Aluminum (Al) toxicity has been studied since it was first identified as a major limiting factor of crop productivity grown in acid soils (Hartwell and Pember, 1918).

Quick Tip

Most plants are sensitive to soil Al concentrations, even in micromolars.

Approximately 40 percent of arable land in the world is acidic (Kochian et al., 2004), including Southern and transitional zones of the United States where warm-season turfgrasses are grown. Aluminum toxicity is closely associated with low soil pH (under 5.0), where such soils release Al for uptake and therefore adversely affect plant growth. Generally, all soils contain about 8 percent Al by weight and become toxic only when the soil pH is lower than 5.0.

At low soil pH, soil Al becomes soluble being available for plant uptake. When soil pH is close to neutral or above, soil Al is precipitated and not available for plant uptake. Therefore, raising soil pH by liming is an efficient way to reduce Al toxicity in acid soils.

However, liming agents move slowly through the soil profile, and repeat applications add costs for agricultural production. Also, excessive lime applications may cause a new nutrient imbalance, such as potassium (K) deficiency (Foy et al., 1978).

Photograph 1. Shoot mass decline of TifEagle bermudagrass in response to 240, 480 and 720 millimeters of aluminum.

When exposed to Al, plant growth is negatively affected because Al inhibits plant root tip cell division and cell elongation (Clarkson, 1965). In addition, plants grown in acidic soils experience nutrient imbalances and deficiencies (phosphorus [P], potassium [K], calcium [Ca] and magnesium [Mg]), reduced root and shoot growth (Photograph 1) and reduced stress tolerance (Marschner, 1991).

The effects of Al toxicity on nutrient uptake, especially P and Ca, for cool-season turfgrasses and wheat cultivars have been reported (Foy and Murray, 1998b). In addition, genetic differences in Al tolerance of cool-season turfgrasses have been reported (Liu et al., 1995; Foy and Murray, 1998a).

Research on warm-season turfgrass Al tolerance is limited. However, Liu (2005) reported differences in seeded bermudagrass cultivars to Al tolerance, and Wu et al. (1981) reported different Al tolerances of four vegetative-propagated bermudagrass cultivars. Therefore, the objectives of this study were to determine if genetic differences in Al tolerance existed among selected warm-season turfgrasses and how nutrient concentrations in root and shoot tissue were affected when exposed to micromolar Al concentrations.

Low to moderate Al exposure

Study I consisted of three Al treatments (240 μm, 480 micrometers [μm] and 720 μm) at pH of 4.0 with two controls (0 μm of Al) at pH 4.0 and 6.5 for six weeks under greenhouse conditions.

Table 1.

Treatments were arranged in a randomized complete block design with three replications. Pot dimensions were 15 centimeters (cm) (6 inches) in diameter and 12 cm (4.8 inches) in height with eight holes (0.40 inches) at the bottom to allow for drainage. For each turf species selected (Table 1), 30 single meristem shoots from 2-year old well-rooted turf were planted in 100 percent sand obtained from Golf Agronomics, with roots and shoots clipped to ensure similar length.