Correlated Biogeographic Variation of Magnesium across Trophic Levels in a Terrestrial Food Chain

Using samples from eastern China (c. 25 – 41° N and 99 – 123° E) and from a common garden experiment, we investigate how Mg concentration varies with climate across multiple trophic levels. In soils, plant tissue (Oriental oak leaves and acorns), and a specialist acorn predator (the weevil Curculio davidi), Mg concentration increased significantly with different slopes from south to north, and generally decreased with both mean annual temperature (MAT) and precipitation (MAP). In addition, soil, leaf, acorn and weevil Mg showed different strengths of association and sensitivity with climatic factors, suggesting that distinct mechanisms may drive patterns of Mg variation at different trophic levels. Our findings provide a first step toward determining whether anticipated changes in temperature and precipitation due to climate change will have important consequences for the bioavailability and distribution of Mg in food chain.     

人工埋藏植物种子对鼠类采食下辽东栎坚果存活及萌发率的影响

辽东栎林（Q. liaotungensis)是北京东灵山地区典型地带植被。过去研究表明,鼠类对辽东栎更新有很大影响。本研究主要调查3个问题：（1）采食辽东栎坚果的鼠类种类;（2）将坚果埋藏于土中能否减少鼠类对坚果的采食,并提高出苗率？（3）地表植被是否影响辽东栎的出苗率？1996年9月在北京东灵山地区山地选取5个类型的样地37块,每样地在地表放置10粒坚果,检查地表种子消失率。使用木板夹来调查采食坚果的鼠类种类,诱饵分别为坚果和花生米。于1997年10月,选取5块样地,间隔25 m,每样地在1m²范围内埋50粒坚果,深度5 cm,次年5月调查出苗情况。研究结果表明,大林姬鼠、社鼠和黑线姬鼠为取食坚果的主要种类,取食比例与其丰富度有关。370粒坚果放在地表后,1d、10d、20d的消失率分别达15.1%、78.1%、和 100%。250粒坚果埋入土层后,出苗率达11.2%,苗平均高度为7.8cm,出苗率与地表植被盖度有一定负相关。本研究认为,人工埋藏植物种子可以减少鼠类捕食坚果,并能增加其出苗率。     

Distribution,Accumulation, and Cycling of Several Mineral Elements of the Lower Subtropical Evergreen Broad-Leaved Forest in Heishiding Nature Reserve

The distribution, accumulation, and cycling of N, P, K, Na, Ca, and Mg in terms of their concentration in the biomass was quite different from those in soil in Heishiding Nature Reserve (111°53′ E, 23°27′ N). The concentrations of N, Ca and P were higher in plant, and much lower in soil. The average content of the elements in different organs was in the order as: leaf>branch>bark>root>wood, although this was not true for all the elements. Trunk and leaf had the most and the least accumulation of the elements, respectively, and branch and root were comparable. In the forest, most of the elements (97 %) were concen- trated in the tree layer. The total amount of elements in the ecosystem was 3324.2 kg· ha-1 among which N amounted 1470.5, P 51.0, K 1097.7, Na 22.6, Ca 566.2, and Mg 116.2. Yearly absorption of the elements was 432.2 kg · ha-1 among which N amounted 207.1, P 6.5, K 144.9, Na 6.9, Ca 52.6, and Mg 14. 1; and element absorption among different organs accounted as 35.0 kg · ha-1 · a-1 in wood, 14.8, in bark, 66.1 in branch, 143.2 in leaf, 25.3 in root, and 147.7 in fine root (D<3 mm). Total return of the elements from litterfall, death and fallen trees was 311.8 kg · ha-1 · a-1, among which N accounted for 154.3, P 4.7, K 102.1, Na 6.2, Ca 34.5, and Mg 10.0. Return from different organs was: wood 10.2, bark 4.3, branch 17.0, leaf 123.0, root (not in- cluding fine root) 9.4, and fine root 147.7. Total retention was 120.4 kg · ha-1 · a-1 among which N accounted for 52.8, P 1.8, K 42.8, Na 0. 7, Ca 18. 1, and Mg 4.1; retention in different organs was: wood 24.8, bark 10.5, branch 49.1, leaf 20. 2, and root 15.9. Ca, Mg and P have higher cycling and utilization efficiencies.     

