Abstract
The aim of the present study was to analyze the growth and physiological performance of two coexisting species, Trifolium fragiferum, and Trifolium repens, under the effect of NaCl and rhizobial symbiosis. Seeds of T. fragiferum and T. repens were collected from populations in the wild, and plants were cultivated in an automated greenhouse, two plants per container. Three basic types of planting were performed: (1) both plants were T. fragiferum (single species), (2) one T. fragiferum and one T. repens (species coexistence), (3) both plants were T. repens (single species). For every basic type, three subtypes were made: (1) non-inoculated, (2) inoculated with rhizobia taken from T. fargiferum, (3) inoculated with rhizobia taken from T. repens. For every subtype, half of the containers were used as control, and half were treated with NaCl. Shoot fresh mass of plants was significantly (p < 0.001) affected by species coexistence, inoculant, and NaCl. Three significant two-way interactions on plant shoot growth were found: between species coexistence and NaCl (p < 0.001), inoculant and species (p < 0.05), and NaCl and species (p < 0.001). A significant three-way interaction between inoculant, NaCl, and species (p < 0.001) indicated different responses of shoot growth of the two species to inoculant type and NaCl. NaCl treatment was an important factor for T. fragiferum, resulting in better growth in conditions of species coexistence, but the positive effect of bacterial inoculant was significantly more pronounced. A decrease in peroxidase activity in leaves was a good indicator of relative NaCl tolerance, while the absence/presence of rhizobial inoculation was reflected by changes in leaf chlorophyll concentration and photochemical activity of photosystem II. It can be concluded that interaction between biotic and abiotic factors affected the outcome of the coexistence of the two Trifolium species. Distribution of T. fragiferum in sea-affected habitats seems to be related to a higher competitive ability with allied species at increased substrate salinity, based on better physiological salinity tolerance.
Highlights
Returning to the initial hypothesis, namely, that rare species T. fragiferum can outcompete more common species T. repens only in conditions of increased substrate salinity, it appeared that NaCl treatment had a higher positive effect on the growth of T. fragiferum in conditions of species coexistence, but the positive effect of bacterial inoculant in coexisting species, especially by rhizobia isolated from T. repens, was significantly more pronounced
For rhizobia-inoculated T. fragiferum plants under single species conditions, the Performance Index significantly increased by NaCl treatment only at the end of the experiment, but this effect was not evident under species coexistence (Figure 2)
During the coexistence of allied species, the interaction between biotic and abiotic factors can affect the outcome of the species coexistence, as significant two-way interactions and a significant three-way interaction on plant shoot growth of Trifolium species were found in the present study
Summary
Considering species habitat specificity and geographical range of distribution, functional aspects of plant species’ rarity are extremely important. One promising approach can be the comparison of closely related species growing in the same habitat [2]. Competition between closely related plant species often is a neglected aspect in ecophysiological studies. When differences in rarity between the coexisting species are evident, more rare species most likely represent a reflection of less competitive and/or adaptive ability in comparison to the more common ones. It is argued that species on the border of distribution have suppressed adaptive potential resulting in decreased fitness [3]. From a physiological point of view, competitive ability and adaptive potential can be assessed through measuring differences in persistence and growth, and by means of determining variation in physiological and biochemical parameters of adaptive nature
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
