Plant and Soil Nitrogen in an Ombrotrophic Peatland,Southern Canada

Ecosystems - We examined the concentration of nitrogen (N) and δ15N in vegetation and peat in the Mer Bleue bog, Ontario, Canada. Compared with other ecosystems, N concentration in bog plant...     

Microbial Metabolic Potential for Carbon Degradation and Nutrient (Nitrogen and Phosphorus) Acquisition in an Ombrotrophic Peatland

This study integrated metagenomic and nuclear magnetic resonance (NMR) spectroscopic approaches to investigate microbial metabolic potential for organic matter decomposition and nitrogen (N) and phosphorus (P) acquisition in soils of an ombrotrophic peatland in the Marcell Experimental Forest (MEF), Minnesota, USA. This analysis revealed vertical stratification in key enzymatic pathways and taxa containing these pathways. Metagenomic analyses revealed that genes encoding laccases and dioxygenases, involved in aromatic compound degradation, declined in relative abundance with depth, while the relative abundance of genes encoding metabolism of amino sugars and all four saccharide groups increased with depth in parallel with a 50% reduction in carbohydrate content. Most Cu-oxidases were closely related to genes from Proteobacteria and Acidobacteria, and type 4 laccase-like Cu-oxidase genes were >8 times more abundant than type 3 genes, suggesting an important and overlooked role for type 4 Cu-oxidase in phenolic compound degradation. Genes associated with sulfate reduction and methanogenesis were the most abundant anaerobic respiration genes in these systems, with low levels of detection observed for genes of denitrification and Fe(III) reduction. Fermentation genes increased in relative abundance with depth and were largely affiliated with Syntrophobacter. Methylocystaceae-like small-subunit (SSU) rRNA genes, pmoA, and mmoX genes were more abundant among methanotrophs. Genes encoding N₂ fixation, P uptake, and P regulons were significantly enriched in the surface peat and in comparison to other ecosystems, indicating N and P limitation. Persistence of inorganic orthophosphate throughout the peat profile in this P-limiting environment indicates that P may be bound to recalcitrant organic compounds, thus limiting P bioavailability in the subsurface. Comparative metagenomic analysis revealed a high metabolic potential for P transport and starvation, N₂ fixation, and oligosaccharide degradation at MEF relative to other wetland and soil environments, consistent with the nutrient-poor and carbohydrate-rich conditions found in this Sphagnum-dominated boreal peatland.     

Ecological Stoichiometry of Microbial Biomass Carbon,Nitrogen and Phosphorus on Bauxite Residue Disposal Areas

Abstract

Ecological succession by microbial activity on bauxite residue disposal areas (BRDAs) would accumulate nutrients and convert the residue into a soil-like material. However, the role of microorganisms in nutrient cycling remains elusive on BRDAs. Carbon (C), nitrogen (N) and phosphorus (P) ecological stoichiometry is a critical indicator of nutrient cycling in an ecosystem. In order to investigate the changes in nutrients following long-term natural weathering process, the contents of C, N, P, microbial biomass carbon (MBC), nitrogen (MBN), and phosphorus (MBP) were measured in chronological stacks of bauxite residue. Deeply, their ecological stoichiometric characteristics were analyzed. Compared to freshly stacked residue, organic carbon (OC), total nitrogen (TN) and available phosphorus (AP) have increased 89%, 1640%, and 369% after 20?years, respectively. The C/N in 20-year-old residue (BR20) is 12.41, which close to the mean range of soil C/N in China. Bauxite residue C/P and N/P increased significantly with the stacking age increased. MBC/MBN decreased from 6.75 to 4.52 after stacked for 5?years, whilst MBC/MBP increased from 23.74 to 59.16 with stacking age. Data analysis of C, N, P and MBC, MBN, MBP in bauxite residue correlated significantly, indicating that microbial biomass can be used as a biological indicator to evaluate bauxite residue quality. This study revealed that BRDAs ecosystem development reaches homeostasis gradually, whilst CNP and MBCNP substrate ratio can be used as an effective tool to explore the mechanism of nutrient cycling.     

