Plant distribution soil factors Soil moisture

Plant distribution: soil factors • • Soil moisture availability Transpiration and the plant’s water budget Adaptations to drought and waterlogging Plant nutrition Symbioses and nutrient availability Soil p. H and heavy metal toxicity Soil salinity

Soil-Plant. Atmosphere continuum Brady, N. C. and Weil, R. R. , 1999. The nature and properties of soils. Prentice Hall, Upper Saddle River, NJ, 881 pp.

Soil moisture availability • Global circulation patterns control PPT (e. g. areas under semi-permanent subtropical highs vs. temperate westerlies) • Global radiation patterns control PET • Regional patterns (orographic PPT and rainshadows) • Soil infiltration capacity • Local patterns: topography, drainage and aspect

Global mean annual rainfall

Global variation in surface soil moisture Note date http: //hydro. iis. u-tokyo. ac. jp/~kei/Earth/WTABD. html#01

Regional patterns of PPT and PET in western North America

Regional moisture gradients (Oregon) Coastal rain forest steppe >>1000 mm ppt Interior shrub~200 mm ppt

Local moisture gradients: south-facing slope North-facing slope topography and aspect in southern California

Vegetation and the soil moisture gradient: N. CA redwood forest

Fog as a source of moisture in coastal habitats (esp. critical in coastal deserts) Cloud forest, Canary Islands Rainfall ~250 mm per year! “Proyecto David” uses fog catchers to reforest the island of Lanzarote Pearce, F. New Scientist, 08 August, 2006

Stemflow and soil moisture heterogeneity (micro-gradients) Moisture values in k. Pa Brady, N. C. and Weil, R. R. , 1999. The nature and properties of soils. Prentice Hall, Upper Saddle River, NJ, 881 pp.

Stomata: Plant transpiration and respiration Guard cells respond to: -light -CO 2 -water stress

Stoma [pl: stomata] maximizing CO 2 uptake while minimizing H 2 O loss; density 50 -200 per mm 2 of leaf surface Closing triggered by ABA (abscisic acid) when soil water supply cannot keep up with transpiration

The transpiration pump: values express tension required to extract water from medium, in k. Pa.

Priming the transpiration pump

Max. water transpired per day (l) Water use by deciduous trees Foliage (kg [dry wt. ]) Data derived from 20 -30 yr old deciduous trees [Denmark]

Soil moisture and groundwater Brady, N. C. and Weil, R. R. , 1999. The nature and properties of soils. Prentice Hall, Upper Saddle River, NJ, 881 pp.

Soil moisture availability

Rainfall events and soil moisture availability

Rooting patterns in the desert flora of southern Arizona Note root segregation between cactus and creosote bush Depth (cm) 40

How much suction?

Typical transpiration rate* Efficiency of the stomatal valve * mg H 20 /dm 2/h Stomata = cuticular transpiration Plant type

Mean survival time of leaves and shoots cut from plant types (hrs)* >1000 * measures drought tolerance

Water available from stomatal closure to first appearance of damage mg H 20 /dm 2/h >20000 (stems)

Photosynthesis and water use: C 3, C 4 and CAM plants • C 3: Plants that survive solely on C 3 fixation (Calvin cycle) tend to thrive in areas where sunlight intensity is moderate, temperatures are moderate, carbon dioxide concentrations are around 200 ppm or higher, and ground water is plentiful. • C 4: C 4 plants have a competitive advantage over C 3 plants under conditions of drought, high temperatures and nitrogen limitation. • CAM: CAM plants open stomata at night, when the temp. is low, thus water vapor diffuses out of leaf more slowly. CO 2 is stored overnight, and then converted to carbohydrates the following day using light energy. Summarized from wikipedia

Optional photosynthetic pathways in a desert succulent (Agave deserti) normal well-watered

Water conservation: palisade tissue in expandable stems of desert succulents

Waxy leaves and sunken stomata reduce water loss Thick upper leaf cuticle Cross-section of a leaf of the California lilac (Ceanothus sp. ), a common shrub of the California chapparal stomata guard hairs crypt

Global variation in water table depth (m) Note date http: //hydro. iis. u-tokyo. ac. jp/~kei/Earth/WTABD. html#01

Topographic gradients Huggett, R. J. , 2004. Fundamentals of Biogeography. Routledge, London, 439 pp.

