Fine root standing stock and production in young beech and spruce stands

Abstract Fine roots (defined by a maximum diameter of 2 mm) and assimilatory organs are the compartments which rotate carbon much faster than any other tree part. We focused on quantification of fine roots in young European beech and Norway spruce trees growing under the same ecological conditions. Standing stock of fine roots was estimated by soil coring during 2009 - 2012. Fine root production was established by the in-growth bag method. Standing stock and productions of fine roots were comparable in both tree species. The quantity of fine root biomass (at a soil depth of 0 -50 cm) varied inter-annually between 6.08 and 7.41 t per ha in the beech and from 5.10 to 6.49 t per ha in the spruce stand. Annual production of fine roots (soil depth of 0 - 30 cm) was between 1.11 and 1.63 t ha-1 in beech and between 0.95 and 1.54 t.ha-1 in spruce. We found that fine root standing stock at the beginning of each growing season was related to climatic conditions in the previous year. Annual fine root production was influenced by the climatic situation of the current year. In general, a maximum standing stock of fine roots as well as a relatively slow fine root turnover is expected in young forest stands. Whereas production of fine roots prevailed over mortality in a favorable year (sufficiency of precipitations and slightly above-average temperatures in 2010), there was a reverse situation in an unfavorable year (drought episodes in 2011). We concluded that although both forest types represented contrasting turnovers of assimilatory organs (once a year and once in 5 years in beech and spruce respectively), fine root turnover rates were very similar (approx. once per four years). Resumé V ostatnom období sa výskum venuje jemným frakciám koreňových systémov drevín najmä z dôvodu ich výrazného prínosu pri obehu uhlíka v lesných ekosystémoch. Naše štúdium jemných koreňov (tieto sa definovali maximálnou hrúbkou 2 mm) sa sústredilo do bučín a smrečín v štádiu mladina, rastúcich na výskumnom objekte Vrchslatina. Pomocou dvoch metód, konkrétne pôdne vývrty (v hĺbke pôdy 0 - 50 cm) a vrastavé valce (v 0 - 30 cm) sa zis tila zásoba biomasy a nekromasy, ako aj produkcia jemných koreňov. Z týchto údajov sa odvodil ich obeh (vyjadrený ako pomer medzi produkciou a zásobou biomasy) a mortalita. Takéto sledovania sa vykonali počas štyroch rokov (2009 - 2012), pritom sa zohľadnili aj klimatické pomery, tzn. priemerné teploty vzduchu a úhrny zrážok. Výsledky poukázali na pokles zásoby biomasy jemných koreňov s hĺbkou pôdy, pritom výraznejší bol pri smreku (tzn. plytšia distribúcia jemných koreňov) než pri buku. Zásoba jemných koreňov bola mierne vyššia v bučine (priemer za roky 2009 - 2012 bol 6,57 t na ha) než v smrečine (6,01 t na ha), pritom medziročne výrazne varírovala. Ročná produkcia jemných koreňov bola veľmi podobná v obidvoch porastoch (priemer za roky 2009 - 2012 bol 1,37 t na ha za rok v bučine a 1,29 t na ha za rok v smrečine), pritom aj tu sa zistili veľké medziročné rozdiely. Kým v roku 2010 prevládala produkcia jemných koreňov nad ich mortalitou, opačná situácia bola v roku 2011. Zásoba, produkcia a mortalita jemných koreňov pravdepodobne súvisela s klimatickými pomermi v jednotlivých rokoch. Zvýšenú mortalitu jemných koreňov spôsobili najpravdepodobnejšie epizódy sucha. V obidvoch porastoch sa zistili podobné obehy jemných koreňov (približne jedenkrát za 4 roky). Pri porovnaní našich výsledkov s inými prácami sa konštatovali vysoké zásoby jemných koreňov, avšak nízke hodnoty ich obehu. Tento stav jemných koreňov pravdepodobne súvisí s mladým vekom sledovaných porastov, resp. s priaznivými pôdnymi pomermi na stanovišti.

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