Metabolic Self-regulation of Pisum sativumL. Under Varying Soil Fertility in South Africa

Legumes have been used to improve soil fertility however, most legume research focuses on crop and not forage legumes. Forage legumes, including Pisum sativumL., increase the nutritional value in pastures and provide high amounts of soil protein and minerals required for plant growth. We investigated the effects of varying soil composition on plant growth, symbiosis establishment, and nutrient acquisition. We also aimed to compare phenolic compound production, since phenolics are reported to play a vital role in plant defense, pollination/dispersal, and symbiosis with quorum-sensing plant growth-promoting bacteria. Using quantitative techniques, we evaluated the effect of nutrient deficiency in plant–microbe symbiosis, nutrition, and carbon costs, as well as the phenolic concentrations in P. sativum. Four distinct regional soils in KwaZulu-Natal (KZN), geographically covering grassland and savannah ecosystems, were used as growth substrates. Plants maintained their root dry weights and growth rates across the four soil types. Low pH, total cations, and high exchange acidity in Bergville soil resulted in decreased total plant dry weights. P. sativumgrown in Izingolweni soils relied more on atmospheric N fixed by endophytic/associative bacteria from the genera Cupriavidus, Paenibacillus, Cohnella,and Bacillus, while those grown in Hluhluwe soils relied on soil N. Plant associative microbes might modulate nutrient availability for plant uptake in nutrient poor grassland and savannah ecosystems. P. sativumacclimatized to changes in soil nutrient concentrations and pH in the studied ecosystems by changing N source preferences and phenolic concentrations. The acclimatization of plants is likely modulated by the presence of rhizospheric microorganisms interacting with the plants.