Characteristics of culm structure and carbon and nitrogen concentrations in dead bamboo culms of two Phyllostachys species

The tissue structure of a bamboo stem (culm) differs from that of woody species, exhibiting a large cavity in the internode surrounded by a cortex with high silica concentration. Thus, to obtain an accurate estimation of the necromass, as well as carbon (C) and nitrogen (N) stocks in dead bamboo culms, we examined the basic characteristics of culm structure as well as the C and N concentrations of decomposing culms of Phyllostachys bambusoides and P. heterocycla. We collected dead culms of the two bamboo species from 15 bamboo stands in central and southwestern Japan, and analyzed the relationship between the ratio of wall volume to culm disk volume and culm diameter, as well as the changes of C and N concentrations in dead culms with wall density, which can be used as an indicator of the degree of decomposition. The ratio of wall volume to culm volume tended to decrease with increasing culm diameter for both species. The C concentration did not change, but the N concentration increased with decreasing wall density. The wall density was related to the C/N ratio, which is a chemical parameter of the degree of decomposition. The culm structure should be considered when estimating culm density. The mean C concentration can be used for estimating the C stock of decomposing culms irrespective of decomposition level. N concentration, however, should be determined according to decomposition level for N stock estimation.     

Bamboo,fire and flood: consequences of disturbance for the vegetative growth of a clumping,clonal plant

The clumping growth form of tropical bamboos suggests a consolidator strategy in the face of intense competition rather than an ability to exploit disturbance. We investigated the annual growth and culm demographic responses to disturbance by fire and flood of vegetatively mature clumps of a riparian stand of Bambusa arnhemica. Linear-mixed models were employed to control for the non-independence of culm fates within clumps and clump growth among years. As the stand was monodominant and the species is gregariously monocarpic, responses can be interpreted independently of interspecific competition and trade-offs with sexual reproduction. Disturbance depressed clump growth but the culm demographic responses to fire and flood were quite different. Few culms were destroyed during the fire but damage depressed their subsequent survival, leading to declines in clump basal area. Fire also triggered the release of ramet buds, but the additional recruits were small and short-lived. Prolonged and early flooding in one of the study years depressed culm recruitment in clumps low on the lagoon bank but there was possible compensatory recruitment in the following year. There was no convincing evidence that sparse clumps recruited culms better than dense clumps, though culm recruitment was negatively correlated with culm survival. Fire and prolonged flooding are inevitable elements of the environment occupied by B. arnhemica, but we interpret the species’ response as persisting in the face of disturbance rather than exploiting the opportunities created by it.     

苦竹-杉木混交林界面区克隆分株秆形和地上生物量分配的适应策略

苦竹(Pleioblastus amarus)是优质笋材兼用竹种,分布广。为探究界面区苦竹分株秆形及地上构件生物量分配格局的变化特征,解析苦竹对异质生境适应机制,该研究选取了相邻的苦竹林和苦竹-杉木(Cunninghamia lanceolata)混交林两种林分类型,分别测定了苦竹林和混交林中心区及界面区不同龄级立竹秆形和秆、枝、叶的生物量,分析立竹秆形及地上构件生物量积累、分配、异速生长关系的差异。结果表明:(1)界面区1 a立竹生物量积累及分配差异增大,其中苦竹林界面区各构件相对生物量和叶生物量分配比例提高,而混交林界面区各构件相对生物量和叶生物量分配比例降低; 2 a立竹生物量积累及分配比例的差异缩小,界面区两边2 a立竹各构件相对生物量和生物量分配比例均无明显差异。(2)界面区立竹秆形特征及1 a立竹各构件生物量异速生长关系均无明显变化,而苦竹林界面区2 a立竹秆的增长速率提高,枝、叶的增长速率降低。综上认为,苦竹通过权衡资源分配关系,明显改变界面区立竹秆形及生物量分配格局,以提高克隆分株对异质环境的适合度。     

