum vulgare) genotypes were compared when grown at high and low nitrogen levels in field conditions during the 2007 and 2008 Canadian growing seasons, and in potted and hydroponic growth-chamber conditions. Genotypic NUpE, NUtE and NUE were calculated and compared between field and growth-chamber environments.

Key Results

Growth chamber and field tests generally showed consistent NUE characteristics. In the field, Vivar, Excel and Ponoka, showed high NUE phenotypes across years and N levels. Vivar also had high NUE in growth-chamber trials, showing NUE across complex to simplistic growth environments. With the high NUE genotypes grown at low N in the field, NUtE predominates over NUpE. N metabolism-associated amino acid levels were different between roots (elevated glutamine) and shoots (elevated glutamate and alanine) of hydroponically grown genotypes. In field trials, metabolite levels were different between Kasota grown at high N (elevated glutamine) and Kasota at low N plus Vivar at either N condition.

Conclusions

Determining which trait(s) or gene(s) to target to improve barley NUE is important and can be facilitated using simplified growth approaches to help determine the NUE phenotype of various genotypes. The genotypes studied showed similar growth and NUE characteristics across field and growth-chamber tests demonstrating that simplified, low-variable growth environments can help pinpoint genetic targets for improving spring barley NUE.     

A multi-environmental study of recent breeding progress on nitrogen use efficiency in wheat (Triticum aestivum L.)

Key message

By comparing 195 varieties in eight trials, this study assesses nitrogen use efficiency improvement in high and low nitrogen conditions in European winter wheat over the last 25 years.

Abstract

In a context where European agriculture practices have to deal with environmental concerns and nitrogen (N) fertiliser cost, nitrogen use efficiency (NUE) has to be improved. This study assessed genetic progress in winter wheat (Triticum aestivum L.) NUE. Two hundred and twenty-five European elite varieties were tested in four environments under two levels of N. Global genetic progress was assessed on additive genetic values and on genotype × N interaction, covering 25 years of European breeding. To avoid sampling bias, quality, precocity and plant height were added as covariates in the analyses when needed. Genotype × environment interactions were highly significant for all the traits studied to such an extent that no additive genetic effect was detected on N uptake. Genotype × N interactions were significant for yield, grain protein content (GPC), N concentration in straw, N utilisation, and NUE. Grain yield improvement (+0.45 % year^?1) was independent of the N treatment. GPC was stable, thus grain nitrogen yield was improved (+0.39 % year^?1). Genetic progress on N harvest index (+0.12 % year^?1) and on N concentration in straw (?0.52 % year^?1) possibly revealed improvement in N remobilisation. There has been an improvement of NUE additive genetic value (+0.33 % year^?1) linked to better N utilisation (+0.20 % year^?1). Improved yield stability was detected as a significant improvement of NUE in low compared to high N conditions. The application of these results to breeding programs is discussed.     

Nitrogen use efficiency of organically fertilized white cabbage and residual effects on subsequent beetroot

Background and aims

The low N availability in organic cropping systems requires an efficient use of the limited N sources. The study aimed to analyze the N efficiency of organically fertilized white cabbage on a crop and crop rotation basis.

Methods

Effects of soil-incorporated lupine seedlings and seed meal on the N use efficiency (NUE) and individual NUE components of cabbage were investigated in field experiments. Cabbage was followed by beetroot to quantify residual fertilizer effects.

Results

Generally, NUE decreased with increasing N availability. Nitrogen uptake efficiency, however, was low at low N supply and increased curvilinearly to an asymptotic maximum. Variation in harvest index between and within experimental years was explained by differences in thermal growing time and initial cabbage growth, respectively. The increase in beetroot N supply by fertilizer treatments averaged 18 % of applied lupine seed N corresponding to 63 % of the incremental N in cabbage residues.

Conclusions

Dry matter partitioning alters during cabbage yield formation in favor of the harvest residue fraction if abiotic stress like water shortage occurs directly after crop establishment, being associated with reduced NUE. The residual effect depends largely on the re-utilization of incremental fertilizer N in cabbage residues and thus on the short-term net N mineralization of organic fertilizers.     

Impact of biochar application on nitrogen nutrition of rice, greenhouse-gas emissions and soil organic carbon dynamics in two paddy soils of China

Aims

Two field microcosm experiments and ¹⁵N labeling techniques were used to investigate the effects of biochar addition on rice N nutrition and GHG emissions in an Inceptisol and an Ultisol.

