Topographic heterogeneity is an important determinant of the distribution of resources and species and of species assembly. For example, the lack of microtopography in degraded salt marshes might restrict processes involved in the recovery of such ecosystems, such as seed retention. Therefore, we conducted a restoration study in degraded middle to high salt marshes, where self-recovery might be restricted by poor seed retention. We investigated the impact of microtopographic structures on seed retention and the re-establishment of pioneer vegetation patches. Our results showed that hollowed microtopographic structures are effective tools for allowing the re-establishment of pioneer vegetation patches by acting as seed traps and sustaining the recovery process that follows. Larger, deeper microtopographic structures entrapped more seeds and formed larger patches over the long term compared with smaller structures, highlighting the value of such structures to the successful recovery of degraded salt marshes.
It is well known that establishment limitation is stronger than seed limitation in aquatic ecosystems. Therefore, it seems crucial during the recruitment recovery process to overcome this establishment limitation on bare or degraded patches. Microtopographic structures have been shown to act as trap agents in saltmarshes. They can facilitate establishment, but this effect has not been quantitatively examined and assessed. This study examined the facilitative effect of microtopographic structures on plant recruitment in a dynamic saltmarsh system by conducting a series of field experiments along a saltmarsh tidal gradient. A simple plant life‐cycle model was used to evaluate the dynamics of the plant recruitment process facilitated by microtopographic structure and the importance of each life stage. The influence of abiotic factors on each life stage was also assessed, to identify the determinants during the life history. It was revealed that seed retention was the limiting factor in a bare saltmarsh area, rather than seed dispersal. Microtopographic structures can provide trap agents to facilitate seed anchorage. During seed retention, the stability of the microtopographic structure, especially its relative surface elevation difference, can be influenced by tidal events and the associated sediment process, which then affects seed retention efficiency. Microtopographic structure has a strong environmental filtering effect that can revise the potential dispersed seed and emergence patterns, and the determinant of the final establishment pattern along a tidal gradient is the retention pattern resulting from the interactions between microtopographic structures and tidal events. Furthermore, it can be designed into the early stage of recovery or restoration process so that it facilitates pioneer plant establishment. These early recruitment patches will speed up the recovery or succession process by (1) providing local seed sources, (2) retaining more seeds via the established vegetative structures, and (3) modifying microhabitat factors.
Molecular markers associated with known quantitative trait loci (QTLs) for type 2 resistance to Fusarium head blight (FHB) in bi-parental mapping population usually have more than two alleles in breeding populations. Therefore, understanding the association of each allele with FHB response is particularly important to marker-assisted enhancement of FHB resistance. In this paper, we evaluated FHB severities of 192 wheat accessions including landraces and commercial varieties in three field growing seasons, and genotyped this panel with 364 genome-wide informative molecular markers. Among them, 11 markers showed reproducible marker-trait association (p < 0.05) in at least two experiments using a mixed model. More than two alleles were identified per significant marker locus. These alleles were classified into favorable, unfavorable and neutral alleles according to the normalized genotypic values. The distributions of effective alleles at these loci in each wheat accession were characterized. Mean FHB severities increased with decreased number of favorable alleles at the reproducible loci. Chinese wheat landraces and Japanese accessions have more favorable alleles at the majority of the reproducible marker loci. FHB resistance levels of varieties can be greatly improved by introduction of these favorable alleles and removal of unfavorable alleles simultaneously at these QTL-linked marker loci.
1. Designing effective restoration strategies is a priority in recovering salt marsh plants. Hydrological connectivity is a main driver underpinning the success of the plant recovery process and can regulate life-history process-based restoration strategies. However, the relationship between these is unclear.2. Plant recovery needs to go through a whole life-history process, from seed to adult. Common restoration strategies are seed addition (SA) or seedling transplantation (ST), which start from seed germination and seedling growth stage.Besides these two strategies, another strategy starting from seed retention stage, microtopographic adjustment (MA), was designed to study the relationship with hydrological connectivity. A framework was also constructed to assess a gradient of hydrological connectivity between marsh plain and sea. We conducted several field experiments to test their relationships.3. The composite measurement of hydrological connectivity with five geomorphic variables can well represent the variation of environmental factors. Soil moisture, inundation frequency and sediment deposition were positively correlated, while soil salinity and hardness were negatively correlated with hydrological connectivity.4. The success of different restoration strategies varied with hydrological connectivity. MA showed a monotone decreasing trend, while SA and ST showed a unimodal trend as hydrological connectivity increased. Importantly, each strategy occupies a non-overlapping optimum range along the hydrological connectivity gradient.There is low hydrological connectivity for MA (0-0.28), middle hydrological connectivity for SA (0.28-0.55) and high hydrological connectivity for ST (0.55-1). Synthesis and applications.Our findings expand the quantification of the hydrological environment beyond elevation, distance or other single index to include a range of elements of hydrological connectivity, thus illustrating the underlying mechanisms of hydrological connectivity which regulate restoration strategies based on different life stages. The results provide a reliable framework to assess hydrological connectivity and offer guidance to select the optimum restoration strategy under different hydrological connectivities or to regulate the hydrological connectivity variables (topography on marsh plain and morphology of tidal | 1315
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