Soil seed banks of pure spruce (Picea abies) and adjacent mixed species stands

The soil seedbank of long living seeds of herbs, graminoids and shrubs can survive several decades in the soil and germinate after disturbances like windthrow or clearcutting. The main goal of this study was to evaluate the risk of weeds, which may limit the success of conversions of secondary pure spruce stands (Picea abies) to mixed species stands. In a first step, germination experiments were performed in the greenhouse on soil samples collected under adjacent pure spruce and mixed species stands (mainly mixtures of spruce and beech –Fagus sylvatica) on two different soil substrates (Flysch: nutrient rich, basic soil; Molasse: nutrient poor, acidic soil). Seedling density and species richness were higher on the nutrient rich soil on Flysch. Comparisons between seedlings that emerged from soil samples collected at the end of the vegetation period and in spring justify the statement of the hypothesis that mixed spruce-beech stands advance the transient seed bank while pure spruce stands stimulate the persistent seed bank. In a second step, the seed banks of different soil horizons down to 35 cm soil depth were studied in a multivariate statistical design for the most dominant species J. effusus, C. pallescens and R. idaeus, which are known to form long-term persistent seeds. Effects of bedrock material (Flysch, Molasse), species composition (pure spruce, mixed species) and treatment (control, nitrate) were tested. The total sum of these three species was significantly higher on Flysch than on Molasse. However, species composition indicated no significant differences, although there was a trend of higher amounts of germinating seeds under pure spruce. Nitrate treatments did not promote germination of viable buried seeds, indicating that the number of emerged seedlings is a realistic indicator of the seed bank density for the studied stands. It is concluded that overstorey tree species composition is not an important controlling factor for seed germination of the studied species after disturbances. The majority of emergents are the graminoids J. effusus and C. pallescens which were not present at all in the aboveground vegetation. Viable seeds were found down to 35 cm soil depth, although most seeds were concentrated in the upper 10 cm soil. Hence, care should be taken if management strategies create conditions that are generally favorable to germination. The success of forest regeneration or a conversion of pure spruce to mixed species stands could be endangered by any disturbance, which causes an immediate increase of light levels.     

Greater accumulation of litter in spruce (Picea abies) compared to beech (Fagus sylvatica) stands is not a consequence of the inherent recalcitrance of needles

Background and aims

Replacement of beech by spruce is associated with changes in soil acidity, soil structure and humus form, which are commonly ascribed to the recalcitrance of spruce needles. It is of practical relevance to know how much beech must be admixed to pure spruce stands in order to increase litter decomposition and associated nutrient cycling. We addressed the impact of tree species mixture within forest stands and within litter on mass loss and nutritional release from litter.

Methods

Litter decomposition was measured in three adjacent stands of pure spruce (Picea abies), mixed beech-spruce and pure beech (Fagus sylvatica) on three nutrient-rich sites and three nutrient-poor sites over a three-year period using the litterbag method (single species and mixed species bags).

Results

Mass loss of beech litter was not higher than mass loss of spruce litter. Mass loss and nutrient release were not affected by litter mixing. Litter decay indicated non-additive patterns, since similar remaining masses under pure beech (47%) and mixed beech-spruce (48%) were significantly lower than under pure spruce stands (67%). Release of the main components of the organic substance (C_org, N_tot, P, S, lignin) and associated K were related to mass loss, while release of other nutrients was not related to mass loss.

Conclusions

In contradiction to the widely held assumption of slow decomposition of spruce needles, we conclude that accumulation of litter in spruce stands is not caused by recalcitrance of spruce needles to decay; rather adverse environmental conditions in spruce stands retard decomposition. Mixed beech-spruce stands appear to be as effective as pure beech stands in counteracting these adverse conditions.     

