Coadaptation of Plants to Multiple Stresses in Acidic Soils

Abstract

Soil acidification is an increasing problem in agricultural production and ecological stability worldwide. An understanding of the mechanisms by which plants adapt to acidic soils would help address this problem. Poor plant growth in acidic soils results from a variety of factors, including proton toxicity; deficiencies in nitrogen, phosphorus, calcium, magnesium; and toxicities of various metals (aluminum (Al), manganese, iron). Aluminum toxicity is generally the primary limitation for plant growth in acidic soils. Although much research has focused on Al toxicity in recent decades, it is rarely the only limiting factor in acidic soils. The occurrence of Al toxicity depends on many other factors that coexist with Al in acidic soils. The interactions between Al and such factors are important determinants of Al toxicity to plants under field conditions. In this review, therefore, instead of focusing only on mechanisms of Al tolerance, we examine the effects of the interactions between Al and other limiting factors on plant adaptation to acidic soils. We summarize research on the interactions between Al and nitrogen, phosphorus, pH, and iron. Accordingly, three strategies are proposed to improve plant growth in acidic soils: a combined application of lime and nutrients, depending on the types of soils and plants; development of plant varieties tolerant to multiple stresses; and inoculation of plants with certain beneficial microbes. This review emphasizes the ability of plants to coadapt to multiple stresses in acidic soils.

Aluminum–Nitrogen Interactions in the Soil–Plant System

“…Acid soils are characterized by poor nitrification and high levels of soluble Al, while neutral to calcareous soils show high nitrification and lower levels of Al toxicity ( Zhao et al, 2014 ; Che et al, 2015 ). The two main inorganic N sources available for plant growth are NH 4 + and NO 3 - .…”

“…Since low pH increases the concentrations of soluble Al in soils, the alkalization of the rhizosphere was proposed to be an important mechanism of plant Al tolerance ( Matsumoto, 2000 ; Kochian et al, 2004 ; Ma, 2007 ). However, several studies demonstrated that H + could alleviate Al toxicity because H + competed with Al 3+ for adsorption to the root surface ( Kinraide et al, 1992 ; Godbold et al, 1995 ; Zhao et al, 2009 ; Zhao et al, 2014 ). A supply of H + also alleviated Al toxicity in bacteria ( Kinraide and Sweeney, 2003 ) and yeast ( Zhao et al, 2017 ).…”

“…Acid soils occur mainly in humid tropical and temperate areas ( von Uexküll and Mutert, 1995 ), where water and heat are generally abundant for plant growth, implying that acid soils have huge productive potential. However, plant productivity in acid soils is limited primarily by aluminum (Al) toxicity accompanied by deficiencies of some nutrients ( Zhao et al, 2014 ). The improvement of crop productivity in acid soils depends on the dual enhancement of plant Al tolerance and nutrient-use efficiency.…”

“…On the other hand, Al may directly affect the transport and metabolism of nutrients within plants. Interactions between Al and many nutrients often occur within soils and plants ( Zhao et al, 2014 ). Most reports have focused on the effects of various externally added nutrients on Al phytotoxicity ( Zhao et al, 2014 ), but the effects of Al on the uptake of these nutrients by plants and their corresponding mechanisms have received relatively little attention.…”

“…In contrast, Al reduced root N uptake and its upward translocation to shoots in sorghum and corn ( Gomes et al, 1985 ; Pintro et al, 1996 ). Aluminum promoted the growth of plants supplied with ammonium (NH 4 + ) but inhibited that of plants supplied with NO 3 - ( Zhao et al, 2014 ). Nitrogen is a metabolic element involved in the synthesis of amino acids and proteins within plants.…”