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 = 0.75, 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.

► The SPAD-502 meter measures relative chlorophyll levels in Eichhornia crassipes leaves. ► The readings serve as a proxy allowing non-destructive in situ estimates of leaf nitrogen levels. ► SPAD readings provide accurate estimates when properly calibrated (e.g., for location, herbivory, etc.).