The value of wetlands for water quality improvement: an example from the St. Johns River watershed,Florida

Wetlands provide many valuable ecosystem functions such as sediment and nutrient retention, high biological productivity and biodiversity, flood control, and opportunities to recreate. Despite their importance, estimating the value of wetlands is difficult as the worth of these functions and services is not easily quantified. The overall objective of this study was to estimate the value of freshwater wetlands in the Saint Johns River (SJR) watershed, Florida based on their ability to remove nutrients, namely nitrogen (N) and phosphorus (P). We used a combination of literature review, geospatial analysis of land cover, and regression analysis to determine the total wetland area in the SJR watershed and the rates of nitrogen and phosphorus burial in the wetlands. We then estimated the economic value of these wetlands based on the replacement cost of nutrient removal by wastewater treatment plants. Nitrogen burial rates ranged from 27 g/m²/year to a background rate of 6.56 g/m²/year, and phosphorus burial rates range from 1.31 g/m²/year to a background of 0.11 g/m²/year. Using these rates, we calculate wetlands of the SJR catchment remove 79,873 MT of nitrogen annually just from burial in the soil, with a replacement cost of between $240 million to $150 billion per year. The amount of phosphorus buried yearly is more than 2400 MT with an annual replacement cost of $17 to $497 million. Though they are based on limited data and include a variety of watershed-scale research limitations, these findings highlight the significant potential value of conserving functional wetlands based solely on their nutrient retention functions. If we were to consider the benefits associated with other wetland functions such as flood control, biological productivity, and biodiversity in addition to their ability to retain nutrients, the value of the SJR wetlands would be even greater.     

Litter fall of the paperbark tree (Melaleuca cuticularis) in the marshes of the Blackwood River Estuary,Western Australia

Paperbark low closed forest, dominated by Melaleuca cuticularis, produced 430 g (dry weight), m^?2 of litter over a year, containing some 3.4 g.m^?2 of nitrogen and 77 mg.m^?2 of phosphorus. Twigs and bark made up more than 50% of the total annual litter fall. The twigs and bark contribute most of the nitrogen (54 %) and phosphorus (56%), compared with leaf fall (37% and 35%) and flower and fruit fall (8% and 9%). The fall of leaves, twigs and bark was primarily related to wind, and flower and fruit fall was greatest after flowering. The litter must make a significant contribution to the accretion of peat. Since the forest covers some 200 ha of the lower Blackwood River estuary, it may contribute some 8001 of litter to the ecosystem each year, containing some 6600 kg of nitrogen and 154 kg of phosphorus.     

Soil phosphorus supply controls P nutrition strategies of beech forest ecosystems in Central Europe

Phosphorus availability may shape plant–microorganism–soil interactions in forest ecosystems. Our aim was to quantify the interactions between soil P availability and P nutrition strategies of European beech (Fagus sylvatica) forests. We assumed that plants and microorganisms of P-rich forests carry over mineral-bound P into the biogeochemical P cycle (acquiring strategy). In contrast, P-poor ecosystems establish tight P cycles to sustain their P demand (recycling strategy). We tested if this conceptual model on supply-controlled P nutrition strategies was consistent with data from five European beech forest ecosystems with different parent materials (geosequence), covering a wide range of total soil P stocks (160–900 g P m^?2; <1 m depth). We analyzed numerous soil chemical and biological properties. Especially P-rich beech ecosystems accumulated P in topsoil horizons in moderately labile forms. Forest floor turnover rates decreased with decreasing total P stocks (from 1/5 to 1/40 per year) while ratios between organic carbon and organic phosphorus (C:P_org) increased from 110 to 984 (A horizons). High proportions of fine-root biomass in forest floors seemed to favor tight P recycling. Phosphorus in fine-root biomass increased relative to microbial P with decreasing P stocks. Concomitantly, phosphodiesterase activity decreased, which might explain increasing proportions of diester-P remaining in the soil organic matter. With decreasing P supply indicator values for P acquisition decreased and those for recycling increased, implying adjustment of plant–microorganism–soil feedbacks to soil P availability. Intense recycling improves the P use efficiency of beech forests.     

