Nitrogen forms affect root structure and water uptake in the hybrid poplar

The study analyses the effects of two different forms of nitrogen fertilisation (nitrate and ammonium) on root structure and water uptake of two hybrid poplar (Populus maximowiczii x P. balsamifera) clones in a field experiment. Water uptake was studied using sap flow gauges on individual proximal roots and coarse root structure was examined by excavating 18 whole-root systems. Finer roots were scanned and analyzed for architecture. Nitrogen forms did not affect coarse-root system development, but had a significant effect on fine-root development. Nitrate-treated trees presented higher fine:coarse root ratios and higher specific root lengths than control or ammonium treated trees. These allocation differences affected the water uptake capacity of the plants as reflected by the higher sapflow rate in the nitrate treatment. The diameter of proximal roots at the tree base predicted well the total root biomass and length. The diameter of smaller lateral roots also predicted the lateral root mass, length, surface area and the number of tips. The effect of nitrogen fertilisation on the fine root structure translated into an effect on the functioning of the fine roots forming a link between form (architecture) and function (water uptake)

Fat Mass and Obesity-Associated Gene (FTO) in Eating Disorders: Evidence for Association of the rs9939609 Obesity Risk Allele with Bulimia nervosa and Anorexia nervosa

Objective: The common single nucleotide polymorphism (SNP) rs9939609 in the fat mass and obesity-associated gene (FTO) is associated with obesity. As genetic variants associated with weight regulation might also be implicated in the etiology of eating disorders, we evaluated whether SNP rs9939609 is associated with bulimia nervosa (BN) and anorexia nervosa (AN). Methods: Association of rs9939609 with BN and AN was assessed in 689 patients with AN, 477 patients with BN, 984 healthy non-population-based controls, and 3,951 population-based controls (KORA-S4). Based on the familial and premorbid occurrence of obesity in patients with BN, we hypothesized an association of the obesity risk A-allele with BN. Results: In accordance with our hypothesis, we observed evidence for association of the rs9939609 A-allele with BN when compared to the non-population-based controls (unadjusted odds ratio (OR) = 1.142, one-sided 95% confidence interval (CI) 1.001-infinity; one-sided p = 0.049) and a trend in the population-based controls (OR = 1.124, one-sided 95% CI 0.932-infinity; one-sided p = 0.056). Interestingly, compared to both control groups, we further detected a nominal association of the rs9939609 A-allele to AN (OR = 1.181, 95% CI 1.027-1.359, two-sided p = 0.020 or OR = 1.673, 95% CI 1.101-2.541, two-sided p = 0.015,). Conclusion: Our data suggest that the obesity-predisposing FTO allele might be relevant in both AN and BN. Copyright (C) 2012 S. Karger GmbH, Freibur

Pasture degradation modifies the water and carbon cycles of the Tibetan highlands

The Tibetan Plateau has a significant role with regard to atmospheric circulation and the monsoon in particular. Changes between a closed plant cover and open bare soil are one of the striking effects of land use degradation observed with unsustainable range management or climate change, but experiments investigating changes of surface properties and processes together with atmospheric feedbacks are rare and have not been undertaken in the worlds two largest alpine ecosystems, the alpine steppe and the Kobresia pygmaea pastures of the Tibetan Plateau. We connected measurements of micro-lysimeter, chamber, 13C labelling, and eddy covariance and combined the observations with land surface and atmospheric models, adapted to the highland conditions. This allowed us to analyse how three degradation stages affect the water and carbon cycle of pastures on the landscape scale within the core region of the Kobresia pygmaea ecosystem. The study revealed that increasing degradation of the Kobresia turf affects carbon allocation and strongly reduces the carbon uptake, compromising the function of Kobresia pastures as a carbon sink. Pasture degradation leads to a shift from transpiration to evaporation while a change in the sum of evapotranspiration over a longer period cannot be confirmed. The results show an earlier onset of convection and cloud generation, likely triggered by a shift in evapotranspiration timing when dominated by evaporation. Consequently, precipitation starts earlier and clouds decrease the incoming solar radiation. In summary, the changes in surface properties by pasture degradation found on the highland have a significant influence on larger scales

Pasture degradation modifies the water and carbon cycles of the Tibetan highlands

