Changes In Root Biomass Research Articles

Spatiotemporal Scaling of Vegetation Growth and Soil Formation: Explicit Predictions

Core Ideas Universal exponents of percolation describe vegetation growth and soil formation. The variability in the coefficient of vegetation growth relates to evapotranspiration. The variability in the coefficient for soil formation relates to net infiltration. The variability in the coefficient of net primary productivity relates to nutrients. In a previous study, vegetation linear extent and soil depth as functions of time were proposed to follow percolation‐based scaling laws of power‐law form. Although the power‐law exponents are specified by theory, the fundamental length, x0, and time, t0, scales must be generated from physical arguments. In principle, these length and time scales can vary widely with climate, soil, and plant variables. In the previous study, approximate values, microns and seconds, were proposed for x0 and t0, based on typical soil flow rates, x0/t0, under saturated conditions, and the concept of a single pore having a diameter measured in microns. But the focus here is on development of predictive relationships for soil depth and vegetation linear extent as functions of time and, thus, on guidance for choosing specific values for x0 and t0. In the present study, it is argued that the relevant flow rate for soil formation is net (deep) infiltration, whereas for vegetation extent, the relevant flux must equate to transpiration. In vegetation, linear extent refers (approximately) equivalently to plant height, or root radial extent. Here root radial extent is taken as half the diameter of the projected root system. Since the root radial extent and the root biomass are by definition related through the root fractal dimensionality, the proposed relevance of transpiration to root radial extent implies a specific relationship between transpiration and root productivity, a measure of the root biomass added in a year. When above‐ground and below‐ground biomass are closely related, one can infer a proportionality of net primary productivity to root biomass changes. The general concepts are tested on large data‐bases for the temporal evolution of plant heights and soil depths, as well as the productivity as a function of evapotranspiration and soil calcic and gypsic horizon depths.

Seasonal changes and vertical distribution of root standing biomass of graminoids and shrubs at a Siberian tundra site

Shrub expansion is common in the tundra biome and has been linked to climate warming. However, the underlying mechanisms are still not fully understood. This study aimed to investigate the seasonal and vertical rooting patterns of different plant functional types, which is important for predicting tundra vegetation dynamics. We harvested root samples by soil coring and investigated seasonal changes in root biomass and vertical root distribution across a vegetation gradient, focusing on the differences between graminoids and dwarf shrubs, at a northeastern Siberian tundra. Graminoid fine root biomass increased significantly during the growing season, whereas that of shrubs was already high at the beginning and did not change later on. Shrubs had a much shallower rooting pattern than graminoids. Also, shrub roots did not respond to increases in permafrost thawing depth over the growing season, whereas graminoids grew fine roots in deeper, recently thawed soil layers during the growing season. Our results show that shrubs are predominantly shallow-rooted and grow roots earlier than graminoids, which allows shrubs to take advantage of the nutrient pulse after snowmelt in the early growing season. In contrast, the deep-rooted graminoids can access the nutrients in deeper soil and may profit from increasing permafrost thawing depth. The outcome of the competitive interactions between graminoids and shrubs in tundra may depend on the balance between the benefits associated with earlier root growth and deeper root distribution, respectively. The shrub expansion with climate warming observed in recent decades suggests that earlier root growth in the upper soil layer may be more important than increased rooting depth later in the growing season.

