Two recent studies (Nieminen 2008b, 2009) focused on the interaction between wood ash and carbohydrate supply in microcosms. The enchytraeid C. sphagne — torum was chosen as the target organism because of its importance in boreal forest soil, and because studies have consistently shown that it is sensitive to wood ash. The abundance of microbial-feeding nematodes provided information on microbial production.

Nieminen (2008b) studied the interactive effects of sucrose and loose wood ash on enchytraeids and nematodes in organic Norway spruce forest soil from which enchytraeids had been extracted using the Baermann wet funnel technique (O’Con­nor 1957). After extraction, the humus was sieved, weighed into 20 cotton-plugged glass jars and 20 individuals of the enchytraeid C. sphagnetorum were returned and each microcosm was inoculated with microflora and microfauna. Nieminen (2008b) treated the microcosms with loose wood ash (480 mg per microcosm,

1,0 kg ha-1) and sucrose (1.6 g per microcosm, 1.3 Mg C ha-1) in a full factorial design.

After a 3-month incubation at constant temperature, the dry matter content of organic soil was 22 ± 0.5% (mean ± standard error, n = 20) irrespective of treat­ment (Nieminen 2008b). Addition of wood ash increased the soil pH from

5.2 ± 0.1 to 6.9 ± 0.2 in both sucrose-amended and non-amended soil. Sucrose addition increased and wood ash addition reduced enchytraeid length. Sucrose addition increased nematode abundance by more than 100% on average. Wood ash addition alone decreased enchytraeid abundance compared with the control (Fig. 4.1).

Nieminen (2009) studied the interactive effects of three levels of solid sucrose (0, 0.88 or 8.8 g, equalling 0, 100 and 1,000 kg C ha-1; the intermediate treatment was omitted in the original article) and two levels of birch ash (0 or 1.175 g per microcosm, equalling 500 kg ha-1) in pots containing a layer of organic Norway spruce forest soil on mineral soil. In addition to one Norway spruce (Picea abies (L.) H. Karst. ssp. abies) seedling, these pots also contained the grasses Deschamp — sia flexuosa (L.) Trin. and Calamagrostis epigejos (L.) Roth and the experiment was continued in a greenhouse for one growing season (Nieminen 2009).

Wood ash increased the soil pH from 5.4 ± 0.06 to 5.7 ± 0.06 irrespective of carbon addition (Nieminen 2009). Sucrose increased the moisture of organic soil from 40 ± 0.02% to 57 ± 0.11% fresh mass in C1000 (analysis of variance, sucrose x ash F224 = 4.9, p = 0.017; control: simple effect of sucrose F2,24 = 11.4, p < 0.001), but this was partially counteracted by wood ash (mois­ture percentage 46 ± 0.05% in AC1000; F124 = 7.5, p = 0.011). Enchytraeids went close to extinction in control pots, but in C1000 treatments reached 1.8 times the initial density regardless of wood ash (sucrose F2,24 = 10.5, p < 0.001).

Enchytraeid length varied from 3.66 ± 0.28 mm in C1000 to 5.07 ± 1.46 mm in AC1000 ash-treated pots and the wood ash effect was significant. Wood ash increased nematode abundance (ash F124 = 5.6, p = 0.027). The nematode com­munity in control pots consisted mainly of bacterial feeders (50% of individuals; in particular, Rhabditis sp.) and predators (Mononchus sp.), and all others amounted to less than 25% of individuals.