© Author(s) 2014. The Tibetan Plateau has a significant role with regard to atmospheric circulation and the monsoon in particular. Changes between a closed plant cover and open bare soil are one of the striking effects of land use degradation observed with unsustainable range management or climate change, but experiments investigating changes of surface properties and processes together with atmospheric feedbacks are rare and have not been undertaken in the world's two largest alpine ecosystems, the alpine steppe and the Kobresia pygmaea pastures of the Tibetan Plateau. We connected measurements of micro-lysimeter, chamber, 13C labelling, and eddy covariance and combined the observations with land surface and atmospheric models, adapted to the highland conditions. This allowed us to analyse how three degradation stages affect the water and carbon cycle of pastures on the landscape scale within the core region of the Kobresia pygmaea ecosystem. The study revealed that increasing degradation of the Kobresia turf affects carbon allocation and strongly reduces the carbon uptake, compromising the function of Kobresia pastures as a carbon sink. Pasture degradation leads to a shift from transpiration to evaporation while a change in the sum of evapotranspiration over a longer period cannot be confirmed. The results show an earlier onset of convection and cloud generation, likely triggered by a shift in evapotranspiration timing when dominated by evaporation. Consequently, precipitation starts earlier and clouds decrease the incoming solar radiation. In summary, the changes in surface properties by pasture degradation found on the highland have a significant influence on larger scales

In situ measurement of fine root water absorption in three temperate tree species - Temporal variability and control by soil and atmospheric factors

Miniature heat balance-sap flow gauges were used to measure water flows in small-diameter roots (3-4 mm) in the undisturbed soil of a mature beech-oak-spruce mixed stand. By relating sap flow to the surface area of all branch fine roots distal to the gauge, we were able to calculate real time water uptake rates per root surface area (J(S)) for individual fine root systems of 0.5-1.0m in length. Study aims were (i) to quantify root water uptake of mature trees under field conditions with respect to average rates, and diurnal and seasonal changes of J(S), and (ii) to investigate the relationship between uptake and soil moisture theta, atmospheric saturation deficit D, and radiation 1. On most days, water uptake followed the diurnal course of D with a midday peak and low night flow. Neighbouring roots of the same species differed up to 10-fold in their daily totals of J(S) ( < 100-2000 g m(-2) d(-1)) indicating a large spatial heterogeneity in uptake. Beech, oak and spruce roots revealed different seasonal patterns of water uptake although they were extracting water from the same soil volume. Multiple regression analyses on the influence of D, I and theta on root water uptake showed that D was the single most influential environmental factor in beech and oak (variable selection in 77% and 79% of the investigated roots), whereas D was less important in spruce roots (50% variable selection). A comparison of root water uptake with synchronous leaf transpiration (porometer data) indicated that average water fluxes per surface area in the beech and oak trees were about 2.5 and 5.5 times smaller on the uptake side (roots) than on the loss side (leaves) given that all branch roots < 2 mm were equally participating in uptake. Beech fine roots showed maximal uptake rates on mid-summer days in the range of 48-205 g m-2 h(-1) (i.e. 0.7-3.2 mmol m(-2) s(-1)), oak of 12-160 g m(-2) h(-1) (0.2-2.5 mmol m(-2) s(-1)). transpiration rates ranged from 3 to 5 and from 5 to 6 mmol m(-2) s(-1) for sun canopy leaves of beech and oak, respectively. We conclude that instantaneous rates of root water uptake in beech, oak and spruce trees are above all controlled by atmospheric factors. The effects of different root conductivities, soil moisture, and soil hydraulic properties become increasingly important if time spans longer than a week are considered. (c) 2005 Gesellschaft fur Okologie. Published by Elsevier GmbH. All rights reserved

In situ water absorption by tree fine roots measured in real time using miniature sap-flow gauges

1. Root water uptake is a key process in the circulation of water in forest ecosystems. Until recently, water absorption by tree fine roots could not be measured in situ in undisturbed soil. 2. We present a new technique that allows continuous recording of the water absorption of fine root endings in mature stands without altering soil structure, hydrology or mycorrhizal infection. 3. The approach combines miniature sap-flow gauges mounted on small-diameter tree roots (3-4 mm) with a complete extraction and visual surface analysis of the adjacent absorbing fine root endings. This technique yields continuous data on water absorption per fine root surface area, and allows analysis of the spatial heterogeneity of root water uptake in the rhizosphere of forests. 4. We present the results of laboratory and field calibration experiments with Fagus sylvatica L. roots (3-4 mm), which show a good agreement between gauge flow data and synchronous gravimetric flow measurements for flows between 2 and >50 g h(-1) . Gauge readings were unreliable during low flows (<2 g h(-1) ) at night. In these periods, which cover approximate to10% of daily flow, we used an empirically derived linear relationship between root temperature difference and flow. 5. Measurements on F. sylvatica root endings during 10 summer days showed daily water absorption maxima ranging between 0.20 (rainy days) and 0.58 mmol m(-2) root surface area s(-1) (bright or overcast days). The corresponding daily maxima of leaf transpiration rate were approximate to10 times higher (2-4 mmol m(-2) leaf area s(-1) ). 6. The combination of miniature sap-flow gauges and determination of fine root surface area provides a promising tool for analysing water absorption by tree root systems in situ