Production rate ofEichhornia crassipes (Mart.) Solms in river Ganga water

The production rate ofEichhornia crassipes was stimulated by water of the river Ganga and by prevailing environmental conditions. It was highest in October (4.76 g.m^–2.d^–1) and was positively correlated with ammonia nitrogen and total phosphorus in the water but negatively correlated with total alkalinity and transparency. The average annual production of 14.13 t.ha^–1.a^–1 is equivalent to the average production of 0.067 t.ha^–1.a^–1 phosphorus and 0.40 t.ha^–1.a^–1 nitrogen. The concentrations of total nitrogen and total phosphorus of the plant varied seasonally. They decreased with increasing production rate in summer and monsoon.     

Sedimentation rates in a Swiss-Italian lake measured with sediment traps

Tripton sedimentation was investigated in the eutrophic Lake Lugano (Ponte Tresa basin) from October 1979 to October 1980. The annual amount of tripton collected was 748 g · m^–2 · y^–1. Phosphorus, nitrogen and organic carbon fluxes into the hypolimnion were estimated to be 1.9, 16.2 and 121 g · m^–2y^–1 respectively. Mineralization rates into the trophogenic layer varied from 11% to 19% per day during summer stratification. The regeneration processes contribute about 60% of the calculated P deficit in the epilimnion. The tripton is decomposed mostly in the metalimnion, out of the euphotic zone; from here the phosphorus is carried back to the overlying waters by diffusion processes.     

An algae — Desert snail food chain: Energy flow and soil turnover

Summary The feeding ecology of adult desert snails (Sphincterochila zonata), inhabiting a loess plain in the Negev Desert, was studied during a 7-year period. Energy flow and soil turnover determinations were made at the individual and population level on the basis of field observations and data derived from laboratory simulations. Sphincterochila zonata were only active on 8–27 winter days annually, otherwise they were dormant. The snails fed exclusively on algae that grew on the soil surface following rain. The mean annual dry-weight biomass of algae was 197.4(±118.1) gr·m^-2. The dry weight biomass of snails ranged from 0.02–0.14 gr·m^-2. Annual production in the food chain varied substantially from year to year (1–1539 Kj·m^-2), but the net annual energy balance of the snails was always positive. Soil crust turnover, resulting from grazing of snails on algae, was estimated at 142 kg·hectare^-1 during the study period.The annual magnitude of energy flow and soil turnover is determined by the soil surface moisture regime which in turn, is a function of rainfall patterns. Sphincterochila zonata may serve an important role in Negev ecosystems by dispersing soil algae and altering soil structure. The snails are not subject to substanding predation by rodents but may occasionally serve as an important food source for migrating birds.     

氮磷硅添加对青藏高原高寒草甸垂穗披碱草叶片碳氮磷的影响

以甘南高寒草甸常见牧草垂穗披碱草(Elymus nutans)为研究对象,比较不同氮磷硅添加下,垂穗披碱草叶片对元素添加的反应。研究发现:氮添加显著提高土壤中硝态氮和铵态氮的含量;磷添加提高了土壤中全磷和速效磷的含量;高浓度的硅单独、硅与氮或磷混合可提高土壤中硝态氮的含量或全磷和速效磷的含量;氮和磷单独添加分别能提高垂穗披碱草叶片全氮和全磷含量,高浓度的硅单独、硅与氮或磷混合添加都能提高垂穗披碱草叶片全氮和全磷的含量。就硅元素而言,高浓度的硅添加,硅与氮或磷混合添加能提高土壤硝态氮、全磷和速效磷的含量,促进垂穗披碱草对土壤中氮磷的吸收,从而使植物叶片中氮磷的含量增加。     

Nutrient budgets and biogeochemistry in an experimental agricultural watershed in Southeastern China

