Effects of sod-cutting on the nematode community of a secondary forest of Pinus sylvestris L.

Atmospheric S and N compounds accumulate in the surface layers of the forest soil environment, where they affect soil biota and nutrient availability for tree growth. In addition to measures to reduce the input of atmospheric deposition, removal of the ectorganic layers by sod-cutting may contribute to the recovery of the soil ecosystem. In this study, we examined the effects of sod-cutting on the nematode fauna of a Scots pine forest, 1 and 3 years after treatment. Sod-cutting reduced the total numbers of nematodes, nematode taxa, and Maturity Index. The first taxa that colonized the newly developing organic layers after sod-cutting had low colonizer-persister (c-p) values, and appeared to have originated from the tree canopy and mineral soil. Colonization, presumably from nearby untreated plots, was observed 3 years after the sod-cutting. The initial (after 1 year) nematode community of the new organic layer comprised hyphal-, bacterial-, and algal-feeding nematodes, whereas plant-feeders, predators, and omnivores were not detected. The composition of the nematode fauna in the ectorganic layers 15 and 39 months after sod-cutting was highly similar to that of the nematode fauna of the early stages of a primary succession of Scots pine forest in a reference area in the Netherlands. In the mineral soil only insect parasites were negatively affected by sod-cutting.     

Nutrient budget in ecosystems

Methods to calculate nutrient budgets in forest and grassland ecosystems are analyzed on the basis of a large number of published materials and original data. New estimates of the belowground production in forest ecosystems with due account for the growth of fine roots are suggested. Nutrient retranslocation from senescent plant tissues to growing plant tissues and nutrient leaching from the forest canopy are discussed. The budgets of major nutrients (N, P, K, and Ca) in tundra, forest, and steppe ecosystems are calculated. Nutrient cycles in two forest ecosystems—a coniferous stand dominated by Picea abies and a broad-leaved stand dominated by Quercus robur—are analyzed in detail. It is shown that the more intensive turnover of nutrients in the oak stand is also characterized by a more closed character of the nutrient cycles.     

Non-symbiotic bacterial diazotrophs in crop-farming systems: can their potential for plant growth promotion be better exploited?

Biological N₂ fixation (BNF) by associative diazotrophic bacteria is a spontaneous process where soil N is limited and adequate C sources are available. Yet the ability of these bacteria to contribute to yields in crops is only partly a result of BNF. A range of diazotrophic plant growth-promoting rhizobacteria participate in interactions with C₃ and C₄ crop plants (e.g. rice, wheat, maize, sugarcane and cotton), significantly increasing their vegetative growth and grain yield. We review the potential of these bacteria to contribute to yield increases in a range of field crops and outline possible strategies to obtain such yield increases more reliably. The mechanisms involved have a significant plant growth-promoting potential, retaining more soil organic-N and other nutrients in the plant-soil system, thus reducing the need for fertiliser N and P. Economic and environmental benefits can include increased income from high yields, reduced fertiliser costs and reduced emission of the greenhouse gas, N₂O (with more than 300 times the global warming effect of CO₂), as well as reduced leaching of NO₃⁻-N to ground water. Obtaining maximum benefits on farms from diazotrophic, plant growth promoting biofertilisers will require a systematic strategy designed to fully utilise all these beneficial factors, allowing crop yields to be maintained or even increased while fertiliser applications are reduced.     

N, P and K budgets for crop rotations on nine organic farms in the UK

Abstract. Nitrogen (N), phosphorus (P) and potassium (K) budgets were calculated for nine organic farms in the UK. The farms were situated on sandy loams, silty clay loams and silty loams over chalk with stockless farming systems and cattle, pig and poultry enterprises with a significant proportion of arable cropping. A soil surface nutrient budget was calculated for the target rotation on each farm using information about field management and measurements of the soil, crops and manure. Losses of N through leaching and volatilization were calculated independently using the nitcat and manner models. Nutrient budgets for seven of the farm rotations showed an N surplus, six a P surplus and three a K surplus. The ratio of N inputs supplied in the form of biological fixation : manure : atmospheric deposition was approximately 2 : 2 : 1 for stocked systems and 2 : 0 : 1 for stockless systems. Phosphorus surpluses resulted from supplementary P fertilizer (rock phosphate) and additional feed for non-ruminant livestock. The stockless system without P fertilizer resulted in a large P deficit and stocked systems, which relied on recycling manure alone, a small P deficit. Only rotations with large returns of manure or imported feed showed a K surplus or a balanced K budget.     