In situ measurement of water absorption by fine roots of three temperate trees: species differences and differential activity of superficial and deep roots

The spatial heterogeneity of water uptake by fine roots under field conditions was analyzed in situ with miniature sap flow gauges in a mature beech-oak-spruce mixed stand. Sap flow rate (J), sap flow density (J(d)), and root surface-area-specific flow rate (uptake rate, J(s)) were measured for eight to 10 small-diameter roots (3-4 mm) per species in the organic layer (superficial roots) and in the mineral soil (30-80 cm, deep roots) during four months in summer 1999. We calculated J(s) by relating J to the surface area of the section of the fine root system distal to the position of the gauge on the root. When measured synchronously, roots of the three species did not differ significantly in mean J(s), although oak roots tended to have lower rates. However, J(d) decreased in the sequence spruce > beech > oak in most measurement periods. Microscopic investigation revealed differences in fine root anatomy that may partly explain the species differences in J(d) and J(s). Oak fine roots had a thicker periderm than beech and spruce roots of similar diameter and spruce roots had fewer fine branch rootlets than the other species. Synchronously recorded J(d) and J(s) of nearby roots of the same tree species showed large differences in flow with coefficients of variation from 25 to 150% that could not be explained by patchy distribution of soil water. We hypothesize that the main cause of the large spatial heterogeneity in root water uptake is associated with differences between individual roots in morphology and ultrastructure of the root cortex that affect root radial and root-soil interface conductivities. The high intraspecific variation in J(s) may mask species differences in root water uptake. Superficial roots of all species typically had about five times higher J(d) than deep roots of the same species. However, J(s) values were similar for superficial and deep roots in beech and spruce because small diameter roots of both species were more branched in the organic layer than in mineral soil. In oak, deep roots had lower J(s) (maximum of 100 g m(-2) day(-1)) than superficial roots (about 1000 g m(-2) day(-1)). We conclude that temperate tree species in mixed stands have different water uptake capacities. Water flow in the rhizosphere of forests appears to be a highly heterogeneous process that is influenced by both tree species and differences in uptake rates of individual roots within a species

In situ measurement of water absorption by fine roots of three temperate trees: species differences and differential activity of superficial and deep roots

The spatial heterogeneity of water uptake by fine roots under field conditions was analyzed in situ with miniature sap flow gauges in a mature beech-oak-spruce mixed stand. Sap flow rate (J), sap flow density (J(d)), and root surface-area-specific flow rate (uptake rate, J(s)) were measured for eight to 10 small-diameter roots (3-4 mm) per species in the organic layer (superficial roots) and in the mineral soil (30-80 cm, deep roots) during four months in summer 1999. We calculated J(s) by relating J to the surface area of the section of the fine root system distal to the position of the gauge on the root. When measured synchronously, roots of the three species did not differ significantly in mean J(s), although oak roots tended to have lower rates. However, J(d) decreased in the sequence spruce > beech > oak in most measurement periods. Microscopic investigation revealed differences in fine root anatomy that may partly explain the species differences in J(d) and J(s). Oak fine roots had a thicker periderm than beech and spruce roots of similar diameter and spruce roots had fewer fine branch rootlets than the other species. Synchronously recorded J(d) and J(s) of nearby roots of the same tree species showed large differences in flow with coefficients of variation from 25 to 150% that could not be explained by patchy distribution of soil water. We hypothesize that the main cause of the large spatial heterogeneity in root water uptake is associated with differences between individual roots in morphology and ultrastructure of the root cortex that affect root radial and root-soil interface conductivities. The high intraspecific variation in J(s) may mask species differences in root water uptake. Superficial roots of all species typically had about five times higher J(d) than deep roots of the same species. However, J(s) values were similar for superficial and deep roots in beech and spruce because small diameter roots of both species were more branched in the organic layer than in mineral soil. In oak, deep roots had lower J(s) (maximum of 100 g m(-2) day(-1)) than superficial roots (about 1000 g m(-2) day(-1)). We conclude that temperate tree species in mixed stands have different water uptake capacities. Water flow in the rhizosphere of forests appears to be a highly heterogeneous process that is influenced by both tree species and differences in uptake rates of individual roots within a species