蕨类植物碳氮磷化学计量特征及其与土壤养分的关系

为探讨蕨类植物碳氮磷化学计量特征与土壤养分的关系,对福建省亚热带森林林下芒萁和乌毛蕨地上部分和地下部分的碳、氮、磷(C、N、P)含量和0~10 cm和10~20 cm两个土层的养分含量进行了测定。结果表明,无论是芒萁还是乌毛蕨,地上部分的N、P含量均高于地下部分,而C含量则无显著差异,导致地上部分的C∶N和C∶P均低于地下部分。与乌毛蕨相比,芒萁地上部分的N、P含量更低,地上和地下部分的C含量、C∶N和C∶P以及N、P含量的变异系数和表型可塑性指数则更高,表明芒萁采取了较高的养分利用效率和"表现最大化"的策略,而乌毛蕨则选择了较低的养分利用效率和"表现维持"的方式。两种蕨类植物地上和地下部分的N含量与土壤N含量(0~20 cm)均无显著相关。芒萁两个部位的P含量则均与土壤P含量(0~10 cm和10~20 cm)呈显著正相关,乌毛蕨P含量总体上与土壤P含量的相关性不显著(除地下部分的P含量与10~20 cm土层的P含量呈弱的正相关外)。这表明芒萁具有作为亚热带森林土壤P库指示植物的潜力。     

天坑森林植物叶-凋落物-土壤C、N、P生态化学计量特征

为探究广西乐业大石围天坑森林群落的C、N、P养分循环特征,比较了天坑内外森林群落的植物叶片-凋落物-土壤C、N、P含量及其化学计量比,采用相关性分析和冗余分析等统计方法研究其内在联系和相互影响。结果表明,与天坑外部森林相比,天坑内部森林植物叶片和凋落物呈现出C低N、P高,土壤为C、N低P高的格局。植物叶片C:N、C:P与凋落物C、N:P显著正相关,植物叶片C与土壤P显著负相关;天坑外部森林的植物叶片N、N:P与土壤N:P显著负相关,植物叶片C:N与土壤C、C:N显著正相关,说明天坑森林内部凋落物的C、P养分可能主要来源于植物叶片,而天坑外部森林的植物叶片C、N主要来自土壤。土壤C:N:P对植物叶、凋落物的C:N:P变化的解释率分别为90.7%和50.6%,其中土壤P对植物叶和凋落物的C:N:P计量特征变化的解释度最高,坑内生境植物对P含量变化更为敏感、坑外植物对于N含量变化更为敏感,表明天坑内部森林可能是P素受限位点、天坑外部森林是N素受限位点。喀斯特天坑内部森林和外部森林植物叶-凋落物-土壤的C:N:P的差异和联系,体现了天坑内外森林群落的养分循环特征和植物群落的适应性。     

Carbon,Nitrogen and Phosphorus Accumulation and Partitioning,and C:N:P Stoichiometry in Late-Season Rice under Different Water and Nitrogen Managements

Water and nitrogen availability plays an important role in the biogeochemical cycles of essential elements, such as carbon (C), nitrogen (N) and phosphorus (P), in agricultural ecosystems. In this study, we investigated the seasonal changes of C, N and P concentrations, accumulation, partitioning, and C:N:P stoichiometric ratios in different plant tissues (root, stem-leaf, and panicle) of late-season rice under two irrigation regimes (continuous flooding, CF; alternate wetting and drying, AWD) and four N managements (control, N0; conventional urea at 240 kg N ha⁻¹, UREA; controlled-release bulk blending fertilizer at 240 kg N ha⁻¹, BBF; polymer-coated urea at 240 kg N ha⁻¹, PCU). We found that water and N treatments had remarkable effects on the measured parameters in different plant tissues after transplanting, but the water and N interactions had insignificant effects. Tissue C:N, N:P and C:P ratios ranged from 14.6 to 52.1, 3.1 to 7.8, and 76.9 to 254.3 over the rice growing seasons, respectively. The root and stem-leaf C:N:P and panicle C:N ratios showed overall uptrends with a peak at harvest whereas the panicle N:P and C:P ratios decreased from filling to harvest. The AWD treatment did not affect the concentrations and accumulation of tissue C and N, but greatly decreased those of P, resulting in enhanced N:P and C:P ratios. N fertilization significantly increased tissue N concentration, slightly enhanced tissue P concentration, but did not affect tissue C concentration, leading to a significant increase in tissue N:P ratio but a decrease in C:N and C:P ratios. Our results suggested that the growth of rice in the Taihu Lake region was co-limited by N and P. These findings broadened our understanding of the responses of plant C:N:P stoichiometry to simultaneous water and N managements in subtropical high-yielding rice systems.     

