Abstract
Variation of total fine-root biomass among types of tree stands has previously been attributed to the characteristics of the stand layers. The effects of the understory vegetation on total fine-root biomass are less well studied. We examined the variation of total fine-root biomass in subtropical tree stands at two sites of Datian and Huitong in China. The two sites have similar humid monsoon climate but different soil organic carbon. One examination compared two categories of basal areas (high vs. low basal area) in stands of single species. A second examination compared single-species and mixed stands with comparable basal areas. Low basal area did not correlate with low total fine-root biomass in the single-species stands. The increase in seedling density but decrease in stem density for the low basal area stands at Datian and the quite similar stand structures for the basal-area contrast at Huitong helped in the lack of association between basal area and total fine-root biomass at the two sites, respectively. The mixed stands also did not yield higher total fine-root biomasses. In addition to the lack of niche complementarity between tree species, the differences in stem and seedling densities and the belowground competition between the tree and non-tree species also contributed to the similarity of the total fine-root biomasses in the mixed and single-species stands. Across stand types, the more fertile site Datian yielded higher tree, non-tree and total fine-root biomasses than Huitong. However, the contribution of non-tree fine-root biomass to the total fine-root biomass was higher at Huitong (29.4%) than that at Datian (16.7%). This study suggests that the variation of total fine-root biomass across stand types not only was associated with the characteristics of trees, but also may be highly dependent on the understory layer.
Highlights
Fine roots account for approximately 40% of the total net primary production in forest ecosystems globally and supply most of the nutrients and water to the aboveground biomass [1]
We investigated the fine-root biomass stock (FRB) of tree and non-tree species for two categories of basal area in stands of single tree species and in single-species vs. mixed stands with comparable basal areas in subtropical China
Kucbel et al (2011) reported that stands with lower basal area had lower total FRB in Norway spruce forests [34].Our results showed that the total FRB did not vary with tree basal area in the C. lanceolata plantations
Summary
Fine roots account for approximately 40% of the total net primary production in forest ecosystems globally and supply most of the nutrients and water to the aboveground biomass [1]. The first is positive, whereby mixed forests with more tree species have more FRB than do corresponding single species stands [2,3,4,5,6], driven by niche complementarity (coexisting species occupy different soil space) and the “selection” effect (inclusion of a productive species) [7]. Niche complementarity was observed in mature and closed forest stands and occurred in very young tree communities before canopy closure [2, 3]. The effects of stem density and basal area on FRB are controversial in single- species stands. Canopy closure, and site fertility may influence the findings related to stem density, since considerable effects of these three factors on FRBs have been observed [17,18,19,20]
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