缺苞箭竹密度对养分元素贮量、积累与分配动态的影响

研究了缺苞箭竹(Fargesiadenudate)-紫果云杉(Piceapurpurea)原始林下不同密度缺苞箭竹群落的养分元素贮量与分配动态以及养分元素在一个生长季节内的积累量。结果表明:地上、地下部分的N、P、K、Ca、Mg贮量均随着箭竹密度的增加而增大,养分元素贮量排序为:K>N>Ca>P>Mg。密度较大的箭竹群落(D1和D2)中,地上部分的N、P和K贮量大于地下部分,而密度较小的箭竹群落(D3)中P和K贮存于地下部分的比例较大,3个群落中的地下部分Ca和Mg贮量均大于地上部分,且地下部分的养分元素贮量的比例随着箭竹密度的增加而减少。养分元素的总积累量排序为:K>N>Ca>P>Mg,且地上部分和群落的总积累量随着箭竹密度的增加而增加,总积累率以D1群落最大,3个群落的养分元素积累率大小顺序为:Mg>Ca>P>N>K。地下部分(根系和鞭)养分元素贮量比例随着箭竹密度的增加而下降,而地上部分(叶、枝和竹杆)养分元素贮量比例随着箭竹密度增加而上升。密度对缺苞箭竹养分贮量、积累和分配动态有深刻影响。     

密度对缺苞箭竹凋落物养分归还及养分利用效率的影响

在缺苞箭竹-紫果云杉原始林下,选取3个密度(D1、D2、D3)的缺苞箭竹,研究了密度对缺苞箭竹凋落物量、养分归还量及养分利用效率的影响.结果表明:3个密度缺苞箭竹的年凋落物量分别为793.2、1135.7和1458.5kg.hm-2,C归还量分别为370.7、516.2和671.5kg.hm-2,5种主要养分归还量分别为16.3、22.9和29.3kg.hm-2,均随密度的增大而增加.各密度养分年归还量中均以Ca最高(占总量的48%～58%),P和Mg最低(3%～5%),总体排序为Ca>N>K>Mg、P.除高密度(D3)缺苞箭竹在8月有一个凋落与养分归还小峰外,10月生长季末是各密度缺苞箭竹凋落及养分归还高峰期.不同密度缺苞箭竹叶N和K的再分配能力无显著差异,P的再分配能力随密度的增大而增强,Ca、Mg则显著积累.缺苞箭竹P的养分利用效率随密度的增大而增高,表明P可能是缺苞箭竹生长更新的限制因子.     

土壤养分库对缺苞箭竹叶片养分元素再分配的影响

研究了王朗自然保护区3个密度的缺苞箭竹群落的土壤养分库和叶片养分元素再分配能力的相互关系。结果表明,不同密度箭竹群落的土壤N、K贮量没有显著差异,土壤P贮量随着密度增加而显著减少（P〈0．01）,土壤Ca和Mg贮量则随着密度增加而增加。不同密度的箭竹叶片N和K的再分配能力没有显著差异,叶片P的再分配能力随着密度的增加而显著增加,Ca和Mg随着箭竹密度的增加在凋落叶中有显著积累的趋势。这表明,基于密度的箭竹叶片养分元素再分配能力与土壤养分库的大小密切相关,可能的机理过程是不同密度的箭竹在生长发育过程中改变了土壤养分库的大小,土壤养分库通过反馈机制导致箭竹叶片养分元素再分配能力的变化,体现了土壤与植被之间的互动关系。综合分析表明,P可能是限制缺苞箭竹生长发育的重要因子。     

缺苞箭竹密度对其生物量分配格局的影响

研究了一个生长季节内缺苞箭竹(Fargesia denudata) 紫果云杉(Picea purpurea)原始林下不同密度缺苞箭竹群落的生物量及其分配格局.结果表明,缺苞箭竹群落生物量、净生产量、平均单株生物量、地上部分生物量、地下部分生物量随密度的增加而增大,而缺苞箭竹地上部分净增长率却随密度的增加而降低.在一个生长季节内,缺苞箭竹地上部分与地下部分生长相关性随密度的增加而增大.除指数生长期(7、8月)外,缺苞箭竹地上部分/地下部分生物量比在生长季节内随密度增加而增大,但在缺苞箭竹生长的指数生长期,中等密度有较大的地上部分/地下部分生物量比.缺苞箭竹生物量在各器官的分配取决于密度和生长时期,密度对缺苞箭竹的生物量分配格局有显著影响.     

