BIO120 Fall 2024 Plant Ecophysiology Lecture Notes PDF

Lecture 16: Plant ecophysiology Plants can’t evade stress by moving But they can make their own food; they are (mostly) autotrophs Photosynthesis requires light, CO2, and water, and also a reasonable temperature Leaf, stem, and root traits reflect adaptation to their environments, with...

Lecture 16: Plant ecophysiology Plants can’t evade stress by moving But they can make their own food; they are (mostly) autotrophs Photosynthesis requires light, CO2, and water, and also a reasonable temperature Leaf, stem, and root traits reflect adaptation to their environments, with examples of adaptations in desert plants Epiphytes in rainforests 1 © BIO120 Fall 2024  Stigma (receives Anthers pollen) (bear pollen) earth.com 2 © BIO120 Fall 2024 Like animals, plants are extraordinarily diverse in form and function 3 © BIO120 Fall 2024 Physiological ecology is different for plants because they are: Sessile, with little scope for behaviour; animals can escape adverse conditions, but plants must tolerate them Autotrophic; they make their own food through photosynthesis All plants need the same few things to grow: light, CO2, water, and soil nutrients (especially nitrogen, phosphorus, and potassium, or NPK) 4 © BIO120 Fall 2024 Photosynthesis: a quick refresher Photosynthesis Light CO2 + H2O Carbohydrate + O2 ATP energy Respiration Plants must bring together CO2, water, and light in functioning photosynthetic tissues Enzymes also require an OK temperature For growth, plants have to acquire more carbon through photosynthesis than they lose through respiration; carbon balance is therefore key 5 © BIO120 Fall 2024  Net primary productivity (NPP) C gained via photosynthesis – C lost via respiration = NPP 6 © BIO120 Fall 2024 Photosynthetic structures embody adaptation to environmental stresses Photosynthetic (green) structures are usually leaves (but can be stems) Plants take in CO2 through stomata evolution.berkeley.edu But plants also transpire; they lose water through stomata (singular stoma) 7 © BIO120 Fall 2024 Photosynthetic structures embody adaptation to environmental stresses Leaf size and shape: SA:V ratios important again Benefits of large leaf surface area: good for harvesting light, CO2 Costs of large leaf surface area: bad for overheating, water loss by transpiration through stomata 8 © BIO120 Fall 2024 How do plants cope with overheating/water loss? Most plants fix carbon by C3 photosynthesis Rubisco is the enzyme that accepts CO2 But at high temperatures, Rubisco often captures O2 instead of CO2, which is bad for plants (“photorespiration”) Some plants have evolved: C4 photosynthesis: the enzyme PEP carboxylase first accepts CO2, reducing photorespiration CAM photosynthesis: plants close stomata during the day to reduce water loss, open stomata at night to let in CO2; photosynthesis still needs light, so they store CO2 as malate until daytime 9 © BIO120 Fall 2024  Plants with large leaves also combat overheating by: Growing in shady habitats Evaporative cooling by opening stomata www.isv.cnrs-gif.fr/jg/images/stomata.jpg 10 © BIO120 Fall 2024  Evaporative cooling needs plentiful water— not always available. Plants with large leaves combat water loss by: Closing stomata… …but that shuts off all gas exchange, including CO2 input, so photosynthesis shuts down. Plant stops growing… …and risks overheating & tissue damage Therefore, fundamental trade-off between water conservation and rapid growth Consequences most obvious in desert plants 11 © BIO120 Fall 2024 Keeping cool while conserving water: Sonoran Desert, Arizona As little as ~75mm a year of rain Summer temperatures often over 40 ° C and can reach 48 °C A cactus doesn’t live in the desert because it likes the desert; it lives there because the desert hasn’t killed it yet. Any plant that you find growing in the desert will grow a lot better if you take it out of the desert. The desert is like a lot of lousy neighborhoods: nobody living there can afford to move. Too little water, too much light, temperature too high: the desert has all of these inconveniences ratcheted up to their extremes. Biologists don’t much study the desert, since plants represent three things to