不同林龄樟子松叶片养分含量及其再吸收效率

树木叶片的养分再吸收效率能够反映树木对养分保存、利用以及对养分贫瘠环境的适应能力。以科尔沁沙地东南缘章古台地区樟子松人工林为研究对象,分析了11、20、29、45年生树木叶片的基本特征、养分含量及其再吸收效率。结果表明:叶片衰老后其质量和面积明显减少;叶片凋落前的平均养分含量没有表现出随樟子松年龄增加而出现有规律的变化;凋落叶片中的N、P、K、Mg含量表现出随年龄增加而增加的趋势,而Ca的趋势与之相反;11年生和20年生的樟子松叶片N、P、K的再吸收效率相似,都显著高于29年生和45年生樟子松(P<0.05),而樟子松叶片对Mg的再吸收效率表现出随年龄增大而显著降低,Ca随叶片的衰老而不断累积,再吸收效率表现为负值,20年生的樟子松叶片Ca再吸收效率最大,11年生和45年生最低。樟子松叶片的N、P、K、Mg养分再吸收效率随年龄增加而降低的趋势表明,随年龄增加樟子松对贫瘠养分生境的适应能力逐渐降低,反映了樟子松养分保存方面的衰退特征。     

Biomass,decomposition and nutrient release of Vaccinium myrtillus leaf litter in four forest stands

Biomass and nutrient transfer (N, P, K, Ca, Mg) of bilberry (Vaccinium myrtillus L.) leaf litter fall, as well as decomposition and nutrient release, were studied in four mature forest stands situated in Central and South Sweden. Bilberry leaf litter fall amounted to between 33 and 55 kg ha^‐1 yr^‐1 in the four stands. Only minor differences between sites were noted for litter concentrations of N, P and Ca, whereas K and Mg showed somewhat larger variability. Relative amounts of the five nutrient elements in the litter fall were generally in the order N > Ca > K > Mg > P. The amounts of nutrients returned to the forest floor by the annual leaf litter fall in the stands ranged from 0.4 to 0.8 kg ha^‐1 for N, 0.4 to 0.6 kg ha^‐1 for Ca, 0.2 to 0.7 kg ha^‐1 for K, 0.1 to 0.2 kg ha^‐1 for Mg and 0.04 to 0.08 kg ha^‐1 for P.

The decomposition of the local bilberry leaf litter was followed by means of litterbags during three years. At all sites there was an extremely rapid mass loss from the litter (between 45% and 54%) during the first four to five months of decomposition. After this initial phase, the decomposition rates decreased markedly and after three years the accumulated mass losses of the litters varied between 64% and 78% at the studied sites. After two and three years of decomposition, three of the sites exhibited almost similar litter mass losses whereas at the fourth site the litter was decomposed to a significantly lower degree. The pattern of nutrient release from the decomposing bilberry leaf litter differed somewhat from site to site. Minor differences were, however, noted for P, Ca and Mg while N and K were more strongly retained in the litter at one of the sites.     

Seasonal changes of nutrient levels and nutrient resorption in Avicennia marina leaves in Yingluo Bay,China

Avicennia marina is a typical mangrove species of subtropical coastlines of China. However, little is known about the retention of nutrients by this species in oligotrophic, coastal environments. In this study, seasonal changes in nitrogen (N) and phosphorus (P) concentrations, N:P ratio and total phenolic concentration in A. marina leaves during senescence were studied. Avicennia marina leaves had high N and P concentrations but the seasonal pattern of N concentration was different from that of P concentration. The A. marina forest was N-limited as the N:P ratio of mature leaves was less than 14. Nitrogen resorption efficiency was higher than P resorption efficiency, and the concentrations of N and P in senescent leaves indicated that N resorption was mostly complete whereas P resorption was incomplete. Avicennia marina leaves contained low tannin concentrations, particularly condensed tannins, as the leaf extracts did not react with acid butanol. Total phenolic concentrations were not correlated with N concentrations in mature and senescent leaves of A. marina. These findings suggest that the high N resorption efficiency and low nutrient losses play an important role in nutrient conservation strategies for A. marina forests, whereas low tannin concentations have limited effects on nutrient cycling.     

