1/6/2024 0 Comments Intervals ephemeral![]() ![]() Thus, phenological stage determined the timing of maximum response. Each species responded differently to the set of pulses, with the greatest response occurring early in the growth phase when plants were small and growth rates were high. The exception to this pattern was the shrub Chrysothamnus, which responded to all pulse treatments and the control supply with equivalent growth rates and biomass production. At least one of the pulse treatments increased biomass production relative to controls in all but one species. Surprisingly, most of the species grown under the control, continuous N supply had lower growth rates, fewer tillers, and less biomass production than plants receiving N in a pulse. As a control, we applied the same total quantity of N that was in each of the individual pulses as a continuous series of applications at twice-weekly intervals over 10 wk in the spring. We investigated the growth responses and biomass production of six Great Basin plant species growing in monocultures in the field following a single pulse of nitrogen applied in early, mid, or late spring. During humid intervals, sheet-floods and high-sinuosity rivers transported a more mud-rich sediment load into the basin, where eolian activity was minimal.The ability to exploit short-duration nutrient pulses may be an important factor in the competitive balance of plants and in shaping plant community structure. During arid intervals, ephemeral braided streams transported sandy bed-load into the erg-margin area, where eolian reworking took place. ![]() These climatic fluctuations apparently controlled both sediment yield to the basin and the depositional conditions in the erg-margin region. The stacked drying-upward or drying-wetting-upward sequences suggest that this long-term climatic change was characterized by a number of fluctuations between relatively arid and humid conditions. The general time trend is interpreted as a gradual change toward a more humid climate. Individual sequences show much lateral variation but characteristically contain lower, muddy, ephemeral-stream deposits and upper, sandy, ephemeral-stream deposits sand-sheet deposits or incipientdune deposits. Sediments of the overlying association contain up to six drying-upward or drying-wetting-upward sequences but are apparently only fully preserved in the outer erg-margin zone. The basal association thins markedly toward the west-northwest. Sequences of the inner erg-margin zone contain dune facies in their upper parts, sequences in the intermediate erg-margin zone contain sand-sheet facies, and those in the outer erg-margin zone contain sabkha facies. ![]() The sediments of the basal association are composed of three drying-upward or locally drying-wetting-upward sequences that can be traced from the erg margin 100 km slightly upwind (that is, toward the west-northwest) into the outer erg-margin zone. The succession is divided into a basal erg-margin association (8-27 m) dominated by eolian facies and an overlying erg-margin association (as much as 90 m thick) composed mainly of fluvial and lacustrine facies. The erg-margin deposits, which extend across a 50- to 100-km-wide region, are composed of dune, eolian sand-sheet, mud-flanked eolian, sabkha, ephemeral-stream and lacustrine facies. The Moenave Formation (Dinosaur Canyon Member) and the closely associated Wingate Sandstone in southern Utah represent the southwestern erg margin of the Lower Jurassic Wingate erg. ![]()
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