青藏高原东缘亚高山针叶林碳氮磷生态化学计量特征

为深入理解针叶林生态系统植物叶片和土壤碳(C)、氮(N)、磷(P)生态化学计量特征及其内在相互关系,该研究以青藏高原东缘亚高山岷江冷杉(Abies faxoniana)林(针叶林Ⅰ)、云杉(Picea asperata)林(针叶林Ⅱ)、油松(Pinus tabuliformis)林(针叶林Ⅲ)为研究对象,测定了3种林分针叶、灌木、草本和土壤的碳、氮、磷含量及其比值。结果表明：(1)3种针叶林植物叶片C、N含量表现为草叶>针叶>灌叶>土壤;C∶N、C∶P、N∶P表现为灌叶最高、针叶和草叶次之,土壤最低。其中C、N、P含量均表现为云杉林>冷杉林>油松林;同一针叶林不同组分C、N、P含量均表现为草叶>针叶>灌叶。(2)不同针叶林C∶N和C∶P均表现出油松林>冷杉林>云杉林,而叶片C∶N、C∶P均表现为灌叶>针叶>草叶。(3)针叶林植物叶片N与P含量呈显著正相关关系,针叶与灌叶的C含量、针叶 灌叶 草叶之间的N、P含量以及C∶N、C∶P均呈显著正相关关系;针叶的C含量与其自身的N、P含量呈极显著负相关关系,针叶与土壤TP和N∶P、灌叶与土壤TP含量、草叶与土壤N∶P均呈显著负相关关系,体现了营养元素在针叶林针叶、灌叶、草叶和土壤之间的相互循环和转移。研究认为,青藏高原东缘亚高山针叶林植物生长受N限制,该区域土壤有机质的矿化作用较慢,在针叶林的保护和经营过程中,要加大对林下植被的保护,提高土壤肥力,从而达到维护森林长期生产力的作用。     

青藏高原高寒草甸植物群落结构和功能对氮、磷、钾添加的短期响应

对中国科学院海北高寒草甸生态系统定位站的矮嵩草草甸水肥样地进行了氮、磷、钾及其组合的施肥处理,研究了施肥对植物群落结构和功能的影响。结果表明:(1)施肥使矮嵩草草甸植物群落物种丰富度减少,不同施肥处理下物种丰富度大小分别为:对照钾磷氮氮磷磷钾氮钾氮磷钾。(2)在氮磷配合施肥处理下,矮嵩草草甸植物群落Shannon-Wiener指数显著高于对照,而其它施肥处理对Shannon-Wiener指数影响不显著。(3)在同一施肥处理下,禾草类和莎草类的重要值明显高于豆科和杂类草功能群,不同施肥处理使禾草、莎草、豆科植物的重要值增加,而杂类草重要值减少。(4)与对照相比,不同施肥(除钾外)处理可不同程度的增加植物群落的高度。(5)除钾、磷钾养分添加对矮嵩草草甸地上生物量的影响与对照差异不显著外,其它养分及其组合添加都极显著增加了群落地上生物量,且大小顺序依次为氮磷氮磷钾磷氮钾氮磷钾钾对照。(6)施用不同种类的肥料后,矮嵩草草甸各功能群地上生物量的比例变化明显,禾草和莎草的比例均增加,杂类草的比例减少,而豆科植物无规律性。(7)熵值法综合评价短期施肥处理对矮嵩草草甸群落的影响表明,氮磷、氮磷钾配合施肥是青藏高原高寒草甸最佳施肥选择。     

