茯苓碳氮磷化学计量学特征

为探明茯苓的碳、氮、磷生态化学计量学特征,采集了云南省11个州、市42个居群的茯苓样本,分析了其菌核与表皮中碳(C)、氮(N)、磷(P)的化学计量特征.结果 表明:茯苓菌核中C、N、P的含量分别为40.24％-43.58％、0.176％-0.532％和0.020％-0.077％;C∶N、C∶P和N∶P的范围分别为93....     

Nitrogen and the Baltic Sea: managing nitrogen in relation to phosphorus

The Baltic is a large, brackish sea (4 x 10(5) km2) extending from 54N to approximately 66N, with a fourfold larger drainage area (population 8 x 10(7). Surface salinity (2 to 8 PSU) and hence biodiversity is low. In the last century, annual nutrient loads increased to 10(6) metric tons N and 5 x 10(4) ton P. Eutrophication is evident in the N-limited south, where cyanobacteria fix 2 to 4 x 10(5) ton N each summer, Secchi depths have been halved, and O2-deficient bottom areas have spread. Production remains low in the P-limited north. In nutrient-enriched coastal areas, phytoplankton blooms, toxic at times, and filamentous macroalgae reduce amenity values. Loads need to be reduced of both N, to reduce production, and P, to limit N-fixing cyanobacterial blooms. When large N-load reductions have been achieved locally, algal biomass has declined. So far, P loads have been reduced more than N loads. If this continues, a P-limited Baltic proper may result, very different from previous N-limited conditions. Reaching the management goal of halved anthropogenic N and P loads at minimum cost will require better understanding of biogeochemical nutrient cycles, economic evaluation of proposed measures, and improved stakeholder participation.     

不同密度下沙地樟子松碳、氮、磷化学计量及养分重吸收特征

以樟子松纯林为对象,研究了6种密度(490、750、1110、1550、1930、2560株.hm-2)下不同器官(当年生叶、一年生叶、当年生枝、一年生枝和细根)的C、N、P化学计量特征及叶片N、P重吸收效率.结果表明:随着林分密度增加,当年生和一年生叶C含量及当年生和一年生枝P含量呈降低趋势(1550株.hm-2除外...     

Carbon,nitrogen and phosphorus stoichiometry of Myrica nana in Yunnan,China

Aims Carbon (C), nitrogen (N) and phosphorus (P) play important roles in plant growth and physiological functions. We aimed at exploring the intrinsic relationships of C, N and P in Myrica nana—a common shrub in Yunnan Province—as well as their relationships with pant biomass and soil nutrients.
Methods We measured the concentration of C, N and P of M. nana from 29 sites for their magnitudes and correlations with soil nutrients.
Important findings 1) The arithmetic mean value of C, N and P concentration in the roots, stems and leaves of M. nana was 45.94%, 0.54%, 0.03%, and 46.32%, 0.58%, 0.03%, and 49.05%, 1.70%, 0.06%, respectively. C, N and P concentrations in the leaves were significantly higher than those in the roots and the stems. The C:N:P in roots, stems and leaves was 1531:18:1, 1544:19:1, and 818:10:1, respectively. 2) The C concentration and N:P in leaves of M. nana decreased with the increase of biomass of M. nana; the leaf C concentration was significantly correlated with biomass (p < 0.01), while the correlation between N:P and biomass was not significant (p > 0.05). The leaf N increased with the increase of plant biomass, the P was significantly correlated with biomass (p < 0.05), but the correlation between N concentration and biomass was not significant (p > 0.05). N:P in leaves was 34.2, suggesting that plant growth was limited by P. 3) C, N and P concentration in the roots were significantly correlated with soil P (p < 0.05), with N, P concentrations correlated with soil P positively (p < 0.01) and C negatively (p < 0.05). C concentration in the stems was significantly and negatively correlated with soil C, N, with significant correlation with C, N, and P concentration (p < 0.01). P concentration in the stems was significantly and positively correlated with soil P concentration (p < 0.01), while leaf P significantly and positively correlated with soil C, N and P (p < 0.01); leaf C concentration was significantly and negatively correlated with soil P (p < 0.01).     

