云南中山湿性常绿阔叶林中降雨对养分淋溶的影响

 作者在云南哀牢山生态站对中山湿性常绿阔叶林进行了定位研究,根据1990～1992年所取得的观测资料,对林外大气降雨,林内雨及树干茎流的养分浓度,养分季节变化及养分贡献进行了分析和讨论,探讨了大气降雨对养分淋溶的影响。结果表明：N、P、K、Ca、Mg浓度在林外降雨、林内降雨及树干流中有很大的差异。其养分浓度和养分输入均为雨季>干季,且养分浓度除林外降雨中N浓度外,均表现树干茎流>林内雨>林外降雨。此外,对降雨和淋溶作用对林地养分物质输入的贡献也进行了分析和讨论。     

广西南宁桉树人工林降雨再分配特征

为了解桉树人工林生态系统的降水再分配特征,改进桉树人工林经营方案,以提高林地保水保肥能力,本文依托广西南宁桉树林生态系统定位观测研究站,通过观测2015年7月—2016年5月历时11个月的尾巨桉林外降雨、林内降雨、穿透雨和树干径流,分析尾巨桉林冠降雨再分配特征。结果表明,研究期间的降雨总量1536 mm,穿透雨总量1042mm,占降雨总量68%;树干径流总量9.2 mm,占降雨总量0.6%;林冠截留总量490 mm,占降雨总量32%。月降雨量与穿透雨呈对数函数关系,当月降雨量超过25 mm即产生穿透雨;穿透雨和穿透率随降雨强度的增加而增加,当次降雨强度达暴雨以上时,林外降雨几乎全部形成林内降雨。在小雨、中雨、大雨和暴雨4种降雨强度条件下,累计降雨量与累计穿透雨均呈二次多项式递增函数,其中小雨和中雨的穿透雨初始时间滞后初始降雨分别约20min和10 min,而大雨和暴雨的穿透雨初始时间与降雨同步。树干径流虽在本文降雨分配计算过程中忽略不计,但其作用不可忽视。月降雨量与截留量呈递增幂函数关系,与截留率呈递减指数函数关系。     

鼎湖山酸沉降背景下主要森林类型水化学特征初步研究

雨水的水质在通过森林后会发生变化．如果雨水是酸性的,这种变化会更加明显．通过一年多时间在鼎湖山主要森林类型采样分析发现,鼎湖山大气降水pH值低,酸雨频率高;阔叶林穿透雨pH值比大气降水高,树干径流和地表水pH值比大气降水低,土壤自然酸化非常严重;混交林穿透雨和地表水酸度比大气降水低,树干径流酸度则大于大气降水;针叶林穿透雨和树干径流都有进一步酸化趋势,但地表水pH值比大气降水高．3种林型比较,阔叶林林冠缓冲能力最强,针叶林土壤缓冲能力最大．3种林型,林内降水和地表水养分N、P、K、Ca、Mg和Na含量除N外都明显高于大气降水．各林型树干径流对养分富集能力强于穿透水,养分在大气降水中的浓度低于在地表水中的浓度．针叶林林内降水比混交林和阔叶林养分含量高,但地表水中养分浓度比后两者低．从地表水的养分浓度看,阔叶林和混交林养分亏损更为严重．     

科尔沁沙地樟子松林降雨再分配特征

以中国科学院乌兰敖都荒漠化实验站35年生樟子松人工林为研究对象,通过对降雨、穿透雨、树干径流和林冠截留的观测,研究樟子松林对降雨再分配作用,分析各部分产生的阈值,确定降雨有效补给量。结果表明:2015年5—9月共观测到降雨事件31次,呈现小数量、低强度的特征,樟子松林地穿透雨、树干径流和林冠截留分别占同期降雨量的69.28%、1.26%和29.45%。林地有效补给量为117.67 mm,占降雨量的70.54%。穿透雨随降雨量增加而线性增加,发生阈值为0.85 mm降雨量;树干径流与降雨量呈二次多项式关系,当降雨量达到2.44 mm时,产生树干径流;林冠截留随降雨量呈现幂函数关系,截留率随降雨量呈指数减少趋势。降雨再分配比例受降雨等级影响,当降雨等级为15~20 mm时,林内有效降雨比例最高(90.35%)。明确樟子松林降雨再分配特征和比例变化对理解降雨补给作用和林地衰退的水分机制具有重要意义。     