缺苞箭竹群落密度对土壤养分库的影响

研究了王朗自然保护区内缺苞箭竹(Fargesia denudata)群落3个密度在1个生长季(5～10月)内不同土壤层次的养分贮量及其季节动态.结果表明,土壤(0～30 cm)总P、速效P贮量均随密度的增加而显著减少(P<0.01);而土壤总Ca、Mg贮量则随密度的增加而增加;土壤N、K(全量或速效)贮量密度间差异不大.在不同密度的箭竹群落样地内,除了D1样地土壤总钾贮量大于Ca外,土壤层(0～30 cm)不同养分贮量(全量)大小顺序均为Ca>K>Mg>N>P.表层(L1)速效N、P和K浓度在7月份均有显著降低的现象,随后又逐渐回升.养分的变化幅度则普遍存在着表层(L1)大于下层(L2、L3),高密度(D3)大于低密度(D1),速效P大于速效N、K的现象.土壤总养分贮量与浓度在土壤层次上的分布特征明显不同,3个密度样地中L1(0～10 cm)层的N、P、K、Ca、Mg贮量均低于L2(10～20 cm)和L3(20～30 cm)层.分析表明,箭竹群落土壤层养分贮量与密度密切相关,可能是由于密度影响到了箭竹对土壤养分的吸收、凋落物养分的归还、微生物活性等养分循环各个环节,从而导致了土壤养分贮量的改变.其中,密度对P、Ca贮量影响最大,Mg其次,对N、K影响最弱.随着箭竹密度的增加,越来越低的土壤总P、速效P贮量也表明,P素可能是箭竹生长发育的主要限制因子,P不足可能是导致箭竹开花的重要诱因.     

干热河谷区不同林龄赤桉叶中养分含量和再吸收率的比较及其线性回归分析

以种植于干热河谷区的赤桉(Eucalyptus camaldulensis Dehnh.)幼龄林、中龄林和成熟林为研究对象,分析了赤桉鲜叶和凋落叶中养分(包括N、P、K、Ca、Mg和Na)的含量和化学计量比,并计算各养分的再吸收率;在此基础上,对鲜叶和凋落叶中各养分的含量与再吸收率进行线性回归分析.结果表明:成熟林赤桉鲜叶和凋落叶的有机碳、全氮、全磷、全钾和全钠含量总体上高于幼龄林,而全钙和全镁含量则低于幼龄林;且鲜叶中的全氮、全磷、全钾、全钠和全镁含量总体上高于凋落叶,而有机碳和全钙含量则低于凋落叶.成熟林赤桉鲜叶和凋落叶的C:N比、鲜叶的N:P比和N:K比以及凋落叶的K:P比和Ca:Mg比均低于幼龄林,但其鲜叶的K:P比和Ca:Mg比及凋落叶的N:P比和N:K比则高于幼龄林;且不同林龄鲜叶的C:N比、K:P比和Ca:Mg比均低于凋落叶.各林龄赤桉叶的Ca再吸收率及幼龄林和中龄林叶的Na再吸收率均为负值,而其余养分的再吸收率均为正值;随林龄增长,N、K和Mg的再吸收率先升高后降低,而P、Ca和Na的再吸收率却先降低后升高;总体上看,赤桉叶中各养分的再吸收率从高到低依次为P、N、K、Mg、Na、Ca.线性回归分析结果表明:赤桉鲜叶的全钾和全钠含量分别与K和Na再吸收率呈极显著正相关(P<001),全钙含量与Ca再吸收率呈显著正相关(P<005);而凋落叶的全氮含量与N再吸收率呈极显著负相关,全镁含量与Mg再吸收率呈显著负相关.综合分析结果显示:林龄对赤桉叶的养分含量和再吸收率有明显影响,其保存养分的能力随林龄增长呈现先增强后减弱的趋势.     

杨树人工林凋落物养分归还功能研究

对杨树中龄林、成熟林凋落物量、组成特征、季节动态及凋落物中N、P、K、Fe、Ca、Mg含量进行了定位观测和实验测定.结果表明:杨树成熟林的年凋落物量为4.45 t·hm-2·a-1,是中龄林的1.42倍,两者存在显著差异(ρ＜0.05);叶是凋落物的主要形式,分别占中龄林、成熟林总凋落物量的70.1%和81.5%;凋落物量具有明显的季节动态,表现为"双峰"型;成熟林养分归还量是68.4 kg·hm-2·a-1,是中龄林48.96 kg·hm-2·a-1的1.4倍;两林分各养分年归还量的大小顺序为N＞Ca＞K＞Mg＞Fe＞P;杨树成熟林的N、P、Fe、Mg4种元素的利用率大于中龄林的,而K和Ca元素的利用率却相反.     

