Effect of elevated CO₂, temperature and drought on photosynthesis of nodulated alfalfa during a cutting regrowth cycle

Abstract

Rising atmospheric CO 2 may increase potential net leaf photosynthesis under short-term exposure, but this response decreases under long-term exposure because plants acclimate to elevated CO 2 concentrations through a process known as downregulation. One of the main factors that may influence this phenomenon is the balance between sources and sinks in the plant. The usual method of managing a forage legume like alfalfa requires the cutting of shoots and subsequent regrowth, which alters the source/sink ratio and thus photosynthetic behaviour. The aim of this study was to determine the effect of CO 2 (ambient, around 350 vs. 700 mmol mol À1 ), temperature (ambient vs. ambient þ 4 C) and water availability (well-irrigated vs. partially irrigated) on photosynthetic behaviour in nodulated alfalfa before defoliation and after 1 month of regrowth. At the end of vegetative normal growth, plants grown under conditions of elevated CO 2 showed photosynthetic acclimation with lower photosynthetic rates, V cmax and ribulose-1,5-bisphosphate carboxylase/ oxygenase (rubisco) activity. This decay was probably a consequence of a specific rubisco protein reduction and/or inactivation. In contrast, high CO 2 during regrowth did not change net photosynthetic rates or yield differences in V cmax or rubisco total activity. This absence of photosynthetic acclimation was directly associated with the new source-sink status of the plants during regrowth. After cutting, the higher root/shoot ratio in plants and remaining respiration can function as a strong sink for photosynthates, avoiding leaf sugar accumulation, the negative feed-back control of photosynthesis, and as a consequence, photosynthetic downregulation.

Alfalfa nutritive quality as influenced by drought in South-Eastern Oasis of Tunisia

“…This can be considered as a strategy to allow the accumulation of nutrients in roots and may allow these plants to maintain their water status by a low rate of water uptake. These results are in agreement with those of (Erice et al 2006) in nodulated alfalfa and in four alfalfa genotypes. Comparative results had been obtained for a number of plants (Navas & Garnier 2002;Lei et al 2006;Markesteijn & Poorter 2009).…”

Effects of root temperature on leaf gas exchange and xylem sap abscisic acid concentrations in six Cucurbitaceae species

“…Temperature stress has significant impacts on physiological metabolism both in roots and shoots by influencing processes such as photosynthesis, respiration, ion and water uptake, antioxidant metabolism, and signal transduction (Allen and Ort 2001, Atkin and Tjoelker 2003, Erice et al 2006, Hewezi et al 2006). There exists signal communication between roots and shoots in plants and the relationship between them has been an important research topic especially under sub-and supra-optimal growth conditions (Jackson 1997, Hansen and Dörffling 1999, Sobeih et al 2004, Felle et al 2005, Else et al 2006, Nakagawa and Kawaguchi 2006.…”

Responses of leaf photosynthesis, pigments and chlorophyll fluorescence within canopy position in a boreal grass (Phalaris arundinacea L.) to elevated temperature and CO₂ under varying water regimes

“…Moreover, the synthesis of Chl was inhibited leading to decreases in the light-harvesting protein associated with photosystem II (PSII) (Hu et al 2010). Consequently, we asked the questions with respect to whether the response of plants changes in response to combined elevation in temperature and CO 2 and combined treatments of climate and irrigation (Hamerlynck et al 2000, Erice et al 2006). Additionally we looked at this in the context of the variation in impacts according to leaf canopy position (Del Pozo et al 2007).…”