During a two-year field study, an annual nutrient budget and cycles were developed for a small agricultural watershed. The study emphasized the integrated unit of the watershed in understanding the biogeochemistry. It was found that the total nutrient input was 39.1× 10⁴ kg nitrogen and 3.91×10⁴ kg phosphorus in the year 1995, of which the greatest input of nutrients to the watershed was chemical fertilizer application, reaching 34.7×10⁴ kg (676 kg/ha) nitrogen and 3.88×10⁴ kg (76 kg/ha) phosphorus. The total nutrient output from the watershed was 13.55×10⁴ kg nitrogen and 0.40×10⁴ kg phosphorus, while the largest output of nitrogen was denitrification, accounting for 44.1% of N output; the largest output of phosphorus was sale of crops, accounting for 99.4% of P output. The results show that the nutrient input is larger than output, demonstrating that there is nutrient surplus within the watershed, a surplus which may become a potential source of nonpoint pollution to area waters. The research showed that both denitrification and volatilization of nitrogen are key ways of nitrogen loss from the watershed. This suggests that careful management of fertilizer application will be important for the sustainable development of agriculture.The research demonstrated that a multipond system within the watershed had high retention rate for both water and nutrients, benefiting the water, nutrient and sediment recycling in the terrestrial ecosystem and helping to reduce agricultural nonpoint pollution at its source. Therefore, this unique watershed system should be recommended due to its great potential relevance for sustainable agricultural development.     

Snail populations,beech litter production,and the role of snails in litter decomposition

Summary The population densities of snails living in beech litter were studied form March 1968 to April 1969. Litter production over one year was measured and the role of snails in litter disappearance assessed.Snails were extracted from litter using a modified Vágvölgyi (1952) flotation method, extraction efficiencies being 84%. The mean annual population density of the twenty-one species of snail recorded on the main sampling site was estimated at 489/m². Carychium tridentatum was the most numerous species, with a mean density of 200/m². Acanthinula aculeata, Punctum pygmaeum and Vitrea contracta also had fairly high mean densities. The mean annual biomass was 699 mg dry wt./m² or 278 mg ash-free dry wt./m². Hygromia striolata and Oxychilus cellarius/alliarius were the most important species in terms of biomass on the main site. Within the limits of accuracy imposed by the sampling regime the population densities of four out of five of the species (C. tridentatum, A. aculeata, V. contracta, Retinella pura) studied remained unchanged throughout the year, whereas P. pygmaeum had a significantly higher autumn population. C. tridentatum populations were highly aggregated at all times of the year, most markedly so in June. Other species were aggregated at certain times of the year only. Samples taken from other sites showed total population densities of snails ranging from 185–1082 snails/m².A total tree litter production of 652 g/m²/annum was recorded of which 584g/m²/annum was of beech material. 72% fell in the October–December period. 58% of the beech litter-fall was leaves, 5.2% bud-scales, 27% fruits and 10% twigs and bark. Summation of appropriate field layer peak standing crops amounted to 23.3 g/m². This was considered as potential litter and was equivalent to 3.4% of the total litter input. The litter standing on the woodland floor in Septermber 1968 was 2,700 g/m², hence, assuming a steady state, litter turnover time was estimated as 4.5 years.It was calculated that the total snail population ingested 0.35–0.43% of the annual litter input, of which 49% was assimilated. The role of the individual species is examined in relation to concepts of key species in ecosystem functioning. The possible role of slugs in decomposition processes is also discussed.     

Influence of domestic sewage on growth and nitrogen fixation of Azolla pinnata R. Br.

Biomass production of Azolla pinnata R.Br., cultured in sewage effluents under full sunlight, correlated closely with the changes of orthophosphate phosphorus (P) in the medium: it was highest (13.18 g m⁻²) in August as opposed to 6.34 g m⁻² in January, though the environmental influence was also remarkable. Phosphorus contents in different media, particularly in one receiving a higher quantity of sewage effluents, gradually increased to 20.30 μg 1⁻¹ in January, reaching a maximum in May (37.60 μg 1⁻¹), followed by a gradual decline with a further rise in August (32.70 μg 1⁻¹). The seasonal variation in phosphorus content of the medium was closely associated with the carbon, phosphorus and nitrogen contents of plant tissue, as well as the heterocyst frequency of the symbiont, Anabaena azollae Strasb. The respective increases in nitrogen, carbon and phosphorus contents of plant tissue in mg 1⁻¹ during August were 39.80, 280.00 and 2.20, compared with values of 28.20, 245.00 and 1.50 during January, while the heterocyst frequencies were 15.96 and 10.92, respectively.     

