Smith / Hinckley Resource Physiology of Conifers

Acquisition, Allocation, and Utilization
1. Auflage 2013
ISBN: 978-0-08-092591-2
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 396 Seiten

Reihe: Physiological Ecology

Coniferous forests are among the most important of ecosystems. These forests are widespread and influence both the financial and biological health of our globe. This book focuses attention on conifers and how these trees acquire, allocate, and utilize the resources that sustain this crucial productivity. An international team of experts has surveyed and synthesized information from an expanding area of inquiry. The first half of the book describes how resources are acquired both by means of photosynthesis and through root systems. The latter half of the volume focuses upon how resources are stored and used. As conifers continue as a resource and ever increasingly important contributor to the regional and global environmental sustainability, this book will help establish how much sustainability can be expected and maintained.

Autoren/Hrsg.

Smith, William K.

Hinckley, Thomas M.

Leseproben

2

Water and Nutrient Acquisition by Roots and Canopies

Ram Oren and David W. Sheriff

Publisher Summary

This chapter discusses the generalities based on results from observational studies of unmanipulated plants and of stands. It reviews information from experimental manipulation of nutrient and water availability. Water and nutrient supply rates, as well as internal and external deficits, can have major effects on physiological activity and growth. Moist soil and wet canopy surfaces facilitate nutrient uptake through roots and foliage, respectively. Water uptake is affected by the number and distribution of roots in relation to the distribution of soil moisture, and by the wetness and hydraulic permeability of foliage. Nutrient uptake is similarly affected by tissue characteristics and nutrient concentration, and also depends on the moisture regime in the bulk soil and in the vicinity of absorbing surfaces. The chapter explores the uptake of water and nutrient by roots and canopies by employing various methods.

I Introduction

Water and nutrient supply rates, as well as internal (plant) and external (soil) deficits, can have major effects on physiological activity and growth. Effects of water or nutrient deficits on growth can be demonstrated separately, but they often interact, as shown by Allen (1990) for several species, and by Turner (1982) for Moist soil and wet canopy surfaces facilitate nutrient uptake through roots and foliage, respectively. Water uptake is affected by the number and distribution of roots in relation to the distribution of soil moisture, and by the wetness and hydraulic permeability of foliage. Nutrient uptake is similarly affected by tissue characteristics and nutrient concentration, but also depends on the moisture regime in the bulk soil and in the vicinity of absorbing surfaces.

In this chapter, we discuss generalities based on results from observational studies of unmanipulated plants and of stands. We also consider information from experimental manipulation of nutrient and water availability. A more thorough treatment of the effects of mycorrhizae and anthropogenic pollution on water and nutrient acquisition is given in Chapter 3 (this volume) and in Matyssek (1994), respectively.

II Methodology

A Foliar Acquisition

Much of the knowledge about uptake of water and nutrients through foliage was acquired via research on three very different topics: (1) uptake of nutrients and dissolved CO2 by aquatic plants; (2) uptake of foliar applied fertilizers, herbicides, plant growth regulators, and systematic insecticides; and (3) uptake of water and nutrients from wet canopy surfaces, particularly in relation to anthropogenically enriched, or polluted, air, cloud, and fog water. In this chapter we report on processes involved in foliar acquisition of water and nutrients by terrestrial plants, and provide examples from research on conifers.

B Acquisition by Roots

Various methods have been employed to investigate the uptake of nutrients by whole plants. Assessing relationships between nutrient availability and uptake is most often accomplished using the following methods:

1. Measurement of uptake rate of an element per unit of root (area, length, or weight). Uptake by the plant is calculated by using a measured or estimated quantity for the root system.

2. Determining nutrient pools in the whole plant at different times using measured concentrations of elements in samples of plant organs and total dry weights of each organ.

3. Determining nutrient pools and fluxes in soil by sampling, and calculating uptake as the amount of nutrient that cannot be accounted for.

In most cases, a theoretical or empirical relationship is evaluated with regard to supply of a certain ion (using either its input to the soil or an index of availability in the soil) and its uptake. Sometimes the effect of supply of one element on uptake of others is also assessed. This can often lead to problems in interpretation because, for example, increased supply of one element may result in an increase in growth rate. Greater growth will usually increase absolute rates of uptake of all nutrients, but can reduce concentrations in plant tissues of those not in abundant supply.