中国东黄海海岛5种常见草本的碳氮磷化学计量特征

研究不同纬度海岛共有植物种的碳(C)氮(N)磷(P)化学计量变异特征,有助于剔除植物谱系的影响,揭示植物对海岛环境条件变化的适应策略.本研究以中国东部9个典型海岛的5种常见共有草本植物艾草、狗尾草、葎草、麦冬、酢浆草为研究对象,测定和分析了其地上部分和根系的C、N、P化学计量比,及其与土壤C、N、P含量,温度和降水的关系.结果表明: 9个海岛5种草本地上部分C、N、P含量分别为352.16～518.16、10.81～34.43、0.58～2.38 mg·g^-1,C∶N、N∶P、C∶P分别为11.98～38.99、4.67～27.47、133.39～748.54;根系C、N、P含量分别为312.28～493.34、9.26～23.27、0.40～2.10 mg·g^-1,C∶N、N∶P、C∶P分别为18.18～46.79、8.53～37.38、174.45～1120.40.海岛常见草本的地上部分N、P含量均随着纬度的升高而增高,而N∶P随着纬度的升高而减小;P含量较N含量具有更高的变异性和环境依赖性,气候因子可以解释草本地上部分N、P、N∶P变异的60%;但草本的根系N、P及N∶P不依赖纬度变化而变化,气候因子只解释了根系中的N、P变异的6%～10%.气候因子和土壤养分对植物地上部分及根系的变异贡献率不同,土壤N与P含量对草本植物根系的P含量有显著影响,植物地上部分P含量与土壤P含量呈显著正相关,土壤特性解释了根系N、P变异的37%.研究表明,在剔除植物谱系的影响后,纬度差异导致的环境变化是5种海岛常见草本地上部分的N、P及N∶P变异的主要原因,土壤养分是根系P变异的主要原因.     

Phytoplankton community responses to nutrient and iron enrichment under different nitrogen to phosphorus ratios in the northern Baltic Sea

The impact of nutrient enrichment on the phytoplankton community structure, and particularly cyanobacteria, was studied in a 3-week mesocosm experiment conducted in August 2001 in the Archipelago Sea, a part of the northern Baltic Sea. The factorial design experiment included daily additions of nitrogen (N) and phosphorus (P) at two mass ratios, 1N:1P and 7N:1P, respectively, additions of iron (Fe) and a synthetic chelator, ethylenediaminetetraacetic acid (EDTA). The floating enclosures (400 l) were sampled for analyses of phytoplankton biomass and community structure, phytoplankton primary production, chlorophyll a, nutrients, and hepatotoxins. Chlorophyll a concentration, phytoplankton biomass and primary production increased most in the 7N:1P treatment. The increase was mainly due to an abundant growth of chlorophytes (Dictyosphaerium subsolitarium, Kirchneriella spp., Monoraphidium contortum, and Oocystis spp.), pennate diatoms (especially Nitzschia spp.), dinophytes and the chroococcalean cyanobacterium Synechococcus sp. The nutrient enrichments had no effect on the total biomass of N₂-fixing cyanobacteria. Nevertheless, the biomass of Anabaena spp. was highest in the enrichments with a low N/P ratio. Chlorophyll a concentration and total phytoplankton biomass were not affected by Fe or EDTA, but Fe alone had a positive effect on the chlorophyte Kirchneriella sp. The N₂-fixing cyanobacteria Aphanizomenon sp. responded positively to Fe alone and to both Fe and EDTA added together. The hepatotoxin concentration increased during the experiment, but no clear responses to nutrient enrichments were found. Our study showed species-specific responses to nutrient enrichments among the N₂-fixing cyanobacteria. Although the total phytoplankton production was not Fe-limited; the availability of Fe clearly affected the phytoplankton community structure.     

