title: Deviation from niche optima affects the nature of plant-plant interactions along a soil acidity gradient.
abstract: There is increasing recognition of the importance of niche optima in the shift of plant-plant interactions along environmental stress gradients. Here, we investigate whether deviation from niche optima would affect the outcome of plant-plant interactions along a soil acidity gradient (pH = 3.1, 4.1, 5.5 and 6.1) in a pot experiment. We used the acid-tolerant species Lespedeza formosa Koehne as the neighbouring plant and the acid-tolerant species Indigofera pseudotinctoria Mats. or acid-sensitive species Medicago sativa L. as the target plants. Biomass was used to determine the optimal pH and to calculate the relative interaction index (RII). We found that the relationships between RII and the deviation of soil pH from the target's optimal pH were linear for both target species. Both targets were increasingly promoted by the neighbour as pH values deviated from their optima; neighbours benefitted target plants by promoting soil symbiotic arbuscular mycorrhizal fungi, increasing soil organic matter or reducing soil exchangeable aluminium. Our results suggest that the shape of the curve describing the relationship between soil pH and facilitation/competition depends on the soil pH optima of the particular species.
authors.affiliation: College of Life Sciences, Zhejiang University, Hangzhou 310058, People's Republic of China.
authors.forename: Lei
authors.initials: L
authors.lastname: He
authors.affiliation: College of Life Sciences, Zhejiang University, Hangzhou 310058, People's Republic of China.
authors.forename: Lulu
authors.initials: L
authors.lastname: Cheng
authors.affiliation: College of Life Sciences, Zhejiang University, Hangzhou 310058, People's Republic of China.
authors.forename: Liangliang
authors.initials: L
authors.lastname: Hu
authors.affiliation: College of Life Sciences, Zhejiang University, Hangzhou 310058, People's Republic of China chandt@zju.edu.cn.
authors.forename: Jianjun
authors.initials: J
authors.lastname: Tang
authors.affiliation: College of Life Sciences, Zhejiang University, Hangzhou 310058, People's Republic of China chen-tang@zju.edu.cn.
authors.forename: Xin
authors.initials: X
authors.lastname: Chen
mesh_terms: D000535:Aluminum / Q000737:chemistry; D018533:Biomass; D017753:Ecosystem; D007887:Fabaceae / Q000254:growth & development / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D038821:Mycorrhizae / Q000254:growth & development; D012987:Soil / Q000737:chemistry*
chemical_list: D012987:Soil; D000535:Aluminum
keywords: acidity stress gradient; niche optima; plant–plant interaction; species tolerance