Root biomass and soil carbon response to growing perennial grasses for bioenergy

Dedicated bioenergy crops such as switchgrass (Panicum virgatum L.), miscanthus [Miscanthus x giganteus (Mxg)], indiangrass [Sorghastrum nutans (L.) Nash], and big bluestem (Andropogon gerardii Vitman) can provide cellulosic feedstock for biofuel production while maintaining or improving soil and environmental quality. To better understand bioenergy crop effects on soils, we studied changes in soil properties of a Tomek silt loam under inorganic fertilization of switchgrass after 4 years and warm-season grass monocultures and mixtures after 6 years in eastern Nebraska. The first experiment had two study factors: two switchgrass harvest dates (August and November) and nitrogen (N), phosphorus (P), and potassium (K) fertilization rates. Nitrogen fertilizer levels (0, 60, and 120 kg N ha−1) were the main plots, while P levels (0, 22, and 44 kg P ha−1) were the split plots and K levels (0, 11, and 22 kg K ha−1) were the split-split plots. The second experiment included six bioenergy feedstocks comprised of four monocultures [switchgrass (cv. Shawnee and an experimental strain tracked as Kanlow N1), indiangrass (Chief), and miscanthus (Mxg)] and two mixtures [big bluestem (Goldmine) + indiangrass (Warrior) + switchgrass (Shawnee) and big bluestem (Bonanza) + indiangrass (Scout) + switchgrass (Shawnee)]. Soil samples were analyzed for root biomass, soil organic C (SOC), total N, bulk density, aggregate stability, and pH. In the first experiment, inorganic fertilization and harvest dates had no effect on switchgrass root biomass, SOC pools, soil aggregate stability, and other properties. In the second experiment, cumulative root biomass under Chief indiangrass monoculture was lower than that under other grass monocultures and mixtures except miscanthus. These results suggest that inorganic fertilization and harvest dates do not affect soil properties in the short term, but Chief indiangrass monoculture may have lower root biomass than other grasses. Overall, fertilization management did not induce changes in root biomass and soil properties, but Chief indiangrass monoculture had lower cumulative root biomass compared with mixtures and switchgrass monocultures, suggesting that cultivar selection will affect root biomass accumulation. Further monitoring is needed to determine long-term changes in root biomass and soil properties under these bioenergy crop systems.

Effect of nutrient additions and site hydrology on belowground production and root nutrient contents in two wet grasslands

Belowground production can be a significant part of total plant biomass and represents a significant pool of carbon and other nutrients. Changes in root biomass and nutrient contents can influence root decomposition and nutrient turnover rates, thereby impacting ecosystem processes and functions. In-growth core bags were used in a long-term nutrient addition study to determine net belowground primary production (NBPP), root nutrient (C, N and P) percentages and stoichiometry under different nutrient treatments in two wet grasslands with either mineral or organic soil. It was hypothesized that fertilization will lead to reduced NBPP, but increased root nutrient contents, and that these differences will be greater over time. The fertilizer was added in two half doses in a growing season over seven years with NBPP and the nutrient measures sampled in years 2, 3, 5 and 7. Between-year differences in the measured parameters were tested by repeated measures ANOVA, while one-way ANOVAs were run to compare between-treatment differences in each year within each site. Linear regressions were run to relate NBPP, root nutrient content and the stoichiometric ratios to changes in site hydrology. NBPP and root nutrient contents changed over time, especially in the organic soil grassland, but were largely unaffected by the nutrient additions. Site hydrology, sometimes interacting with the nutrient treatments, appeared to be the more important factor. Prolonged flooding of the two grasslands in the latter two years of measurements led to significantly reduced NBPP, and N and P% especially in the organic soil site. The response of wet grassland belowground structures to changing hydrologic conditions, in tandem with nutrient addition, may be useful in developing management plans to deal with the expected effect of climate change on water availability at the local and regional scales.

Physiological and morphological responses of Leymus chinensis to saline‐alkali stress