Impact of common European tree species and Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) on the physicochemical properties of the rhizosphere

Trees play a crucial role in nutrient cycling and ecosystem fertility, notably through rhizosphere processes. The aim of this study was to compare soil physicochemical properties between bulk soil and rhizosphere of several tree species, and to compare rhizosphere properties between fertilized and non-fertilized conditions. The soil sampling was performed in Breuil-Chenue forest (North-East of France) in seven stands: native forest (old beech (Fagus sylvatica L.) and oak (Quercus sessiliflora Smith) coppice with standards; CwS), beech, oak (Quercus petraea [Matt.] Liebl.), Douglas-fir and fertilised Douglas-fir, Norway spruce (Picea abies Karst.) and fertilised Norway spruce. Systematic soil sampling was performed at 0–3, 3–10, and 10–23 cm in 20 calibrated pits. The rhizosphere of the different species was generally enriched in C, N, Ca, Mg, and K. Interestingly, the same positive effect was observed in the fertilised plots. The rhizosphere effect varied between tree species for C, “base” cations, pH_water and cation exchange capacity. This study reveals that interactions between roots, microorganisms and soil can enrich the pool of nutrients in the rhizosphere compared to bulk soil whatever the soil fertility conditions, and that the magnitude of the rhizosphere effect depends on tree species.     

Relationships between tree dimension and coarse root biomass in mixed stands of European beech (Fagus sylvatica L.) and Norway spruce (Picea abies[L.] Karst.)

Relationships between tree parameters above ground and the biomass of the coarse root system were examined in six mixed spruce-beech stands in the Solling Mountain region in northwest Germany. The selected stands were located on comparable sites and covered an age range of 44 to 114 years. Coarse roots (d?\ge?2 mm) of 42 spruce and 27 beech trees were sampled by excavating the entire root system. A linear model with logarithmic transformation of the variables was developed to describe the relationship between the coarse root biomass (CRB, dry weight) and the corresponding tree diameter at breast height (DBH). The coefficients of determination (R ²) attained values between 0.92 for spruce and 0.94 for beech; the logarithmic standard deviation values were between 0.29 and 0.43. A significantly different effect of tree species on the model estimates could not be detected by an analysis of co-variance (ANCOVA). For spruce, the derived relationships were similar to those reported in previous studies, but not for beech. Biomass partitioning in the tree compartments above and below ground differs significantly between spruce (coarse root/shoot ratio 0.16±0.06) and beech (coarse root/shoot ratio 0.10±0.03) in the mixed stands. These results are similar to those given in other studies involving pure spruce and beech stands on comparable sites in the region, although the ratios of pure stands in other regions growing under different site conditions are somewhat higher. Comparing trees of the same DBH classes, root/shoot ratios of spruce are 1.2 to 3 times higher than those of beech. Dominant spruce trees (DBH>60 cm) attained the highest ratios, suppressed beech trees (DBH<10 cm) the lowest. Site conditions of varying climate and soils and interspecific tree competition are likely to affect root/shoot ratio and DBH-coarse root biomass relationships. The greater variability in beech compared with spruce indicates a high 'plasticity' and adaptability of beech carbon allocation. Thus, the derived equations are useful for biomass estimates of coarse roots involving trees of different ages in mixed stands of spruce and beech in the Solling Mountains. However, application of these relationships to stands in other regions would need further testing.     

Effects of changes in tree species composition on water flow dynamics – Model applications and their limitations

Water-plant relations play a key role in the water cycling in terrestrial ecosystems. Consequently, changes in tree species composition may have distinct effects on the water retention capacity as well as on the pattern of streamflow generation. Such changes may result from modified interception properties and transpiration related to differences in canopy properties and root distribution. In order to evaluate the potential hydrological effects of the current silvicultural conversion from monocultural conifer stands into mixed or pure deciduous stands the hydrological model BROOK90 was applied to two forested upland catchments in Germany. The Rotherdbach catchment (9.4 ha, 93 yr-old Norway spruce) is situated in the Eastern Ore Mountains. The Schluchsee catchment (11 ha, 55-yr-old Norway spruce) is located in the higher altitudes of the Black Forest. The calibrated model is capable to describe rather well the temporal variation of streamflow but also the portions of the individual flow components. Data for a beech scenario were adapted for each site using a standard parameter set for deciduous trees provided by BROOK90. The annual discharge in the fictional beech stand at Rotherdbach is 30 to 50% higher compared to spruce with an increase of soil moisture and especially the slow streamflow components. This mainly results from low interception rates during winter time. In contrast, the spruce stand has a permanently higher interception rate. Effects of tree species conversion are moderate at Schluchsee. The annual discharge of a fictional beech stand at Schluchsee is 7 to 14% higher compared to spruce. There in contrast to Rotherdbach, effects of tree species conversion on soil moisture dynamics are small since vertical percolation in the highly permeable soil dominates and precipitation is abundant. Practical forestry will favorably establish mixed beech–spruce rather than pure beech stands. However, it is critical to simulate mixed stands with BROOK90. Therefore, a simple summation of model results from spruce and beech according to their respective area in a fictional mixed stand can only be a first approximation. Advanced hydrological simulation of mixed stand conditions should regard interactions of tree species and spatial parameter distribution. However, this is not yet feasible due to a distinct lack of information. As a consequence, there is a strong need to collect relevant hydrological and ecophysiological data in mixed stands in the future.     

