Biomass Allometry And Allocation Of Common Understory In A Natural Secondary Forest In Maoershan, Northeast China

The temperate forest in northeastern China plays a key role in the national and global carbon budgets accounting. Typical understory plants including tree-like plants (Syringa reticulata, Acer ginnaa, Padus asiatica, Rhamnus davuricus, Rhamnus yoshinoi, Euonymus verrucosoides, Euonymus alatus, Corylus mandshurica, Viburnum sargentii) and typical shrubs (Lonicera maackii, Viburnum burejaeticum, Sorbaria sorbifolia, Philadelphus schrenkii, Spiraea ussuriensis, Acanthopanax senticosus, Deutzia amurensis) caterigories accumulate a substantial amount of nutrients and carbon. However, fewer studies were conducted for biomass and allometry of these species. In this study, allometric equations for each biomass component (foliage ML, new branch MNB, old branch MOB, small root MSR, large root MLR, branch MBR, aboveground MAG and belowground MBG) and total biomass (MT) for sixteen understory species were developed, allometry of component biomass against plant size, and each biomass components versus other of understory was analyzed. The results were as bellows:I.We sifted 162 biomass equations including 144 specific-species models and 18 mixed-species models and 19 optimal models including 18 specific-species models and 1 mixed-species models of which formats are linear or quadratic polynomial. The formats and variables of optimal biomass equation varied with species and biomass components, and the R2 values of these biomass equations were over 0.800. The optimal equations for tree-like plants were power functions with stem diameter at 10cm (D10) as a predictor. For typical shrubs, most of these equations are also power functions using crown area multiplying height (CAH) and crown area (CA) as variable whereas including some linear and quadratic polynomial. When species-specific models were not established, mixed model was more convenient to estimate biomass of understory plants. Including plant height (H, m) as independent variable in biomass equations only improved the accuracy of biomass estimates for one tree-like shrub but not for most of typical shrubs, and it was similar to the increase of R2 value with adding stem length (L, m) in allometric equations, and most of the increase of R2 values with adding H is bigger than those of adding length.2. The relation of biomass components against plant size and the relation of biomass components versus others complied with allometry theory (P＜0.05), and power scaling was plastic. For tree-like plants, the power of biomass components scaling D10 varied from 1.712±0.071 (MSR∝D10) to 2.576±0.041 (MOB∝D10). For typical shrubs, the power of biomass scaling components varied from 0.688±0.054 (MSR∝CA) to 1.293+0.075 (MOB∝CA), the power of foliage, new branch, and large root biomass scaling CA was isometry, the power of biomass components scaling CAH varied from was 0.527±0.037 (MSR∝CAH) to 1.017+0.041 (MOB∝CAH), and the scaling of old biomass against CAH were isometry. Powers of biomass component scaling others varied from 0.643 (MNB∝MOB)-129 (MBR∝MR), and powers of foliage biomass scaling new branch biomass, old branch biomass scaling large root biomass and aboveground biomass scaling belowground biomass were close to isometry, powers of new branch biomass scaling old branch biomass and small root biomass scaling large root biomass were between 0.67 to 0.75, only the power of foliage biomass (ML) scaling branch biomass (MBR) was close to 0.75, and foliage biomass scaling root biomass was close to 0.86.3. In our study, biomass allocation of understory complied with an allometric theory and optimal partitioning theory, the range of foliage biomass allocation (FA), new branch biomass allocation (NA), old branch biomass allocation (OA), small root biomass allocation (SRA), large root biomass allocation (LRA) and root shoot ratio (R/S) were 5.83%-20.60%,0.83%-7.42%, 36.25%-68.24%,1.32%-6.75% and 16.38%-42.88%, respectively. Biomass allocation varied with species and plant size etc., comparing with tree-like species, FA, NA, LRA and R/S of typical shrubs were bigger, only OA of typical shrubs were smaller (P＜0.05). With plants growing, LA, NA, SRA and R/S decreasing and OA increasing significantly (P<0.05), and only LRA of tree-like species did not change significantly (P>0.05). In this area, biomass structure of understory was similar to the overwood, only components biomass proportion existed discrepancy, as LA, NA and RA of understory were higher, and only OA was lower compared with these of overwood.