Antagonistic interactions between hummock formation and microtopography in wetlands modulate soil seed bank dynamics via biotic-abiotic coupling

Abstract

The soil seed bank (SSB) is a vital component of plant biodiversity and serves as a crucial, yet often overlooked, resource for the near-natural restoration of degraded wetland ecosystems. Carex hummocks are common and distinctive features of these ecosystems. Environmental heterogeneity resulting from hummock formation and microtopography plays a significant role in maintaining and enhancing the biodiversity of plants. Although linear positive correlations between environmental heterogeneity and aboveground plant communities (APCs) have been widely documented, the mechanisms by which hummock formation and microtopography influence SSBs are unclear. To address this knowledge gap, we investigated the effects of three stages of hummock formation (5–10, 50–60, and 100–150 years) and three microtopographic conditions (apex, interspace, and brae of the Carex hummock) on the ecological characteristics of SSBs using a field experiment. The results revealed that hummock formation, microtopography, and their interactions significantly influenced SSBs and APCs. Specifically, both the richness and density at hummock apex (HA) were significantly higher than those in other areas. During hummock formation, SSBs exhibited a higher rate of richness growth than the APC and exhibited significant variations across microtopographic conditions. The similarity between SSBs and the APC progressively declined throughout the hummock formation period, while the highest species composition similarity consistently observed at the HA. Soil organic matter and ammonium nitrogen were identified as critical factors affecting SSB dynamics. Structural equation modeling further revealed that microtopography had a direct negative effect on SSBs, whereas hummock formation and its interaction with microtopography positively influenced SSBs by mediating biotic and abiotic soil properties and APC dynamics. In summary, the results collectively demonstrated that hummock formation and microtopography promoted SSB richness and density, as this process resulted from complex antagonistic and synergistic interactions. This study deepens our understanding of microtopographic evolution in wetland ecosystems and its key implications for the nature-based rehabilitation and adaptive management of degraded wetlands.