Response of homeostasis and growth of seepweed Suaeda heteroptera to simulated nitrogen and phosphorus deposition in soils
The homeostasis of element composition in the organisms is one of central concepts of ecological stoichiometry. Investigating stoichiometric homeostasis of element nitrogen (N) and phosphorus (P) could be considered ecological strategies, competition as well as regulation, acclimation or adaptation of plant. We conducted the cultural tank for planting seepweed Suaeda heteroptera. Our main questions were: 1) How does the homeostatic regulation of N, P and N:P ratio in the plant to N and P in the ambient soils, and 2) How does the responses of growth of plant to N and P in the ambient soils. We used different ratios of N to P in the solutions for watering seepweed twice a day to mimic nutrient deposition in order to investigate the responses of stoichiometric homeostasis of N and P in the organism and allometric growth of plant to the N and P enrichment in soils. All experiments including 12 treatments and 1 control were divided in triplicate. The N deposition treatment is 2 mg/L of P plus 0, 4, 8, 12, 16, 20 mg/L of N and the P deposition treatment is 5 mg/L of N plus 0, 1, 2, 3, 4, 5 mg/L of P, respectively. 150 days after planting, we collected plant samples aboveground and soil samples. The contents of N and P in the plants, concentrations of total N, total P, ammonia-N, nitrate-N, available-P in the soils was determined respectively.
“strict homeostasis” of N in the seepweed (1.752 ± 0.038 mol/kg for N deposition, 1.738 ± 0.037 mol/kg for P deposition) was found in simulated N and P deposition experiments while stoichiometric homeostasis of P in the seepweed was observed. The content of P in the seepweed shows sigmoid logistic increase with increasing N deposition. N deposition stimulates the accumulation of P in the seepweed. The homeostatic regulation coefficient for P HP is 1.327 and for N:P ratios HN:P is 0.792. The relationship between growth of height of the seepweed and available-N (ammonia-N and nitrate-N) and available-P in soils could be described as sigmoid logistic model. Allometric growth of height and concentration of P with weight of the seepweed were observed. The homeostasis of N and P in the seepweed is observed in the simulated N and P deposition. The growth of seepweed is promoted in the simulated N and P deposition.