The association between a nurse cushion plant and a cluster root‐bearing tree species alters the plant community structure

Abstract

Several plant species have the potential to facilitate the presence of other plant species in the community, and yet most of our knowledge on this phenomenon comes from studies considering only one facilitator species. What happens when there are two facilitator species in the community? Are the facilitation effects by one species being altered by the presence of a potentially second facilitator species and vice‐versa (i.e. bidirectional facilitation)? Knowing that cushion plants ameliorate stress and improve soil fertility and that cluster root‐bearing species mobilize soil phosphorus (P), we investigated the potential occurrence of bidirectional facilitation via stress amelioration and nutrient exchange in the cushion plant Acaena integerrima (Rosaceae) and the cluster root‐bearing tree species Embothrium coccineum (Proteaceae). In southern Chile, where both species naturally occur, we compared aspects of the vegetative and reproductive performance of each species growing in association or not. We also determined if Embothrium alters the nurse effects of Acaena cushions on other species by evaluating species richness, frequency, and abundance in cushion plants with and without Embothrium. To infer the existence of nutrient exchange, we determined soil and leaf nutrient levels of both species. Species richness, frequency and abundance were higher within than outside Acaena cushions. Although the presence of Embothrium did not enhance the overall positive effects of Acaena on species composition, nine species occurred more frequently when Embothrium was present. Embothrium occurred more frequently and had a higher survival and leaf nitrogen (N) concentration when growing with Acaena than without it, although its growth and leaf P concentration were lower. In contrast, Acaena had a lower number of and mass of fruits per inflorescence and a higher leaf P concentration when growing with versus growing without Embothrium. Synthesis. The cushion plant Acaena integerrima facilitates the occurrence of many species in the community, including the cluster root‐bearing species Embothrium coccineum, which in turn enhances the facilitation effect of Acaena on certain species. When Embothrium and Acaena occur together, the latter improves its nutritional status but reduces its fitness, implying a lack of bidirectional facilitation.

Apoplastic histochemical features of plant root walls that may facilitate ion uptake and retention

“…We suggest that the lignified thickenings and pectins in the roots of Cardamine hupingshanensis , Alternanthera philoxeroides , Eichhornia crassipes , and Pistia stratiotes may trap ions before the hypodermis matures. These ions are then retained in the lignified walls, giving these species a competitive advantage over indigenous plants, particularly in oligotrophic environments [ 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 39 , 40 , 41 , 42 , 43 , 44 ]. Finally, the dense, fine roots of Cardamine hupingshanensis may allow the plant to hyperaccumulate Se in a manner that is similar to the hyperaccumulation of Cd in the dense root hairs of certain Arabidopsis thaliana genotypes [ 10 , 88 ] and in the phenol-rich cluster roots of species in the Proteaceae [ 21 , 22 , 23 , 24 , 25 , 49 , 50 , 51 , 52 ].…”

“…These ions are then retained in the lignified walls, giving these species a competitive advantage over indigenous plants, particularly in oligotrophic environments [ 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 39 , 40 , 41 , 42 , 43 , 44 ]. Finally, the dense, fine roots of Cardamine hupingshanensis may allow the plant to hyperaccumulate Se in a manner that is similar to the hyperaccumulation of Cd in the dense root hairs of certain Arabidopsis thaliana genotypes [ 10 , 88 ] and in the phenol-rich cluster roots of species in the Proteaceae [ 21 , 22 , 23 , 24 , 25 , 49 , 50 , 51 , 52 ]. This ability to hyperaccumulate ions supports the adaptation of these plants to phosphorus deprivation and/or nutrient-poor environments [ 22 , 23 , 26 , 50 , 52 ].…”

“…Similarly, plants in the Proteaceae have evolved cluster roots with lignified or phenol-rich cortical walls to adapt to environments deficient in phosphorus and other nutrients [ 21 , 22 , 23 ]. Plants with cluster roots potentially facilitate alterations in plant community structure [ 24 ] and outcompete species without cluster roots [ 25 ]. Thus, cluster roots are highly desirable in crop breeding [ 26 ].…”

Effect of different shrub species on their sub‐canopy soil and vegetation properties in semiarid regions

“…Similarly, Foronda et al (2019) indicated that plant diversity in semiarid gypsum communities accumulated in the vicinity of shrubs. In addition, Piper, Fajardo, & Baeza (2019) stated that shrubs facilitated the occurrence of many species in the plant community.…”

Effect of shrub encroachment on their sub-canopy soil and vegetation properties

“…Similarly, Foronda (2019) indicated that plant diversity in semiarid gypsum communities accumulated in the vicinity of shrubs. Also, Piper (2019) stated that shrubs facilitated the occurrence of many species in the plant community.…”