By FI Woodward, Department of Botany, University of Cambridge, UK
Symposia of the Society for Experimental Biology, 1988, 42:59-75
Abstract
An understanding of the mechanisms (click here) by which temperature influences the distribution of species and vegetation has been attempted by modelling population growth and establishing those stages of the plant life cycle which, when diminished by extremes of temperature, for example, may have the greatest impact on plant survival. This analysis suggests that the heat sum of the growing season, measured as day-degrees, controls the distribution of annual vegetation. For perennial vegetation both the heat sum of the growing season and the annual, absolute minimum temperature are critical. Climatic correlations and experimental analyses indicate that, in northern Europe, the northern latitudinal and upper altitudinal limits of lowland and southern vegetation are directly controlled by climate. In contrast, the southern and lower altitudinal limits of upland and northern vegetation are likely to be controlled by temperature-sensitive competition with southern or lowland species. Many of the temperature-sensitive processes of plant growth and development, such as the non-linearity of extension growth and variations in the threshold temperatures of processes, may increase the realized heat sum at a particular geographical location. However, in more northerly climates, photoperiodic control is crucial in avoiding precocious development in the highly variable climatic conditions of early spring.
Figure 1
Extensive (click here) and transient metabolic reprogramming in chloroplasts under heat stress. Major events of metabolic reprogramming in response to heat stress include chlorophyll breakdown, generation of reactive oxygen species (ROS), antioxidant defense, protein turnover, and metabolic alterations with carbon assimilation. With respect to the systemic acquired acclimation to heat stress in plants, diverse metabolic reprogramming in chloroplasts is required for optimizing plant growth and development during high temperature stresses.
By Bob Silberg
...“There are places in the world where, (click here) for these important breadbasket crops, they are already close to a thermal limit for that crop species,” Schimel said. Adding to the burden, he said, “this analysis (the EGU study) does not take into account the fact that pests and pathogens may spread more rapidly at higher temperatures.”
And Schimel pointed out that heat can imperil agriculture even when crops don’t die. “If you get really high temperatures or very dry conditions during critical parts of the development of the crop, it produces essentially no grain. For example, above certain temperature thresholds, corn doesn't die but it doesn't grow seed. It doesn't grow a corncob. And other crops are similar to that, where the development of the actual food part of the crop is dramatically inhibited above critical temperatures.”
But what about that fertilization effect from carbon dioxide? “It does help a bit, but it doesn't make the underlying problem go away,” he said. “And by the way, if the plant was growing really fast when it died, it still died.”
Can we avoid the extra half-percent temperature increase? Schimel agrees that we should try hard to do so, but cautions that we don’t know how to fine-tune global warming with that much precision. “If we aim for 2 degrees, we might hit 3 degrees,” he said. “If we aim for 1.5 degrees, we might still hit 2 degrees.”
