The Responses Of Phenological Characteristic Of Crop And Herbage To Climate Change In Northeastern Tibetan Plateau

As an independent and complete natural geographical unit,the Qinghai-Tibet Plateau has the unique advantages of complete vegetation types,obvious spatial heterogeneity,sensitivity to global changes and light human disturbance,which makes the temporal and spatial changes of vegetation phenology and its response to climate change become the focus of global change research.Most of the existing researches are carried out using remote sensing data.The remote sensing data from different sources have great uncertainty on the monitoring results of phenology,and the vegetation phenology research in this area has not yet reached a conclusion.This study focused on the phenological period of crops and pastures in the northeastern part of the Qinghai-Tibet Plateau.Using phonology data of crops and pastures from 24 agricultural and animal husbandry meteorological observatories established by the meteorological department of Qinghai Province in the 1980 s and grassland community phenological data,corresponding yield or biomass data,meteorological data and other auxiliary basic data observed by 20 ecological meteorological observatories which were established in 2003,we explored temporal and spatial dynamics of crops or pasture phenology and interactions between climate change and phenological characteristics under different climates and altitudes in the northeastern Tibetan Plateau.The main results and conclusions are as follows:(1)From 1961 to 2016,the annual average temperature in the northeastern part of the Qinghai-Tibet Plateau increased significantly at a rate of 0.38 °C/10a(P<0.01)which was higher than the national temperature increase rate of 0.32 °C/10 a.The temperature increase in winter is the most obvious,reaching a rate of 0.55°C / 10 a.The heating rates of the highest and lowest temperatures were 0.44 °C/10 a and 0.59 °C/10a(P<0.01),respectively,and the increase was asymmetric.The heating rate in the northern region is higher than that in the southern pastoral area,and the temperature increase in the Qaidam Basin is the most obvious,reaching a rate of 0.49 °C/10a(P<0.01),followed by the eastern area of Qilian Mountains.The lowest temperature of 0.59 °C/10 a showed a very significant increase(P<0.01),which was more obvious than the highest temperature.The annual precipitation increased slightly,with an average increase of 5.9mm/10 a,and the trend of precipitation increased much more obviously since the beginning of the century.The precipitation in the Qinghai Lake area is the largest(13.0mm/10a),followed by the Sanjiangyuan area and the Qaidam Basin,while the change of the eastern agricultural area is not obvious.The interannual precipitation has a decreasing trend from the southeast to the northwest,and the rainy belt with annual precipitation greater than 500 mm has formed along Zaduo,Chenduo,Malang and Henan areas.The annual sunshine hours are between 2351.5-3397.7h,which is characterized by the strip-shaped distribution from the Qaidam Basin in the northwest to the southeastern part of the Jiuzhi area.The sunshine duration of the Sanjiangyuan area in the mid-latitude of the 56 a is increasing.In other regions,the number of sunshine hours decreased,and the decrease of sunshine hours in summer was the most obvious.The accumulated temperatures of 0°C,3°C,5°C and 10°C were significantly increased by 73°C/10 a.The number of days of biological limit temperature ≥10°C,≥5°C,≥3°C and ≥0°C has changed significantly,extended at 4.5d/10 a,3.9d/10 a,3.8d/10 a,4.1d/10 a respectively.(2)The wheat sowing period in the Qaidam Basin was significantly delayed from 1980 to 2007,and the delay rates of Nomhong and Delingha were 14.5 d/10 a and 7.4 d/10 a respectively(P<0.01).The maturity period showed an early trend,and the advance trend of Nomuhong reached 4.8d/10a(P<0.01).The growth period showed a shortening trend and the shortening rates of Golmud,Nomuhong and Delingha were 4.7d/10 a,19.3d/10 a,8.3d/10a(P<0.01)respectively.The shortening of the sowing-seedling period is the reason for the shortening of the vegetative growth stage,and the shortening of the milky-maturity to maturity period is the main reason for the shortening of reproductive growth.The shortening of vegetative growth is more pronounced than the shortening of reproductive growth.The ground temperature has obvious correlation with sowing and maturity.The higher the ground temperature,the earlier the sowing date;the later the maturity period,and the higher the yield accumulation.The temperature in May-September has a significant positive correlation with the yield of spring wheat.