The influence of flower removal on tuber yield and biomass characteristics of Helianthus tuberosus L. in a semi-arid area

Highlights

• Effects of removal of flowers on total biomass and tuber yield were investigated.

• Tuber yield was highest when all flowers were removed.

• Total biomass was highest when 50 % of the flowers were removed.

• Calorific value of stems was highest when 25 % of the flowers were removed.

Abstract

Jerusalem artichoke (Helianthus tuberosus L.) is an important source of biomass for biofuels production. To evaluate its potential as a feedstock for biofuel, calorific value, ash, and carbon (C) and nitrogen (N) contents were investigated under different flower removal treatments during 2015–2016 in the Inner Mongolia autonomous region of China. Total biomass of flower removal treatments was significantly (P < 0.05) higher than that of the control, and the highest value was obtained when 50 % of the flowers were removed (735 g plant⁻¹). Tuber biomass increasing gradually as the proportion of flowers removed increased. The highest value of tuber biomass was obtained when 100 % flowers were removed (228 g plant⁻¹). Tuber yield of the 33 % and 50 % flower removal treatments was significantly higher than that of the 25 % flower removal treatment and control. The caloric value and N and C contents of tuber was improved while ash content of tuber was decreased with flower removal, compared to no flower removed. Total energy was the highest with removal of 50 % of the flowers 19,041 J plant⁻¹). In contrast, the highest value of aboveground energy yield occurred with removal of 25 % of the flowers (7076 J plant⁻¹), while underground energy yield was greatest with removal of 100 % of the flowers (4058 J plant⁻¹). Removing 100 % flowers is an effective method to increase tuber yield and quality of Jerusalem artichoke in a semi-arid environment.

Introduction

With the decrease of fossil fuel reserves, the contradiction between fossil fuel reserves and consumption becomes increasingly acute and demand for biomass energy becomes more urgent (Gunnarsson et al., 2014). At the same time, the development and utilization of biomass energy is conducive to reducing greenhouse gas emissions and improving the environment (Clark and Munn, 1986). Jerusalem artichoke (Helianthus tuberosus L.), which is composed of root, leaf, stem, tuber, and flower components, originated from North America and is one of the few crops that was introduced from North America to Europe and Asia (Dias et al., 2016). Tubers contain a high concentration of inulin, a fructose polymer that decomposes to fructose by exo-inulinase, and which can be fermented to produce ethanol with a conversion rate of 83–99 % (Panchev et al., 2011; Gunnarsson et al., 2014). Jerusalem artichoke has high ecological adaptability and can tolerate drought, cold, saline, and alkali soil conditions (Bergh et al., 2003). It has been planted in conditions where it is difficult to cultivate other crops. Therefore, the cultivation of Jerusalem artichoke is conducive to making full use of land resources, improving the economic benefits of land resources, and reducing the pressure on land caused by increased human population (Denoroy, 1996).

Methods to increase tuber yield of Jerusalem artichoke has become a popular research topic, and a large number of experiments have evaluated factors such as planting density, water and fertilizer management, and variety selection (Monti et al., 2008; Nashaar et al., 2009; Obernberger et al., 1997). In addition to genetic, environmental, and management factors, plant biological yield is also closely related to the growth and development of plants and distribution of photoassimilates among plant organs. Growth and development of Jerusalem artichoke includes a vegetative growth stage and a reproductive growth stage (Denoroy, 1996). The vegetative growth stage mainly involves the growth and development of the root, stem, leaf, and other vegetative organs. The leaves convert light energy into chemical energy in the form of carbohydrates through photosynthesis and the carbohydrates are redistributed around the plant and stored in the different organs (Nardini and Luglio, 2014). The reproductive growth stage mainly involves the flower and tuber growth, while root, stem, and leaf growth are stagnant (Gao et al., 2016). The reproductive growth stage involves the redistribution of the substances stored in the vegetative growth stage (Monti et al., 2008; Nashaar et al., 2009; Obernberger et al., 1997). Important evaluation criteria in biomass energy supply selection and quality evaluation include calorific value, and the contents of ash, carbon (C) and nitrogen (N) (Gao et al., 2016). The calorific value refers to the combustion heat of the specific dry mass, and it is considered a main index when biomass is transformed into equivalent energy (Soja and Haunold, 1991). Ash content has an important impact on the heat production of raw materials. Previous studies have shown that for every 1% increase in ash content, the calorific value of a raw material decreases by about 0.2 MJ/kg (Cassida et al., 2005). The conversion process from biomass raw materials to biofuels requires a series of thermochemical reactions. The mineral elements contained in ash, especially the alkali metals, produce a large amount of waste residue and a large amount of corrosive substances under the condition of high temperature combustion, leading to the decline of bioenergy material conversion rate (Cassida et al., 2005). A large amount of corrosive substances can cause damage to conversion equipment, thus increasing the conversion cost (Heuvelink, 1996; Marcelis, 1996; Guo et al., 2002; Cassida et al., 2005). Carbon and N are the main combustion substances in plants, and their content is positively correlated with calorific value (Gao et al., 2012).

Flowers are the main organs of plants, which have important effects on dry matter and sugar accumulation and their distribution profiles, quality of fruit, and changes of endogenous hormones (Jiao et al., 1998; Wang et al., 2004; Li et al., 2014). For Jerusalem artichoke, flower and tuber formed simultaneously during the growth of Jerusalem artichoke, and the influencing substances accumulated in the early stage were transported to tubers and flowers respectively (Denoroy, 1996). Therefore, in this experiment, the biomass, calorific value, and contents of ash, C, and N of different organs from Jerusalem artichoke were compared under different conditions of flower removal. The aim of this study was to test the hypothesis that flower removal could influence distribution of carbohydrates to tubers, so as to increase the yield of tubers, and to provide reference for high yield cultivation and utilization potential of Jerusalem artichoke.