亚热带不同植被恢复阶段林地凋落物层现存量和养分特征

为揭示亚热带森林植被自然恢复过程中,凋落物层现存量及其养分元素储存能力的演变,采用空间代替时间的方法,在位于亚热带丘陵区的长沙县选取地域相邻、生境条件基本一致的檵木+南烛+杜鹃灌草丛（Loropetalum chinense+Vaccinium bracteatum +Rhododendron simsii scrub-grass-land,LVR）、檵木+杉木+白栎灌木林（L.chinense+Cunninghamia lanceolata+Quercus fabri shrubbery,LCQ）、马尾松+柯+檵木针阔混交林（Pinus massoniana +Lithocarpus glaber +L.chinense coniferous-broad leaved mixed forest,PLL）、柯+红淡比+青冈常绿阔叶林（L.glaber+Cleyera japonica+Cyclobalanopsis glauca evergreen broad-leaved forest,LAG）作为一个恢复序列,设置固定样地,采集未分解层（U层）、半分解层（S层）、已分解层（D层）凋落物样品,测定凋落物层现存量和主要养分元素含量、储量及其释放率,分析植物多样性指数与凋落物层现存量、养分元素含量的相关性。结果表明：1）凋落物层及各分解层凋落物现存量随着植被恢复而增加;同一恢复阶段D层凋落物现存量最高,占凋落物层现存量的41.59%-51.02%,不同分解层凋落物现存量的差异随着植被恢复而增大;各恢复阶段凋落物分解率为0.44-0.61,周转期为1.65-2.28 a。2）凋落物层及各分解层凋落物主要养分元素含量均表现为：N > Ca > Mg > K > P,随着植被恢复呈现出不同的变化特征,其中N、P含量总体上呈增加趋势,K含量LAG（除U层外）最高,PLL最低,Ca含量LCQ最高,PLL最低,Mg含量LAG（除U层外）最高,LVR最低;同一恢复阶段N、P（除PLL、LAG外）、K、Ca、Mg含量随着凋落物的分解而下降。3）不同恢复阶段凋落物层主要养分元素的储量依次为：N > Ca > Mg > K > P;凋落物层及各分解层凋落物主要养分元素总储量及各种养分元素的储量总体上随着植被恢复而增加;同一恢复阶段随着凋落物的分解,N、P储量增加,而K、Ca、Mg储量变化不大;随着植被恢复,凋落物层养分元素储存能力和转化归还能力提高,特别是N,养分元素总释放率下降,有利于养分的固持。4）乔木层、灌木层、草本层的植物多样性指数对凋落物层现存量和主要养分元素含量的影响不同,其中乔木层的影响最明显。     

神农架常绿落叶阔叶混交林凋落物养分特征

凋落物是联结陆地生态系统植物与土壤养分的重要媒介,了解凋落物养分特征有助于理解陆地生态系统物质循环的机理。该研究于2015年收集了神农架地区常绿落叶阔叶混交林的新鲜凋落物及现存凋落物,测定其不同器官中大量元素(C、N、P、K、Ca、Mg)的含量,据此分析其养分含量、养分归还量、养分储量及化学计量比的特征。结果发现:该常绿落叶阔叶混交林新鲜凋落物的C、K养分含量显著高于现存凋落物,N、P、Ca、Mg养分含量显著低于现存凋落物;其凋落物大量元素的养分归还量及养分储量大小顺序均为C Ca N Mg K P,分别为1569.84、52.44、34.82、6.24、5.24、1.30 kg hm~(-2) a~(-1)及1835.29、87.87、51.17、12.12、3.90、1.95 kg hm~(-2) a~(-1);其新鲜凋落物及现存凋落物的C∶N∶P分别为1307.33∶27.73∶1及976.48∶26.77∶1,新鲜凋落物的C∶N、C∶P显著高于现存凋落物,N∶P无显著区别。研究表明,新鲜凋落物与现存凋落物养分含量之间的差异与不同元素在分解过程中的可淋溶性及生物固持等因素有关。该地区常绿落叶阔叶混交林凋落物养分归还量及养分储量相对于亚热带阔叶林平均水平较低;且显著低于喀斯特地区同类型森林,主要与其凋落物产量、降水量及植被类型有关。该森林生态系统新鲜凋落叶与中国及全球范围内阔叶树种凋落叶相比C∶N较低,C∶P、N∶P较高,这可能是由于该地区N沉降及P限制现象较为严重所致。     