Species differences in timing of leaf fall and foliage chemistry modify nutrient resorption efficiency in deciduous temperate forest stands

Extensive variation in fractional resorption of mineral elements from plant leaves is still not fully understood. In multi-species forest stands, species leaf fall phenology and leaf constitution may significantly modify the timing of nutrient return to the soil and overall plant nutrient loss. We studied leaf fall and nutrient loss kinetics, and leaf composition in three natural, temperate, deciduous broadleaf forest stands to determine the role of timing of leaf abscission and nutrient immobilization in cell walls on nutrient resorption efficiency of senescing leaves. Nitrogen (N), phosphorus and potassium contents decreased continuously in attached leaves after peak physiological activity during mid-season. Changes in nutrient contents of attached leaves were paralleled by decreases in nutrient contents in freshly fallen leaf litter. In different species and for different nutrients, resorption of nutrients from senescing leaves proceeded with different kinetics. The maximum nutrient resorption efficiency (the fraction of specific nutrient resorbed from the leaves at the end of leaf fall) did not depend on the mid-seasonal nutrient concentration. Species with earlier leaf fall resorbed leaf nutrients at a faster rate, partly compensating for the earlier leaf fall. Nevertheless, the litter-mass weighted mean nutrient contents in leaf litter were still larger in species with earlier leaf fall, demonstrating an inherent trade-off between early leaf fall and efficient nutrient resorption. This trade-off was most important for N. Losses of the non-mobile nutrients calcium and magnesium were unaffected by the timing of leaf fall. There was large variation in the maximum N resorption efficiency among species. Correlations among leaf chemical variables suggested that the maximum N resorption efficiency decreased with the increasing fraction of cell walls in the leaves, possibly due to a greater fraction of N occluded in cell wall matrix. We conclude that species leaf fall phenology and leaf chemistry modify the timing and quantities of plant nutrient losses, and that more diverse forest stands supporting a spectrum of species with different phenologies and leaf types produce litter with more variable chemical characteristics than monotypic stands.     

Ecological studies on subtropical evergreen broad-leaved forest in Okinawa, Japan: Litter production and nutrient input

Patterns of litterfall and nutrient input in a subtropical evergreen broad-leaved forest in northern Okinawa, Japan, were studied during May, 1996–April, 1999. The mean annual rate of litterfall in the five sampling plots ranged from 6.84 to 8.93 Mg ha⁻¹ yr⁻¹, of which 63.3–68.5% were leaves; 22.4–29.1% woody parts (including branches < 5.0 cm in diameter and bark); 2.8–5.0% sexual organs and 4.6–6.3% miscellaneous material. Significant differences were found among plots and among years. Significantly monthly differences pronounced seasonal patterns in litterfall were observed. Total litterfall and leaf litter showed negative correlations with relative basal area of the dominant species,Castanopsis sieboldii; and showed positive correlations with mean height of the stands. The dominant species,C. sieboldii produced an average of 2.36 Mg ha⁻¹ yr⁻¹ of leaf litter, which covered 30.5% of the annual litter production, and the nutrient input from those litterfall contributed 32.3, 28.3, 30.2, 22.2, 32.5, and 30.5% of total N, P, K, Ca, Mg, and Na, respectively. Nutrient use efficiency in litter production was high, especially for P and K compared with other broad-leaved forests in Japan indicating that P and K may be limiting in Okinawan evergreen broad-leaved forest.     