不同基因型甘蔗种质资源的表型遗传多样性

植物的碳、氮、磷化学计量特征能反映植物对土壤营养元素的利用效率,岩溶区植物经过长期的进化形成了自身独特的生理生态和生态化学计量特征,通过岩溶区植物叶片碳、氮、磷化学计量可以揭示岩溶生态系统各组分之间的养分循环规律.该研究在桂林毛村岩溶区次生林中选择3个20 m×20 m 的样方,采用多元统计方法分析了岩溶区森林12种典型植物叶片共186个样品的碳、氮、磷的生态化学计量特征,研究它们之间的相互关系,探讨碳、氮、磷化学计量学在岩溶生态系统中的生态指示作用.结果表明：(1)虽然岩溶区石灰土氮和磷的含量较高,但由于其有效性低,植物对养分的吸收和利用缓慢,岩溶区石灰土植物的生长仍然受到 N 和 P 的共同限制;(2)由于岩溶区植物叶片中 N 和 P 的含量显著偏低导致较高的 C∶N 和 C∶P 值(C∶N 的平均值为80．86;C∶P 的平均值为639．65);(3)利用 N∶P＜14表明氮受限制,N∶P＞16表明磷受限制,14＜N∶P＜16表明 N 和 P 共同限制的标准判断植物叶片受 N 或 P 的限制在岩溶区不完全适合;(4)元素间相关性分析表明,叶片的 C 和 N 呈极显著负相关关系(P ＜0．01),C 和 P 呈显著负相关关系(P ＜0．05),N 和 P之间呈现极显著正相关关系(P ＜0．01).这体现了植物体内两营养元素含量需求变化的相对一致性.研究结果有助于了解岩溶区森林植物的适生机制及其生态地球化学过程,可为岩溶区生态治理提供理论依据.     

不同基因型甘蔗种质资源的表型遗传多样性

为探明甘蔗原种和地方种的遗传多样性和亲缘关系,以期筛选出优良甘蔗种质和优良杂交亲本.该研究对18份甘蔗原种和地方种的14个数量性状进行了表型遗传多样性分析.结果表明：通过14个数量性状的变异系数(coefficient of variance,CV)和性状之间的相关分析,18份甘蔗原种和地方种的数量性状遗传变异主要来自甘蔗蔗糖分、单茎重、叶宽、茎径和纤维分;对14个数量性状进行主成分分析提取获得了4个主成分因子,分别命名为“品质因子”、“生长因子”、“成熟度因子”和“光合因子”,主成分因子累积贡献率达83．482％;进一步通过对主成分因子开展综合评价分析,获得数量性状综合表型高于平均水平的10份材料,依次为 Sampana→甜圪塔→合庆草甘蔗→桂林竹蔗→坦桑尼亚→芒戈→古芝蔗→大岛再来→托江红→春尼;聚类分析基于不同的遗传距离可将18份种质聚为5个类别,潜在的优良杂交组合是 Sampana 和甜圪塔或 Sampana 和合庆草甘蔗,表明在甘蔗遗传育种亲本选择上既要考虑各性状主要因子的互补,又要保持一定的遗传距离.该研究认为,在甘蔗育种工作中,利用因子分析法进行表型遗传多样性分析,将更加有助于亲本和杂交组合的选择.     

Long-term dynamics of zooplankton in the southeastern Baltic Sea

Long-term research in the Baltic Sea revealed the basic trends of zooplankton community variations depending on oceanographic processes. Alternation of the periods of increase and decrease in salinity of the Baltic Sea against the background of climate changes (temperature increase) and eutrophication affect the state of the entire Baltic ecosystem, including zooplankton. For these periods, the dynamics of zooplankton in the Baltic Sea were analyzed based on literature data and results of regular research in the southeastern Baltic Sea during 1998–2007. The changes in the hydrological situation were accompanied by significant changes in the zooplankton community. In the 1990s–2000s, the abundance and biomass of brackish-water and thermophilous species primarily of Cladocera and Copepoda increased markedly. The role of the previously dominant marine copepod Pseudocalanus elongatus decreased due to salinity reduction in the deep-water part of the Baltic Sea. Maximum development of zooplankton occurred in years of the greatest warming-up of the water (2001, 2005–2007) against the background of a general positive trend of zooplankton abundance in the last decade.     

