Overview of Plant Physiological Ecology General objectives and questions addressed Key people (recent) Key terms Key Components of plant response to environment: Carbon uptake Nutrient uptake Water balance Energy Balance Effects of environmental factors (CO2, Temperature, wind, light, etc.) Cost-benefit analyses for resource allocation Survey of recent papers - topic coverage Example paper: Coleman and Bazzaz, Ecology 1992 Vol. 73:1244 Some references: BioScience 37 No.1 January 1987 Nobel, P. S. 1991. Physicochemical and Environmental Plant Physiology. Academic Press, NY Townsend, C. R. and P. Calow. 1981. Physiological Ecology: an evolutionary approach to resource use. Sinauer, Sunderland, MA General objectives of plant physiological ecology: Seek biochemical and physiological mechanisms underlying features of organisms that may be adaptive and relate these mechanisms to organism performance under natural conditions Relate physiological responses to species abundances and distributions Provide methods to ascertain the interactions between various environmental factors in affecting individual plant success (e.g. survival and reproduction) Provide a basis for linking environmental responses of individuals to population and other hierarchical levels of response Main historical trends: Field and Laboratory techniques: Light effects (leaf and canopy level) Gas transport Leaf energy Balance Growth models (plant and canopy) Ecotypic responses Plant distribution Microclimate analysis Stress environments (tundra, desert) People: W.D. (Dwight) Billings - adaptive characeteristics in stressful environments Olle Bjorkman - Sun and shade photosynthetic physiology J. Clausen, D. D. Keck and W. M. Heisey - ecotypic differentiation and transplant experiments David Gates - energy balance - biophysical ecology John Montieth - microclimate analysis F. W. T. Penning de Vries - plant growth analysis R. O. Slatyer - water relations Current major players: Fakhri Bazzaz - resource allocation Martyn Caldwell - below ground physiology Stuart Chapin - mineral nutrition James Ehleringer - light effects Graham Farquhar - leaf physiology, water/carbon relations Chris Field - photosythesis/nitrogen effects Hal Mooney - species distributions Barry Osmond - stress effects Park Nobel - cactus physiology, biophysical approaches Robert W. Pearcy - photosythnthetic physiology, plant architecture Some Terms: Flux (or flux density) - the rate of movement of some material per unit time per unit area (or volume) flux density = proportionality constant x Force Fick's Law - Flux of a species is proportional to the concentration gradient Diffusivity - constant of proportionality (though may be function of conditions) in Fick's law Conductance - proportionality in discrete version of flux density definition e.g. stomatal conductance is g in Flux of water = - g ( c internal - c external) where c internal = water concentration internal to stomate and c external = water concentration external to stomate measures ease with which material flows - larger conductance means higher fluxes Resistance - inverse of conductance - measures the resistance to flow of a material - the larger the resistance the smaller the flux Boundary layer - the region near a surface of relatively "still" air - in which turbulent transfer does not occur - the unstirred layers Chemical potential - the free energy of a chemical species available for doing work - the larger the difference between chemical potential of a species in two locations the larger the flux density of the species Water potential - chemical potential of water rescaled in an appropriate way - it represents the work involved in moving one mole of water from a pool of pure water at atmospheric pressure and conatant temperature to an arbitrary point in the system. If water potential is not constant, then water will tend to flow towards the region where water potential is lower. Carbon Uptake: Photosynthesis: Depends on leaf photosynthtic capacity (rate of C gain per unit leaf area at saturating light, ambient O2 and CO2, high humidity, optimum temperature) High resources imply generally higher photosythtic capacity (some desert plants) Very plastic - sun versus shade leaves depends on N availability determined by amount and activity of photosynthtic enzymes (RUBISCO) Actual photosynthetic rate determined by trade-off between stomatal and biochemical components Alternative biochemical pathways: C3 - Calvin Benson cycle requiringone carboxylation which predominates C4 - two carboxylations required, first producing a 4-C compound then fixed by RUBISCO - these two carboxylations occur in separate cells in which CO2 is pumped from mesophyll to bundle sheath cells - reduces competive inhibition of RUBISCO by oxygen - many grasses (Maize) - adaptive under high temperatures and radiation CAM - similar to C4 only two carboxylations occur in same cell - stomata open at night, not day - many variants exist - succulents Leaf carbon balance - calculated by summing uptake of C over leaf lifespan minus the construction and metabolic costs - time to provide a "profit" depends on environment and leaf type. - much less known about respiration than about photosynthesis Allocation patterns - C allocation between leaves, stem, below ground, reproduction, defense depends greatly on architectural constraints on species, environment during development - canopy structure produces self shading and a variety of mechanical constraints on plant development (see Karl Niklas. 1992. Plant biomechanics: an engineering approach to plant form and function. University of Chicago Press) Nutrient Uptake: N is primary limitation on growth, as evidenced by variety of mechanisms evolved to enhance N uptake - mycorrhizal associates, fixation of atmospheric N mediated through bacteria, carnivory - most plants rely on absorption through roots though. Components of transport are : absorption (roots make up 50-80% of dry matter production for plants, active transport of ions against a concentration gradient, translocation from site of absorption to leaves, and assimilation which converts N from inorganic to organic forms usable by the plant N concentration is closely correlated with photosythetic capacity - for C3 plants, 75% of N is in chloroplasts Nitrogen Use efficiency, calculated as photosynthetic capacity per unit leaf N varies widely with N concentration Water balance: Water is major factor limiting plant growth - due to trade-off between photosythesis and transpiration. Ratio of transpiration to photosynthesis (gradient in water vapor concentration divided by gradient in CO2 concentration) is typically > 50 Can be strong local competition for water - variety of rooting strategies have evolved in desert conditions Movement between soil-plant atmosphere continuum, affected by significant investments in root tissue, high fineroot turnover rates, storage and transport in stems (amount of stem material correlated with size of canopy in trees) Extensive lterature on stomatal dynamics indicates that though stomatal control may be affected in part by leaf water status, it also is affected by root water status - so that canopy water loss is coupled to to moisture environment of roots. Stomatal control still a very contentious area - humidity, C gain, nutrient status, water all play a role. Models of Cowan and Farquhar predict stomatal dynamics to maintain a constant "gain ratio" over a day. Energy Balance: Takes account of radiant heating, aerodynamics, stomatal dynamics to predict relationships between leaf temperature, transpiration and leaf size and shape under varying environmental conditions. Can be done at canopy level as well - particularly well developed for crop species, and forests Topics from 1990's search on plant physiological ecology in 4 ecology journals: Summary: Field/lab methods 5 Air pollution 2 Carbon investment 5 Models 1 Plant form 1 defense costs 1 plant-insect 2 competition 1 water use 3 nutrient dynamics 4 soil properties 1 photosynthetic acclimation 1 light responses 3 habitat distribution 2 Temperature response 1 Total 33 articles