Lignin signatures show the effects of changes in heather and bracken cover on the composition of organic matter in a moorland soil profile

Bracken (Pteridium aquilinum) is aggressively displacing heather (Calluna vulgaris) on many moorlands in Britain. We investigated the use of lignin derivatives to identify the distribution of soil organic matter (SOM) derived from bracken in moorland soil profiles formed under heather. Phenylpropanoids extracted from recently senesced litters, roots and SOM, using alkaline CuO oxidation, showed distinct signatures for bracken and heather, with vanillyl moieties dominating bracken litter extracts and vanillyl and syringyl dominating heather litter extracts. Ratios of vanillyl and syringyl concentrations characterised the SOM derived from heather and bracken better than the concentrations of the individual moieties. The analysis showed up to a depth of 5 cm under pure bracken cover, and at the interface between heather and bracken, the SOM was largely derived from bracken litter but below that depth SOM was apparently derived from heather. The use of these methods to identify the plant origin of SOM not only enables understanding the effects of changing vegetation cover on organic matter dynamics in moorland soils but could also facilitate management techniques in moorland/heathland restoration which involve the removal of comparatively nutrient-rich SOM derived from bracken. Received: 30 November 1997 / Accepted: 11 April 1998     

Effects of soil organic matter and nitrogen supply on competition between Festuca ovina and Deschampsia flexuosa during inland dune succession

We tested the prediction that the successional replacement of plant species during succession on inland sand dunes results from the effects of an increase in nitrogen mineralization on competitive interactions. The growth and competitive strength of Festuca ovina and Deschampsia flexuosa on soil substrates with different amounts of soil organic matter or nitrogen supply were measured. Small tillers of Festuca ovina and Deschampsia flexuosa were grown in monocultures and 1:1-mixtures on soil columns with undisturbed layers of soil organic matter from different successional age. There was (a) no visible soil organic matter, (b) a thin soil organic layer (0.5 cm) and (c) a thicker soil organic layer (6.0 cm) present on the soil columns. The species were also grown on columns with no visible soil organic matter (bare sand) with two different levels of N fertilization to mimic the increased N mineralization in the older successional stages.In monoculture, Festuca produced more biomass on the substrates with a soil organic layer compared to the unfertilized sand substrate. It also produced more biomass on sand substrates with N fertilization. Deschampsia produced more biomass in treatments with a soil organic layer compared to the bare sand treatments, but did not respond to the ammonium-nitrate addition. In competition, Festuca seemed to be the stronger competitor on the unfertilized sand substrate. Festuca was also the better competitor on the N fertilized sand treatments, while on the treatments with a soil organic layer Deschampsia was the winning species. Our results do not support the hypothesis that an increase in N supply is responsible for the replacement of Festuca by Deschampsia that concur with the accumulation of soil organic matter during succession in inland dunes.     

Interactive effects of elevated CO2, warming, and drought on photosynthesis of Deschampsia flexuosa in a temperate heath ecosystem

