Experimental Ecophysiology and Biochemistry of Trees and Shrubs

Humberto González Rodríguez, Ratikanta Maiti, Ch. Aruna Kumari

• Publisher: Apple Academic Press
• Year: 2020
• ISBN:
  9781000449006
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Science General
• Index: Biological Sciences

The existence and competition of trees and shrubs to sustain and put forth growth under varied environmental conditions is dependent on the interactions that occur between the plant metabolic processes and the prevailing environmental conditions. In order to understand the productivity of trees and shrubs, it is a prerequisite to know the experimental techniques of these vital processes. This volume provides a comprehensive presentation of this topic.

The first part of this book deals with various aspects of experimental ecophysiology and recent research results of studies on plant pigments, epicuticular wax, leaf nutrients, carbon fixation, all supported by literature. The second part of the volume describes various laboratory techniques such as diffusion, imbibition, calorimetry, atomic absorption, mineral nutrition, nutrition analysis of forage, litterfall chemistry, nutrient cycle, etc. The third and fourth parts deal with advances in the techniques in the development of ecophysiology.

The book will serve as an important handbook and resource for students, faculty and teachers, technicians, and researchers and scientists involved in forest science dealing with ecophysiology and biochemistry of woody and crop plants.

PART I
EXPERIMENTAL ECOPHYSIOLOGY AND BIOCHEMISTRY

INTRODUCTION

The experimental ecophysiology and biochemistry mention only the up to date research advances of a few aspects of experimental ecophysiology, conclusion, and research needs in Part I, while it discusses the techniques in detail in Part II. Each aspect is stated in the following sequence viz., introduction including literature surveys, methodology, recent results and conclusion, research needs, and references.

The research studies included in this part were undertaken at the experimental station of the Facultad de Ciencias Forestales, Universidad Autonoma de Nuevo Leon, located in the municipality of Linares (24°47´N; 99°32´W), at an elevation of 350 masl. The climate at this locality is mostly subtropical or semiarid. The summers are warm, where the mean monthly air temperature shows a large variation of 14.7°C in January to 23°C in August. Often, the temperatures may go up to 45°C in summer. The average annual precipitation of this area is around 805 mm and it mostly exhibits the bimodal type of rainfall distribution. The Tamaulipan thornscrub or woodlands are major vegetation types in the area (Gonzấlez-Rodríguez et al., 2011). Prevailing soils are deep, dark-gray, lime-gray, lime-clay vertisols, rich in montmorillonite, which shrinks and swells noticeably in response to changes in soil water content (INEGI, 2002). For physiology details please refer ‘Plant Physiology’ by Taiz and Zeiger (2002).

The techniques used and results obtained are discussed briefly in the following chapters.

CHAPTER 1

Leaf Pigments

1.1 INTRODUCTION

Plants have different types of pigments that perform a significant role in the photochemical reactions, plant metabolism, and in the physiological performance of plants. The chlorophyll pigments (a, b) of chloroplasts play a most important role in the capture of light energy via the photochemical process of photosynthesis leading to the synthesis of the carbohydrate, i.e., converting light energy into the chemical energy (Taiz and Zeiger, 2002).

Apart from chlorophyll pigments, plants also possess pigments like carotenoids, xanthophylls; flavonoids, etc., involved in the protection of chlorophyll pigments from photooxidation, imparts colors to flowers and fruits, act as antioxidants, and take part in the other plant metabolic processes. Each leaf pigment has varied structural characteristics, the contents of which act as indices of protection against the environmental conditions that the plants come across during the course of their growth and development. It is well known that both chlorophyll pigments and carotenoids play a major role in the higher plant photosynthetic processes.

Carotenoids are the naturally occurring fat-soluble pigments found in algae, plants, and also in some of the photosynthetic bacteria, also playing a role in the photosynthetic process. Further, in some non-photosynthetic bacteria, these pigments are found to have a protective role against the damage by light and oxygen (Biswel, 1995; Gitelson et al., 1999). Carotenoids are also known to occur in animals, though animals lack the ability to synthesize them, they obtain and include carotenoids from their diets. These produce bright coloration, serve as antioxidants, and also function as a source of vitamin A activity in animals (Britton, 1995). Besides the above, they also play a role in plant reproduction owing to their capability to attract pollinators because of the presence of bright coloration and also assist in seed dispersal (Yeum and Russell, 2002).

