Biomass production and nitrate metabolism of Atriplex hortensis L. (C3 plant) and Amaranthus retroflexus L. (C4 plant) in cultures at different levels of nitrogen supply

Abstract

Pure and mixed cultures of the dicotyledons Atriplex hortensis L. (C plant) and Amaranthus retroflexus L. (C plant) were maintained under open air conditions in standard soil at low and high nitrogen supply levels.A comparison of shoot dry weight and shoot length in the various series shows that the growth of the aboveground parts of both species was severely reduced under low N conditions. In both pure and mixed cultures the differences resulting from low N vs. high N conditions was less pronounced with Atriplex (C plant) than with Amaranthus (C plant). The root dry weight of the two species was not reduced so much under low N conditions as was the shoot dry weight. The low N plants were found to contain a larger proportion of their biomass in the roots than did the high N plants. In general the root proportion of Atriplex was greater than that of Amaranthus. The contents of organic nitrogen and nitrate and the nitrate reductase activity (NRA) per g dry weight of both species decreased continually throughout the experiments. With the exception of young plants, the low N plants always had tower contents of organic nitrogen and nitrate and nitrate reductase activities than did the high N plants. The highest values of NRA were measured in the leaf laminae. The eaves also exhibited the highest concentrations of organic nitrogen. The highest nitrate concentrations, however, were observed in the shoot axis, and in most cases the lowest nitrate values were found in the laminae. At the end of ne growing season this pattern was found to have been reversed with Atriplex, but not with Amaranthus. Thus Atriplex was able to maintain a higher NRA in the laminae than Amaranthus under low N conditions.The transpiration per leaf area of the C plant Amaranthus during the course of a day was substantially lower than that of the C plant Atriplex. There were no significant differences in transpiration between the low N and high N series of Amaranthus. The low N plants of Atriplex, however, clearly showed in most cases higher transpiration rates than the corresponding high N plants. These different transpiration rates of the high N and the low N Atriplex plants were also reflected in a distinct C discrimination.The sum of these results points to the conclusion that the C plant Atriplex hortensis can maintain a better internal inorganic nitrogen supply than the C plant Amaranthus retroflexus under low N conditions and an ample water supply, due to the larger root proportion and the more pronounced and flexible transpiration of the C plant.

The biology of Canadian weeds. 130. Amaranthus retroflexus L., A. powellii S. Watson and A. hybridus L.

“…Amaranthus retroflexus exhibited a higher photosynthetic rate for a given leaf nitrogen level, particularly at high leaf N contents, than the C 3 species Chenopodium album and Atriplex hortensis L. (Gebauer et al 1987;Sage and Pearcy 1987b). The net assimilation rate of A. retroflexus also was greater than that of C. album at high levels of applied nitrogen, but the reverse was true at low N (Sage and Pearcy For personal use only.…”

“…Nitrogen deficiency resulted in a reduction of dry matter allocation to the leaves and an increase to the roots and stem (Gebauer et al 1987), as well as leaf necrosis and premature senescence in A. retroflexus, but not in C. album (Sage and Pearcy 1987a). Similarly, Ghorbani et al (1999) found that although A. retroflexus seedlings could emerge and grow at relatively low soil nitrogen levels (3 to 25 kg ha -1 ), height, number of leaves, leaf area, dry weight, and nitrogen and carbon content all increased with increasing soil nitrogen levels.…”

“…WUE declined with decreasing leaf N in A. retroflexus, but not in C. album. The transpiration rate in A. retroflexus and A. powellii was not affected by different nitrogen contents (Hunt et al 1985a, c;Gebauer et al 1987). Stomatal density on the adaxial epidermis of the leaves of A. powellii varied with the amount of nitrate applied from 96 stomata mm -2 at a concentration of 1 mmol L -1 nitrate, to 256 stomata mm -2 at 5 mM (Hunt et al 1985b).…”

Seasonal changes in nitrate use by three woody species: the importance of the leaf-expansion period

“…Therefore, in temperate regions, plant NRA should increase in early spring, when developing leaves demand more N, and soil NO 3 --N availability is generally higher than in winter but temperatures are still lower than in late spring and summer. Foliar NRA peaks in the relatively early stages of leaf growth in various species (Högberg et al 1986(Högberg et al , 1992Gebauer et al 1987;Stadler and Gebauer 1992;Ohlson and Högbom 1993;Pearson and Ji 1994;Troelstra et al 1995). Nonetheless, previous studies did not refer to the effect of the growth stage of leaves on NRA, with the exception of some studies of annual crop species, which discussed the relationship between NRA and leaf ontogeny in seedlings (Santoro and Magalhães 1983;Kenis et al 1992).…”

Plant physiological responses to hydrologically mediated changes in nitrogen supply on a boreal forest floodplain: a mechanism explaining the discrepancy in nitrogen demand and supply

“…In some temperate tree species, a sharp peak in leaf NRA(+NO 3 ) has been observed in the mid-leaf expansion period that is ascribed to compensation for the decline in leaf N concentration during leaf expansion (Koyama et al 2008). Many other species also show maximum NRA(+NO 3 ) in the relatively early stages of leaf development (Gebauer et al 1987;Högberg et al 1986Högberg et al , 1992Ohlson and Högbom 1993;Pearson and Ji 1994;Stadler and Gebauer 1992;Troelstra et al 1995). In this study, no clear peak was observed in the early study period, possibly because leaf expansion occurs very rapidly in the boreal forest and had finished by the time our sampling started.…”