AbstractIn this study, soil containing four different concentrations of salt was used to grow Leymus chinensis, which was sampled over 120 days between the beginning of spring and the end of fall. During this time, its physiological and morphological characteristics were analyzed. Maximal superoxide dismutase and betaine content were observed under moderate saline‐alkaline stress treatment (A3), and with increasing saline‐alkaline stress, there was a linear increase in the contents of Na+, proline, malondialdehyde (MDA), organic acids (OAs), catalase, peroxidase, soluble protein and total soluble sugar. However, the K+ content and the K+/Na+ ratio decreased significantly. Under saline‐alkaline stress, the K+, betaine, OA and soluble protein levels in the leaves were higher than those in the rhizomes, whereas the proline, MDA, protective enzyme and total soluble sugar levels in the leaves were lower than those observed in the rhizomes. The node density varied with increases in saline‐alkali stress, and each node index was maximal at A3. Under saline‐alkali stress, the rhizome biomass, leaf biomass and root–shoot ratio first decreased and then increased, whereas the change in root biomass showed a contrary tendency, and the specific root length increased gradually. There was a significant correlation between the root–shoot ratio, specific root length, and the physiological indexes. These results show that under different degrees of saline‐alkali stress, L. chinensis is likely to use a series of adaptive physiological and morphological responses; the physiological responses were primarily related to the allocation of biomass and energy, root length, and the allocation of biomass between the aboveground and belowground organs.

Soil C:N stoichiometry controls carbon sink partitioning between above-ground tree biomass and soil organic matter in high fertility forests

The release of organic compounds from roots is a key process influencing soil carbon (C) dynamics and nutrient availability in terrestrial ecosystems. Through this process, plants stimulate microbial activity and soil organic matter (SOM) mineralization thus releasing nitrogen (N) that sustains gross and net primary production (GPP and NPP, respectively). Root inputs also contribute to SOM formation. In this study, we quantified the annual net root-derived C input to soil (Net-Croot) across six high fertility forests using an in-growth core isotope technique. On the basis of Net-Croot, wood and coarse root biomass changes, and eddy covariance data, we quantified net belowground C sequestration. Belowground C accumulation and GPP were inversely related to soil C:N, but not to climate or stand age. Soil C content and C:N were also related to soil texture. At these high fertility sites, biomass growth did not change with soil C:N; however, biomass growth-to-GPP ratio significantly increased with increasing soil C:N. This was true for both our six forest sites and for another 23 high fertility sites selected at a global scale. We suggest that, at high fertility sites, plant N demand interacts with soil C:N stoichiometry and microbial activity, resulting in higher allocation of C to above ground tree biomass with increasing soil C:N ratio. When C:N is high, microbes have a low C use efficiency, respire more of the fresh C inputs by roots and prime SOM decomposition, thereby increasing N availability for tree uptake. Soil C sequestration would therefore decrease, whereas the extra N released during SOM decomposition can promote tree growth and ecosystem C sink allocation in aboveground biomass. Conversely, C is sequestered in soil when low soil C:N promotes microbial C use efficiency and new SOM formation and stabilization on clay particles.

Plant diversity and identity effects on predatory nematodes and their prey.

There is considerable evidence that both plant diversity and plant identity can influence the level of predation and predator abundance aboveground. However, how the level of predation in the soil and the abundance of predatory soil fauna are related to plant diversity and identity remains largely unknown. In a biodiversity field experiment, we examined the effects of plant diversity and identity on the infectivity of entomopathogenic nematodes (EPNs, Heterorhabditis and Steinernema spp.), which prey on soil arthropods, and abundance of carnivorous non-EPNs, which are predators of other nematode groups. To obtain a comprehensive view of the potential prey/food availability, we also quantified the abundance of soil insects and nonpredatory nematodes and the root biomass in the experimental plots. We used structural equation modeling (SEM) to investigate possible pathways by which plant diversity and identity may affect EPN infectivity and the abundance of carnivorous non-EPNs. Heterorhabditis spp. infectivity and the abundance of carnivorous non-EPNs were not directly related to plant diversity or the proportion of legumes, grasses and forbs in the plant community. However, Steinernema spp. infectivity was higher in monocultures of Festuca rubra and Trifolium pratense than in monocultures of the other six plant species. SEM revealed that legumes positively affected Steinernema infectivity, whereas plant diversity indirectly affected the infectivity of HeterorhabditisEPNs via effects on the abundance of soil insects. The abundance of prey (soil insects and root-feeding, bacterivorous, and fungivorous nematodes) increased with higher plant diversity. The abundance of prey nematodes was also positively affected by legumes. These plant community effects could not be explained by changes in root biomass. Our results show that plant diversity and identity effects on belowground biota (particularly soil nematode community) can differ between organisms that belong to the same feeding guild and that generalizations about plant diversity effects on soil organisms should be made with great caution.

