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.

Potassium (K) is highly mobile in plants at all levels, that is, from individual cell to xylem and phloem transport. This cation plays a major role in (1) enzyme activation; (2) protein synthesis; (3) stomatal function; (4) stabilization of internal pH; (5) photosynthesis; (6) turgorrelated processes; and (7) transport of metabolites. Citrus trees generally do not show visible deficiency symptoms across a wide range of K status in the leaves, except when the leaf concentrations drop below 3-4 mg kg21. However, fruit quality is quite sensitive to varying levels of K availability. High levels of K cause large fruit size with thick and coarse peel. In contrast, K deficiency produces smaller fruits with thin peel. With regard to juice properties, K nutrition has a significant role in juice acidity; that is, high juice acidity with high K availability, while low K availability causes decrease in juice acidity. High K availability in the soil can reduce the uptake of other cations, primarily magnesium,...

The knowledge of the nutrient distribution in trees is important to establish sound nutrient management programs for citrus production. Six-year-old Hamlin orange trees [Citrus sinensis (L.) Osb.] on Swingle citrumelo [Poncirus trifoliata (L.) Raf. x Citrus paradisi Macfad.] rootstock, grown on a sandy Entisol in Florida were harvested to investigate the macro and micronutrient distributions of biomass components. The biomass of aboveground components of the tree represented the largest proportion of the total. The distribution of the total tree dry weight was: fruit = 30.3%, leaf = 9.7%, twig = 26.1%, trunk = 6.3%, and root = 27.8%. Nutrient concentrations of recent mature leaves were in the adequate to optimal range as suggested by interpretation of leaf analysis in Florida. Concentrations of Ca in older leaves and woody tissues were much greater than those in the other parts of the tree. Concentrations of micronutrients were markedly greater in fibrous root as compared to woody roots. Calcium made up the greatest amount of nutrient in the citrus tree (273.8 g per tree), followed by N and K (234.7 and 181.5 g per tree, respectively). Other macronutrients comprised about 11% of the total nutrient content of trees. The contents of various nutrients in fruits were: N = 1.20, K = 1.54, P = 0.18, Ca = 0.57, Mg = 0.12, S = 0.09, B = 1.63 x 10-3, Cu = 0.39 x 10-3, Fe = 2.1 x 10-3, Mn = 0.38 10-3, and Zn = 0.40 10-3 (kg ton-1). Total contents of N, K, and P in the orchard corresponded to 66.5, 52.0, and 8.3 kg ha-1, respectively, which were equivalent to the amounts applied annually by fertilization.

Nitrogen (N) is the most important nutrient for plant growth and production. Nitrogen uptake efficiency is dependent on a number of factors. Water management influences the transformation of N sour...