Changes in diversity and storage function of ectomycorrhiza and soil organoprofile dynamics after introduction of beech into Scots pine forests

Diversity and storage function of mycorrhiza as well as soil organoprofile formation were investigated in a chronosequence of a pure Scots pine (Pinus sylvestris L.) stand, of Scots pine stands that were underplanted with beech (Fagus sylvatica L.) and in three pure beech stands of different age. Mycorrhiza diversity was higher in the pure beech stands compared to the pure pine stand. Beech and pine trees in the mixed stands had similar dominant mycorrhiza morphotypes. However, trees in two of the three pure beech stands were mycorrhized with other types. Mycorrhizal abundance and nutrient amounts of mycorrhizae associated with beech trees were higher in the mixed and in the pure beech stands compared to pine mycorrhizae indicating that nutrient uptake was higher in older beech than in older pine trees. Humus quality varied from pine to beech stands. Plant litter storage in the humus layer was highest in the youngest mixed stand and lowest in the oldest beech stand. Humus forms changed from moder grass-type in the pure Scots pine stand to mor-like moder and moder rich in fine humus with increasing age of beeches in the mixed stands. The older beech stands were characterised by oligomull and mull-like moder as the dominating humus forms. The ecologically favourable humus forms, i.e., nutrient rich humus forms in the older beech stands correlate well with the higher mycorrhizal diversity and abundance as well as the higher nutrient storage of their mycorrhizae in these stands. The results are also discussed with regard to the 'base-pump effect' of beech trees.     

Mg and Ca root uptake and vertical transfer in soils assessed by an in situ ecosystem-scale multi-isotopic (26Mg & 44Ca) tracing experiment in a beech stand (Breuil-Chenue, France)

Background and aims

The sustainability of forest ecosystems may be at stake especially in forests on base-poor soils due to reduced nutrient deposition and intensified silvicultural practices. Understanding nutrient availability and cycling is therefore essential to manage forest soil fertility. This study aims to assess in a beech plot Mg and Ca vertical transfer in soil and root uptake using an isotopic tracing experiment.

Methods

A simulated rainfall containing a small amount (960 g?Mg.ha^?1; 530 g Ca.ha^?1) of highly enriched ²⁶Mg and ⁴⁴Ca was sprayed on the forest floor of a 35-yr-old beech plot. The isotopic composition of fine roots and of the soil exchangeable Mg and Ca pool was monitored during 1 year. A pool and flux model (IsoMod) was developed to predict the labeling of the soil and vertical transfer of tracers.

Results

Tracers (⁴⁴Ca and ²⁶Mg) were immediately retained in the thin litter layer. During the following year, Mg and to a lesser extent Ca were progressively released. After 1 year, the exchangeable Mg and Ca pools of the upper mineral layer (0–5 cm) were strongly labeled (~660?‰, representing ~55 % of the tracer input and ~370?‰, ~41 % of the tracer input respectively). A significant proportion (~8 % ²⁶Mg, ~2 % ⁴⁴Ca) of tracer was leached through the soil, below 10 cm. This amount was much larger than what was predicted using a simple mixing model. The Ca and Mg isotopic composition of fine roots at all depths was close or lower than that of exchangeable Ca and Mg respectively.