Foliar macronutrient concentrations of forest understorey species in relation to Ellenberg's indices and potential relative growth rate

In order to investigate broad patterns of variation of the foliar mineral nutrient concentrations of herbaceous plant communities in the ground layer of W Europe forests, correlations were examined between Ellenberg's indices (N-index: mineral nitrogen availability, R-index: pH, F-index: soil moisture and L-index: light intensity) and literature values of macronutrient concentrations for 84 forbs and 39 graminoid species. Significant, positive correlations were found between the R-index and the plants' concentration of Ca and K (forbs only) and between the N-index and the plants' concentration of K, P (forbs only) and N (forbs and graminoids). Multiple regressions showed that the N-index was the best predictor of the plants' concentration of N (forbs and graminoids), P (forbs) and Ca (graminoids) and the R-index of the plants' concentration of Ca and K (forbs). The mineral nutrient concentrations of graminoids were lower and less strongly correlated with Ellenberg's indices than those of forbs. It is argued that the mineral nutrient concentrations in the plants match the availability of mineral nutrients in the soil for N, P (N-index) and Ca (R-index), but not for K and Mg. Significant, positive correlations were found between potential relative growth rate and the concentration of some elements (N, P, K and Ca in forbs, Ca and Mg in graminoids). This suggests that the increase in the concentration of these elements in plants along fertility gradients is due, at least partly, to genetically controlled alterations of leaf anatomy associated with increasing potential relative growth rate.     

The Rengen Grassland Experiment: relationship between soil and biomass chemical properties, amount of elements applied, and their uptake

The Rengen Grassland Experiment (RGE) was established in the Eifel Mountains (Germany) on a low productive Nardetum in 1941. Since then, the following fertilizer treatments have been applied with a late two-cut system: unfertilized control, Ca, CaN, CaNP, CaNPKCl and CaNPK₂SO₄. We aimed to understand how concentrations of macro (N, P, K, Ca and Mg), micro (Cu, Fe, Mn and Zn) and trace (As, Cd, Cr, Ni and Pb) elements in the plant biomass were affected by long-term fertilizer application, soil chemical properties and biomass production. In 2008, biomass samples from the first cut (early July) and the second cut (mid-October) were collected and analyzed. The simultaneous application of N, P and K decreased nitrogen concentration in the aboveground biomass, but substantially increased biomass production. Late cutting management decreased forage quality in highly productive more than in low productive plant communities. The concentrations of P and K in the plant biomass were positively related to P and K application and, therefore, to plant available P and K concentrations in the soil. The concentrations of some micro (Fe, Mn and Zn) and trace (As, Cd, Cr, Ni and Pb) elements in the plant biomass were negatively correlated with the amount of elements supplied by fertilizers and biomass production, probably because of the dilution effect. Long-term fertilizer application resulted in the accumulation of macro (P, Ca and Mg), micro (Fe and Mn) and trace (As and Cr) elements in the soil, but in many cases this accumulation was not connected with an increase in the concentrations of these elements in the plant biomass. Nutritional status, as indicated by the biomass N:P ratio, was consistent with N or P limitation as indicated by the nitrogen and phosphorus nutrition indices. Furthermore, additional K (co-)limitation was indicated by the N:K and K:P ratios in the biomass from the NP treatment. The results from the RGE indicate that there is no simple positive relationship between the applied elements and their concentrations in the plant biomass.     

滇南喀斯特地区不同季节土壤和灌木叶片化学计量特征及对水分添加的响应

干旱是影响南方喀斯特地区植物生长的重要限制因子, 气候变化会影响该地区的降水量和分布格局。研究该地区土壤和植物化学计量特征及其水分响应格局, 具有重要意义。自2017年4月开始, 在云南建水喀斯特植物群落进行加水试验, 2018年4月(旱季)和8月(雨季)分别采集土壤和优势灌木鞍叶羊蹄甲(Bauhinia brachycarpa)和假虎刺(Carissa spinarum)叶片样品, 测定碳、氢、氮、磷、硫、钾、钙、镁、铝、钠、铁、锰、锌、铜14种元素含量。结果表明, 水分添加影响了表层土壤中碳、氮、钠的含量, 相比于旱季, 雨季土壤中钠和硫含量明显减少, 其余土壤元素在水分添加和季节变化下并未表现出明显差异。土壤水分含量的增加使得鞍叶羊蹄甲和假虎刺叶片中钾含量下降, 钙含量上升。在水分条件变化下, 两种植物叶元素含量的稳定性与植物中元素的含量有关, 含量越接近极大值(基本元素碳、氢、氮等)或极小值(微量元素铜、锌等)的元素其变异系数越小(越稳定), 两种植物中含量接近于1 mg·g^-1的元素磷、硫、镁的变异系数最高。在土壤水分条件变化下, 假虎刺中碳、氮、磷等大量元素含量的稳定性显著高于鞍叶羊蹄甲。降水变化和水分添加导致的土壤水分变化, 对滇南喀斯特地区土壤和植物中不同元素含量的影响不同, 这些结果将为该地区的土壤、植被修复和管理提供科学参考。     