Wood Ash Effects on Soil Solution and Nutrient Budgets in A Willow Bioenergy Plantation

The management of wood ash is an important factor in the environmental and economic analysis of wood burning. Wood ash can be applied to energy crops as a fertilizer, which can help replace nutrients removed during harvest. The objectives of this study were to examine the temporal and spatial dynamics of nutrient elements applied in wood ash to an intensively cultured, short-rotation willow bioenergy system. Wood ash was applied at the rates of 10 and 20 Mg ha^–1 yr^–1 to coppiced willow, Salix purpurea, clone SP3, from 1992 to 1994. The relative abundance of nutrients in applied wood ash was Ca > K > Mg > P > N. There was little effect of wood ash on N or P concentrations in soil solution measured at 20 and 40 cm depth. Soil solution concentrations of base cations were elevated in the last two years of the study by 30 to 90%, depending on the element and treatment, in plots receiving wood ash. Wood ash treatments had little influence on foliar leaching. Wood ash treatment also had few significant effects on willow growth or on the contents of N, P, K, Ca, and Mg in foliage and stems. The addition of P, K, Ca, and Mg in wood ash was more than enough to compensate for harvest removals and leaching losses. This study demonstrated that wood ash can supply most nutrients removed during harvest in willow plantations, with the exception of N, without adverse effects on groundwater or vegetation.     

Effects of habitat management on heathland response to atmospheric nitrogen deposition

A field experiment was carried out to investigate the impact of four different management treatments on the response of Calluna-dominated heathland to nitrogen additions of 0 or 30 kg ha⁻¹ yr⁻¹ at a lowland heath in Surrey, England. Post-management Calluna regeneration, growth and canopy development were significantly affected by both the form of management and by nitrogen addition. The effect of nitrogen on shoot growth was lower, in absolute terms, in those plots which had undergone more intensive management treatments. Seedling establishment was higher in plots which received a simulated accidental burn treatment, reflecting the greater proportion of bare ground and the high degree of physical disturbance associated with this treatment. Invasion by Deschampsia seedlings was increased by nitrogen addition, particularly in simulated accidental burn plots. In the long term, the need to maintain a low nutrient environment to favour Calluna dominance, particularly in the face of elevated nitrogen deposition, favours the use of managements which result in the export of a significant proportion of the organic nitrogen stores. However, further study is required to ensure that initial enhancement of seedling invasion by grass and other species, associated with these more intense managements, does not outweigh the long term benefits of associated nutrient removal.     

Leaching and crop uptake of N, P and K from organic and conventional cropping systems on a clay soil

In this study, three types of cropping systems with different nutrient management strategies were studied on a clay soil with the aim of comparing leaching of N, P and K and obtaining knowledge on nutrient budgets. A conventional cropping system with cereals and application of mineral fertilizers (CON) was compared with two organic cropping systems, one without animal manure in which green manure crops were used for N supply (OGM) and one where animal manure (cattle slurry) was applied (OAM). Leaching and crop uptake of N, P and K, and soil mineral N were measured in pipe‐drained plots over a 6‐year period. The mean annual leaching loads of N were moderate and did not differ significantly (P > 0.05) between treatments; 13 kg N ha^?1 in CON, 11 kg N ha^?1 in OGM and 7.4 kg N ha^?1 in OAM. Average annual P leaching showed greater variation than N leaching and was significantly greater in OGM (0.81 kg ha^?1 year^?1) than in CON (0.36 kg ha^?1) and OAM (0.41 kg ha^?1). For all cropping systems, removal in harvested crops was the most important export of nutrients from the field and constituted between 80 and 94% of total N outputs (harvested and leached N). Yields of cereals in the organic systems were considerably less (15–50%) than in the CON system, leading to a less efficient use of N than in the conventional system.     

Earthworm impacts on soil organic matter and fertilizer dynamics in tropical hillside agroecosystems of Honduras