三峡库区马尾松根和叶片的生态化学计量特征

[目的]对马尾松根系和叶片养分(C、N、P、K、Ca、Mg)进行研究,探讨生长季和非生长季根系和叶片的化学计量学特征和养分分配特征,以及根和叶片养分的相关性。[方法]本研究分别在2014年7月和11月,利用土柱法采集根样和高枝剪采集枝条第二节上的健康叶样,然后再进行室内测试分析。[结果]表明:(1)非生长季与生长季相比,根C养分含量、C:N和N:P比值均下降,N、P、K、Ca、Mg养分含量含量均增加。(2)根C养分含量随直径增大而增加,N、P、K、Ca、Mg养分含量随直径增大而减小。(3)径级、取样时间以及两者交互作用对根系C、N、P、K、Ca、Mg养分含量和C、N、P养分化学计量比存在极显著影响(P0.01),同时取样时间对粗根C、N养分含量以及C:N比无显著影响。(4)细根(2 mm)C和N元素含量存在极显著的负相关关系,N和P元素含量存在极显著的正相关关系,同时C:N比值和N:P比值变异分别由各自两元素含量共同决定;粗根(2 3 mm)C、N计量比值和N:P比值变异分别主要由N元素含量和P元素含量决定;(5)从地上叶到地下根,C、N、P、K养分含量呈减少趋势,Ca、Mg养分含量呈增加趋势。同时,根和叶片养分含量相关性较弱,除C、K养分之外。[结论]马尾松根系养分含量与叶片养分的关系较弱,且分别对各养分的相对需求量不同;与生长季相比,非生长季马尾松根系N、P、K、Ca、Mg含量显著增加;C、N元素和N、P元素的耦合关系只出现在细根中。     

沙地柏对毛乌素沙地3种生境中养分资源的反应

为了揭示沙地柏对毛乌素沙地不同生境中养分资源的适应性反应 ,分析了固定沙地、流动沙地和滩地中土壤养分状况、生物量和养分在植株不同结构中的分配以及植株对不同养分的利用和重吸收效率。结果表明 :(1) 3种生境中的氮、磷、钾、钙和镁含量存在不同程度差异 ;(2 )生物量、氮和磷在叶片中分配比率随氮和磷含量的降低而增大 ,而在根中的分配恰好相反 ;(3)氮和磷重吸收效率、钾利用效率和重吸收效率、钙和镁利用效率随相应养分含量的降低而增大 ,氮和磷利用效率随氮和磷可利用性的降低而降低 ;(4)叶片和根系对养分内循环的贡献恰好相反 ;(5 )根分布对不同养分异质性的影响存在差异。     

Nutrient dynamics associated with leaf litter decomposition of three agroforestry tree species (<Emphasis Type="Italic">Azadirachta indica,Dalbergia sissoo</Emphasis>, and <Emphasis Type="Italic">Melia azedarach</Emphasis>) of Bangladesh

Azadirachta indica A. Juss, Dalbergia sissoo Roxb., and Melia azedarach L. are little studied species in nutrient return capabili- ties from leaf litter decomposition to maintenance of the soil fertility despite their importance in agroforestry practices of Bangladesh. A leaf litter decomposition experiment was conducted using a litterbag tech- nique to assess the nutrient return efficiency of these species. The de- composition rate of leaf litter was highest for M. azedarach and lowest for D. sissoo. Rainfall and temperature of study sites showed a signifi- cant (p<0.05) positive relationship with the rate of leaf litter decomposi- tion. The highest decay constant was observed for M. azedarach (6.67). Nitrogen and Phosphorus concentration in leaf litter showed a decreased trend sharply at the end of the first month, whereas rapid decrease of Potassium concentration was reported within 10 days. Conversely, higher concentration of nutrient was observed at the later stages of decomposi- tion. All three species showed a similar pattern of nutrient release (K > N > P) during the decomposition process of leaf litter. Among the studied species, D. sissoo was best in terms of N and P return and A. indica was best in terms of K return.     

