Academic journal article Estonian Journal of Ecology

Fine Root Biomass and Production in a Salix Viminalis and Salix Dasyclados Plantation/peenjuurte Biomass Ja Produktsioon Paju (Salix Viminalis Ning Salix Dasyclados) Energiavosas

Academic journal article Estonian Journal of Ecology

Fine Root Biomass and Production in a Salix Viminalis and Salix Dasyclados Plantation/peenjuurte Biomass Ja Produktsioon Paju (Salix Viminalis Ning Salix Dasyclados) Energiavosas

Article excerpt

INTRODUCTION

Short rotation forest (SRF) plantations are used as a renewable source of energy. In temperate conditions, the annual wood biomass production of Salix species may approach 20 tonnes of dry wood matter per hectare (Heinsoo et al., 2002; Stolarski et al., 2008). In recent decades, applications of SRF have combined biomass production for energy and pollutant management (Mirck et al., 2005). In vegetation filters, roots take up wastewater nutrients and plant rhizosphere provides an aerobic environment to microbes that enhance nitrification of waste compounds (Mitch & Gosselink, 2000). Moreover, willows are effective in phytoextraction of heavy metals such as Cd and Zn from contaminated soils due to their high metal concentrations and high biomass (Keller et al., 2003).

Data on belowground biomass in SRF, root distribution in the soil, and allocation patterns are important, but relatively scarce compared to abundant reports on aboveground growth and yield. Since fine roots grow, die, and decompose rapidly, the amounts of carbon and nitrogen that cycle through them are high (Ruess et al., 2003). However, low fine root decomposition rates were found in an Estonian SRF plantation (Puttsepp et al., 2007). Roots function as important storage sites for carbohydrates and nitrogen in SRF species (Bollmark et al., 1999) and re-growth after coppicing is completely dependent on (coarse) root reserves. Improved knowledge on root biomass and production will enable to evaluate the total productivity of a SRF stand. Information on belowground processes is also needed for a proper establishment of Salix plantations in order to purify wastewater and remediate contaminated soils. Moreover, root studies will help to improve the management of plantations and promote their long-term vigour.

Rytter (2001) studied the biomass partitioning in young lysimeter-grown Salix viminalis plants and found that the ratio of belowground to aboveground biomass decreases from 0.3-0.4 in the first growing year to 0.1 in subsequent years. The reduction of the root to shoot biomass ratio during ageing was reported for different SRF trees (Dickmann & Pregitzer, 1992). According to Rytter (2001), the fine root to aboveground production is variable ranging from 0.4 to 1.2, and depends on soil and year. The proportion of aboveground biomass and therefore also annual wood yield increase during the first years in conventional forests (Cannell, 1989). After canopy closure the proportion partitioned to wood remains almost constant (Cannell, 1989).

This study aimed to analyse the biomass and spatial distribution of fine roots in a Salix viminalis and S. dasyclados SRF plantation. The effect of fertilization on the annual fine root production was also studied. Allocation of annual production into different plant parts was determined to improve our understanding of different options for increasing the harvestable yield in SRF.

MATERIAL AND METHODS

Plant material

The experiment was conducted in a SRF plantation of Saare, eastern Estonia (58[degrees]42'N and 26[degrees]55'E). The plantation was established on a mineral soil of brown gleyic podzoluvisol type with a sandy loam texture in May 1993 with cuttings of six S. viminalis clones and one S. dasyclados clone using a randomized block design. Each clone was planted in double rows (distance between the rows 1.25 and 0.75 m) into four plots (plot size 16 m x 16 m or 8 m x 16 m). The planting density was 2 cuttings per [m.sup.2]. In May 1994, shoots were cut at 5 cm above the ground to promote denser sprouting. Two plots per clone were annually fertilized with 60-168 kg N [ha.sup.-1], 0-37 kg P [ha.sup.-1], and 0-70 kg K [ha.sup.-1] during the first rotation. The exact scheme of fertilization is presented in Heinsoo et al. (2002). Mechanical and chemical weed control was carried out in 1993 and 1994.

Fine root biomass and production were estimated in one fertilized and one control plot of S. …

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