Wetlands are essential ecosystems that provide a variety of ecological functions, including carbon sequestration, water purification, climate regulation, and biodiversity maintenance. As global warming intensifies, environmental factors such as changes in precipitation, fluctuations in groundwater levels, and alterations in soil moisture and salinity profoundly affected the structure and function of wetland plant communities.

Recently, a research team led by Prof. HAN Guangxuan from the Yantai Institute of Coastal Zone Research of the Chinese Academy of Sciences (CAS) conducted a series of studies at the Yellow River Delta Field Observation and Research Station of the Coastal Wetland Ecosystem of CAS. Their studies included experiments that manipulated the genotypic richness of Phragmites australis, simulated changes in precipitation, regulated groundwater levels, and examined soil organic carbon (SOC) dynamics under different vegetation types. The recent study was published in Global Ecology and Conservation.

Using the Yellow River Delta Field Observation and Research Station, the researchers performed a common garden experiment to explore the relationship between the genotypic richness of Phragmites australis and ecosystem multifunctionality. The results indicated that in the coastal wetlands of the Yellow River Delta, the genotypic richness of P. australis had varying effects on different ecosystem functions (EFs). Notably, it exerted a significant negative impact on soil bacterial richness. Further analysis revealed that as genotypic richness increased, the average index of ecosystem multifunctionality showed a declining trend, likely due to inter-genotypic competition that reduced overall ecosystem multifunctionality.

Moreover, under different ecosystem function thresholds (i.e., the proportion of function indicators reaching their maximum values set at 20%, 40%, and 60%), higher genotypic richness promoted a greater number of function indicators to reach their maximum values. However, at a higher threshold level (80%), increased genotypic richness instead reduced the number of ecosystem function indicators reaching their maximum values. This suggests that increased plant genotypic richness may weaken ecosystem multifunctionality, so the potential impacts of introducing new genotypes should be carefully assessed to avoid impairing ecosystem functions.

A three-year study (2020-2022) using a precipitation gradient manipulation platform monitored net ecosystem CO₂ exchange (NEE) and plant life composition (perennials vs. annuals). Results indicated that the wetland consistently functioned as a CO₂ sink (NEE < 0). Changes in soil salinity, driven by precipitation fluctuations, were crucial in altering plant composition. Perennials like Phragmites australis and Imperata cylindrica thrived with increased precipitation, boosting biomass and NEE. Conversely, reduced precipitation caused soil salinity stress, allowing salt-tolerant annuals such as Suaeda salsa and Tripolium pannonicum to dominate. However, these annuals had lower biomass, leading to decreased primary productivity and NEE. Overall, the study emphasizes how precipitation impacts plant composition and NEE, providing insights for wetland ecological management.

Observations from a groundwater-controlled experimental platform show that biomass allocation in wetland plant communities is mainly influenced by dominant species. As groundwater depth decreases, soil electrical conductivity increases, plant diversity declines, and the dominant species shifts from Phragmites australis (common reed) to Suaeda salsa. Shallower groundwater levels lead to higher soil salinity and nutrient levels, prompting plants to allocate more biomass to aboveground structures for competitive advantage. This increase in aboveground biomass is linked to reduced plant diversity and changes in species composition.

The study, based on four vegetation zones in the Yellow River Delta tidal wetlands, reveals significant differences in SOC levels across vegetation types. Suaeda salsa-dominated mudflats show the highest SOC, while Phragmites australis-dominated areas have the lowest. Variations in SOC within a one-meter depth were also noted across vegetation types. Mantel analysis and Structural Equation Modeling (SEM) reveal that soil water content (SWC) regulates SOC levels by influencing vegetation type.

The relationship between genetic diversity and ecosystem functions (EFs). (Image by HAN Guangxuan's group) 

Effects of precipitation changes on plant community life form composition and NEE. (Image by HAN Guangxuan's group)

Response of biomass allocation in wetland plant communities to changes in groundwater depth. (Image by HAN Guangxuan's group)

The mechanisms through which soil properties influence organic carbon under different vegetation types. (Image by HAN Guangxuan's group)