Earthworms are important processors of soil organic matter (SOM) and nutrient turnover in terrestrial ecosystems. In agroecosystems, they are often seen as beneficial organisms to crop growth and are actively promoted by farmers and extension agents, yet their contribution to agroecosystem services is uncertain and depends largely on management. The Quesungual slash-and-mulch agroforestry system (QSMAS) of western Honduras has been proposed as a viable alternative to traditional slash-and-burn (SB) practices and has been shown to increase earthworm populations, yet the effect of earthworms on soil fertility and SOM in QSMAS is poorly understood. This study examined the role of Pontoscolex corethrurus in QSMAS by comparing their influence on aggregate-associated SOM and fertilizer dynamics with their effects under SB and secondary forest in a replicated field trial. Both the fertilized QSMAS and SB treatments had plots receiving additions of inorganic ¹⁵N and P, as well as plots with no inorganic N additions. Earthworm populations were manipulated in field microcosms at the beginning of the rainy season within each management treatment via additions of P. corethrurus or complete removal of existing earthworm populations. Microcosms were destructively sampled at harvest of Zea mays and soils were wet-sieved (using 53, 250 and 2000 μm mesh sizes) to isolate different aggregate size fractions, which were analyzed for total C, N and ¹⁵N. The effects of management system were smaller than expected, likely due to disturbance associated with the microcosm installation. Contrary to our hypothesis that earthworms would stabilize organic matter in soil aggregates, P. corethrurus decreased total soil C by 3% in the surface layer (0-15 cm), predominantly through a decrease in the C concentration of macroaggregates (>250 μm) and a corresponding depletion of C in coarse particulate organic matter occluded within macroaggregates. Earthworms also decreased bulk density by over 4%, but had no effect on aggregate size distribution. Within the two fertilized treatments, the QSMAS appeared to retain slightly more fertilizer derived N in smaller aggregate fractions (<250 μm) than did SB, while earthworms greatly reduced the recovery of fertilizer N (34% decrease) in both systems. Although management system did not appear to influence the impact of P. corethrurus on SOM or nutrient dynamics, we suggest the lack of differences may be due to artificially low inputs of fresh residue C to microcosms within all management treatments. Our findings highlight the potential for P. corethrurus to have deleterious impacts on soil C and fertilizer N dynamics, and emphasize the need to fully consider the activities of soil fauna when evaluating agroecosystem management options.     

Nutrient Solution and Nutrient Soil Solution Parameter Evolution in Tomato with Dynamic Fertigation under Saline Conditions

This trial was carried out to study the evolution of the nutrient parameters of the nutrient solution applied to tomato plants (Lycopersicum sculentum Mill. Forteza) cultivated in Mediterranean greenhouse conditions under different fertigation management models. The dynamic model is based on soil water content, which was measured by tensiometers, and on soil solutions obtained with suction cups (porous ceramic cup water samplers). The local traditional method consists of following technical recommendations, and the classical model requires the estimation of Crop Factor (Kc) and knowing the nutrient extraction. Nutrient solution and water applied are functions of the fertigation management criteria. The water used for fertigation was classified as C₄-S₃ according to the Riverside classification system. The cultivation period lasted from 15 August to 20 April. The nutrient parameters studied in nutrient and soil solution were pH, electrical conductivity (EC), nitrate (NO₃ ^?), phosphate (H₂PO₄ ^?), potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺), sodium (Na⁺), and chloride (Cl^?). The pH shows similar trends under the different treatments. Electrical conductivity is in the range of 2.8–4.5 dS m^?1. Chloride, sodium, magnesium, and sulfate are exclusively modified by the salt concentration in the irrigation water, so it can be assumed that the three treatments vary equally. Nitrate, potassium, phosphate, and calcium are modified depending on each fertigation management method. Soil solution is modified by the nutrient solution applied. Dynamic management allows low nutrient concentration in the nutrient solution to be maintained and keeps soil nutrient concentration low, reducing fertilizer losses and therefore aquifer contamination.     

Nutrient release from decomposing leaf mulches of karité (Vitellaria paradoxa) and néré (Parkia biglobosa) under semi-arid conditions in Burkina Faso, West Africa

Information on decomposition and nutrient release from leaf litter of trees in agroforestry parkland systems in Sub-Saharan Africa is scarce despite the significant role of these trees on soil fertility improvement and maintenance. Decomposition and nutrient release patterns from pruned leaves of the two most common species of parklands of the semi-arid zone of West Africa: Vitellaria paradoxa C.F. Gaertn (known locally as karité) and Parkia biglobosa (Jacq.) Benth. (known locally as néré), were investigated by a litter-tube study in Burkina Faso. Litter quality, methods of leaf exposure to the soil and combination with fertilizers were the factors studied. Leaves of néré had a higher nutrient content (C, N, P, Ca) and contained more ash and lignin than leaves of karité. Karité leaves had a greater content of K, cellulose and polyphenols. The pruned leaves of karité and néré showed two distinct decomposition patterns. Néré leaves decomposed more rapidly, with less than 32% of the initial weight remaining after the rainy season (4 months) while karité leaves decomposed more slowly with 43% of the leaf litter remaining after the rainy season. Addition of urea and compost did not significantly affect the rate of decomposition. Significant interaction was observed between species and method of leaf exposure for the first sampling date. Leaf litter of néré buried in soil gave the highest weight loss (34% of the initial mass in 1 month) compared with exposed leaf litter of néré and karité, and buried leaf litter of karité. Except for N, nutrient release patterns were similar for both species but the nutrient release rates were higher for néré leaves compared with karité leaves. N was immobilised in karité leaves most likely due to low N and high phenolic content. The rate of nutrient release from karité leaves followed the general trend K>P>N.     

