Stoichiometric and nutrient resorption characteristics of dominant tree species in subtropical Chinese forests

This study investigated seasonal patterns in stoichiometric ratios, nutrient resorption characteristics, and nutrient use strategies of dominant tree species at three successional stages in subtropical China, which have not been fully understood. Fresh leaf and leaf litterfall samples were collected in growing and nongrowing seasons for determining the concentrations of carbon (C), nitrogen (N), and phosphorus (P). Then, stoichiometric ratios (i.e., C:N, C:P, N:P, and C:N:P) and resorption parameters were calculated. Our results found that there was no consistent variation in leaf C:N and C:P ratios among different species. However, leaf N:P ratios in late‐successional species became significantly higher, indicating that P limitation increases during successional development. Due to the P limitation in this study area, P resorption efficiency and proficiency were higher than corresponding N resorption parameters. Dominant tree species at early‐successional stage adopted “conservative consumption” nutrient use strategy, whereas the species at late‐successional stage inclined to adopt “resource spending” strategy.     

Litterfall and Element Fluxes in a Natural Hardwood Forest and a Chinese‐fir Plantation Experiencing Frequent Typhoon Disturbance in Central Taiwan

Chinese fir (Cunninghamia lanceolata) is the most important forest plantation species in subtropical Asia and is rapidly replacing natural forests. Such land‐use change may affect ecosystem nutrient cycling through changes in litterfall nutrient flux. Tropical cyclones often cause pulses of litterfall. Previous studies, however, have mostly focused on the effects of a single cyclone with little effort examining the effects of repeated cyclones. We examined litterfall in a natural hardwood forest and a Chinese‐fir plantation in central Taiwan experiencing an average of one typhoon per year. The natural hardwood forest had 54 percent higher annual litterfall (11,400 kg/ha/yr) than the Chinese‐fir plantation (7400 kg/ha/yr). Four typhoon‐affected months (typhoon period) contributed to approximately 60 percent of the litterfall and litterfall element flux in the natural hardwood forest and 80 percent in the Chinese‐fir plantation, with contributions from individual typhoons varied by more than twofold. Litterfall N and P concentrations were significantly higher in typhoon period than in non‐typhoon period, likely the result of limited retranslocation. Precipitation was a better predictor of quantity of typhoon‐associated litterfall than wind velocity. Both types of forests in southeastern China beyond the reach of typhoons have litterfall peaks in the dry season. In contrast, we measured higher litterfall during the typhoon period than during the dry season, suggesting that in regions with frequent cyclones, cyclones drive temporal variation of litterfall. Global climate change is affecting the frequency and intensity of cyclones; therefore, knowledge of typhoon‐litterfall dynamics is indispensable for understanding the effects of climate change on ecosystem nutrient cycling.     

不同坡位对琉球松人工林凋落物及其养分归还量的影响

对日本冲绳岛北部不同坡位的琉球松人工林凋落物量及其养分归还量进行了为期3年的观测研究,结果表明,琉球松成林年凋落物量为6．54～8．05Mg·hm^-2·年^-1,其凋落高峰出现在6、7月份．台风干扰对年凋落物量及其季节动态影响显著．凋落物不同组分的养分含量差异明显．年均养分归还总量为113．4～154．6kg·hm^-2·年^-1,其中氮素归还量最大,占42．2％;各养分归还量的大小依次为N>Ca>K>Mg>Na>P．两调查林分由于立地条件的显著差异,年均凋落物量及其相应的养分归还量亦存在明显差异．在立地条件较好的下坡,林分P1的年均凋落物量达8．05Mg·hm^-2·年^-1,高于立地条件相对较差的上坡的林分P2的23．1％;其相应的年养分归还量为：N66、04,P1.63,K17．42,Ca48.31,Mg14.65和N。6、57kg·hm^-2·年^-1,分别高于林分P2的39.7％、48.8％、39．4％、32.9％、24.8％和49.3％．两林分凋落物的养分利用效率分别是N为122和138,P为4934和5945,K为462和523,林分P1明显低于林分P2,这与林分P2的立地条件较差相关．可见,所调查的琉球松林是一种高效的养分利用系统。     

