| As global climate change intensifies,terrestrial ecosystems has been profoundly changed.The natural grassland in Qinghai-Tibet Plateau and Inner Mongolia Plateau are particularly sensitive to global climate change.Global warming,changes in precipitation patterns,and increasing atmospheric nitrogen deposition have not only changed the productivity,community structure,and species diversity of natural grassland communities,but also affected the spatial distribution patterns of populations to varying degrees.In this study,the spatial pattern analysis was used to explore the effect of simulated nitrogen deposition,nutrient addition,warming and precipitation on spatial distribution pattern of dominant species in temperate meadow of Inner Mongolia and alpine meadow in Qinghai-Tibet Plateau.The goal of this research was to reveal the response of population distribution pattern to global climate change.The experimental gradient of nitrogen deposition and nutrient addition in warm meadow grassland were 2.5g N/m~2,5g N/m~2,10g N/m~2,10g P/m~2 and 10g N+10g P/m~2,respectivly.The added nitrogen concentration in alpine meadow is as the same as that in warm meadow grassland,and the phosphorus addition is 5g P/m~2.The simulated warming and precipitation control treatment in alpine meadow grassland involved:warming and increasing precipitation,warming and reducing precipitation,increasing precipitation at normal temperature,reducing precipitation at normal temperature and increasing temperature.Increasing or decreasing precipitation was by about 50%,and warming treatment was increased by about 0.56°C.The fixed position samples in each treatment were perennial observed,and the spatial position of different dominant plants was obtained by photographic positioning method.The spatial distribution pattern of different scales was analyzed by Ripley's K function.The main findings and conclusions are as follows:1.The spatial distribution pattern of dominant plant populations showed the same trend in simulating nitrogen deposition and nutrient addition in two different natural grassland types.However,there were some distinction due to differences in species.At small scale,the dominant rhizomatous grasses in temperate meadow(Leymus chinensis)and alpine meadow(Elymus nutans)showed significant spatial cluster under the impact of nitrogen-phosphorus addition in compared with the control area.However,E.nutans was more susceptible to phosphorus accumulation than L.chinensis.The cluster of dominant tussock graminoids specie(Stipa aliena)in the alpine meadow increased with the increasing nitrogen concentration,while the spatial distribution pattern of dominant tussock graminoids specie(Stipa baicalensis)in temperate meadow(L.chinensis)was not affected by nutrient addition.2.The interspecific relationship of dominant plants is affected by varying degrees of nitrogen addition.In temperate meadow,high concentrations of nitrogen input(i.e.10g N/m2)enhanced the competition between dominant plants,while low concentrations of nitrogen(i.e.2.5 g N/m2)increased positive interspecific association.By contrast,high concentrations of nitrogen input increased positive interspecific association in the alpine meadow,while low concentrations of nitrogen had little influence on interspecies relationship.3.The dominant rhizomatous grasses in the temperate meadow(L.chinensis)in temperate meadow was more sensitive to water and nitrogen coupling.The degree of spatial cluster(scale:9-24 cm)and population density in the years of higher precipitation were significantly higher than those in normal years.The biomass of L.chinensis showed a significant positive correlation with annual precipitation and nitrogen deposition.However,the spatial distribution patterns of dominant broadleaf(Artemisia tanacetifolia)was not influenced.However,biomass showed a significant negative correlation with the concentration of nitrogen and was inhibited by the expansion of L.chinensis population.4.Alpine meadows have lower temperatures and relatively higher soil moisture content,but the effects of changes in temperature and precipitation on the spatial distribution pattern of dominant plants are also characterized by species.The increasing cluster of tussock graminoids(S.aliena)increased with warming at the medium scale(scale:19-25cm),while the spatial distribution pattern of other plant populations did not change significantly.The spatial cluster pattern of rhizomatous grass population(E.nutans)increased significantly under increased water treatment(scale:1-7cm scale)and decreased water(scale:1-11cm scale)treatment.Warming and increased precipitation increased cluster at all observed scale(scale:1-25 cm).S.aliena population pattern increasing clustering in increased precipitation(scale:20-25 cm)and warming and decreased precipitation(scale:12-25 cm).The above results indicate that water is still an important factor affecting the distribution pattern of alpine meadow populations,and the temperature is more affected by the hydrothermal coupling.5.Warming had significantly affected the interspecific relationship of dominant species in alpine meadow by aggravating competition between rhizomatous grasses and miscellaneous grass,leading to the stronger competition between E.nutans and A.diplostephioides in mesoscale(2-22cm).The effects of precipitation on interspecific relationships were different:competition between S.aliena and E.nutans would be more intensive when rainfall increased or decreased,resulting in spatially clustering groups.There was a positive correlation between tussock graminoids or rhizomatous grasses and miscellaneous grasses in the initial stages of reducing precipitation treatment.However,with the continuous drought,the positive interaction gradually would be weakened and finally disappeared.In general,different natural grassland types,different life types and their interspecific relationships have different responses to global warming,change of precipitation pattern and the increasing atmospheric nitrogen deposition.This difference depends,on the one hand,on the way plants use resources and their competitiveness.On the other hand,it is restricted by the balance of soil nutrients.Rhizomes,among different grassland types,shows strong resource utilization efficiency and competitiveness,and are most sensitive to changes in water and nutrients.Especially in the case of strong clustering under increased nutrient,water-nitrogen coupling and hydro-thermal coupling,and has a certain indicating effect.This study provides a new perspective and data for revealing the theoretical study of the impacts of global change on ecosystems,and has certain reference value for grassland management in the context of global climate change. |
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