Belowground Ecosystem Recovery During Grassland Restoration: South African Highveld Compared to US Tallgrass Prairie

Conversion of cultivated land to grassland is globally practiced to reverse soil degradation, but belowground ecosystem response to restoration has never been compared between old and new world temperate grasslands. We used a chronosequence approach to model change in root biomass and quality (indexed by C:N ratio), microbial biomass and composition [indexed by phospholipid fatty acids (PLFAs)], soil aggregate structure, and soil C and N stocks in the South African Highveld and compared recovery of these variables to a grassland restoration chronosequence in the US tallgrass prairie. We hypothesized soil C recovery, and mechanisms promoting soil C and N accrual would be convergent between these distant temperate grasslands with similar growing season precipitation, history of cultivation, and undergoing restoration with C4-grasses. Total PLFA richness and concentrations of most microbial groups rose to represent uncultivated grassland in the highveld (similar to tallgrass prairie), but in contrast to tallgrass prairie, the fungi:bacteria ratio did not increase with restoration age. In the highveld, root biomass accumulation was lower, but root quality became more representative of the never-cultivated grassland than in restorations in tallgrass prairie. Soil aggregate recovery was slightly faster in tallgrass prairie, and the pattern of macroaggregate C recovery was divergent due to less depletion in cultivated soil and higher stock of C in the uncultivated soil relative to the highveld. More rapid restoration of total soil C and N stocks in the highveld was attributed to greater soil C saturation deficit at the onset of restoration, development of higher quality root systems that promote the microbial biomass and soil aggregation, and climate conditions (distinct periodicity of rainfall and high aridity) that likely impose more limitation to decomposition relative to the tallgrass prairie ecosystem.

Estimating tree biomass and changes in root biomass following clear-cutting ofBrachystegia-Julbernardia(miombo) woodland in central Zambia

SUMMARYThis study aimed at developing allometric models from destructive sample field data for estimating both aboveground and belowground tree biomass and assessing changes in root biomass after old-growthBrachystegia-Julbernardia(miombo) woodland clearing in central Zambia. Logarithmic linear models were selected for estimating tree biomass because they gave the most accurate (low mean error) predictions. On average aboveground and belowground biomass in regrowth woodland represented 29% and 41%, respectively, of the biomass in old-growth woodland. The root:shoot ratios were 0.54 and 0.77 in old-growth and regrowth woodland, respectively. Ten years after clear-cutting old-growth woodland, root biomass loss was about 60% of the original biomass. The main cause of post clearing root biomass loss was fire which at the study sites occurred annually or biannually. Control of fire in cleared sites should be encouraged in forest management for carbon storage and sequestration in miombo woodland of southern Africa.

An optimized fine root sampling methodology balancing accuracy and time investment

Aims Tree roots are spatially highly heterogeneous and it thus requires large numbers of samples to detect statistically significant changes in root biomass. The objectives of this study were to understand and quantify the sources of error in the assessment of fine root biomass (<2 mm) during the second year of a highdensity Populus plantation. Methods Soil cores were collected in winter (n035) and in summer (n020), and fine roots were picked by hand for varying lengths of time: 1, 2, 5, 20, 40, and 60 min. The root biomass data were used to identify the best combination of the time spent for root picking and the number of samples collected, that minimizes the overall uncertainty (i.e. the combination of the spatial error due to the incomplete sampling and the temporal error due to the incomplete core processing). Results On average, 25 min was enough time to pick 90 % of the fine root biomass in winter, while in summer only 10 min were needed. In winter fewer samples were needed, but more time for picking was necessary as compared to summer when root biomass was higher. Conclusions Fine root sampling can be optimized by minimizing the uncertainty of the biomass estimates and simultaneously decreasing root sampling time investment.