A modelling approach to the analysis of pressure-flow in Phragmites stands

Field studies have shown that resistance to convective gas-flow within the culm-rhizome gas-space system of Phragmites tends to be higher in ‘die-back’ as opposed to healthy stands. However, the collection of reliable data and its interpretation is complicated by many factors. To help interpret field measurements and further our understanding of convective flows in general, we have developed mathematical models based on the humidity-induced convective-flow generating potential of culms. Among other things, these make it possible to study the effects on pressure flows of increasing flow resistances in rhizomes and between culms, of different pressure-generating potentials of interlinked culms and of different numbers of efflux culms. A multi-culm and rhizome model is described together with some simple examples of the way it can prove helpful in interpreting some of the field observations from healthy and die-back sites.Increased venting resistance reduced flows curvilinearly; increasing the counter pressure to mimic those induced by other interlinked living culms reduced flows linearly. In some of the multi-culm examples shown counter-pressure exerted an effect approximately the same as that of rhizome and venting resistance, but as culm numbers declined it assumed even greater importance. The value of conductivity derived from applying pressures to the stubble of excised culms and measuring the flows induced, proved to be a composite measure of the effective conductivity of the whole rhizome-culm train rather than that of the rhizome plus major vent. The expression 1−(P_d/P_s) — the delivery coefficient — where P_d is the dynamic pressure in the base of the intact culm, and P_s the static pressure developed by the culm with the outflow blocked, was identified as a useful and easily obtained measure of the ability of an individual intact culm to contribute to the convective gas-flow in a stand, and one which should be relatively unaffected by weather conditions. For identical interlinked culms it was shown that the flows from all culms fitted exactly along the same line of declining flow versus dynamic pressure irrespective of the numbers of culms or number and position of outflow vents.     

A simple method to estimate the rate of the bamboo expansion based on one-time measurement of spatial distribution of culms

Moso bamboo (Phyllostachys edulis) groves have been expanding in Japanese forests, thus an assessment of the rate of bamboo grove expansion is a critical issue. Previous studies used time-series data which span typically more than a few years in order to determine the expansion of bamboo groves. This method cannot be used when time-series data were not available. In this study, we developed and tested a simple indicator based on one-time measurement of spatial distribution of culms to estimate the rate of bamboo grove expansion. Among 19 locations at four sites, the distribution patterns of culms from the pure bamboo stands to the expanding front were highly correlated with the actual edge expansion rate (E) based on the aerial photographs collected over ca. 15- and 30-year periods. In contrast, the culm density in the original stand itself was not correlated with E. These results suggest that one-time measurement of the distribution patterns of living culms (but not stand density) could be a useful indicator for estimating the expansion rates of bamboo groves.     

Culm strength of barley : correlation among maximum bending stress, cell wall dimensions, and cellulose content

Grass culms are known to differ in breaking strength, but there is little physicochemical data to explain the response. The fourth internode of four brittle and two nonbrittle barley (Hordeum vulgare L.) strains were used for physical and chemical studies of culm strength. Inner and outer culm diameters of brittle strains (3.6 ± 0.2 and 5.0 ± 0.1 millimeters) were not significantly different from those of nonbrittle strains (3.9 ± 0.2 and 5.2 ± 0.2 millimeters). Maximum bending stress, at which the culm was broken, was 192 ± 34 g/mm² for brittle and 490 ± 38 g/mm² for nonbrittle strains. Wall thickness and cell dimensions of epidermal, sclerenchyma, and parenchyma cells were measured in culm cross sections. The area of cell wall per unit cell area for each tissue was significantly correlated with the maximum bending stress (r = 0.93 for epidermis, 0.90 for sclerenchyma, and 0.84 for parenchyma). Cell walls of brittle culms had 6 to 64% as much cellulose content as those of nonbrittle culms. Maximum bending stress correlated significantly with cellulose content of the cell walls (r = 0.93), but not with the contents of noncellulosic compounds. The lower cellulose content of the brittle culm was significantly correlated with brittleness.     

