THE EXPECTED EFFECTS OF CLIMATE-CHANGE ON WHEAT DEVELOPMENT

Air temperature and the atmospheric concentrations of carbon dioxide a re expected to rise. These two factor have a great potential to affect development, growth and yield of crops, including wheat. Rising ait t emperature may affect wheat development more than rising atmospheric C O2 as there is not yet evidence that elevated CO:! concentrations can directly induce changes in wheat development. In winter wheat, tempera ture has a complex effect on development due to its strong interaction with vernalization and photoperiod. In this paper, potential effects of rising temperature on the development of winter wheat from sowing t o heading are considered in the light of this complex controlling mech anism. Data from a large series of field trials made in Romania is ana lysed at first and, subsequently, the IATA-Wheat Phenology model is us ed to calculate the impact of air warming on wheat development under d ifferent climate change scenarios. Data from the field trials showed v ery clearly the occurrence of a complex temperature/photoperiod/vernal ization interaction for field sown crops and demostrated that the phot operiodic and vernalization responses have a key role in controlling t he duration of the emergence-heading period. Temperature plays, instea d, a central role in controlling seed germination and crop emergence a s well as leaf inititiation and leaf appearance rate. The results of m odel analysis showed very well that the impact of an even or uneven di stribution of warming effects may be very different. In the first case , the model predicted that the duration of the vegetative period was a t least partly reduced in some years. In the second case, the model su ggested that if warming will be more pronounced in winter than in spri ng, as predicted for some areas of the world by General Circulation Mo dels, we may expect an increase in the duration of the vegetative phas e of growth. On the contrary, in case of a spring warming but unchange d winter temperatures, we may expect a substantial decrease in the dur ation of the vegetative period.