Abstract
Nitrogen is consistently reported to be an essential element which limits plant growth in grazed ecosystems. Subsequently mechanisms facilitating efficiency of nitrogen allocation and utilization may be an essential component of grazing resistance. Therefore, the objectives of this project were to: 1) identify the degree of nitrogen transfer within a three-tiller sequence of a native bunchgrass, 2) examine the alteration of nitrogen allocation in response to selective defoliation, 3) examine metapopulation level nitrogen pools as partitioned among tiller generations, 4) examine nitrogen transfer from older to younger tiller generations and the reciprocal and 5) contrast root and foliar absorbed nitrogen transfer among tiller generations. These studies were conducted within the conceptual framework of adaptive physiological responses associated with clonal growth and grazing resistance in native bunchgrasses. Growth chamber experiments were conducted using Schizachyrium scoparium as the model species and nitrogen-15 (^15N) tracer techniques to identify nitrogen transfer within a three-tiller hierarchical sequence. Defoliation of selective generations resulted in preferential nitrogen import (per gram basis) by defoliated tillers within 24 hrs and remained accelerated throughout the 120 hr experimental period. Preferential nitrogen import into defoliated tillers coincides with carbon isotope studies and suggest that these two essential elements are allocated in a similar manner. Elevated levels of import may facilitate photosynthetic tissue replacement and enhance plant competitive ability. Reciprocal nitrogen transfer was observed between primary (1°) and secondary (2°) tillers throughout the 120 hr experimental period. The degree of nitrogen transfer between tiller generations appears to be a function of the number of intervening tiller generations whereby nitrogen transfer from 1° to tertiary (3°) tillers is only 50% of that transferred from 1° to 2° tillers. In addition, nitrogen pools found in 1° and 2° tillers at the metapopulation level provides a source of nitrogen which may be imported by 3° tillers and facilitate juvenile tiller survival during establishment .
Welker, Jeffrey Martin (1985). Nitrogen transfer among tillers within the bunchgrass Schizachyrium scoparium var. frequens. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -597636.