Methods

Biochar N bioavailability and effect of biochar on fertilizer nitrogen-use efficiency (NUE) were studied by ¹⁵N-enriched wheat biochar (7.8803 atom% ¹⁵N) and fertilizer urea (5.0026 atom% ¹⁵N) (Experiment I). Corn biochar and corn stalks were applied at 12 Mg?ha^?1 to study their effects on GHG emissions (Experiment II).

Results

Biochar had no significant impact on rice production and less than 2 % of the biochar N was available to plants in the first season. Biochar addition increased soil C and N contents and decreased urea NUE. Seasonal cumulative CH₄ emissions with biochar were similar to the controls, but significantly lower than the local practice of straw amendment. N₂O emissions with biochar were similar to the control in the acidic Ultisol, but significantly higher in the slightly alkaline Inceptisol. Carbon-balance calculations found no major losses of biochar-C.

Conclusion

Low bio-availability of biochar N did not make a significantly impact on rice production or N nutrition during the first year. Replacement of straw amendments with biochar could decrease CH₄ emissions and increase SOC stocks.     

Evidence from field nitrogen balance and 15N natural abundance data for the contribution of biological N2 fixation to Brazilian sugarcane varieties

Aims

In Brazil N fertilization of sugarcane (Saccharum spp.) is low compared to most other countries. ¹⁵N-aided studies and the occurrence of many N₂-fixing bacteria associated with cane plants suggest significant contributions from biological N₂ fixation (BNF). The objective of this study was to evaluate BNF contributions to nine cane varieties under field conditions using N balance and ¹⁵N natural abundance techniques.

Methods

The field experiment was planted near Rio de Janeiro in 1989, replanted in 1999 and harvested 13 times until 2004. Soil total N was evaluated at planting and again in 2004. Samples of cane leaves and weeds for the evaluation of ¹⁵N natural abundance were taken in 2000, 2003 and 2004.

Results

N accumulation of the commercial cane varieties and a variety of Saccharum spontaneum were persistently high and N balances (60 to 107?kg?N ha^?1?yr^?1) significantly (p?<?0.05) positive. The δ¹⁵N of leaf samples were lower than any of the weed reference plants and data obtained from a greenhouse study indicated that this was not due to the cane plants tapping into soil of lower ¹⁵N abundance at greater depth.

Conclusion

The results indicate that the Brazilian varieties of sugarcane were able to obtain at least 40?kg?N ha^?1?yr^?1 from BNF.     

Comparative responses of ‘Gala’ and ‘Fuji’ apple trees to deficit irrigation: Placement versus volume effects

Aims

Climate, soil water potential (SWP), leaf relative water content (RWC), stomatal conductance (g_s), fruit and shoot growth, and carbohydrate levels were monitored during the 2008 and 2009 growing seasons to study the responses of ‘Gala’ and ‘Fuji’ apple trees to irrigation placement or volume.

Methods

Three irrigation treatments were imposed, conventional irrigation (CI), partial root-zone drying (PRD, 50% of CI water on one side of the root-zone, which was alternated periodically), and continuous deficit irrigation (DI, 50% of CI water on both sides of the root-zone).

Results

After each irrigation season, DI generated twice the soil water deficit (SWD_int) than PRD (average of dry and wet sides) and a greater integrated leaf water deficit (LWD_int) than PRD and CI. Both PRD and DI reduced g_s by 9 and 15% over the irrigation period. RWC of both PRD and DI was directly related to SWP and inversely related (non-linear) to vapor pressure deficit (VPD), whereas it was unrelated to g_s. Considering individual sampling days, g_s of ‘Gala’ leaves was inversely related to VPD mainly until early August (fruit at cell expansion phase and high VPD), while it was directly related to VPD in September (no fruit and low VPD). On the contrary, g_s of ‘Fuji’ leaves was inversely related to VPD from late August until mid October (low VPD and fruit at cell expansion phase). Fruit growth was not affected by irrigation, whereas shoot and trunk growth was reduced by DI. Irrigation induced sporadic and inconsistent changes in carbohydrate contents or partitioning, with a general tendency of DI leaves to degrade and PRD to accumulate sorbitol and sucrose in dry periods.

Conclusions

‘Gala’ trees exhibited a more conservative water use than ‘Fuji’ trees due primarily to different timing of fruit growth and crop loads. Different levels of SWD_int, rather than changes in stomatal control and carbohydrate partitioning, seem to play a major role in determining a better water status in PRD than in DI trees.     