Some Bag Experiments on Tibbs Run Lake,W.V., A Eutrophic Acidified Lake

Tibbs Run Lake was sampled from December 1979 to December 1980, monthly during the winter and biweekly during the spring, summer, and autumn. Primary production was measured from March 1980 to February 1981, either monthly or biweekly, as indicated above. The mean annual hydrogen ion concentration was equivalent to pH 4.33. This pH was 46% lower (based on H⁺ concentrations) than the 1977–1978 mean. The low pH of the lake is due to inputs of acid precipitation and the low buffering capacity of the watershed. Predictions of further reductions in the lake pH, based on mean annual hydrogen ion concentrations and hydrogen ion retention coefficients (RH) from Shellito (1979) and this study, indicate that the lake pH should reach an equilibrium with the precipitation pH between 1982 and 1985, assuming the precipitation pH continues to average 4.10. The stratified period mean chlorophyll a and total phosphorus concentrations were 22.1 mg/m³ and 19.3 μg/1, respectively. Total phosphorus loading to the lake was 0.233 gP/m²/yr. To examine the effects of neutralization and fertilization with phosphorus an in situ bag enclosure experiment, lasting 16 days, was performed during the summer of 1980. In the bags, phosphorus (20 μg/1 on days 0,4,8,12 as KH₂PO₄) was added alone and in combination with a base addition (IN KOH). The base additions raised the pH to approximately 7.8. Other treatments included base addition alone and a control. The maximum chlorophyll a concentration was found in the phosphorus treatment (∼30 mg/m³) on day 6. The phosphorus plus base treatment exhibited a 10 day lag before reaching a maximum chlorophyll a concentration (∼27 mg/m³) on day 16. The highest production rate was found in the phosphorus plus base treatment on day 12 (∼27 mgC/m³/hr.). A similar bag experiment, lasting 46 days, was performed during the late summer and early autumn of 1980. The treatments were the same as in the first experiment, however, the nitrate-nitrogen depletion in the lake and treatments necessitated the addition of nitrogen (2 mg/1 as NaNO₃) to one of each replicate treatment on day 5. On day 34, the maximum chlorophyll a concentrations were found in the phosphorus plus base nitrogen treatment (∼120 mg/m³) and the phosphorus plus nitrogen treatment (∼38.8 mg/m³). The control plus nitrogen treatment was submerged and possibly contaminated on day 5. All treatments not receiving nitrogen, except for the phosphorus plus base treatment, decreased in the chlorophyll a concentration throughout the experiment. The phosphorus plus base treatment peaked in the chlorophyll a concentration on day 45 (∼28 mg/m³) despite non-detectable levels of nitrate-nitrogen. The maximum primary production rate was found in the phosphorus plus base plus nitrogen treatment (∼32 mgC/m³/hr.) on day 11.     

The contribution of ammonia excreted by zooplankton to phytoplankton production in Narragansett Bay

Ammonia excreted by mixed zooplankton populations over an annual(1972–1973) cycle in Narragansett Bay varied from 0.04to 3.21 µg at NH₃-N dry wt^–1 day^–1, exclusiveof two exceptional rates measured one year apart: 11.74 and18.39 µg at NH³-N mg dry wt^–1 day^–1. Grossphytoplankton production integrated over the year (1972–1973)averaged 151 mg C m^–3 day^–1 for an 8 m water column;peaks of 332 and 905 mg C m^–3 day^–1 occurred duringthe winter-spring and summer blooms, respectively. Excretedammonia, integrated seasonally and annually, contributed only0.2% and 4.9% of the nitrogen required for observed gross productionduring the winter-spring and summer blooms, respectively, and4.4% annually. However, excreted ammonia may be an importantsource of the nitrogen required by Skeletonema costatum, thedominant diatom in Narragansett Bay, during the post-bloom periodwhen 186% of the nitrogen required for its net production wasmet by ammonia excretion. A combination of zooplankton ammoniaexcretion and benthic ammonia flux contributed 22% of the nitrogenrequired for the annual gross production (440 g C m^–2)while 51% of the nitrogen required for the net production ofSkeletonema was accounted for by regenerated nitrogen. ¹This research was supported by NSF grant GA 31319X awardedto Dr.T.J.Smayda.     