Conclusions

An in situ ecosystem-scale ²⁶Mg and ⁴⁴Ca isotopic tracing experiment was successfully carried out. Tracers were at first strongly retained in the litter layer, then progressively transferred to soil horizons below. Nutrient cycling of Mg and Ca were proven to be very different. Mg had a higher mobility in the soil than Ca, and nutrient uptake sources were proven to be different.     

The Role of Wood Ants (Formica rufa group) in Carbon and Nutrient Dynamics of a Boreal Norway Spruce Forest Ecosystem

Wood ants (Formica rufa group) are regarded as keystone species in boreal and mountain forests of Europe and Asia by their effect on ecosystem carbon (C) and nutrient pools and fluxes. To quantify the impact of their activity on boreal forest ecosystems, C, nitrogen (N), phosphorus (P), potassium (K) and calcium (Ca) pools and fluxes in wood ant nests (WAN), and soil were assessed along a 5-, 30-, 60-, and 100-year-old Norway spruce (Picea abies L. Karsten) dominated successional gradient in eastern Finland. Amounts of C and nutrients in WAN increased with stand age, but contained less than 1% of total C and nutrient pools in these stands. The CO₂-efflux from nests was also insignificant, as compared to CO₂-efflux from the forest floor. Annually, the amount of C brought by wood ants into their nests as honeydew, prey and nest-building materials ranged from 2.7 to 49.3 kg ha^?1 C, but this is only 0.1–0.7% of the combined net primary production of trees and understorey in boreal forests. The difference between wood ant nest C inputs and outputs was very small in the younger-aged stands, and increased in the older stands. Carbon accumulation rates in nests over a 100 year period are estimated to be less than 10 kg ha^?1 a^?1. In contrast to C, annual inputs of N, P, and K are larger compared to wood ant nest nutrient pool size, ranging from 3 to 6% of the annual tree stand and understorey uptake. This indicates a more rapid turnover and transport of N, P, and K out of WAN, and suggests that wood ants increase the cycling rate of these nutrients in boreal forests.     

The vertical distribution of N and K uptake in relation to root distribution and root uptake capacity in mature Quercus robur, Fagus sylvatica and Picea abies stands

We have measured the uptake capacity of nitrogen (N) and potassium (K) from different soil depths by injecting ¹⁵N and caesium (Cs; as an analogue to K) at 5 and 50 cm soil depth and analysing the recovery of these markers in foliage and buds. The study was performed in monocultures of 40-year-old pedunculate oak (Quercus robur), European beech (Fagus sylvatica) and Norway spruce (Picea abies (L.) Karst.) located at an experimental site in Palsgård, Denmark. The markers were injected as a solution through plastic tubes around 20 trees of each species at either 5 or 50 cm soil depth in June 2003. After 65 days foliage and buds were harvested and the concentrations of ¹⁵N and Cs analysed. The recovery of ¹⁵N in the foliage and buds tended to be higher from 5 than 50 cm soil depth in oak whereas they where similar in spruce and beech after compensation for differences in immobilization of ¹⁵N in the soil. In oak more Cs was recovered from 5 than from 50 cm soil depth whereas in beech and spruce no difference could be detected. Out of the three investigated tree species, oak was found to have the lowest capacity to take up Cs at 50 cm soil depth compared to 5 cm soil depth also after compensating for differences in discrimination against Cs by the roots. The uptake capacity from 50 cm soil depth compared with 5 cm was higher than expected from the root distribution except for K in oak, which can probably be explained by a considerable overlap of the uptake zones around the roots and mycorrhizal hyphae in the topsoil. The study also shows that fine roots at different soil depths with different physiological properties can influence the nutrient uptake of trees. Estimates of fine root distribution alone may thus not reflect the nutrient uptake capacity of trees with sufficient accuracy. Our study shows that deep-rooted trees such as oak may have lower nutrient uptake capacity at deeper soil layers than more shallow-rooted trees such as spruce, as we found no evidence that deep-rooted trees obtained proportionally more nutrients from deeper soil layers. This has implications for models of nutrient cycling in forest ecosystems that use the distribution of roots as the sole criterion for predicting uptake of nutrients from different soil depths.     