Taxonomic effect on plant base concentrations and stoichiometry at the tips of the phylogeny prevails over environmental effect along a large scale gradient

Despite the well‐known importance of all elements to plant growth and nutrient fluxes in ecosystems, most studies to date have been restricted to the roles of foliar nitrogen (N) and phosphorus (P). Much less is known about cycling and pools of base cations in ecosystems and the drivers of variation in cation concentrations among plant species, even though these cations are paramount for plant and ecosystem function. In particular, little is known about the contributions of taxonomic position and environmental variation on base cation concentrations. The extent to which concentrations of elements in plants are determined by phenotypic response to their availability in current environments versus by inherent species‐specific uptake and processing adaptations, should be most directly evident at the tips of the phylogeny, where inherent variation among species should reflect relatively recent adaptation to environmental variation since their common ancestry. To test this hypothesis, we explored the geographic pattern and the effects of taxonomy, climate and soil on concentrations and stoichiometry of the base cations potassium (K), sodium (Na), calcium (Ca) and magnesium (Mg) across a lineage of Artemisia species and their close relatives across northern China. We found that species identity explained the largest proportion of the total variance for all four base cations (38.3–53.8%) and their stoichiometry (35.2–59.6%). K, Na and Ca concentrations increased significantly with climate seasonality, while Ca concentration decreased with annual temperature and precipitation. Plant K concentration, K:Ca and K:Mg were negatively correlated with soil organic carbon concentrations, but positively with soil pH. Our results suggest that taxonomy still needs to be fully considered for interpreting variation in vegetation nutrition and stoichiometry along broad geographical gradients even for species at the tips of the phylogeny.     

Litter fall and nutrient dynamics in a Nigerian rain forest seven years after a ground fire

Abstract. Seasonal litter fall and mineral element content (N, P, Ca, Mg, K) of regrowth forest communities at the base and on the slope of an inselberg in Ile-Ife, Nigeria, were studied 7 yr after a ground fire ravaged the forest. Litter fall (tha^?1 yr^?1) was 4.6 (total), 4.2 (leaf), 0.3 (small wood < 2.5 cm diameter) and 0.1 (reproductive parts: fruits and flowers) in the base community and 6.4 (total), 5.4 (leaf), 0.9 (small wood) and 0.1 (reproductive parts) in the slope community. There was significant monthly variation in litter fall in the two communities with lowest amount of litter recorded during the wettest months of the year (May - August) and the highest amount during the dry season. Significant monthly variation (P<0.05) in Ca, Mg and K concentration in leaf litter and for Mg (P < 0.01) in fruit litter occurred, with the lowest concentration recorded during the wettest months (May-August). In leaf and wood litter the order of mineral element concentration was Ca>N>K> Mg > P while in fruit litter it was N > K > Ca > Mg > P. Quantities of mineral element (kg ha^-1 yr¹) returned to the soil via litterfall were N: 66; P: 4; Ca: 97; Mg: 15; K: 45 in base forest, and N: 112; P: 5; Ca: 142; Mg: 20; K: 66 in slope forest. Through leaf litter >88.5% of these elements was returned into the two communities, through wood > 4.0% and through reproductive organs > 0.3%. The order of quantities of these elements returned in leaf and wood litter was Ca > N > K > Mg > P, in fruit litter N ～ K > Ca > Mg > P. Significant monthly variation in the amounts of the various elements returned were recorded in leaf litter, but not in wood and fruit litter. The lowest amount of various elements was returned during the wettest months (May-August) which coincided with the period of the lowest element concentration and litter fall.     