岩溶地区不同石漠化程度下草地细根对土壤养分的贡献

细根分解和周转是土壤有机质和养分的重要来源。为探明不同石漠化程度天然草地细根对土壤养分的贡献,于2017年3月至次年1月,采用土柱法和分解袋法,研究不同石漠化程度下天然草地的细根生物量、分解和养分释放动态及对石漠化的响应。结果表明:3种不同石漠化程度下草地的细根生物量随季节均呈现先增加后降低的趋势,随石漠化程度的加剧均呈现逐渐降低的趋势,潜在、中度和强度石漠化草地的细根生物量分别为3355.65、2944.02 g/m~2和1806.80 g/m~2。细根分解速率呈现先快后慢的趋势,分解300天后的残留率均低于50%。细根有机碳、全氮、全磷和全钾的释放过程具有显著不同,释放模式最终均表现为"释放",潜在、中度和强度石漠化草地细根的有机碳、全氮、全磷、全钾的年归还量分别为32.46—161.08、0.24—3.88、0.08—0.32、0.15—2.78 g/m~2。随石漠化程度的加剧,细根生物量和分解率呈现逐渐降低趋势,土壤有机碳、全氮归还量呈现逐渐增加趋势。     

Species richness and vegetation structure in a limestone grassland after 15 years management with six biomass removal regimes

Species richness, species composition and standing crop were studied in a limestone grassland in northern Switzerland after 13 and 15 years of experimental management with 6 management regimes differing in form, time and frequency of biomass removal. The management regimes with a cut at least every 2nd year had a higher species number per 40 m² and 1 m² than those cut less frequently, abandoned or annually burned. Annual burning and a cut every 5th year lead to a similar decrease in species richness as abandonment. Differences in species richness between different regimes increased with increasing spatial resolution of observation. Many species occurred in a plot during only one of the two sample years. This turnover of species was the highest in plots with the lowest species numbers, and increased with increasing spatial resolution. Standing crop was highest in plots burned annually (290 g m^?2), and lowest in plots cut annually in July (1989 g m^?2). Standing crop and litter increased with decreasing frequency of cutting. *** DIRECT SUPPORT *** A02DO006 00005     

Population dynamics and production of the tropical freshwater shrimp Caridina nilotica (Decapoda: Atyidae) in the littoral of Lake Sibaya

SUMMARY. Seasonal changes in population structure, standing stock levels and production of Caridina nilotica were studied at three sites in the littoral margins of subtropical Lake Sibaya between January 1975 and March 1976. Average population density at these sites declined from a maximum of c. 1400 to a minimum of c. 350 individuals per m² (3.4–0.4 g m^?2 dry wt) during the study, possibly as a result of emigration into peripheral vegetation inundated by rising lake levels. Shrimps bred perennially and, although egg stocks and instantaneous birth rates (b) were highest during summer, no corresponding increases in populaton density were observed, suggesting that the seasonally higher birth rates were offset by higher mortality rates. Population size structure and size-specific sex ratios did not change seasonally to any marked extent. Relative abundance declined with size and females grew larger than males. Clutch size increased linearly as a function of female carapace length. Estimates of overall mean annual somatic production (g m^?2 year^?1 dry wt) for the three sites between January 1975 and January 1976 ranged between c. 132 (egg-ratio method), 37.5 (summation of growth increments) and 24 (Hynes-Hamilton method) at an annual mean standing stock level of 2.7 g m^?2 dry wt (calorific value, 20.34 kJ g^?1 dry wt). Production at sites 1, 2 and 3 decreased in line with declining annual mean standing stocks (5.32, 3.67 and 0.23 g m^?2, respectively). The growth increment method gave an overall mean annual P/B value of 13.9. Egg production amounted to a further 5.6, 3.6 and 0.1 g m^?2 year^?1 dry wt (calorific value, 28.01 kJ g^?1) at sites 1, 2 and 3, or 2.7 g m^?2 year^?1 on average.     

