In situ estimates of waterhyacinth leaf tissue nitrogen using a SPAD-502 chlorophyll meter

Previous investigations with Eichhornia crassipes and its biological control agents Neochetina bruchi and N. eichhorniae identified leaf tissue nitrogen (N) as a driver in their interactions. However, traditional methods for determining plant tissue N content are cumbersome, time-consuming, and destructive-and thus unsuited for rapid in situ evaluations. We therefore tested the utility of a hand-held chlorophyll meter as a means of producing in situ estimates of N in the leaves of this floating aquatic weed. The Minolta SPAD-502 chlorophyll meter provided excellent estimates (F= 385.96, P< 0.0001) of leaf tissue N levels. SPAD readings varied within leaves (F= 78.66, P< 0.0001), so average readings per leaf were used. The relationship between SPAD readings and tissue N levels was affected by the phenological stage of the leaf (F= 102.79, P <0.0001), but not leaf size (F= 0.7 5, P= 0.3867). The estimates were also unaffected by fertilizer level (F= 0.95, P=0.4354), but were marginally affected by herbivory (F= 3.86, P=0.0505). Thus, with suitable calibration (e.g., different field sites, presence and type of herbivory) output from the SPAD-502 could be used to provide consistent estimates for the nitrogen content of E. crassipes leaves. Published by Elsevier B.V.