Rice BRITTLE CULM 3 (BC3) encodes a classical dynamin OsDRP2B essential for proper secondary cell wall synthesis

“Brittle culm” mutants found in Gramineae crops are suitable materials to study the mechanism of secondary cell wall formation. Through positional cloning, we have identified a gene responsible for the brittle culm phenotype in rice, brittle culm 3 (bc3). BC3 encodes a member of the classical dynamin protein family, a family known to function widely in membrane dynamics. The bc3 mutation resulted in reductions of 28–36% in cellulose contents in culms, leaves, and roots, while other cell wall components remained unaffected. Reductions of cell wall thickness and birefringence were observed in both fiber (sclerenchyma) and parenchymal cells, together with blurring of the wall’s layered structures. From promoter-GUS analyses, it was suggested that BC3 expression is directly correlated with active secondary cell wall synthesis. These results suggest that BC3 is tightly involved in the synthesis of cellulose and is essential for proper secondary cell wall construction.     

疏伐对黄土丘陵区刺槐林蒸腾的影响

黄土高原地区植被建设已达到土壤水分承载力的阈值,需要对现有林分进行结构优化并提升其生态功能。不合理的林分密度是导致黄土丘陵区刺槐林土壤干化、生长衰退的主要原因之一。疏伐可以优化林分结构,并能够通过控制蒸腾耗水来调控土壤水分,是促进刺槐林可持续生长的有效手段。疏伐对黄土丘陵区刺槐林蒸腾有何影响,目前并不清楚。研究基于树干液流法估算了4个不同疏伐强度（样地1：52%、样地2：48%、样地3：35%、样地4：未疏伐）下刺槐单株尺度的液流速率与林分尺度的日平均蒸腾量,并分析了不同时间尺度下液流速率与环境因子的关系,以阐明疏伐对黄土丘陵区刺槐林蒸腾的影响。结果表明：（1） 单株尺度刺槐蒸腾速率（即液流速率）随疏伐强度减小（林分密度增大）呈现下降趋势（样地1：0.53 kg cm^-2 d^-1、样地2：0.41 kg cm^-2 d^-1、样地3：0.31 kg cm^-2 d^-1、样地4：0.33 kg cm^-2 d^-1）;（2） 观测期林分尺度日平均蒸腾量随疏伐强度减小呈现上升趋势（样地1：0.90 mm/d、样地2：1.18 mm/d、样地3：1.04 mm/d、样地4：1.44 mm/d）;（3） 在半小时尺度与日尺度上,各样地液流速率与环境因子的关系没有显著差异,半小时尺度单株液流速率均与太阳辐射相关性最高（相关系数0.883-0.908）,液流速率日变化过程与环境因子日变化过程存在时滞现象;日尺度单株液流速率与饱和水汽压亏缺相关性最高（相关系数0.843-0.913）,样地间日尺度单株液流速率的差异性随着饱和水汽压亏缺增大而增大。研究结果初步反映了疏伐导致的林分密度变化对刺槐蒸腾的影响,将为黄土丘陵区刺槐林的结构改造、功能提升和土壤水分调控提供理论支持。     

Changes in chemical characteristics of surface soils in hinoki cypress (Chamaecyparis obtusa) forests induced by the invasion of exotic Moso bamboo (Phyllostachys pubescens) in central Japan

Invasion of contiguous forests by a giant bamboo (Moso bamboo, Phyllostachys pubescens) has the potential to induce changes in the chemical characteristics of soils due to the high growth rate of this species. We evaluated the impact of bamboo invasion into hinoki cypress (Chamaecyparis obtusa) forests on soil properties under varying conditions of shoot density at three study sites (Kanpachi, Seto, and Noguchi) in central Japan. We established three successive quadrats along bamboo invasion (allotted to a bamboo stand, a mixed stand of bamboo and hinoki, and a hinoki stand) at every site. Then, we measured the density and basal area of bamboo and hinoki shoots. Surface soil was sampled from each quadrat to analyze pH, water content, and exchangeable cation contents. The values of soil pH were significantly higher in the mixed stands than the hinoki stands at all sites, showing positive correlations with exchangeable Ca contents in the soil. Exchangeable K and Mg contents in the soil of the mixed stand showed significant differences compared with the hinoki stand only in Seto, but these values in the mixed stand were similar to those in the bamboo stand. This characteristic is consistent with the invasion degree determined from the density ratio of living bamboo culms to living hinoki trunks: Seto > Kanpachi > Noguchi. We conclude that increases in the soil pH due to bamboo invasion into hinoki forests resulted in distinct and sensitive changes in the soil chemistry.     

