Influence of light and form of nitrogen on chlorine requirement of kiwifruit

Abstract

SUMMARYThe extent to which light, potassium, and form of nitrogen (ammonium and nitrate-nitrogen) modified the requirement by kiwifruit (Actinidia deliciosa var. dcliciosa) for chlorine was examined in solution culture. A greater concentration of chloride was required in the nutrient solution for maximum growth under low irradiance than under high irradiance. In the absence of chloride, growth was severely restricted and the response to potassium was significantly reduced, especially under low light.Greater concentrations of chloride accumulated in the leaves of plants grown under high irradiance than under low irradiance. Increasing the concentration of nitrate in tbe leaves either by growing the plants under low light or by increasing the quantity of nitrate in the nutrient solution, substantially reduced tbe accumulation of chloride. The decrease in the concentration of chloride was accompanied by an increase in the concentration of nitrate. Thus the combined concentration of nitrate and chloride was relatively constant over a wide range of treatments suggesting that a negative feedback mecbanism may be operating in this species. However, while nitrate was preferentially accumulated by kiwifruit plants it could not substitute fully for chloride. Once the concentration of chloride in the leaves was decreased below 70//mol g ' d. wt by competing nitrate ions, growth was substantially reduced. It is concluded that the effect of light on the chloride status of kiwifruit plants can largely be explained in terms of the strong competitive effect from nitrate ions, witb greater concentrations of nitrate accumulating in rhe leaves under low irradiance than under high irradiance.Tbe negative effect of potassium on the chloride status of the plants is not considered to be a specific physiological effect but rather the consequence of chloride, along with other non-limiting nutrients, accumulating in the tissues of the severely potassium deficient plants.The ecological implications of the results are discussed in relation to features of the habitat in China where kiwifruit vines have evolved. The results of tbe present study are entirely consistent with this species having evolved in an environment where tbe availability of cbloride and ammonium is relatively high while that of nitrate is severely restricted. It is concluded that the high concentration of chloride required in the tissues of kiwifruit vines is an adaptation which minimizes the expenditure of energy on the generation of osmotic pressure in the tissues rather than specifically maintaining charge balance.

Influence of anions on the potassium status and productivity of kiwifruit (Actinidia deliciosa) vines

“…In the 1989 season, soil samples (0-150mm) were taken from each sub-plot 3 weeks after fertiliser application, and analysed for ammonium acetate (1 M, pH 7) exchangeable K, Ca(NO3) 2 (0.05 M)-extractable CI (Smith et al, 1988), CaH2PO 4 (0.01 M, pH 4)-extractable SO]--S, and KC1 (2M)-extractable N O 3 -N contents. Leaf samples (youngest fully expanded leaves) were taken from every sub-plot on 9 occasions during the growing season.…”

“…Kiwifruit seedlings ('M56' × 'Hayward') were grown in solution culture, using a programmed nutrient addition technique (Asher and Cowie, 1970), assuming a relative growth rate of 0.12 g g-1 day- (Smith et al, 1988) and desirable tissue nutrient concentrations as described previously (Smith et al, 1988). All nutrients, except those used to establish the variable concentrations of the 4 anions, were added to the solution in the pots in frequent small doses.…”

“…The symptoms we observed here were similar to those of N deficiency in kiwifruit (Smith et al, 1987a). Competition between C1 and NO 3 ions for uptake (Smith et al, 1988) may exacerbate N deficiency and hence lead to an increased incidence of associated symptoms. In contrast, SO~-ions do not compete for uptake with NO 3 ions (Leggett and Epstein, 1956;Smith, 1980).…”

Occurrence of a stable nitrate reductase inActinidiaspp.

“…Seedlings were germinated in acid-washed sand, then transferred to solution culture once they had reached c. 1-2 cm in height (2-3 leaflets). Calculation of the quantities of various nutrients required for successive 3-or 4-day growth periods was based on the assumptions and methods in Smith et al (1988), which were followed without modification. As in Smith et al (1988), we assumed that the concentration of N required for non-limiting growth was 2.86 mol/kg dry weight, and that an optimum ratio of ammonium-N:nitrate-N in solution was 40:60.…”

“…Calculation of the quantities of various nutrients required for successive 3-or 4-day growth periods was based on the assumptions and methods in Smith et al (1988), which were followed without modification. As in Smith et al (1988), we assumed that the concentration of N required for non-limiting growth was 2.86 mol/kg dry weight, and that an optimum ratio of ammonium-N:nitrate-N in solution was 40:60. Bulk samples of fibrous root (< 2 mm in diameter) or youngest-mature-leaf blades (minus petioles) were harvested from plants after 60-80 days when they were elm tall, washed with distilled water, dried, then frozen in liquid N 2 , ground to a fine powder, and stored at-80°C.…”