Nutrient Input and Carbon and Microbial Dynamics in an Ombrotrophic Bog

Slow rates of plant production and decomposition in ombrotrophic bogs are believed to be partially the result of low nutrient availability. To test the effect of nutrient availability on decomposition, carbon dioxide (CO₂) flux dynamics, microbial biomass, and nutrients, we added nitrogen (N) with phosphorus (P) and potassium (K), to prevent limitation of the latter 2 nutrients, over 2 growing seasons to plots at Mer Bleue peatland, Ontario, Canada. After the first growing season, increasing N fertilization (with constant P and K) decreased in vitro CO₂ production potential and increased microbial biomass measured with a chloroform fumigation-extraction technique in the upper peat profile, while by the end of the second season, CO₂ production potential was increased in response to N plus PK treatment, presumably due to more easily decomposable newly formed plant material. In situ CO₂ fluxes measured using chamber-techniques over the second year corroborated this presumption, with greater photosynthetic CO₂ uptake and ecosystem respiration (ER) during high N plus PK treatments. The more efficient microbial community, with slower CO₂ production potential and larger biomass, after the first year was characterized by larger fungal biomass measured with signature phospholipid fatty acids. The majority of N was likely quickly sequestered by the vegetation and transferred to dissolved organic forms and microbial biomass in the upper parts of the peat profile, while additional P relative to controls was distributed throughout the profile, implying that the vegetation at the site was N limited. However, in situ CO₂ flux data suggested the possibility of P or NPK limitation. We hypothesize that nutrient deposition may lead to enhanced C uptake by altering the microbial community and decomposition, however this pattern disappears through subsequent changes in the vegetation and production of more readily decomposable plant tissues.     

不同种源中间锦鸡儿碳氮磷化学计量特征研究

中间锦鸡儿(Caragana liouana)是中国毛乌素沙地的主要灌木建群种,在其主要分布区采集9个不同地理种源的种子,栽种至同质园,并测定不同器官(根、茎、叶)碳(C)、氮(N)、磷(P)含量,比较种源和器官间碳氮磷化学计量特征的差异及元素之间的相关性。结果显示:(1)不同种源中间锦鸡儿根、茎、叶的C含量差异显著,分别为361.12~426.30mg·g~(-1)、412.32~463.13mg·g~(-1)、419.21~478.94mg·g~(-1);N含量种源间差异显著,分别为20.52~33.67mg·g~(-1)、15.77~23.92mg·g~(-1)、27.60~36.44mg·g~(-1);P含量种源间差异显著,分别为1.52~3.73mg·g~(-1)、1.24~2.14mg·g~(-1)、1.44~2.38mg·g~(-1);不同器官的C/N、C/P、N/P也表现出种源间显著差异。(2)种源和器官对中间锦鸡儿碳氮磷化学计量特征的影响程度存在差异,种源对P、C/P、N/P影响较大,器官对C、N、C/N影响较大。(3)相关性分析表明,N、P分别对C/N和C/P的变异起主导作用,并共同影响N/P的变异。研究表明,中间锦鸡儿的碳氮磷化学计量特征在长期的适应进化过程中已产生遗传分化,并形成了自身的养分利用策略。     

Bacterial and Fungal Communities in a Degraded Ombrotrophic Peatland Undergoing Natural and Managed Re-Vegetation

