Improved methodologies for prairie inoculation.

摘要

Prairie restoration is intended to create self-sustaining, resilient prairies, in an attempt to ameliorate biodiversity loss and soil deterioration associated with widespread conversion of native grasslands to agriculture. Legumes are a key component of the nitrogen-limited prairie ecosystem because of their ability to supply nitrogen. Legumes can prevent the explosion of weeds associated with nitrogen fertilizer use, speed up native plant establishment, and enhance plant diversity. Evidence suggests that lack of suitable symbionts for various prairie legume species may explain legume absence. Thus, their successful establishment may rely on the appropriate selection of rhizobial inoculants. The need to develop suitable inoculants for prairie restoration has prompted the study of prairie legume rhizobia, their natural occurrence and diversity, and the search for more effective means for inoculant delivery in restoration setting. This research undertakes two current topics regarding prairie legumes: (1) Improved methodologies for prairie inoculation. The questions addressed were: (a) Can new inoculant carriers and/or alternative means for inoculant delivery allow better prairie legume establishment? (b) Do these new inoculation methodologies allow inoculant rhizobial strains to persist and nodulate the host over time? (c) What are the effects of inoculation on soil biological properties? and (2) New insights on prairie legume-rhizobia interactions, with a focus on potential agricultural uses of Desmanthus-associated rhizobia native to Uruguay. The questions addressed were: (a) How genetically diverse are the native Uruguayan rhizobia associated with Desmanthus ? (b) To which genus/species do they belong? (c) Does N2-fixation efficiency of native isolates vary when tested on several Desmanthus species and in different environments? Briefly, results from the first study show that the clay-based granular inoculant was an effective means to deliver inoculant-quality rhizobia. Both total legume counts and legume species richness were significantly improved by granular clay inoculation in the second growing season, compared to the uninoculated controls. This inoculation procedure allowed a legume-rich prairie to be restored (5.5 legume species per unit area vs. 4.8 species found in 29 remnant old settler prairies that were surveyed). The study on Desmanthus-associated rhizobia native to Uruguay showed that they are genetically highly diverse and belong to at least two genera and three different rhizobial species: Rhizobium giardinii, R. leguminosarum, and Mesorhizobium amorphae. They also vary greatly in the amounts of N2 fixed. The overall conclusions of these two studies suggest a new paradigm for inoculation of native legumes. We suggest that further efforts should involve granular clay carriers, and that strains with broad host-ranges should be further investigated and selected at an earlier stage in the process of strain selection. The fact that Desmanthus-associated strains native to Uruguay were successful N 2 fixers should contribute to the adoption of Desmanthus spp. -- Rhizobium spp. combinations for agricultural purposes.