西南桦和尾巨桉凋落叶分解及其与土壤性质的相关性

[目的]探讨南亚热带西南桦和尾巨桉人工纯林的凋落叶分解动态及其与土壤化学性质之间的相关关系.[方法]采用原位分解袋法研究凋落叶的分解过程.[结果]表明:西南桦、尾巨桉人工林凋落叶分解系数分别为0.96 a^-1和0.88 a^-1.在为期12个月的分解试验中,2种凋落叶有机C含量在整个分解过程中呈逐渐下降趋势;全K含量和C/N比在分解前期迅速下降,之后趋于平缓;全N含量和全P含量在整个分解过程中呈逐渐上升趋势;2种凋落叶N/P比则呈先升高后下降的趋势.无论是分解前期还是分解后期,凋落叶质量损失与N含量均呈显著正相关(前期R=0.877;后期R=0.855),与C/N均呈显著负相关(前期R=-0.735;后期R=-0.697).与尾巨桉林地土壤性质相比,西南桦凋落叶分解提高了林地0~10、10~20 cm土壤的有机C、全N、全P、全K、N/P,对2030 cm土壤有机C、全K、pH值、C/N、N/P则未产生显著影响.相关分析表明:凋落叶初始有机C含量与土壤有机C、全N、全P、全K、N/P显著相关;凋落叶初始全N含量与土壤全N、pH值、C/N显著相关.[结论]凋落叶的养分含量与土壤养分的关系紧密;与尾巨桉相比,西南桦凋落叶的养分含量明显较高,分解速率更快,释放到土壤中的养分也更多.     

Variation in the chemical composition of green leaves and leaf litters from three deciduous tree species growing on different soil types

The chemical composition of green leaves and leaf litters of sweet chestnut (Castanea sativa), oak (Quercus robur) and beech (Fagus sylvatica) were determined for 26 sites grouped into high fertility (HF) and low fertility (LF) soils according to base saturation and N-mineralization potentials. Measurements were made of total carbon, acid detergent fibre (ADF), Klason lignin, holo-cellulose, sugar constituents of hemicellulose and phenylpropanoid derivatives of lignin, and nutrient concentrations (N, Ca, P, Mg, K and Mn). Leaf and litter constituents varied within and between species according to soil groups, but beech showed contrasting responses to oak and chestnut. Beech leaves had lower ADF, lignin and cellulose on HF soils than LF soils, whereas oak and chestnut leaves had higher ADF, lignin and cellulose on HF than the LF soils. Conversely, the same constituents in beech leaf litter were higher on HF soils than LF soils, but lower in oak and chestnut leaf litter on HF soils than LF soils. The phenylpropanoid derivatives of lignin and sugar constituents of hemicellulose also showed similar variations in relation to soil groups with contrasting patterns for in leaves and litters. Re-absorption of N from leaves before litter fall was negatively correlated with soil N mineralization potential for beech (highest on LF soils) but showed an unexpected, positive relationship for oak and chestnut (highest on HF soils). These intra-specific differences of leaf and litter chemistry in relation to soil fertility status are unprecedented and largely unexplained. The observed patterns reflect phenotypic responses to soil type that result in continuum of litter quality, within and between tree species, that have been shown in related studies to significantly influence litter decomposition rates.     

Litterfall,decomposition and nutrient release of <Emphasis Type="Italic">Shorea robusta</Emphasis> and <Emphasis Type="Italic">Tectona grandis</Emphasis> in a sub-tropical forest of West Bengal,Eastern India

We studied leaf litter fall, decomposition and nutrient release patterns of Shorea robusta and Tectona grandis by using a litter bag technique to better understand the release pattern of nutrients to soil from leaf litter. Annual litterfall varied from 13.40 ± 2.56 t ha^?1 a^?1 for S. robusta to 11.03 ± 3.72 t ha^?1 a^?1 for T. grandis and the decay constant (k) of decomposed leaf litter was distinctly higher for T. grandis (2.70 ± 0.50 a^?1) compared to S. robusta (2.41 ± 0.30 a^?1). Biomass loss was positively correlated with the initial litter C, WSC, C/N and ash content in S. robusta and N, P and K concentration for T. grandis. Biomass was negatively correlated with lignin and L/N ratio for S. robusta and L, WSC, L/N and C/N ratio for T. grandis (P < 0.01). Nutrient use efficiency (NUE) and nutrient accumulation index (NAI) of S. robusta was higher than for T. grandis. The retranslocation of bioelements from senescent leaves ranked as P > N > K. Annual N, P and K input to soil through litterfall differed significantly between the two species in the following order: N>K>P. S. robusta was superior in terms of K and P return and T. grandis was superior in terms of N return. The two tree species showed a similar patterns of nutrient release (K > P > N) during decomposition of their leaf litter. Nutrients of N, K and P were the primary limiting nutrients returned to soil through litterfall with important roles in soil fertility and forest productivity.     

