Explaining hydrological niches: the decisive role of below‐ground competition in two closely related Senecio species

Abstract

Summary1. Evidence from plant-community structure suggests that niche segregation between plant species is widespread, but the mechanisms are still generally obscure. We used experimental mesocosms to investigate the role of above-and below-ground competition in defining the distinct niche distributions of two Senecio species that separate along a water-table gradient in meadow habitats. In a target-border design, Senecio target plants were surrounded by six fence-sitting plants of Phleum pratense and fully factorial, randomised treatments for above-ground and below-ground competition, water level and nitrogen were applied. 2. Below-ground competition was found to be the most influential factor for plant biomass and seed production, whereas above-ground competition had negligible effects. Judging from their performances under different combinations of water level and nitrogen fertilization, the Senecio species showed different types of niche differentiation. Senecio aquaticus showed a preference for waterlogged over dry soils irrespective of the presence or absence of competition. Senecio jacobaea showed no preference for any hydrological condition, as long as below-ground interaction was prevented. In the presence of competing roots, it showed the expected preference for dry soils, especially under N-fertilized conditions. 3. Below-ground competition was especially intense under conditions of high supply of edaphic resources and even had the potential to entirely abolish any positive effects of increased water-or nitrogen-supply. This supports the highly debated view that the importance of below-ground competition increases rather than decreases with below-ground resource supply. A functional mechanism for the dry-habitat niche of S. jacobaea is suggested by the severe effect of competition on this species in waterlogged soil, especially when nitrogen was added. Since such conditions favoured growth of competing neighbours, the intensified depletion of other soil resources may have been the cause of the poor performance by S. jacobaea. 4. Synthesis. Niche differentiation can either be a genetically fixed preference or a result of current competition. Below-ground competition was found to be a much stronger driver of niche differentiation than generally assumed. Even in highly productive systems it can be the principal type of interaction, which is contrary to common assumptions and which might be the case when some but not all edaphic resources are in ample supply.

Effects of hydrology and competition on plant growth in a freshwater marsh of northeast China

“…In this study, the non-waterlogging treatment (0 cm water level) caused an increase in C. lasiocarpa biomass in the monoculture, but generally had no significant difference relative to mild-waterlogging treatment (10 cm water level) in all mixtures. This may be because interspecific competition suppresses the plant's growth at the physiological optimum (Laird and Schamp 2008;Bartelheimer et al 2010). Just as the relative yield of C. lasiocarpa showed in this study, the interference from D. angustifolia decreased with rising water level in 1:1 and 1:2 mixtures.…”

Root and shoot competition: a meta‐analysis

“…Most studies used a solid below-ground material (plastic, wood or metal) to partition the roots of potential competitors, while 12 experiments from three studies employing the Target technique used below-ground partitions consisting partly or fully of fine mesh net (Marvel, Beyrouty & Gbur 1992;Cahill 1999;Bartelheimer, Gowing & Silvertown 2010). The effect of root competition was lower overall in this subgroup compared with the 30 experiments from four studies also employing the Target technique but using solid below-ground partitions; however, this difference was not significant (not shown).…”

“…Cahill 1999Cahill , 2002, while others find no interaction (e.g. Lamb, Shore & Cahill 2007;Bartelheimer, Gowing & Silvertown 2010). Cahill (1999) found that the level of interaction varied with productivity from no interaction in unfertilized sites to positive interaction in fertilized sites.…”

Non-Native Plants Disrupt Dual Promotion of Native Alpha and Beta Diversity

“…2a), suggests competitive exclusion of native species by non-native species (Seabloom et al 2003). Possible mechanisms of competitive exclusion include reduced sites available for germination (Walker et al 2003) and limiting access to water, nutrients or both (Stubbs and Wilson 2004;Bartelheimer et al 2010;Everard et al 2010). The lack of significant reduction of native alpha diversity by Coriaria (Fig.…”