Tree species (Picea abies and Fagus sylvatica) effects on soil water acidification and aluminium chemistry at sites subjected to long-term acidification in the Ore Mts., Czech Republic

The effect of European beech (Fagus sylvatica) and Norway spruce (Picea abies) on acid deposition and soil water chemistry was studied at a site in the Ore Mts., Czech Republic, that has been subjected to decades of elevated acidic deposition. Dry deposition onto the spruce canopy significantly increased acid input to the soil in comparison to the beech canopy. As a result soil waters were more acidic; Al, SO4(2-), and NO3- concentrations were significantly higher; and Ca and K concentrations were lower in the spruce stand than in the beech stand. The concentrations of potentially toxic inorganic aluminium (Al(in)) were, on average, three times higher in the spruce stand than in the beech stand. Thus, Al played a major role in neutralizing acid inputs to mineral soils in the spruce stand. Despite the higher dissolved organic carbon (DOC) concentrations in spruce organic soil solutions, organic Al (Al(org)) accounted for only 30% of total Al (Al(tot)), whereas in beech organic soil solutions Al(org) was 60% of Al(tot). Soil waters in the beech stand exhibited Al(in) concentrations close to solubility with jurbanite (Al(SO4)OH.5H2O). The more acidic soil waters in the spruce stand were oversaturated with respect to jurbanite. The Bc/Al(in) ratio (Bc = Ca + Mg + K) in O horizon leachate was 4.6 and 70 in spruce and beech stands, respectively. In beech mineral soil solutions, the Bc/Al(in) ratio declined significantly to about 2. In the spruce stand, mineral soil solutions had Bc/Al(in) values below the critical value of 1. The observed Bc/Al(in) value of 0.4 at 30 cm depth in the spruce stand suggests significant stress for spruce rooting systems. A more favourable value of 31 was observed for the same depth in the beech stand. The efficiency of the spruce canopy in capturing acidic aerosols, particulates, and cloud water has resulted in the long-term degradation of underlying soils as a medium for sustainable forest growth.     

Forest Continuity as a Key Determinant of Soil Carbon and Nutrient Storage in Beech Forests on Sandy Soils in Northern Germany

Forest (or tree) age has been identified as an important determinant of the carbon (C) storage potential of forest soils. A large part of Central Europe’s current forested area was affected by land use change with long periods of cultivation in past centuries suggesting that the organic C stocks in the soil (SOC) under recent forest may partly be legacies of the past and that stand age effects have to be distinguished from forest continuity effects (that is, the time since re-afforestation). We examined the influence of mean tree age and forest continuity on the SOC pool and the stores of total N and available P, Ca, Mg, and K in the soil (mineral soil and organic layer) across a sample of 14 beech (Fagus sylvatica) forests on sandy soil with variable tree age (23–189 years) and forest continuity (50-year-old afforestation to ancient (‘permanent’) forest, that is, >230 years of proven continuity). Ancient beech forests (>230 years of continuity) stored on average 47 and 44% more organic C and total N in the soil than recent beech afforestation (50–128 years of continuity). Contrary to expectation, we found large and significant C and N pool differences between the forest categories in the mineral soil but not in the organic layer indicating that decade- or century-long cultivation has reduced the subsoil C and nutrient stores while the organic layer element pools have approached a new equilibrium after only 50–128 years. PCA and correlation analyses suggest that forest continuity cannot be ignored when trying to understand the variation in soil C stocks between different stands. Forest clearing, subsequent cultivation, and eventual re-afforestation with beech resulted in similar relative stock reductions of C and N and, thus, no change in soil C/N ratio. We conclude that the continuity of forest cover, which may or may not be related to tree age, is a key determinant of the soil C and nutrient stores of beech forests in the old cultural landscape of Central Europe.     