密度对四季竹叶片C、N、P化学计量和养分重吸收特征的影响

以四季竹纯林为对象,研究了4种密度(D1:24600～29800株·hm-2;D2:37500～42600株·hm-2;D3:46500～52800株·hm-2;D4:76500～85500株·hm-2)下1～3年生立竹的成熟叶和凋萎叶的C、N、P化学计量特征及养分重吸收规律.结果表明:随竹林密度的增大,成熟叶C、N、P含量和凋萎叶C、P含量总体下降,凋萎叶N含量先升高后降低,D4密度时成熟叶C含量急剧下降;叶片C/N和C/P呈升高趋势,N/P先升高后降低.D3、D4密度的叶片N、P养分利用效率显著高于D1、D2密度;叶片N、P重吸收率分别呈先降后升和持续升高的趋势.D1～D3密度的成熟叶N/P为16.24～19.37,四季竹生长受P的限制,促进叶片建成,种群生长旺盛.D4密度的成熟叶N/P为13.42～15.74,N限制作用增强,叶片凋萎脱落,种群生长受到抑制.四季竹通过调节叶片的C、N、P含量及其化学计量比,提高了N、P利用效率及重吸收能力,以适应高密度下环境资源的激烈竞争.在本试验条件下,D3密度是四季竹适宜的经营密度.     

Carbon:phosphorus stoichiometry and food chain production

Incident light was manipulated in large plankton towers containing algae, microbes, and herbivores. Paradoxically, food chain production was lower with greater light energy input. This apparent paradox is resolved by recognizing stoichiometric constraints to food chain production. At high light, elevated algal biomass was achieved mainly by increases in cellular carbon. Consumers have a high phosphorus demand for growth, and thus a large excess of carbon inhibited, rather than stimulated, their growth. These experiments may help us predict the consequences of anthropogenic perturbations in nutrients, carbon, and solar energy. They also may help us to understand the wide range of consumer biomass and production at a given level of primary productivity in ecosystems.     

Temporal and spatial variation of coastal zooplankton in the Baltic Sea

When analysing temporal variation monthly mean abundances of zooplankton sampled at a eoastal station in the northern Baltic Sea between 1976 and 1988 showed the lowest between-year variation in the summers The coefficients of variation were estimated at 50% for rotifers in June. 70% for cladocerans in August and between 30 and 50% for different copepodite stages in August Moreover in the summers, all dominating zooplankton groups were abundant Estimates of yearly biomass or production of zooplankton must, however, be based on frequent sampling during the whole year because of large differences between months in zooplankton composition and abundance
In 1989. spatial variation was analyzed by sampling zooplankton on three occasions along a 9 8 km transect with 15 stations, 700 m apart All taxonomic/life-stage groupings of zooplankton were heterogeneously distributed Geostatistical analysis did not give a definite answer to what the minimum distance between stations should be to obtain independent samples but indicated that 700 to 1400 m would be sufficient in most cases For most of the zooplankton groupings the coefficients of variation in the sampled area were estimated at 20-40% on all sampling occasions     

Carbon,nitrogen and O2 fluxes associated with the cyanobacterium Nodularia spumigena in the Baltic Sea

Photosynthesis, respiration, N₂ fixation and ammonium release were studied directly in Nodularia spumigena during a bloom in the Baltic Sea using a combination of microsensors, stable isotope tracer experiments combined with nanoscale secondary ion mass spectrometry (nanoSIMS) and fluorometry. Cell-specific net C- and N₂-fixation rates by N. spumigena were 81.6±6.7 and 11.4±0.9 fmol N per cell per h, respectively. During light, the net C:N fixation ratio was 8.0±0.8. During darkness, carbon fixation was not detectable, but N₂ fixation was 5.4±0.4 fmol N per cell per h. Net photosynthesis varied between 0.34 and 250 nmol O₂ h⁻¹ in colonies with diameters ranging between 0.13 and 5.0 mm, and it reached the theoretical upper limit set by diffusion of dissolved inorganic carbon to colonies (>1 mm). Dark respiration of the same colonies varied between 0.038 and 87 nmol O₂ h⁻¹, and it reached the limit set by O₂ diffusion from the surrounding water to colonies (>1 mm). N₂ fixation associated with N. spumigena colonies (>1 mm) comprised on average 18% of the total N₂ fixation in the bulk water. Net NH₄⁺ release in colonies equaled 8–33% of the estimated gross N₂ fixation during photosynthesis. NH₄⁺ concentrations within light-exposed colonies, modeled from measured net NH₄⁺ release rates, were 60-fold higher than that of the bulk. Hence, N. spumigena colonies comprise highly productive microenvironments and an attractive NH₄⁺ microenvironment to be utilized by other (micro)organisms in the Baltic Sea where dissolved inorganic nitrogen is limiting growth.     