Testing the distinctness of shoot ionomes of angiosperm families using the Rothamsted Park Grass Continuous Hay Experiment

? The ionome is the elemental composition of a tissue or organism. Phylogenetic variation in the ionomes of plant shoots has been widely reported based on controlled experiments, vegetation surveys and literature meta-analyses. However, environmental effects on phylogenetic variation in shoot ionomes have not been quantified. This study tests the hypothesis that phylogenetic variation in shoot ionomes is robust to environmental perturbation and that plant families can be distinguished by their shoot ionomes. ? Herbage was sampled from six subplots of the Rothamsted Park Grass Experiment. Subplots had received contrasting fertilizer treatments since 1856. Herbage was separated into its constituent species (n?=?21) and concentrations of eleven mineral elements were determined in dried shoot material. ? Shoot concentrations of calcium (Ca), zinc (Zn), manganese (Mn), magnesium (Mg) and sodium (Na) showed significant variation associated with plant species, and responded similarly to fertilizer treatments in diverse plant species. Species?×?treatment interactions were indicated for phosphorus (P), potassium (K), nickel (Ni), copper (Cu) and iron (Fe). Plant families could be distinguished by their shoot ionomes. The most informative elements for discriminant analysis were Ca?>?Mg?>?Ni?>?S?>?Na?>?Zn?>?K?>?Cu?>?Fe?>?Mn?>?P. ? Whilst shoot ionomes were sensitive to fertilizer treatment, phylogenetic variation in a subset of the shoot ionome (Ca, Zn, Mn, Mg) was robust to this environmental perturbation.     

Partitioning of Dry Matter and Mineral Nutrients During a Reproductive Cycle of the Mistletoe Amyema linophyllum (Fenzl.) Tieghem Parasitizing Casuarina obesa Miq.

Budgets for utilization of dry matter, nitrogen and a rangeof mineral elements were constructed for the reproductive season(September 1988–May 1989) of plants of the mistletoe Amyemalinophyllum (Loranthaceae) parasitizing the swamp she oak (Casuarinaobesa Miq.) at Gingin, W. Australia. Shed buds comprised 55%of the allotment of dry matter to reproduction, shed flowers7%, abscised perianths and styles 15%, prematurely shed fruits15%, and successfully ripened fruits a mere 12%. Commitmentto reproductive biomass peaked sharply in October, while thegenerally higher rate of allocation to vegetative biomass declinedfrom beginning to end of the 9-5 month reproductive cycle. Investmentsof dry matter in new leaves and secondary thickening of previousseason's stems were several-fold greater budget items than productionof new stems and shedding of leaves. There was no evidence ofpre-senescence retrieval of N, P, and K from leaves, and concentrationsof Ca, Mg, Na, and Cl increased steadily in dry matter withleaf age. Values for reproductive effort (RE) for dry matterand specific mineral elements were calculated as commitmentto reproduction divided by commitment to reproduction plus vegetativebiomass (? 100). Due to highly differential partitioning ofcertain elements between reproductive and vegetative parts,RE values for minerals for the reproductive season ranged widely,viz. 7% for Ca, 10% for Mn, 15% for Mg, 17% for N, 25% for Kand Zn, 26% for Cu, and 35% for P. The comparable RE for drymatter was 29%. The weight ratio for net intake of nutrientelements from the host by A. linophyllum for the reproductiveseason was 21?5:20?2:6?6:1?6:1 (N:K:Ca:Mg:P), while the meanweight ratio for the concentrations of these elements in xylem(tracheal) sap of the Casuarina host was 13?9:15?6:4?1:30:1,respectively. The data are discussed in relation to the demonstrationof a direct lumen-to-lumen tracheary continuity between hostand mistletoe in mature regions of the haustorial interface. Key words: Mistletoe, resource allocation, mineral nutrition, reproductive effort, host:parasite relationships     

Soil-plant element relationships in a tundra ecosystem

The objectives of this study were to (1) provide a baseline estimate of soil and plant element concentrations for an intensive research site at Imnavait Creek in northern Alaska, and (2) examine the relationships between soil and plant elements in an arctic ecosystem. Soil and plant element concentrations were highly variable along biotic, spatial, and temporal axes. Deciduous shrubs had higher leaf concentration of N, P. K and Mg, whereas an evergreen shrub had higher leaf concentrations of Ca, Mn, Al and Si. Based on high required solution phase turnover rates, the most likely elemental deficiencies are N > P > K > Ca = Mg. Based on low required solution phase turnover rates and high soil concentrations. Fe, Mn, Zn and Cu deficiencies are unlikely. Manganese could be present in toxic concentrations. The nutrient bottleneck in tundra ecosystems appears to be the rate of nutrient movement to the solution phase.     

