title: Response of a stoichiometrically imbalanced ecosystem to manipulation of nutrient supplies and ratios.
abstract: Cuatro Ciénegas Basin (CCB) is a desert ecosystem that hosts a large diversity of water bodies. Many surface waters in this basin have imbalanced nitrogen (N) to phosphorus (P) stoichiometry (total N:P > 100 by atoms), where P is likely to be a limiting nutrient. To investigate the effects of nutrient stoichiometry on planktonic and sediment ecosystem components and processes, we conducted a replicated in situ mesocosm experiment in Lagunita, a shallow pond located in the southwest region of the basin. Inorganic N and P were periodically added to mesocosms under three different N:P regimes (P only, N:P = 16 and N:P = 75) while the control mesocosms were left unamended. After three weeks of fertilization, more than two thirds of the applied P was immobilized into seston or sediment. The rapid uptake of P significantly decreased biomass C:P and N:P ratios, supporting the hypothesis that Lagunita is P-limited. Meanwhile, simultaneous N and P enrichment significantly enhanced planktonic growth, increasing total planktonic biomass by more than 2-fold compared to the unenriched control. With up to 76% of added N sequestered into the seston, it is suspected that the Lagunita microbial community also experienced strong N-limitation. However, when N and P were applied at N:P = 75, the microbes remained in a P-limitation state as in the untreated control. Two weeks after the last fertilizer application, seston C:P and N:P ratios returned to initial levels but chlorophyll a and seston C concentrations remained elevated. Additionally, no P release from the sediment was observed in the fertilized mesocosms. Overall, this study provides evidence that Lagunita is highly sensitive to nutrient perturbation because the biota is primarily P-limited and experiences a secondary N-limitation despite its high TN:TP ratio. This study serves as a strong basis to justify the need for protection of CCB ecosystems and other low-nutrient microbe-dominated systems from anthropogenic inputs of both N and P.
authors.affiliation: School of Life Sciences, Arizona State University, Tempe, Arizona, United States of America.
authors.forename: Zarraz M
authors.initials: ZM
authors.lastname: Lee
authors.affiliation: School of Life Sciences, Arizona State University, Tempe, Arizona, United States of America.
authors.forename: Laura
authors.initials: L
authors.lastname: Steger
authors.affiliation: School of Life Sciences, Arizona State University, Tempe, Arizona, United States of America.
authors.forename: Jessica R
authors.initials: JR
authors.lastname: Corman
authors.affiliation: School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, United States of America.
authors.forename: Marc
authors.initials: M
authors.lastname: Neveu
authors.affiliation: School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, United States of America.
authors.forename: Amisha T
authors.initials: AT
authors.lastname: Poret-Peterson
authors.affiliation: Departamento de Ecología Evolutiva, Instituto de Ecología, Universidad Nacional Autónoma de México, Coyoacán, México D. F., México.
authors.forename: Valeria
authors.initials: V
authors.lastname: Souza
authors.affiliation: School of Life Sciences, Arizona State University, Tempe, Arizona, United States of America.
authors.forename: James J
authors.initials: JJ
authors.lastname: Elser
mesh_terms: D002244:Carbon / Q000032:analysis / Q000378:metabolism; D003889:Desert Climate; D017753:Ecosystem; D005308:Fertilizers; D019015:Geologic Sediments / Q000382:microbiology; D008800:Mexico; D009584:Nitrogen / Q000032:analysis*; D010758:Phosphorus / Q000032:analysis*; D010839:Phytoplankton / Q000502:physiology
chemical_list: D005308:Fertilizers; D010758:Phosphorus; D002244:Carbon; D009584:Nitrogen