The Resistance And Resilience Of Grassland Productivity To Extreme Drought

Globally,extreme droughts are likely to become more frequent,more intense,and longer in duration with climate change.Extreme drought has caused severe impacts on grassland which is very sensitive to the changes of precipitation.However,there are 4scientific questions have not yet been well explored:(1)the differences in the resistance and resilience of grassland aboveground net primary productivity(ANPP)in different grassland ecosystems.(2)The effects of multi-year extreme drought on ANPP resistance and the response of ANPP resilience with increasing recovery time(3)The effects of different extreme drought patterns on ANPP resistance and resilience.(4)The mechanisms that drive changes in ANPP resistance and resilience.We relying on the China extreme drought network,and set up 6 experimental sites according to the precipitation gradient in Inner Mongolia grassland,including meadow grassland,typical grassland and desert grassland.The treatments are control(CON),reducing 66%rainfall in four months of the growing season for 4 years and then recover 2 years(CHR),reducing 100% rainfall in two months of the growing season for 4 years and then recover 2 years(INT).We measured the total,different functional groups,dominant and non-dominant species ANPP to explore 3 questions: the differences in the resistance and resilience in different grassland ecosystems;the changes in resistance and resilience over time;the differences in resistance and resilience to different extreme drought patterns.We also measured plant diversity,plant functional traits,and collected precipitation,temperature,and aridity indices at each site to explore the mechanisms that drive changes in ANPP resistance and resilience.The main results are as follows:(1)Extreme drought reduced total ANPP,the total ANPP decreasing by 20%,52%,55%,52%,72%,and 53% from wettest to driest sites,respectively.The resistance of total ANPP was mainly driven by the resistance of grasses and dominant species.(2)The total ANPP showed a cumulative effect in response to the multi-year extreme drought,resistance decreases with increasing duration of drought.Combining the six sites and two extreme drought treatments,the total ANPP decreased by 28%,42%,43% and 62%,respectively over the 4-year period.The total ANPP cumulative effect was mainly driven by the cumulative effect of forb and subordinate species ANPP.Species richness and plant height resistance decreased with drought time was also important reason.(3)The total ANPP resistance to CHR was higher than INT.Combining the 4-year results from the 6 sites showed that the total ANPP was reduced by 40% and 49% under the CHR and INT treatments,respectively.Species richness and forb ANPP were more affected by INT treatment at most sites and years,resulting in a greater effect of INT on total ANPP.(4)Total ANPP showed high resilience after the cessation of extreme drought.The total ANPP at all six sites fully recovered to CON levels in the first year after the cessation of extreme drought treatment.In the second year of recovery,total ANPP showed a super-recovery,which was 5% and 9% higher under the CHR and INT treatments than those in CON.The compensatory effect between grass and forb ANPP,dominant and subordinate species ANPP promoted rapid recovery of total ANPP at most sites.Complete recovery of plant height,leaf nitrogen content and leaf dry matter content area also ensured complete recovery of total ANPP.In conclusion,the total ANPP of desert grassland was most sensitive to extreme drought,multi-year extreme drought can decrease the total ANPP resistance,changes in precipitation distribution due to different extreme drought patterens can also have a large impact on resistance.However,the resilience of grassland ecosystems was high,with total ANPP recovering rapidly after extreme drought ceases.This study elucidates the response and recovery of grassland ecosystem productivity to extreme drought at the regional scale,and clarifies the mechanism of response and recovery.Our study provides an important theoretical basis for preventing extreme drought from hindering the development of grassland animal husbandry and the harm of ecological environment in northern China.