Threshold effect of the groundwater depth on the photosynthetic efficiency of <Emphasis Type="Italic">Tamarix chinensis</Emphasis> in the Yellow River Delta

Background and aims

Functional traits may underlie differences in niches, which promote plant species co-existence, but also differences in competitive ability, which drive competitive exclusion. Empirical evidence concerning the contribution of different traits to niche differentiation and the ability to supress and tolerate competitors is very limited, particularly when considering belowground interactions.

Methods

We grew 26 temperate grassland species along a density gradient of interspecific competitors to determine which belowground traits a) explain species’ ability to suppress and tolerate neighbours and b) contribute to niche differentiation, such that species with dissimilar trait values experience reduced competition.

Results

We found that having larger root systems with extensive horizontal spread and lower root tissue density enabled efficient suppression of neighbours but did not significantly contribute to the ability to tolerate competition. Species with deeper root systems, lower specific root length and less branched roots were better at tolerating competition, but these traits did not significantly affect the ability to suppress neighbours. None of the measured traits contributed significantly to niche differentiation, either individually or in combination.

Conclusions

This study provides little support for belowground traits contributing to species co-existence through niche differentiation. Instead, different sets of weakly correlated traits enable plants to either suppress or tolerate their competitors.