Nutrient dynamics within amazonian forest ecosystems

Summary A comparative analysis on the rate of fine litterfall and its associated nutrient fluxes was carried out in a mixed forest on Tierra Firme, a tall Amazon Caatinga and a Bana on podsolized sands near San Carlos de Rio Negro. There was seasonality in leaf fall and total litterfall in mixed forest and tall Amazon Caatinga forest but no definite trend in the Bana. Litterfall curves were significantly correlated among sites indicating common regulating factors in the three forests. Leaf litter from mixed forest on Tierra Firme was richer in N with extremely low Ca and Mg concentrations; tall Amazon Caatinga litter had higher P and Mg concentration, while Bana litter was low in N but K concentration was twice as high as in the other two forests. Annual fine litterfall in Tierra Firme mixed forest was nearly 4 times higher than in Bana, But N flux was 10 times higher, while Ca and Mg fluxes were similar. Tall Amazon Caatinga had Ca and Mg fluxes in litterfall 2–3 times higher than the other two forests. Within-stand efficiency of nitrogen, calcium and magnesium use, as measured by biomass/nutrient ratios, differentiates Tierra Firme from Caatinga and Bana forest: Tierra Firme has the lowest N, but the highest Ca and Mg use efficiencies. Higher P use efficiency was measured in Bana followed by Tierra Firme and Caatinga; while Tierra Firme and Caatinga showed similar higher K use efficiencies than Bana. N/P ratios indicates that Tierra Firme forest is limited by P availability, while low N availability predominates in Caatinga. Bana appears limited by both N and P. These differences probably relate to variations in degree of sclerophylly and leaf duration which determine leaf nutrient concentrations in the ecosystems studied.     

Nutrient fluxes via litterfall and leaf litter decomposition vary across a gradient of soil nutrient supply in a lowland tropical rain forest

The extent to which plant communities are determined by resource availability is a central theme in ecosystem science, but patterns of small-scale variation in resource availability are poorly known. Studies of carbon (C) and nutrient cycling provide insights into factors limiting tree growth and forest productivity. To investigate rates of tropical forest litter production and decomposition in relation to nutrient availability and topography in the absence of confounding large-scale variation in climate and altitude we quantified nutrient fluxes via litterfall and leaf litter decomposition within three distinct floristic associations of tropical rain forest growing along a soil fertility gradient at the Sepilok Forest Reserve (SFR), Sabah, Malaysia. The quantity and nutrient content of small litter decreased along a gradient of soil nutrient availability from alluvial forest (most fertile) through sandstone forest to heath forest (least fertile). Temporal variation in litterfall was greatest in the sandstone forest, where the amount of litter was correlated negatively with rainfall in the previous month. Mass loss and N and P release were fastest from alluvial forest litter, and slowest from heath forest litter. All litter types decomposed most rapidly in the alluvial forest. Stand-level N and P use efficiencies (ratios of litter dry mass to nutrient content) were greatest for the heath forest followed by the sandstone ridge, sandstone valley and alluvial forests, respectively. We conclude that nutrient supply limits productivity most in the heath forest and least in the alluvial forest. Nutrient supply limited productivity in sandstone forest, especially on ridge and hill top sites where nutrient limitation may be exacerbated by reduced rates of litter decomposition during dry periods. The fluxes of N and P varied significantly between the different floristic communities at SFR and these differences may contribute to small-scale variation in species composition.     