(3)There are differences in the responses of species to climate change at the species scale,while the differences in the northern regions are more complicated.The fore-grass pastures in most areas of Sanjiangyuan showed an early trend,while three of the nine pastures observed in the Qinghai Lake area showed an early trend,and six showed a postpush trend.In most areas,the flowering period showed an early trend,the yellow-sweet period showed a post-pushing trend,and the growing season showed a prolonged trend.The yellow-wheat period changed more obviously than other phenological changes.At the community scale,the grassland phenology of 20 stations showed obvious regional differentiation.In most areas of Qinghai Lake and Qilian Mountains,the grassland greening period was generally delayed.Most areas in the upper reaches of the Yellow River showed consistent trends in returning to green.The greening period of most of the areas in the source area of the Yangtze River and the Lancang River have been postponed.Ten regions with an altitude below 3500 m showed consistent delays,while the changes in the time of returning to green with higher altitudes were significantly different.(4)On the community scale,the greening period of 20 grassland communities was concentrated between 120-145 d.The greening time of alpine meadow grassland or the warm grassland grass community such as Haitang and Xinghai was earlier than other areas for many years.The greening time of the two highest areas(the Weihe River grassland and the Qingshui River grassland)had always been the latest.Precipitation plays an important role in grassland regreening in the northeastern part of the Qinghai-Tibet Plateau.In general,the greening period of the grassland community in the north of the 500 mm precipitation line is postponed,and the time of south area is advanced.Most of the yellow-dry time is concentrated between 255-275 d,which is more concentrated than the regreening time.In the Banma and Nangqian areas,the yellow-dry time were the latest in 93% of the years.The Tuotuo River and Qingshui River with the highest altitudes have the shortest growth season,and in Haibei and Qilian are with the lowest altitudes have the longest growth season,and the altitude has obvious influence on the growing season but is not the only determining factor.60% of the grassland growing season has a tendency to shorten.The growing season of the grassland around the Qinghai Lake,grassland in the Qilian Mountains,also the Yangtze River and the Lancang River source area is shortened,while the growing season in the upper reaches of the Yellow River is prolonged.(5)In the past 14 years,the above-ground biomass of grassland in the northeastern Tibetan Plateau has a significant response to monthly mean temperature and precipitation changes,but different community types have different responses to climate change.The average monthly temperature in most months was positively correlated with the peak biomass of alpine meadows and alpine grasslands,while the monthly average temperatures in October and June of the previous year were significantly negatively correlated with the peak biomass of warm grassland.The monthly precipitation is positively correlated with the aboveground biomass of alpine meadows,but there is a big difference of the correlation between of alpine steppe and warm steppe about the above-ground biomass;it is worth noting that in warm and humid climates,the increase in the peak value of alpine meadow above-ground biomass is faster than that in the alpine grassland,while the increase in the peak biomass of the warm grassland is significantly smaller.(6)For two time periods from 1989-1999 to 2000-2010,in high altitude areas,the average phenological period was advanced for 6-25 days and the growing season was extended by 3 days;in low-altitude areas,was re-greening period was advanced for 1 day,the remaining phenological periods were delayed by 1-9 days,and the growing season was extended by 6 days.The growth of alpine alfalfa in high-altitude areas is more susceptible to climate change and its habitat is more fragile.(7)The increase of the minimum temperature in the high-altitude area is greater than that in the low-altitude area,while the increase of the maximum temperature is lower than in the low-altitude area.Climate warming makes the growth and development of crops prolonged.In order to avoid the impact of frost and other disasters,the strategy of actively adapting to climate change is that the wheat sowing period in the high altitude area of the plateau is postponed,and the warming leads to the early maturity,shortened growth period and increased production fluctuations;while the low-altitude spring wheat planting period was not advanced,the maturity period was basically unchanged,the growth period was prolonged,and the yield decreased.Tillering is the “buffer” of the environment and the group.The adaptation of wheat to the environment and the automatic regulation of the wheat population are largely carried out by tillering.The interannual fluctuations of alfalfa in high altitude areas are higher than those in low altitude areas.Forage grass growth is more susceptible to climate change and its habitat is much more fragile.In the same area,the phenological changes of crops and pastures were basically the same,but the change range was significantly smaller than that of natural pastures.From 1987 to 2004,the emergence(germination)period of crops and pastures was significantly advanced,and the emergence period of crops advanced significantly at the trend of 5.9d/10a(P<0.01),and the germination period of forages advanced significantly at the trend of 10.6d/10a(P<0.05).