Marker-assisted introgression of a QTL region to improve rust resistance in three elite and popular varieties of peanut (Arachis hypogaea L.)

Key message

Successful introgression of a major QTL for rust resistance, through marker-assisted backcrossing, in three popular Indian peanut cultivars generated several promising introgression lines with enhanced rust resistance and higher yield.

Abstract

Leaf rust, caused by Puccinia arachidis Speg, is one of the major devastating diseases in peanut (Arachis hypogaea L.). One QTL region on linkage group AhXV explaining upto 82.62 % phenotypic variation for rust resistance was validated and introgressed from cultivar ‘GPBD 4’ into three rust susceptible varieties (‘ICGV 91114’, ‘JL 24’ and ‘TAG 24’) through marker-assisted backcrossing (MABC). The MABC approach employed a total of four markers including one dominant (IPAHM103) and three co-dominant (GM2079, GM1536, GM2301) markers present in the QTL region. After 2–3 backcrosses and selfing, 200 introgression lines (ILs) were developed from all the three crosses. Field evaluation identified 81 ILs with improved rust resistance. Those ILs had significantly increased pod yields (56–96 %) in infested environments compared to the susceptible parents. Screening of selected 43 promising ILs with 13 markers present on linkage group AhXV showed introgression of the target QTL region from the resistant parent in 11 ILs. Multi-location field evaluation of these ILs should lead to the release of improved varieties. The linked markers may be used in improving rust resistance in peanut breeding programmes.     

Long-term effects of boron and copper on phenolics and monoterpenes in Scots pine (Pinus sylvestris L.) needles

Backgroud and aims

Plant boron (B) status is known to affect plant secondary metabolites but most studies have been short termed and in controlled environments. Copper (Cu) effects on phenolics are better known at toxic than at low levels. Here, the chemistry of Scots pine (Pinus sylvestris L.) needles was studied 20 years after fertilisation with B and Cu in a long-term field experiment on a drained boreal peatland.

Methods

Phenolic compounds were analysed from three needle year classes using high performance liquid chromatography (HPLC) and condensed tannins with modified acid-butanol assay. Monoterpenes in the youngest needles were analysed by gas chromatography–mass spectrometry (GC–MS).

Results

Needle B concentrations were at deficient level in controls (5.7 μg g^?1), but at the optimum level (12 μg g^?1) still 20 years after fertilisation. Copper concentrations were low but not deficient (4.0 μg g^?1 in unfertilised, 4.8 μg g^?1 in fertilised). Needle ageing increased the concentrations of individual phenolics in most cases, but decreased the concentration of condensed tannins. The concentrations of several individual phenolics were reduced by B fertilisation compared to B-deficient control, significantly in the cases of (+)-catechin and a neolignan. The concentrations of eight compounds and the sum of small-molecule phenolics were higher in Cu fertilised trees. Condensed tannins and monoterpenes were not affected by the micronutrients.

Conclusions

Boron and copper additions affected mostly the same phenolic compounds, but B decreased while Cu increased their concentrations, Cu effects being clearer. The higher phenolic concentrations in B deficient trees were not likely large enough to explain leader dieback in B-deficient trees. The effects and interactions of these micronutrients need to be further studied in field conditions to establish firstly if the changes in phenolics are consistent among species, and secondly what mechanisms lead to the changes. Although small, the changes in phenolic concentrations may affect the interactions of the trees with their biotic and abiotic environment, when consistent over many years.     

Functional groups show distinct differences in nitrogen cycling during early stand development: implications for forest management

Background and aims

Nutrient acquisition of forest stands is controlled by soil resource availability and belowground production, but tree species are rarely compared in this regard. Here, we examine ecological and management implications of nitrogen (N) dynamics during early forest stand development in productive commercial tree species with narrow (Populus deltoides Bartr. and Platanus occidentalis L.) and broad (Liquidambar styraciflua L. and Pinus taeda L.) site requirements while grown with a range of nutrient and water resources.

Methods

We constructed N budgets by measuring N concentration ([N]) and N content (N _C ) of above- and belowground perennial and ephemeral tissues, determined N uptake (N _UP ), and calculated N use efficiency (NUE).