Biomass and density responses in tallgrass prairie legumes to annual fire and topographic position

Annually burned tallgrass prairie is purported to be a nitrogen-limited system, especially when compared to unburned prairie. To test the hypothesis that legumes, potential nitrogen-fixers, would increase in relative abundance in annually burned sites, we assessed their density and biomass for two seasons on upland and lowland soils in annually burned and unburned watersheds. Total legume density was significantly higher in burned (8.0 ± 1.0 [SE] stems/m²) than in unburned watersheds (3.0 ± 0.3 stems/m²). Species with higher (P < 0.05) densities in burned than in unburned prairie included Amorpha canescens, Dalea candida, Dalea purpurea, Lespedeza violacea, Psoralea tenuiflora, and Schrankia nuttallii. Desmodium illinoense was the only legume that responded negatively to annual fire. Total legume biomass did not differ between burned (11.3 ± 1.3 g/m²) and unburned prairie (10.5 ± 0.9 g/m²). Biomass productions of Dalea candida and Psoralea tenuiflora were higher (P < 0.05) in burned than in unburned sites, but biomasses of other legumes were similar between burn treatments. Average individual stem masses of Amorpha canescens and Baptisia bracteata were significantly greater in unburned than in burned prairie. Legumes were affected differentially by topographic location. Total legume density was higher (P < 0.05) on lowland soils (6.6 ± 1.0 stems/m²) than on upland soils (4.3 ± 0.5 stems/m²). However, total legume biomass was not different between lowland soils (12.0 ± 1.2 g/m²) and upland soils (9.9 ± 1.0 g/m²). Densities and biomasses of Amorpha canescens, Desmodium illinoense, and Lespedeza capitata were higher on lowland sites than on upland sites, whereas densities and biomasses of Baptisia bracteata and Dalea purpurea were higher on upland than on lowland soils. Most legume species are either fire tolerant or exhibit a positive response to fire and their persistence in annually burned prairie suggests that they may play an important role in the nitrogen budget of this ecosystem.     

Population Dynamics,Growth and Productivity of Abra ovata (Mollusca,Bivalvia) in the Evros Delta (North Aegean Sea)

Monthly samples of Abra ovata were collected during February 1983-January 1984 in the Evros Delta (N. Aegean Sea). Population density (mean annual value = 2407.5 ind · m⁻²) was characterized by seasonal variation. An analysis of the length frequency distributions shows that one annual recruitment of juveniles (> 2 mm) occurred in October-January; and also that, throughout the year, two age groups existed in the population. One growth ring was formed on the shells of the oldest age group during July-August. Mean growth in shell length can be described by Bertalanffy function. A positive correlation existed between shell length and decalcified dry weight. Secondary production in A. ovata, calculated by the instantaneous growth method, showed a mean biomass of 29.221 g dry weight m⁻²yr⁻¹, a productivity of 17.086 g dry weight m⁻²yr⁻¹ and an annual turnover ratio of 0.59.     

Internal phosphorus loading to shallow Edinboro Lake in northwestern Pennsylvania

The summer stratification phosphorus budget for eutrophic Edinboro Lake in northwestern Pennsylvania was determined. Phosphorus loading from internal sources contributed 141 kg, (79%) and 55 kg, (68%) of the mass phosphorus increase in the lake in 1981 and 1982, respectively. Calculated anaerobic sediment release rates of total phosphorus were 9.9 and 3.7 mg m^–2 day^–1 for these two years. The observed summer maximum chlorophyll a concentration was 1.5–3 times greater than that predicted by existing models. Year-to-year variability in the internal phosphorus load for this lake and others is discussed. Without a data base that will permit the comparison of lakes and with and without a significant supply of internal phosphorus, prediction of the relative importance of internal loading in a particular lake will be difficult.     

