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.
Highlights
Crassulacean acid metabolism (CAM) is characterized by nocturnal CO2 assimilation by phosphoenolpyruvate carboxylase (PEPC) and nocturnal organic acid accumulation, mainly malate, into the vacuole
Several studies performed on CAM plants have shown the importance of nutrient availability, mostly nitrogen, on CAM expression
Nitrogen deficiency was proven to be an important abiotic condition to increase the magnitude of CAM in Guzmania monostachia, a facultative CAM species, and several obligate CAM Kalanchoë spp
Summary
Crassulacean acid metabolism (CAM) is characterized by nocturnal CO2 assimilation by phosphoenolpyruvate carboxylase (PEPC) and nocturnal organic acid accumulation, mainly malate, into the vacuole. The diurnal“CO2 pump” from C4 acid decarboxylation favors the carboxylase instead of the oxygenase activity of RUBISCO, which reduces photorespiration and increases the efficiency of photosynthesis in CAM plants [4,5]. Obligate CAM plants mainly perform CAM independent of proximate environmental conditions [9,10]. Facultative CAM species perform C3 photosynthesis under nonstressful environmental conditions, whereas under stressful conditions such as elevated atmospheric CO2 concentrations, salinity, water deficit, nutrient availability, light, and temperature regimes, they switch to CAM [11,12,13,14,15]. Due to the lack of information regarding the relationship between mineral nutrients and CAM, we discuss how nutrients can modulate the CAM pathway, which mineral nutrients seem to be more important for increasing or decreasing CAM expression, the metabolic costs and benefits of inorganic and organic sources of nitrogen, which is the most limiting macronutrient for plant growth, and how this nutrient is related to the performance of CAM
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