Effects of forest-pasture edge on C,N and P associated with <Emphasis Type="Italic">Caesalpinia eriostachys</Emphasis>, a dominant tree species in a tropical deciduous forest in Mexico

Forest fragmentation in tropical ecosystems can alter nutrient cycling in diverse ways. We have analysed the effects of the forest-pasture edge on nutrient soil dynamics in a tropical deciduous forest (TDF) in Mexico. In two remnant forest fragments, both larger than 10 ha, litterfall, litter and soil samples associated to the tree Caesalpinia eriostachys were collected at five distances from the pasture edge into the inner forest (10 m in the pasture and 0–10, 30–40, 70–80 and 100–110 m towards the forest interior). We measured the concentrations of carbon (C), nitrogen (N) and phosphorus (P) in litterfall, surface litter and soil, and soil microbial C (C_mic) and microbial N (N_mic). Soil nutrient concentrations and C_mic and N_mic were lower in the pasture soils than in the forest soil samples. Total C and N pools, and C_mic and N_mic in the pasture were lower than in the forest. In contrast, net N immobilization and the increase in N_mic from rain to dry season increased from the edge to the inner forest. Soil P concentration was lower in the pasture and at the first distance class in the forest margin (0–10 m) than in the sites located further into the forest, while litter P concentration had the inverse pattern. Litterfall P was also reduced near the edge and increased towards the forest interior. As a consequence, litterfall C:P and N:P ratios decreased from the edge to the inner forest. These results suggest that the forest–pasture edge disrupts P dynamics within the first 10 m in the forest. Thus, plants' use of nutrients and productivity could be altered in the edge of fragmented forests.     

Comparison of the litterfall and forest floor organic matter and nitrogen dynamics of upland forest ecosystems in north central Wisconsin

It has been suggested that a feedback exists between the vegetation and soil whereby fertile (vs infertile) sites support species with shorter leaf life spans and higher quality litter which promotes rapid decomposition and higher soil nutrient availability. The objectives of this study were to (1) characterize and compare the C and N dynamics of dominant upland forest ecosystems in north central Wisconsin, (2) compare the nutrient use efficiency (NUE) of these forests, and (3) examine the relationship between NUE and site characteristics. Analyzing data from 24 stands spanning a moisture / nutrient gradient, we found that resource-poor stands transferred less C and N from the vegetation to the forest floor, and that N remained in the forest floor at least four times longer than in more resource-rich stands. Analyzing data by leaf habit, we found that less N was transferred to the forest floor annually via litterfall in conifer stands, and that N remained in the forest floor of these stands nearly three times longer than in hardwood stands. NUE did not differ among forests with different resource availabilities, but was greater for conifers than for hardwoods. Vitousek's (1982) index of nutrient use efficiency (I_NUE1)=leaf litterfall biomass / leaf litterfall N) was most closely correlated to litterfall specific leaf area and percent hardwood leaf area index, suggesting that differences in species composition may have been responsible for the differences in NUE among our stands. NUE2, defined as ANPP / leaf litterfall N, was not closely correlated to any of the site characteristics included in this analysis.     

Nutrient accessions in a mixed conifer–angiosperm forest in northern New Zealand

Nutrient accessions in litterfall are described for a mixed conifer (mostly Agathis australis D.Don (Lindl.), New Zealand kauri) and angiosperm temperate forest in northern New Zealand to determine the relative contributions to nutrient cycling of the conifer and angiosperm components of the forest. Concentrations for many nutrients were significantly lower in conifer litterfall fractions than for equivalent angiosperm fractions. Angiosperm leaves had concentrations of N and P twice those found in conifer leaf fall. Despite a large contribution to litterfall from weight, conifer reproductive parts (mostly cone scales) were very low in nutrients (especially N, P and Ca). Whereas angiosperm litterfall constituted < 45% of total litterfall by weight, nutrient accessions from the angiosperm component accounted for 45–60% of total nutrient accessions and the conifer fraction for only 30–45%, almost the exact reverse of their contributions to litterfall by weight. Of the macronutrients, P (3 kg ha^–1 year^–1) showed the lowest rate of accession in litterfall while Ca (84 kg ha^–1 year^–1) showed the highest. Faunal detritus, although < 1% of total litterfall by weight, contributed 10% of total P and 4% of total N reaching the forest floor via the litterfall pathway each year. The C:N and C:P ratios in litterfall and litterstore were all well above the levels at which mineralization is likely to occur. Based on the estimated residence times, long‐term immobilization was more likely for N than for P. The annual pattern of nutrient accessions differed for the two components, with angiosperm accessions highest in spring and summer, and conifer accessions highest in autumn, due largely to a peak in litterfall of reproductive parts at that time of year. It is argued that differences in litter quality, decomposition rates and spatial and temporal patterns of litterfall for angiosperm versus conifer components of the forest, in conjunction with long‐term disturbance regimes, may contribute to conifer–angiosperm coexistence.     

