The Responses Of Nutrient,biomass And Diversity To Changing Soil P H In The Temperate Grassland Of Northern China

The effect of soil pH,one of the most important chemical properties of soils,on ecosystem functioning has been widely recognized by researchers.Although previous studies have found that the relationship between biomass and diversity,a hot topic in ecological research,is influenced by environmental factors,no study so far has tested the congruence of biomass-diversity responses to changing soil pH obtained from approaches of observational studies and manipulative experiments in grasslands.Here,by combining manipulative and observational approaches,we investigated the biomass-diversity relationship in response to soil pH in Inner Mongolia grasslands.We found that(1)Along a soil pH gradient transect,the concentrations of organic carbon,total nitrogen,total potassium,nitrate nitrogen,available phosphorus and potassium were negatively correlated to soil pH at 0-10 and 10-30 cm soil layers.Total phosphorus was not significantly correlated to soil pH.Ammonium nitrogen concentration was significantly negatively correlated with soil pH of both 0-10 cm and 10-30 cm layers.In the acid/alkaline addition experiments,with increasing soil pH,the concentration of nitrate nitrogen increased in 0-10 cm soil layer but decreased in 10-30 cm soil layer.Ammonium nitrogen,available phosphorus and potassium were negatively correlated with 0-10 cm and 10-30 cm soil pH.(2)Along the soil pH gradient transect,aboveground and root nutrient concentrations in different functional groups in relation to soil pH could be characterized by one-peak curves.The concentrations of plant nitrogen,phosphorus and potassium were highest when soil pH values were at the level of 7.28-8.45.In the acid/alkaline addition experiments,The concentrations of nitrogen in leaves also showed a significant U-shaped curve in relation to soil pH.The relationship between root nitrogen concentration in 0-10 cm layer and soil pH showed a one-peak curve.In contrast,root nitrogen concentration in 10-30 cm layer was negatively correlated with soil pH.The concentrations of phosphorus both in leaves and roots showed a one-peak curve in relation to soil pH.Plant potassium concentration was not significantly correlated to soil pH.(3)Along this studied soil pH gradient transect,both aboveground biomass and species richness showed a significant U-shaped curve in relation to soil pH.In contrast,belowground biomass was negatively correlated to soil pH.In the acid/alkaline addition experiments,the relationship between aboveground biomass and soil pH was characterized by a one-peak curve.This was also true for species richness in relation to soil pH at desert and typical grassland.(4)Along the soil pH gradient transect,diversity was positively correlated to aboveground but not to belowground biomass.Redundancy analysis of biomass and diversity and environmental factors showed that mean annual precipitation,soil C/N and soil pH explained most variations of these relationships.In the acid/alkaline addition experiments,a positive biomass-diversity relationship was found in desert grasslands,but not in typical grasslands(Dongsuqi and Dongwuqi)or in meadow grasslands.Redundancy analysis between biomass and diversity and environmental factors revealed that the biomass-diversity relationship was mainly affected by soil pH in desert and typical grasslands.Overall,along the aridity transect,the changes in soil and plant nutrients,plant community biomass and diversity with changing soil pH were influenced by environmental factors such as temperature,precipitation and soil type.Short-term changes in soil pH could directly affect the absorption and utilization of nutrients by plants through affecting the availability of nitrogen,phosphorus and potassium in soils,all of which might cause changes in plant species and even community structure.Changes in soil nutrient availability and pH collectively affected productivity and diversity and the relationship between them.The opposite results found in manipulative experiments vs.observational studies might be attributed to the fact that the observations along transect reflect the results of long-term adaptation.In contrast,manipulative experiments reflect the short-term response to environmental changes.