The soil fauna community in pure and mixed stands of beech and spruce of different age: trophic structure and structuring forces

This study investigates the response of the soil fauna community to replacement of beech by spruce or by mixed stands of beech and spruce. Stands of different age were investigated in a factorial design with the factors tree species (beech and spruce) and stand age (30 and 120 yr). The input of leaf/needle litter did not differ significantly between the study sites. By contrast, the amount of organic matter in upper soil layers (L/F, H/Ah) of spruce forests strongly exceeded that of beech forests particularly in mature stands. The increase in organic matter in spruce stands was not associated by an increase in the amount of microbial biomass. Biomass of eight (bacterivorous, fungivorous and omnivorous nematodes, enchytraeids, earthworms, isopodes, mycetophilid and cecidomyiid Diptera) of the twelve microbi‐detritivorous soil animal groups studied was significantly increased in beech forests; only that of one group (elaterid beetles) was increased in spruce forests and three groups did not respond significantly (collembolans, oribatid mites, sciarid Diptera). This indicates that in the forests studied neither habitat space (amount of organic matter in L/F and H/Ah layers) nor the amount of microbial biomass controlled microbi‐detritivores. Rather, the quality of litter materials and the concentration of microbial biomass therein appeared to be most important. Herbivores and predators also were favoured by beech: the biomass of one (rhizophagous nematodes) of the three herbivorous groups studied were significantly increased in beech stands and none in spruce stands; the biomass of four (predatory nematodes, centipedes, carabid and cantharid beetles) of the seven carnivorous groups studied were increased in beech stands, none in spruce stands. Generally, the biomass ratio between prey and predators was at a minimum in mature beech and mixed stands indicating more intense top‐down control in these forests. Overall, the study documents that replacement of beech by spruce strongly alters the soil food web. Mixed stands were more similar to spruce stands in respect to the biomass of soil animal groups but predator–prey interactions appeared to be more similar in mature beech and mixed stands. Differences between tree species usually were more pronounced in 120 compared to 30 yr old stands indicating that the development of stand characteristics is slow.     

Climate effects on productivity and resource-use efficiency of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica [L.]) in stands with different spatial mixing patterns

Species mixing is widely held to stabilize productivity, increase resilience and contribute to risk minimization in forest stands in need of special as a result of longevity. However, research on the effects of mixing on productivity and resource consumption so far yielded fairly incoherent results rather than general findings. We focused on the effects of the spatial mixing pattern and the annual climate conditions on the mixing effect, which to date have seldom been considered as modifiers of mixing effects. Nine years of intensive survey of four pure stands of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica [L.]) and two mixed plots with different mixing pattern showed: (1) mixing hardly changed annual net primary productivity at stand level when Norway spruce and European beech are cultivated group-wise but increased by 37 % on account of a higher efficiency of water and light use in individual tree-wise mixture. (2) Favourable climatic conditions increased the superiority of mixed versus pure stands productivity, while, in particular, water stress cancelled the benefit of mixing considerably. (3) An interaction between the spatial pattern and variable climatic conditions was revealed. Both improved light and water use were found in favourable years in close inter-specific intermingling. However, in unfavourable years the spatial pattern played a less pronounced role in terms of productivity.     

Effects of fertilization and liming on the chemical soil conditions and element distribution in forest soils

Summary The distribution and storage of major elements in acid soils from a spruce and a beech forest was investigated after fertilization of NH₄NO₃ and KCl followed by Ca and Mg fertilization by 2 liming applications. All fertilizers were applied on top of the soil without mixing. Most of the added Ca and Mg was detected in the humus layer, a significant part of it still in carbonatic form. The effect of liming on mineral soil pH is very low, and was only observed in the 0–10 cm layer. However, base saturation of the mineral soil increased. The storage of C and N of the humus layer was not affected. N fertilization increased the N storage of the soil only under beech, but was followed by heavy NO₃-losses with seepage water under spruce. High leaching rates for K were also found in the spruce stand. The amount of K that was not leached increased the pool of exchangeable K in the deeper soil layer.     

Effect of temperate forest tree species on soil dehydrogenase and urease activities in relation to other properties of soil derived from loess and glaciofluvial sand

