Biomass structure and carbon accumulation in above-ground and root biomass in grey alder Alnus incana (L.) Moench. young stands on agricultural land | Biomasas struktūra un oglekļa uzkrāšanās virszemes un sakņu biomasā baltalkšņa Alnus incana (L.) Moench. jaunaudzēs lauksaimniecības zemēs

Latvian. Rakstā analizēta baltalkšņu jaunaudžu (Ba) Alnus incana (L.) Moench. biomasas struktūra, doti koeficienti virszemes, sakņu un celma frakciju biomasas aprēķināšanai, izejot no stumbra tilpuma. Dots oglekļa (C) uzkrāšanās apjoms biomasas frakcijās. Pētījumi veikti Ba jaunaudzēs (1-10 gadi) lauksaimniecības zemēs. Ba jaunaudzēs, damaksnim un vērim pielīdzinātos augšanas apstākļos, paraugkoku stumbra caurmērs 1,3 m augstumā virs sakņu kakla pārstāvēts intervālā dmin = 1,9 cm un dmaks = 6,8 cm, augstums hmin = 4,4 m un hmaks = 7,9 m. Vidējais koku skaits – 7300 koki haE-1. Vidējā svaigi cirsta paraugkoka stumbra biomasa ir 4,6 ±1,5 kg, zaru – 1,5 ±0,5 kg un lapu masa 1,2 ±0,4 kg. Savukārt vidējā paraugkoka balstsakņu, sīksakņu un celma biomasa ir 2,6 ±0,6 kg; tajā skaitā absolūti sausa celma biomasa – 0,8 ±0,4 kg, bet balstsakņu un sīksakņu biomasa – 1,7 ±0,4 kg. Pētījuma rezultāti un aprēķini rāda, ka vidējā absolūti sausa koka virszemes biomasa Ba jaunaudzēs ir 23,4 ±2,6 t haE-1; attiecīgi stumbra biomasa – 14,7 ±1,5 t ha-1, zaru – 4,8 ±0,5 t ha-1 un lapu – 3,9 ±0,4 t haE-1. Absolūti sausa balstsakņu, sīksakņu un celma biomasa vidēji ir 8,7 ±0,3 t haE-1, kas sastāda 27% no kopējās koka biomasas. Lielākā svaigi cirsta koka uzsūcošo sakņu masa Ba jaunaudzēs ir 0-10 cm dziļumā – 0,6 ±0,2 t haE-1. Dziļākos augsnes slāņos tā pakāpeniski samazinās. Kopējā uzsūcošo sakņu svaiga biomasa augsnes slānī 0-40 cm dziļumā ir 0,8 ±0,2 t haE-1. Biomasas frakciju pārrēķina koeficientu summa Σci un koka stumbra caurmērs 1,3 m augstumā virs sakņu kakla ir savstarpēji neatkarīgas pazīmes (tas attiecas arī uz atsevišķiem koeficientiem), tādēļ biomasas aprēķināšanai lietojamas biomasas frakciju pārrēķina koeficientu aritmētiskās vidējās vērtības: stumbram – 0,8720, zariem – 0,2800, lapām – 0,2388, celmam – 0,1849, rupjajām saknēm – 0,3922. Oglekļa saturs absolūti sausas koksnes dažādās koka virszemes frakcijās svārstās no 47,2 ±0,5% stumbra koksnē līdz 52,6 ±0,6% lapās, savukārt mizā – 51,6 ±0,7% un zaru koksnē – 48,2 ±1,2%. Vidējais C saturs absolūti sausas koksnes sakņu biomasas frakcijās un celma biomasā ir 47,0 ±0,9% C.

