Mechanisms governing the responses to anthracnose pathogen in Juglans spp.

Juglans nigra and Juglans regia are two highly economically important species for wood and fruit production that are susceptible to anthracnose caused by Gnomonia leptostyla. The identification of genotypes resistant to anthracnose could represent a valid alternative to agronomic and chemical management. In this study, we analyzed 72 walnut genotypes that showed a variety of resistance phenotypes in response to natural infection. According to the disease severity rating and microsatellite fingerprinting analysis, these genotypes were divided into three main groups: (40) J. nigra resistant, (1) J. nigra susceptible, and (31) J. regia susceptible. Data on leaf emergence rates and analysis of in vivo pathogenicity indicated that the incidence of anthracnose disease in the field might be partially conditioned by two key factors: the age and/or availability of susceptible leaves during the primary infection of fungus (avoidance by late flushing) and partial host resistance. NBS profiling approach, based on PCR amplification with an adapter primer for an adapter matching a restriction enzyme site and a degenerate primer targeting the conserved motifs present in the NBS domain of NBS-LRR genes, was applied. The results revealed the presence of a candidate marker that correlated to a reduction in anthracnose incidence in 72 walnut genotypes.

Soil [N] modulates soil C cycling in CO2-fumigated tree stands: a meta-analysis.

Under elevated atmospheric CO(2) concentrations, soil carbon (C) inputs are typically enhanced, suggesting larger soil C sequestration potential. However, soil C losses also increase and progressive nitrogen (N) limitation to plant growth may reduce the CO(2) effect on soil C inputs with time. We compiled a data set from 131 manipulation experiments, and used meta-analysis to test the hypotheses that: (1) elevated atmospheric CO(2) stimulates soil C inputs more than C losses, resulting in increasing soil C stocks; and (2) that these responses are modulated by N. Our results confirm that elevated CO(2) induces a C allocation shift towards below-ground biomass compartments. However, the increased soil C inputs were offset by increased heterotrophic respiration (Rh), such that soil C content was not affected by elevated CO(2). Soil N concentration strongly interacted with CO(2) fumigation: the effect of elevated CO(2) on fine root biomass and -production and on microbial activity increased with increasing soil N concentration, while the effect on soil C content decreased with increasing soil N concentration. These results suggest that both plant growth and microbial activity responses to elevated CO(2) are modulated by N availability, and that it is essential to account for soil N concentration in C cycling analyses.

Response and potential of agroforestry crops under global change.

The use of agroforestry crops is a promising tool for reducing atmospheric carbon dioxide concentration through fossil fuel substitution. In particular, plantations characterised by high yields such as short rotation forestry (SRF) are becoming popular worldwide for biomass production and their role acknowledged in the Kyoto Protocol. While their contribution to climate change mitigation is being investigated, the impact of climate change itself on growth and productivity of these plantations needs particular attention, since their management might need to be modified accordingly. Besides the benefits deriving from the establishment of millions of hectares of these plantations, there is a risk of increased release into the atmosphere of volatile organic compounds (VOC) emitted in large amounts by most of the species commonly used. These hydrocarbons are known to play a crucial role in tropospheric ozone formation. This might represent a negative feedback, especially in regions already characterized by elevated ozone level.

Net carbon storage in a poplar plantation (POPFACE) after three years of free-air CO2 enrichment.

A high-density plantation of three genotypes of Populus was exposed to an elevated concentration of carbon dioxide ([CO(2)]; 550 micromol mol(-1)) from planting through canopy closure using a free-air CO(2) enrichment (FACE) technique. The FACE treatment stimulated gross primary productivity by 22 and 11% in the second and third years, respectively. Partitioning of extra carbon (C) among C pools of different turnover rates is of critical interest; thus, we calculated net ecosystem productivity (NEP) to determine whether elevated atmospheric [CO(2)] will enhance net plantation C storage capacity. Free-air CO(2) enrichment increased net primary productivity (NPP) of all genotypes by 21% in the second year and by 26% in the third year, mainly because of an increase in the size of C pools with relatively slow turnover rates (i.e., wood). In all genotypes in the FACE treatment, more new soil C was added to the total soil C pool compared with the control treatment. However, more old soil C loss was observed in the FACE treatment compared with the control treatment, possibly due to a priming effect from newly incorporated root litter. FACE did not significantly increase NEP, probably as a result of this priming effect.

