Precision water recharge facilitates spikelet development and seed growth in Carex schmidtii: Implications for near-natural restoration of degraded semi-arid wetlands.

The expansion of irrigated agriculture in semi-arid regions exacerbates the degradation of wetland ecosystems. Precision water recharge can facilitate near-natural restoration of degraded wetlands by alleviating the conflict between wetlands and agricultural water use. However, although the ecological significance of precision water recharge as a nature-based solution for restoring wetland vegetation has been widely acknowledged, the mechanisms driving its role in spikelet development and seed growth in Carex schmidtii Meinsh. remain poorly understood despite their critical impact on reproduction and genetic information transfer. To address this knowledge gap, this study compared the characteristics of spikelet development and seed growth in C. schmidtii under four hydrological conditions (drought, moist, water depth of 5 cm, and water depth of 10 cm) and four re-watering treatments (maintaining constant water levels and re-watering to the initial hydrological regime on the 15th, 30th, and 45th days). We also investigated the ecological and photosynthetic characteristics of the leaves. The hydrological conditions and re-watering treatments significantly affected spikelet development, seed growth, leaf development, and photosynthetic pigment accumulation in C. schmidtii. Compared to other treatments, moist conditions and re-watering to the initial hydrological regime on the 15th day (IH2-RT2) significantly enhanced spikelet characteristics (length, diameter, and biomass) and seed growth traits (length, width, height, volume, thousand-seed weight, and seed test weight). Furthermore, leaf ecological characteristics (length, width, perimeter, and area) and chlorophyll content (chlorophyll a, b, and total chlorophyll) in C. schmidtii under IH2-RT2 exhibited higher values compared to other treatments. Spikelet development characteristics and seed growth traits exhibited significant correlations with leaf ecological characteristics and chlorophyll content. The interaction between leaf ecological characteristics and chlorophyll content explained 39.64% and 43.15% of the variation in spikelet development and seed growth, respectively. A structural equation model further demonstrated that hydrological regimes and re-watering treatments directly affected spikelet development and seed growth while indirectly influencing spikelet development and subsequent seed growth by altering leaf width and chlorophyll b content. Overall, hydrological regimes and re-watering treatments significantly influenced spikelet development and seed growth in C. schmidtii through multiple pathways. The utilization of flood and snowmelt water resources, along with the integrated management of agricultural and wetland water resources, can serve as key strategies for the efficient use of water resources in semi-arid regions. This study provides important insights for wetland vegetation restoration in semi-arid regions worldwide.