Effects Of Dry-hot Wind On Carbon Assimilation Of Winter Wheat At Grain Filling Stage In Canopy And Leaf Scales

The trend of dry-hot wind is likely to increase with global warming. The winter wheat is one of the food crops in the Huanghuaihai area, and in this area, winter wheat often suffers dry-hot wind during grain-filling stage. In this study, the effects of dry-hot wind on canopy carbon assimilation and leves photosythesis of winter wheat at grain filling from canopy and leaves two scales using the eddy covariance flux observation technology, LI-6400 photosynthesis/transpiration measurement technology and the dry-hot wind simulation generator. Canopy carbon flux was continuously measured in 2003-2013 using the eddy covariance system in a winter wheat field in Yucheng station, Shandong Province. The dry-hot wind index threshold was determined as the 95th percentile of (Ta_max).Two typical couples of dry-hot wind (DHW) and non-dry-hot wind (non-DHW) days in 2004 and 2012 were selected and compared to determine the characteristics and mechanism of the effects of DHW on net ecosystem productivity (NEP, daytime), which was used to denote winter wheat canopy carbon assimilation rate. In the leaf scale, the winter wheat flag leaf was treated with different time of the dry-hot wind using dry-hot wind simulation device, and the experiment was set up to 6 treatments. The results showed that:1. Effects of dry-hot wind on canopy carbon asimilation of winter wheat at grain filling stage:(1)Ta_max in the DHW days were 3.10℃ and 3.17℃ higher than those in the non-DHW days respectively in 2004 and 2012. Then total amounts of daytime NEP in DHW days were 3.25 mg(CO2)·m-2·s-1 (with decreasing rate of 19.77%) and 6.04 mg(CO2)·m-2·s-1 (with decreasing rate of 19.17%) lower respectively than that in non-DHW days in 2004 and 2012. (2)NEP had a significant quadratic curve correlation with PAR, but no significant when PAR was greater than 1000μmol·m-2·s-1, at that time NEP accounted for over 52.31% of total daytime NEP for both DHW and non-DHW days. The difference in NEP between DHW and non-DHW days increased with increasing PAR, especially when PAR was greater than 1000 μmol·m-2·s-1. (3)There were no significant correlations between relative humidity of atmosphere (RH) and NEP, whether during whole day or when PAR was greater 1000 μmol·m-2·s-1. For the whole days, NEP had no significant correlation with air temperature (Ta) in the DHW and non-DHW days. (4)However, during the daytime with PAR> 1000 μmol·m-2·s-1, NEP had significant negative correlation with Ta. NEP decreased by 7.28%-9.53% in 2004 and by 6.94%-10.42% in 2012 with every 1℃ increase in Ta. In conclusion:dry-hot wind inhibited the carbon asimilation at the grain-filling process of winter wheat in the North China Plain, even though temperature and humidity of winter wheat at grain filling stage did not reach the standard of dry-hot wind index in the meteorological profession, and Ta was the main factor affecting it. While the contribution of Ta to daytime NEP inhibition was 59%-83%, total NEP decreased by 6.05%-6.37% with 1℃ increase in Ta.2. Effects of dry-hot wind on leaf photosynthetic characteristics of winter wheat grain filling period:(1)in the low light (PAR<300 μmol·m-2·s-1), dry-hot wind had no significant effects on Pn, but in the high light (PAR>300 μmol·m-2·s-1), Pn declined rapidly after dry-hot wind forcing 15 min, and Pn still declined after dry-hot wind forcing 30 min; but Pn changed insignificantly as the forcing time increased. After it was forced 120 min, the instantaneous Pn decreased by 53.63% compared with CK, and the stress index was 1.11; (2)dry-hot wind treatment could reduce the Pmax, enhance the ability of the flag leaf to adapt to the weak light, and reduce the ability to adapt to strong light. In addition, dry-hot wind treatment could enhance the Rd flag leaf; within 15-60 min, there were stronger effects of dry-hot wind on Rd, but no significant rule between each parameter in different time of dry-hot wind treatment; (3)dry-hot wind treatment within 60 min, stomatal limitation was the main cause for the effects of dry-hot wind on Pn, while more than 60 min, the main cause was nonstomatal limitation; (4)dry-hot wind had no significant effects on chlorophyll content during all forcing...