Free-air CO2 enrichment (FACE) enhances biomass production in a short-rotation poplar plantation.

This paper investigates the possible contribution of Short Rotation Cultures (SRC) to carbon sequestration in both current and elevated atmospheric CO2 concentrations ([CO2]). A dense poplar plantation (1 x 1 m) was exposed to a [CO2] of 550 ppm in Central Italy using the free-air CO2 enrichment (FACE) technique. Three species of Populus were examined, namely P. alba L., P. nigra L. and P. x euramericana Dode (Guinier). Aboveground woody biomass of trees exposed to elevated [CO2] for three growing seasons increased by 15 to 27%, depending on species. As a result, light-use efficiency increased. Aboveground biomass allocation was unaffected, and belowground biomass also increased under elevated [CO2] conditions, by 22 to 38%. Populus nigra, with total biomass equal to 62.02 and 72.03 Mg ha-1 in ambient and elevated [CO2], respectively, was the most productive species, although its productivity was stimulated least by atmospheric CO2 enrichment. There was greater depletion of inorganic nitrogen from the soil after three growing seasons in elevated [CO2], but no effect of [CO2] on stem wood density, which differed significantly only among species.

Photosynthesis and stomatal conductance responses of poplars to free-air CO2 enrichment (PopFACE) during the first growth cycle and immediately following coppice.

• Using the Poplar Free Air CO2 Enrichement (PopFACE) facility we investigated the effects of elevated [CO2 ] on the diurnal and growth cycle responses of photosynthesis and conductance in three poplar species. • In situ diurnal measurements of photosynthesis were made on Populus alba, P. nigra and P. ×euramericana and, in parallel, in vivo maximum capacity for carboxylation (Vc,max ) and maximum rates of electron transport (Jmax ) were determined by gas exchange measurement. • Light saturated (Asat ) and daily integrated (A') photosynthesis increased at elevated [CO2 ] in all species. Elevated [CO2 ] decreased Vc,max and Jmax for P. nigra and Jmax for P.¥euramericana but had no effect on stomatal conductance in any of the species throughout the first growth cycle. During post-coppice re-growth, elevated [CO2 ] did not increase Asat in P. nigra and P.×euramericana due to large decreases in Vc,max and Jmax . • A 50% increase in [CO2 ] under these open-air field conditions resulted in a large and sustained increase in Asat . Although there were some differences between the species, these had little effect on photosynthetic rates at the growth [CO2 ]. Nevertheless the results show that even fast growing trees grown without rooting volume restriction in the open may still show some down-regulation of photosynthetic potential at elevated [CO2 ].

Spatial distribution of photosynthetic response to long-term influence of elevated CO(2) in a mediterranean macchia mini-ecosystem.

During an open-top chamber experiment performed in evergreen 'macchia' ecosystem, which was represented by the clumps of natural vegetation dominated by Quercus ilex trees, the trees were exposed to one of two CO(2) concentrations (ambient CO(2), AC-variant and elevated CO(2), i.e. ambient plus 350 &mgr;mol CO(2) mol(-1), EC-variant) continuously over 5 years. Clumps of natural vegetation were enclosed in open top chambers (OTCs). Within the crowns of investigated Quercus ilex trees in OTCs, two crown layers i.e. sunny (E-leaves) and shaded (S-leaves), were identified as differing in solar radiation environment. To evaluate the effect of elevated CO(2), as well as the functional differentiation in assimilation activity of E- versus S-leaves, gas exchange and chlorophyll ā fluorescence techniques were used. The stimulatory effect of the long-term elevated CO(2) on the A(N)-PPFD relation was evident in E- and S-leaves of investigated Quercus trees. The A(Nmax) sensitivity of AC-variant leaves to the sudden application of elevated CO(2) was higher for S-leaves (42%) than for E-leaves (24%). The PPFD saturated rate of regulated thermal energy dissipation (ERD) confirmed the foliage differentiation caused by the long-term influence of elevated CO(2). The ERD of E- and S-leaves in the AC-variant were 1.11 times of that in the EC-variant. However, the estimated rates of photochemistry (ERP) of E- and S-leaves in the EC-variant were 1.35 and 1.22 times of E- and S-leaves in the AC-variant. The achievement of the critical value of q(P)=0.4 in E- and S-leaves from the EC-variant under lower values of PPFD compared to the AC-variant indicates a higher degree of PSII over-reduction. Thus, elevated CO(2) can be responsible for an increased susceptibility of photosynthetic apparatus to high irradiance. The obtained results support the hypothesis on the foliage vertical distribution effect on the whole canopy response to elevated CO(2). The S-layers of the canopy can play an important role in providing storage space for photosynthesis under elevated CO(2).