Results

Forest stands regulated [N] within species-specific operating ranges without clear temporal or treatment patterns, thus demonstrating equilibrium between tissue [N] and biomass accumulation. Forest stand N _C and N _UP increased with stand development and paralleled treatment patterns of biomass accumulation, suggesting productivity is tightly linked to N _UP . Inclusion of above- and belowground ephemeral tissue turnover in N _UP calculations demonstrated that maximum N demand for narrow-sites adapted species exceeded 200?kg?N ha^?1?year^?1 while demand for broad-site adapted species was below this level. NUE was species dependent but not consistently influenced by N availability, suggesting relationships between NUE and resource availability were species dependent.

Conclusions

Based on early stand development, species with broad site adaptability are favored for woody cropping systems because they maintain high above- and belowground productivity with minimal fertilization requirements due to higher NUE than narrow site adapted species.     

Optimizing nitrogen economy under drought: increased leaf nitrogen is an acclimation to water stress in willow (Salix spp.)

Background and Aims

The major objective was to identify plant traits functionally important for optimization of shoot growth and nitrogen (N) economy under drought. Although increased leaf N content (area basis) has been observed in dry environments and theory predicts increased leaf N to be an acclimation to drought, experimental evidence for the prediction is rare.

Methods

A pedigree of 200 full-sibling hybrid willows was pot-grown in a glasshouse in three replicate blocks and exposed to two water regimes for 3 weeks. Drought conditions were simulated as repeated periods of water shortage. The total leaf mass and area, leaf area efficiency (shoot growth per unit leaf area, E_A), area-based leaf N content (N_A), total leaf N pool (N_L) and leaf N efficiency (shoot growth per unit leaf N, E_N) were assessed.

Key Results

In the water-stress treatment, shoot biomass growth was N limited in the genotypes with low N_L, but increasingly limited by other factors in the genotypes with greatest N_L. The N_A was increased by drought, and drought-induced shift in N_A varied between genotypes (significant G × E). Judged from the E_A–N_A relationship, optimal N_A was 16 % higher in the water-stress compared with the well-watered treatment. Biomass allocation to leaves and shoots varied between treatments, but the treatment response of the leaf : shoot ratio was similar across all genotypes.

Conclusions

It is concluded that N-uptake efficiency and leaf N efficiency are important traits to improve growth under drought. Increased leaf N content (area basis) is an acclimation to optimize N economy under drought. The leaf N content is an interesting trait for breeding of willow bioenergy crops in a climate change future. In contrast, leaf biomass allocation is a less interesting breeding target to improve yield under drought.     

Effect of low salinity on ion accumulation, gas exchange and postharvest drought resistance and habit of Coriandrum sativum L.

Aims

Drought resistance of crops is one of the great challenges for the world’s agricultural systems. Although the concept of ‘drought hardening’ has been known for many years, very little has been done on pre-harvest treatment that can help leafy vegetable crops resist drought stress on a retailer’s shelf. Our hypothesis was that for pot-grown vegetables a saline treatment could be found that would reduce transpiration pre- and post-harvest, but not harvestable yield.

Methods

Coriander (Coriandrum sativum L.) was used as a model plant; several accessions (k-4, k-43, k-52, k-60 and k-62) from N.I. Vavilov Research Institute of Plant Industry, Russia and two commercial cultivars—Kashmir and Americanum—were studied. Plant growth, weight, transpiration, net CO2 assimilation, respiration, wilting, apparent petioles rigidity, leaf sodium content, elemental analysis and osmotic potential were assessed.

Results

We found that minor salinity (12.5?mM Na2SO4) triggered both drought and salt resistance mechanisms, which regulate appearance and shelf-life of pot-grown coriander.

Conclusion

We found that the drought avoidance mechanisms (i.e. decreased transpiration and increased water use efficiency) and salt tolerance mechanisms induced by pre-harvest treatment could significantly postpone wilting and improve post-harvest habit of a leafy vegetable crop.     

Influence of selenium (Se) on carbohydrate metabolism, nodulation and growth in alfalfa (Medicago sativa L.)

Background and aims

Extensive worldwide dryland degradation calls for identification of functional traits critical to dryland plant performance and restoration outcomes. Most trait examination has focused on drought tolerance, although most dryland systems are water and nutrient co-limited. We studied how drought impacts both plant water relations and nitrogen (N) nutrition.