human society: food, medicine, and wood. You’ll never get any of those things from the desert. Thus a desert botanist is a rare scientist indeed …” -- Hope Jahren, Lab Girl 12 © BIO120 Fall 2024 Palo Verde (Parkinsonia sp.) 13 © BIO120 Fall 2024 Palo Verde = “green stick” Photosynthetic bark on trunks & branches; can grow without incurring heat load & water loss through leaves 14 © BIO120 Fall 2024 Microphylly in Palo Verde 15 © BIO120 Fall 2024  Leaves in tropical rainforests vs deserts Tropical rainforests: Deserts: warm and wet hot and dry (leaves so big they (tiny leaves) can be used as umbrellas) louandadventure.wordpress.com 16 © BIO120 Fall 2024  17 © BIO120 Fall 2024 Getting rid of leaves entirely: cacti Microphylly taken to extremes: no leaves! Santa Rita prickly pear (Opuntia santa-rita) 18 © BIO120 Fall 2024 Episodic patterns of H2O availability in Sonoran desert: Rillito River, Tucson, Arizona 19 © BIO120 Fall 2024 Saguaro cactus (Carnegiea gigantea) Restricted to Sonoran desert, adapted to episodic rains Grows to 15 m, 200 yr, 5+ tonnes CAM photosynthesis Extensive, shallow roots Accordion-pleated trunk allows expansion Can absorb 800 L of water from one storm, use it gradually for growth Mnemonic digression for water storage: David Grundman (d. 1982) 20 © BIO120 Fall 2024 Cacti: extensive but shallow roots 21 © BIO120 Fall 2024  Tropical trees: also extensive but shallow roots (for a different reason) Tropical rainforests have a shallow layer of nutrient-rich soil Extensive, shallow roots are an adaptation to acquire scarce nutrients (phosphorus, nitrogen, etc.) Photo: Marisa Ishimatsu 22 © BIO120 Fall 2024  Root “foraging” Legume species (Medicago truncatula) Split-root experiment Rebecca Low N High N Doyle 23 © BIO120 Fall 2024 Legumes also “search” for “Bad” nitrogen-fixing bacteria “Good” bacteria in soil bacteria 24 © BIO120 Fall 2024 Roots “forage” for both nitrogen and symbionts Rebecca Adapted from Batstone et al. (2017, New Phytol.) Batstone 25 © BIO120 Fall 2024  Animals can evade stress through behaviour: what about plants? Do plants have behaviour? Deciduous habit: dropping leaves during dry or cold seasons reduces water stress and tissue damage Tropical Dry season Rainy season dry forest, Guanacaste, Costa Rica Photo: www.gdfcf.org 26 © BIO120 Fall 2024 Leaf shape also influences gas exchange through laminar vs. turbulent air flow over surfaces More laminar flow Vehicles are designed to minimize turbulence More turbulent flow But for cooling leaves, more turbulence is better! 27 © BIO120 Fall 2024  Morphological plasticity: sun and shade leaves from one red oak tree More laminar flow, More turbulence, less cooling better cooling Photo: Lucy Hutyra Shade leaf Sun leaf 28 © BIO120 Fall 2024  Monstera deliciosa, sun and shade leaves: dissected outlines cause turbulent airflow Wikimedia brittanica 29 © BIO120 Fall 2024  Recursive digression: Convective cooling aided by turbulence Cool! www.pestproducts.com Art Wolfe Lepus arcticus Lepus californicus 30 © BIO120 Fall 2024 Contemporary art meets convergent evolution: many of these are not cacti! Martin Creed: Work No. 960, 2008. Cactus plants. 13 parts, dimensions variable. Courtesy of the artist and Gavin Brown’s enterprise, New York. Installation view, Martin Creed Plays Chicago, MCA Chicago, 2012. Photo: Nathan Keay, © MCA Chicago. 31 © BIO120 Fall 2024  Cactaceae Asteraceae Asclepiadaceae Euphorbiaceae Cactus family Daisy family Milkweed family Spurge family 32 © BIO120 Fall 2024 Can plants in rainforests be water stressed? Yes, if they’re epiphytes Bromeliad “tank” epiphytes, National Geographic 33 © BIO120 Fall 2024  Epiphytes grow on trees, so they aren’t able to put their roots into the soil, leading to water stress and nutrient shortages 34 © BIO120 Fall 2024  35 © BIO120 Fall 2024 Epiphytic Rhipsalis cactus, Brazil: cacti are “pre-adapted” to epiphytic 36 life © BIO120 Fall 2024  Lecture 16– Key things to know Topics & concepts – photosynthesis, transpiration, net primary productivity, trade-off between water conservation and growth, stomata, how different environments select on leaf size and shape, microphylly, root foraging, deciduousness, convergent evolution, epiphyte 37 © BIO120 Fall 2024