Dinitrogen-fixing Acacia species from phosphorus-impoverished soils resorb leaf phosphorus efficiently

Nitrogen (N) and phosphorus (P) resorption from senescing leaves were studied, and the contribution of N and P cycling through litterfall to soil nutrient patchiness was investigated for four Acacia species in the Great Sandy Desert in north-western Australia. N and P concentrations of mature and recently shed leaves were analysed and compared; soils under the canopies of the shrubs and soils in gaps (open areas) between the shrubs were also analysed and compared for N and P concentrations. Mature leaf P concentrations of the plants were considerably lower than the global average values, and N : P ratios of mature leaves were high. Plants derived 0-75% of their leaf N from symbiotic N(2)-fixation. N-resorption efficiency was between 0 and 43%, and P-resorption efficiency was between 32 and 79%; all plants were more efficient at P resorption than at N resorption, and litter N : P ratios were significantly higher than mature leaf N : P ratios. Soils of the study sites were P-impoverished. Total soil N and P concentrations were higher under the canopy than in gaps, but bicarbonate-extractable P concentration was higher in gaps. Nutrient cycling through litterfall results in soil nutrient patchiness and forms 'islands of fertility' under the canopies of the shrubs.     

Nitrogen and phosphorus resorption in trees of a Mexican tropical dry forest

Resorption efficiency (RE) and proficiency, foliar nutrient concentrations, and relative soil nutrient availability were determined during 3 consecutive years in tree species growing under contrasting topographic positions (i.e., top vs. bottom and north vs. south aspect) in a tropical dry forest in Mexico. The sites differed in soil nutrient levels, soil water content, and potential radiation interception. Leaf mass per area (g m^–2) increased during the growing season in all species. Soil P availability and mean foliar P concentrations were generally higher at the bottom than at the top site during the 3 years of the study. Leaf N concentrations ranged from 45.4 to 31.4 mg g^–1. Leaf P varied from 2.3 to 1.8 mg g^–1. Mean N and P RE varied among species, occasionally between top and bottom sites, and were higher in the dry than in the wet years of study. Senesced-leaf nutrient concentrations (i.e., a measure of resorption proficiency) varied from 13.7 to 31.2 mg g^–1 (N) and 0.4 to 3.3 mg g^–1 (P) among the different species and were generally indicative of incomplete nutrient resorption. Phosphorus concentrations in senesced leaves were higher at the bottom than at the top site and decreased from the wettest to the the driest year. Soil N and P availability were significantly different in the north- and south-facing slopes, but neither nutrient concentrations of mature and senesced leaves nor RE differed between aspects. Our results suggest that water more than soil nutrient availability controls RE in the Chamela dry forest, while resorption proficiency may be interactively controlled by both nutrient and water availability.     