Expansion of bamboo forests caused by reduced bamboo-shoot harvest under different natural and artificial conditions

To elucidate the expansion of bamboo (Phyllostachys pubescens Mazel ex Houzeau de Lehaie) forests, we used multiple linear regression analysis and determined whether there were site differences for data obtained in Hirasawa, Otaki-machi, Chiba Prefecture, and Kofuki, Takehara City, Hiroshima Prefecture, Japan. Vegetation maps from 1984 and 2001 for Hirasawa, and from 1986, 1996, 2000, and 2006 for Kofuki, were compared, and the annual expansion rate of each P. pubescens forest was calculated. We evaluated nine indices, including original bamboo forest area, neighbouring vegetation, slope inclination and aspect, distance from roads, and shipment of bamboo shoots. Shipment of bamboo shoots was a positive factor for P. pubescens forest expansion, whereas the proportion of adjacent short vegetation, northness (the cosine of slope aspect), and area negatively affected the expansion in Hirasawa (R ² = 0.683). On the other hand, distance from roads and eastness (the sine of slope aspect) positively affected expansion, while slope inclination was a negative factor in Kofuki (R ² = 0.942). We calculated that P. pubescens forests expanded at about 2% per year in regions of reduced shipments of bamboo-shoot harvest. We showed that not only natural conditions but also management factors affect P. pubescens forest expansion. Regional differences in natural and anthropogenic effects on expansion were also found.     

Indirect method to estimate convective gas flow through culms of a <Emphasis Type="Italic">Phragmites australis</Emphasis> stand

We propose an indirect method to estimate continuously the rate of convective gas flow in a Phragmites australis stand. In this method, the rate of gas flow is estimated using the dynamic pressure differential in a culm and the convective conductance of the culm. The rate of gas flow obtained by this indirect method coincided well with that obtained by the direct method in which a culm is detached and then reconnected to the stubble using a mass flow meter. We monitored the total gas flux through a P. australis stand in a field and found that it fluctuated diurnally with the dynamic pressure differential in culms, showing a highest rate of 26lairm^–2 ground area h^–1 at noon. The total daily gas flux was about 170lairm^–2. Our indirect method has advantages in simultaneous and continuous measurements for a cluster of culms. This method will be of use not only to quantify various gas dynamics through aquatic plants in aquatic ecosystems but also to elucidate the ecosystem processes and properties that regulate these gas dynamics.     

Impact of Culm Harvest on Seed Production in a Monocarpic Bamboo

Successful regeneration of bamboos from seed is a key issue in the ecology of many tropical regions and the livelihoods of their inhabitants. The gregarious monocarpy of many bamboos may be driven by a need to satiate seed predators by seeding in abundance at infrequent intervals. In long‐lived clonal monocarps, seed production is expected to be positively related to the success of the clone in generating more and larger ramets during its lifetime. Ramification may be constrained by harvesting of culms, but it is unclear whether the reduction in productivity is proportional to the loss of reproductive biomass. We counted the seed produced by 661 culms (ramet stems) sampled from 90 clumps of the gregariously monocarpic bamboo Schizostachyum dullooa that is intensively harvested by villagers in northeastern India. The smallest clumps had fewer culms and few or no culms more than one year old. Seed production was indeed positively related to culm size and the number of culms in a clump. First‐year culms were markedly more productive than older culms after controlling for culm diameter and clump size. There was a negative effect of clump size on productivity per culm which may occur because clumps that had been harvested heavily were able to exploit resources retained in rhizomes from harvested culms. Nevertheless, small clumps produced much less seed than larger clumps, generating a risk of unknown magnitude that heavily harvested stands of monocarpic bamboos may be unable to satiate seed predators during their single opportunity for reproduction.     

