Field-scale variability in site conditions explain phenotypic plasticity in response to nitrogen source in Pinus radiata D. Don

Abstract

Aims. Productivity of forest ecosystems is constrained by site resource availability and utilisation at an individual tree level. A better understanding of nitrogen (N) nutrition addition to forest ecosystems is critical for maintaining optimal plantation productivity, given the influence of an environment gradient, genetics, and their interactions. Methods. We studied the aboveground growth response in a plantation setting of ten commercial P. radiata genotypes to N-fertilisation using three different N sources, and also assessed the effect of on-site environmental factors on this response. We compared, on equimolar basis, the effect of N-fertilisation with inorganic N (NH4NO3), organic N (L-arginine), and the two N sources combined (L-arginine:NO3-) to that of unfertilised trees on tree height, diameter, descriptors of microsite variability, and climate / seasonal information. After 2.5 years of fertilisation, genotype-specific variation in aboveground growth response to N sources were measured, and these were significantly influenced by field-scale heterogeneity. Results. Across P. radiata genotypes, trees treated with inorganic N forms showed suppressed growth compared to unfertilised trees, while trees fertilised with organic N (either alone or in combination with inorganic N) were not significantly different than the untreated controls. We provide evidence of 2 significant interactions between N source and genotype, N source and cover as well as genotype and microsite variability affecting temporal trends in tree volume. Conclusions. We conclude that an understanding of field-scale variability in soil properties and associated environmental variables is essential for understanding genotype performance as they are crucial determinants of intraspecific variation in response to N-fertilisation. INTRODUCTION Given the longevity of sessile species, phenotypic plasticity provides an opportuntity to sense, change, and adapt their growth and physiological responses to cope with changes in environmental conditions (Bradshaw 1965; Corcuera et al. 2010). An ongoing challenge is to clarify which biological traits are manifested as genotypic variation from evolutionary and breeding history (G), phenotypic response to environmental variability (E) or combinations of both (G × E). Abundant evidence supports the hypotehsis that plant species and population responses differ across different environments (e.g. Schlichting and Levin 1984; Valladares et al. 2000). However, genotype-specific variation can be exhibited when grown in comparable conditions, affecting adaptive capacity and, consequently, tree performance (Souza et al. 2017). The flexibility and adaptability of tree genotype requires special attention, not only to understand the complexity of traits in breeding programmes, but also for the greater ecological impact that the increasing inter-seasonal climate changes may have in long-lived organisms. Pinus radiata D. Don (alt. Monterey pine) is the most common introduced softwood plantation species growing in temperat...

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