Impacts of climate changes on crop physiology and food quality

Carbon emissions related to human activities have been significantly contributing to the elevation of atmospheric [CO(2)] and temperature. More recently, carbon emissions have greatly accelerated, thus much stronger effects on crops are expected. Here, we revise literature data concerning the physiological effects of CO(2) enrichment and temperature rise on crop species. We discuss the main advantages and limitations of the most used CO(2)-enrichment technologies, the Open-Top Chambers (OTCs) and the Free-Air Carbon Enrichment (FACE). Within the conditions expected for the next few years, the physiological responses of crops suggest that they will grow faster, with slight changes in development, such as flowering and fruiting, depending on the species. There is growing evidence suggesting that C(3) crops are likely to produce more harvestable products and that both C(3) and C(4) crops are likely to use less water with rising atmospheric [CO(2)] in the absence of stressful conditions. However, the beneficial direct impact of elevated [CO(2)] on crop yield can be offset by other effects of climate change, such as elevated temperatures and altered patterns of precipitation. Changes in food quality in a warmer, high-CO(2) world are to be expected, e.g., decreased protein and mineral nutrient concentrations, as well as altered lipid composition. We point out that studies related to changes in crop yield and food quality as a consequence of global climatic changes should be priority areas for further studies, particularly because they will be increasingly associated with food security. (c) 2009 Elsevier Ltd. All rights reserved.Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG)Minas Gerais State Research Foundation (Fapemig)National Council for Scientific and Technological Development (CNPq, Brazil)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)FAPESP[07/59708-1]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)CNPqConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Ministry of Science and Technology of BrazilMinistry of Science and Technology of BrazilEletronorte (Para State, Brazil)Eletronorte (Para State, Brazil

Responses of Senna reticulata, a legume tree from the Amazonian\ud floodplains, to elevated atmospheric CO2 concentration\ud and waterlogging

Tree species from the Amazonian floodplains have to cope with low oxygen availability due to annual pulses of inundation that can last up to 7 months. Species capable of adapting to flooding and/or waterlogged conditions usually partition their storage to favor starch and allocate it to roots, where carbohydrates are used to maintain respiration rates during waterlogging. In spite of climate change, virtually nothing is known about how elevated atmospheric CO2 concentration ([CO2]) will affect plants when combined with waterlogging. In this work, we used open top chambers to evaluate the effect of elevated [CO2] during a period of terrestrial phase and in subsequent combination with waterlogged conditions to determine if the surplus carbon provided by elevated [CO2] may improve the waterlogging tolerance of the fast-growing Amazonian legume tree Senna reticulata. During the terrestrial phase, photosynthesis was ca. 28 % higher after 30, 45 and 120 days of elevated [CO2], and starch content in the leaves was, on average, 49 % higher than with ambient [CO2]. Total biomass was inversely correlated to the starch content of leaves, indicating that starch might be the main carbohydrate source for biomass production during the terrestrial phase. This response was more pronounced under elevated [CO2], resulting in 30 % more biomass in comparison to ambient [CO2] plants. After 135 days at elevated [CO2] an inversion has been observed in total biomass accumulation, in which ambient [CO2] presented a greater increment in total biomass in comparison to elevated [CO2], indicating negative effects on growth after long-term CO2 exposure. However, plants with elevated [CO2]/waterlogged displayed a greater increment in biomass in comparison with ambient [CO2]/waterlogged that, unlike during the terrestrial phase, was unrelated to starch reserves. We conclude that S. reticulata displays mechanisms that make this species capable of responding positively to elevated [CO2] during the first pulse of growth. This response capacity is also associated with a “buffering effect” that prevents the plants from decreasing their biomass under waterlogged conditions.FAPESP (Grant Number 07/59708- 1

Cell wall hydrolases act in concert during aerenchyma development in sugarcane roots

BACKGROUND AND AIMS: Cell wall disassembly occurs naturally in plants by the action of several glycosyl-hydrolases during different developmental processes such as lysigenous and constitutive aerenchyma formation in sugarcane roots. Wall degradation has been reported in aerenchyma development in different species, but little is known about the action of glycosyl-hydrolases in this process. METHODS: In this work, gene expression, protein levels, and enzymatic activity of cell wall hydrolases were assessed. Since aerenchyma formation is constitutive in sugarcane roots, they were assessed in segments corresponding to the first 5 cm from the root tip where aerenchyma develops. KEY RESULTS: Our results indicate that the wall degradation starts with a partial attack to pectins (by acetyl esterases, endopolygalacturonases, β-galactosidases, and α-arabinofuranosidases) followed by the action of β-glucan/callose hydrolyzing enzymes. At the same time, there are modifications in arabinoxylan (by α-arabinofuranosidases), xyloglucan (by XTH), xyloglucan-cellulose interactions (by expansins), and partial hydrolysis of cellulose. Saccharification revealed that access to the cell wall varies among segments, consistent with an increase in recalcitrance and composite formation during aerenchyma development. CONCLUSION: Our findings corroborate the hypothesis that hydrolases are synchronically synthesized leading to cell wall modifications that are modulated by the fine structure of cell wall polymers during aerenchyma formation in the cortex of sugarcane roots

Senna reticulata : a viable option for bioenergy production in the Amazonian region

Senna reticulata is an Amazonian tree that quickly accumulates high biomass. It grows widely in the north of Brazil occupying degraded regions and is popularly known as “matapasto” (pasture-killer) due to its aggressive colonization strategy. When its aerial parts are harvested, S. reticulata recolonizes the pasture quickly recovering biomass production. In this work, we examined the potential of S. reticulata for bioenergy production in the Amazon region and the effect of a CO2 enriched atmosphere on its biomass composition. Nearly 50% of the biomass of the aerial parts is non-structural carbohydrates (NSC). Concerning structural carbohydrates, pectins (25% and 23%), hemicelluloses (11% and 16%), and cellulose (4% and 14%) contents were very similar in leaves and stems, respectively. Lignin varied considerably among organs, being 35% in roots, 7% in stems, and 10% in leaves. Although elevated CO2 did not change significantly cell wall pools, lignin content was reduced in leaves and roots. Furthermore, starch increased 31% in leaves under elevated CO2, which improved saccharification by 47%. We conclude that Senna reticulata is a suitable species for use as a bioenergy feedstock in the tropics and specifically for remote communities in the Amazonian region