Giorgio Testa

Physiological responses of Arundo donax ecotypes to drought: a common garden study

Genetic analyses have suggested that the clonal reproduction of Arundo donax has resulted in low genetic diversity. However, an earlier common garden phenotyping experiment identified specimens of A. donax with contrasting biomass yields (ecotypes 6 and 20). We utilized the same well‐established stands to investigate the photosynthetic and stress physiology of the A. donax ecotypes under irrigated and drought conditions. Ecotype 6 produced the largest yields in both treatments. The A. donax ecotypes exhibited identical high leaf‐level rates of photosynthesis (PN) and stomatal conductance (Gs) in the well‐watered treatment. Soil drying induced reductions in PN and Gs, decreased use of light energy for photochemistry, impaired function of photosystem II and increased heat dissipation similarly in the two ecotypes. Levels of biologically active free‐abscisic acid (ABA) and fixed glycosylated‐ABA increased earlier in response to the onset of water deficit in ecotype 6; however, as drought progressed, the ecotypes showed similar increases in both forms of ABA. This may suggest that because of the low genetic variability in A. donax the genes responding to drought might have been activated similarly in the two ecotypes, resulting in identical physiological responses to water deficit. Despite the lack of physiological ecotypic differences that could be associated with yield, A. donax retained a high degree of PN and biomass gain under water deficit stress conditions. This may enable utilization of A. donax as a fast growing biomass crop in rain‐fed marginal lands in hot drought prone climates.

Crop Physiology in Relation to Agronomic Management Practices

This chapter describes the physiology of kenaf from seed germination and root development till the effects of water and nutrients stress on grown plants. Review on kenaf agro-physiology of experiments carried out worldwide are presented and discussed mainly at the canopy and whole-plant level with the aim to help producers to make decisions and planning of production. However, few literature reports experimental results on the physiology of this multipurpose crop especially in terms of assimilation rate and its relation with environmental and agronomic factors. Knowledge on gas exchange rate and stomatal conductance may be a key support in understanding the physiology of Kenaf in terms of water requirements, its ability of light conversion into carbonaceous molecules influencing crop production potential and, indirectly, the carbon sequestration activity. In kenaf seedling development takes place when temperatures are higher than 10 °C, supporting the idea that kenaf is a macrothermal plant and optimal sowing has to be carried out during spring-summer, depending on the area of cultivation. Kenaf is very sensitive to reduced soil water availability, however, under moderate water stress conditions the crop maintains root development while reducing final biomass yield. Recent studies from Greece and Italy showed that even though kenaf uses CO2, solar radiation, water, and nitrogen less efficiently than C4 crops its assimilation rates can reach 50–58 kg of CO2 ha−1 h−1. However, great differences in terms of net photosynthesis have been reported by various authors, which may be related to the different environmental variables and agronomic managements during field and controlled experimental environments, such as air temperature, light intensity, water supply, nutrients availability, relative humidity, wind, cultivar, plant density, and soil type. Similar results were reported in the literature regarding stomatal conductance and transpiration rates. In experiments carried out during the night, stomatal conductance and transpiration rate determined water looses probably affecting the water requirement of the crop. Kenaf could be described as opportunistic in relation to water availability, with a high rate of stomatal conductance and transpiration when soil water is available but with markedly reduced leaf conductance and transpiration rate when water is limited. Extinction coefficient for light (K L ) and nitrogen (K N ), under water limited conditions, were found to be always smaller than under irrigated conditions, as a result of irregular adjustment of leaf orientation to incident radiation particularly during midday. Vertical Specific Leaf Nitrogen (SLN) distributions were found in canopies when leaf area index (LAI) was >1.5. It was observed a strong association between SLN and PAR distributions in irrigated kenaf canopies. Due to its tropical origin, kenaf behaves as a short-day plant remaining vegetative until daylength falls below 12.9 or 12.45 h. Flowering of late-maturity cultivars is under photoperiodic control; conversely, photoperiod does not influence the flowering of early maturity cultivars. Radiation use efficiency (RUE) in kenaf is positively associated with specific leaf nitrogen. RUE decreased under water deficit and nitrogen supply. Water use efficiency (WUE) decreased as the level of irrigation increased. It was higher than other C3 crops, but lower as compared to C4 crops tested in the same environments. Information on nutrient use efficiency (NUE) for kenaf is scarce and not well quantified to date. Higher NUE values were reported for micronutrients than for macronutrients. This last characteristic needs further investigation, since improvement of NUE is an essential and challenging prerequisite for the expansion of bioenergy crop productions into less fertile soils and marginal lands.

The Importance of Perennial Grasses as a Feedstock for Bioenergy and Bioproducts

Abstract This chapter describes the increasing importance of perennial grasses as a biomass source for both energy and nonenergy applications in Europe. Special emphasis is given to the current legislation on renewable energy and concerns regarding the use of food crops for first-generation biofuel production that led to food versus fuel debates, land use change scenarios, and other environmental concerns. Perennial grasses as the “ideotype” of bioenergy crops, bioenergy chains involving perennial grasses, environmental sustainability, and future research perspectives to bring these species into cropping systems are also underlined. Perennial grasses are lignocellulosic, low-cost feedstock, able to grow in variegate environments and to thrive on marginal lands. They have been indicated as the leading candidate feedstock for the modern biobased economy to produce a number of high added-value products (i.e., biopharmaceuticals, nutrient supplements, biopolymers), biomaterials (i.e., buildings, phonic insulating, mulching and biodegradable products for gardening and animal bedding), energy carriers (advanced biofuels, heat and power), and by-products (i.e., soil organic fertilizers, green chemistry products). However, research is still needed in breeding, agronomy, postharvest logistics, and bioconversion to deliver new elite varieties to expand the European market and allow potential yield and desired biomass quality to be reached, while maximizing resources and conversion efficiencies.

Suitability of Perennial Grasses for Energy and Nonenergy Products

Abstract Perennial grasses are herbaceous, lignocellulosic plants. Their chemical composition is made up primarily of structural polysaccharides, namely, celluloses and hemicelluloses, of lignin, and of small fractions of nonstructural components, such as extractives, protein, lipids, pectin, and ash. The recalcitrance of lignocellulosic material has been recognized as one of the most important sustainability characteristics of this plant type, since it contributes to natural resistance to pests and diseases. However, the recalcitrance of the plant cell wall constrains the hydrolysis of structural carbohydrates for biochemical conversions, namely, second-generation bioethanol and anaerobic digestion. On the other hand, perennial grasses are suitable for thermochemical conversions; however, ash melting temperatures should be carefully evaluated for high-temperature processes. This chapter describes the suitability of lignocellulosic perennial grasses to thermochemical and biochemical processes for energy application and other alternative uses toward the biobased economy in Europe. The main chemical composition and factors affecting perennial grass biomass quality are discussed, and examples of the most widely used bioconversion processes involving perennial grasses are reported.