%AShan, Shan%ADevens, Hannah%AFahey, Timothy%AYanai, Ruth%AFisk, Melany%BJournal Name: Ecosystems %D2022%I %JJournal Name: Ecosystems %K %MOSTI ID: 10316180 %PMedium: X %TFine Root Growth Increases in Response to Nitrogen Addition in Phosphorus-limited Northern Hardwood Forests %XResource allocation theory posits that increased soil nutrient availability results in decreased plant investment in nutrient acquisition. We evaluated this theory by quantifying fine root biomass and growth in a long term, nitrogen (N) 9 phosphorus (P) fertilization study in three mature northern hardwood forest stands where aboveground growth increased primarily in response to P addition. We did not detect a decline in fine root bio- mass or growth in response to either N or P. Instead, fine root growth increased in response to N, by 40% for length (P = 0.04 for the main effect of N in ANOVA), and by 36% for mass, relative to controls. Fine root mass growth was lower in response to N + P addition than predicted from the main effects of N and P (P = 0.01 for the interaction of N 9 P). The response of root growth to N availability did not result in detectable responses in fine root biomass (P = 0.61), which is consistent with increased root turnover with N addition. We propose that the differential growth response to fertilization between above- and belowground components is a mechanism by which trees enhance P acquisition in response to increasing N availability, illustrating how both elements may co- limit northern hardwood forest production. %0Journal Article