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Location: Home > Research Areas > Soil Nutrient Cycling and Control Mechanisms
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Plant-soil interactions and soil C and N cycling

Plant-soil interactions in the rhizosphere

Photosynthetic C released to the rhizosphere by plants drives several ecological processes, including inter-species interactions and soil C and N cycling. Rice (Oryza sativa L.) is a major source of food for more than half of the world’s population. Weeds pose a great biological constraint to rice productivity. Hence rice production is currently characterized by the heavy use of synthetic herbicides. Rice allelopathy, which results from allelochemicals biosynthesized and released from rice itself, may be an alternative to the chemical control of paddy weeds. A research group from IAE-CAS focuses on the ecological role and underlying mechanisms of rice allelopathy. Our research has revealed that symbiosomes of allelopathic rice and endogenous bacteria can not only directly suppress weeds through the release of allelochemicals such as flavonoids or terpenoids, but can also mediate the competition between rice and weeds or soil microbes by releasing jasmonic acid and quorum-sensing signal molecules (Kong et al. 2007, 2008a, 2008b; You et al. 2011). We confirmed that allantoin can be obtained from rice plants (Wang et al. 2007) and that endogenous allantoin exuded from rice roots into rhizosphere soils can exert a wide variety of biological effects on associated weeds and microbes (Wang et al. 2012). We found a positive relationship between allantoin levels in grains and seedling survival in seedbeds under low temperature or water deficit, indicating that allantoin in rice grains may play an important role in affording plant stress protection (Wang et al. 2012). Application of allantoin would stimulate shifts in microbial community composition and increase microbial diversity as well as living microbial biomass in paddy soils (Wang et al. 2010). The production of allantoin by rice was affected by the presence of barnyard grass, and its concentration varied among rice cultivars. We found that rice from allelopathic cultivars was sensitive to the presence of competing barnyard grass and responded by decreasing production of growth-stimulating allantoin, thereby regulating the growth of barnyard grass (Sun et al. 2012). This work reveals the ecological role of allelopathic chemicals in regulating the interactions between rice and weeds and thus improves our understanding of the underlying mechanisms for weed suppression by allelopathic rice varieties. 

Responses of plant-soil interactions to global climate change

A better understanding of plant-soil interactions under global climate change would improve our ability to predict consequences of those interactions for plant community composition and productivity under various conditions. We examined the response of soil nematodes in a wheat field to elevated atmospheric CO2 and found that N fertilization and crop residue addition could influence the impacts of elevated CO2 on the abundance and diversity of soil nematodes (Li et al. 2009). The addition of residue stimulated the response of structure index to the elevated CO2 and inhibited the response of plant parasites. Under low N treatments, the abundance of total nematodes, bacterivores, and omnivores-carnivores was more sensitive to the elevation of CO2. We also investigated the effects of elevated ozone concentration [O3] on the components of soil microbial food webs and compared responses of food webs to ozone concentrations in ozone-sensitive and ozone-tolerant wheat cultivars. We found that the fungal PLFA and the ratio of fungi to bacteria decreased following elevated [O3], especially in the rhizoshperic soil of ozone-tolerant wheat (Li et al. 2012).

 

Furthermore, the abundance of specific functional genes involved in C fixation and degradation, N fixation, and sulfite reduction was significantly altered in response to elevated [O3] and wheat cultivars. The ozone-sensitive cultivar appeared to harbor microbial functional communities in the rhizosphere, and was more responsive to elevated [O3] than the ozone-tolerant cultivar (Li et al. 2013). The shifts of functional gene representation in wheat rhizosphere microbial communities under elevated [O3] would have great implications for soil functions. Results from these studies suggest that the impacts of elevated [O3] on below-ground communities are closely related to the sensitivity of crop cultivars.

 

 







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