Characteristics of flag leaf photosynthesis and root respiration of four historical winter wheat varieties released over recent decades in semi-arid Northwest China

Abstract

A pot-culture experiment was conducted to characterize the flag leaf photosynthesis ('Pn') and root respiration in four historical winter wheat cultivars on the Loess Plateau in Northwest China. We compared 4 varieties of winter wheat ('Triticum aestivum' L.) that were released over the recent decades. These are Bima 1 (released in the 1950s) and Changwu 7125 (released in the 1970s) that represent the old varieties, and Changwu 131 (released in the 1980s) and Changwu 135 (released in the 2000s) that represent the new varieties. At antithesis, Flag Leaf Pn was significantly higher (p ≤ 0.05) for the new varieties than for the old ones during the day (between 11:00h and 15:00h) except in the early morning (at 11:00h) and the late afternoon (at 17:00h). By contrast, root respiration in the old varieties was higher than in the new ones in the morning (07:00 - 09:00h) and evening (19:00 - 23:00h), whereas it exhibited the opposite pattern between 11:00h and 17:00h. The new varieties also maintained significantly higher values of effective PSII quantum yield (ΦPSII), apparent rate of photosynthetic electron transport (ETR), coefficient of photochemical quenching ('q'P) and coefficient of non-photochemical quenching (NPQ) than the old varieties at low soil-water content.The differences in chlorophyll fluorescence performance suggested that the new varieties might be more drought tolerant than the old ones, in consistence with that the former produced higher grain yields under drought conditions than the latter. Our study indicates that, over the past 6 decades photosynthetic activities and drought tolerance had improved, while root respiration has fallen resulting in yield increases in the new winter wheat varieties compared with old varieties on the semi-arid Loess Plateau of China.