Abstract
According to the stress gradient hypothesis, competition intensity decreases or changes to facilitation with increasing environmental stress. However, the role of water level and nutrient heterogeneity in influencing plant-plant competition is far from clear. Relative yield total, relative yield, total N (TN) and total P (TP) contents, and N∶P ratios for Carex brevicuspis and Polygonum hydropiper were investigated in an experiment including 3 sediment types corresponding to different levels of nutrient availability (type Ι: 0–15 cm sand and 15–30 cm clay; type II: 0–30 cm mixture with 1∶1 sand and clay volume; and type III: 0–15 cm clay and 15–30 cm sand) and 2 water levels (0 and 15 cm). Facilitation occurred at 15-cm water level in the type I and type II sediments. The presence of C. brevicuspis facilitated the growth of P. hydropiper at the 15-cm water level in all sediment types. However, growth of C. brevicuspis was promoted only at the 15-cm water level in type Ι sediments. At the 0-cm water level, growth of each species was limited by the other species. TN, TP, and N∶P ratios of P. hydropiper were higher in the type III sediment than in the other 2 sediment types and at the 15- than the 0-cm water level. TN and TP contents of C. brevicuspis were highest in type I and type III sediments, respectively. The N∶P ratio of C. brevicuspis was higher in type I sediment than in the other 2 sediments and at the 15- than the 0-cm water level. Competition between these 2 species shifted to facilitation as the water level increased, and this facilitation might be regulated by sediment nutrient heterogeneity.
Published Version
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