| In the context of global climate change,a large number of climate models predict that the frequency of extreme rainfall and extreme drought will greatly increase in the future and lead to changes in rainfall patterns.Plants,litters and soils are important participants and substrates in ecosystem nutrient cycling.How their nutrient elements respond to changes in rainfall patterns is of great significance for maintaining ecosystem stability and sustainable service functions.This study was carried out at the trough experimental site of the Jinfo Mountain Karst Ecosystem National Field Observation and Research Station,Southwest University.Forty awnings were built in the natural plant community,and the total rainfall was kept unchanged by blocking some rainfall and then filling up,but only the frequency and time distribution pattern of rainfall intensity was changed,so as to simulate the influence of future rainfall pattern change on the material cycle of the ecosystem.Starting from plant leaves,litters and soil,this study collected leaves of 7 kinds of annual herbaceous plants growing in the rainfall experiment field,measured the contents of 8 nutrient elements C,N,P,K,Ca,Fe,Mg and Mn,calculated the stoichiometric ratio of C,N and P.We analyzed how the nutrient elements and stoichiometric ratio of plant leaves responded to the change of rainfall pattern,and verified whether the element in plant leaves conforms to the " Stability of Limiting Elements Hypothesis ";The contents of C,N,P and K in 17 litters were measured by decomposition bag method,and the stoichiometric ratio of C,N and P was calculated.The effects of changes in rainfall pattern on the decomposition of litters in karst areas and the nutrient release and stoichiometry during decomposition were explored;The contents of C,N,P,K,Ca,Fe,Mg and Mn in soil were determined by five-point sampling method and the stoichiometric ratios of C,N and P were calculated.The effects of rainfall pattern change on soil nutrient elements and their stoichiometric characteristics were investigated.The main results are as follows:(1)The increase of extreme rainfall intensity and frequency inhibited the absorption of nutrient elements in plant leaves.Compared with normal rainfall,the contents of other elements except Ca and Mg in leaves tended to decrease.The N:P values of plant leaves under different rainfall treatments were all less than 10.According to the N:P Threshold Hypothesis,the growth of all plants was restricted by N.The N:P ratio of leaves was significantly lower than the global average,and the N:P ratio of the control group was the lowest,indicating that the plant growth rate was higher under the four rainfall patterns,and the increase of extreme rainfall frequency contributed to the increase of plant growth rate.The element content in leaves is relatively stable,which is less sensitive to rainfall changes,and the element with higher plant demand is more stable,which is consistent with the hypothesis of limited element stability.(2)The change of rainfall pattern had no significant effect on the release of elements in litters,except for the release of element P,which increased significantly at 2and 4 months of decomposition.However,after 6 months of decomposition,there was no significant difference in the release of element P in litters of different treatment groups.After the change of rainfall pattern,the number of heavy rainfall increased,and the leaching process of litters was enhanced,leading to the mass loss and decomposition of elements in the form of ions or inorganic compounds in the early decomposition of litters.The change of rainfall pattern had little effect on the C:N ratio of litters,but had similar effect on the C:P ratio and N:P ratio of litters.The main factor affecting the mass loss of litters is the quality of litters themselves(litter type),and the change of rainfall pattern has no significant effect on the mass loss of litters.(3)In the 10 months of experimental treatment,the response of soil elements to the change of rainfall pattern was not strong,only the contents of P,Mg and Ca were different among different treatment groups,while the contents of SOIL C,N,K,Mn and Fe were not significantly changed.It may be because of the lag effect of rainfall changes that short-term rainfall pattern changes have a weak impact on soil nutrients,failing to reach a significant level.After stratified sampling of soil in rainfall control experiment base,it was found that C,N,P,K elements were higher in the first layer of soil,with "surface aggregation" phenomenon.Soil C:P and N:P had the same change trend among different rainfall patterns.The results showed that the changes of short-term extreme rainfall intensity and frequency only had limited effects on plant leaf,litter-soil nutrient elements and stoichiometric characteristics in karst areas.The change of rainfall pattern inhibited the absorption of nutrient elements in plant leaves and reduced the content of nutrient elements in leaves.The change of rainfall pattern had no significant effect on the release of elements and decomposition of litters,but promoted the decomposition of litters to a certain extent.Short-term change of rainfall pattern had a weak effect on soil nutrient content,and the effect did not reach a significant level.This study elucidates the effects of short-term rainfall patterns on the nutrient elements contents in plant leaves,litter and soil.The results of this study help to better reveal the regulation mechanism of nutrient elements among grassland ecosystem components and the response strategy of ecosystem element cycling process to future rainfall pattern change in karst region,and provide an important reference for the protection and restoration of fragile ecosystem in karst region. |
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