Impacts of prescribed burnings on litter production,nitrogen concentration, δ13C and δ15N in a suburban eucalypt natural forest of subtropical Australia

Purposes

Prescribed burning is projected to be adopted more frequently with intensifying climate change; thus, a long-term study is necessary to understand the burning impacts on forest productivity and carbon (C) and nitrogen (N) cycling. Litter fall production rate can be used to indicate burning impacts on forest productivity, whereas N concentration, and C and N isotope composition (δ¹³C and δ¹⁵N) can be used to infer burning impacts on C and N cycling in plant-soil system.

Materials and methods

In this study, the impacts of low-intensity prescribed burning on litter production, N concentration, and C and N isotope compositions were continuously investigated for 6 years at five study sites in a natural eucalypt forest of subtropical Australia.

Results and discussion

Higher leaf litter production rate, N concentration and δ¹⁵N, and lower δ¹³C could be seen shortly after prescribed burning. The higher leaf litter N concentration and lower δ¹³C were likely due to the ease of competition for soil N and moisture from understory vegetation in the short term by prescribed burning. Leaf δ¹⁵N and N concentration were closely correlated, and seasonal changes in leaf litter production rate, δ¹³C and δ¹⁵N were observed. Burning season and related severity might determine the suppression degree of understory vegetation. Time since fire (TSF) was a significant impact factor influencing the litter fall production rate, N concentration, δ¹³C and δ¹⁵N of leaf litter fall for a decade following prescribed burning. However, monthly rainfall and temperature were less consistent in their impacts.

Conclusions

Nitrogen limitation was enhanced by prescribed burning through the removal of litter and understory vegetation in the N poor forest and might be responsible for the long-term burning impacts. Low-intensity prescribed burning might have a long-lasting impact on forest litter productivity in nutrient poor forests in subtropical Australia.

     

Long-term soil feedback on plant N allocation in defoliated grassland miniecosystems

Defoliation of plants is known to have effects on soil organisms and nutrient availability in grassland communities, but few studies have examined whether changes in soil attributes can further feed back to plant growth and plant nutrient content. To examine defoliation-induced soil feedbacks, we established replicated miniecosystems with a grass Phleum pratense, defoliated half of the systems, collected soil from both defoliated and non-defoliated systems and planted new seedlings into each soil. The two soils did not differ in promoting shoot and root growth. However, seedlings that grew in the soil collected from defoliated systems had higher shoot N content, allocated relatively more N to shoots and had lower root N concentration than those growing in the soil collected from non-defoliated systems. Our study provides novel evidence that defoliation can generate long-lasting changes in grassland soil that in turn can affect plant N allocation.     

Base Cation Supply in Spruce and Beech Ecosystems of the Strengbach Catchment (Vosges Mountains, N-E France)

In spruce and beech stands, mineral budgets for a rotation period were calculated from measured element fluxes. The release of base cations by mineral weathering was calculated with the steady state soil chemistry model PROFILE. The calcium release rate by weathering of the mineral fine earth was extremely low. For the period of one rotation, mineral weathering cannot provide enough Ca to compensate timber harvesting and leaching. Forest sustainability depends strongly on the amounts of Ca gained from deposition and lost by biomass removal. Magnesium was supplied by atmospheric deposition and mineral weathering. Calculated weathering rates were close to present soil losses. However, as the model assumes that all dissolution reactions are congruent, the computed release rate of Mg from illite might be too high. Main inputs of K to the soil solutions were primarily attributed to canopy leaching and litterfall in upper horizons and to mineral weathering in deeper horizons. The cation budget of the beech stand was much more equilibrated than that of the spruce stand. Given possible changes in silviculture and deposition chemistry, the sustainability of the present stands is rather improbable with respect to their mineral supply.     