Global change factors affect plant carbon uptake in concert. In order to investigate the response directions and potential interactive effects, and to understand the underlying mechanisms, multifactor experiments are needed. The focus of this study was on the photosynthetic response to elevated CO(2) [CO2; free air CO(2) enrichment (FACE)], drought (D; water-excluding curtains), and night-time warming (T; infrared-reflective curtains) in a temperate heath. A/C(i) curves were measured, allowing analysis of light-saturated net photosynthesis (P(n)), light- and CO(2)-saturated net photosynthesis (P(max)), stomatal conductance (g(s)), the maximal rate of Rubisco carboxylation (V(cmax)), and the maximal rate of ribulose bisphosphate (RuBP) regeneration (J(max)) along with leaf δ(13)C, and carbon and nitrogen concentration on a monthly basis in the grass Deschampsia flexuosa. Seasonal drought reduced P(n) via g(s), but severe (experimental) drought decreased P(n) via a reduction in photosynthetic capacity (P(max), J(max), and V(cmax)). The effects were completely reversed by rewetting and stimulated P(n) via photosynthetic capacity stimulation. Warming increased early and late season P(n) via higher P(max) and J(max). Elevated CO(2) did not decrease g(s), but stimulated P(n) via increased C(i). The T×CO2 synergistically increased plant carbon uptake via photosynthetic capacity up-regulation in early season and by better access to water after rewetting. The effects of the combination of drought and elevated CO(2) depended on soil water availability, with additive effects when the soil water content was low and D×CO2 synergistic stimulation of P(n) after rewetting. The photosynthetic responses appeared to be highly influenced by growth pattern. The grass has opportunistic water consumption, and a biphasic growth pattern allowing for leaf dieback at low soil water availability followed by rapid re-growth of active leaves when rewetted and possibly a large resource allocation capability mediated by the rhizome. This growth characteristic allowed for the photosynthetic capacity up-regulations that mediated the T×CO2 and D×CO2 synergistic effects on photosynthesis. These are clearly advantageous characteristics when exposed to climate changes. In conclusion, after 1 year of experimentation, the limitations by low soil water availability and stimulation in early and late season by warming clearly structure and interact with the photosynthetic response to elevated CO(2) in this grassland species.     

The effects of variable nitrogen and phosphorous concentrations on Eriophorum vaginatum tillers grown in nutrient solutions

Eriophorum vaginatum tillers were collected at Eagle Creek, Alaska and cultivated in aerated solutions under controlled environmental conditions. The nutrient solutions contained traces, 1.05 and 21 mg l⁻¹ N (nitrate) and traces, 0.15 and 3.10 mg l⁻¹ P (phosphate), pH was maintained at 5.5. The high N, 21 mg l⁻¹, and P, 3.18 mg l⁻¹, nutrient solution produced significant biomass increases. Functional leaf areas were significantly enhanced by high N and P doses in the solutions. Root surface areas varied considerably between treatments; however, significant differences were not found. The mean root surface area of a tiller reached 126 cm² (range 35–290 cm²), whereas the functional leaf area was 6.8 cm² (range 3.3–20.3 cm²). Tillers growing in the highest N + P solutions produced twice the number of daughter tillers as tillers growing in solutions with trace amounts of N and P.     

The effects of ammonium sulphate deposition and root sinks on soil solution chemistry in coniferous forest soils

The effects of enhanced (NH_{4 2}SO₄deposition on soil solution cation and anion concentrations and annualionic fluxes were followed using a standardised experimental protocolin six European coniferous forests with contrasting soil types, pollutioninputs and climate. Native soil cores containing a ceramic suction cupwere installed in the field, roofed and watered every two weeks withlocal throughfall or local throughfall with added(NH₄)₂SO₄ at 75 kgNH₄ ⁺-N ha^-1 a^-1. Livingroot systems were established in half of the lysimeters.Untreated throughfall NH₄ ⁺-N deposition at thesites ranged from 3.7 to 29 kg ha^-1 a^-1Soil leachates were collected at two weekly intervalsover 12 months and analysed for volume, andconcentrations of major anions and cations. Increasesin soil solution NO₃ ^- concentrations inresponse to N additions were observed after 4–9months at three sites, whilst one sandy soil with highC:N ratio failed to nitrify under any of thetreatments. Changes in NO₃ ^- concentrationsin soil solution controlled soil solution cationconcentrations in the five nitrifying soils, withAl³⁺ being the dominant cation in the more acidsoils with low base saturation. The acidification responses ofthe soils to the (NH_{4 2}SO₄additions were primarily related to the ability of thesoils to nitrify the added NH₄ ⁺. pH and soiltexture seemed important in controllingNH₄ ⁺ leaching in response to the treatments,with two less acidic, clay/clay loam sites showingalmost total retention of added NH₄ ⁺, whilstnearly 75% of the added N was leached asNH₄ ⁺ at the acid sandy soils. The presenceof living roots significantly reduced soil solutionNO₃ ^- and associated cation concentrations attwo of the six sites. The very different responses of the sixsoils to increased (NH₄)₂SO₄deposition emphasise that the establishment of N critical loadsfor forest soils need to allow for differences in N storagecapacity and nitrification potential.     