The UK hosts 15–19% of global upland ombrotrophic (rain fed) peatlands that are estimated to store 3.2 billion tonnes of carbon and represent a critical upland habitat with regard to biodiversity and ecosystem services provision. Net production is dependent on an imbalance between growth of peat-forming Sphagnum mosses and microbial decomposition by microorganisms that are limited by cold, acidic, and anaerobic conditions. In the Southern Pennines, land-use change, drainage, and over 200 years of anthropogenic N and heavy metal deposition have contributed to severe peatland degradation manifested as a loss of vegetation leaving bare peat susceptible to erosion and deep gullying. A restoration programme designed to regain peat hydrology, stability and functionality has involved re-vegetation through nurse grass, dwarf shrub and Sphagnum re-introduction. Our aim was to characterise bacterial and fungal communities, via high-throughput rRNA gene sequencing, in the surface acrotelm/mesotelm of degraded bare peat, long-term stable vegetated peat, and natural and managed restorations. Compared to long-term vegetated areas the bare peat microbiome had significantly higher levels of oligotrophic marker phyla (Acidobacteria, Verrucomicrobia, TM6) and lower Bacteroidetes and Actinobacteria, together with much higher ligninolytic Basidiomycota. Fewer distinct microbial sequences and significantly fewer cultivable microbes were detected in bare peat compared to other areas. Microbial community structure was linked to restoration activity and correlated with soil edaphic variables (e.g. moisture and heavy metals). Although rapid community changes were evident following restoration activity, restored bare peat did not approach a similar microbial community structure to non-eroded areas even after 25 years, which may be related to the stabilisation of historic deposited heavy metals pollution in long-term stable areas. These primary findings are discussed in relation to bare peat oligotrophy, re-vegetation recalcitrance, rhizosphere-microbe-soil interactions, C, N and P cycling, trajectory of restoration, and ecosystem service implications for peatland restoration.     

入侵植物曼陀罗对本地植物功能性状和土壤碳、氮、磷化学计量特征的影响

为探讨不同入侵压力下入侵植物对本地植物功能性状土壤碳、氮、磷化学计量特征的影响,以入侵植物曼陀罗（Datura stramonium）及共存本地植物为研究对象,调查了无入侵区、轻度入侵区和重度入侵区（按入侵种盖度比例划分）的植物种类、株数、株高及本地植物群落的物种多样性,分析了各区入侵植物和本地植物叶片的比叶面积、碳含量、氮含量、碳氮比、叶片建成成本以及不同土层的碳、氮、磷化学计量特征。结果显示：随曼陀罗入侵压力的增加,本地植物种类及株数逐渐减少;曼陀罗株高和叶片氮含量在不同入侵压力下均显著高于本地植物,且随入侵压力的增加具有升高趋势;叶片碳氮比显著低于无入侵区本地植物;比叶面积、叶片碳含量和叶片建成成本等与入侵区本地植物相比不具有显著差异。随曼陀罗入侵压力的增加,土壤全氮含量、全碳含量、氮磷比与碳磷比显著增加,而全磷含量与碳氮比显著下降;土壤碳氮化学计量特征呈现出一定的表聚效应。这些研究结果表明,曼陀罗具有较高的资源捕获能力,并且改变了入侵地土壤特性,进而增强自身竞争能力以提高入侵力,这些可能是曼陀罗成功入侵的原因之一。     

不同杉木林分类型土壤团聚体生态化学计量特征

在野外调查的基础上,选择成土母质相同、坡向坡度相似、海拔基本一致的杉木-米老排、杉木-火力楠和杉木纯林3种杉木人工林采集土壤样品,通过干筛法分离＞2 mm、2～0.25 mm和＜0.25 mm 3个团聚体组分,研究其土壤团聚体有机碳、全氮、全磷的含量及其生态化学计量特征,以阐明不同杉木林分类型土壤团聚体碳氮磷生态化学计...     

Absorption of Nitrogen, Phosphorus, and Potassium from Nutrient Sprays by Leaves

Barley, Brussels sprout, French bean, tomato, and sugar-beetplants grown in soil in pots and sprayed, usually daily, forseveral weeks, with nutrient solutions containing nitrogen,phosphorus, potassium, and a spreader, with precautions to preventthe spray solution falling on the soil, had higher nutrientcontents and dry weights than control plants sprayed with waterand spreader only. Increase in nutrient content occurred withhigh or low levels of nutrient supply to the roots and was approximatelyproportional to the concentration of spray and to the frequencyof spraying. The nitrogen content of sugar-beet plants was increased equallyby spraying with solutions supplying ammonium sulphate, calciumnitrate, or urea in equivalent concentrations. Nutrient uptake from solutions sprayed on leaves influenceduptake by the roots so that the additional amounts of nutrientcontained in sprayed plants may be greater or smaller than theamount absorbed from the spray by the leaves.     

