Plant diversity and overyielding: insights from belowground facilitation of intercropping in agriculture

Abstract

SummaryDespite increasing evidence that plant diversity in experimental systems may enhance ecosystem productivity, the mechanisms causing this overyielding remain debated. Here, we review studies of overyielding observed in agricultural intercropping systems, and show that a potentially important mechanism underlying such facilitation is the ability of some crop species to chemically mobilize otherwise-unavailable forms of one or more limiting soil nutrients such as phosphorus (P) and micronutrients (iron (Fe), zinc (Zn) and manganese (Mn)). Phosphorus-mobilizing crop species improve P nutrition for themselves and neighboring non-P-mobilizing species by releasing acid phosphatases, protons and/or carboxylates into the rhizosphere which increases the concentration of soluble inorganic P in soil. Similarly, on calcareous soils with a very low availability of Fe and Zn, Fe-and Zn-mobilizing species, such as graminaceous monocotyledonous and cluster-rooted species, benefit themselves, and also reduce Fe or Zn deficiency in neighboring species, by releasing chelating substances. Based on this review, we hypothesize that mobilization-based facilitative interactions may be an unsuspected, but potentially important mechanism enhancing productivity in both natural ecosystems and biodiversity experiments. We discuss cases in which nutrient mobilization might be occurring in natural ecosystems, and suggest that the nutrient mobilization hypothesis merits formal testing in natural ecosystems.

Genetic diversity affects ecological performance and stress response of marine diatom populations

“…Overyielding may also emerge because of facilitation, where diatom-associated bacteria that are genotype specific may chemically mobilize otherwise unavailable forms of micronutrients. This has not been shown in diatom-bacteria studies, but similar mechanisms are known from terrestrial plant systems (Li et al, 2014). Alternatively, the 'portfolio effect' involving a suite of species (suite of genotypes in our case) that exhibit differential responses to environmental perturbations creates stability that preserves the integrity of a physiological trait (Tilman, 1999(Tilman, , 2006.…”

Crop acquisition of phosphorus, iron and zinc from soil in cereal/legume intercropping systems: a critical review

“…This can occur directly through positive mechanisms, e.g. the amelioration of harsh environmental conditions, including favourable alteration of light, temperature and soil moisture, and increased availability of limiting soil nutrients (Sekiya et al, 2011;L. Li et al, 2014).…”

Underutilized Crops and Intercrops in Crop Rotation as Factors for Increasing Biodiversity on Fields

“…In case of phosphorus-mobilizing, crop species improve P nutrition for themselves and neighbouring non-P-mobilizing species by releasing acid phosphatases, protons and/or carboxylates into the rhizosphere which increases the concentration of soluble inorganic P in soil. Similarly, on calcareous soils with a very low availability of Fe and Zn, Fe-and Znmobilizing species, such as graminaceous monocotyledonous and cluster-rooted species, benefit themselves, and also reduce Fe or Zn deficiency in neighbouring species, by releasing chelating substances [31].…”