Structure and chromosomal localization of DNA sequences related to ribosomal subrepeats in Vicia faba.

Subrepeating sequences of 325 bp found in the ribosomal intergenic spacer (IGS) of Vicia faba and responsible for variations in the length of the polycistronic units for rRNA were isolated and used as probes for in situ hybridization. Hybridization occurs at many regions of the metaphase chromosomes besides those bearing rRNA genes, namely chromosome ends and all the heterochromatic regions revealed by enhanced fluorescence after quinacrine staining. The DNA homologous to the 325 bp repeats that does not reside in the IGS was isolated, cloned and sequenced. It is composed of tandemly arranged 336 bp elements, each comprising two highly related 168 bp sequences. This structure is very similar to that of the IGS repeats and ca. 75% nucleotide sequence identity can be observed between these and the 168 bp doublets. The most obvious difference lies in the deletion, in the former, of a 14 bp segment from one of the two related sequences. It is hypothesized that the IGS repeats are derived from the 336 bp elements and have been transposed to ribosomal cistrons from other genome fractions. The possible relations between these sequences and others with similar structural features found in other species are discussed.

Quantification of two-year-old hybrid poplar root systems: morphology, biomass, and (14)C distribution.

Root morphology, biomass, and (14)C distribution were studied in two 2-year-old Populus trichocarpa x P. deltoides hybrids, which originated from hardwood cuttings, to determine the pattern of root distribution in a plantation and to refine methods for root recovery. The trees were labeled with (14)CO(2) and harvested after a 72-hour chase period. Roots attached to each labeled tree were analyzed for morphological traits at the time of harvest. Detached roots from within a 1-m(3) volume of soil surrounding each tree were separated from the soil and sorted on the basis of rooting depth and root diameter. Lateral roots > 2 mm in diameter had a largely horizontal orientation at their point of origin from the cutting and extended horizontally up to 4 m from the cutting. This resulted in considerable overlap of root systems in the plantation. Results from (14)C labeling indicated that 24 +/- 4% (+/- SD) of the carbon exported from branches-labeled within two weeks after branch budset-was translocated to the root system. Dilution of the root (14)C label indicated that from 0 (> 5 mm diameter roots) to 75% (< 2 mm diameter roots) of the roots recovered from within the 1-m(3) volume of soil surrounding a harvested tree originated from other trees. Total root biomass was 6 +/- 1 Mg ha(-1) for both hybrids. Sixty percent of the root biomass was recovered directly from excavation, 16% from coarse-sieving excavated soil, and 24% from re-sorting sieved soil. The study indicated that root growth of hybrid poplars may be rapid and extensive and that detailed sorting of soil subsamples substantially improves the recovery of fine roots < 2 mm in diameter.

Legumin of Vicia faba major: accumulation in developing cotyledons, purification, mRNA characterization and chromosomal location of coding genes.