Density regulation during the regeneration of two monocarpic bamboos: self-thinning or intraclonal regulation?

Abstract. The population dynamics of two monocarpic bamboos, Sasa kurilensis and S. tsuboiana, were studied for more than 10 years after establishment following mass flowering. Both species show vigorous rhizomatous vegetative reproduction after growing up to maturity, but horizontal expansion in the seedling stage was much more vigorous in S. tsuboiana than in S. kurilensis. The pattern of changes in culm density in the two species was strikingly similar: culm densities of both species increased until they reached full-density states, after which they decreased in accordance with seedling growth. However, the mode of regulation in culm density was different. S. kurilensis seedlings were composed of only a few culms and scarcely extended their rhizomes during the observation period. Such poor lateral expansion resulted in asymmetric competition as observed in many non-clonal plants, and consequently their culm density decreased as a result of the mortality of genets due to self-thinning. In S. tsuboiana seedlings, the number of culms per genet increased considerably by frequent tillering and sprouting from rhizomes. However, after reaching full density state, the Bud Utility Ratio (BUR), (the proportion of the rhizome nodes with culms to the total number of rhizome nodes), decreased drastically. In this manner, S. tsuboiana regulated culm density intraclonally as is observed in the stable states of many clonal plants. Hence it is important for the understanding of the regeneration process in clonal species to clarify when and how their seedlings extend rhizomes during their growth.     

Biomass and net production in a bambooPhyllostachys bambusoides stand

Biomass and net production were measured in aPhyllostachys bambusoides stand in Kyoto Prefecture, central Japan, which had carried out gregarious flowering in 1969 and has been recovering vegetatively. The culm density fluctuated around an average value of 12 040 ha⁻¹ during the research period (1985–91). Annual recruirment and mortality rates of culms were 1340 and 1133 ha⁻¹, respectively. The mean diameter at breast height increased from 7.28 cm in 1985 to 8.68 cm in 1991, and the biomass of culms increased from 71.3 to 111.6t ha⁻¹ over the same time period. Branch and leaf biomasses were almost constant, 10.0 and 9.4t ha⁻¹ on average, respectively. The leaf area index of the stand was 11.6 ha ha⁻¹, which is one of the largest values found in Japanese forests. The belowground biomass of 32.6t ha⁻¹ for rhizomes and 14.8t ha⁻¹ for fine roots resulted in the smaller ratio of aboveground parts to the root system (2.38) than those determined for forest stands. The amount of litterfall, excluding culms and large branches, was large (9.13t ha⁻¹ year⁻¹), corresponding to those measured in equatorial stands. The aboveground net production was 24.6t ha⁻¹ year⁻¹, larger than the average value reported for forest stands under similar weather conditions.     

A COMPARISON OF PERIPHYTIC ALGAL BIOMASS AND COMMUNITY STRUCTURE ON SCIRPUS VALIDUS AND ON A MORPHOLOGICALLY SIMILAR ARTIFICIAL SUBSTRATUM1

Chemically inert, cylindrical rods positioned in the littoral of two eutrophic Alberta lakes supported higher periphytic algal biomass (measured as total chlorophyll a) than nearby morphologically similar culms of Scirpus validus Vahl. during most of the summer. Upon initiation of macrophyte senescence, biomass on the two substrata became more similar. Experiments were conducted to investigate the basis for these observations. Whole extracts of intact vegetative Scirpus culms had no effect on periphyton photosynthesis, suggesting that the natural substrata do not produce water-soluble allelochemicals. Various modifications of the rod surfaces (roughening, wax coating, wax color) were used to test whether surficial properties of Scirpus culms influenced periphyton accumulation. Roughened rods supported levels of biomass similar to those of smooth rods, and both substrata developed structurally complex periphyton communities. Rods covered with paraffin wax had periphyton communities that were lower in biomass and structurally more simple than those on un-coated rods or on Scirpus culms. Coloring of the wax coating had no consistent effect on periphyton accumulation. We hypothesize that the hydrophobic cuticle on actively growing Scirpus culms retards the development of precursors for attachment by periphytic algae. Upon senescence of the culm and loss of epidermal integrity, colonization of culm surfaces by periphytic algae may occur in a manner similar to that on artificial substrata.     

