Root exudates and their ecological consequences in forest ecosystems: Problems and perspective

doi:10.17521/cjpe.2018.0156

Abstract

Abstract:

Researches on rhizosphere ecological processes and the underlying mechanisms have become one of the most active and sensitive hotspots in soil science. Root exudates have specialized roles in mediating the nutrient cycling and signal transduction within root-soil-microbe interactions. They are the key driving factors in regulating the functions of rhizosphere micro-ecosystem, and serve as a major premise for the concept and ecological processes in rhizosphere. However, due to the instinctive advantages of crops, such as short life cycles and convenient operation, most previous studies on root exudation mainly focused on agricultural ecosystems and were primarily targeted at providing practical guidelines. In contrast, there have been relatively few investigations on root exudates of trees, which highly limited the comprehensive knowledge of the potential mechanisms of root exudates in mediating soil biogeochemical processes in forest ecosystems. Hence, in this review, based on the main findings in our previous studies and the emerging frontiers in rhizosphere ecology, we specifically reviewed the ecological consequences and key remaining challenges in researches on root exudation in forests. Finally, we identify several topics and research outlooks for guiding future work to facilitate studies on root exudation and its ecological consequences in forest ecosystems.

http://jtp.cnki.net/bilingual/detail/html/ZWSB201811001

Key words: rhizosphere, root exudate, root-soil interactions, soil biogeochemical processes, rhizosphere functional traits, forest

Hua-Jun YIN, Zi-Liang ZHANG, Qing LIU. Root exudates and their ecological consequences in forest ecosystems: Problems and perspective[J]. Chin J Plant Ecol, 2018, 42(11): 1055-1070.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2018.0156

https://www.plant-ecology.com/EN/Y2018/V42/I11/1055

Figures/Tables 5

Fig. 1 Conceptual framework of rhizosphere biogeochemical processes in forests under global climate change.

Fig. 2 Proposed mechanisms for the exudate-induced acceleration of the microbial mineralization of soil organic carbon in the rhizosphere (i.e., rhizosphere priming effects). A, The traditional view is that root exudate compounds stimulate microbial growth and activity via co-metabolism, and so increase the overall physiological potential of the decomposer community for carbon mineralization. B, The alternative mechanism proposed here takes into account that large quantities of soil C are inaccessible to microbes owing to associations with mineral phases. Root exudates that can act as ligands effectively liberate C through complexation and dissolution reactions with protective mineral phases, thereby promoting its accessibility to microbes and accelerating its loss from the system through microbial mineralization.

Fig. 3 Diagrammatic representation of the Regulatory Gate Hypothesis. I phrase is the abiological transformation of non-bioavailable soil organic matter (SOM). II phrase is the biological mineralization of bioavailable SOM.

Fig. 4 Two pathways of root-derived carbon (C) input (i.e., root- and mycelium-derived C) to soils in forest ecosystems. N, nitrogen.

Fig. 5 Broadening functional traits of root and microbe in rhizosphere and enriching the suite of belowground functional traits.

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