Foliar demand and resource economy of nutrients in dry tropical forest species

Important phenological activities in seasonally dry tropical forest species occur within the hot‐dry period when soil water is limiting, while the subsequent wet period is utilized for carbon accumulation. Leaf emergence and leaf area expansion in most of these tree species precedes the rainy season when the weather is very dry and hot and the soil cannot support nutrient uptake by the plants. The nutrient requirement for leaf expansion during the dry summer period, however, is substantial in these species. We tested the hypothesis that the nutrients withdrawn from the senescing leaves support the emergence and expansion of leaves in dry tropical woody species to a significant extent. We examined the leaf traits (with parameters such as leaf life span, leaf nutrient content and retranslocation of nutrients during senescence) in eight selected tree species in northern India. The concentrations of N, P and K declined in the senescing foliage while those of Na and Ca increased. Time series observations on foliar nutrients indicated a substantial amount of nutrient resorption before senescence and a ‘tight nutrient budgeting’. The resorbed N‐mass could potentially support 50 to 100% and 46 to 80% of the leaf growth in terms of area and weight, respectively, across the eight species studied. Corresponding values for P were 29 to 100% and 20 to 91%, for K 29 to 100% and 20 to 57%, for Na 3 to 100% and 1 to 54%, and for Ca 0 to 32% and 0 to 30%. The species differed significantly with respect to their efficiency in nutrient resorption. Such interspecific differences in leaf nutrient economy enhance the conservative utilization of soil nutrients by the dry forest community. This reflects an adaptational strategy of the species growing on seasonally dry, nutrient‐poor soils as they tend to depend more or less on efficient internal cycling and, thus, utilize the retranslocated nutrients for the production of new foliage biomass in summer when the availability of soil moisture and nutrients is severely limited.     

鼎湖山南亚热带季风常绿阔叶林凋落物的养分动态

本文探讨鼎湖山季风常绿阔叶林调落物养分特征,分析了其动态、季节间与种间变异、构成特征等。结果表明,该群落各种群含氮量的季节变化较小,各个种的变异系数多在15％以下,但磷、钾和钠的变异较大。无论在群落还是在种的水平上,各种营养成份间均没有显著的相关性。除磷外,不同种问养分含量有显著差异,季节间则除镁外无显著差异,磷在红壤地区土壤中难于利用的主要原因可能是不同植物在磷的利用上趋同．全年通过凋落物回归土壤的养分量为氮99．88kghm-2,磷15．03kghm-2．钾27．01kghm-2,钙37．11kghm-2;镁12．19kghm-2。在该群落中,椎栗是对落叶养分贡献最大的种,荷木其次。8月是当年凋落物养分量最高的月份,主要是由于台风作用产生大量的枝叶折落,12月则是最低月份,两者在构成上的主要区别是8月份枝条所持养分量极大,而12月份枝条极少。全年凋落物养分出现两次高峰,4月和8月,而以较寒冷的1、2、11、12月份最低。     

Vegetation in contrasting soil water sites of upland herbaceous grasslands and N:P ratios as indicators of nutrient limitation

Effects of differences in long-term water supply were examined on soil characteristics, primary production and species composition in a wet and a dry site of an upland herbaceous grassland. Also the responses of species to N and P enrichments were examined. N and P concentrations of non-legume species were positively related, indicating that biomass N:P ratios seem to be mainly determined by N:P supply ratios. Forbs had generally higher concentrations than graminoids. Intermittent water inundation of soil in the wet site resulted in greater soil N and P availability. The greater productivity of this site promoted the growth of forbs. A fertilizer experiment showed that biomass was limited by N only in the wet site, but by both nutrients in the dry one. The species with the higher N and P concentrations were favored more after N and P enrichment, respectively; however, species enhancement was not related to N:P ratios of species. This indicates that N and P concentrations of species, rather than N:P ratios of species, are better predictors of species responses to N and P enrichment. N:P ratios of whole communities were 8.73 for the wet and 11.36 for the dry site. These values in comparison with the responses of plant communities to N and P fertilization show that thresholds of N:P ratios indicative of N or P limitation are much lower than those found for European wetlands.     