Climate Records,Isotopes, and C:N Stoichiometry Reveal Carbon and Nitrogen Flux Dynamics Differ Between Functional Groups of Ectomycorrhizal Fungi

Ecosystems - A major functional division in ectomycorrhizal fungi is between taxa with hydrophobic ectomycorrhizae (strong proteolytic capabilities, deep nitrogen (N) acquisition, and extensive...     

海南岛海岸带木麻黄和厚藤叶片碳、氮、磷含量及其化学计量特征

海岸带植物叶片的化学计量学特征及其影响因素可以为改善海岸带的生态环境提供理论依据。选取海南岛沿岸12个市（县）海岸带木麻黄防护林的木麻黄和周边沙滩上的藤本植物厚藤为研究对象,通过测定木麻黄与厚藤叶片中的碳（C）、氮（N）和磷（P）含量,分析两种植物叶片C、N和P的化学计量学特征及其差异,探究不同环境因子对两种植物叶片C、N、P含量、C：N、C：P和N：P的影响,以期寻找影响海岸带植被生长的主要限制因素。结果表明：海南岛木麻黄叶片C、N和P的平均含量分别是399.06±20.29、12.56±1.04、1.04±0.35 g·kg^-1,C：N、C：P和N：P分别为32.04±2.82、420.65±121.27和12.92±3.21;厚藤叶片C、N和P的平均含量分别是364.31±30.20、12.84±1.96和2.06±0.64 g·kg^-1,C：N、C：P和N：P分别为29.13±4.95、185.85±63.14和6.47±2.12。相关性分析结果表明：木麻黄叶片的N含量与年平均气温和年平均降水量呈显著正相关关系,P含量与年平均降水量呈极显著正相关关系,C：P和N：P与年平均降水量呈显著负相关关系;厚藤叶片C含量与年平均气温呈显著正相关,C：N与年平均降水量呈显著负相关。木麻黄叶片的N含量与10~20 cm土层的SOC呈显著负相关关系,C：N与10~20 cm土层的SOC呈显著正相关,C：P与0~10 cm土层的C：N呈显著正相关关系;厚藤叶片的C含量与10~20 cm土层的SOC呈显著负相关关系,P含量与0~10 cm土层的TN含量,N：P和10~20 cm的SOC含量呈正相关关系,C：N与0~10 cm土层的C：N呈显著正相关关系,C：P与0~10 cm的TN含量呈显著负相关关系而与0~10 cm土层的C：N呈极显著正相关关系,N：P与0~10 cm土层的TN含量呈显著负相关关系。研究结果表明海南岛海岸带植被叶片的碳氮含量较低,N可能是影响该区域植物生长的主要因子,同时,植被生长受到年平均气温、年平均降水量的共同影响,受土壤养分含量影响低,环境因子对不同类型的植物的影响并不相同。     

Estimating Annual Soil Carbon Loss in Agricultural Peatland Soils Using a Nitrogen Budget Approach

Around the world, peatland degradation and soil subsidence is occurring where these soils have been converted to agriculture. Since initial drainage in the mid-1800s, continuous farming of such soils in the California Sacramento-San Joaquin Delta (the Delta) has led to subsidence of up to 8 meters in places, primarily due to soil organic matter (SOM) oxidation and physical compaction. Rice (Oryza sativa) production has been proposed as an alternative cropping system to limit SOM oxidation. Preliminary research on these soils revealed high N uptake by rice in N fertilizer omission plots, which we hypothesized was the result of SOM oxidation releasing N. Testing this hypothesis, we developed a novel N budgeting approach to assess annual soil C and N loss based on plant N uptake and fallow season N mineralization. Through field experiments examining N dynamics during growing season and winter fallow periods, a complete annual N budget was developed. Soil C loss was calculated from SOM-N mineralization using the soil C:N ratio. Surface water and crop residue were negligible in the total N uptake budget (3 – 4 % combined). Shallow groundwater contributed 24 – 33 %, likely representing subsurface SOM-N mineralization. Assuming 6 and 25 kg N ha-1 from atmospheric deposition and biological N2 fixation, respectively, our results suggest 77 – 81 % of plant N uptake (129 – 149 kg N ha^-1) was supplied by SOM mineralization. Considering a range of N uptake efficiency from 50 – 70 %, estimated net C loss ranged from 1149 – 2473 kg C ha^-1. These findings suggest that rice systems, as currently managed, reduce the rate of C loss from organic delta soils relative to other agricultural practices.     