Seasonal changes in litter fall and its quality from three sub-tropical fruit tree species at Nelspruit, South Africa

Litter fall from upper storey trees in agroforestry systems contributes to nutrient cycling for the benefit of all components of the system besides serving as mulch. This study examined the seasonal changes in the quantity and quality of leaf litter fall from three sub-tropical fruit trees viz: avocado (Persea americana L.), mango (Mangifera indica L.) and litchi (Litchi chinensis L.) which have potential for use in agroforestry. Leaf litter production was estimated using nylon mesh litter traps erected over five randomly selected trees of each species in a completely randomised design. Litter quality was determined by analysing ash content and polyphenol, carbon, cellulose, lignin and nutrient concentrations over a 2?year period (2007?C2008). Total annual leaf litter production during the study period (dry matter basis) was 8.3, 6.3 and 5.6?t?ha^?1?year^?1 for litchi, mango and avocado, respectively. In both years, leaf litter fall was greatest during autumn and lowest during winter in all species. There were no significant differences in S, Ca, Mg and Mn concentrations in the leaf litter, but polyphenol, N, P and K concentrations differed significantly (P?<?0.05) between species. It was concluded that litter quality from all three tree species was low and would require appropriate management to improve its quality.     

马占相思等5个树种叶中养分含量和养分利用效率的研究

测定了阔叶树马占相思、木荷和红锥及针叶树杉木和加勒比松叶中的养分含量。结果表明 :5个树种中马占相思叶的N、P、K含量最高 ,杉木叶的Ca、Mg含量最高 ,而加勒比松叶的 5种养分含量最低。马占相思、红锥和加勒比松叶的养分含量为N >K >Ca >P >Mg ,而木荷和杉木叶的养分含量为N >K >Ca >Mg >P。各树种养分利用效率为P或Mg >Ca >K >N。     

模拟外源性氮磷对马占相思凋落叶分解及土壤生化特性的影响

[目的]研究外源性氮和磷对马占相思凋落叶的分解速率、分解过程中N、P、K含量和土壤生化特性的影响,以便为森林土壤养分管理提供参考。[方法]以广东省云勇林场马占相思林下凋落叶为试验材料,采用尼龙网袋分解法,设置对照(CK)、施N(10 g·m~(-2))、施P(5 g·m~(-2))、施N+P(N 10 g·m~(-2)+P 5 g·m~(-2))4种处理,每隔3个月取样1次,并测定凋落叶残留量和N、P、K含量。[结果]表明:施N、P和N+P处理对马占相思凋落叶的分解均为促进作用。各处理马占相思凋落叶的N含量在分解过程中大致保持稳定,施P和N+P处理的凋落叶P含量在分解过程中总体呈波动性上升,而各处理的凋落叶K含量变化规律不明显。施N、P和N+P处理提高了马占相思林土壤的有机质和全N含量,促进脲酶、磷酸酶及过氧化氢酶的活性。[结论]施N、P和N+P处理促进了马占相思凋落叶的分解,有利于马占相思林的养分循环。     

Nutrient distribution and accumulation patterns of natural secondary forests in the Loess Plateau of Shanxi Province, northern China

