We examined effects of external supplies of nitrogen (N) and phosphorus (P) from the environment and internal supplies of N and P from within litter tissue on wild rice shoot and root litter decomposition and N and P dynamics. To investigate the effects of external supplies, wild rice shoot and root litterbags were decayed in mesocosms in the field over 115 days with either added N or P or a control in ambient conditions. To investigate the effects of the internal nutrient supply, wild rice plants were grown with added N, P, both N and P, or no supplemental nutrient, to produce enriched litters, which were then decayed for 168 days under controlled temperature in the laboratory. Both external and internal N and P supplies affected shoot litter decay more than decay of root litter. Increased external P supply significantly increased the rate of wild rice shoot decay and P mineralization but adding N had no effect on decay rates through time. Neither adding N nor P influenced root decay. Enrichment of P internally in the litter through fertilization increased the concentration of P (0.16%) and water-soluble compounds (28.7% WS) in shoot litter compared to control shoot litter (0.11% P, 19.8% WS), which likely caused the significant increase in shoot decay rates, particularly in the labile pool. In contrast, N enrichment not only increased plant growth but also increased lignin concentrations (7.5%) compared to control shoot litter (2.7% lignin) for added structural support. This significantly inhibited decay and nearly doubled the amount of mass remaining after 168 days (42.1% OM) when compared to control shoots (22.4% OM). Increased lignin likely overrides a concomitant increase in nitrogen concentration in shoot litter and appears to control wild rice decomposition. Lignin and phosphorus appear to play a key role in driving wild rice decay through the effects on litter quality.
Bibliographical noteFunding Information:
This research was funded through a grant provided by the National Science Foundation Ecosystems Ecology Program . Thanks to the Fond du Lac Band of Lake Superior Ojibway for providing sediments, seeds and field support. Thanks to Marissa Garry and Josh Bednar for field and lab assistance.
- Emergent graminoid
- Litter quality
- Nutrient immobilization