Low temperatures decrease CO2 assimilation and growth in the tropical rambutan

Abstract

In glasshouse experiments, high temperatures increased vegetative growth in the tropical rambutan (Nephelium lappaceum L. seedlings of cv. Rapiah). In absolute terms, there was generally a greater response to night temperature (day/night temperatures of 32714°C vs. 32728°C) than to day temperature (22714°C vs. 32714°C), and better growth at 32728°C than at 32722°C. The effects of temperature on nutrient concentrations were small, whereas average leaf water potential (ΨL) during the day was -1.5 MPa at 32728°C, 0.1 to 0.4 MPa higher with nights of 14° or 22°C, and 0.7 MPa higher at 22714°C. Average net C02 assimilation rate (A) was 5.3 μ-mol m−2 s−1 at 32722° and 32728°C, 50% lower at 32714°C and 80% lower at 22714°C. When seedlings of cv. Rapiah were grown in water baths, the two critical root temperatures at which 90% of maximum plant weight occurred were similar for leaves and stems (about 24° to 30°C), but lower for roots (19° to 25°C). There was only a small effect of temperature on the concentration of most nutrients, and on average day time ΨL, whereas average A was 4.5 (μmol m s−1 at 28°C, 30% lower at 20°C, and 80% lower at 15° and 38°C. These experiments show that rambutan growth was strongly reduced when night or root temperatures fell to 14° or 15°C. The main effect was through lower Co−2 assimilation, whereas the changes in water and nutrient status were relatively small. Areas where night or root temperatures remain at or below 14°C for prolonged periods should be avoided for rambutan production.