Inclusion of Intra- and Interspecific Facilitation Expands the Theoretical Framework for Seagrass Restoration

Restoration is increasingly utilized as a strategy to stymie the loss of coastal habitats. Coastal habitat restoration has predominantly emphasized designs that minimize physical stress and competition. As evidence of the pervasiveness of this approach, we conducted a global survey of seagrass restorationers and found a strong affinity for stress-avoidant designs with adult shoots in dispersed rather than aggregated configurations. To test the alternative hypothesis that including positive interactions can enhance restoration success, we experimentally incorporated: (i) interspecific facilitation (clam additions) into seed sowing, and (ii) both intra- and interspecific facilitation (planting a single-large versus multiple-small patches and adding clams) into shoot planting. Clam additions to seeds significantly enhanced plant biomass and patch size; and nutrient analysis suggested the causative mechanism was clam enhancement of available nitrogen. In contrast, adult outplant growth was enhanced by intra- but not inter-specific facilitation. Dispersed configurations consistently declined, whereas large-intact patches, which had the same initial biomass as dispersed plots, increased in patch area and doubled in shoot density. These results demonstrate that expanding restoration strategies to include positive interactions with respect to seagrass ontogeny has the capability to switch the trajectory of restoration from failure to success.

Facilitation between ecosystem engineers, salt marsh grass and mussels, produces pattern formation on salt marsh shorelines

Interspecific facilitation between ecosystem engineers, such as salt marsh grass and mussel aggregations, is a key process that structures communities and enhances biodiversity. Scale-dependent pattern formation via self-organization is ubiquitous in terrestrial, aquatic and marine ecosystems. Despite their prevalence and ecological importance, these two phenomena have rarely been linked. We provide empirical evidence that the facilitative interaction in salt marshes between smooth cordgrass Spartina alterniflora and the ribbed mussel Geukensia demissa produces distinct spatial patterns along marsh shorelines. These findings advance our understanding of linkages between facilitation and pattern formation in nature, and are particularly relevant to conservation and restoration of salt marshes threatened by climate change and sea-level rise.

Interspecific root interactions enhance photosynthesis and biomass of intercropped millet and peanut plants

Intercropping is commonly practiced worldwide because of its benefits to plant productivity and resource-use efficiency. Belowground interactions in these species-diverse agro-ecosystems can greatly contribute to enhancing crop yields; however, our understanding remains quite limited of how plant roots might interact to influence crop biomass, photosynthetic rates, and the regulation of different proteins involved in CO2 fixation and photosynthesis. We address this research gap by using a pot experiment that included three root-barrier treatments with full, partial and no root interactions between foxtail millet (Setaria italica (L.) P.Beauv.) and peanut (Arachis hypogaea L.) across two growing seasons. Biomass of millet and peanut plants in the treatment with full root interaction was 3.4 and 3.0 times higher, respectively, than in the treatment with no root interaction. Net photosynthetic rates also significantly increased by 112–127% and 275–306% in millet and peanut, respectively, with full root interaction compared with no root interaction. Root interactions (without barriers) contributed to the upregulation of key proteins in millet plants (i.e. ribulose 1,5-biphosphate carboxylase; chloroplast β-carbonic anhydrase; phosphoglucomutase, cytoplasmic 2; and phosphoenolpyruvate carboxylase) and in peanut plants (i.e. ribulose 1,5-biphosphate carboxylase; glyceraldehyde-3-phosphate dehydrogenase; and phosphoglycerate kinase). Our results provide experimental evidence of a molecular basis that interspecific facilitation driven by positive root interactions can contribute to enhancing plant productivity and photosynthesis.