Soil moisture variations affect short‐term plant‐microbial competition for ammonium, glycine, and glutamate

Abstract

We tested whether the presence of plant roots would impair the uptake of ammonium (), glycine, and glutamate by microorganisms in a deciduous forest soil exposed to constant or variable moisture in a short-term (24-h) experiment. The uptake of 15NH4 and dual labeled amino acids by the grass Festuca gigantea L. and soil microorganisms was determined in planted and unplanted soils maintained at 60% WHC (water holding capacity) or subject to drying and rewetting. The experiment used a design by which competition was tested in soils that were primed by plant roots to the same extent in the planted and unplanted treatments. Festuca gigantea had no effect on microbial N uptake in the constant moist soil, but its presence doubled the microbial uptake in the dried and rewetted soil compared with the constant moist. The drying and rewetting reduced by half or more the uptake by F. gigantea, despite more than 60% increase in the soil concentration of . At the same time, the amino acid and -N became equally valued in the plant uptake, suggesting that plants used amino acids to compensate for the lower acquisition. Our results demonstrate the flexibility in plant-microbial use of different N sources in response to soil moisture fluctuations and emphasize the importance of including transient soil conditions in experiments on resource competition between plants and soil microorganisms. Competition between plants and microorganisms for N is demonstrated by a combination of removal of one of the potential competitors, the plant, and subsequent observations of the uptake of N in the organisms in soils that differ only in the physical presence and absence of the plant during a short assay. Those conditions are necessary to unequivocally test for competition.

Comparison of glycine uptake by pak choi in organic and conventional soil under different glycine concentrations: A pot study

“…In this study, the slopes of the regression lines for excess 13 C : 15 N in plants were less than 1. A significant loss of 13 C in the process of soil amino acid mineralization, root respiration, and root‐to‐shoot Gly transport ( Farrar , 1985; Van der Werf and Nagel , 1996; Månsson et al, 2014) might cause the relatively lower 13 C : 15 N ratio. Moreover, the rapid metabolism and loss of 13 C from a portion of absorbed Gly in the process of root‐to‐shoot Gly transport, or 15 N released through root exudation might cause the relatively lower 13 C : 15 N ratio in shoot than root tissues ( Warren , 2012).…”

“…The ability of plants to take up amino acid‐N is affected by many factors such as amino acid concentration ( Sauheitl et al, 2009), light ( Xu et al, 2008), CO 2 ( Jin and Evans , 2010), soil moisture ( Månsson et al, 2014), interspecific variation ( Weigelt et al, 2005; Andresen et al, 2008; Harrison et al, 2008; Scott and Rothstein , 2009), plant cultivar ( Reeve et al, 2008, 2009), soil fertility ( Weigelt et al, 2003), and spatiotemporal variation ( Gao et al, 2014). Land use change is among the most considerable human‐induced activities that greatly alter the soil N cycle.…”

Grazing modifies inorganic and organic nitrogen uptake by coexisting plant species in alpine grassland

“…Plant-available N includes both organic (e.g., peptides and free amino acids) and inorganic forms (i.e., NH 4 + and NO 3 − ) (Chapin et al 1993;Averill and Finzi 2011;Månsson et al 2014). Increasing numbers of studies have shown that organic N can be an important N source for plants (Jones et al 2005;Näsholm et al 2009;Warren 2014), especially in cold terrestrial ecosystems such as arctic and alpine ecosystems due to slow N mineralization rates (Jones et al 2004;Schimel and Bennett 2004;Xu et al 2006).…”

Warming decreased and grazing increased plant uptake of amino acids in an alpine meadow

“…; Geisseler and Horwath ; Mansson et al. ), and the turnover rate may be controlled by overall decomposability of soil C and N limitation to microbial growth (Melillo et al. ; Murphy et al.…”

“…; Averill and Finzi ; Geisseler and Horwath ; Mansson et al. ), and organic N uptake by plants is a significant component of terrestrial N cycle (Schimel and Bennett ). It was found that both mycorrhizal and nonmycorrhizal plants were capable of absorbing amino acid–N (AA–N) in situ in various natural and farmland ecosystems in temperate (Owen and Jones ; Harrison et al.…”