Carbon,nitrogen and phosphorus stoichiometry in leaves and fine roots of dominant plants in Horqin Sandy Land

Aims The stoichiometric characteristics of carbon (C), nitrogen (N) and phosphorus (P) in plant organism is vital to understand plant adaptation to environment. In particular, the correlations of elemental stoichiometric characteristics between leaf and fine root could provide insights into the interaction and balance among the plant elements, nutrient use strategies and plant response to global change.Methods We measured C, N, P contents and C:N, C:P, N:P in leaves and fine roots of 60 dominant plants in Horqin sandy land. The 60 plant species were classified into five life forms and two categories such as perennial forb, annual forb, perennial grass, annual grass, shrub, legume, and non-legume. We statistically analyzed the differences and correlations of C, N and P stoichiometry either between fine root and leaf or among five life forms.Important findings The average C, N and P concentrations in leaves of 60 plant species in Horqin sandy land are 424.20 mg·g^-1, 25.60 mg·g^-1 and 2.10 mg·g^-1, respectively. In fine roots, the corresponding element concentrations are 434.03 mg·g^-1, 13.54 mg·g^-1, 1.13 mg·g^-1. N and P concentrations in leaf are approximately twice as high as averages in fine root. Furthermore, similar N:P between leaf and fine root indicates conservative characteristic of elemental stoichiometry in plant organism, suggesting that nutrients distribution is proportional between aboveground and underground of plants. There are significant difference of C, N, P, C:N, C:P and N:P in leaf and root among five life forms. N and P in forb and C:N and C:P in grass are averagely higher than those in other life forms. N:P in annual forb and grass, however, are lower than those in other life forms. C, N in legume are higher than those in non-legume, while C:N in legume is lower than in non-legume. These results imply that nutrient use strategies are significantly different among plant life forms. Correlations analysis showed that N and P in leaf or fine root positively correlated, but C and N, C and P in fine root negatively correlated, suggesting coupling relationship among C, N and P in leaf and fine root. Subsequently, we detected positively significant correlations in C, N, P and their ratios between leaf and fine root, suggesting proportional distribution of photosynthate and nutrient between aboveground and underground during plant growth. Generally, these results supplied fundamental data to understand mass turnover and nutrients cycling of leaves and roots in sand land.     

氮磷施肥对拟南芥叶片碳氮磷化学计量特征的影响

研究植物碳(C)氮(N)磷(P)化学计量特征, 有助于了解C、N、P元素的分配规律和确定限制植物生长的元素类型, 理解生长速率调控的内在机制。该研究基于盆栽施肥试验, 测定不同N、P供应水平下拟南芥(Arabidopsis thaliana)叶片的生物量和C、N、P含量, 分析拟南芥的限制元素类型、验证生长速率假说、探讨N、P的内稳性差异和C、N、P元素间的异速生长关系。主要结果如下: 盆栽试验基质中限制元素是P, 施N过多可能引起毒害作用; 拟南芥的生长符合生长速率假说, 即随着叶片N:P和C:P的增加, 比生长速率显著减小; 叶片P含量存在显著的调整系数(3.5), 但叶片N含量与基质N含量之间无显著相关; 叶片N和P含量具有显著的异速生长关系, 但不符合N-P^3/4关系, 施P肥导致表征N、P异速生长关系的幂指数(0.209)显著低于施N肥处理(0.466)。该研究首次基于温室培养实验分析了拟南芥C、N、P的化学计量特征及其对N、P添加的响应, 研究结果将为野外研究不同物种、群落或生态系统的化学计量特征提供参考。     

Allocation strategies in crustacean stoichiometry: the potential role of phosphorus in the limitation of reproduction