Root characteristics of C4 grasses limit reliance on deep soil water in tallgrass prairie

C4 grass species in the mesic tallgrass prairie of central North America can exhibit both high root production and deep rooting in the soil profile (>2 m). Differences in root growth and the types of roots produced vary according to local environmental gradients and management practices. The production of deep roots in tallgrass prairie has been historically presumed as a mechanism for water uptake when surface soils are dry. We examined changes in root biomass, total root length, root width, and theoretical hydraulic conductivity using roots collected from deep soil cores in upland and lowland topographic positions in grazed and ungrazed watersheds of the Konza Prairie Biological Station in north-eastern Kansas, USA. Root biomass, total root length, and theoretical hydraulic conductivity were highest in roots found in the top 20 cm of the soil profile, and then declined exponentially with increasing soil depth. Compared to grazed areas, ungrazed locations had more root biomass and total root length of roots in the most superficial soil layers. No differences in rooting profiles were present among topographic contrasts. Theoretical hydraulic conductivity of axial root xylem did not vary by topographic position or grazing contrasts, and declines in conductivity by depth were driven by changes in the number of vessels per stele, rather than changes in vessel size. Irrespective of differences by grazing treatment or topographic position, significant reductions in root biomass, total root length, and theoretical hydraulic conductivity of grass roots at soil depths greater than 1 m suggest deep roots in this grassland have limited functional significance for water uptake.

三峡库区马尾松根系生物量的空间分布

Roots play an important role in individual plant carbon budgets and ecosystem-level carbon and nutrient cycling.Considerable research has concentrated on the vertical distribution and seasonal dynamics of fine root biomass.However,the spatial distribution of root biomass has been poorly studied.Our objectives are to determine how fine root biomass changes with horizontal distance,and to examine the spatial distribution of fine root biomass in stands of different ages. The horizontal and vertical distribution of root(0—10mm diameter) biomass for three Pinus massoniana plantations of different ages,20,30 and 46 year-old,in the Three Gorges Reservoir area,Hubei Province,China,was studied.Ten cm diameter soil cores were collected in July,2010 at different horizontal distances(0.5,1.0,1.5 and 2.0m) from the stem.Each soil core was separated into five sections at depths of 0—10,10—20,20—30,30—40 and 40—60 cm.Roots(0—10mm) were first separated into living and dead roots.Then both categories were classified into two diameter classes,that was,two groups for fine roots(0—1mm and 1—2mm),and two groups for coarse roots(2—5mm and 5—10mm).Roots were dried at 80℃ to a constant mass and weighed. Our results indicated the average fine root biomass of P.massoniana in the Three Gorges Reservoir area was 0.56 t/hm2,which is within the range of worldwide fine root biomass(2—5mm diameter),but lower than the average fine root biomass of subtropical evergreen needleleaf forest.The total root biomass(≤ 10mm diameter) for P.massoniana forest for the 20,30 and 46 year-old stands was 2.40,4.72 t/hm2,and 2.94 t/hm2,respectively,and differences between them were statistically significant(P0.05).However,the fine root biomass(0—2mm diameter) declined insignificantly with an increase in forest age(P0.05).In all three stands,living root biomass was much higher than dead root biomass.Fine root biomass in all the stands peaked at 1.0 m from the stem,but fine root biomass in stands of different ages changed differently as the horizontal distance increased.Fine root biomass was mainly concentrated in the upper soil layer and decreased as soil depth increased.For all ages of stands,47.53%—71.73% of living roots were observed in the 0—20cm soil layer.The majority of coarse roots(2—10mm diameter) were at a depth of 20—60cm.We concluded smaller roots were more sensitive to environmental change than larger roots,based on an analysis of the interactions between the spatial distribution of fine root biomass and soil depth,distance from stem and stand age.Spatial distribution of fine root biomass was very significantly influenced by soil depth(P0.01),but effects of stand age and horizontal distance from the tree stem were not significant(P0.05).Also,all these factors had no significant influence on the spatial distribution of coarse root biomass(P0.05).The results indicate more consideration should be given to research on the spatial distribution of roots and the effects of these integrated factors on root distribution.