Changes in nutrient use efficiency, status and retranslocation in young post-fire regeneration Pinus halepensis in response to sudden N and P input, irrigation and removal of competing vegetation

The capacity of Mediterranean species to adapt to variable nutrient supply levels in a global change context can be a key factor to predict their future capacity to compete and survive in this new scenario. We aimed to investigate the capacity of a typical Mediterranean tree species, Pinus halepensis, to respond to sudden changes in N and P supply in different environmental conditions. We conducted a fertilisation, irrigation and removal of competing vegetation experiment in a calcareous post-fire shrubland with an homogeneous young (5 years old) population of P. halepensis in order to investigate the retranslocation and nutrient status for the principal nutrients (N, P, Mg, K, S, Ca and Fe), and the nutrient use efficiency (NUE) of the most important nutrients linked to photosynthetic capacity (N, P, Mg and K). P fertilisation increased P concentration in needles, P, N, Mg and K retranslocations, and NUE calculated as biomass production per unit of nutrient lost in the litterfall. The P fertilisation was able to increase the aboveground biomasses and P concentration 3 years after P fertiliser application. Those responses to P fertilisation were enhanced by the removal of competing vegetation. The N needle and litterfall concentration decreased after P fertilisation and this effect was greater when the P fertilisation was accompanied by removal of competing vegetation. The increase of P availability decreased the P-NUE and increased the N-NUE when these variables were calculated as aboveground biomass production per unit of P present in the biomass. Both P-NUE and N-NUE increased when calculated as total aboveground production per unit of nutrient loss. The results show that it is necessary to calculate NUE on a different basis to have a wider understanding of nutrient use. The irrigation did not change the needle nutrient concentrations and the litterfall production, but it significantly changed the nutrient litterfall concentrations and total aboveground contents (especially P and K). These results show a high capacity of P. halepensis to quickly respond to a limiting nutrient such as P in the critical phases of post-fire regeneration. The increase in P availability had a positive effect on growth and P concentrations and contents in aboveground biomass, thus increasing the capacity of growth in future periods and avoiding immediate runoff losses and leachate. This capacity also strongly depends on neighbour competition.     

Litter Nutrient Dynamics During Succession in Dry Tropical Forests of the Yucatan: Regional and Seasonal Effects

Land-use change in the tropics is creating secondary forest at an unprecedented rate. In the tropical Americas, mature dry tropical forest is rapidly being converted to secondary forest during the fallow period of shifting cultivation. We investigated litter phosphorus (P) and nitrogen (N) dynamics in forests recovering from shifting cultivation of maize (corn) in three regions of the Southern Yucatan Peninsula, Mexico. Our goal was to understand how nutrient and water availability affect forest recovery following conversion of mature forest to agricultural land. To investigate such changes at a regional scale, newly fallen litter was collected monthly along a seasonal, a successional, and a precipitation gradient. Reflecting possible P limitation, litter P concentration declined with forest age, while litter N concentration did not differ between age classes. Average litter P concentration from the southern, wettest region was 0.87 mg/g, almost twice the litter P concentration in the drier central and northern regions (0.44 and 0.45 mg/g, respectively). Average N concentrations of litter from the three regions ranged from 1.1% to 1.2%, with no regional differences. However, minima in both P and N concentration from all regions were pronouncedly timed with peak litterfall, suggesting nutrient retranslocation during periods of water stress. Additionally, successional differences in litter P were clearest during wetter months. P nutrient-use efficiency was lowest in the southern region and highest in the central and northern study regions. N nutrient-use efficiency was up to 40 times lower than P nutrient-use efficiency and showed no regional differences. Overall, our results suggest that litter nutrient dynamics in secondary dry tropical forests of the Southern Yucatan are strongly influenced by water and nutrient availability, especially P, as well as land-use history.     

