RESUMEN

Root exudates are an important pathway for plant-microbial interactions and are highly sensitive to climate change. However, how extreme drought affects root exudates and the main components, as well as species-specific differences in response magnitude and direction, are poorly understood. In this study, root exudation rates of total carbon (C) and its components (e.g., sugar, organic acid, and amino acid) were measured under the control and extreme drought treatments (i.e., 70% throughfall reduction) by in situ collection of four tree species with different growth rates in a subtropical forest. We also quantified soil properties, root morphological traits, and mycorrhizal infection rates to examine the driving factors underlying variations in root exudation. Our results showed that extreme drought significantly decreased root exudation rates of total C, sugar, and amino acid by 17.8%, 30.8%, and 35.0%, respectively, but increased root exudation rate of organic acid by 38.6%, which were largely associated with drought-induced changes in tree growth rates, root morphological traits, and mycorrhizal infection rates. Specifically, trees with relatively high growth rates were more responsive to drought for root exudation rates compared with those with relatively low growth rates, which were closely related to root morphological traits and mycorrhizal infection rates. These findings highlight the importance of plant growth strategy in mediating drought-induced changes in root exudation rates. The coordinations among root exudation rates, root morphological traits, and mycorrhizal symbioses in response to drought could be incorporated into land surface models to improve the prediction of climate change impacts on rhizosphere C dynamics in forest ecosystems.

Asunto(s)

RESUMEN

OBJECTIVE:To investigate the correlation of total saponins and total polysaccharides content in the roots of Pari-dis rhizoma genus plants with Arbuscular mycorrhizal fungi(AMF)infection rate and rhizosphere soil nutrients. METHODS:Tak-ing 16 pieces of Paridis rhizoma herbs and rhizosphere soil in Three Gorges Reservoir Area as the research object,mycorrhizal in-fection rate and infection intensity,the contents of total saponins and total polysaccharides in roots and stem,and rhizosphere soil nutrient contents were all determined. SPSS18.0 software was adopted for data multiple comparison and correlation analysis. RE-SULTS:Paridis rhizoma genus plants roots in Three Gorges Reservoir Area could form a good symbiotic relationship with AMF. In-fection rate ranged from 85.19% to 99.80%,and infection intensity ranged from 16.55% to 72.27%. Paridis rhizoma from differ-ent origins and varieties had significant difference in the contents of total saponins and total polysaccharides (P<0.05). Soil pH was moderate,the average content of total nitrogen was in insufficient level,the average concentration of the remaining nutrients belonged to middle levels or above. Correlation analysis showed that the mycorrhizal infection rate and infection intensity of Paridis rhizoma were not significantly correlated with its quality. The total saponins were significantly negatively correlated with organic matter and available nitrogen. The total saponins and total polysaccharides were positively correlated with available phosphorus,po-tassium and pH value,but they were not significantly correlated with the other soil nutrients. CONCLUSIONS:Paridis rhizoma is selective to different soil nutrients. Rich soil available phosphorus and potassium supply are in favor of the synthesis and accumula-tion of total saponins and total polysaccharides in Paridis rhizoma roots.

RESUMEN

Arbuscular mycorrhizal (AM) fungi protect plants against aluminum (Al) toxicity, but the mechanisms of Al and phosphorus (P) interactions in relation to Al tolerance in mycorrhizal plants are only poorly understood. In this study, varying Al and P treatments were applied to soybean plants cultivated in the presence or absence of three different AM fungi. The results showed that plants in symbiotic association with Gigaspora margarita displayed higher Al tolerance than Rhizophagus irregularis or Glomus claroideum. The effectiveness of G. margarita appeared to be associated with more abundant arbuscules and less affected intraradical hyphae compared to no Al controls. The highest levels of Al toxicity mitigation were observed with the combination of high P availability and AM fungal inoculation, which was associated with a concomitant increase in the expression of the AM-inducible phosphate (Pi) transporter gene GmPT9 in soybean. Taken together, these results suggest that AM symbiosis can alleviate Al toxicity in soybean through enhanced P nutrition, as well as, the alteration of the abundance of mycorrhizal infection structures. These findings highlight the importance of P nutrition status in ameliorating Al toxicity in mycorrhizal plants.

Asunto(s)