| The change of land use pattern/cover change is an important research content of global change and clipping is one of the important way of land use.However,the response of grassland ecosystems in different regions to multiple clipping frequencies is still unknown.In this study,two fenced natural grasslands in semi-arid and semihumid areas of the loess plateau were selected for a two-year field control experiment.The effects of clipping frequnecy on grassland ecosystem productivity and plant phytostoichiometry and the difference between the two regions were studied,aims at stoichiometric were evaluated by measuring aboveground biomass and plant nitrogen and phosphorus content.The differences of these effects between the two places are analyzed,which provides scientific theoretical guidance for the utilization and management of natural grassland in the Loess Plateau.Field control experiments included 9 treatments:C0(no clipping at growing season),C1(one clipping at the most vigorous growing season),C2,C3,C4,C5,C6,C8,C12(2?3?4?5?6?8?12 times clipping during growing season).The results showed that1)The above ground biomass of semi-arid grassland and semi-humid grassland increased at first and then decreased with the increase of clipping frequency in 2017 and 2018.During the growing season of 2018,the rainfall of the two places was higher than that of 2017,and in 2018,the above ground biomass of semi-arid plots and semihumid plots in C0,C1 and C0,C2 and C3 treatments were higher than those in 2017.And the increase in semi-humid plots is higher than that in semi-arid plots.However,the above ground biomass in semi-arid and semi-humid plots decreased and remained basically unchanged in 2018 compared with 2017 in semi-arid and semi-humid plots with high clipping frequency(C2-C12,C4-C12)in semi-arid and semi-humid plots,respectively2)Different clipping frequencies have a tendency to reduce soil water content in areas with less precipitation(in 2017 and 2018 growth seasons,the rainfall was 288 mm and 432 mm,respectively),but have no significant effect on soil water content in areas with higher precipitation(in 2017 and 2018 growth seasons,the rainfall was 483 mm and 605 mm,respectively).In the years with less rainfall(2017)and the area(semi-arid plots),there was a significant positive correlation between above-ground biomass and soil water content.3)Different clipping frequencies had little effect on soil nutrient content include TN?TP?AP and IN in short time,but there were significant differences and no uniform rules in individual years or in individual clipping plots.There was no significant difference in carbon storage in the surface layer of soil among different clipping frequencies.4)In areas with high rainfall,different clipping frequencies had a greater influence on the carbon and nitrogen of microbial biomass,which resulted in a significant positive correlation between the carbon and nitrogen of soil microorganisms and the aboveground biomass,and a significant negative correlation between the carbon and nitrogen ratio of soil microorganisms and the biomass.In regions with low rainfall,different clipping frequencies also had a certain effect on the microbial biomass of carbon and nitrogen,but there was no obvious rule.5)Plant N and P content increased with clipping frequency in both places,but plant P content increased more in areas with less rainfall,indicating that clipping had a greater effect on plant P uptake rate in areas with less soil water content.There was a significant negative correlation between plant nitrogen and phosphorus content and aboveground biomass in semi-arid and semi-humid plots.Plant N and P were negatively correlated with biomass in areas with more rainfall,but were not significantly correlated with biomass in areas with less rainfall.In regions with less precipitation,plant growth changed from P limit to N limit with the increase of clipping intensity,while in regions with more rainfall,plant growth was always within P limit. |
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