Carbon cycling in cultivated land and its global significance

Long-term data from Sanborn Field, one of the oldest experimental fields in the USA, were used to determine the direction of soil organic carbon (SOC) dynamics in cultivated land. Changes in agriculture in the last 50 years including introduction of more productive varieties, wide scale use of mineral fertilizers and reduced tillage caused increases in total net annual production (TNAP), yields and SOC content. TNAP of winter wheat more than doubled during the last century, rising from 2.0–2.5 to 5–6 Mg ha^–1 of carbon, TNAP of corn rose from 3–4 to 9.5–11.0 Mg ha^–1 of carbon. Amounts of carbon returned annually with crop residues increased even more drastically, from less than 1 Mg ha^–1 in the beginning of the century to 3–3.5 Mg ha^–1 for wheat and 5–6 Mg ha^–1 for corn in the 90s. These amounts increased in a higher proportion because in the early 50s removal of postharvest residues from the field was discontinued. SOC during the first half of the century, when carbon input was low, was mineralized at a high rate: 89 and 114 g m^–2 y^–1 under untreated wheat and corn, respectively. Application of manure decreased losses by half, but still the SOC balance remained negative. Since 1950, the direction of the carbon dynamics has reversed: soil under wheat monocrop (with mineral fertilizer) accumulated carbon at a rate about 50 g m^–2 y^–1, three year rotation (corn/wheat/clover) with manure and nitrogen applications sequestered 150 g m² y^–1 of carbon. Applying conservative estimates of carbon sequestration documented on Sanborn Field to the wheat and corn production area in the USA, suggests that carbon losses to the atmosphere from these soils were decreased by at least 32 Tg annually during the last 40–50 years. Our computations prove that cultivated soils under proper management exercise a positive influence in the current imbalance in the global carbon budget.     

Assessing fine-root biomass and production in a Scots pine stand – comparison of soil core and root ingrowth core methods

Soil core and root ingrowth core methods for assessing fine-root (< 2 mm) biomass and production were compared in a 38-year-old Scots pine (Pinus sylvestris L) stand in eastern Finland. 140 soil cores and 114 ingrowth cores were taken from two mineral soil layers (0–10 cm and 10–30 cm) during 1985–1988. Seasonal changes in root biomass (including both Scots pine and understorey roots) and necromass were used for calculating fine-root production. The Scots pine fine-root biomass averaged annually 143 g/m² and 217 g/m² in the upper mineral soil layer, and 118 g/m² and 66 g/m² in the lower layer of soil cores and ingrowth cores, respectively. The fine-root necromass averaged annually 601 g/m² and 311 g/m² in the upper mineral soil layer, and 196 g/m² and 159 g/m² in the lower layer of soil cores and ingrowth cores, respectively. The annual fine-root production in a Scots pine stand in the 30 cm thick mineral soil layer, varied between 370–1630 g/m² in soil cores and between 210 – 490 g/m² in ingrowth cores during three years. The annual production calculated for Scots pine fine roots, varied between 330–950 g/m² in soil cores and between 110 – 610 g/m² in ingrowth cores. The horizontal and vertical variation in fine-root biomass was smaller in soil cores than in ingrowth cores. Roots in soil cores were in the natural dynamic state, while the roots in the ingrowth cores were still expanding both horizontally and vertically. The annual production of fine-root biomass in the Scots pine stand was less in root ingrowth cores than in soil cores. During the third year, the fine-root biomass production of Scots pine, when calculated by the ingrowth core method, was similar to that calculated by the soil core method. Both techniques have sources of error. In this research the sampling interval in the soil core method was 6–8 weeks, and thus root growth and death between sampling dates could not be accurately estimated. In the ingrowth core method, fine roots were still growing into the mesh bags. In Finnish conditions, after more than three growing seasons, roots in the ingrowth cores can be compared with those in the surrounding soil. The soil core method can be used for studying both the annual and seasonal biomass variations. For estimation of production, sampling should be done at short intervals. The ingrowth core method is more suitable for estimating the potential of annual fine-root production between different site types.