Methods

We grew a suite of grasses common to the Intermountain West under both well-watered and drought conditions in the greenhouse. These grasses represented three congener pairs (Agropyron, Elymus, Festuca) differing in their habitat of origin (“wetter” or “drier”). We measured growth, water relations, N resorption efficiency and proficiency and photosynthetic N use efficiency in response to drought.

Results

Drought decreased growth and physiological function in the suite of grasses studied, including a negative impact on plant N resorption efficiency and proficiency. This effect on resorption increased over the course of the growing season. Evolutionary history constrained species responses to treatment, with genera varying in the magnitude of their response to drought conditions. Surprisingly, habitat of origin influenced few trait responses.

Conclusions

Drought impacted plant N conservation, although these responses also were constrained by evolutionary history. Future plant development programs should consider drought tolerance not only from the perspective of water relations but also plant mineral nutrition, taking into account the role of phylogeny.     

Effects of seed nickel reserves or externally supplied nickel on the growth,nitrogen metabolites and nitrogen use efficiency of urea- or nitrate-fed soybean

Background and aims

Nickel (Ni) has a critical role in the urea metabolism of plants. This study investigated the impact of seed Ni content along with external Ni supply on the growth, various nitrogen (N) metabolites and N use efficiency (NUE) of soybean plants.

Methods

Soybean plants raised from Ni-poor or Ni-rich seeds were grown in nutrient solution with or without external Ni supply and fed with either urea or nitrate as the sole N source. The changes in growth, leaf chlorophyll levels, Ni and N concentrations of different plant parts, tissue accumulation of various N metabolites and N uptake of soybean as well as NUE and its components were examined.

Results

Nickel starvation reduced the shoot biomass of urea-fed plants by 25 % and the leaf chlorophyll levels by up to 35 %, but nitrate-fed plants were unaffected. Visual toxicity symptoms were not observed in urea-fed plants. Under urea supply, Ni-deficient plants had lower levels of total N, protein and free amino acids in various organs. Root uptake of urea was severely depressed in Ni-deprived plants. Availability of Ni did not have any effect on the NUE of nitrate-fed plants, whereas its deficiency reduced the NUE of urea-fed plants by 30 %. The growth and N nutritional status of urea-fed soybean were significantly improved by high seed Ni reserves as well as external Ni supply.

Conclusion

Adequate Ni supply is required for maximizing the growth, root uptake of urea and NUE of urea-fed plants. Seed Ni reserves contribute significantly to the Ni and thus N nutritional status of soybean.     

Spatial root distribution of plants growing in vertical media for use in living walls

Background and Aims

For plants growing in living walls, the growth potential is correlated to the roots ability to utilize resources in all parts of the growing medium and thereby to the spatial root distribution. The aim of the study was to test how spatial root distribution was affected by growing medium, planting position and competition from other plants.

Methods

Five species (Campanula poscharskyana cv. ‘Stella’, Fragaria vesca cv. ‘Småland’, Geranium sanguineum cv. ‘Max Frei’, Sesleria heufleriana and Veronica officinalis cv. ‘Allgrün’) were grown in three growing media (coir and two of rockwool) in transparent boxes under greenhouse conditions. Root frequency was registered and the activity of individual root systems was studied via ¹⁵N uptake and plant dry weight was measured.

Results

Plants in coir had stronger root growth in all parts of the medium than plants in rockwool. Upwards root growth was limited for plants in the middle or lower parts of the medium and ¹⁵N measurements confirmed that only plants in the bottom of the box had active roots in the bottom of the medium. The species differed in root architecture and spatial root distribution.

Conclusions

The choice of growing medium, plant species and planting position is important for a living wall as it affects the spatial root growth of the plants.     

Carbon and nitrogen partitioning during the post‐anthesis period is conditioned by N fertilisation and sink strength in three cereals