Does the stress tolerance of mixed grassland communities change in a future climate? A test with heavy metal stress (zinc pollution)

Will species that are sensitive/tolerant to Zn pollution still have the same sensitivity/tolerance in a future climate? To answer this question we analysed the response of constructed grassland communities to five levels of zinc (Zn) supply, ranging from 0 to 354 mg Zn kg −1 dry soil, under a current climate and a future climate (elevated CO 2 and warming). Zn concentrations increased in roots and shoots with Zn addition but this increase did not differ between climates. Light-saturated net CO 2 assimilation rate ( A sat) of the species, on the other hand, responded differently to Zn addition depending on climate. Still, current and future climate communities have comparable biomass responses to Zn, i.e., no change in root biomass and a 13% decrease of above-ground biomass. Provided that the different response of A sat in a future climate will not compromise productivity and survival on the long term, sensitivity is not altered by climate change.

Changes in soil respiration across a chronosequence of tallgrass prairie reconstructions

Close relationships among climatic factors and soil respiration (Rs) are commonly reported. However, variation in Rs across the landscape is compounded by site-specific differences that impede the development of spatially explicit models. Among factors that influence Rs, the effect of ecosystem age is poorly documented. We hypothesized that Rs increases with grassland age and tested this hypothesis in a chronosequence of tallgrass prairie reconstructions in central Iowa, U.S.A. We also assessed changes in root biomass, root ingrowth, aboveground net primary productivity (ANPP), and the strength of soil temperature and moisture in predicting Rs. We found a significant increase in total growing season Rs with prairie age (R2=0.79), ranging from 714gCm−2 in the youngest reconstruction (age 4) to 939gCm−2 in the oldest prairie (age 12). Soil temperature was a strong predictor of intra-seasonal Rs among prairies (R2=0.78–0.87) but mean growing season soil temperature and moisture did not relate to total Rs. The increase in Rs with age was positively correlated with root biomass (r=0.80) and ANPP (r=0.87) but not with root ingrowth. Our findings suggest that growing season Rs increases with tallgrass prairie age, root biomass, and ANPP during young grassland development.

Collembola respond to aphid herbivory but not to honeydew addition

Abstract. 1. Euedaphic collembola alter their soil distribution in response to above‐ground aphid herbivory of Poa annua L. Graminae, a host grass.2. Two mechanisms potentially underpin this effect. Carbon‐rich aphid honeydew falling onto the soil surface may affect mycophagous collembola; alternatively aphid‐induced changes in root biomass may be necessary to produce changes in collembola abundance.3. When compared to a plant‐only control, aphid herbivory increased the number of collembola in the top 5 cm of soil, reduced both foliar and root biomass, and increased shoot/root ratio. Honeydew addition had no effect on collembola numbers or any recorded host‐plant parameter.4. Honeydew deposition is not responsible for the increased numbers of collembola found in the upper soil after aphid herbivory; aphid‐induced reductions in root biomass may be the most important factor explaining knock‐on effects of aphid herbivory on soil fauna.

