Makoto et al. J Wood Sci (2021) 67:49 https://doi.org/10.1186/s10086-021-01981-9 Journal of Wood Science RAPID COMMUNICATION Open Access Infuence of soil properties on the heartwood colour of Juglans mandshurica var. sachalinensis in a cool temperate forest Kobayashi Makoto1*† , Elizaveta Susloparova2†, Ikutaro Tsuyama3, Takuya Shimase3, Satoshi Nakaba4, Naoki Takahashi5 and Toshiya Yoshida6 Abstract Heartwood colour is often an important factor in determining timber prices. However, the determinants of intraspe‑ cifc variation in heartwood colour, which is useful information for sustainable wood marketing, are little understood, especially at the local scale in cool temperate forests. Because heartwood is produced as a secondary compound and photosynthesis is regulated by nitrogen (N) in cool temperate forests, we hypothesized that (1) soil conditions deter‑ mine heartwood colour even at a local scale within a tree species and (2) N, specifcally, can be an important driver of the intraspecifc variation in heartwood colour in the trees of cool temperate forests. To test these hypotheses, we investigated the relationship between the colour values (luminescence, redness, and yellowness) of heartwood from Juglans mandshurica var. sachalinensis and the soil parameters in a cool temperate forest. Among the soil properties, not soil N but soil magnesium (Mg) contents alone had a signifcant infuence on the redness and yellowness of the heartwood. Higher soil Mg contents resulted in increased redness and yellowness of the heartwood in our study, probably due to the increase in phenolics and the colouring of the tannins in the heartwood with Mg. Our results indicate that even at a local scale, soil condition can determine the intraspecifc variation in heartwood colour and that forest managers can utilize edaphic information to predict heartwood colour for timber marketing. Keywords: Soil nutrients, Heartwood colour, Ecosystem service, Local timber production Introduction [2], making the economic value of the wood markedly Wood colour is often an important factor in deter- different (e.g., the heartwood colour of birch in Japan, mining timber prices. Thus, understanding the deter- [3]). Previous studies have revealed that environmen- minants of wood colour is useful for effectively using tal factors such as soil properties are important in ecosystem services and the sustainable marketing determining wood colour [2, 4]. For instance, in Costa of wood [1, 2]. Species differences are well known to Rican plantations across the country, the wood colour be determinants of wood colour. On the other hand, of Tectona grandis varies with soil type and coinciden- even within the same species, wood colour can differ tal difference of chemical properties; pH; and calcium (Ca), magnesium (Mg), and iron (Fe) contents [2]. For *Correspondence: [email protected] five tree species in Mali, soil type is an important fac- †Kobayashi Makoto and Elizaveta Susloparova contributed equally to this tor, driving the intraspecific variation in wood colour manuscript 1 Teshio Experimental Forest, Field Science Center for Northern Biosphere, (especially redness and yellowness) across the nation Hokkaido University, Horonobe, Hokkaido 098‑2943, Japan [4]. For Juglans nigra in the USA, the luminance of Full list of author information is available at the end of the article wood differs between two states due to differences © The Author(s) 2021. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/. Makoto et al. J Wood Sci (2021) 67:49 Page 2 of 5 in soil properties [5]. The heartwood colour of Cryp- Sampling and wood colour measurements tomeria japonica differs depending on the soil mois- A disc sample was obtained at a height of 30 cm from ture contents across a topographic region and the the bottom of the stem in each individual. In total, coincidental soil conditions [6]. However, there is a 17 mature individuals were sampled. Te number of large knowledge gap about the determinants of heart- intraspecifc individual replications was comparable to wood colour in cold biomes, although forests in cold Montes et al. [4]. Te average diameter at breast height biomes are important for timber production [7]. In (DBH) was 45 cm. Te obtained samples were dried at summary, little is known about the drivers of intraspe- 70 °C for 2 weeks. Although the drying process at 70 °C cific variation in heartwood colour at a local scale in can change the wood colour from the original one, we cold biomes, which makes it difficult for local forest