1. Elemental composition (carbon : nitrogen : phosphorus, C : N : P) was analysed in eggs and juveniles of two crustaceans, Daphnia magna (Cladocera) and the crayfish Astacus astacus (Decapoda). Stoichiometry was also analysed for the carapace, muscle tissue, hepatopanchreas and gills of Astacus. 2. For both species the C : P ratio was significantly higher in eggs than juveniles, but there was a constant, homeostatic elemental ratio in eggs during embryogenesis (Astacus) and with different C : N : P in maternal food (Daphnia). 3. Differences in the stoichiometry of major tissue categories in Astacus suggest that there are distinct allocation strategies of elements to various somatic tissues as well as to reproduction versus somatic tissues overall. 4. There are strong ontogenetic shifts in the allocation of energy and elements in both species, as for crustaceans in general. During maturity there may be a trade‐off with regard to the allocation of C, N or P to somatic or reproductive tissue, and poor food quality (high C : P in food) could pose other constraints on reproductive capacity than does food shortage (low C). 5. Egg production may be at least as sensitive to low P as is somatic growth and could result in a marked decrease in overall population growth rate more severe than would be expected from individual growth rate alone.     

Carbon,nitrogen and phosphorus ecological stoichiometry of Lateolabrax macultus and Acanthogobius ommaturus in the Estuary of Yangtze River,China

Most stoichiometric models do not consider the importance of ontogenetic changes in body nutrient composition. Among aquatic animals, body elemental ontogenetic changes may be particularly important in fish due to bone formation at larval–juvenile development stage. We investigated the stoichiometric characteristics and ontogenetic variation of carbon (C), nitrogen (N), phosphorous (P) and calcium (Ca) in the whole fish without gut of Lateolabrax macultus and Acanthogobius ommaturus from the Yangtze Estuary. Some differences were found in the whole-fish nutrient content across species as well as fish length and mass groups. Mean body content of L. macultus was 41.2% for C (34.9–44.9%), 11.8% for N (10.3–12.9%), and 3.3% for P (1.4–5.4%) and the molar ratio of C:N:P was 32:8:1. A. ommaturus had the following mean compositions: carbon, 43.4% (40.0–45.9%); nitrogen, 13.2% (11.7–14.1%); phosphorus, 2.9% (1.6–6.0%) and molar ratio of C:N:P was 38:10:1. The variation of C content in of L. macultus was minimum (0.05), followed by N (0.06), and the variation of P content was the highest (0.22). The variation of C content in A. ommaturus was minimum (0.03), followed by N (0.04), and the variation of P content was also the highest (0.27). Both species varied the least in C, moderate in N and the most in P. Comparing the two species, A. ommaturus was significantly higher for C, N, C:P, N:P and significantly lower for P and C:N than L. macultus. The positive correlation between C and N contents was significant (P < 0.01) for both species. In contrast, C and P concentrations showed little correlation (P > 0.05). The contents of C, N in L. macultus showed significant negative correlation with total length and wet mass, respectively, while C:N ratio showed significant positive correlation with them. As for A. ommaturus, the content of C and the ratio of C:N showed significant negative correlation with total length and wet mass, respectively. The two estuarine fishes in this study mainly consumed fish, shrimps and crabs, which could be the reason that the stoichiometry of L. macultus and A. ommaturus are higher than other freshwater fishes that have been reported previously. In both species, the content of calcium was highly correlated with the content of body P, which indicated that the change of the content of P is associated with bone formation in ontogeny. Fish shape, scale type, the ratio of head length/standard length and the degree of ossification of the internal skeleton and outer integument might have caused the results that L. macultus had higher contents of P and Ca than A. ommaturus.     

Seasonal oxygen,nitrogen and phosphorus benthic cycling along an impacted Baltic Sea estuary: regulation and spatial patterns

