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1. The rhizosphere priming effect (RPE) is increasingly considered an important regulator of below-ground C and N cycling, with implications for terrestrial ecosystem feedback to global change. Even so, there is a lack of knowledge about the mechanisms underlying RPEs.2. We used novel stable isotope probing methods to investigate RPEs in an experiment with Scots pine and Norway spruce seedlings, two of the most common boreal forest species. We determined root exudation rates, RPEs on SOM decomposition and gross N mineralization, and the contribution of different microbial functional groups to the observed RPEs.3. Pine induced positive and spruce induced negative RPEs on SOM decomposition, while no RPE on gross N mineralization was observed. Negative RPEs in the spruce treatment were attributed to an opportunistic subset of the fungal community that was growing on root-derived 13 C while depleting available N, thus reducing the activity of microbial SOM decomposers. In the pine treatment, available N was likely sufficient to support the root-induced decomposition activities of fungal decomposers, resulting in positive RPEs.4. The findings suggest that RPEs, promoted by root stimulation of distinct subsets of the microbial community, can either contribute to conserving the soil C stock or to depleting it, depending on plant species and soil N availability.

Background: Leghemoglobin is an oxygen transporter and a hemoprotein found in nodule roots of nitrogen fixator plants from Leguminosae family. Leghemoglobin is produced in response to presence of bacteria belonging to Rhizobia family. Structurally, leghemoglobin is similar to hemoglobin and has a kind of heme iron structure.  Study of leghemoglobin as a heme iron containing agent can open up a new way for treatment and natural prevention of iron deficiency anemia and substitution with mineral iron salts. Methods: Five different cultivars of alfalfa plants including Esfahani, Bammi, Yazdy, Nik shahri, and Hamedani were cultivated in gardening farm of the faculty of agriculture in Shahid Chamran University in a linear form. Cultivation was done with biological fertilizer containing Sinorhizobium meliloti for test groups and without fertilizer for sham groups. After 60 days, the samples were harvested, and the amount of leghemoglobin produced in nodules was quantified using LaRue and Child fluorometric method. Results: The results from five cultivars of alfalfa planted with biological fertilizer showed a significant increase in viscosity of leghemoglobin in nodules of the test group in comparison with sham group (P<0.0001). Moreover, the high viscosity of leghemoglobin in nodules of Bammi cultivar indicated the capacity of this plant to produce leghemoglobin in Ahvaz. Conclusion: According to the findings of this study, Bammi cultivar of alfalfa is a good option for future studies and even production of high amounts of leghemoglobin in Khuzestan Province.