| Global warming accelerates the global water cycle.In northeast China,the rainfall amount and rainfall distribution have fluctuated greatly in the past 50 years,resulting in the change of rainfall pattern.Rainfall pattern alteration will have important influence on plant growth,reproduction and phenology.Germination is the beginning of plant life history.Under suitable conditions,annual weeds can germinate throughout the growing season,forming a germination series from early spring to early autumn.Annual plants have strong adaptability and quick response to environmental changes,so they are ideal materials for studying phenology and seed germination characteristics under environmental condition changes.This study was conducted in rainout shelters to simulate rainfall amount and rainfall interval alterations,and delayed germination by different sowing time.This study aimed at exploring effects of rainfall pattern changes on phenology and offspring seed germination characteristics of Chenopodium album and Amaranthus retroflexus and to reveal the mechanism of annual plants adapt to the environment changes.Additionaly,we expected to providing scientific accumulation for grassland management and weed control.Main results are as follows:(1)Delayed germination had significant effects on vegetative growth period,flowering period,flowering period and seed maturity period of both C.album and A.retroflexus.For example,in the 4th sowing times in 2017,vegetative growth period of C.album experienced 70.3d,54.9d,42.3d and 29.5d,while A.retroflexus experienced 55.0d,39.5d,43.1d and 27.9d,respectively.In 2018,C.album experienced 75.9d,57.0d,38.8d,31.1d,and A.retroflexus experienced 56.8d,47.5d,36.1d and 29.9d,respectively.Besides,difference between sowing time in the same year reached a significant level(P < 0.05).The results showed that the vegetative growth period of the two plants was significantly shortened with the delay sowing.(2)Rainfall pattern change had different effects on phenology of C.album and A.retroflexus at different sowing time.For example,In the 2nd sowing of C.album in 2017,seed maturity period of 15 d rainfall interval experienced 17.2 days under multi-year average rainfall amount,which was significantly higher than the 12.4 days of 5d rainfall interval.At 3rd sowing time,seed maturity period of increasing 30% rainfall amount was 17.9 days at 5d rainfall interval,which was significantly longer than 15.6 days of multi-year average amount.At 3rd sowing time of A.retroflexus in 2017,seed maturity period of 5d rainfall interval experienced 25.3 days under increasing 30% rainfall amount,which was significantly longer than that of 18.6 days under 15 d rainfall interval.At 1st,2nd and 4th sowing time,rainfall pattern change had no significant effect on seed maturity of A.retroflexus.The results showed that the response of the two plants to rainfall pattern change highly depended on sowing time.(3)Under two temperatures(15/25 ?,25/35 ?),offspring seed germination rate,germination index and the germination potential of A.retroflexus decreased significantly with sowing time delayed.In addition,C.album had similar trends with A.retroflexus in 2018.The results showed that delayed germination had significant effects on the offspring seed germination characteristics of two plants,which was harmful to germination.(4)Rainfall pattern changes had complex influence on offspring seed germination characteristics of C.album and A.retroflexus at different sowing time.The maximum germination rate,germination index and germination potential of C.album and A.retroflexus mostly occurred at 15 d rainfall interval.This indicated that prolonged rainfall interval was beneficial to offspring seed germination of C.album and A.retroflexus.(5)Germination characteristics showed the same response to different germination temperatures of C.album and A.retroflexus.Offspring seed germination rate,germination index and germination potential were the maximum in 15/25 ? of C.album,and most of that were significantly higher than 5/15 ? and 25/35 ?.Under 5/15 ?,offspring seed of A.retroflexus were hardly germinated.Furthermore,germination characteristics under 25/35 ? was significantly higher than 15/25 ?.The results indicated that lower temperature and higher temperature were not beneficial to offspring seeds germination of C.album,while A.retroflexus was suitable for higher germination temperature. |
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