Prolonged diapause and seed predation by the acorn weevil,Curculio robustus,in relation to masting of the deciduous oak Quercus acutissima

Many researchers have studied the relationship between masting by trees and seed predation by insects. Most of these studies have been plant centered, with little focus on the insect perspective. To estimate the effect of mast seeding on insect seed predators, the life‐history traits of these insects must also be considered because some seed insects can survive lean years by prolonged diapause. In this study, I examined larval infestation of acorns and life‐history traits of the acorn weevil, Curculio robustus (Roelofs) (Coleoptera: Curculionidae), in relation to acorn production of the deciduous oak Quercus acutissima Carruthers (Fagaceae) in a coppice stand in central Japan in 2004–2009. Curculio robustus females oviposit into Q. acutissima acorns, inside which the larvae develop. Mature larvae leave acorns and burrow into the soil, where they overwinter. Although germination did occur in acorns infested by weevil larvae, the percentage of germination was lower in acorns damaged by many larvae. Acorn production in Q. acutissima varied considerably among years. Both the number of C. robustus larvae infesting acorns and the percentage of acorns infested were affected by the amount of acorns produced by Q. acutissima, and two successive lean years appeared to have a considerable impact on C. robustus population size. Consequently, only a small fraction of the acorns produced were lost to predation in a mast year after two successive lean years. However, C. robustus could survive the two successive lean years because of prolonged larval diapause, probably leading to a marked decrease in population size. These findings suggest that masting in Q. acutissima succeeds as a predator satiation strategy in response to acorn damage by C. robustus, and that C. robustus has developed prolonged diapause as a counter‐adaptation.     

元谋干热河谷燥红土和变性土上植物叶片的元素含量及其重吸收效率

采用盆栽试验,研究元谋干热河谷燥红土和变性土上生长的植物叶片以及凋落叶营养元素含量,并分析养分重吸收效率对土壤类型与物种互作的响应.结果表明: 土壤类型对叶片N、P、Ca、Mg、Cu、Zn、Fe、N∶P以及凋落叶N、P、Mn、N∶P均有显著影响;燥红土植物叶片与凋落叶N、Mn含量和N∶P显著高于变性土,而燥红土植物叶片P、Ca、Mg、Fe、Cu、Zn和凋落叶P含量显著低于变性土.燥红土植物叶片N含量较变性土高34.8%,而P含量低40.0%;在叶片凋落时,N、P、K表现为重吸收,而其他元素呈富集状态.燥红土凋落叶Ca、Mg、Mn富集系数显著高于变性土.物种仅对叶片N含量有显著影响,物种与土壤交互作用对植物叶片和凋落叶元素含量影响不显著,表明各土壤类型对不同物种元素含量的影响方式较为一致.土壤类型对植物元素含量的影响可进一步作用于干热河谷植物凋落物分解、植物-土壤的养分反馈以及生物地球化学循环.     

神农架常绿落叶阔叶混交林碳氮磷化学计量比

生态化学计量学是研究生态过程中化学元素平衡的科学, 碳(C)、氮(N)、磷(P)化学计量比是生态系统过程及其功能的重要特征。该研究测定了神农架常绿落叶阔叶混交林植物器官、凋落物及土壤的C、N、P含量, 利用生物量加权法计算其化学计量比, 并分析该生态系统不同组分间及不同器官间化学计量比的差异。研究结果发现: 在不同组分之间, C含量、C:N及C:P表现为植物>凋落物>土壤; N、P含量及N:P表现为凋落物>植物>土壤。在不同植物器官间, C含量的差异较小, 其变异系数相对N、P含量较低且保持稳定; N、P含量为叶片最高且变异系数最低; N:P为树皮最高, 而枝的变异系数最低。常绿与落叶树种的叶片N、P含量差异显著。与不同森林类型的化学计量比相比, 该常绿落叶阔叶混交林植物群落的C:P及N:P较低, 凋落物的C:P及N:P较高, 土壤的C、N、P化学计量比与亚热带常绿阔叶林基本一致, 生态系统的C:N相对较低。利用生物量加权法计算得到的该森林生态系统不同组分的C、N、P化学计量比的大小关系与前人利用枝叶取样算术平均的结果存在较大差异。C、N、P含量及其化学计量比在不同器官的分配及内稳性与器官的生理功能关系密切。     