The wood-decaying fungus Hygrophoropsis aurantiaca increases P availability in acid forest humus soil, while N addition hampers this effect

We evaluated the influence of the brown rot fungus Hygrophoropsis aurantiaca on P solubility in the humus layer of a podzolic forest soil. This fungus is known to exude large amounts of oxalic acid that may stimulate weathering of minerals and increase dissolution of humus, which in turn may increase P availability in the soil surrounding the fungus. Humus was inoculated using small wooden pieces colonised by the fungus. The presence of the fungus resulted in elevated concentration of PO₄⁻ in the humus solution. In a second experiment birch seedlings grown in the same humus were able to utilise the PO₄⁻ mobilised by the fungus to increase their internal P content. The factor determining this increased P uptake and the increased available P might be oxalate produced by fungus. The acid may directly dissolve P or change organic forms of P making it more susceptible to reaction with phosphatases. This fungal effect on P solubility diminished when N was added to the soil in the form of a slow release N fertilizer (methyl urea), or when a soil with a higher soil N concentration was used. We found a strong correlation between NH₄⁺ concentration and total organic carbon in the soil solution at high NH₄⁺ concentrations, suggesting the dissolution of humus as a result of the high NH₄⁺ content in the solution. This study demonstrates that the wood-decaying fungus H. aurantiaca influences nutrient turnover in forest soil, and thereby nutrient uptake by forest trees. An intensified harvest of forest products such as whole tree harvesting may decrease the active biomass of the wood decomposers and may thereby change the availability of P and the leaching of N.     

Marginal effects of silvicultural treatments on soil nutrients following harvest in a Chinese fir plantation

Despite the widespread recognition that silvicultural treatments (prescribed harvest residue burning, site preparation and replanting) applied following clearcutting may cause soil erosion and nutrient loss in Chinese fir ( Cunninghamia Lanceolata (Lamb.) Hook) plantations, it is unclear which specific treatment leads to nutrient loss and whether an appropriate implementation of the treatments during the dry season could avert nutrient loss altogether. To address these two questions, nutrient changes in Alliti-Udic Ferrosols soils within a Chinese fir plantation located in Huitong County, Hunan Province, were investigated through the analysis of soil samples sequentially collected at depths of 0–15 cm and 15–30 cm before and after harvest with the residue material kept in place, a prescribed residue burning operation, site preparation and tree replanting initiative took place. Individual treatments significantly affected the soil pH value, organic matter and C and available N at depths of 0–15 cm, but did not significantly influence soil bulk density, total N and P contents and available P contents. The soil pH value decreased with successive application of the treatments. Soil organic C increased by way of the remaining residue after clearcutting, but declined after prescribed residue burning and ultimately returned to pre-harvest values after site preparation as a result of soil displacement and burning ash. Available N contents decreased significantly after clearcutting and residue burning, but the reduction was more or less offset after site preparation took place. Results after all silvicultural treatments were applied showed that no significant reduction in soil organic matter, C and N and P occurred to date in the Chinese fir plantation studied, suggesting that nutrient loss could be averted if the treatments were implemented during the dry season.     

Modelling of soil nutrient budgets: an assessment of agricultural sustainability in Nepal

Abstract. Sustaining soil fertility under agricultural intensification and expansion onto marginal lands is a significant challenge in the Nepalese Middle Mountains. In a detailed watershed study it was shown that the overall soil fertility is poor, forest soils display the poorest conditions as a result of biomass removal, and sustaining agriculture is questionable due to the transformation from traditional to multiple cropping systems. Parent material is a significant factor influencing low phosphorus status while insufficient inputs create deficiencies in total carbon, nitrogen and bases. A nutrient budget model was developed to assess inputs, redistribution and losses relative to soil fertility. Yield, input and management data obtained from farm interviews, and soil analysis data were used in the calculation of nutrient budgets. Results from modelling indicate declining soil fertility under rainfed agriculture, forest and rangelands, and marginal conditions under irrigated agriculture subject to intensive cultivation. Nutrient deficits were relatively low for irrigated rice-wheat systems, which benefit from nutrient inputs via sediments and irrigation waters, but the introduction of triple cropping showed greater deficits. Nutrient balances were most critical under rainfed maize production where 94% of the farms were in deficit. Current shortages of organic matter make elimination of nutrient deficits problematic but improvement of composting, biological N-fixation and fertilizer efficiency and reducing erosion were found to be potential options.     

