Fine root branch orders contribute differentially to uptake, allocation, and return of potentially toxic metals.

Growing evidence has revealed high heterogeneity of fine root networks in both structure and function, with different root orders corporately maintaining trees' physiological activities. However, little information is available on how fine root heterogeneity of trees responds to environmental stresses. We examined concentrations of seven potentially toxic metals (Cr, Ni, Cu, Zn, As, Cd, and Pb) within fine root networks and their correlations with root morphological and macro-elemental traits in six Chinese subtropical trees.

[Effects of litter and mineral nitrogen input on soil organic carbon decomposition in subtropical mixed forest in Dinghu Mountain, South China].

In July-December 2010, a complete factor-controlled experiment was conducted to study the effects of litter and mineral nitrogen addition on soil organic matter decomposition (soil respiration) at the depths of 0-10 cm and 20-30 cm in Dinghu Mountain National Reserve. Coniferous needle litter and broadleaved litter were added, respectively, and 70 g N x m(-2) x yr(-1) of NH4 NO3 was applied to simulate soil nitrogen saturation whereas soil mineral nitrogen was removed by ion-exchange membrane to simulate the decreased nitrogen absorption by root. The addition of both needle litter and broadleaved litter increased the respiration rate of soil-litter system significantly from July to November, but this effect disappeared in December.

Fine root mercury heterogeneity: metabolism of lower-order roots as an effective route for mercury removal.

Fine roots are critical components for plant mercury (Hg) uptake and removal, but the patterns of Hg distribution and turnover within the heterogeneous fine root components and their potential limiting factors are poorly understood. Based on root branching structure, we studied the total Hg (THg) and its cellular partitioning in fine roots in 6 Chinese subtropical trees species and the impacts of root morphological and stoichiometric traits on Hg partitioning. The THg concentration generally decreased with increasing root order, and was higher in cortex than in stele.

[Four hypotheses about the effects of soil nitrogen availability on fine root production and turnover].

With global changes such as increasing temperature and enhanced N deposition, soil nitrogen (N) availability is predicted to increase substantially, and how fine root dynamics responds to the altered soil N has become one of the key questions in terrestrial ecology. As such, a number of hypotheses have been proposed to explain the relationship between increasing soil N availability and fine root production, mortality, and turnover. This article considered four major hypotheses: with increasing soil N availability, 1) both fine root production and turnover rate would increase, 2) both fine root production and turnover rate would decrease, 3) fine root production would decrease while fine root turnover rate would increase, and 4) fine root production would increase while fine root turnover rate would decrease.

[Effects of nitrogen fertilization on ectomycorrhizal infection of first order roots and root morphology of Larix gmelinii plantation].

In this paper, the first order roots of Larix gmelinii plantation under N fertilization were sampled from different soil depths in different seasons to study their morphology under effects of ectomycorrhizal fungi. The results showed that the infection rate of ectomycorrhizal fungi on the first order roots was significantly affected by soil N availability, soil depth, and season. N fertilization induced a decrease of the infection rate, and the decrement varied with soil depth and season.