Fine root architecture, morphology, and biomass of different branch orders of two Chinese temperate tree species

Abstract

We have limited understanding of architecture and morphology of fine root systems in large woody trees. This study investigated architecture, morphology, and biomass of different fine root branch orders of two temperate tree species from Northeastern China-Larix gmelinii Rupr and Fraxinus mandshurica Rupr -by sampling up to five fine root branch orders three times during the 2003 growing season from two soil depths (i.e., 0-10 and.10-20 cm). Branching ratio (R b ) differed with the level of branching: R b values from the fifth to the second order of branching were approximately three in both species, but markedly higher for the first two orders of branching, reaching a value of 10.4 for L. gmelinii and 18.6 for F. mandshurica. Fine root diameter, length, SRL and root length density not only had systematic changes with root order, but also varied significantly with season and soil depth. Total biomass per order did not change systematically with branch order. Compared to the second, third and/or fourth order, the first order roots exhibited higher biomass throughout the growing season and soil depths, a pattern related to consistently higher R b values for the first two orders of branching than the other levels of branching. Moreover, the differences in architecture and morphology across order, season, and soil depth between the two species were consistent with the morphological disparity between gymnosperms and angiosperms reported previously. The results of this study suggest that root architecture and morphology, especially those of the first order roots, should be important for understanding the complexity and multi-functionality of tree fine roots with respect to root nutrient and water uptake, and fine root dynamics in forest ecosystems.

Whole-tree dynamics of non-structural carbohydrate and nitrogen pools across different seasons and in response to girdling in two temperate trees

“…Soils are Hap-Boric Luvisols, which vary from in depth from 30 to >50 cm, with high organic matter content (14 % in top 10 cm of soil layer) and good drainage. More details on the soil characteristics and site can be found in Wang et al (2006).…”

“…This root sampling method was feasible because the soil in our site was rich in organic matter (14 %) and had a loose loam texture which eased the separation of roots from the soil; in addition, the roots had a relatively shallow distribution in the soil. The majority of roots were concentrated in the top 30 cm for larch and in the top 50 cm for ash (Wang et al 2006). Roots of different branch orders were then sampled (Pregitzer et al 2002).…”

“…and ash (Fraxinus mandshurica Rupr.) were selected for girdling treatment because: (1) they are both dominant tree species in natural forests of Northeast China and are key plantation species, with larch representing 65 % of conifer plantations and ash 10 % of hardwood plantations (Wang et al 2006); (2) the two species have different growth forms and growth strategies and thus may have different strategies of C and N storage (Gaucher et al 2005). Larch is a fast-growing conifer, while ash is a broad-leaved species that grows more slowly.…”

“…Larch is a fast-growing conifer, while ash is a broad-leaved species that grows more slowly. The northern temperate climate zone where these species are found is characterized by strong seasonality (Wang et al 2006), thereby facilitating detection of the role(s) of different plant organs in supplying and refilling NSC and N over a growing season. Our specific hypotheses were: (1) in both species, seasonal dynamics of NSC and N concentrations will be similar despite the large differences in the pool size among different organs because of the similar seasonality of tree growth in the two species (both being deciduous and growing at the same site); (2) in both species, storage organs holding a larger proportion of tree NSC or N will mobilize more NSC or N for new tissue growth at the beginning of the growing season; (3) after stem girdling, NSC stores in nonabsorptive roots will be mobilized to maintain absorptive roots until depletion, and the species with a smaller belowground NSC store will show a greater decline of root NSC store in response to girdling.…”

Fine root architecture, morphology, and biomass response to cutting in a Chinese cork oak (Quercus variabilis Blume) forest

“…where R b i-j is the ratio between the number of fine roots in the branch order (N i ) and the number of its parent root (N j ) (Fitter et al, 1991;Wang et al, 2006).…”