employed this drying temperature because it is com- managers to predict wood colour, information that is mon to dry the wood at this temperature range for needed for marketing. wood industry in Japan and one of our major aims of Heartwood substances are heartwood-specifc sec- this study is the contribution to the better wood mar- ondary metabolites produced during tree growth [8]. keting. After drying, the surface of the fat-grained tan- Furthermore, tree growth in cold biomes, such as cool gential face was carefully polished with sandpaper to temperate forests, is known to be regulated by nitrogen prepare it for heartwood colour analysis. For each sam- (N) availability [9]. Based on these facts, we hypothe- ple, three points were selected, and the heartwood col- size that (1) soil condition drives the intraspecifc vari- our was measured using a colour meter (ZE6000, Nihon ation in heartwood colour at a local scale (within a few Denshoku-kogyo, Japan) under stable temperature and kilometres) and (2) N, specifcally, can be the determin- humidity conditions. Before the measurements, cali- ing factor of heartwood colour within a tree species in bration was conducted using a white standard reference cool temperate forests. To test these hypotheses, we supplied by the same company. Te measurement was investigated the relationship between the colour index set within the visible range of 400–700 nm at intervals of the heartwood of Juglans mandshurica var. sacha- of 10 nm. According to HunterLab (1995), we estimated linensis and the soil parameters in a cool temperate the heartwood wood colour in three coordinates: the forest of northern Japan, which is the northern edge L value (luminescence) represents the position on the of the distribution of this species. J. mandshurica var. black–white axis (L00 represents black; L0100 repre- sachalinensis is one of the most economically valuable sents white), a value defnes the position on the red– tree species in northern Japan; thus, understanding the green axis (+ 100 values indicate red; − 100 values determinants of the heartwood colour of this species indicate green), and b value defnes the position on the would be helpful in the utilization and marketing of yellow–blue axis (+ 100 values indicate yellow; − 100 timber resources by local forest managers. values indicate blue). Methods/experimental Soil measurements Study site From the areas surrounding each tree, three subsam- Wood samples from mature individuals of J. mand- ples of soil (from a depth of 0–20 cm) were obtained; shurica var. sachalinensis were obtained in a natural the three subsamples were merged to form a composite mixed forest in Nakagawa town, northern Hokkaido, representative sample for each tree. Te soil analysis was Japan. Te understory was mainly covered by dwarf conducted following the methods presented by a previ- bamboo (Sasa sananensis (Fr. et Sav.) Rehder), which is ous study [10]. In short, by using the total wet weight the dominant species in northern Japan, and the thick- of the samples and gravimetric water contents, the bulk ness of the litter layer was about 2–3 cm. Between 1981 density of the soil was calculated. To determine the pH, and 2010, the average mean annual air temperature of 10 g of soil was shaken with 25 mL of deionized water, this area was 5.5 °C and the annual precipitation was and the solution was measured with a pH meter (B212, 1225 mm (Japan Meteorological Agency 2020). To Horiba, Japan). Te total N concentration was measured assess the importance of environmental gradients at a with a CHNS/O analyser (2400II, Perkin Elmer, USA). local scale (which is the important unite for the local Following [5], the exchangeable nutrients (P, Ca, Mg, K, forest manager), all the individuals were separated from Fe, Al, Cu, Mn, Zn, and S) were extracted with 100 mL each other by less than 3 km horizontally and 50 m ver- 1N ammonium acetate solution from 10 g fresh sam- tically; therefore, the climate variables can be regarded ples, and their contents in the extracts were determined as relatively homogeneous. Te bedrock of the study by inductively coupled plasma spectroscopy (IRIS, Jar- site was terrace deposits from the late Holocene. rel Ash, Franklin, MA). Te concentrations of all the Makoto et al. J Wood Sci (2021) 67:49 Page 3 of 5 nutrients and cations were determined on the basis of the soil dry mass. Statistical analysis Te correlations between each of the colour values and each of the soil properties were analysed with a general- ized linear model (GLM).