Environmental Interpretation Of More Flowers Than Fruits In The Cold Desert Perennial Ephemeral Iris Tenuifolia(Iridaceae)

Iris tenuifolia Pall.is a perennial early spring species that grows in the desert regions of northern xinjiang in China.In a natural habitat with windiness,the temperature varies greatly from day to night,and weather conditions during the flowering period are changeable,the species has the characteristics of large and colorful flowers,petaloid style,lamellar stigma,insect pollination,underground fruiting,more flowers than fruits per cluster.To understand the more flowers than fruits and sexual reproduction strategy of I.tenuifolia,we studied the floral morphologies,flowering pattern,breeding system and pollination characteristics of I.tenuifolia.The main results are as follows:(1)Iris tenuifolia begin to flower in late March or early April.In 2018 and 2019,the duration of florescence was 11 days and 22 days,the peak flowering was 6 days and 9 days respectively.The individual flowering phenology were concentrated and explosive of this species at the population level.The flower longevity was 3.96±0.99 days,no smell,the nectar secretion was mainly concentrated within 50 hours after flowering,nectar volume was 8.89 ± 7.90 μL per flower,sugar concentration of nectar was 28.85 ± 3.98%;The duration of pollen viability and stigma receptivity were 96 hours and 84 hours.The results of artificial pollination experiments showed that self-pollination and geitonogamy did not produce fruits,indicating that the breeding system of this species belongs to outcrossed;Anthophora altaica and Anthophora sp with long snouts were the main pollinators,they were all pollinated while burrowed into the pollination unit feeding nectar at the base of the perianth tube.There was a significant positive correlation between flowering display size and the visit frequency when control the display size of bush and numbers of flowers(R2=0.16,P<0.001),this indicates that the explosive flowering pattern can increase flower display and attract pollinators to visit flowers.(2)When there is windness and sunny day,the fruit set(F=867.43,P<0.05)and seed set(F=246.09,P<0.05)of artificial pollination were significantly higher than that of natural pollination,indicating that the existence of pollen restriction in this species;compared with adverse weather(windy and sunny,windness and cloudy,windy and cloudy days),the visit frequency(F=14.22,P<0.05),number of pollens deposition on the stigma(F=3.45,P<0.05),fruit set(F=4.89,P<0.05)and seed set(F=5.45,P<0.05)were also significantly under than that of windness and sunny days,this suggests that severe weather can reduce pollinator activity,lead pollinator limitation and exacerbating pollens limitation.Under the conditions of watering,fertilizing,flower thinning,fruit thinning and cross treatment,there was no significant difference in the fruit set(F=1.83,P=0.11)and seed set(F=1.11,P=0.35)between treated bushs and untreated bushs,it indicates that the fruit set and seed set of I.tenuifolia are less affected by resources.In the cold desert early spring environment of in northern Xinjiang,the big corolla,more nectar volume,longer flower longevity,concentrated and explosive flowering pattern can increase flower display,and attractting pollinators and enhance visitation of I.tenuifolia,there by ensure sexual reproductive success and improve the offspring fitness by outcrossing.In addition,the species relies on insect-pollination and has pollen limitations,the low temperature and windy desert environment in early spring can significantly reduce pollinator activities,increase pollen limitations,reduce fruit set and seed set of I.tenuifolia.