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Nitrogen fertilisation reduces sink strength of poplar ectomycorrhizae during recovery after drought more than phosphorus fertilisation
- Nickel, U. T., Winkler, J. B., Mühlhans, S., Buegger, F., Munch, J. C., Pritsch, K.
- Plant and soil 2017 v.419 no.1-2 pp. 405-422
- agroforestry, carbon, chitinase, chlorophyll, drought, ectomycorrhizae, endo-1,4-beta-glucanase, enzyme activity, fertilizer application, flavonols, gas exchange, irrigation, leaves, nitrogen, nitrogen fertilizers, nutritional status, phosphorus, phosphorus fertilizers, photosynthesis, root tips, stress tolerance
- BACKGROUND AND AIMS: Drought reduces the carbon (C) flux from leaves (source) to mycorrhizal roots (sink); however, during recovery from drought, C flux exceeds the levels observed in irrigated controls. This process could be source- or sink-controlled. We studied this source–sink relationship in an agronomically used poplar clone grown at different levels of nitrogen (N) and phosphorus (P) fertilisation as used in silvoarable agroforestry systems. METHODS: We conducted a fully factorial pot experiment combining four fertiliser and two drought regimes. Gas exchange and chlorophyll and flavonol indices were regularly monitored. One week after rewatering, we performed ¹³CO₂ pulse labelling. At harvest, enzyme activities of ectomycorrhizal root tips were determined. RESULTS: After one week of recovery, we observed an excess in C allocation to ectomycorrhizae (ECM) in non-N-fertilised treatments. However, net photosynthesis only recovered to the level of continuously irrigated controls. Drought increased chitinase, cellulase, phosphatase and peptidase activities, but the latter only in N-fertilised treatments. CONCLUSIONS: We add evidence that the allocation of recently assimilated C is most likely sink-controlled. Less C allocation to recovering ECM supplied with fertiliser may be either due to better nutritional status and hence higher stress tolerance, or due to partitioning between above and below-ground sinks.