Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

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Climate Change 2007: The Physical Science Basis.

Mineral Nutrition of Higher Plants, 2nd edition, H. Marschner. Academic Press, London (1995), 889, (ISBN 0-12-473543-6). Price: 29.95 Pound Sterling

Because lignin limits the use of wood for fiber, chemical, and energy production, strategies for its downregulation are of considerable interest. We have produced transgenic aspen (Populus tremuloides Michx.) trees in which expression of a lignin biosynthetic pathway gene Pt4CL1 encoding 4-coumarate:coenzyme A ligase (4CL) has been downregulated by antisense inhibition. Trees with suppressed Pt4CL1 expression exhibited up to a 45% reduction of lignin, but this was compensated for by a 15% increase in cellulose. As a result, the total lignin–cellulose mass remained essentially unchanged. Leaf, root, and stem growth were substantially enhanced, and structural integrity was maintained both at the cellular and whole-plant levels in the transgenic lines. Our results indicate that lignin and cellulose deposition could be regulated in a compensatory fashion, which may contribute to metabolic flexibility and a growth advantage to sustain the long-term structural integrity of woody perennials.

Biotechnology on genetic control of lignin biosynthesis in trees -Repression of lignin biosynthesis promotes cellulose accumulation and growth in transgenic trees-

We review the research literature and summarize the major processes by which riparian vegetation influences chemical water quality in streams, as well as how these processes vary among vegetation types, and discuss how these processes respond to removal and restoration of riparian vegetation and thereby determine the timing and level of response in stream water quality. Our emphasis is on the role that riparian vegetation plays in protecting streams from nonpoint source pollutants and in improving the quality of degraded stream water. Riparian vegetation influences stream water chemistry through diverse processes including direct chemi- cal uptake and indirect influences such as by supply of organic matter to soils and channels, modification of water movement, and stabilization of soil. Some processes are more strongly expressed under certain site condi- tions, such as denitrification where groundwater is shallow, and by certain kinds of vegetation, such as channel stabilization by large wood and nutrient uptake by faster-growing species. Whether stream chemistry can be managed effectively through deliberate selection and management of vegetation type, however, remains uncer- tain because few studies have been conducted on broad suites of processes that may include compensating or reinforcing interactions. Scant research has focused directly on the response of stream water chemistry to the loss of riparian vegetation or its restoration. Our analysis suggests that the level and time frame of a response to restoration depends strongly on the degree and time frame of vegetation loss. Legacy effects of past vegetation can continue to influence water quality for many years or decades and control the potential level and timing of water quality improvement after vegetation is restored. Through the collective action of many processes, vegeta- tion exerts substantial influence over the well-documented effect that riparian zones have on stream water qual- ity. However, the degree to which stream water quality can be managed through the management of riparian vegetation remains to be clarified. An understanding of the underlying processes is important for effectively using vegetation condition as an indicator of water quality protection and for accurately gauging prospects for water quality improvement through restoration of permanent vegetation. (KEY TERMS: assessment; biogeochemistry; buffers; legacy effects; nonpoint source pollution; resilience; resto- ration; rivers ⁄streams; soils; watershed management.)

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The Role of Riparian Vegetation in Protecting and Improving Chemical Water Quality in Streams

http://www.salmone.org/wp-content/uploads/2008/09/transgenics-are-imperative-for-biofuel-crops.pdf

Transgenics are imperative for biofuel crops

In agroecosystems, nitrogen is one of the major nutrients limiting plant growth. To meet the increased nitrogen demand in agriculture, synthetic fertilizers have been used extensively in the latter part of the twentieth century, which have led to environmental challenges such as nitrate pollution. Biological nitrogen fixation (BNF) in plants is an essential mechanism for sustainable agricultural production and healthy ecosystem functioning. BNF by legumes and associative, endosymbiotic, and endophytic nitrogen fixation in non-legumes play major roles in reducing the use of synthetic nitrogen fertilizer in agriculture, increased plant nutrient content, and soil health reclamation. This review discusses the process of nitrogen-fixation in plants, nodule formation, the genes involved in plant-rhizobia interaction, and nitrogen-fixing legume and non-legume plants. This review also elaborates on current research efforts involved in transferring nitrogen-fixing mechanisms from legumes to non-legumes, especially to economically important crops such as rice, maize, and wheat at the molecular level and relevant other techniques involving the manipulation of soil microbiome for plant benefits in the non-legume root environment.

Current Progress in Nitrogen Fixing Plants and Microbiome Research.

Asian soybean rust (ASR), caused by Phakopsora pachyrhizi Syd., is a widespread disease of soybean [Glycine max (L.) Merr.] with the potential to cause serious economic losses. The objective of this study was to genetically map red-brown lesion type resistance from the cultivar Hyuuga. A population of 117 recombinant inbred lines (RILs) from the cross of Dillon (tan lesion) x Hyuuga (red-brown [RB] lesion) was rated for ASR lesion type in the field and inoculated with P. pachyrhizi in the greenhouse. The RB resistance gene mapped between Satt460 and Satt307 on linkage group (LG)-C2. When field severity and lesion density in the greenhouse were mapped, the Rpp?(Hyuuga) locus explained 22 and 15% of the variation, respectively (P < 0.0001). The RB lesion type was associated with lower severity, fewer lesions, and reduced sporulation when compared to the tan lesion type. A population from the cross of Benning x Hyuuga was screened with simple sequence repeat (SSR) markers in the region on LG-C2 flanked by Satt134 and Satt460. Genotype at these markers was used to predict lesion type when the plants were exposed to P. pachyrhizi. All the lines selected for the Hyuuga markers in this interval had the RB lesion type and they averaged approximately 50% fewer lesions compared to lines with tan lesions. Sporulation was only detected in 6% of the RB lines compared with 100% of the tan lines. Marker-assisted selection can be used to develop soybean cultivars with the Rpp?(Hyuuga) gene for resistance to ASR.