Uvalle Sauceda et al. (2008) observed the presence of variations in chlorophyll a and b and carotenoids according to the seasons. These seasonal variations in these pigment contents were observed in the native shrubs of northeastern Mexico also. These variations in the contents of these pigments also exhibited remarkable variations between the years and species. The research outcomes of Uvalle Sauceda et al. (2008) have revealed the climate effect on the production of the different pigments in plants. Similarly, Castrullo et al. (2000) have studied the variations in the chlorophyll content in some members of the cultivated and wild species of family Famiaceae.

Though the earlier research studies have shown the variations in the pigments content according to the seasonal variations, these variations on other pigments were not studied in our research. Tatini et al. (2005) have studied the roles of specific xanthophylls in light utilization, particularly the role of flavonoids in the integrated mechanism of respiration and photoprotection. Similarly, Kalituho et al. (2007) studied the roles of specific xanthophylls in light utilization, in Arabidopsis thaliana at high solar radiation.

The native shrubs and trees existing in the semiarid regions of the northeastern Mexico are used as main resources of food for a broad range of ruminants and white-tailed deer (Ramirez, 1999). Apart from providing food, these are also important in the supply of high-quality fuel and timber for fencing and construction (Reid et al., 1990; Fullbright et al., 1991). Though most of the species in this region are economically important, their growth is also under the influence of the prevailing climatic conditions. The variations in the climatic conditions may bring about the difference in the production of the photosynthetic pigments. Keeping this in view, a study was undertaken in 37 native trees and shrubs of the northeastern Mexico to determine variations in leaf pigments content in summer and in the winter season.

1.2 MATERIALS AND METHODS

1.2.1 PLANT MATERIAL

Thirty-seven native plant species were randomly selected from an area of 2,500 m (50 m × 50 m) representative of the thornscrub. The area was selected from the undisturbed thornscrub plot, which is situated at the research site. Most of the plant species of the thornscrub have several uses. They are used as sources of forage for the domestic livestock and wildlife, fuelwood, charcoal, timber for construction, fences, medicine, agroforestry, and reforestation practices in disturbed sites (Reid et al., 1990).

1.2.2 TISSUE SAMPLING PROCEDURES AND DETERMINATION OF PLANT PIGMENTS

The terminal shoots with fully expanded leaves were sampled from the middle side of five plants (replicates) of each species. The sampled leaves of each species were kept in plastic bags and stored in icebox under dark conditions till the end of the sampling of leaves from all the 37 tree species. These cooled samples were then taken to the laboratory for the pigment contents analysis. The pigment contents were ascertained from these samples within 12 h after collections. For the chlorophyll a, chlorophyll b, and carotenoids content estimation, 5.0 g fresh weight of leaf tissue were extracted in 80% (v/v) aqueous acetone. The extracts were then vacuum filtered through a Whatman No.1 filter paper. Later, the pigment measurements were determined spectrophotometrically in 50 ml of plant pigment sample extract with a Perkin-Elmer UV/VIS Spectrophotometer (Model Lambda 25). Absorbances of chlorophyll a, chlorophyll b, and carotenoids extracts were determined at wavelengths of 663, 645 and 470 nm, respectively. Results are described on a fresh weight basis (mg of plant pigment per g fresh weight). Total chlorophyll (a+b), chlorophyll ratio (a to b) and chlorophyll (a+b) to carotenoids ratio were also determined. The procedure is briefly outlined in the flow diagram in Figure 1.1.

1.3 RESULTS AND CONCLUSIONS

Gonzalez-Rodriguez et al. (2017) studied chlorophyll a, chlorophyll b, and carotenoids contents of 37 species of trees and shrubs in the summer season, in Linares, Northeast of Mexico. Among the species, large variations were observed in the contents of chlorophyll (a, b, and total) and also in carotenoids.

For example, Chlorophyll a was minimum (around 0.6 mg) in Leucophyllum frutescens, Acacia berlandieri and maximum (1.8 mg) in Leucaena leucocephala, while the Chlorophyll b was minimum in Forestiera angustifolia, Acacia berlandieri, Acacia palmeri, Leucophyllum frutescens (0.1 to 0.2 mg). However, in Leucaena leucocephala a maximum of 0.4 mg of chlorophyll b was observed. Similarly, the Carotenoids con...