AOBPreview published online on January 4, 2007
Annals of Botany, doi:10.1093/aob/mcl258
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© The Author 2007. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org
Effect of Nitrogen Form and Root-zone pH on Growth and Nitrogen Uptake of Tea (Camellia sinensis) Plants
1 Institute for Plant Nutrition and Soil Science, Kiel University, Kiel, D-24098, Germany
2 Tea Research Institute of Chinese Academy of Agricultural Sciences and Key Laboratory for Tea Chemical Engineering of Ministry of Agriculture, Hangzhou 310008, China
3 K+S Polska sp. z o.o. Pl. Wiosny Ludów 2, 61-831 Pozna
, Poland
* For correspondence. E-mail jruan{at}mail.tricaas.com
Received: 23 June 2006 Returned for revision: 28 July 2006 Accepted: 12 October 2006
BACKGROUND AND AIMS: Tea (Camellia sinensis) is considered to be acid tolerant and prefers ammonium nutrition, but the interaction between root zone acidity and N form is not properly understood. The present study was performed to characterize their interaction with respect to growth and mineral nutrition.
METHODS: Tea plants were hydroponically cultured with NH4+, NO3– and NH4++NO3–, at pH 4·0, 5·0 and 6·0, which were maintained by pH stat systems.
KEY RESULTS: Plants supplied with NO3– showed yellowish leaves resembling nitrogen deficiency and grew much slower than those receiving NH4+ or NH4++NO3– irrespective of root-zone pH. Absorption of NH4+ was 2- to 3·4-fold faster than NO3– when supplied separately, and 6- to 16-fold faster when supplied simultaneously. Nitrate-grown plants had significantly reduced glutamine synthetase activity, and lower concentrations of total N, free amino acids and glucose in the roots, but higher concentrations of cations and carboxylates (mainly oxalate) than those grown with NH4+ or NH4++NO3–. Biomass production was largest at pH 5·0 regardless of N form, and was drastically reduced by a combination of high root-zone pH and NO3–. Low root-zone pH reduced root growth only in NO3–-fed plants. Absorption of N followed a similar pattern as root-zone pH changed, showing highest uptake rates at pH 5·0. The concentrations of total N, free amino acids, sugars and the activity of GS were generally not influenced by pH, whereas the concentrations of cations and carboxylates were generally increased with increasing root-zone pH.
CONCLUSIONS: Tea plants are well-adapted to NH4+-rich environments by exhibiting a high capacity for NH4+ assimilation in their roots, reflected in strongly increased key enzyme activities and improved carbohydrate status. The poor plant growth with NO3– was largely associated with inefficient absorption of this N source. Decreased growth caused by inappropriate external pH corresponded well with the declining absorption of nitrogen.
Key words: Ammonium, growth, nitrate, nitrogen form, nitrogen uptake, root-zone pH, tea, Camellia sinensis