We studied the biomass and its allocation in natural secondary forests, as well as the amounts, accumulation and distribution of nutrient elements (N, P, K, Ca and Mg) in sample plots established in the Loess Plateau in Shanxi Province, northern China. The results show that biomass in natural secondary forests amounted to 36.09 t/hm², of which the tree layer accounted for 46%, the shrub layer for 29%, the herb layer for 13% and the litter layer for 12%. The total storage of the five nutrient elements is 1089.82 kg/hm². Nutrient storage in the tree layer is the largest, at 41%. The sequence of storage of the elements varied among different layers and is given as follows: shrub layer 31.27%, herb layer 12.55% and litter layer 15.36%. The accumulation of nutrient elements in the tree layer, ordered from high to low, is: branches > roots > stems >bark > leaves. The total storage of the five nutrient elements in the soil is 634.97 t/hm², where the accumulation of the nutrients accounts for 95.32% (N), 99.64% (P), 99.91% (K), 99.84% (Ca) and 99.95% (Mg) of the total amounts. The accumulation coefficients of different organs in the tree layer are, from high to low: leaves > branches > roots > bark > stems. The accumulation coefficients in the different layers are listed as follows: shrub layer > tree layer > herb layer and for the elements as: N > P > Ca > K > Mg. __________ Translated from Journal of Beijing Forestry University, 2008, 30(3): 57–62 [译自: 北京林业大学学报]     

Influence of nitrogen and phosphorus fertilizers on amount and nutrient content of litterfall in a regrowth eucalypt forest

The effects of fertilizer treatment on nutrient transfers to the forest floor were examined in regrowth Eucalyptus diversicolor F. Muell. forest. Dry weight and nutrient content of leaf litterfall and total litterfall were measured for 3 years in a stand to which two levels of N (0, 200 kg ha^-1 year^-1) were applied each year at each of three levels of a single initial application of P (0, 30, 200 kg ha^-1). Annual accessions of litter to the forest floor were significantly increased by additions of both N (by 17%, 18% and 21% in the 3 years) and 200 kg P ha^-1 (by 8%, 8% and 4% in the 3 years) but there was no interaction between effects of N and P treatments. Fertilizer application also had a significant effect on the nutrient content of leaf litterfall and total litterfall. Concentration of N in leaf litterfall was 9% to 23% greater on plots treated with N fertilizer compared to untreated plots. The amounts of N in litterfall were about 30% greater on N-treated compared to untreated plots. On plots treated with 200 kg P ha^-1, P concentrations in leaf litter were 50% to 100% greater than in litter from plots receiving no P. Application of 200 kg P ha^-1 increased the amounts of P in annual litterfall by 32% to 87%. The greatest increase in P accessions occurred soon after fertilizer treatment. The amounts of Ca, K, and Na in litterfall were also significantly increased by fertilizer application. For Ca and K this was due partly to increases in element concentrations in litterfall following application of treatments. The effect of fertilizers on internal recycling of plant nutrients and on litter accumulation and nutrient dynamics in forest floor litter is discussed.     

Nutrient return via litterfall in two contrasting Pinus sylvestris forests in the Pyrenees under different thinning intensities

Thinning influence on litterfall chemical composition (N, P, K, Ca and Mg) was studied for 30 months in two contrasting Pinus sylvestris L. stands in the western Pyrenees mountain range (Northern Spain): Aspurz (625 m.a.s.l, high productivity, Mediterranean climate) and Garde (1335 m.a.s.l, low productivity, continental climate). Two different thinning intensities were carried out by removing 20% and 30% of pre-thinning basal area. In accordance with site quality differences between sites N, K, Ca and Mg total soil returns via litterfall were significantly higher in Aspurz than in Garde. However, P, K, Ca and Mg concentrations were higher in Garde and N higher in Aspurz. Changes in nutrient concentrations over time varied depending on litterfall fractions, showing a variety of patterns; seasonal (N, P, K) or erratic patterns (Ca, Mg) in Aspurz, and seasonal (N, P), biannual (Ca, Mg) or erratic (K) patterns in Garde. In addition to these patterns, differences in nutrient concentrations between years were found in needle litter in Aspurz but not in Garde. Nitrogen returns to forest floor via litterfall were more constant in Aspurz but followed a pulse dynamics in Garde, with the opposite for P, due to important returns from the miscellaneous fraction in the Mediterranean site. Thinning reduced nutrient returns via litterfall in both sites, but significant differences were found only in summer. These results suggest that Aspurz (Mediterranean stand) is more sensitive in the short-term to human intervention than Garde (continental stand) and therefore site-specific forest management plans should be used within more general region-wide plans in order to ensure sustainability of forests.     

