Nitrogen-15 partitioning within a three generation tiller sequence of the bunchgrass Schizachyrium scoparium: response to selective defoliation
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Authors: J. M. Welker, D. D. Briske, and R. W. Weaver
Date: 1987
Journal: Oecologia
Volume: 74
Number:
Pages: 330-334
Summary of Methods: In a controlled environment, at Texas A&M University, researches studied nitrogen partitioning among three generations of tillers, within the bunchgrass Schizachyrium scoparium, as a potential mechanism of herbivory tolerance. Nitrogen-15 was transported from the root-labelled primary tiller to anatomically attached secondary and tertiary tiller generations within 24 hours, based on relative enrichment values. The consistent occurrence of relative enrichment values among shoots and roots of the three tiller generations through time indicate a similar demand for nitrogen within the nondefoliated tiller sequence. However, all combinations of interaction among defoliation treatment, harvest date, tiller generation, and tissue component were significant for relative enrichment. Essentially, the total amount, 98%, of 15N excess absorbed by the primary tiller remained within the labelled tiller sequence. Partial defoliation of secondary tillers increased relative enrichment of secondary shoots 110%, but decreased relative enrichment of the roots 30% at 24 hours. At 72 and 120 hours, relative enrichment values of shoots decreased to values comparable to nondefoliated secondary tillers, but relative enrichment of the roots decreased further to values 75% lower than those of nondefoliated secondary tillers at 120 hours. Partial defoliation of tertiary tillers increased relative enrichment values of both shoots and roots throughout the 120 hour experimental period. Following tertiary tiller defoliation, relative enrichment of the primary shoots decreased 70% and 60% at 72 and 120 hours, respectively; while relative enrichment of root tissues remained comparable to primary tillers within nondefoliated tiller sequences. Preferential nitrogen concentration occurred in response to partial tiller defoliation without an increase in total nitrogen requirement per tiller generation associated with defoliation.
Article Summary / Main Points: None
Vegetation Types:
MLRA Ecoregions:
Agrovoc Control Words: Riparian zones Rangelands Wildlife
Article Review Type: Refereed
Article Type: Experimental Research
Keywords: 15n partitioning, herbivory, grass bug, bunchgrass, schizachyrium scoparium, nitrogen allocation
Annotation: Plants were grown for 8 months to develop three generation tiller sequences utilized as experimental units. Treatments consisted of : 1) a control in which none of the tillers within three-tiller sequence were defoliated, 2) defoliation of secondary tillers to a height of 7 cm, and 3) defoliation of tertiary tillers to a height of 7 cm. Plants were arranged in a randomized block design consisting of three harvest times (24, 72, 120 hours following labelling), three defoliation treatments, three replicates per treatment and six tissue categories per replicate.
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