Fine root biomass, necromass and chemistry during seven years of elevated aluminium concentrations in the soil solution of a middle-aged Picea abies stand

Toxic effects of aluminium (Al) on Picea abies (L.) Karst. (Norway spruce) trees are well documented in laboratory-scale experiments, but field-based evidence is scarce. This paper presents results on fine root growth and chemistry from a field manipulation experiment in a P. abies stand that was 45 years old when the experiment started in 1996. Different amounts of dissolved aluminium were added as AlCl3 by means of periodic irrigation during the growing season in the period 1997–2002. Potentially toxic concentrations of Al in the soil solution were obtained. Fine roots were studied from direct cores (1996) and sequential root ingrowth cores (1999, 2001, 2002) in the mineral soil (0–40 cm). We tested two hypotheses: (1) elevated concentration of Al in the root zone leads to significant changes in root biomass, partitioning into fine, coarse, living or dead fractions, and distribution with depth; (2) elevated Al concentration leads to a noticeable uptake of Al and reduced uptake of Ca and Mg; this results in Ca and Mg depletion in roots. Hypothesis 1 was only marginally supported, as just a few significant treatment effects on biomass were found. Hypothesis 2 was supported in part; Al addition led to increased root concentrations of Al in 1999 and 2002 and reduced Mg/Al in 1999. Comparison of roots from subsequent root samplings showed a decrease in Al and S over time. The results illustrated that 7 years of elevated Altot concentrations in the soil solution up to 200 μM are not likely to affect root growth. We also discuss possible improvements of the experimental approach.

Tolerance of understory plants subject to herbivory by roe deer

Current understanding of plant–herbivore interactions postulates that forest understory species are less tolerant to herbivory by large mammals than grassland species. As yet, research on forest species has focused on extensive biomass loss. However, forest dwelling ungulates are often selective browsers, hence biomass loss experienced by forage species is mostly limited to specific plant modules. We investigated the impact of herbivory on common forage species of roe deer Capreolus capreolus by simulating browsing on wild transplants of the two herbs Geum urbanum and Prenanthes purpurea, and the two graminoids Carex sylvatica and Luzula luzuloides. Two clipping regimes simulated different browsing frequencies, whereas shading and full day light represented light conditions in closed forests and gaps, respectively. Single clipping did not affect above ground biomass production of any species, independent of light conditions. Repeated biomass loss led to undercompensation in L. luzuloides, marginal compensation in C. sylvatica, and full compensation in G. urbanum and P. purpurea measured as above ground biomass production. The change in root biomass after clipping was positively correlated with the change in above ground biomass production in all four species. In contrast, nitrogen concentration was negatively correlated with above ground biomass in the graminoids, whereas no relationship between nitrogen and biomass was found in the herbs. Although light conditions and plant provenance affected biomass production, we found no effect of light conditions on plant reactions to herbivory. These results suggest that forest understory species, graminoids as well as herbs, are tolerant to herbivory by selective browsers such as roe deer. As in grassland ecosystems, the degree of compensatory growth depends on amount and frequency of biomass loss.

Root respiration in temperate mountain grasslands differing in land use

AbstractIn grasslands the proportionally largest emission of CO2 comes from the soil. This study aimed to assess how root respiration, a major flux component, is affected by land management and changes in land use. Respiration of roots, separated to classes of different diameter, was measured in 11 temperate mountain grasslands, including meadows, pastures and abandoned sites at three geographic locations. Specific root respiration was affected by nitrogen (N) concentration, root class and land use. The relationship between root N concentration and respiration differed between locations. With increasing root diameter there was a decrease in root respiration, N concentration, respiration per unit N and Q10. In grasslands abandoned for several years specific root respiration was lower than in meadows, pastures and a recently abandoned site. This was due to lower root N concentrations and/or lower respiration rates per unit N within each root class. Since root biomass was higher on abandoned grasslands, total ecosystem root respiration did not differ consistently between sites. Ecosystem root respiration showed distinct seasonal changes due to changes in root biomass, which were less pronounced on abandoned grasslands. Fine roots generally made up the largest portion of ecosystem root respiration, their contribution varying between 35% and 96%. On meadows, clipping increased soil and root respiration by increasing soil temperature. When corrected for temperature effects soil respiration was reduced by 20–50%, whilst root respiration was little affected, suggesting that carbohydrate reserves sustained root metabolism for several days and that microbial respiration strongly responded to short‐term changes in assimilate supply.