森林土壤动物对凋落物早期分解及养分释放的影响

采用野外缩微实验方法,研究了会同林区常绿阔叶林和杉木人工林土壤动物对凋落物早期分解的影响。结果表明:孔径为2mm的网筒内试验土壤和凋落物中大型土壤动物的类群数和多度均明显少于孔径为4mm的网筒;排除大型土壤动物后,常绿阔叶林中凋落物C、K、Ca、Mg养分浓度显著增加,杉木林中凋落物Mg浓度显著增加,2个样地中的凋落物失重率以及凋落物C、P、Ca、Mg等养分元素的释放率均极显著降低(P0.01);大型土壤动物对不同元素释放率的影响不同,2个样地中对凋落物Ca、Mg元素释放率的影响均较大,杉木人工林中对N和K释放率的影响较小,常绿阔叶林中对P释放率的影响最小。     

Is primary production in holm oak forests nutrient limited?

Correlations between primary production and patterns of nutrient use and nutrient availability were investigated in 18 plots in closed holm oak (Quercus ilex L.) stands in the Montseny mountains (NE Spain), searching for evidence of nutrient limitation on primary production. The plots spanned a range of altitudes and slope aspects within a catchment. Nutrients considered were nitrogen (N), phosphorus (P), potassium (K) and magnesium (Mg) in plant samples, and the above plus calcium (Ca) and sodium (Na) in the soil. Primary production was found by summing the annual aboveground biomass increment to the annual litterfall. Across plots, primary production was correlated with the annual return of nutrients in litterfall, but this relationship probably arose from the common effects of the amount of litterfall on both primary production and nutrient return, and not from any nutrient limitation. Primary production was not significantly correlated with nutrient concentrations in mature leaves nor leaf litterfall, nor with absolute or relative foliar retranslocation of nutrients before leaf abscission, nor with the concentration and content (kg/ha) of total N, extractable P, and exchangeable K, Mg, Ca and Na in the upper mineral soil. We conclude that there is no correlational evidence that primary production is nutrient limited in this holm oak forest.     

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.     

Significance of sequential leaf development for nutrient balance of the cotton sedge,Eriophorum vaginatum L.

Summary The sedgeEriophorum vaginatum in an interior Alaskan muskeg site produced leaves sequentially at about 1.5-month intervals. Each leaf remained active for two growing seasons. Young leaves (even those initiated late in the season) always had high concentrations of N, P, K and Mg and were low in Ca. Stems had high concentrations of nutrients, sugar, amino acid N and soluble organic P in autumn and spring but low concentrations in summer. Growth of leaves in spring was strongly supported by translocation from storage. Leaves approached their maximum nutrient pool before nutrient uptake began in late spring, one month before maximum biomass. Retranslocation of nutrients from aging leaves could support nutrient input into new, actively growing leaves as a consequence of the sequential leaf development. For instance retranslocation from aging leaves accounted for more than 90 and 85% of P and N input to new leaves appearing in early summer and 100% to leaves that appeared later. Leaching losses were negligible. Half time for decay of standing dead litter was 10 years. We suggest that sequential leaf development paired with highly efficient remobilization of nutrients from senescing leaves enables plants to recycle nutrients within the shoot and minimize dependence upon soil nutrients. This may be an important mechanism enablingEriophorum vaginatum to dominate nutrient-poor sites. This may also explain why graminoids with sequential leaf production cooccur with evergreen shrubs and dominate over forbs and deciduous shrubs in nutrient-poor sites in the boreal forest (e.g., in bogs) and at the northern limit of the tundra zone.     

Variable Responses of Lowland Tropical Forest Nutrient Status to Fertilization and Litter Manipulation

Predicting future impacts of anthropogenic change on tropical forests requires a clear understanding of nutrient constraints on productivity. We compared experimental fertilization and litter manipulation treatments in an old-growth lowland tropical forest to distinguish between the effects of inorganic nutrient amendments and changes in nutrient cycling via litterfall. We measured the changes in soil and litter nutrient pools, litterfall, and fine root biomass in plots fertilized with nitrogen (N), phosphorus (P), or potassium (K), and in litter addition and litter removal treatments during 7 years. Soil inorganic N and litter N increased in double-litter plots but not in N-fertilized plots. Conversely, litter P and soil pools of P and K increased in fertilized plots but not in the double-litter plots. Soil and litter pools of N and K decreased in the no-litter plots. Changes in litterfall with added nutrients or litter were only marginally significant, but fine root biomass decreased with both the litter and the K addition. Differences between the two experiments are mostly attributable to the coupled cycling of carbon and nutrients in litter. Increased nutrient inputs in litter may improve plant uptake of some nutrients compared to fertilization with similar amounts. The litter layer also appears to play a key role in nutrient retention. We discuss our findings in the context of possible impacts of anthropogenic change on tropical forests.     