We investigated the effects of several tree species on dehydrogenase and urease activities in soils derived from two different parent materials (glaciofluvial sand and loess) in forested areas in southern Poland. We hypothesized that coniferous forests (pine, spruce) alter the soil cation exchange capacity (CEC) and decrease soil pH and, therefore, might decrease soil enzyme activities compared with broadleaf species growing on similar soils. Eight paired plots (12 × 12 m) were established on glaciofluvial sand in pine (Pinus sylvestris) + oak (Quercus robur) and spruce (Picea abies) + pine stands, as well as on loess-derived soils: beech (Fagus sylvatica) + pine and hornbeam (Carpinus betulus) + pine stands. Each plot was a 4 × 4 m grid with 16 sampling points. In soil samples pH, soil texture, and organic carbon, nitrogen, base cation contents, dehydrogenase and urease activities were determined. On both parent materials, the soil pH was lower under coniferous species than under broadleaf species. The acidifying effect of tree species on sandy soil was in the order of spruce = pine > oak, while that on loess was pine > beech > hornbeam. Hornbeam and oak increased the soil pH and stimulated enzyme activity in the soil. The content of fine fraction enhanced potential enzyme activities in soils, thus the loess soils had greater dehydrogenase and urease activity. The results suggest that pine stores more soil organic C in association with silt increasing the pool of stabilized soil organic C.     

Long term effect of liming and fertilization on ectomycorrhizal colonization and tree growth in old Scots pine (Pinus sylvestris L.) stands

In this study, we surveyed the long term effects of liming and fertilizing in old Scots pine stands on the ectomycorrhiza (ECM) colonization, tree growth and needle nutrient concentration 35 years later. Four mature stands of Scots pine on low productive mineral soil were limed in 1959 and 1964 with total doses of limestone ranging from 3 to 15 Mg ha^?1 and fertilized with nitrogen (N) in 1970. Thirty-five years after the first liming treatment, all stands were analysed for tree growth and needle nutrient concentrations and two of the stands were also analysed for ECM colonization. ECM colonization increased significantly with liming from 61.5% in the control plots to 88% in the plot with the highest limestone dose. ECM colonization increased with increasing pH in the humus layer from 62% colonization at pH?=?3.5 to 90% at pH?=?6.5 and decreased with increasing amount of extractable phosphorus (P) in the humus. Liming did not affect the frequencies of different ECM morphotypes or dead short root tips, the fine root biomass or necromass. ECM colonization was uncorrelated with needle nutrient concentrations or tree increment. Liming did not significantly affect tree growth. However, nutrient concentrations of current-year needles were affected by prior liming. Ca concentrations in current-year needles increased from approximately 15 mg g^?1 in control treatments to more than 30 mg g^?1 in limed plots, whereas concentrations of Mn, Al, Fe, and in two stands, B, decreased due to liming. In conclusion, liming with doses up to 15 Mg ha^?1 was detectable in stands 35 years after treatment. The liming significantly increased the ECM colonization of Scots pine fine roots, increased the needle nutrient concentration of Ca and decreased the needle concentrations of Mn, Al, and Fe.     

Converting paddy fields to Lei bamboo (Phyllostachys praecox) stands affected soil nutrient concentrations, labile organic carbon pools, and organic carbon chemical compositions

Background and aims

Land-use change often markedly alters soil carbon (C) and nitrogen (N) pool sizes with implications for climate change and soil sustainability. The objective of this research was to study the effect of converting paddy fields to Lei bamboo (Phyllostachys praecox) stands on soil C and N and other nutrient pools as well as the chemical structure of soil organic C (SOC) in the soil profile.

Methods

Soils (Anthrosols) from four adjacent paddy field–bamboo forest pairs with a known land-use history were sampled from Lin’an County, Zhejiang Province. Soil water soluble organic C (WSOC), hot water soluble organic C (HWSOC), microbial biomass C (MBC), readily oxidizable C (ROC), water soluble organic N (WSON), and other soil chemical and physical properties were determined. Soil organic C functional group compositions were determined by ¹³C-nuclear magnetic resonance (NMR).

Results

Concentrations of soil available P, available K, and different N forms increased (P?<?0.05) by the land-use conversion. Higher concentrations of SOC and total N (TN) were observed in the subsoil (20–40 and 40–60 cm soil layers) but not in the topsoil (0–20 cm layer) in the bamboo stands than in the paddy fields. The storage of SOC and TN in the entire soil profile (0–60 cm) increased by 56.7 and 70.7 %, respectively, after the land-use change. The increases in the SOC stock of the three soil layers were 11.0, 14.3, and 9.5 Mg C ha^?1, respectively. The conversion decreased WSOC concentrations in the subsoil but increased the ROC concentration in the topsoil. Solid-state NMR spectroscopy of soil samples showed that the conversion increased (P?<?0.05) the O-alkyl C content while decreased the aromatic C content, alkyl C to O-alkyl C ratio (A/O-A), and aromaticity of SOC.