Comparative analyses on the litter in Korean pine Mongolian Scots pine and Dahurian Larch plantations

Comparative analyses were conducted on the nutrient element content and returning amount of main fractional compositions of litter in Korean pine (KP), Mongolian Scots pine (MSP) and Dahurian larch (DL) plantations in Laoshan Plantation Experiment Station of Maoershan Experiment Forest Farm of Northeast Forestry University. The results are as follows: (1) The nutrient element content and returning amount in litter varies among different fractional compositions and tree species, the total returning amount of all nutrient elements and the returning amount of K, Ca, Mg, N and P are DL > MSP > KP, the returning amount of Cu is DL > KP > MSP, the returning amount of Fe and Mn are MSP > DL > KP; (2) To KP and DL plantations, the main nutrient element returned is dead needles; dead branches, bark scales and dead cones account for a little proportion; whereas to MSP plantation, besides dead needles, dead branches and bark scales also play an important role in the return of nutrient elements; (3) A little deal of dead leaves can provided a great deal of returning amount of nutrient elements.     

印度西部5种热带干落叶林中凋落物中生物元素和返回到绿叶中的季节性变化(英文)

本文对印度西部5种热带干落叶林中凋落物里生物元素的季节性变化和它们返回到新鲜叶中季节性变化进行研究。对5个树种:阿拉伯金合欢(Acacia nilotica L.)、金合欢(Acacia leucophloea Roxb.)、柚木(Tectonagrandis L.f.)、绒毛野独活(Miliusa tomentosa Roxb.)和紫矿(Butea mono-sperma Lain.)中凋落物的成熟叶、枝和再生部分的N、P、Ca、Mg、K和Na的浓度,以及老叶和幼叶中浓度间的关系进行调查。对这些树种的总干物质进行记录,并分析它们所含的N、P、Ca、Mg、K和Na的含量。其中阿拉伯金合欢叶子中N的含量最高,而金合欢的叶子里Ca和Mg含量最高。叶中含P最多的是阿托伯金合欢、金合欢和紫矿,而含P最少的是柚木和绒毛野独活。K和Na含量在这些树种中没有明显的区别。观察发现,N、P和K的浓度随季节变化大,但Ca和Mg则不然。唯有钾在所有树种中都是最稳定的,吸收N和P可以用于来年新叶的生长。从老叶和凋落物中吸收的营养会支持新叶的生长,并增加土壤的肥力。图1表4参30。     

Changes in the N and P concentrations,N:P ratios,and tannin content in <Emphasis Type="Italic">Casuarina equisetifolia</Emphasis> branchlets during development and senescence

Changes in the N and P concentrations, N:P ratios, and tannin content in Casuarina equisetifolia branchlets across a coastal gradient were studied at Chishan Forestry Center of Dongshan County, Fujian Province, China. (1) Total phenolics and protein precipitation capacity in young branchlets was significantly higher than in mature and senescent branchlets across a coastal gradient; extractable condensed tannin content was higher in young and mature branchlets than in senescent branchlets. Whereas protein-bound condensed tannins increased with senescence, fiber-bound condensed tannins fluctuated without a consistent pattern; (2) N and P concentrations at various stages of branchlet development across a coastal gradient followed the same order: young branchlets > mature branchlets > senescent branchlets; N:P ratio of young branchlets was the lowest, and increased with maturity and senescence across a coastal gradient; phosphorus resorption efficiency was significantly higher than nitrogen resorption efficiency among corresponding coastal gradients in response to P deficiency (high N:P ratio), but nutrient resorption efficiency was influenced by coastal gradients; (3) significant linear relationships between total phenolics and nutrient contents indicated that polyphenolics had a potential effect on nutrient cycling.