贵州省喀斯特地区原始林水化学特征

降水是森林生态系统的一个主要的养分输入源,观测并分析降水化学对于准确地估算森林生态系统养分循环的养分元素浓度与量显得极为重要。对贵州省茂兰国家自然保护区原始林森林群落2007年9月-2008年8月的降水进行定位观测与分析。结果表明:(1)在林外雨、林内雨、树干流和溪流水中,除了Na+之外,pH值与大部分的养分元素的浓度表现出明显的季节变化,冬季与早春浓度较高,夏季浓度较低。这与各季节的降雨量不同而导致浓度稀释或者浓缩有关。(2)大气降雨通过林冠的过程中,养分元素的浓度出现了较大的变化,林内雨与树干流中的浓度基本高于大气降雨;养分元素变化中,浓度差异较大的元素是K+、Mg2+和Ca2+,K+在林内雨和树干流的浓度分别是大气降雨的14倍和21倍;Mg2+浓度分别为大气降雨的12倍和9倍;Ca2+浓度分别为大气降雨的4倍和3倍,这与大气降雨通过林冠,与树体的养分交换以及树体养分的溶脱有关。(3)通过林内雨,树干流输入样地较多的养分元素是K+和Ca2+,分别是35.8kg.hm-.2a-1和31.5kg.hm-.2a-1;通过溪流水输出的元素中,较多的是Ca2+和Mg2+,分别是-547.4kg.hm-.2a-1和-144.5kg.hm-.2a-1;其次是SO24-,而Na++K++NH4+-N总量不足阳离子总量的1%,Cl-+NO3-总量不足阴离子总量的1%。这可能与母岩风化是碳酸岩类岩石风化有关。(4)年养分的垂直移动量特征显示,土壤0cm到土壤5cm的养分元素量变化较明显,无机态N量的变化可能跟微生物的氮固定、无机化或者植被的吸收有关。(5)研究地的年间养分元素量收支分别为N2.9kg.hm-.2a-1;K25.2kg.hm-.2a-1;Ca-547.4kg.hm-.2a-1;Mg-144.5kg.hm-.2a-1;Na-4.0kg.hm-.2a-1;Cl2.5kg.hm-.2a-1和SO24-S-5.9kg.hm-2.a-1。在年间养分的输入与输出中,无机态N跟K+显示正收支,Ca2+、Mg2+为负收支,而Na+、Cl-相对较稳定。     

温带两种林型对氮沉降的再分配及其生长季动态与影响因子

氮(N)沉降对森林生态系统的结构与功能具有重要的影响,而森林对到达林地的N沉降量及其分配格局的影响尚不清楚。量化了2012—2013年5—10月两个生长季蒙古栎林和杂木林的林内树干径流和穿透雨及其林外大气降雨总氮(TN)、可溶性氮(DN)和颗粒态氮(PN)沉降通量的季节动态,旨在比较两种林型对N沉降的再分配格局及其季节变化,分析影响其变异的主要因子。结果表明:林外大气降雨、蒙古栎林林内、杂木林林内(树干径流+穿透雨)TN沉降平均值分别为:8.49、15.97、13.39 kg hm~(-2)a~(-1),其中DN分别占其TN的76.35%、82.79%和75.02%,PN分别占其TN的26.35%、17.21%和24.98%,蒙古栎林和杂木林林内穿透雨TN沉降量分别占其TN的95.5%和94.5%。蒙古栎林和杂木林冠层淋溶TN沉降量分别为7.48kg hm~(-2)a~(-1)和4.90 kg hm~(2)a~(-1);其中,前者的DN高于后者,但PN呈相反趋势。两种林型的N沉降组分具有明显的季节动态:沉降量均集中在生长季中期(6—8月),生长季前期和末期较低。林外降雨量分别与林外大气降雨、蒙古栎林和杂木林林内的树干径流和穿透雨中的TN、DN浓度呈显著负指数函数关系(P0.001)。连续降雨天数对蒙古栎林、杂木林林内TN、DN浓度的影响表现为连续降雨2 d以内为富集作用,之后为稀释作用。研究表明林冠对大气氮沉降有显著富集作用,其富集强度及时间动态与森林类型和降雨特征有关,建议氮沉降试验应考虑林冠的富集效应。     

杨树人工林生态系统降水再分配及主要离子特征

大气降水是森林生态系统养分输入的主要途径之一,对养分的生物地球化学循环有着重要的意义。对13年生杨树人工林林外雨、树干流、林内雨和地表径流等水文过程中的养分特征进行了调查分析,旨在了解该生态系统的养分输入与输出规律,为杨树人工林可持续经营提供依据。结果表明,从2013年11月至2014年10月,杨树人工林生态系统林外雨量为1154.1 mm,树干流量仅占大气降水量的2.3%,15.4%的大气降水被杨树人工林的冠层截留;林内雨、树干流与大气降水量(林外雨)的动态变化规律相似。各类降水年加权平均pH值表现为林内雨林外雨树干流;各类降水的离子浓度动态变化规律基本一致,即在降水量较小的11月至次年1月份,各阴阳离子的浓度普遍较高,在降水量较大的2—9月份,阴阳离子浓度普遍较低。SO_4~(2-)-S和Ca~(2+)分别是各类降水中的主要阴离子和阳离子;整体上,树干流的离子浓度林内雨大气降水;林内雨是养分输入的主要形式,通过林内雨输入林地较多的养分离子是Ca~(2+)和K~+,分别为70.83 kg hm~(-2)a~(-1)和63.31 kg hm~(-2)a~(-1);地表径流和土壤渗漏是养分输出的主要形式,输出林地较多的离子是Cl~-和Ca~(2+),分别为196.47 kg hm~(-2)a~(-1)和123.09 kg hm~(-2)a~(-1),其次为SO_4~(2-)-S、Mg~(2+)、Na~+、K~+;NH_4~+-N和NO_3~--N的输出量不足输出离子总量的1%。所以,从水文过程看,杨树人工林生态系统无机氮(NH_4~+-N和NO_3~--N)和K~+表现为净积累,净积累量分别为10.9 kg hm~(-2)a~(-1)和56.4 kg hm~(-2)a~(-1),其他离子表现为净损失,其中Cl~-的净损失量达179.8 kg hm~(-2)a~(-1)左右,其他离子损失量50 kg hm~(-2)a~(-1)。     