Effects of High Water Supply on Growth, Water Use, and Nutrient Allocation in Willow and Poplar Grown in a 1-Year Pot Trial

This study was carried out to test ex situ growth and soil nutrient removal efficiency of 1-year-old potted willow and poplar plants. Plants were grown under two different water regimes: low irrigation—around soil field capacity (W)—and high irrigation—five times higher than field capacity (W ₅). Results showed that plant productivity and water use efficiency were greater when trees were grown in the appropriate level of soil water content rather than at excessive moisture levels. Nutrient leaching was also affected by the high irrigation treatment. However, the poplar and willow clones used in this experiment showed different nutrient allocation patterns in the plant–soil–water system. The poplar clone accumulated the highest quantities of N and P in the soil. Willow accumulated N and P mainly in the biomass due to better root development under both treatments. This indicates the better performance of the willow clone in removing N and P from contaminated aquaculture wastewaters during the first growing season.     

The Leaching Behaviour and Balances of Nitrogen and Other Elements under Spring Wheat in Lysimeter Experiment 1985–92

Abstract

In a lysimeter study it was found that moderate rates of ammonium nitrate increased utilization percentages in spring wheat, and the leaching was 10% or less of added N. Over-optimal rates reduced utilization percentages and increased leaching to almost 50% of the highest doses. Late split application of calcium nitrate increased the percentage of N in grain. Furthermore, leaching of N was not reduced, but occurred somewhat later in the fall and winter seasons. Leaching of Cl^? was more rapid and that of SO₄ ^2- was delayed relative to the leaching of NO₃ ^?. Rather large negative N balances were obtained, also after over-optimal application rates, and total N content of the soil was reduced. Compared with the N₀ treatment, differences in soil N residues amounted to 15–25% of added N in seven years. Gaseous losses had apparently taken place both from the added N and from soil N according to the total-N analysis.     

Health of remnant woodlands in fragments under distinct grazing regimes

Fragmented remnant woodlands in agricultural landscapes are of high conservation value world-wide. Many eucalypts in agricultural landscapes of Australia are in decline. We aimed to investigate nutrient enrichment as a process that may contribute to eucalypt decline. We studied remnant woodlands that had been exposed to distinct recent and current livestock grazing treatments: Currently Intense Grazed; Recently Intense Grazed (until 3 years ago); Recent Intermediate Grazed; and Recent Lightly Grazed by livestock. We assessed soil nutrient status and penetrability, eucalypt foliar nutrition and stable isotope ratios for N and C, attributes of understorey vegetation, and tree health. Soils of the Currently Intense Grazed treatment had high levels of ammonium and Colwell-P. Total N, P, C:N ratio and soil penetrability were generally high in Currently Intense Grazed and Recently Intense Grazed treatments relative to Recent Intermediate Grazed and Recent Lightly Grazed treatments. Foliar N, N stable isotope ratios, P and carbon stable isotope ratios (δ¹³C) were generally higher (less negative δ¹³C) in trees on Currently Intense Grazed and Recently Intense Grazed treatments than in trees on Recent Intermediate Grazed and Recent Lightly Grazed treatments. Soil surface litter, tall and low shrubs and rock were positively correlated with tree health. Grasses and eucalypt foliar N, P and δ¹³C were negatively correlated with tree health. Soil nutrient enrichment increased with increasing grazing intensity and was associated with increased weed invasion and with poor tree health that was in turn correlated to increased foliar N and P and less negative δ¹³C in woodland trees in this study. We argue that minimising soil nutrient enrichment of fragmented remnant woodlands is important, given the association of elevated soil nutrition with poor tree health, to ensure the persistence of eucalypts in agricultural landscapes.     

Effects of nitrogen deposition on growth and survival of montane Racomitrium lanuginosum heath

Montane heaths dominated by the moss Racomitrium lanuginosum are in decline, for which increased atmospheric nitrogen (N) deposition may be partially responsible. To test this, field plots in northeast Scotland were treated with either low or high (10 or 40 kg N ha⁻¹year⁻¹) doses of nitrogen (as NO₃⁻ or NH₄⁺) for 2 years. Although Racomitrium tissue N increased after treatment, with greater response for low than high N application, activity of the enzyme nitrate reductase and Racomitrium growth were severely inhibited by increasing N addition. Racomitrium cover declined following N addition and graminoid cover increased, also with greatest effect at high doses. Of all measurements, only nitrate reductase showed a distinction between NO₃⁻ and NH₄⁺ application. The results demonstrate the detrimental effects of even low increases in nitrogen deposition on the moss heath, suggesting that loss of Racomitrium and its replacement by graminoids is strongly linked to increased levels of anthropogenic N pollution.