NIR spectroscopy for plant nutrient analysis ­underwater and in the trees

he enormous variability in the concentration of plant toxins and nutrients in trees, shrubs and forbs requires extensive sampling to accurately represent the nutritional and toxicological landscape and this is an ideal application for quantitative near infrared (NIR) reflectance spectroscopy. The speed of NIR spectroscopy analysis makes it ideally suited to environmental monitoring and ecological investigations where large numbers of replicates need to be measured. Several recent studies, including one focused on underwater plants on the Great Barrier Reef and the second in Bolivian rainforests, show the power of NIR spectroscopy to address large-scale variability in plant–animal interactions.

Dugongs are large (200 kg) marine herbivores that feed mostly on seagrass. Seagrasses are monocotyledonous plants that grow in the intertidal zone but also at depths of up to 30 m. Large herds of dugongs can congregate on seagrass meadows and make repeated, short dives where they graze the leaves of the seagrasses or even uproot and eat the whole plant. We were interested in whether grazing by dugongs improved the quality of the re-growth—in other words, were they able to “farm” seagrass meadows to maintain quality? Using NIR spectroscopy to analyse nutritional components in about 1200 seagrass samples showed that this was indeed the case.1 Grazing by dugongs improved the nutritional quality of meadows significantly. Many other species use seagrass meadows and regular grazing by dugongs is likely to have effects on the whole community of seagrass-dependent species.

A second study sought to understand the impact on logging on populations of black spider monkeys in Bolivian rainforests.2 Annika Felton followed black spider monkeys, observed their food choices and either retrieved freshly dropped fruit and leaves or else climbed to the canopy to retrieve it. Because it was so important to analyse exactly the parts that the monkeys were eating, in many cases, we only had a small amount of material. Fortunately, we were able to develop robust NIR spectroscopy calibration equations to predict the chemical composition and in particular the amount of protein that was available to the monkeys. Annika found that spider monkeys aimed for a target amount of protein each day, regardless of whether they only ate ripe fruit or mixed in other vegetable matter as well and she was able to recommend a selective logging regime that preserved the most important resources in the forest.

Although rainforest logging can be highly destructive for tree dwelling mammals, this story had a happy ending. During the study, Annika and her husband Adam discovered a new species of titi monkey and, in conjunction with the Wildlife Conservation Society, auctioned the naming rights to raise funds ($US650,000) to employ park rangers in perpetuity. The animal is now known as the Golden Palace monkey3 (Callicebus aureipalatii) after the Golden Palace (online) Casino!