冠层高度对毛竹叶片光合生理特性的影响

借助LI-6400便携式光合作用系统,研究了冠层高度对不同林龄毛竹(Phyllostachys pubescens)叶片光合生理特性和水分利用效率(WUE)的季节性影响,为促进毛竹林碳汇能力和生产力提升的林分结构调整等可持续栽培技术提供理论依据。结果表明:(1)出笋期,不同竹龄毛竹叶片净光合速率(Pn)和蒸腾速率(Tr)的日均值呈现出冠层上部小于冠层下部的梯度变化趋势,且2a生毛竹不同冠层Pn日均值大于3a生毛竹;孕笋行鞭期,不同林龄毛竹各时间点Pn值和日均值、以及2年生毛竹各时间点的Tr值均为冠层上部大于冠层下部。各生长季节,不同林龄毛竹个体叶片的气孔导度(Gs)均与Tr的变化趋势一致。(2)2年生毛竹各季节仅冠层上部叶片会出现"光合午休",而3年生毛竹仅于出笋期时各冠层叶片出现"光合午休"现象。(3)出笋期毛竹叶片WUE日均值随着冠层高度增加而增加,这种变化趋势不受竹龄影响;而孕笋行鞭期,仅2年生毛竹叶片WUE日均值随着冠层高度增加而下降。不同冠层高度的孕笋行鞭期毛竹叶片WUE日均值都显著高于出笋期;冠层高度对毛竹叶片气体交换特性和WUE的影响受生长发育关键期的季节因素影响,且毛竹叶片WUE与Gs之间存在负相关关系,其不受毛竹个体年龄和叶片冠层高度影响。(4)不同生长季节各冠层叶绿素a/b值均随着冠层高度下降而降低,不同林龄毛竹叶片叶绿素含量基本随着冠层自上而下呈逐渐增加的趋势。各生长季节,不同林龄个体叶片氮素含量、比叶重随冠层高度垂直变化趋势与叶片Pn日均值的垂直变化趋势一致。研究认为,毛竹不同冠层部位叶片通过改变形态、氮素含量来适应不同生长季节生长环境的变化,以便充分利用光能提高光合能力。     

Spartina alterniflora loisel root structure and meiofaunal abundance

Meiofauna were collected from adjacent areas with and without Spartina alterniflora Loisel culms. Environmental complexity resulting from root structure cannot be determined by simply observing S. alterniflora culm distribution. There were no significant differences between the two areas with respect to root density or root sizes; however, the number of live roots was significantly higher in the area containing Spartina culms. Nematodes, the most abundant taxon were positively correlated with live root density. In contrast, the number of dead roots and harpacticoid copepods were higher in the area without culms. This study suggests that nematodes are positively associated with micro-oxygenated zones produced by live S. alterniflora roots. Other measures of biogenic structure, such as total root density or root size fractions are not important in affecting nematode abundance.     

热消散液流测定系统研究竹子蒸腾的问题和解决思路

旺盛的蒸腾是竹子迅速生长的重要代谢保障,对林区生态系统水循环和水量平衡发挥关键作用,如何准确估测竹林的蒸腾耗水是迫切需要解决的方法难题。目前研究树木水分生理和森林水文广泛采用的热消散液流测定方法(TDP)却少有在竹林中应用,而仅有的几项研究报道由于缺乏严谨的实验验证,结果误差较大而缺少说服力。作者认为,竹壁结构异质性和竹竿中央空腔造成热量的不均匀分布是基于热通量交换的液流测定系统测量竹子蒸腾不准确的主要原因,提出以自行设计的注水变压液流特性测定法和传统的整树容器称重法,验证热消散液流测定系统估测竹子水分利用的适用性。本文还结合竹子的种群结构和无次生生长的特点,提出竹株借助相互连接的地下茎进行水分再分配,异株补偿水力限制,蒸腾主要受年龄而不是竹形大小影响的观点,建议通过分析竹子蒸腾的年龄效应,研究不同种植密度竹林水分利用的变化规律,为竹林生产和集水区水源管理提供有效的林型设计和措施。     