Competition between heather and grasses on Scottish moorlands: Interacting effects of nutrient enrichment and grazing regime

Abstract. Considerable losses and degradation of heathlands (in moorlands and lowlands) have been reported across Europe, with Calluna vulgaris (heather) being replaced by other species, often grasses. Increasing atmospheric nitrogen deposition and overgrazing have been suggested as the driving factors behind this change. This possibility was investigated in a study of the interacting effects of nutrient inputs and grazing on heather and three grass species (Nardus stricta, Deschampsia cespitosa and D. flexuosa) in the field, on a moorland in northeastern Scotland. In addition, the interacting effects of increasing nutrients and Calluna canopy height on N. stricta and D. cespitosa were studied using turves in an outdoor experimental area. In the field, fencing had a larger effect than fertilizer on the growth of all species, except for N. stricta, the species most unpalatable to herbivores. Fencing led to an increase in the height of the Calluna canopy, which may reduce light availability for the grasses. In the turf experiment, the height of the Calluna canopy affected the diameter of the grass tussocks and percentage of green matter (i.e. live leaf material), with plants under the more closed Calluna canopies being smaller. This study suggests that the slow‐growing, evergreen Calluna is a more effective competitor than the faster growing grasses when it has a tall, intact canopy, even at increased levels of nutrient supply. However, overgrazing promotes gap formation in the Calluna canopy, providing an opportunity for grasses to take advantage of increased nutrients. Thus the conservation of heather moorlands requires an understanding of the grazing level which allows Calluna to maintain sufficient canopy structure to outcompete grasses for light.     

Effects of litters with different concentrations of phenolics on the competition between Calluna vulgaris and Deschampsia flexuosa

We hypothesized that the outcome of competition between ericaceous plants and grasses is strongly affected by the concentrations of phenolics in the litter that they produce. To test the effect of phenolic-rich litter on soluble soil nitrogen concentrations, plant nitrogen uptake and inter-specific competition, we conducted a greenhouse experiment with the shrub Calluna vulgaris and the grass Deschampsia flexuosa and their leaf litters. Two litters of C. vulgaris were used, with equal nitrogen concentration but different (high and low) concentrations of total phenolics. The D. flexuosa leaf litter contained lower concentrations of phenolics, but higher concentrations of nitrogen than the C. vulgaris litters. The plants were grown in monocultures and in mixed cultures. Inorganic and dissolved organic nitrogen were measured monthly during the experiment. After four months, we measured above- and belowground biomass and the nutrient concentrations in above- and belowground plant parts. In monocultures, C. vulgaris produced more shoot and root biomass on its own litter than with no litter. Growth of Calluna was reduced on grass litter. D. flexuosa plants produced most biomass on their own litter type, whether in monocultures or in mixed cultures. Addition of Calluna litter stimulated the growth of D. flexuosa both in monoculture and in mixtures. The grass plants outcompeted Calluna both on shrub litter and on grass litter but not when grown without litter. The two C. vulgaris litter types that differed in their concentration of phenolics did not differ in their effects on the competition between the two species or on the production of inorganic and dissolved organic nitrogen. We conclude that the nitrogen content of the litter is more important as a plant feature driving competition between shrubs and grasses than the concentrations of phenolics.     

The diel activity pattern of mountain hare (Lepus timidus) on managed heather moorland in Scotland

The research presented in this paper provides an insight into the behavioral ecology of mountain hares on heather moorland in the Lammermuir Hills of southeast Scotland. We examine the seasonal and diel activity patterns using camera traps over a period of 12 months. The rate of camera detections was calculated for the different divisions of the 24‐hr cycle (daylight, dusk, night, and dawn). During autumn and winter (October–February), the activity pattern was crepuscular with greater activity at dusk than at dawn. Daylight activity was relatively low, and there was a regular pattern of small peaks of activity during the night. In spring and summer (March–September), peaks of crepuscular activity remained evident but daylight activity was much more prevalent than during autumn and winter, and night activity was lower. We discuss the problematic definition of twilight and present an explanation for seasonal changes in the pattern of diel activity that is linked to the reproductive cycle of the mountain hare.     