Nutrient content and seasonal fluctuations in the leaf component of coark-oak (Quercus suber L.) litterfall

Nutrient content and seasonality of the leaf component in cork-oak litterfal were studied over a two year period in two cork-oak forest sites differing in biomass and edaphic condition in the north-eastern Iberian peninsula. Fallen senescent leaves compared to young leaves showed higher non-mobile nutrient concentrations and lower mobile nutrient concentrations, specially P, N, K, and Mg. At both sites, seasonal fluctuations affected both leaf production and leaf mineral content. The maximum leaf fall period correspond to the start of the vegetative growth and to the lowest N and P concentration in the falling leaves. The opposite was true for the winter, when litterfal was minimal and N and P content in falling leaves was at a maximum.The comparison between falling leaves and canopy leaves suggests that the analysis of fallen leaves can be a useful measure of N and P nutrition in cork-oak. We found site dependent differences in nutrient content and nutrient remobilization. In comparison with Q. ilex, although litter production was in the same range, nutrient retranslocation was greater for Q. suber.     

Litter production and forest floor nutrient dynamics in pine and hardwood stands of New Brunswick, Canada

Biomass and nutrient transfer (N, P, K, Ca, Mg) of overstory (branches and leaves) and understory litter fall were examined over a two year period in four jack pine stands aged 16, 29, 49 and 57 years and four mixed hardwood stands aged 7, 17, 20 and 29 years. Relative amounts of the five nutrients in litter fall for both series of stands were N > K ≷ Ca > P = Mg. Return of mineral elements to the forest floor was generally twice as high on the hardwood stands as for similarly aged pine stands. Overall return of nutrients plotted versus stand age generally exhibited a plateau relationship, with relatively little difference among stands; however, some exceptions occurred. Understory contribution to litter fall was very important on these stands, since in most cases the nutrient mass in understory litter was usually similar to or higher than that from the tree layer. Data on forest floor biomass, nutrient distribution and turnover rates of these stands were also presented; mobility of nutrients in the forest floor was in the order K > Mg ≥ P ≥ Ca ≥ N.     

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。     

林地覆盖经营对雷竹鞭根主要养分内循环的影响

为了给林地覆盖经营雷竹(Phyllostachys violascens)林可持续经营提供理论参考,探讨了休养式覆盖经营(覆盖3a后休养3a)、长期覆盖经营(覆盖6a)和不覆盖雷竹林(CK)2年生壮龄竹鞭及其1级、2级根N、P、K、Mg、Ca、Fe浓度和养分迁移、内循环率的差异。结果表明:不同覆盖经营年限雷竹林N、P、K、Mg、Ca和Fe浓度总体上1级根显著高于2级根。1级根和2级根中均存在N、P、K、Mg的养分内循环,且1级根养分内循环率大于2级根,Fe、Ca内循环不明显。N、P、K、Mg养分浓度与养分迁移速率随时间的推延,1级根为持续降低,2级根为先升高后降低。与不覆盖雷竹林相比,休养式林地覆盖经营总体上提高了1级、2级根的N、P、K、Ca的浓度和P、K、Mg的迁移速率、N、P、K的迁移量、P、K的养分内循环率以及1级根Mg的浓度和迁移量、2级根N的迁移速率和Mg的内循环率;长期林地覆盖经营虽提高了雷竹1级根N、K的浓度和N的迁移量及2级根N的浓度和内循环率,但总体上降低了1级根P、K、Mg和2级根N、P、Mg的迁移量与1级、2级根P、Mg的迁移速率及P、K、Mg的养分内循环率。研究表明:雷竹林鞭根中存在明显的养分内循环,且1级根对养分内循环的贡献较大。休养式林地覆盖经营利于雷竹林对养分的循环利用,而长期覆盖经营阻碍了根系对养分的平衡吸收,减弱了根系养分的内循环,不利于雷竹林的生长更新。