Leaf N resorption efficiency and litter N mineralization rate have a genotypic tradeoff in a silver birch population

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 (H = 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. NH 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.

Intrapopulation genotypic variation in leaf litter chemistry does not control microbial abundance and litter mass loss in silver birch, Betula pendula

“…In line with our earlier observations of high and persistent intrapopulation genotypic variation of N and secondary metabolites in B. pendula senescent leaves (Mikola et al 2018;Paaso et al 2017), we found that the N concentration of partly decomposed litter had substantial genotypic variation. In the senescent leaves, the genotypic variation was found to explain 34% of the total phenotypic variation (Mikola et al 2018), which corresponds with the earlier estimates of and 27% of green leaf N concentrations explained by genotype in Populus trichocarpa (Guerra et al 2016) and Pinus radiata (Li et al 2015), respectively.…”

“…The site has six replicate blocks, each divided into 2×2 m planting plots (Mikola et al 2014), and for the present study, a litter patch (diameter ca. 30 cm, 10 g of litter as dry mass equivalent) was established in a random selection of the plots for each of the trees sampled in the Kuikanniitty site (Mikola et al 2018). Allocation of tree individuals to field blocks followed the blocking at the Kuikanniitty growing site, and within each block the litter of different genotypes was randomly allocated to the planting plots.…”

“…Litter chemistry was analyzed for 7-month old litter and bacterial and fungal abundance for 7-and 11-month old litter. In each case, ten to twenty random leaves were picked from the patch and transported to a laboratory, where they were ground in liquid N and stored in -80 o C. Litter chemistry included concentrations of N, condensed tannins, lignin, intracellular phenolics, epicuticular flavone aglycones and epicuticular triterpenes, which were available from the studies by Paaso et al (2017) and Mikola et al (2018), except for the N concentration of the 7-month old litter, which was analyzed for this study. Nitrogen concentration was analyzed using a LECO CNS-2000 Analyzer (LECO Corporation, USA) and the concentration of condensed tannins using the acid butanol assay (Hagerman 2002).…”

“…Our study species, Betula pendula Roth, has a wide distribution in Europe, being particularly abundant in the eastern parts (Atkinson 1992;Hynynen et al 2010). Using genotypes randomly selected from a B. pendula population in south-eastern Finland, significant intrapopulation genotypic variation has earlier been found for many B. pendula traits, including green foliage secondary chemistry (Laitinen et al 2000), leaf N resorption efficiency (Mikola et al 2018) and litter decomposition rate (Silfver et al 2007(Silfver et al , 2015.…”

“…To examine (1) if the high intrapopulation genotypic variation of N and secondary metabolites in B. pendula senescent leaves (Paaso et al 2017;Mikola et al 2018) have predictable, long-term effects on litter decomposition rate when the litter is placed on heterogeneous forest ground, and particularly, (2) if these effects can be understood by the effects of metabolites on bacterial and fungal abundances, we established a 35-month litter decomposition trial using the same genotypes, originating from a single B. pendula population, which were previously studied by Paaso et al (2017) and Mikola et al (2018). We supplemented the data available from these studies by measuring litter N concentration after early decomposition, and predicted that microbial abundance and litter mass loss would follow the variation in the concentrations of N and secondary metabolites in the senescent leaves.…”