Journal
PLANT AND SOIL
Volume 329, Issue 1-2, Pages 249-258Publisher
SPRINGER
DOI: 10.1007/s11104-009-0149-0
Keywords
Juglans mandshurica Maxim.; Juglone; Larix gmelini Rupr.; Mixed-species plantation; Root exudates; Autotoxicity
Categories
Funding
- National Natural Science Foundation of China [NSFC30671663]
- Innovation Program of Institute of Applied Ecology, Chinese Academy of Sciences [SLYQY0608]
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The establishment and productivity of a Manchurian walnut (Juglans mandshurica Maxim.) plantation can be improved by inter-planting with larch (Larix gmelini Rupr.) in Northeast China, but the potential mechanism remains obscure. We carried out a series of experiments in a 20-year-old mixed-species plantation, as well as in Manchurian walnut and larch plantations. Manchurian walnut seedlings had difficulty surviving in the Manchurian walnut plantation because their growth was inhibited by their own soil and root exudates. In sharp contrast, Manchurian walnut seedlings grew well in larch and mixed-species plantations. Larch soil and root exudates greatly stimulated the growth of Manchurian walnut seedlings in controlled conditions. In particular, larch root exudates can increase the soil microbial populations, including bacteria, actinomycetes, azotobacter and cellulose-decomposing microorganisms; larch root exudates can also increase the enzyme activities of saccharase, urease, proteinase and polyphenol oxidase. Significant results led to a rapid degradation of the root-exuded phytotoxic juglone from Manchurian walnut. Manchurian walnut root exudates contained juglone at a high concentration of 121.3 +/- 6.6 mg g(-1), while juglone concentrations in the soil beneath Manchurian walnut trees ranged from 2.9-6.2 A mu g g(-1) soil. It appears from the results that juglone may be released from Manchurian walnut roots into the soil in a sufficient quantity but rapidly degrades due to interactions with soil factors. Furthermore, juglone was more resistant toward degradation in the Manchurian walnut soil (t (1/2) = 7.36 A +/- 0.63 h) when compared to the larch soil (t (1/2) = 4.66 A +/- 0.82 h). The results suggest that larch may improve the establishment and productivity of Manchurian walnut in a mixed-species plantation through the release of root exudates.
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