Tissue analysis is commonly used in ecology and agronomy to portray plant nutrient signatures. Nutrient concentration data, or ionomes, belong to the compositional data class, i.e., multivariate data that are proportions of some whole, hence carrying important numerical properties. Statistics computed across raw or ordinary log-transformed nutrient data are intrinsically biased, hence possibly leading to wrong inferences. Our objective was to present a sound and robust approach based on a novel nutrient balance concept to classify plant ionomes. We analyzed leaf N, P, K, Ca, and Mg of two wild and six domesticated fruit species from Canada, Brazil, and New Zealand sampled during reproductive stages. Nutrient concentrations were (1) analyzed without transformation, (2) ordinary log-transformed as commonly but incorrectly applied in practice, (3) additive log-ratio (alr) transformed as surrogate to stoichiometric rules, and (4) converted to isometric log-ratios (ilr) arranged as sound nutrient balance variables. Raw concentration and ordinary log transformation both led to biased multivariate analysis due to redundancy between interacting nutrients. The alr- and ilr-transformed data provided unbiased discriminant analyses of plant ionomes, where wild and domesticated species formed distinct groups and the ionomes of species and cultivars were differentiated without numerical bias. The ilr nutrient balance concept is preferable to alr, because the ilr technique projects the most important interactions between nutrients into a convenient Euclidean space. This novel numerical approach allows rectifying historical biases and supervising phenotypic plasticity in plant nutrition studies.

The "ionome", or plant elemental signature, is the elemental composition of an organisms, that may vary with genotypic traits and phenotypic plasticity. Cloudberry (Rubus chamaemorus L.) is a circumboreal wild berry naturally growing in oligotrophic oceanic bogs of Quebec and Labrador. Our objective was to relate cloudberry stand productivity to the ionomes of female ramets and explore the cause of nutrient imbalance in low-performing stands. We analyzed 13 elements in female ramets collected in 86 natural sites where crop productivity varied widely. We computed orthogonally arranged balances reflecting plant stoichiometric rules and soil biogeochemistry. Balances were expressed as isometric log ratios (ilr) between ad hoc sub-compositions. Balances were synthesized into a Mahalanobis distance optimized based on receiving operating characteristics (ROC). The critical Mahalanobis distance was found to be 5.29 for cutoff berry yield of 3.8 g·m −2 with test performance of 0.88, as measured by the area under the ROC curve. Although past research on cloudberry focused mainly on the N/P ratio, this exploratory mineral balance analysis indicated that imbalance in the [P,N | S,C] and [Al | Nutrients] partitions appeared to be the factors limiting the most cloudberry productivity in the bogs. Some highly productive stands showed relatively high C fixation and K use efficiency. Due to the complexity of interactions, diagnosis should be conducted computing first a global imbalance index (Mahalanobis distance), then examining in the balance domain binary partitions departing most from reference, and finally appreciating relative shortage, sufficiency or excess of elements in the concentration domain.

Natural peatlands are an important source of berries in northern countries. One possible avenue to improve crop yield in natural peatlands is to apply fertilizers, ombrotrophic peatlands being very low in nutrients. In order to reduce the impact of this practice on an otherwise natural habitat, slow-release organic fertilizers might be more appropriate than mineral fertilizers. However, mineralization and dispersion of organic fertilizers in peatlands need to be determined along with their impact on crop yield. In the present study, we focused on cloudberry fruit that despite a high commercial potential is limited by low and variable yield. We thus tested the effect of an organo-mineral fertilizer in two peatlands on nutrient dispersion, plant growth, flowering frequency and fruit yield of cloudberry. The organo-mineral fertilizer, composed of crab and fish meal supplemented with potassium chloride, was applied annually for three years. The treatment was repeated in two natural ombrotrophic peatlands: one covered with lichen and the other a more typical sphagnum bog. The dispersion study indicated very limited dispersion of most nutrients. There was no effect of the fertilizer on cloudberry growth and fruit yield or on the nutrient concentrations of its tissues. We concluded that the fertilizer did not mineralize to sufficient extent. Mineralization of potential organic fertilizers would need to be tested in natural peatlands before being applied to cloudberry patches.