Mineral Elements in Root of Wild Saposhnikovia divaricata and Its Rhizosphere Soil

Mineral elements are important components of medicinal herbs, and their concentrations are affected by many factors. In this study, Ca, Mg, Na, K, Fe, Mn, Cu, and Zn concentrations in wild Saposhnikovia divaricata and its rhizosphere soil collected from seven locations at two different times in China were measured, and influences of rhizosphere soil on those minerals in plant were evaluated. The results showed that mean concentrations of eight minerals in plant samples decreased in the order: Ca > Mg > Na > K > Fe > Zn > Mn > Cu, and those in the soil samples followed the following order: Na > Fe > Ca > K > Mg > Mn > Zn > Cu. Mean concentrations of Ca, Na, Mg, and K in plants were higher than those in soils, while higher mean concentrations of the other four minerals were found in soils. It was found that there was a positive correlation of Mg, Na, and Cu concentrations in the plant with those in the soil respectively, but a negative correlation of Mn concentration in plant with that in the soil. Except Ca, K, and Mn, the other five minerals in plant were all directly affected by one or more chemical compositions of soil. The results also indicate that pH value and concentrations of total nitrogen, Mg, Mn, and Cu in soil had significant correlations with multimineral elements in plant. In a word, mineral elements uptake of S. divaricata can be changed by adjusting the soil fertility levels to meet the need of appropriate quality control of S. divaricata.     

加拿大一枝黄花对土壤营养元素吸收与转运特征

选择临海沿江镇加拿大一枝黄花重度入侵区域,分别收集植物与土壤样品,研究加拿大一枝黄花对土壤中7种营养元素的吸收、转运特征。研究结果表明：7种营养元素在植物组织中的平均含量排序为：Zn〉K〉Ca〉N〉Mg〉P〉Mn。而且不同器官对同一种元素的积累存在显著差异,总体规律表现为叶和花蕾积累元素最多,其次是枝条和根状茎,根和茎则积累最少。地上器官对各元素的转移能力表现出明显差异,但各器官均对氮素有较强的转运能力,转运因子均明显高于1。地下器官（根和根状茎）对氮素有较高的富集能力,富集因子同样明显高于1。7种元素在加拿大一枝黄花不同器官的吸收转运存在着一定的促进或者拮抗作用。在花蕾、枝条和根中,磷吸收分别与Mg、Mn和Zn吸收呈现显著负相关;在花蕾中,氮的吸收和Mn的吸收呈现显著正相关;在不同器官里,K、Ca、Mg、Zn和Mn吸收之间多呈现正相关。     

Element concentrations in the boreal forest moss Hylocomium splendens: variation related to gradients in vegetation and local environmental factors

This study aims at assessing the suitability of Hylocomium splendens as a biomonitor for heavy metal deposition and contributing to the understanding of mineral nutrient uptake mechanisms in forest floor bryophytes. Concentrations of Ca, Mg, K, Cd, Cu and Pb were determined in Hylocomium splendens segment samples collected at 196 permanent vegetation plots from eleven monitoring areas, where the vegetation-environment relationships had previously been thoroughly studied. Element concentrations in Hylocomium splendens were related to environmentally interpreted vegetational gradients, cover of understorey vascular plants, and local environmental conditions, including element concentrations in humus, soil moisture and tree impact, by means of correlation analyses performed separately for each area. A combined test was performed for each Hylocomium splendens variable over all eleven areas, showing that concentrations of Ca, Cd and Mg in Hylocomium splendens were strongly correlated with the main vegetational gradient and with pH and concentrations of Ca and total N in humus, indicating considerable uptake of nutrients by Hylocomium splendens from water that has been in contact with humus. These relationships were less strong in the climatically most humid areas. Concentrations of all elements were more or less strongly correlated with one or more variables reflecting tree influence (tree density as measured by basal area and two crown influence indices) reflecting that throughfall precipitation, modified by leaching from the canopy, partly accounts for input of elements, especially for K, Cd and Mg. Only concentrations of Pb, Cd and Cu were significantly correlated, negatively, with vascular plant cover, indicating that supply of elements by leaching from understorey vascular plant foliage is negligible. The concentration of Cu in Hylocomium splendens was only weakly correlated, and the concentration of Pb unrelated to vegetational gradients and most environmental conditions. The results indicate that atmospheric deposition accounts for most of the input of Pb, confirming the suitability of Hylocomium splendens as a biomonitor for this element. For elements such as Cd local environmental conditions should be carefully considered, even when data from regional moss surveys are to be interpreted. This revised version was published online in June 2006 with corrections to the Cover Date.     