Further knowledge of the processes conditioning nitrogen use efficiency (NUE) is of great relevance to crop productivity. The aim of this paper was characterise C and N partitioning during grain filling and their implications for NUE. Cereals such as bread wheat (Triticum aestivum L. cv Califa sur), triticale (× Triticosecale Wittmack cv. Imperioso) and tritordeum (× Tritordeum Asch. & Graebn line HT 621) were grown under low (LN, 5 mm NH₄NO₃) and high (HN, 15 mm NH₄NO₃) N conditions. We conducted simultaneous double labelling (¹²CO₂ and ¹⁵NH₄¹⁵NO₃) in order to characterise C and N partitioning during grain filling. Although triticale plants showed the largest total and ear dry matter values in HN conditions, the large investment in shoot and root biomass negatively affected ear NUE. Tritordeum was the only genotype that increased NUE in both N treatments (NUE_total), whereas in wheat, no significant effect was detected. N labelling revealed that N fertilisation during post‐anthesis was more relevant for wheat and tritordeum grain filling than for triticale. The study also revealed that the investments of C and N in flag leaves and shoots, together with the ‘waste’ of photoassimilates in respiration, conditioned the NUE of plants, and especially under LN. These results suggest that C and N use by these plants needs to be improved in order to increase ear C and N sinks, especially under LN. It is also remarkable that even though tritordeum shows the largest increase in NUE, the low yield of this cereal limits its agronomic value.     

The effects of snowpack properties and plant strategies on litter decomposition during winter in subalpine meadows

Background and aims

Approximately 50 % of belowground organic carbon is present in the northern permafrost region and due to changes in climate there are concerns that this carbon will be rapidly released to the atmosphere. The release of carbon in arctic soils is thought to be intimately linked to the N cycle through the N cycle’s influence on microbial activity. The majority of new N input into arctic systems occurs through N₂-fixation; therefore, N₂-fixation may be the key driver of greenhouse gases from these ecosystems.

Methods

At Alexandra Fjord lowland, Ellesmere Island, Canada concurrent measurements of N₂-fixation, N mineralization and nitrification rates, dissolved organic soil N (DON) and C, inorganic soil N and surface greenhouse gas fluxes (CO₂, N₂O and CH₄) were taken in two ecosystem types (Wet Sedge Meadow and Dryas Heath) over the 2009 growing season (June-August). Using Structural Equation Modelling we evaluated the hypothesis that CO₂, CH₄ and N₂O flux are linked to N₂-fixation via the N cycle.

Results

The soil N cycle was linked to CO₂ flux in the Dryas Heath ecosystem via DON concentrations, but there was no link between the soil N cycle and CO₂ flux in the Wet Sedge Meadow. Methane flux was also not linked to the soil N cycle, nor surface soil temperature or moisture in either ecosystem. The soil N cycle was closely linked to N₂O emissions but via nitrification in the Wet Sedge Meadow and inorganic N in the Dryas Heath, indicating the important role of nitrification in net N₂O flux from arctic ecosystems.

Conclusions

Our results should be interpreted with caution given the high variability in both the rates of the N cycling processes and greenhouse gas flux found in both ecosystems over the growing season. However, while N₂-fixation and other N cycling processes may play a more limited role in instantaneous CO₂ emissions, these processes clearly play an important role in controlling N₂O emissions.     

Physiological adaptations of five poplar genotypes grown under SRC in the semi-arid Mediterranean environment

Key message

The genotype ‘Neva’ under high plant density showed the highest biomass yield and optimal physiological strategies and could be the most suitable choice under semi-arid environment

Abstract

The poplars (Populus spp.) are the most sensitive plants to water deficit conditions among the woody species utilized for biomass production for energetic purposes; their productivity is associated with water availability in the soil. In the Mediterranean environment, crops are mainly limited by evapotranspirative demand that is not balanced by rainfall supply. As new hybrids with high growth rates and resistance to water stress are selected, the use of poplar as an energy crop may increase in Southern regions of Mediterranean Europe. The growth dynamics and physiological characteristics of poplar hybrid genotypes have been monitored for 2 years at a site with a Mediterranean climate, Apulia region, that could be used for energy crops. Unrooted cuttings of three recently selected genotypes of poplar (‘Neva’, ‘Dvina’ and ‘Lena’) and two “traditional” genotypes (‘Luisa Avanzo’ and ‘Bellini’) were planted in the spring of 2010 at two different densities: (a) low plant density = 1,667 cuttings ha^?1 (LPD); (b) high plant density = 6,667 cuttings ha^?1 (HPD). The genotypes ‘Lena’ and ‘Dvina’ showed the lowest survival rates and the poorest growth among the hybrid poplar tested. The genotype ‘Bellini’ had low stomatal sensitivity to soil water content and a moderate productive performance. The genotypes ‘Luisa Avanzo’ and ‘Neva’ had a good degree of rooting and sprouting, high values of leaf relative water content (RWC_l) and low values of stomatal conductance (g _s) during the summer months. In “Neva”, these characteristics were associated with the best yields (4 t ha^?1) in HPD.