Experiments were carried out on Vicia faba major involving (1) determination of the pattern of legumin accumulation during seed development, (2) protein purification from mature cotyledons, (3) the characterization of legumin mRNA, and (4) the chromosomal localization of the genes coding for legumins. In developing cotyledons the synthesis of legumin begins 28 days after petal desiccation (DAPD), and 4 days after initiation of vicilin synthesis. The two subunits (αA and ßA) of legumin A appear 2 days earlier than those (αB and ßB) of legumin B. While the accumulation of vicilin peaks on the 30th DAPD, that of legumin continues during further seed development, and the synthesis of legumin mRNA peaks on the 37th DAPD. Northern blot hybridizations using two DNA plasmids containing cDNA inserts with sequence homology to the A- and B-type legumin genes, respectively, indicated that legumin mRNAs extracted from cotyledons 36 DAPD band below the 18S RNA band. In addition, a faint band below that of the 25S RNA band can be observed in legumin mRNAs extracted from cotyledons at an earlier developmental stage (30 DAPD). By means of polyacrylamide gel electrophoresis in the presence or absence of SDS and 2-mercaptoethanol, two fractions could be eluted after zonal isoelectric precipitation of the globulins from mature seeds: one fraction contains mainly vicilin, the other, legumin. In situ hybridization showed that legumin genes are arranged in two clusters: the genes coding for legumin A are located in the longer arm of the one between the two shortest subtelocentric chromosome pairs whose centromere is in a less terminal position; those coding for legumin B are located in the non-satellited arm of the longer submetacentric pair.

Biochemical versatility of amphiploids derived from crossing Dasypyrum villosum Candargy and wheat: genetic control and phenotypical aspects.

The biochemical complexity and its consequence has been investigated in the amphiploids M x v and CS x v derived from crossing the tetraploid wheat Triticum turgidum var durum cv 'Modoc' and the hexaploid wheat T. aestivum cv 'Chinese Spring', respectively, with Dasypyrum villosum. Electrophoretic analysis of variation in six enzyme systems (GOT, ADH, GPI, SOD, EST, and LPX) and in high molecular weight glutenin seed storage proteins indicated that in the amphiploids these proteins were specified by a minimum of seven sets of homologous genes on wheat and D. villosum chromosomes and that in each set there were allelic differences. The enzymes detected in each amphiploid were fully accounted for by simple additivity of protomers specified by the homologous genes inherited from their parents. The amphiploids also expressed novel oligomeric enzymes not produced in either one of their parents. The ascertained expression for all the alleles inherited by both parents and the resulting biochemical complexity suggested that some peculiar feature of the amphiploids such as high nitrogen content in the plant and in the kernels and their immunity to the powdery mildew disease caused by both Erysiphe graminis f.sp. tritici and E. graminis f. sp. haynaldiae may be the consequence of the indicated complexity but specified by other sets of genes. The biochemical complexity of the M x v amphiploid may be the basis for its versatility as new crop species.

Chromosomal location of isozyme and seed storage protein genes in Dasypyrum villosum (L.) Candargy.

The zymogram phenotypes of glucose-phosphate isomerase (GPI), alcohol dehydrogenase-1 (ADH-1), glutamate oxaloacetate transaminase (GOT), superoxide dismutase (SOD), lipoxygenase (LPX), esterase (EST) and the banding patterns of gliadin and glutenin seed storage proteins were determined for Triticum aestivum cv. 'Chinese Spring' (CS), Dasypyrum villosum, the octoploid amphiploid T. aestivum cv. 'Chinese Spring' D. villosum (CS × v) (2n=8x=56; AABBDDVV), and for five CS-D. villosum disomic addition lines. The genes Gpi-V1, Adh-V1, Got-V2, and Sod-V2 coding for GPI-1, ADH-1, GOT-2, and SOD-2 isozymes were located in D. villosum on chromosome 1V, 4V, 6V, and 7V, respectively. Genes coding for gliadin- and glutenin-like subunits are located in D. villosum chromosomes 1V. There are no direct evidence for chromosomal location of genes coding for GOT-3, EST-1 and LPX-2 isozymes. The linkage between genes coding for glutenin-like proteins and GPI-1 isozymes in chromosome 1V is evidence of homoeology between chromosome 1V and the chromosomes of homoeologous group 1 in wheat.