Inoculation with Ericoid Mycorrhizal Fungi Alters Root Colonization and Growth in Nursery Production of Blueberry Plants from Tissue Culture and Cuttings

In nursery production, inoculation with mycorrhizal fungi is thought to be most beneficial when colonization occurs as early as possible during plant growth. Unrooted tissue culture plantlets (TC) and hardwood cuttings (HC) of different cultivars of highbush blueberry plants (Vaccinium corymbosum L.) were inoculated with mixed inoculum of three different isolates of ericoid mycorrhizal fungi (EMF) in a commercial blueberry nursery. Plants were monitored for root colonization by EMF and plant growth to determine if inoculation with EMF influences rooting, subsequent plant growth, or EMF colonization during one (HC) or two (TC) years after inoculation. Tissue culture plants became naturally colonized by EMF, however, the intensity of this natural colonization was low and inoculation with EMF increased colonization for some cultivars, especially in the first few months after inoculation. This suggests that low colonization during nursery production of blueberry may be at least partially a result of low inoculum potential of the growing medium. However, we found that the frequency and intensity of colonization of certain cultivars decreased substantially after plants were transplanted and moved to an outside growing area. This decrease in colonization suggests that; (1) the fungi used for inoculation may not be suitable for this cultivar under the specific cultural conditions used in the nursery, (2) changes in cultural conditions from transplanting inhibited further colonization of the fungi that were present in the initial stages of propagation, or (3) there were possible changes in the type of fungi on the root system. Inoculation of TC plants with EMF caused measurable changes in root and aboveground plant morphology and biomass partitioning during the first two growing seasons; however, we found that the responses to inoculation with EMF can vary with cultivar, suggesting that a level of plant-fungus specificity may exist in EMF associations with blueberry plants that influences plant growth. Inoculation of HC with EMF increased colonization frequency and intensity on cuttings under the cultural practices used in the nursery; however, colonization decreased between 3 months and 5 months after sticking suggesting that the specific cultural conditions used during propagation decrease colonization by both natural and inoculated populations of the fungi. Even though colonization decreased during propagation, inoculation reduced the time required for rooting and caused measurable changes in root biomass of rooted cuttings. This increased root biomass may lead to increased quality and performance of rooted cuttings after transplanting.

Nitrogen input mediates the effect of free‐air CO2 enrichment on mycorrhizal fungal abundance

AbstractPlots containing Lolium perenne L., Trifolium repens L. or a mixture of both plant species were exposed to elevated atmospheric CO2 (eCO2) for 10 consecutive seasons using free‐air CO2 enrichment technology at ETH Zürich, Switzerland. The CO2 treatment was crossed with a two‐level nitrogen (N) fertilization treatment. In the tenth year, soil samples were collected on three occasions through the growing season to assess the impact of eCO2 and N fertilization on mycorrhizal fungal abundance. Soil moisture content, which varied with harvest date, was linked to the vegetation type and was higher under eCO2. Root weight density was affected by vegetation type: lower for clover, higher for grass. Root weight density was stimulated by eCO2 and decreased by high N fertilization. The percent root length colonized by mycorrhizal fungi was lowest in the clover plots and highest in the grass plots. High N significantly decreased root length colonized. There was no overall effect of eCO2 on root length colonized; however, there was a significant eCO2× N interaction: eCO2 increased root length colonized at high N, but decreased root length colonized at low N. Extraradical mycorrhizal hyphal density was linked to soil moisture content. Extraradical mycorrhizal hyphal density was not affected by eCO2 or high N individually, but as for root length colonized, there was a significant eCO2× N interaction: eCO2 increased extraradical mycorrhizal hyphal density at low N but not at high N. These environmental effects on root colonization and external mycorrhizal hyphae were independent of soil moisture content and root weight density. This field study demonstrated a significant mediating effect of N fertilization on the response of arbuscular mycorrhizal fungi to eCO2 irrespective of any change in root biomass.