Conclusions

Conversion of paddy fields to bamboo stands increased soil nutrient availability, and SOC and TN stocks. Effects of land-use change on C pools and C chemistry of SOC varied among different soil layers in the profile. The impact of the land-use conversion on soil organic C pools was not restricted to the topsoil, but changes in the subsoil were equally large and should be accounted for.     

Effects of rodents on plant cover,soil hardness,and soil nutrient content: a case study on tuco-tucos (Ctenomys minutus)

We analyzed the effects of tuco-tucos (Ctenomys minutus, Ctenomyidae) on plant cover, plant biomass, soil hardness, soil pH, and variables related to nutrient disposition (P, K, Mg, and Ca), using data from three areas in the South Brazilian coastal plain. In each area, samples were taken from sites with and without C. minutus and results are presented in a concatenate way. Our results show that the presence of C. minutus modifies total plant biomass, grass cover, bare soil, soil hardness, soil pH, and nutrient content. Soils horizons at the depths of 10 and 20 cm are significantly softer in sites with C. minutus and phosphorus and potassium had higher concentrations. The content of magnesium and calcium were not affected. Soil pH was significantly lower where tuco-tucos occurred. Altogether, our results show that these animals may have a significant effect on vegetation composition and dynamics as well as on soil properties.     

Variation in fine root biomass of three European tree species: Beech (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.), and Scots pine (Pinus sylvestris L.)

Abstract

Fine roots (<2 mm) are very dynamic and play a key role in forest ecosystem carbon and nutrient cycling and accumulation. We reviewed root biomass data of three main European tree species European beech, (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.) and Scots pine (Pinus sylvestris L.), in order to identify the differences between species, and within and between vegetation zones, and to show the relationships between root biomass and the climatic, site and stand factors. The collected literature consisted of data from 36 beech, 71 spruce and 43 pine stands. The mean fine root biomass of beech was 389 g m^?2, and that of spruce and pine 297 g m^?2 and 277 g m^?2, respectively. Data from pine stands supported the hypothesis that root biomass is higher in the temperate than in the boreal zone. The results indicated that the root biomass of deciduous trees is higher than that of conifers. The correlations between root biomass and site fertility characteristics seemed to be species specific. There was no correlation between soil acidity and root biomass. Beech fine root biomass decreased with stand age whereas pine root biomass increased with stand age. Fine root biomass at tree level correlated better than stand level root biomass with stand characteristics. The results showed that there exists a strong relationship between the fine root biomass and the above-ground biomass.     

Resistance of European tree species to drought stress in mixed versus pure forests: evidence of stress release by inter‐specific facilitation

While previous studies focused on tree growth in pure stands, we reveal that tree resistance and resilience to drought stress can be modified distinctly through species mixing. Our study is based on tree ring measurement on cores from increment boring of 559 trees of Norway spruce (Picea abies [L.] Karst.), European beech (Fagus sylvatica [L.]) and sessile oak (Quercus petraea (Matt.) Liebl.) in South Germany, with half sampled in pure, respectively, mixed stands. Indices for resistance, recovery and resilience were applied for quantifying the tree growth reaction on the episodic drought stress in 1976 and 2003. The following general reaction patterns were found. (i) In pure stands, spruce has the lowest resistance, but the quickest recovery; oak and beech were more resistant, but recover was much slower and they are less resilient. (ii) In mixture, spruce and oak perform as in pure stands, but beech was significantly more resistant and resilient than in monoculture. (iii) Especially when mixed with oak, beech is facilitated. We hypothesise that the revealed water stress release of beech emerges in mixture because of the asynchronous stress reaction pattern of beech and oak and a facilitation of beech by hydraulic lift of water by oak. This facilitation of beech in mixture with oak means a contribution to the frequently reported overyield of beech in mixed versus pure stands. We discuss the far‐reaching implications that these differences in stress response under intra‐ and inter‐specific environments have for forest ecosystem dynamics and management under climate change.