Soil biota are critical drivers of plant growth, population dynamics, and community structure and thus have wide-ranging effects on ecosystem function. Interactions between plants and soil biota are complex, however, and can depend on the diversity and productivity of the plant community and environmental conditions. Plant-soil biota interactions may be especially important during stressful periods, such as drought, when plants can gain great benefits from beneficial biota but may be susceptible to antagonists. How soil biota respond to drought is also important and can influence plant growth following drought and leave legacies that affect future plant responses to soil biota and further drought. To explore how drought legacies and plant community context influence plant growth responses to soil biota and further drought, we collected soils from 12 grasslands varying in plant diversity and productivity where precipitation was experimentally reduced. We used these soils as inoculum in a growth chamber experiment testing how precipitation history (ambient or reduced) and soil biota (live or sterile soil inoculum) mediate plant growth and drought responses within an experimental plant community. We also tested whether these responses differed with the diversity and productivity of the community where the soil was collected. Plant growth responses to soil biota were positive when inoculated with soils from less diverse and productive plant communities and became negative as the diversity and productivity of the conditioning community increased. At low diversity, however, positive soil biota effects on plant growth were eliminated if precipitation had been reduced in the field, suggesting that diversity loss may heighten climate change sensitivity. Differences among species within the experimental community in their responses to soil biota and drought suggest that species benefitting from less drought sensitive soil biota may be able to compensate for some of this loss of productivity. Regardless of the plant species and soil origin, further drought eliminated any effects of soil biota on plant growth. Consequently, soil biota may be unable to buffer the effects of drought on primary productivity or other ecosystem functions as extreme events increase in frequency.
The aim of this study was to evaluate physiological responses and elemental composition of three salt tolerant alfalfa (Medicago sativa L.) cultivars, ‘Halo’, ‘Bridgeview’, ‘Rugged’, and two intolerant cultivars ‘Rangelander’ and ‘Vernal’ under five salinity levels (0 dSm−1, 4 dSm−1, 8 dSm−1, 12 dSm−1 and 16 dSm−1) in a sand based hydroponic system in the greenhouse. The germination percentage among the cultivars was highest for ‘Halo’ under salt stress. ‘Rugged’ and ‘Halo’ had higher seed vigor than the other cultivars in 16 dSm−1 EC. Among the alfalfa cultivars, ‘Rugged’ had the highest chlorophyll content at 0–12 dSm−1 EC. There was variation for root (p = 0.01) and shoot (p = 0.03) biomass among the alfalfa cultivars. Salt stress reduced (p < 0.001) plant height and shoot biomass, with 4.2% and 7.9% reduction for each 1 dS m−1 increase, respectively. Shoot biomass showed a positive correlation with plant height (p < 0.001, r = 0.80), chlorophyll content (p < 0.001, r = 0.56), root biomass (p < 0.001, r = 0.51), but was not correlated with seed vigor. This study demonstrated that seed vigor in the germination stage can not be used to predict salt tolerance of alfalfa at mature growth stages, however plant height and leaf chlorophyll content can serve as physiological markers for high shoot biomass selection at mature growth stages under salt stress.
Background and Aims Salt-tolerant Halomonas maura and biological N fixing Rhizobium may increase salinity tolerance of alfalfa (Medicago sativa), especially for alfalfa populations with improved salt tolerance. The objectives of this study were 1) evaluate whether salt-tolerant bacteria and rhizobium increase salinity tolerance of alfalfa; 2) to assess whether recurrent selection for salt tolerance of alfalfa populations would interact with soil bacteria. Methods Three alfalfa generations sequentially selected for improved salt tolerance were inoculated with either salt tolerant (H. maura), non-tolerant (Ensifer meliloti) bacteria, or a 60kg/ha nitrogen amendment in either non- (0ds/m), moderate-(8ds/m), or highly (16ds/m) saline soil in greenhouse. Results Our results showed that N remains a limiting nutrient in moderate to high salinity stress. Furthermore, this experiment showed that recurrent selection of alfalfa in salinity stress causes several adaptations; however, yield loss occurred under a moderate salinity stress during 120 day growth. Improved alfalfa generations in combination with nitrogen amendments were able to mediate the effects of moderate salinity stress. E. meliloti had positive effect during regrowth, and increased proline content, especially in root tissue. However, H. maura provided almost no benefits to plants in salt stress. Conclusion These results suggest that N is important nutrient in alfalfa salt tolerance. Recurrent plant selection combined with N fixing rhizobium could increase alfalfa growth under a multi-harvest system. Improvement of alfalfa traits related to nitrogen utilization and biological N fixation may be vital to alfalfa salt tolerance.
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