Comparative photosynthetic responses in upland and lowland sugarcane cultivars grown in cool and warm conditions

Abstract

The C 4 plant sugarcane (Saccharum sp. Linnaeus) is a chilling-sensitive crop grown at low latitudes for refined sugar and bioenergy. As a leading source of sugar and feedstock for bioethanol production, there is interest in cultivating it at higher latitudes and elevations where sub-optimal temperatures are common. To assess its potential for photosynthetic acclimation to temperature, we compared photosynthetic temperature responses of lowland and upland Hawaiian sugarcane cultivars grown at 32/26 and 21/18 °C day/night temperature. The temperature response of net CO2 assimilation rate (A) of the cultivars was similar in both treatments, with the exception that short-term exposure to 45 °C greatly inhibited A in the 21/18 °C-grown plants of both varieties when subsequently measured below 21 °C. Plants grown at 32/26 °C exhibited a modest inhibition of A below 21 °C following a 45 °C exposure. Little variation between the cultivars was observed in their responses to intercellular CO2 partial pressure and light at varying temperatures. We thus conclude sugarcane does not exhibit a strong thermal acclimation response at moderately sub-optimal to supra-optimal temperatures, but will acclimate to warm growth conditions in a manner that increased tolerance of heat; however, the heat intolerance was manifested as reduced performance at cooler temperatures. This could be problematic in growing regions such as the southeastern USA and China where springtime conditions can include hot days followed by strong cold fronts that brings sub-optimal temperatures.