Litterflow chemistry and nutrient uptake from the forest floor in northwest Amazonian forest ecosystems

Samples of the fraction of net rainfall passing through the forest floor collected at monthly intervals in four pristine forests in Colombian Amazonia, during the period between 1995–1997 were analysed for solute concentrations to estimate the element fluxes from the forest floor into the mineral soil and root nutrient uptake from these forest floors. Results were compared with inputs by throughfall, stemflow, litterfall and fine root decay. Element concentrations were tested for their relationship with litterflow amounts, rainfall intensity and length of the antecedent dry period and differences in element fluxes between ecosystems were assessed. Concentrations of elements in litterflow followed a similar pattern as those in throughfall, which indicates that element outputs from the forest floor are strongly related to those inputs in throughfall. In the forests studied, the average concentrations of elements as K, Mg, orthoP and the pH of the litterflow decreased relative to that in throughfall in most events, while the concentration of elements such as dissolved organic carbon, H, SO₄ and Si increased in litterflow from these forests. Element concentrations in litterflow showed a poor correlation with variables such as litterflow amounts, rainfall intensity and antecedent dry period, except for K which showed a significant correlation (p>0.95) with analysed variables in all forests. Outputs were significantly different between forests (p>0.95); these fluxes, which particularly concerned cations, being the largest in the flood plain, while for anions outputs increased from the flood plain to the sedimentary plain. After adding the nutrient contributed by litter decomposition and fine root decay, the net outputs of main elements from the forest floors were still smaller than inputs by net precipitation (throughfall+stemflow) indicating that the litter layers clearly acted as a sink for most nutrients. Accordingly, the element balances confirm that the forest floors acted as a sink for nutrients coming in by throughfall, stemflow, litterfall and fine root decomposition. P, Mg and N appeared to be the most limiting nutrients and the forests studied efficiently recycled these nutrients.     

Rapid development of phosphorus limitation in temperate rainforest along the Franz Josef soil chronosequence

The aim of this study was to examine how shifts in soil nutrient availability along a soil chronosequence affected temperate rainforest vegetation. Soil nutrient availability, woody plant diversity, composition and structure, and woody species leaf and litter nutrient concentrations were quantified along the sequence through ecosystem progression and retrogression. In this super-wet, high leaching environment, the chronosequence exhibited rapid soil development and decline within 120,000 years. There were strong gradients of soil pH, N, P and C, and these had a profound effect on vegetation. N:P_leaf increased along the chronosequence as vegetation shifted from being N- to P- limited. However, high N:P_leaf ratios, which indicate P-limitation, were obtained on soils with both high and low soil P availability. This was because the high N-inputs from an N-fixing shrub caused vegetation to be P-limited in spite of high soil P availability. Woody species nutrient resorption increased with site age, as availability of N and P declined. Soil P declined 8-fold along the sequence and P resorption proficiency decreased from 0.07 to 0.01%, correspondingly. N resorption proficiency decreased from 1.54 to 0.26%, corresponding to shifts in mineralisable N. Woody plant species richness, vegetation cover and tree height increased through ecosystem progression and then declined. During retrogression, the forest became shorter, more open and less diverse, and there were compositional shifts towards stress-tolerant species. Conifers (of the Podocarpaceae) were the only group to increase in richness along the sequence. Conifers maintained a lower N:P_leaf than other groups, suggesting superior acquisition of P on poor soils. In conclusion, there was evidence that P limitation and retrogressive forests developed on old soils, but N limitation on very young soils was not apparent because of inputs from an abundant N-fixing shrub.Electronic Supplementary Material Supplementary material is available in the online version of this article at .     

Effect of typhoon disturbance on fine litterfall and related nutrient input in a subtropical forest on Okinawa Island, Japan

