Jiacun Gu

Lower order roots more palatable to herbivores: a case study with two temperate tree species

Determining which kinds of roots are likely to be consumed by root herbivores may improve our understanding of the mechanistic control on fine root dynamics. Here, we tested the hypothesis that root herbivores prefer to consume the distal lower order roots in their branching networks. Insecticide was applied to soil to quantify effects of root herbivores on root biomass and production in the first five orders (the distal roots numbered as first-order) in Fraxinus mandshurica and Larix gmelinii plantations from May 2008 to July 2009. Root morphology, chemistry, anatomy and physiology were measured simultaneously across branching orders. Among the first five order roots, significant consumptions by herbivores were found only for the two distal lower order roots throughout growing seasons, with 62% of biomass and 57% of production for F. mandshurica, and 71% and 79% for L. gmelinii, respectively. Our results suggest that the distal lower order roots are more palatable and attractive to root herbivores in both plantations, probably because they have higher tissue N, greater respiration rates and lower cellulose. Thus, overlooking herbivore consumption may lead to large underestimation in root biomass and production, which are critical in determining C budget and nutrient cycles in forest ecosystems.

Root morphology, histology and chemistry of nine fern species (pteridophyta) in a temperate forest

AimsThe variability patterns of fern root characteristics have seldom been studied. Here we explored variability in root morphology, histology and chemistry among fern species of temperate forest, and compared the observed patterns with those of seed plants.MethodsWe sampled nine herbaceous fern species from temperate forest in northeastern China, and measured root morphological, histological and chemical characteristics across branch orders for each species.ResultsAll nine fern species had 3 or 4 root orders. With increasing root order, diameter, tissue density, cortical thickness and vascular cylinder diameter increased, while specific root length (SRL) and tissue nitrogen concentration decreased. These were similar to the variability patterns that have been reported for seed plants, except for cortex. Like seed plants, nine fern species showed close relationships among root morphological, histological and chemical characteristics in first-order roots, such as diameter and cortex, tissue density and nitrogen concentration, suggesting that the general linkage between root structure and function exists in all vascular plants.ConclusionsThe observed variation within fern root systems is comparable to the reported variation in seed plants, indicating that the same functional constraints control the evolution and development of root systems in vascular plants belonging either to the fern or seed plant lineages.

Effects of root diameter, branch order, soil depth and season of birth on fine root life span in five temperate tree species

Fine root life span is a key variable influencing the belowground dynamics of forest ecosystems and is known to be associated with a complex suite of endogenous and environmental factors. We investigated how root life span is influenced by root diameter, branch order, season of birth and soil depth of birth for five temperate tree species growing in monoculture plantations at a common site in northeastern China. The minirhizotron approach was used to estimate root life span from April 2008 to October 2009. Cox proportional hazards regression analysis was employed to determine the impact of those four factors on root life span of each species. There was no consistent difference in fine root life span between evergreen conifers and deciduous hardwoods. A bimodal frequency distribution of root life span was observed for all the species; the majority of roots born in summer and autumn survived to the following year, while roots born in spring mostly died in the current growing season. Root life span tended to increase with root diameter across all species, except Juglans mandshurica. The first two root branch orders within each species generally shared similar life span, with the exception of Picea koraiensis. Root life span tended to be longer at greater depths in the soil profile across all five species. Our results suggest that root life span generally depends on complex interrelations among root anatomy, soil environment and seasonal climatic conditions.

Marked differences in standing biomass, length density, anatomy and physiological activity between white and brown roots in Fraxinus mandshurica Rupr. plantation

AimsRoot browning is closely related to physiological function, but the dynamic and underlying mechanism are poorly understood. Our objective was to explore the interrelationship between root browning, in the context of root branch order, and standing biomass, root length density, and soil resources availability at the ecosystem level.MethodsWe measured the standing biomass and length density of white, brown and black roots of the first three branch orders in Fraxinus mandshurica Rupr.. Root anatomy, morphology, physiological activity, as well as soil total available nitrogen, moisture, and temperature were also determined.ResultsWhite roots had longer specific root length, higher physiological activity, and intact cortex compared with brown roots. Grand means of biomass and length density in white roots were 5.6-fold and 4.4-fold higher than those in brown roots, respectively. Sampling time, soil depth, and branch order generally had significant effects on the biomass and length density of both white and brown roots. In addition, sampling time consistently had significant effects on the brown to white root ratio, whereas the ratio was only moderately correlated with soil temperature.ConclusionsRoot browning has pronounced impacts on tree root resource acquisition and belowground carbon allocation in F. mandshurica at both individual root and ecosystem levels.