Combined effects of nitrogen addition and litter manipulation on nutrient resorption of Leymus chinensis in a semi‐arid grassland of northern China

Plant growth in semi‐arid ecosystems is usually severely limited by soil nutrient availability. Alleviation of these resource stresses by fertiliser application and aboveground litter input may affect plant internal nutrient cycling in such regions. We conducted a 4‐year field experiment to investigate the effects of nitrogen (N) addition (10 g N·m^?2·year^?1) and plant litter manipulation on nutrient resorption of Leymus chinensis, the dominant native grass in a semi‐arid grassland in northern China. Although N addition had no clear effects on N and phosphorus (P) resorption efficiencies in leaves and culms, N fertilisation generally decreased leaf N resorption proficiency by 54%, culm N resorption proficiency by 65%. Moreover, N fertilisation increased leaf P resorption proficiency by 13%, culm P resorption proficiency by 20%. Under ambient or enriched N conditions, litter addition reduced N and P resorption proficiencies in both leaves and culms. The response of P resorption proficiency to litter manipulation was more sensitive than N resorption proficiency: P resorption proficiency in leaves and culms decreased strongly with increasing litter amount under both ambient and enriched N conditions. In contrast, N resorption proficiency was not significantly affected by litter addition, except for leaf N resorption proficiency under ambient N conditions. Furthermore, although litter addition caused a general decrease of leaf and culm nutrient resorption efficiencies under both ambient and enriched N conditions, litter addition effects on nutrient resorption efficiency were much weaker than the effects of litter addition on nutrient resorption proficiency. Taken together, our results show that leaf and non‐leaf organs of L. chinensis respond consistently to altered soil N availability. Our study confirms the strong effects of N addition on plant nutrient resorption processes and the potential role of aboveground litter, the most important natural fertiliser in terrestrial ecosystems, in influencing plant internal nutrient cycling.     

Biology of the bamboo Chusquea culeou (Poaceae: Bambusoideae) in southern Argentina

Over a period of 7 years the biology and phenotypic variability of Chusquea culeou were studied at 5 locations in cool temperate forests of southern Argentina. Excavated rhizomes had an average of 1.1 successful rhizome buds, and an average of 2.1 years elapsed between successive generations of rhizomes. Rhizome buds usually develop within the first four years after a rhizome forms. Height, volume and weight of a culm can be calculated from its diameter 1 m above the ground. Culm size, length of foliage leaf blades, and pattern of secondary branching differed among study sites. Dead culms were numerous and commonly remained erect for more than 7 years after dying. New culm shoots appear in spring and reach full size within a few months. Shoots can grow more than 9 cm/day. Less than half of the shoots survived a year; most were killed by moth larvae. Multiple primary branch buds emerge through the culm leaf sheaths in the second spring. The mean number of branch buds at mid-culm nodes varied between 34.8 and 81.5, and the mean number of primary branches was between 22.8 and 40.8. Number and length of branches, and number and length of foliage leaf blades at each node is related to the position of the node on a culm. Most branches grow about 3 cm and produce 1 to 3 foliage leaves annually. Foliage leaf blades generally live 2 years or more; few survive 6 years. Relative lengths of foliage leaf blades and their spacing along a branch permit recognition of annual cohorts.Both gregarious and sporadic flowering have been reported, and every year a few isolated plants flower and die. Length of the life cycle is unknown. Seedlings require up to 15 years to produce culms of mature size. Foliage branches may live more than 23 years, and culms may survive 33 years. Extensive loss of new shoots to predation suggests that gregarious flowering may be driven by a need to escape parasitism. C. culeou clumps expand slowly. Average annual rate of increase of the number of live culms in a clump was 4.6%. Methods of seed dispersal are undocumented. A dense stand of Chusquea culeou had an estimated phytomass of 179 tons/hectare (dry weight), 28% of which was underground. Net annual production was about 16 t/ha dry weight.