Studies On Indices Of Freezing Injury And Changes Of Possible Planting Boundaries For Different Winter-spring Wheat

Wheat is one of the three major grain crops in China,and its planting area and production account for 21.4%and 20.9%of the national grain crops,respectively.Winter wheat,which represents more than 90%of wheat produced in planting areas and production in China,benefits from the plentiful climate resources in China.However,climate factors are highly volatile and low temperature injuries occurred frequently due to the location in monsoon climate zone.Freezing injury during winter and frost injury in spring are the most important low temperature injuries affecting winter wheat production in China.It is critical to clarify the indices of freezing injury and frost injury,the change of possible planting boundaries and distribution characteristics of freezing injury and frost injury for different winter-spring wheat for the cultivar deployment and safe production of winter wheat.In this thesis,controlled experiments were conducted with different winter-spring wheat to determine the effects of freezing temperatures and freezing days on the mortality and yield formation.The indices of freezing injury and frost injury for different winter-spring wheat were quantified.Then the changes of possible planting boundaries and freezing injury and frost injury in the possible planting areas for different winter-spring wheat were analyzed.The main conclusions were as follows:(1)The freezing tolerance of strong winter wheat and winter wheat was significantly stronger than that of semi-winter wheat and weak spring wheat in early winter.In term of soil temperature at 2.5cm depth,the LT50 values of plants(temperature at which 50%of plants are killed)were-18.5?,-18.3?,-15.0? and-14.1? for strong winter wheat,winter wheat,semi-winter wheat,and weak spring wheat,respectively.For the same cultivar,the freezing tolerance of tillers is stronger than that of younger and older leaves,and the LT50 values of tillers were 2.10C?2.6? and 2.9??5.7?C lower than younger and older leaves,respectively.In the erecting-jointing stage of winter wheat,the LT50 values of tillers is 0.6??2.1? lower than that of younger leaves,and the LT50 values of younger leaves is 0.2?-0.8? lower than that of older leaves.(2)During midwinter,the winter wheat mortality increased with the increase of freezing days.The mortality of strong winter wheat increased by 8.6%for every one day increase in freezing days under-17?(minimum soil temperature at 2.5cm depth).The mortality of winter wheat increased by 3.6%and 22.3%for every one day increase in freezing days under-14? and-17?.The mortality of semi-winter wheat increased by 11.1%and 27.0%for every one day increase in freezing days under-14? and-16?.The mortality of weak spring wheat increased by 9.4%and 40.5%for every one day increase in freezing days under-11? and-14?.Freezing injury reduced spike numbers by the death of plants and tillers,which led to yield reduction.Spike numbers decreased as freezing days increased for all cultivars.For the same cultivar,spike number decreased more for every one day increase in freezing days under lower temperature.An increasing trend in grain number per spike was observed as freezing days increased and can compensate for yield loss to some extent.(3)Minimum air temperature index of severe freezing injury were-20.9?,-20.2?and-18.0? for strong winter wheat,winter wheat and semi-winter wheat during midwinter,respectively.The freezing days(minimum air temperature<-16?)of severe freezing injury were 8d and 3d for winter wheat and semi-winter wheat,respectively.Minimum air temperature index of severe freezing injury were-20.6?,-19.0?,-14.7?and-12.5? for strong winter wheat,winter wheat,semi-winter wheat and weak spring wheat in early winter,respectively.Minimum air temperature index of frost injury were-4.2?,-4.6?,-6.1?C and-5.5? for strong winter wheat,winter wheat,semi-winter wheat and weak spring wheat in erecting-jointing stage,respectively.(4)Compared with the period 1961-1990,the possible northern and southern planting boundaries of strong winter wheat,winter wheat,semi-winter wheat and spring wheat in China moved northward during the period 1991-2017.The possible planting area of strong winter wheat,winter wheat and spring wheat increased by 24.71 ×104 km2,10.82×104 km2 and 21.37×104 km2,while the possible planting area of semi-winter wheat decreased by 0.60×104 km2.Compared with the period 1961-1990,the frequency of freezing injury during winter and frost injury in jointing stage of winter wheat showed a decreasing trend in the period 1991-2017.