Abstract
Anticipated increases in the frequency of heat waves and drought spells may have negative effects on the ability of leguminous trees to fix nitrogen (N). In seedlings of Leucaena leucocephala inoculated with Mesorhizobium loti or Rhizobium tropici, we investigated how the developmental stage and a short drought influenced overall biomass and the accumulation of carbon and N in plant tissues. In early developmental stages, the number of nodules and nodule biomass were correlated with total plant biomass and δ15N, and nodules and roots contributed 33%–35% of the seedling total N. Seedlings associated with R. tropici fixed more N and exhibited higher overall biomass compared with M. loti seedlings. Four and a half months after inoculation (140 days after inoculation, DAI), a short (15-day) drought inhibited seedling growth and caused a decline in total plant N, with the smallest decline in R. tropici seedlings. After 15 days of drought, i.e., 155 DAI, the nodules had accumulated proline, but the total amino acid concentration did not change. Our results indicate that N-fixation is independent of seedlings growth. In addition, R. tropici is a better choice than M. loti as a symbiont for Leucaena seedlings for forest restoration and agroforestry applications under increasingly drier conditions.
Highlights
Leguminous tree species play an important role in ecosystem productivity and diversity due to their association with nitrogen (N)-fixing diazotropic soil bacteria called rhizobia [1]
Fewer nodules were produced by R. tropici plants, but these had a similar biomass compared with the nodules on plants with M. loti
Our study demonstrates that different rhizobia strains in the Leucaena-rhizobium symbiosis had substantial impacts on growth and development, both during early seedling stages and during drought
Summary
Leguminous tree species play an important role in ecosystem productivity and diversity due to their association with nitrogen (N)-fixing diazotropic soil bacteria called rhizobia [1]. This symbiosis can increase net plant productivity [2] and mitigate land degradation through the use of fast-growing. Plants provide organic-acids as an energy source and in exchange are supplied with fixed N [6] This symbiotic interaction is usually highly specific; each rhizobium species and/or strain interacts with only a specific group of legumes [7]. Some rhizobia species, such as Rhizobium sp. strain NGR234 and Mesorhizobium sp., are known to be less plant-specific and to interact with several legume species [7,8,9]
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