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AOBPreview first published online on July 15, 2006
This version published online on July 27, 2006
Annals of Botany, doi:10.1093/aob/mcl147
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© 2006 The Author(s)
Received December 6, 2005
Revised March 17, 2006
Accepted May 31, 2006

Article

Effects of Resource Heterogeneity on Nitrogen Translocation within Clonal Fragments of Sasa palmata: an Isotopic (15N) Assessment

TOMOYUKI SAITOH 1 *, KENJI SEIWA 1, and AYA NISHIWAKI 2

1 Laboratory of Forest Ecology, Department of Biodiversity Science, Tohoku University, Narugo, Miyagi, 989-6711, Japan
2 Field Science Center, Faculty of Agriculture, University of Miyazaki, Kihanadai, Miyazakisi, Miyazaki, 889-2192, Japan

* To whom correspondence should be addressed.
TOMOYUKI SAITOH, E-mail: tsaitoh{at}ffpri.affrc.go.jp


  Abstract

• Background and Aims Clonal fragments of the rhizomatous dwarf bamboo Sasa palmata, which widely predominates in temperate regions of Japan, were grown under heterogeneous resource conditions such as gap understoreys or nutrient-patchy grassland. Clonal fragments develop multiple ramets with long rhizomes and appear to be physiologically integrated by the translocation of assimilates. The glasshouse experiment reported here was designed to clarify the mechanisms of physiological integration of nitrogen more precisely.

• Methods To assess how resource conditions influence the amount of nitrogen translocation, and which organ acts as the strongest sink, two experiments were conducted that traced movement of 15N label between interconnected pairs of ramets to compare homogeneous and heterogeneous light and soil nitrogen conditions.

• Key Results The amount of 15N translocated to leaves was between 9 % and 11 % greater in high-N and high-light ramets in the heterogeneous compared with homogeneous treatments. Under heterogeneous soil nitrogen conditions, translocation increased from individual ramets in resource-rich patches to ramets in resource-poor patches, while the reverse was true under heterogeneous light environments, reflecting differences in the positions of leaves that act as the strongest sinks. Neither the mass increments nor the total mass of clonal fragments was significantly affected by heterogeneity of either light or nutrients, possibly because the experimental period was too short for differences to manifest themselves.

• Conclusions This study clearly demonstrated that nitrogen is readily translocated between ramets, particularly under heterogeneous resource conditions. The translocation patterns were governed by functional ‘division of labour’ mechanisms that resulted in net nitrogen movement from understorey sites to gaps, thereby enhancing the carbon acquisition of the whole fragment. Thus, physiological integration may provide benefits for S. palmata when it is growing under heterogeneous conditions in which there are deficits of certain environmental resources.

Keywords: Clonal fragment, dwarf bamboo, Sasa palmata, nitrogen, physiological integration, gap, forest understorey, soil nitrogen heterogeneity, heterogeneous light environment.
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