English. For young gray alder Alnus incana (L.) Moench. stands established on farmlands analyzed is the biomass/volume ratio for stem above-ground part and roots and determined is the amount of carbon accumulated in selected sample trees. For the given study young grey alder stands of the age up to ten years were chosen with four sample plots established in four-, six-, seven-, and nine-year-old stands found on the sites of the Dm Hylocomiosa and Vr Oxalidosa growing conditions. The d. b. h. for the sample trees was from dmin = 1.9 cm to dmax = 6.8 cm, the height hmin = 4.4 m and hmax = 7.9 m; the average number of stems was 7,300 trees haE-1. The stand inventory parameters were determined following dendrometrical measurements done on circular sample plots (area 100 m2; r = 5.64 m). When estimating the above-ground biomass volume, the sample trees were cut down when in leaf. The above-ground biomass was divided into three fractions: stemwood overbark, branchwood overbark, and foliage; each fraction was weighed separately. For the fraction of root biomass we distinguished between fine roots (Ø is greater than 20mm), small roots (2 is less than Ø is less than 20mm), and coarse roots (Ø is less than 2mm) (Ohashi et al., 2007; Helmisaari et al., 2002; Makkonen, Helmisaari, 1998). In determining the total amount of biomass the stumpwood (above- and below-ground part of the stump) was also accounted for. The total amount of carbon in biomass samples was determined by using the carbon element analyzer LECO CR-12. The amount of accumulated carbon was estimated for seven sample tree fractions: stemwood, branchwood, bark, foliage, stumpwood, roots (coarse and small roots), including fine roots. Establishing the biomass/volume ratio was one of the major tasks of the given study. By multiplying the recalculation coefficient by the stem volume or standing volume we find the amount due to the respective tree fraction in freshly harvested biomass. On the average the mean biomass of freshly harvested sample tree comprised 4.6 ±1.5 kg of stemwood, 1.5 ±0.5 kg of branchwood, 1.2 ±0.4 kg of foliage, and 2.6 ±0.6 kg of roots and stumpwood (stumpwood 0.8 ±0.4; coarse roots 1.7 ±0.4 kg). The calculations made in the given study show that the absolutely dry above-ground biomass in young grey alder stands was on the average 23.4 ±2.6 t haE-1 divided as follows: stemwood 14.7 ±1.5 t haE-1, branchwood 4.8 ±0.5 t haE-1, and foliage 3.9 ±0.4 t haE-1 with the average amount of dry stemwood and root biomass 8.7 ±0.3 t haE-1, which accounted for 27% of the total biomass. In calculating the amount of biomass as a function of the d. b. h. of sample tree a close positive correlation was found to exist between the sample tree d. b. h. and the total amount of above-ground and root biomass, which is described by the determination coefficient R2 = 0.94. In young grey alder stands the highest amount of fine root biomass (0.6 ±0.2 t haE-1) is at the depth of 0-10 cm with the total amount of it at the depth of 0-40 cm as high as 0.8 ±0.2 t haE-1. There is a close correlation between the amount of fine root biomass and the depth of the soil layer described by the determination coefficient R2 = 0.97. With the depth of the soil layer increasing the biomass of fine roots reduces. The sum of biomass/volume ratios for different tree fractions Σci and the d. b. h. are mutually independent traits, which are described by the determination coefficient R2 = 0.03; it implies that for calculating the amount of biomass we may use the mean arithmetic values of the biomass/volume ratios. The sums of biomass/volume ratios show a relatively wide dispersal, which is explained by the dendromertric, phytocenotic and edaphic diversity of sample tree reference samples. Th e carbon content in the above-ground fractions of sample trees varies from 47.2 ±0.5% in stemwood to 52.6 ±0.6% in foliage with this indicator in the bark and branchwood being 51.6 ±0.7% and 48.2 ±1.2%, respectively. As to the fraction of root biomass, the calculations show that the carbon content in roots was 46.8 ±0.8%, in fine roots 47.2 ±1.1%, and 48.9 ±1.0% in stumpwood. When statistically verifying the carbon content between different tree fractions no significant difference was found between the foliage and bark (p is greater than 0.05) as well as between the fractions of stemwood, branchwood, stumpwood, and coarse and fine roots.