Determinants of Leaf Litter Nutrient Cycling in a Tropical Rain Forest: Soil Fertility Versus Topography

We investigated the influence of landscape-level variation in soil fertility and topographic position on leaf litter nutrient dynamics in a tropical rain forest in Costa Rica. We sampled across the three main edaphic conditions (ultisol slope, ultisol plateau, and inceptisol) to determine the effect of soil nutrients on leaf litter nutrient concentrations while controlling for topography, and to examine topographic effects while controlling for soil nutrients. Both leaf litter macronutrient [phosphorus (P), nitrogen (N), sulfur (S), calcium (Ca), potassium (K), magnesium (Mg)] and micronutrient concentrations were quantified throughout a 4-year period. Leaf litter [P], [N] and [K] varied significantly among soil types. The variation in [P], [N], and [K] was explained by soil fertility alone. Leaf litter [S], [Ca], and [Mg] did not vary among the three soil types. Macronutrient (P, K, Mg, S, Ca) concentrations in the leaf litter were much less variable than those of Fe and Al. Lower variability in essential plant nutrients suggests a great deal of plant control over the amount of nutrients resorbed before senescense. Leaf litter macronutrient concentrations varied significantly over the 4-year period, but the temporal variation did not differ among the three edaphic types as anticipated. Hence, although the magnitude of nutrient fluxes may be controlled by local factors such as soil fertility, temporal patterns are likely regulated by a common environmental variable such as precipitation or temperature.     

Environmental correlates of acorn production by four species of Minnesota oaks

We measured acorn production by four species of oaks in central Minnesota over a 17-year period with the goal of understanding the proximate drivers of masting behavior. All four species exhibited significant annual variation and within-population synchrony of acorn production, although masting behavior was more pronounced in the two species that require 1 year to develop acorns (‘1-year’ species) than the two species that require 2 years (‘2-year’ species). There was also strong synchrony between species that require the same number of years to mature acorns, but not between species requiring different numbers of years. Acorn production by three of the four species correlated with spring or summer conditions, while no significant environmental correlate of acorn production was detected for the fourth species. Acorn production by none of the four species correlated significantly with variables calculated from the differences in weather conditions from 1 year to the next. These results, combined with prior studies of oaks, suggest that environmental conditions during key periods of acorn development frequently correlate with acorn production, as expected if such factors bear a direct mechanistic relationship to seed production. On the other hand, the environmental factors involve vary greatly both among species and even among populations of the same species, a result consistent with the hypothesis that environmental correlates are simply cues used by plants to synchronize reproductive investment. In either case, our results do not support the recent proposition that variables based on differences in environmental conditions from 1 year to the next serve as a general cue for masting behavior.     

Spatial and elevational variation in fruiting phenology of a deciduous oak (Quercus crispula) and its effect on foraging behavior of the Asiatic black bear (Ursus thibetanus)

In habitats with elevational gradients, differences in the fruiting phenology of a single key food resource may affect the feeding behavior of an animal. The objectives of the present study were to assess (1) whether or not fruiting phenology and characteristics of Quercus crispula acorns differed with changes in altitude (900?C1,400?m asl) and area; (2) when bears foraged acorns in relation to their phenological development; and (3) where bears engaged in acorn foraging behavior with respect to acorn phenology. No difference in the fruiting phenology of acorns at various altitudes and locations was found, with the exception of changes in color and abscission period. Acorn abscission period occurred later at a site with an elevation of 1,200?m in Tochigi and at another with an elevation of 1,400?m in Gunma, making the available energy of acorns in the tree canopy (AET) greater and available for a longer time period at those two sites. Foraging of acorns by bears was observed at sites of moderate to high altitude between late September and mid-October. A threshold date when acorns became suitable for foraging by bears could not be identified, as the size and nutritional value of acorns increased continuously. Foraging activity of bears observed at moderate and high altitude sites corresponded with locations where AET was available in greater amounts and for a longer period of time for some sites; however, the small sample size precluded accurate assessment.