Other problems in interpretation can be caused by experimental conditions not being representative of the range of temporal and spatial variations found in the field. There may also be errors in estimation of components of biomass, especially those belowground, which can result in unreliable estimates of rates of uptake. This problem increases with plant size, and because measurement errors are smaller in proportion to fluxes, they may decrease as the period between successive measurements increases.

When interpretation is based on measurements of nutrient concentrations in plant tissues, use of several labeled elements in a single study may overcome some difficulties in estimating both uptake and interactions between the supply and uptake of different elements. However, estimation of the belowground component is still difficult. This can be overcome by considering accumulation and fluxes in only one or more aboveground organs, but in this case nutrient storage and changes in nutrient concentrations of belowground tissues are ignored. It is, nevertheless, a practical compromise, best supported where possible (e.g., in monocultures) by uptake determined from fluxes in the soil.

The operationally simplest technique in the field that does not necessitate destructive sampling of plants is to determine nutrient fluxes and pools in the soil (e.g., Smethurst and Nambiar, 1989). Such techniques are subject to several possible sources of error (e.g., Smethurst and Nambiar, 1989), but often provide a desirable combination of a good index of uptake and minimal disturbance to the system.

III Fundamentals

A Foliar Acquisition

Thorough reviews of the topic have been published by Kannan (1986), Raven (1988), Riederer (1989), and Schönherr and Riederer (1989). Here we provide a short overview of fundamental mechanisms that determine rates of water and nutrient uptake by conifer shoots and canopies.

The canopy of conifers may take up water and nutrients by mass flow (Katz ., 1989a; Riederer, 1989) and by diffusion, but will lose these resources only by diffusion. Diffusion of elements and water in a gaseous form occurs mostly through stomata, whereas diffusion in an aqueous phase occurs only through the cuticle (Riederer, 1989). Under certain circumstances, mass flow of water and nutrients may contribute temporarily significant amounts of water and, to a lesser degree, nutrients. However, it is diffusion of water and nutrients that dominate the rates of nutrient and water uptake or loss.

Depending on the species, either stomatous or astomatous surfaces may be more permeable to aqueous-phase diffusion (Kannan, 1969). It may be expected that stomatous surfaces would be more permeable to this flux because cuticles over cells in the substomatal cavity are thinner (Kannan, 1986). However, due to the geometry and the hydrophobic nature of stomatal surfaces, naturally occurring aqueous solutions cannot penetrate stomatal pores (Schönherr and Bukovac, 1972). Thus, an aqueous continuum does not develop from the surface of a leaf to its interior, so a flow of solution through the pores is not possible (Riederer, 1989). Entry of aqueous solutions is, therefore, only through the cuticular wax and cuticle on a leaf’s external surface. These present the main, almost exclusive, barrier to transport of solutes into leaves (Schönherr, 1976; Schönherr and Bukovac, 1970).

In leaves (and probably in expanding twigs), cuticular permeability to water and nutrients is high during periods of expansion, and declines rapidly thereafter. Completion of the cuticle (Lange and Schulze, 1966) and of an epicuticular wax layer (Schönherr and Riederer, 1989) after full expansion may be the cause for this increased resistance. However, damage to leaf cuticles, and rearrangement of cuticular wax caused by wind, can subsequently increase the permeability of leaf surfaces (Grace, 1988; Grace and Russell, 1977). This damage often increases with the age of mature leaves, and this will cause permeability to increase with leaf age after maturity. Leaf cuticles have a permeability coefficient of ~106 mg1, although this varies with humidity: water sorption by cuticles of increased with atmospheric humidity (Chamel ., 1992). Permeability to water and nutrients of the cuticle is high relative to that of epicuticular wax, which is ~300 to 500 times less permeable to water compared to the cuticle (Schönherr, 1976). The permeability of a cuticle may depend on the presence in it of a large pectin fraction of high shrink-swell properties at dehydration-hydration states (Kannan, 1986). Cuticle permeability to ions...