Mapping and Confirmation of the ‘Hyuuga’ Red-Brown Lesion Resistance Gene for Asian Soybean Rust

We report an early investigation into genomic organization and chromosomal transmission in switchgrass based on restriction fragment length polymorphism (RFLP) markers. The segregation of 224 single dose restriction fragments (SDRF) in 85 full-sib progeny of a cross between the genotypes Alamo (AP13) and Summer (VS16) was used to determine linkage associations in each parent. In the seed parent AP13, 11 cosegregation groups were identified by 45 SDRF markers with a cumulative recombination length of 412.4 cM. In the pollen parent VS16, 57 SDRF markers were assigned to 16 cosegregation groups covering a length of 466.5 cM. SDRF markers identified by the same probes and mapping to different cosegregation groups were used to combine the two maps and identify homology groups. Eight homology groups were identified among the nine haploid linkage groups expected in switchgrass. The high incidence of repulsion phase associations indicates that preferential pairing between homologous chromosomes is predominant in switchgrass. Based on marker distribution in the paternal map (VS16), we estimated the recombinational length of switchgrass genome to be 4,617 cM. In order to link 95% of the genome to a marker at a 15-cM distance, a minimum of 459 markers will be required. Using information from the ratio of repulsion to coupling linkages, we infer that switchgrass is an autotetraploid with a high degree of preferential pairing. The information presented in this study establishes a foundation for extending genetic mapping in this crop and constitutes a framework for basic and applied genetic studies.

Investigation of genomic organization in switchgrass (Panicum virgatum L.) using DNA markers

Nitrogen (N) in the agricultural production system influences many aspects of agroecosystems and several critical ecosystem services widely depend on the N availability in the soil. Cumulative changes in regional ecosystem services may lead to global environmental changes. Thus, the soil N status in agriculture is of critical importance to strategize its most efficient use. Nitrogen is also one of the most susceptible macronutrients to environmental loss, such as ammonia volatilization (NH3), nitrous oxide (N2O) emissions, nitrate leaching (NO3), etc. Any form of N losses from agricultural systems can be major limitations for crop production, soil sustainability, and environmental safeguard. There is a need to focus on mitigation strategies to minimize global N pollution and implement agricultural management practices that encourage regenerative and sustainable agriculture. In this review, we identified the avenues of N loss into the environment caused by current agronomic practices and discussed the potential practices that can be adapted to prevent this N loss in production agriculture. This review also explored the N status in agriculture during the COVID-19 pandemic and the existing knowledge gaps and questions that need to be addressed.

Nitrogen losses and potential mitigation strategies for a sustainable agroecosystem

Information regarding the amount of genetic diversity is necessary to enhance the effectiveness of breeding programs and germplasm conservation efforts. Genetic variation between 21 switchgrass genotypes randomly selected from two lowland (‘Alamo’ and ‘Kanlow’) and one upland (‘Summer’) synthetic cultivars were estimated using restriction fragment length polymorphism (RFLP) markers. Comparison of 85 RFLP loci revealed 92% polymorphism between at least two genotypes from the upland and lowland ecotypes. Within ecotypes, the upland genotypes showed higher polymorphism than lowland genotypes (64% vs. 56%). ‘Kanlow’ had a lower percent of polymorphic loci than ‘Alamo’ (52% vs. 60%). Jaccard distances revealed higher genetic diversity between upland and lowland ecotypes than between genotypes within each ecotype. Hierarchical cluster analysis using Ward's minimum variance grouped the genotypes into two major clusters, one representing the upland group and the other the lowland group. Phylogenetic analysis of chloroplast non-coding region trnL (UAA) intron sequences from 34 switchgrass accessions (6 upland cultivars, 2 lowland cultivars, and 26 accessions of unknown affiliation) produced a neighbor-joining dendrogram comprised of two major clusters with 99% bootstrap support. All accessions grouped in the same cluster with the lowland cultivars (‘Alamo’ and ‘Kanlow’) had a deletion of 49 nucleotides. Phenotypic identification of greenhouse-grown plants showed that all accessions with the deletion are of the lowland type. The deletion in trnL (UAA) sequences appears to be specific to lowland accessions and should be useful as a DNA marker for the classification of upland and lowland germplasm.

Molecular Markers for the Classification of Switchgrass (Panicum virgatum L.) Germplasm and to Assess Genetic Diversity in Three Synthetic Switchgrass Populations

Ali Missaoui

Papers

Current Progress in Nitrogen Fixing Plants and Microbiome Research.

Mapping and Confirmation of the ‘Hyuuga’ Red-Brown Lesion Resistance Gene for Asian Soybean Rust

Investigation of genomic organization in switchgrass (Panicum virgatum L.) using DNA markers

Nitrogen losses and potential mitigation strategies for a sustainable agroecosystem

Molecular Markers for the Classification of Switchgrass (Panicum virgatum L.) Germplasm and to Assess Genetic Diversity in Three Synthetic Switchgrass Populations