Abstract:

Drought is one of the key factors limiting the growth of oats （Avena sativa）. This experiment explored the effect of water deficit stress on the photosynthetic system of oats. The oat cultivar studied was ‘Qingyan No.1’ and plants were grown in pots in order to control water supply. A gradient of four water treatments was set up， namely： normal water supply ［CK， 75% field capacity （FWC）］， mild stress （60% FWC）， moderate stress （45% FWC）， and severe stress （30% FWC）. Water deficit stress during the crop growth period was applied at four growth stages， namely： jointing stage water deficit （SJ）， heading stage water deficit （SH）， flowering stage water deficit （SF）， and milky-grain stage water deficit （SM）. Normal water supply throughout the growth period was used as the control treatment （CK）. By exploring the response to water deficit stress of oat chlorophyll fluorescence parameters at different crop growth stages， it was hoped to provide theoretical insight for breeding drought-resistant， water-saving and high-yielding oat cultivars for cultivation on the Tibetan Plateau. It was found that： 1） The overall impact of different water deficit stress levels was： 30% FWC>45% FWC>60% FWC； 2） The overall impact of stress at different growth periods was： SM>SF>SH>SJ； 3） The interaction between stress degree and stress period （Sd×Sp） has the most significant effect on the chlorophyll parameters of oats. The chlorophyll fluorescence parameters were most affected in the treatment with 30% FWC at SM. At this time， non-stomatal factors are the main limitation to photosynthesis， mainly manifested as the inactivation of the PS Ⅱ reaction center and hindered photosynthetic electron transfer. At 60% FWC and SJ， chlorophyll fluorescence parameters were the least affected. The main factor affecting photosynthesis was stomatal limitation； 4） At 45% FWC， in the SH and SF periods the oat plants were able to coordinate transpiration and carbon assimilation through the stomatal conductance of the leaves. 5） Observed changes in chlorophyll fluorescence parameters indirectly reflected changes in the photosynthetic capacity of oats under drought stress. Compared with CK， Y（NO）， NPQ， Y（NPQ） and β increased by 85.52%， 65.21%， 33.76% and 26.60%， respectively， while F_v， F_m， ΦPS Ⅱ， ETR， F_m'， F_s，F₀'， qP， F₀， α and F_v/F_m decreased by 84.86%， 75.41%， 75.03%， 75.00%， 70.89%， 61.38%， 57.73%， 57.06%， 48.86%， 45.61% and 38.50%， respectively. The comprehensive analysis showed that oat chlorophyll fluorescence parameters had different degrees of response to drought during the whole growth period， and the capacity to affect photosynthesis increased synchronously with the water deficit gradient.

Key words: drought stress, growth stage, chlorophyll fluorescence parameters, oats