The regulatory roles of temperature, eutrophication and oxygen availability on benthic nitrogen (N) cycling and the stoichiometry of regenerated nitrogen and phosphorus (P) were explored along a Baltic Sea estuary affected by treated sewage discharge. Rates of sediment denitrification, anammox, dissimilatory nitrate reduction to ammonium (DNRA), nutrient exchange, oxygen (O₂) uptake and penetration were measured seasonally. Sediments not affected by the nutrient plume released by the sewage treatment plant (STP) showed a strong seasonality in rates of O₂ uptake and coupled nitrification–denitrification, with anammox never accounting for more than 20 % of the total dinitrogen (N₂) production. N cycling in sediments close to the STP was highly dependent on oxygen availability, which masked temperature-related effects. These sediments switched from low N loss and high ammonium (NH₄ ⁺) efflux under hypoxic conditions in the fall, to a major N loss system in the winter when the sediment surface was oxidized. In the fall DNRA outcompeted denitrification as the main nitrate (NO₃ ^?) reduction pathway, resulting in N recycling and potential spreading of eutrophication. A comparison with historical records of nutrient discharge and denitrification indicated that the total N loss in the estuary has been tightly coupled to the total amount of nutrient discharge from the STP. Changes in dissolved inorganic nitrogen (DIN) released from the STP agreed well with variations in sedimentary N₂ removal. This indicates that denitrification and anammox efficiently counterbalance N loading in the estuary across the range of historical and present-day anthropogenic nutrient discharge. Overall low N/P ratios of the regenerated nutrient fluxes impose strong N limitation for the pelagic system and generate a high potential for nuisance cyanobacterial blooms.     

Carbon and nitrogen stoichiometry and nitrogen cycling rates in streams

Stoichiometric analyses can be used to investigate the linkages between N and C cycles and how these linkages influence biogeochemistry at many scales, from components of individual ecosystems up to the biosphere. N-specific NH₄⁺ uptake rates were measured in eight streams using short-term ¹⁵N tracer additions, and C to N ratios (C:N) were determined from living and non-living organic matter collected from ten streams. These data were also compared to previously published data compiled from studies of lakes, ponds, wetlands, forests, and tundra. There was a significant negative relationship between C:N and N-specific uptake rate; C:N could account for 41% of the variance in N-specific uptake rate across all streams, and the relationship held in five of eight streams. Most of the variation in N-specific uptake rate was contributed by detrital and primary producer compartments with large values of C:N and small values for N-specific uptake rate. In streams, particulate materials are not as likely to move downstream as dissolved N, so if N is cycling in a particulate compartment, N retention is likely to be greater. Together, these data suggest that N retention may depend in part on C:N of living and non-living organic matter in streams. Factors that alter C:N of stream ecosystem compartments, such as removal of riparian vegetation or N fertilization, may influence the amount of retention attributed to these ecosystem compartments by causing shifts in stoichiometry. Our analysis suggests that C:N of ecosystem compartments can be used to link N-cycling models across streams.     

Carbon,nitrogen and phosphorus net mineralization in organic horizons of temperate forests: stoichiometry and relations to organic matter quality

The rates of mineralization processes influence C sequestration and soil fertility, but despite their importance for ecosystem functioning, C, N and P net mineralization rates are seldom investigated together. Hence, we studied the relationships between net mineralization rates and organic matter stoichiometry in an 8-week incubation experiment with Oi, Oe and Oa horizon material of six beech, one spruce and one pine site. We determined C, N and P net mineralization rates, organic C quality and C:N:P stoichiometry. Net N mineralization only occurred below molar organic matter C:N ratios of 40 (Oi) or 28 (Oa) and N:P ratios of 42 (Oi) or 60 (Oa), and increased with decreasing C:N and N:P ratios. Net P mineralization only occurred below C:P ratios of 1400 (Oi) and N:P ratios of 40 (Oi), and increased with decreasing C:P and N:P ratios. Net N and P mineralization were strongly positively correlated with each other (r = 0.64, p < 0.001), whereas correlations of both net N and net P mineralization with C mineralization were weak. The average C:N:P stoichiometry of net mineralization was 620:4:1 (beech, Oi), 15,350:5:1 (coniferous, Oi), 1520:8:1 (Oe) and 2160:36:1 (Oa). On average, ratios of C:N net mineralization were higher, and ratios of N:P net mineralization lower than organic matter C:N and N:P ratios. This difference contributed to the decrease of C:N ratios and increase of N:P ratios from the Oi to the Oa horizons. In conclusion, the study shows that C, N and P net mineralization rates were closely correlated with the organic matter stoichiometry and that these correlations were modified by the degree of decomposition of the organic matter.