Differential effects of ammonium and nitrate deposition on fen phanerogams and bryophytes

Question: High atmospheric nitrogen (N) deposition has been shown to affect productivity and species composition of terrestrial ecosystems. This study focused on the differential effects of the two inorganic N forms in atmospheric deposition (i.e. ammonium and nitrate). Methods and location: Nutrient addition experiments were carried out during 4 years in a mesotrophic fen in a low‐deposition area in Ireland. In a factorial design, plots were fertilized with ammonium and/or nitrate, in two doses comparable with 35 and 70 kg N ha^?1 y^?1 and compared with an unfertilized control. Results: Vascular plant biomass as well as bryophyte biomass were not affected by N dose but showed significantly different responses to the N form. In the ammonium‐fertilized plots, vascular plant biomass was higher and moss biomass was lower than the control, while nitrate additions had no effect. Vascular plant species density was high (16 species per 0.49 m²) and was not affected by any of the treatments; bryophyte species density was also high (seven species per 0.04 m²) but showed a significant decrease upon ammonium fertilization. Conclusion: The vulnerability of the mesotrophic vegetation to enhanced atmospheric N deposition depends strongly on the N form. If N would be mainly deposited as NO_x, no detrimental effects on the vegetation will occur. If, however, the deposition is mainly in the form of NH_y, the bryophyte vegetation will be seriously damaged, while the vascular plant vegetation will show an increased biomass production with possible shifts in dominance from Carex and herb species to grasses and shrubs.     

Influence of arbuscular mycorrhizal fungi and simulated acid rain on the growth and coexistence of the grasses Calamagrostis villosa and Deschampsia flexuosa

Two grass species — Calamagrostis villosa (Chaix) J.F. Gmelin and Deschampsia flexuosa (L.) Trin. — are expanding in mountain Norway spruce (Picea abies L. Karst.) forests of Central Europe damaged by anthropogenic pollution constituted particularly of acid rain. This invasion of grasses may be caused by the higher irradiance reaching the forest floor after the pollution-induced tree defoliation. The relative abundance of the two grass species is changing during the process of forest decline. Our study investigated the effects of arbuscular mycorrhizal fungi (AMF) on the growth and coexistence of both species under simulated acid rain (SAR) and two levels of irradiance. Three microcosm experiments were conducted to investigate how both grasses are influenced by the AMF when grown separately or together interacting via extraradical mycelium (ERM). A positive growth response to inoculation with Glomus mosseae BEG 25 was found for both grass species when cultivated separately and the mycorrhizal dependence and the growth benefit for D. flexuosa was greater than for C. villosa. However, when both grass species were grown together in the rhizoboxes with separated root and hyphal compartments, the growth effect of the AMF was the opposite, i.e. C. villosa benefited more. The plants did not benefit from the AMF inoculation under the SAR treatment compared with dH2O treatment. The SAR also negatively influenced root length colonised by AMF, length of the ERM, alkaline phosphatase and NADH diaphorase activities of the ERM. The role of the ERM in transporting phosphorus between these grasses was verified by applying the radioisotope ³²P. There was a greater transport of isotopic ³²P between inoculated plants C. villosa and D. flexuosa grown in separated root compartments, as compared to non-inoculated plants. The amount of transported ³²P was low: a maximum of 3% of applied ³²P was detected in the shoots of receiver plants. Mechanical disturbance of the ERM significantly decreased the ³² P transport between plants. The ³²P transport between mycorrhizal plants was higher in the D. flexuosa to C. villosa direction than in the opposite one. Neither the SAR nor the low level of irradiance influenced the amount of transported ³²P. We discuss the role of ERM links between root systems in the coexistence of both grass species. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of heather and oat supplementation on gastrointestinal nematode infections and performance of grazing Cashmere goats

