Biogeosciences, 15, 2991–3002, 2018 https://doi.org/10.5194/bg-15-2991-2018 © Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 License. Calcium content and high calcium adaptation of plants in karst areas of southwestern Hunan, China Xiaocong Wei1, Xiangwen Deng1,2, Wenhua Xiang1,2, Pifeng Lei1,2, Shuai Ouyang1,2, Hongfang Wen1, and Liang Chen1,2 1Faculty of Life Science and Technology, Central South University of Forestry and Technology, Changsha 410004, Hunan Province, China 2Huitong National Field Station for Scientific Observation and Research of Chinese Fir Plantation Ecosystem in Hunan Province, Huitong 438107, China Correspondence: Xiangwen Deng ([email protected]) Received: 26 September 2017 – Discussion started: 23 November 2017 Revised: 22 April 2018 – Accepted: 25 April 2018 – Published: 17 May 2018 Abstract. Rocky desertification is a major ecological prob- tween the aboveground and belowground parts of the 17 lem of land degradation in karst areas. In these areas, the dominant species were calculated, and their correlations with high soil calcium (Ca) content has become an important envi- soil ECa content were analyzed. The results showed that ronmental factor that can affect the restoration of vegetation. these 17 species can be divided into three categories: Ca- Consequently, the screening of plant species that can adapt indifferent plants, high-Ca plants, and low-Ca plants. These to high Ca soil environments is a critical step in vegetation findings provide a vital theoretical basis and practical guide restoration. In this study, three grades of rocky desertifica- for vegetation restoration and ecosystem reconstruction in tion sample areas were selected in karst areas of southwest- rocky desertification areas. ern Hunan, China (LRD: light rocky desertification; MRD: moderate rocky desertification; and IRD: intense rocky de- sertification). Each grade of these sample areas had three sample plots in different slope positions, each of which had 1 Introduction four small quadrats (one in rocky-side areas, three in non- rocky-side areas). We measured the Ca content of leaves, Karst is a calcium-rich environment and a unique ecologi- branches, and roots from 41 plant species, as well as soil cal system. This type of ecosystem is widely distributed, ac- total Ca (TCa) and exchangeable Ca (ECa) at depths of 0– counting for 12 % of the world’s total land area (Zeng et al., 15, 15–30, and 30–45 cm in each small quadrat. The re- 2007; Zhou et al., 2009; Luo et al., 2012). Karst landforms in sults showed that the soil Ca2C content in rocky-side areas China are mainly distributed in southwestern areas. The Hu- was significantly higher than that in non-rocky-side areas nan Province of China has been ranked fourth in the severity (p < 0:05). The mean soil TCa and ECa content increased degree of rocky desertification (Li et al., 2016). Rocky de- gradually along with the grade of rocky desertification, in sertification could lead to frequent natural disasters, reduce the order IRD > MRD > LRD. For all plant functional groups, human survival and development space, threaten local peo- the plant Ca content of aboveground parts was significantly ple’s production, life and life safety, cause ecological deteri- higher than that of the belowground parts (p < 0:05). The oration, reduce arable land resources, aggravate poverty, and soil ECa content had significant effects on plant Ca content affect sustainable economic and social development (Jing et of the belowground parts but had no significant effects on al., 2016). In other words, rocky desertification is an extreme plant Ca content of the aboveground parts. Of the 41 plant form of land degradation in karst areas, and has become a species that were sampled, 17 were found to be dominant major social problem in terms of China’s economic and so- (important value > 1). The differences in Ca2C content be- cial development (Sheng et al., 2015). Soil with high cal- cium (Ca) content in rock desertification areas has become Published by Copernicus Publications on behalf of the European Geosciences Union. 2992 X. Wei et al.: Calcium content and high calcium adaptation one of the most important environmental factors affecting transport of Ca2C (Musetti and Favali, 2003). In addition, the local plant physiological characteristics and distribution Ca oxalate crystals in the plant cells play a role in regulat- in these areas (Ji et al., 2009). Given the origin of rocky de- ing plant Ca content (Ilarslan et al., 2001; Pennisi and Mc- sertification, the main factors that lead to rocky desertifica- Connell, 2001; Volk et al., 2002), and some plants will form tion stem from unreasonable human activities. For example, Ca oxalate crystal cells in order to fix excess Ca2C (Moore et the cultivation of crops on steep slopes can cause vegetation al., 2002). Furthermore, an active Ca efflux system plays an destruction, soil erosion, and then rocky desertification. We important role in the adaptation of plants to high-Ca environ- should therefore focus on vegetation restoration for rocky de- ments (Bose et al., 2011). For example, when leaves mature, sertification remediation (Wang et al., 2004). Consequently, excess Ca2C in plants is excreted via stomata on the back the screening of plant species that can grow successfully in of the leaves, thereby maintaining a lower concentration of high-Ca environments in rocky desertification areas is an ex- leaf Ca (Musetti and Favali, 2003). The regulation of inter- tremely critical step. nal Ca storage depends predominantly on plasma membrane Role of Ca2C in plant physiology: over recent decades, Ca transport and intracellular Ca storage; collectively these progress has been made in identifying the cellular compart- processes can regulate the intracellular Ca2C concentration ments (e.g., endoplasmic reticulum, chloroplasts and mito- to a lower level (Bowler and Fluhr, 2000). Plants that adapt chondria) that regulate Ca balance and signal transduction to high-Ca environments promote excess Ca2C flow through in plants (Müller et al., 2015). Ca2C is an essential nutri- the cytoplasm or store Ca2C in vacuoles via the cytoplasmic ent for plant growth and also participates in signal trans- Ca2C outflow and influx system (Shang et al., 2003; Hether- duction (Poovaiah and Reddy, 1993; Hepler, 2005; Hong-Bo ington and Brownlee, 2004; Wang et al., 2006). This system and Ming, 2008; Batisticˇ and Kudla, 2012). Ca2C is also a consists of Ca2C channels, Ca2C pump and Ca2C = HC re- very important signal component in plants responsive to en- verse conveyor on tonoplast; the former controls Ca2C out- vironmental stresses. The Ca2C signal takes the influential flow, and the latter two pump cytoplasmic Ca2C into vacuole role as a second messenger in hormone signal transduction, (Wu, 2008). Cytoplasmic Ca2C is mainly combined with pro- particularly in the abscisic acid signal transduction process teins and other macromolecules. The concentration of free (Hetherington et al, 2004). Plants can therefore adapt to high Ca2C is generally only 20–200 nmol L−1 and is stored in cell salt, drought and high temperature environments by activat- gaps and organelles such as vacuoles, endoplasmic reticu- ing the Ca2C signal transduction pathway (Bressan et al., lum, mitochondria, and chloroplasts (Wu, 2008). However, 1998). Ca2C is also involved in nutrient cycling coupling pro- excess free Ca2C in the cytoplasm combines with phosphate cess, for example, in the absence of nutrients (such as phos- to form a precipitate, which interferes with the physiolog- phorus), plants will inhibit the activity of nitrate reductase, ical processes associated with the phosphorus metabolism, thereby inhibiting the absorption of nitrate nitrogen, and ul- thus hindering normal signal transduction and causing signif- timately inhibiting the absorption of Ca2C (Reuveni et al., icant detriment to plant growth (White and Broadley, 2003; 2000). Calcium ions combine with pectin in the cell walls of Hirschi, 2004). plants to form pectin Ca, which is a vital component of the in- Variation of Ca2C content in species and soil: The concen- tercellular layer in cell walls, and can buffer the compression tration of free Ca2C in vacuoles varies with plant species, between cells without hindering the expansion of cell surface cell type, and environment, which may also affect the re- area (Kinzel, 1989). Ca also has the function of maintaining lease of Ca2C in vacuoles (Peiter, 2011). Some species main- the structure and function of cell membranes, regulating the tain low calcium content in their aboveground portion by activity of biological enzymes, and maintaining the anion– reducing calcium uptake and transporting it from under- cation balance in vacuoles (Marschner, 2011). ground parts to aboveground parts. Examples of these types Mechanisms of plant defense to high soil Ca2C concentra- of plants are Nephrolepis auriculata, Parathelypteris glan- tions: Ca2C is an essential macronutrient, but low Ca2C con- duligera, Cyrtomium fortunei, Pteris vittata, and so on. In centrations must be maintained within the plant cytoplasm contrast, other plants have a higher demand for calcium, to avoid toxicity (Larkindale and Knight, 2002; Borer et al., for example, Cayratia japonica and Corchoropsis tomentosa 2012). The plant cell not only rapidly increases the free Ca2C maintain high calcium content by enhancing calcium up- concentration of the cytoplasm to adapt to environmental take and transporting it from underground sections to above- changes, but also maintains a low Ca concentration to pre- ground sections (Ji et al., 2009). Zhang (2005) studied the vent harm caused by high Ca. This fine regulatory mech- growth conditions of Eurycorymbus cavaleriei and Rhodo- anism is mainly achieved by Ca2C channels (Shang et al., dendron decorum under different concentrations of Ca2C 2003; Hetherington and Brownlee, 2004; Wang et al., 2005). and found that a high Ca2C concentration (50 mmol L−1/ The vacuoles may account for 95 % of the plant cell vol- could promote growth in Eurycorymbus cavaleriei but in- ume and are able to store Ca2C within the cell.