Helophytes adapt to water and N-enrichment stresses by adjusting and coordinating stoichiometry characteristics in main organs

Response of ecological stoichiometry and homeostasis characteristic to nitrogen addition in Hippophae rhamnoides L

Nitrogen (N) in the atmosphere frequently affects plant growth, ecological stoichiometric equilibrium, and homeostasis stability. However, the effect of N addition application on the growth of Hippophae rhamnoides seedlings remains ambiguous. We investigated the effects of N addition on the ecological stoichiometry and homeostatic characteristics of H. rhamnoides seedlings. Greenhouse cultivation experiments were conducted at five N application levels: 0 kg ha-1 yr-1(CK), 100 kg ha-1 yr-1 (N10), 200 kg ha-1 yr-1 (N20), 400 kg ha-1 yr-1 (N40), 800 kg ha-1 yr-1 (N80). The results showed that pH and available phosphorus (AP) significantly decreased with increasing N, whereas soil C:P and N:P ratios significantly increased under the N40 and N80 treatments. The leaf C:N ratio significantly decreased with increasing N, whereas the N:P ratio increased. With N addition, the C:N ratio of plant stems and roots significantly decreased, whereas the C:P and N:P ratios significantly increased. N addition was significantly correlated with the ecological stoichiometry of plant leaves and soil properties (0.38 and 0.84, respectively). Homeostasis of the organs of H. rhamnoides seedlings exhibited an absolute steady state. The C, N, and C:P ratios of the roots exhibited insensitive states under the N40 treatment. N addition significantly modified both the soil ecological stoichiometry and the stoichiometry of H. rhamnoides seedlings. However, it did not demonstrate a pronounced negative effect on the homeostasis of H. rhamnoides seedlings. This study offers new insights into the ecological adaptation process of H. rhamnoides, particularly concerning its nutrient distribution, utilization strategies, and stability.

Microorganisms Directly Affected Sediment Carbon–Nitrogen Coupling in Two Constructed Wetlands

Clarifying the carbon–nitrogen coupling pattern in wetlands is crucial for understanding the driving mechanism of wetland carbon sequestration. However, the impacts of plants and environmental factors on the coupling of carbon–nitrogen in wetland sediments are still unclear. Sediment samples from plant (Typha angustifolia and Phragmites australis)-covered habitats and bare land were collected in two constructed wetlands in northern China. The contents of different forms of carbon and nitrogen in sediments and plants, and the sediment microbial community were detected. It was found that the sediment carbon to nitrogen (C/N) ratios did not differ significantly in the bare sites of different wetlands, but did in the plant-covered sites, which highlighted the different role of plants in shifting the carbon–nitrogen coupling in different constructed wetlands. The effects of plants on the sediment carbon–nitrogen coupling differed in two constructed wetlands, so the structural equation model was used and found that sediment microorganisms directly affected sediment C/N ratios, while water and sediment physicochemical properties indirectly affected sediment C/N ratios by altering sediment microbial functions. Multiple linear regression models showed that water pH, sediment moisture content, water dissolved oxygen, and water depth had a greater influence on the carbon metabolism potential of the sediment microbial community, while sediment moisture content had the greatest impact on the sediment microbial nitrogen metabolism potential. The study indicates that variations in environmental conditions could alter the influence of plants on the carbon and nitrogen cycles of wetland sediments. Water environmental factors mainly affect microbial carbon metabolism functions, while soil physicochemical factors, especially water content, affect microbial carbon and nitrogen metabolism functions.

Response of C:N:P stoichiometry to long-term drainage of peatlands: Evidence from plant, soil, and enzyme

Drought induced by climate warming and human activities regulates carbon (C) cycling of peatlands by changing plant community composition and soil properties. Estimating the responses of peatlands C cycling to environmental changes requires further study of C: nitrogen (N): phosphorus (P) stoichiometric ratios of soil, plants, and enzyme activities. However, systematic studies on the stoichiometry of above-ground and below-ground ecosystems of peatlands post drainage remain scarce. This study compared stoichimetric ratios of plant and soil and stoichimetric ratios of enzyme activities with different functions in two different parts of a minerotrophic peatland, a natural undisturbed part and a part that had been drained for almost 50 years, in Northern China. For the shrub plants, the average C:N:P ratios of leaf in natural and drained peatland were 448:17:1 and 393:15:1, respectively. This indicated that the growth rate of shrub plants is higher in the drained peatland than in the natural peatland, which makes P element more concentrated in the photosynthetic site. However, from the perspective of the dominant plant, the mean C:N:P ratio of Carex leaf was 650:25:1 in the natural peatland, but was 1028:50:1 for Dasiphora fruticosa in drained peatland. This indicated that the intensification of P-limitation of plant growth after drainage. Soil C:N:P ratios of above water table depth (AWT) were 238:15:1 and 277:12:1, but were 383:17:1 and 404:19:1 for below water table depth (BWT) in the natural and the drained peatland, respectively. Soil C:P ratios were greater than the threshold elemental ratio of C:P (174:1), but the soil C:N ratios were less than the threshold elemental ratio of C:N (23:1), which suggested that P was the most limiting nutrient of soil. The soil microbial activities were co-limited by C&P in Baijianghe peatlands. However, the microbial metabolic P limitation was intensified, but the C limitation was weakened for the above water table depth soil after long-term drainage. There are connection between plant-microbe P limitation in peatlands. The P limitation of microbial metabolism was significant positively correlated with soil C:N but negatively with soil moisture. The increase in the lignocelluloses index suggested considerable decomposition of soil organic matter after peatland drainage. These results of stoichiometric ratios from above- to below ground could provide scientific base for the C cycling of peatland undergone climate change.