Alternate Bearing Affects Nitrogen, Phosphorus, Potassium and Starch Storage Pools in Mature Pistachio Trees

The relationship between crop load and the functional storageof selected macronutrients and starch was assessed to developnutrient budgets and best management fertilization practicesin orchards. Functional storage represents the amount of nutrientsand starch redistributed from perennial tree parts in supportof the spring growth flush. Functional storage was influencedby:(a)nutrient and starch accumulation prior to dormancy; and(b)nutrientand starch demand by vegetative and reproductive organs in spring.Lightly cropping (off-year) trees stored 7, 14 and 2 times asmuch N, P and K, respectively, as heavily cropping (on-year)trees. Similar to many biennial plant species, nutrients thataccumulated during the vegetative phase in off-year trees wereused to support reproductive growth during the subsequent on-year.Soil nutrient uptake contributed more to storage pools thanleaf nutrient resorption in off-year-trees, while the reversewas true in on-year trees. Net nutrient resorption from senescingleaves accounted for all of the N and P and a third of the Kstored in on-year trees. Only between 20–33% of the N,P and K stored in perennial tissues of off-year trees couldbe attributed to leaf nutrient resorption. This is the firststudy to determine the amounts of nutrients stored in the perennialparts of mature, field-grown trees and the relative contributionsof leaf nutrient resorption and soil nutrient uptake to functionalstorage in trees.Copyright 1998 Annals of Botany Company Pistacia vera, nutrient storage, biennial bearing, crop load, leaf nutrient resorption, source-sink relationships.     

Effect of Nitrogen, Phosphorus and Potassium Additions on Plant Biomass and Soil Nutrient Content of a Swale Barrier Strand Community in Louisiana

Fertilization of a swale plant community with various levelsand combinations of nitrogen, phosphorus and potassium resultedin increased plant growth. Nitrogen addition produced the greatestincrease in biomass. At some high nitrogen levels, phosphoruslimited plant production. Potassium fertilization did not influenceplant growth. Phosphorus fertilization decreased the levelsof soil calcium, magnesium and manganese. A shore-perpendiculargradient in apparent saltwater inundation influenced soil pHand the concentrations of iron, phosphorus, and magnesium. Fertilizer effects, swale Scirpus americanus, Spartina patens, nitrogen limitation     

Influence of Nitrogen Supply and Water Stress on Growth and Nitrogen, Phosphorus, Potassium and Calcium Contents in Pearl Millet

Influence of supra-optimal concentrations of N on growth and accumulation of N, K, P and Ca in the shoots and roots in Pennisetum glaucum (L.) R.Br. under water stress was assessed in a pot experiment under glasshouse conditions. Thirty four-day-old plants of two lines, ICMV94133 and WCA-78, were subjected to 224, 336, or 448 mg(N) kg^–1(soil) and soil moisture 100 or 30 % of field capacity for 30 d. Increasing soil N supply decreased growth of both lines under water deficit. Nitrogen content in the shoots of both lines was not affected by supra-optimal levels of N or different watering regimes, but in contrast, the root N content was increased consistently in WCA-78 with increase in soil N content. Shoot P content increased considerably in WCA-78 at the two higher N contents, but it was significantly lower at drought stress than at well-watered treatment. In contrast, shoot or root P content in ICMV94133 did not differ under both watering regimes. Potassium content in the shoots of WCA-78 was considerably increased at the two higher N contents under drought conditions. Root K content was increased in WCA-78 at the highest N content under well-watered conditions, whereas the reverse was true in ICMV94133. Calcium content in the shoots of ICMV94133 was higher under drought stress compared with that at well-watered conditions, but such pattern was not observed in WCA-78. However, root Ca content increased in both lines with increase in N supply.