Juha Mikola1, Tarja Silfver1, Ulla Paaso1, Boy J M H Possen2, Matti Rousi3. 1. Faculty of Biological and Environmental Sciences, Ecosystems and Environment Research Programme, University of Helsinki, Niemenkatu 73, 15140, Lahti, Finland. 2. Natural Resources Institute Finland (Luke), Finlandiantie 18, 58450, Punkaharju, Finland. 3. Natural Resources Institute Finland (Luke), Latokartanonkaari 9, 00790, Helsinki, Finland.
Abstract
Plants enhance N use efficiency by resorbing N from senescing leaves. This can affect litter N mineralization rate due to the C:N-ratio requirements of microbial growth. We examined genotypic links between leaf N resorption and litter mineralization by collecting leaves and litter from 19 Betula pendula genotypes and following the N release of litter patches on forest ground. We found significant genotypic variation for N resorption efficiency, litter N concentration, cumulative three-year patch N-input and litter N release with high broad-sense heritabilities (H2 = 0.28-0.65). The genotype means of N resorption efficiency varied from 46% to 65% and correlated negatively with the genotype means of litter N concentration, cumulative patch N-input and litter N release. NH4+ yield under patches had a positive genotypic correlation with the cumulative patch N-input. During the first year of litter decomposition, genotypes varied from N immobilization (max 2.71 mg/g dry litter) to N release (max 1.41 mg/g dry litter), creating a genotypic tradeoff between the N conserved by resorption and the N available for root uptake during the growing season. We speculate that this tradeoff is one likely reason for the remarkably wide genotypic range of N resorption efficiencies in our birch population.
Plants enhance N use efficiency by resorbing N from senescing leaves. This can affect litter N mineralization rate due to the C:N-ratio requirements of microbial growth. We examined genotypic links between leaf N resorption and litter mineralization by collecting leaves and litter from 19 Betula pendula genotypes and following the N release of litter patches on forest ground. We found significant genotypic variation for N resorption efficiency, litter N concentration, cumulative three-year patch N-input and litter N release with high broad-sense heritabilities (H2 = 0.28-0.65). The genotype means of N resorption efficiency varied from 46% to 65% and correlated negatively with the genotype means of litter N concentration, cumulative patch N-input and litter N release. n class="Chemical">NH4+ yield under patches had a positive genotypic correlation with the cumulative patch N-input. During the first year of litter decomposition, genotypes varied from N immobilization (max 2.71 mg/g dry litter) to N release (max 1.41 mg/g dry litter), creating a genotypic tradeoff between the N conserved by resorption and the N available for root uptake during the growing season. We speculate that this tradeoff is one likely reason for the remarkably wide genotypic range of N resorption efficiencies in our birch population.