Soil-specific response functions of organic matter mineralization to the availability of labile carbon.

Soil organic matter (SOM) mineralization processes are central to the functioning of soils in relation to feedbacks with atmospheric CO2 concentration, to sustainable nutrient supply, to structural stability and in supporting biodiversity. Recognition that labile C-inputs to soil (e.g.

Rhizodeposition shapes rhizosphere microbial community structure in organic soil.

The aims of the study were to determine group specificity in microbial utilization of root-exudate compounds and whole rhizodeposition; quantify the proportions of carbon acquired by microbial groups from soil organic matter and rhizodeposition, respectively; and assess the importance of root-derived C as a driver of soil microbial community structure. Additions of 13C-labelled root-exudate compounds to organic soil and steady-state labelling of Lolium perenne, coupled to compound-specific isotope ratio mass spectrometry, were used to quantify group-specific microbial utilization of rhizodeposition. Microbial utilization of glucose and fumaric acid was widespread through the microbial community, but glycine was utilized by a narrower range of populations, as indicated by the enrichment of phospholipid fatty acid (PLFA) analysis fractions.

Root exudation from Hordeum vulgare in response to localized nitrate supply.

Root proliferation as a response to exploit zones of nutrient enrichment in soil has been demonstrated for a wide range of plant species. However, the effectiveness of this as a strategy to acquire nutrients is also dependent on interactions with the soil microbial community. Specifically, C-flow from roots modifies microbial activity and probably the balance between nutrient mineralization and immobilization processes in the rhizosphere.

Contribution of current carbon assimilation in supplying root exudates of Lolium perenne measured using steady-state C labelling.

Coupling growth of Lolium perenne L. in sterile solution culture with steady-state (13)CO(2) labelling allowed quantification of the contribution of C, assimilated either before or after a specific time point, both to plant compartments and root exudates. Plants were grown for 27 days in atmospheres containing CO(2) with delta(13)C signatures of either -13.

Reduced atmospheric CO2 inhibits nitrogen mobilization in Festuca rubra.

In defoliated grasses, where photosynthesis is reduced due to removal of leaf material, it is well established that remobilization of nitrogen occurs from both older remaining leaves and roots towards the younger growing leaves. In contrast, little is known about the movement of nitrogen within intact grass plants experiencing prolonged inhibition of photosynthesis. We tested the following hypotheses in Festuca rubra L.