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World areas subject to drought are expected to increase under conditions of climate change. The purpose of this study is to clarify the response of grass species that can grow and produce under water stress. Therefore leaf photosynthesis, chlorophyll fluorescence and pigment content response to water stress were studied in two varieties of the C4 grass Eragrostis curvula. Two-year-old plants of cv Ermelo and Consol were grown in plastic pots. Drought stress was imposed by withholding irrigation for 15 days and then rewatering for 5 days. During drought relative water content (RWC) decreased 65% in cv Ermelo, while lower reductions of RWC were observed in cv Consol. During the experiment in cv Ermelo increasing drought stress severity caused large decreases in photosynthetic rates, maximal PSII photochemical efficiency (FV/FM) and leaf pigment content. Cv Consol showed small variations in these parameters. Compared to cv Consol, after 15 days of drought, effective PSII quantum yield (ΦII) was significantly lower in cv Ermelo. Reductions of ΦII were related to significant reductions of open PSII energy capture efficiency (F′V/F′M). Photosynthetic response to increasing PPFD levels and to internal CO2 concentration (Ci) were reduced by drought in cv Ermelo. Compared to well-watered control plants and to cv Consol, drought stressed plants of cv Ermelo showed also reductions of the initial slope of photosynthetic response to Ci and in the photosynthetic rate measured at saturating Ci. Moreover stomatal conductance (g) of both cvs decreased during drought. However, g was lower in drought stressed plants of cv Consol than in cv Ermelo. Water stress caused large reductions in leaf chlorophyll and carotenoid content in cv Ermelo, and small reductions in cv Consol. In drought-sensitive cv Ermelo water stress reduced the capabilities to down regulate PSII functionality through thermal energy dissipation. Results suggest that drought resistance of cv Consol, can be attributed to a higher water use efficiency. [Copyright &y& Elsevier]

Abstract: It is widely accepted that our climate is changing due to the increasing atmospheric concentrations of the ‘greenhouse gases’, and these changes may exercise strong impacts on different economic sectors. In particular for agricultural systems, such a change may have significant impacts on crop yield, cattle breeding and related management practices. Accordingly, the economic viability of agricultural production systems in future scenarios is a main concern especially for policy-making purposes. Up until now, the impact of climate change on agriculture has focused on change in crop yield, whereas a ‘holistic’ approach, considering both benefits (in terms of direct economic income) and detrimental environmental impacts of agricultural practices (soil loss, nitrogen leaching, water balance) has not been considered. On these premises, the objective of the present article was to assess agricultural sustainability on a farm level in Tuscany (central Italy) under the climate change regime, considering both conventional and organic farming systems (CFS and OFS, respectively). In particular, an ecological–economic optimisation model was run for both the present and future scenarios to perform an integrated assessment of sustainability of CFS and OFS on the case-study farm. [Copyright &y& Elsevier]