The unexpected versatility of plants: organic nitrogen use and availability in terrestrial ecosystems

Abstract

The recently recognized importance of organic nitrogen (ON), particularly amino acids, to plant nutrition in many types of agricultural and natural ecosystems has raised questions about plant-microbe interactions, N availability in soils, and the ecological implications of ON use by plants in the light of climate change and N pollution. In this review we synthesize the recent work on availability and plant uptake of amino acids with classic work on ON in soils. We also discuss recent work on the use of natural abundance levels of (15)N to infer N sources for plants. Reliance on ON is widespread among plants from many ecosystems. Authors have reached this conclusion based on laboratory studies of amino acid uptake by plants in pure culture, amino acid concentrations in soils, plant uptake of isotopically labeled amino acids in the field and in plant-soil microcosms, and from plant natural abundance values of (15)N. The supply of amino acids to plants is determined mainly by the action of soil proteolytic enzymes, interactions between amino acids and the soil matrix, and competition between plants and microbes. Plants generally compete for a minor fraction of the total amino acid flux, but in some cases this forms a significant N resource, especially in ecosystems where microbial biomass undergoes large seasonal fluctuations and contributes labile ON to the soil. A quantitative understanding of ON use by plants is confounded by incomplete data on partitioning of ON between plants, mycorrhizal fungi, and competing soil microbes. Further research is needed to predict the ecological implications of ON use by plants given the influence of climatic change and N pollution.

Quantifying the production of dissolved organic nitrogen in headwater streams using 15N tracer additions

“…In soils, extracellular proteases are thought to be responsible for much of the production of labile DON (e.g., amino acids; Schimel and Bennett 2004). Proteolysis of soil proteins and peptides is usually higher than net mineralization and can be a large source of free amino acids (Lipson and Nä sholm 2001). If stream microbes are behaving similarly to their terrestrial counterparts, streams with high ER may also have high protease activity, resulting in high in-stream DON production.…”

Significance of organic nitrogen acquisition for dominant plant species in an alpine meadow on the Tibet plateau, China

“…Letters indicate significant differences at 0.05 error probability level Kuzyakov and Jones 2006), although this may only introduce a small error. Second, we have to consider respiratory losses of C taken up by plant roots in the form of amino acids (Schimel and Chapin 1996;Lipson and Nä sholm 2001). We assumed that the maximal respiratory loss of the 14 C taken up by plants was 15% (Kuzyakov et al 2001;Kuzyakov and Jones 2006).…”

Effectiveness of a Natural Headwater Wetland for Reducing Agricultural Nitrogen Loads

“…The other process that can lead to a decrease in the DON concentration is the uptake of DON by plants. The uptake of organic N has been found to be widespread across different ecosystems and to consist of an important source of N, in particular in ecosystems where microbial biomass is prone to large seasonal fluctuations and contributes to the release of labile organic N [55,61].…”