Surviving waterlogged (anoxic) environments Oxygen is absorbed through pores in bark called lenticels, then diffuses to tissues with low O 2 concentration (e. g. submerged trunk or roots in saturated soil) lenticels

Aerenchyma move oxygen from emergent shoots to submerged roots

Avicennia (grey mangrove) pneumatophores Wetland trees have specialized breathing apparatus - all densely covered with lenticels Taxodium (bald cypress) knee roots Rhizophora (red mangrove) stilt roots

Is there a mangrove zonation* associated with tolerance of anoxia/submergence? *contentious! Image: http: //edis. ifas. ufl. edu/in 1

The soil as a source of bioelements Nutrition (macro and micronutrients) • • nitrogen cycle nitrogen fixation - symbioses P and K supply - symbioses micronutrients and local geology Toxicity • • p. H relations heavy metals (Fe, Mn, Al, …) salinity tolerance mechanisms

Micronutrients Macronutrients Essential bioelements Element Nitrogen Potassium Calcium Magnesium Phosphorus Sulphur Chlorine Iron Manganese Boron Zinc Copper Form NO 3 -, NH 4+ K+ Ca 2+ Mg 2+ HPO 42 SO 42 Cl. Fe 2+, Fe 3+ Mn 2+ BO 33 Cu+, Cu 2+ Molybdenum MO 42 - Conc. in dry plant tissue (ppm) 15, 000 10, 000 5, 000 2, 000 100 100 50 20 20 6 0. 1

The nitrogen cycle Biological fixation (~10%) (87%) (3%) Processors: bacteria, fungi and actinomycetes; mainly 3 2 1 1. Nitrosomonas 2. Nitrobacter 3. Pseudomonas modified from ©M. Pidwirny

N-fixation Nodule cluster on alder root Mediated by bacteria (strains of Rhizobium, Frankia) that infect root hairs of higher plants and initiate a symbiotic interaction, supplying nitrogen (from soil atmosphere) in return for carbohydrates. Plant builds nodule structures that house bacterial colonies. Common in Leguminosae; rare in other plant families. Nodules on acacia roots

N-fixers 1 4 N-fixing plants are colonizers of inhospitable nitrogen-deficient substrates: e. g. 1. vetch on dune sands, 2. lupin on alpine scree, 3. alder on spoil deposits, 4. mesquite on desert alluvial fans BUT: Rhizobium inhibited by acid soil conditions

Effects of N-fixers Variable concentration of nitrogen beneath a mesquite shrub, Arizona.

Environmental controls on the rate of nitrogen cycling Excess or deficient O 2, p. H, H 2 O or heat may affect N-cycle microorganisms v. wet e. g. denitrification N 2 production NO 3 production e. g. nitrification soil v. dry v. wet soil v. dry

Mycorrhizal (“fungus-root”) symbioses: increased absorption of P (and K) fruiting body fungal mantle fungal hyphae

p. H and availability of bioelements

Plant distribution along a p. H gradient

“Heavy metal” solubility on a p. H gradient Iron ppm extracted Aluminium Soil p. H Manganese

Al-tolerant and Al-sensitive grasses: data from northern England Encircled values refer to m. Moles of Al required to inhibit root grawth in 1 -week old seedlings. Arrow points to p. H of seed source.

Root inhibition by aluminium: wheat seedlings Control Treatments

Soil toxicity - salt accumulation in interior basins and coastal marshes Typha (cat-tail) fresh 0. 5 Salt marsh plants can store salt in their tissues (most are succulent), and have specialized glands to excrete excess salt brackish Salicornia (pickleweed) saline hypersaline 18 36 g/l salt