Typhoons are frequent on Okinawa Island, southwestern Japan. The effects of typhoon disturbance on the patterns of fine litterfall and related nutrient inputs in a subtropical evergreen broad-leaved forest were studied over 5 years from May 1996 to April 2001. Annual fine litterfall averaged 7558 kg ha⁻¹ (range from 6188 to 9439 kg ha⁻¹) for six sampling plots over 5 years, which differed significantly among years (p<0.001) but not among plots (p=0.122). A seasonal maximum was most evident for leaf litter component. Woody litter fell more irregularly through the year, and peak fall varied with typhoon and windstorm. The mean ratio of annual litterfall mass of sexual organs to leaves was 0.06, much lower than that in other tropical and subtropical rain forests. Nutrient concentrations varied in litterfall components, but were not significantly different among plots. The lowest concentrations of N and P in leaf litter were observed in March, which is also the month with the greatest leaf fall. However, the highest concentrations were recorded in typhoon season. Nitrogen and P concentrations were 34% and 106% greater in the green leaves that fell during typhoons than in senescent leaves. Mean nutrient inputs by litterfall were: N 83, P 3.2, K 25, Ca 71, Mg 19, Al 12, Na 10, Fe 0.86 and Mn 3.9 kg ha⁻¹ yr⁻¹, and differed significantly among years for all elements (p<0.0005) and among plots only for K (p<0.05) and Mn (p<0.0001). Typhoon disturbance strongly affected annual fine litterfall and related nutrient inputs, which contributed an average of 30% of the annual litterfall mass, and from 30% to 39% (for different nutrient elements) of annual total nutrient inputs. The results from this study suggest that typhoon-driven maintenance of rapid cycling of P and N and their high availability in soil appears to be an important mechanism to maintain productivity in the subtropical forest on Okinawa Island.     

福建和溪亚热带雨林凋落物营养元素动态

探讨了福建和溪亚热带雨林主要营养元素通过凋落物的归还动态．结果表明,该森林一年中凋落物不同组分各元素的含量具有波动性,加权平均含量为Ｎ＞Ｋ＞Ｃａ＞Ｍｇ＞Ｐ（落果Ｃａ＝Ｍｇ、落枝Ｃａ＞Ｋ）。通过凋落物归还Ｎ、Ｐ、Ｋ、Ｃａ、Ｍｇ元素的年库流量,分别为８７．４１、３．８２、４０．８０、２８．８１和１５．３２ｋｇｈｍ（－２）,灰分量为２８４．５７ｋｇｈｍ（－２）,其中以落叶形式居最大,分别各占总量的７３．４％、６８．１％、．７７．２％、７２．９％、７４．５％和７９．９％;各元素的年库流量与年凋落物量的月分布相一致,有明显的季节性．森林地表残留物Ｎ、Ｐ、Ｋ、Ｃａ、Ｍｇ元素的累积储量．分别为５４．８３、２．４５、９．６９、１７．０和９．２５ｋｇｈｍ（－２）．五种元素在林下地表的滞留时间,分别为Ｎ０．６１、Ｐ０．６１、Ｋ０．２３、Ｃａ０．５６和Ｍｇ０．５３年．     

Nutrient dynamics along a precipitation gradient in European beech forests

Precipitation as a key determinant of forest productivity influences forest ecosystems also indirectly through alteration of the nutrient status of the soil, but this interaction is not well understood. Along a steep precipitation gradient, we studied the consequences of reduced precipitation for the soil and biomass nutrient pools and dynamics in 14 mature European beech (Fagus sylvatica L.) forests on Triassic sandstone. We tested the hypotheses that lowered summer precipitation (1) is associated with less acid soils and (2) a reduced accumulation of organic matter on the forest floor, and (3) reduces nutrient supply from the soil and leads to decreasing foliar and root nutrient concentrations. Soil acidity, the amount of forest floor organic matter, and the associated organic matter N and P pools decreased to about a half from wet to dry sites; the C/P and N/P ratios, but not the C/N ratio, of forest floor organic matter were reduced as well. Net N mineralization and P and K pools in the mineral soil did not change with decreasing precipitation. Foliar P and K concentrations (beech sun leaves) increased while N remained constant, resulting in decreasing foliar N/P and N/K ratios. Estimated N resorption efficiency increased toward the dry sites. We conclude that a reduction in summer rainfall significantly reduces the soil C, N and P pools but does not result in decreasing foliar N and P contents in beech. However, the decreasing foliar N/P ratios towards the dry stands indicate that the importance of P limitation for tree growth declines with decreasing precipitation.