Exploring the Relationship between Crassulacean Acid Metabolism (CAM) and Mineral Nutrition with a Special Focus on Nitrogen

Abstract

Crassulacean acid metabolism (CAM) is characterized by nocturnal CO₂ uptake and concentration, reduced photorespiration, and increased water-use efficiency (WUE) when compared to C₃ and C₄ plants. Plants can perform different types of CAM and the magnitude and duration of CAM expression can change based upon several abiotic conditions, including nutrient availability. Here, we summarize the abiotic factors that are associated with an increase in CAM expression with an emphasis on the relationship between CAM photosynthesis and nutrient availability, with particular focus on nitrogen, phosphorus, potassium, and calcium. Additionally, we examine nitrogen uptake and assimilation as this macronutrient has received the greatest amount of attention in studies using CAM species. We also discuss the preference of CAM species for different organic and inorganic sources of nitrogen, including nitrate, ammonium, glutamine, and urea. Lastly, we make recommendations for future research areas to better understand the relationship between macronutrients and CAM and how their interaction might improve nutrient and water-use efficiency in order to increase the growth and yield of CAM plants, especially CAM crops that may become increasingly important as global climate change continues.

Keywords: ammonium; crassulacean acid metabolism (CAM); nitrate; nitrogen; nutrient availability; organic nitrogen sources.

Figure 1

Nocturnal organic acid accumulation in the apical portion of the leaves of Guzmania monostachia kept under water deficit or water plus nutritional deficiency (NO₃⁻ and NH₄⁺, PO₄²⁻, K, or Ca²⁺) for seven days. Data are expressed as the mean (±SE) of three replicate samples. Different capital letters indicate values that were significantly different among species using the same anion (Tukey–Kramer test; P < 0.05). Different lower-case letters indicate values that were significantly different among different carboxylate anions in the same species (Tukey–Kramer test; P < 0.05).

Figure 2

Schematic representation showing the main enzymes participating in NO₃⁻, NH₄⁺, and urea assimilation in plants. NR: nitrate reductase; NiR: nitrite reductase; GS2: glutamine synthetase 2; CPS: carbamoyl phosphate synthetase; Fd-GOGAT: glutamine oxoglutarate aminotransferase; AS: asparagine synthetase; NADH-GDH: glutamate dehydrogenase.