This work aimed to evaluate the effects of tannin-containing heather (Calluna vulgaris, Erica spp.) and energy (oats, Avena sativa) supplementation, combined or not, on feed intake, gastrointestinal nematode infections and performance of goats grazing mountain grasslands. Two successive experiments were established across one grazing season on four paddocks. The first (late April to early August, Period 1) involved two treatments, i.e., supplementation with heather (+H) vs. non-supplementation (−H), each randomly allocated to two paddocks. The second (mid-August to mid-November, Period 2) consisted on four treatments in a 2 × 2 factorial design, i.e., supplementation with heather and oats (+H+O), only heather (+H−O), only oats (−H+O), and no supplementation (−H−O). Results from Period 1 indicated that faecal nematode egg counts (FEC) were lower in +H goats (50% less in August), achieving more favourable live weight (LW) and body condition changes than −H goats. Total dry matter intake (DMI) in June was similar between treatments, with heather accounting for 0.21 of +H goat diets. Kids FEC and LW gains were not affected by heather supplementation. In Period 2, both heather and oat supplementation reduced FEC (45 and 61%, respectively) and improved goat performance, without an interaction between both factors. Total DMI in October was higher in +H+O compared to other treatments (48 vs. 30 g DM kg LW^−0.75 d⁻¹; P < 0.01). Rumen ammonia concentration was lower (P < 0.001) in +H than in −H goats, and in +O than in −O goats, whereas that of volatile fatty acids (VFA) was not affected by treatments, though the molar proportions of some VFA were modified. It is concluded that the combination of both supplements (tannins and energy) contributes to reduce gastrointestinal nematode parasitism and increases goat performance, allowing a lower dependence on conventional chemotherapy.     

Physiological and morphological effects of long-term ammonium or nitrate deposition on the green and red (shade and open grown) Sphagnum capillifolium

Sphagna are vulnerable to enhanced nitrogen (N) deposition. This article reports how the green (shade, under Calluna) and red (open grown) Sphagnum capillifolium respond to ammonium and nitrate additions of 56 kg N ha⁻¹ y⁻¹ over the background of 8-10 kg N ha⁻¹ y⁻¹ on an ombrotrophic bog in the Scottish Borders after seven years. Samples and measurements were made during a range of hydrated and desiccated conditions in the summer of 2009. Both ammonium and nitrate increased moss N concentration, but while ammonium decreased cross-sectional area of leaf hyaline cells and the leaf hyaline/chlorophyllose cell area ratio, nitrate increased both of them and capitulum pH. The changes in leaf morphology have not previously been reported to our knowledge. Especially the red S. capillifolium was affected by ammonium with significant changes in shoot N concentration (+71%) and the cross-sectional area of leaf chlorophyllose cells (+67%), and reductions in shoot dry weight (−30%) and fresh weight (−42%), the cross-sectional area of leaf hyaline cells (−24%), the leaf hyaline/chlorophyllose cell area ratio (−54%), as well as in chlorophyll fluorescence (measured as F_v/F_m) of desiccated capitulum (−65%) (all p < 0.05). These observations show that N deposition may affect moss physiology also through changes in leaf anatomy and morphology. The results also highlight potential sampling issues and causes of variability in N responses when collecting variably pigmented Sphagna.     

Productivity: key factor affecting grazing exclusion effects on vegetation and soil

In this study, we inquire into the effects of short-term goat grazing abandonment on plant species and functional composition, bare ground and net primary productivity (NPP) in two traditionally grazed pastures located in the Canarian Network of Natural Protected Areas and the Natura 2000 Network. In addition, we analyse soil chemical properties, biomass tannin content and energetic value to find out how grazing abandonment affects soil fertility and forage quality of these agroecosystems. Grazing exclusion effects on plant species and functional composition, as well as on soil fertility depended on the productivity of the studied pasture. Erect forbs and shrubs (endemic to Macaronesian region and native) were favoured by grazing removal in the most productive pasture, while soil fertility decreased in the driest and least productive site. An increase in NPP after exclusion was consistent among study sites. Although we consider goat grazing as necessary for maintaining traditional agroecosystems, we also suggest controlling it over time, allowing some periods of rest to give endemic shrub species time to recover from near propagule sources.