The Rate Debate Slowing
Warming Bad - Productivity
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Warming Bad - ProductivityWarming increases plant productivity Albert et al. (K. R. ALBERT1, H. RO-POULSEN2, T. N. MIKKELSEN1, A. MICHELSEN2, L. VAN DER LINDEN1 & C. BEIER, 1Biosystems Division, Risø DTU, Frederiksborgvej 399, 4000 Roskilde and 2Terrestrial Ecology, Department of Biology, University of Copenhagen, Øster Farigmagsgade 2D, 1353 Copenhagen K, Denmark) 2011 (K.R., “Effects of elevated CO2, warming and drought episodes on plant carbon uptake in a temperate heath ecosystem are controlled by soil water status ,” Plant, Cell and Environment (2011) 34, 1207–1222 Pages 1-2) //CL Climate is changing, and the anthropogenic forcing has been thoroughly documented (IPCC 2007). The level of atmospheric CO2 has increased from a pre-industrial level of 270 ppm to current values around 380 ppm, and is expected to increase to around 700 ppm (IPCC 2007). This will lead to temperature increases of 1.4–5.8 °C during the next 100 years, with more pronounced warming during night-time relative to daytime (IPCC 2001). Precipitation changes with prolonged summer droughts, heavy precipita- tion events and higher frequency of extremes are also expected (IPCC 2007). This has attracted focus on ecosys- tem responses to climatic changes and on ecosystem feedbacks to climate, and much effort is invested in under- standing these complex impacts (Rustad 2006, 2008; Heimann & Reichstein 2008). Photosynthetic carbon uptake is controlled directly by the factors that are predicted to change in the future, atmospheric CO2 concentration, temperature and water availability (Morison & Lawlor 1999; Sage & Kubien 2007; Lawlor & Tezara 2009), and will therefore almost certainly be affected by climate change. It is likely that the relative importance of the factors limiting carbon uptake may change as climate change affects various regulators of photosynthesis and ecosystems adjust to the new condi- tions. Carbon demand for storage, growth, metabolism or export also influences the residence time in the carbon pools and the flux rates between them (Körner 2006); this may interact with the factors that control carbon uptake. Elevated CO2 decreases stomatal conductance and increases intercellular CO2 concentration, light saturated net photosynthesis and plant WUE (Curtis & Wang 1998; Ainsworth & Long 2005; Ainsworth & Rogers 2007). Elevated CO2 often down-regulates photosynthetic capac- ity via the maximal velocity of ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylation, Vcmax and to lesser degree the maximal rate of RuBP regeneration, Jmax which may decrease the maximal light and CO2 satu- rated net photosynthesis, Pmax (Drake, Gonzalez-Meler & Long 1997; Moore et al. 1999; Ainsworth & Rogers 2007). This is in part caused by the build-up of carbon compounds produced in the Calvin cycle, and in part caused by limita- tions in the nitrogen supply (Drake et al. 1997; Ainsworth & Rogers 2007). Leaf carbon uptake may be sustained in elevated CO2 if photosynthetic down-regulation does not occur, as reported from grasslands (Hungate et al. 1997a) and forests (Körner et al. 2005). In the long term, however, nutrient availability is likely to be of increasing importance for sustained productivity in elevated CO2 (Oren et al. 2001; Lou et al. 2004; Reich et al. 2006; Menge & Field 2007). Plant water status also affects the magnitude of plant carbon uptake in elevated CO2 (Körner 2000; Volk, Niklaus & Körner 2000; Knapp et al. 2002; Morgan et al. 2004). Elevated CO2 often results in reduced plant water consump- tion and leads to reduced soil water depletion, so-called water savings caused by reduced stomatal conductance (Morison & Gifford 1984; Hungate et al. 1997b; Leuzinger & Körner 2007; Robredo et al. 2007). This enables maintained plant carbon uptake in dry periods in elevated CO2 relative to ambient CO2 (Morison & Gifford 1984; Hungate et al. 1997b; Leuzinger & Körner 2007; Robredo et al. 2007). Changes in plant water availability affect photosynthesis, particularly during dry conditions that limit photosynthesis because of metabolic impairments, as well as diffusion limi- tations (Jones 1985; Chaves 1991; Flexas & Medrano 2002; Lawlor 2002; Lawlor & Cornic 2002; Flexas et al. 2006a). The responsiveness is highly species specific (Knapp et al. 2002; Heisler & Weltzin 2006). However, the carbon balance of a plant enduring a water stress period not only depends on the degree of photosynthetic decline during water deple- tion, but also on the rate and degree of photosynthetic recovery, although information on these aspects is scarce (Flexas et al. 2006b; Galmes, Medrano & Flexas 2007; Lawlor & Tezara 2009). Warming has been demonstrated to increase productivity (Arft et al. 1999; Rustad et al. 2001; Shaw et al. 2002; Dukes et al. 2005; Sage & Kubien 2007), but the impacts of this driver are complex; the confounding of direct and indirect effects can make it difficult to elucidate the underlying mechanisms of the responses of plants and ecosystems (Shaver et al. 2000; Peñuelas & Filella 2001). Warming can directly stimulate photosynthesis via provision of more optimal growth temperatures (e.g. Sage & Kubien 2007), and may be of particular importance in temperate ecosys- tems during periods of sub-optimal temperatures. Increased daytime respiration or changes in temperature acclimation can occur and may reduce the photosynthetic plant carbon uptake (Atkin & Tjoelker 2003). Indirect stimulation of daytime photosynthesis has been demonstrated in response to night-time warming, where an increased night-time plant respiration increased the carbon sink strength and in turn stimulated the following daytime net photosynthesis (Turnbull, Murthy & Griffin 2002; Turnbull et al. 2004). Warming may also affect photosynthesis and plant carbon uptake indirectly through increased length of the growing season (Menzel & Fabian 1999; White, Running & Thornton 1999; Walther et al. 2002; Cleland et al. 2006; Piao et al. 2007), plant phenology changes (Harte & Shaw 1995; Wan et al. 2005) and increased nutrient availability (Rustad et al. 2001). Some authors have argued that the indirect effects, via changes in nutrient and soil water availability, are more important than direct effects (Körner 2000; Shaver et al. 2000; Volk et al. 2000; Morgan et al. 2004; Wan et al. 2005; Lou 2007). Clearly, the effects of warming on plants and ecosystems are not straightforward and depend on the out- comes of the individual effects on many processes. Directory: files files -> Answer True False 2 points Question 2 files -> Integer programming and game theory files -> 4 Integer Programming files -> Bpa vehicle Window Repair Scenario #1 task: Procure vehicle window relacement. 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