Impact of potential climate and CO2 change on productivity of winter wheat (Triticum aestivum L.) - physiological dependances

The aim of the paper herein was to quantify physiological bases of winter wheat grain yield changes caused by global climate and CO2, concentration in atmosphere (CO2) changes for year 2030 in comparison with actual weather of six reference years 1995 to 2000 (RP) in maize growing region of Slovakia. The simulations with dynamic mathematical crop growth model MACROS adapted by us were used. Input data on weather, soil and plant of Ilona variety were measured near and in field trials established in 1995-2000 in Piestany (south western part of the Slovak Republic). The changes of air temperature (T) and rainfalls sum (Z) for year 2030 from ten, for conditions of Slovakia adapted climate change scenarios, and change of CO2 concentration from IPCC IS92a scenario were taken over. More detailed methods are presented in the previous paper together with analysis of T, Z and CO2 influences on winter wheat grain yield non-limited by mineral nutrition, diseases and pests. The average outputs of the simulations for ten simulation inputs of individual climate change scenarios and six reference years for each of climate variables and their combinations showed that final (RP+TZ+CO2) grain yield 2030 year equaled 96.2 % from the present time level (RP) will be caused by two contrary trends of physiological consequences: Due to increase of CO2 concentration alone to 445 ppmv level in 2030 year (RP+CO2) change of grain yield by 24.0 % will be caused through the changes of above-ground dry matter yield by 24.7 %, totaled throughout ontogenesis and for stand level of gross photosynthesis PCGWT by 24.9 %, net photosynthesis PCNT by 25.8 %, total respiration RCRT by 23.4 %, maximum LAI by 21.0 %, transpiration TRWT by 14.4 %, evapotranspiration EVTRT by 7.1 % and photosynthetic efficiency of transpiration (WUPWT = PCGWT/TRWT) by 9.3 %. The warming alone (RP+T) will decrease the relative values of these processes, inclusive of Julian date of grain full ripeness KVO change by -6 days and harvest index (ratio of grain yield to above-ground dry matter yield) change by -3.8 %. In the final change of grain yield in 2030 (RP+TZ +CO2) in comparison with the present time (RP) the positive compensation effect of CO2 koncentration enrichment on mentioned physiological processes is incorporated. Between grain yield and values of above-ground dry matter yield, PCNT, WUPWT, PCGWT, RCRT, LAI max, TRWT and KVO are the positive highly significant correlation coefficients. The increased CO2 concentration and air temperature will cause the changes of canopy transpiration rate per unit of assimilation area TR by -4.3 % and by +8.2 % and photosynthetic efficiency of transpiration WUPWT by +9.3 % and -9.5 %. Some ambiguities of the mentioned relationships and some aspects of breeding and growing technology of winter wheat corresponding with adaptation for conditions of global climate change in maize growing region of Slovakia are also discussed.