广西马尾松和红锥纯林降水再分配及冠层淋溶效应

明析马尾松(Pinus massoniana)和红锥(Castanopsis hystrix)纯林降水再分配及冠层淋溶效应的差异,可为南亚热带针叶人工林改造提供水文数据。依托广西友谊关森林生态系统国家定位观测研究站,通过野外测定和室内分析相结合的方法,利用林下布设的30个自记雨量筒,测定了2016年1—12月的大气降水、穿透雨及树干径流,同时采集7—12月10次降水事件水样,监测其化学成分。结果表明:观测期间降雨总量为1070.2 mm,马尾松和红锥纯林穿透雨分别为823.0和693.2 mm,占降雨量的76.9%和64.8%;树干径流分别为3.2和9.9 mm,占降雨量的0.3%和0.9%;林冠截留量分别为244.0和367.1 mm,占降雨量的22.8%和34.3%,说明马尾松和红锥纯林对降水再分配的作用是不同的,红锥纯林具有更好的林冠截留能力。降水对红锥纯林冠层4种盐基离子(K~+、Mg~(2+)、Na~+、Ca~(2+))的淋溶量为17.53 kg·hm~(-2),是马尾松纯林的0.7倍,但酸缓冲是马尾松纯林的1.6倍。与马尾松纯林相比,红锥纯林具有更好的避免冠层养分淋溶和应对酸沉降的能力。     

两种温带落叶阔叶林降雨再分配格局及其影响因子

林冠对降雨的再分配是森林生态系统的重要生态水文过程,影响着生态系统生物地球化学循环。于2012年5—10月连续测定帽儿山森林生态站的两种温带天然次生林型——蒙古栎林和杂木林的林外降雨、穿透雨及树干径流,旨在量化其降雨再分配过程及其影响因素。结果表明:蒙古栎林的平均穿透雨、树干径流、林冠截留分别占同期林外降雨的76%、7%和17%;杂木林分别占85%、5%和10%。根据模型估算,当降雨量分别超过1.0mm和0.7mm时蒙古栎和杂木林开始出现穿透雨;当降雨量超过3.0mm开始出现树干径流。当降雨量超过5.6mm,树干径流体积会随着树木胸径的增加而显著增加;而当降雨量低于5.6mm则出现相反趋势。穿透雨、树干径流及林冠截留的绝对量均随降雨量的增大而显著增加,但其占降雨量的比例却表现出不同的变化趋势。穿透雨量的空间变异随降雨量和降雨强度的增大显著减小。两种林型的降雨再分配格局因受降雨量、降雨强度等降雨特征和林冠结构的影响而产生差异。     

人工桤柏混交林中降雨对养分物质的淋溶影响

引　言水体养分物的循环是生态系统生物地球化学循环的一个重要组成部分,因此,从生态角度来研究森林的存在对流域的水分循环和物质迁移的影响将是一个十分有意义的工作。目前,欧美各国关于森林与水质的关系研究比较多[5]。我国较多研究森林对河流泥沙悬浮含量影响,或干枝落叶和微生物对腐殖质转化等作用形成的森林养分循环,而较少研究森林降雨重新分配作用对森林养分循环的影响[1,2],因此,本文选择了亚热带人工桤柏混交林,通过观测降雨过程中林外降雨、林内降雨、树干流及其相应水质的变化,结合林外降雨、林内降雨和树干流的时空变化特性,分…     

鼎湖山季风常绿阔叶林大气降雨、穿透雨和树干流的养分特征研究

对鼎湖山季风常绿阔叶林大气降雨、穿透雨和树干茎流中的5种养分元素K、Ca、Mg、N、P进行了测定,结合水量分配规律,研究了森林降雨过程中养分在水相中的含量变化特征和输入规律。结果表明：(1)所有离子浓度均为大气降水<穿透雨<树干流,且增幅较大,而平均浓度以K+和总氮(TN)含量最高;总磷(TP)、磷酸盐(HPO42-)、总有机磷(TOP)含量均最低。(2) 大气降雨中的离子平均浓度中以总有机氮(TON)的变异系数最大,为1.282;最小的是NO3-(0.502);穿透雨中变异系数最大的是TOP(2.357);最小的是TN(0.621)。树干流中各养分元素浓度与树种的相关性不显著(P>0.05)。(3) 季风常绿阔叶林树干流和穿透雨各养分对森林土壤的年输入量为TN>K+>Ca2+>Mg2+>TP,树干流和穿透雨对森林土壤层Ca2+的输入大于凋落物分解输入。因此,大气降雨是养分从林冠层转移到土壤层的重要因素。     

模拟降雨减少对刺槐人工林土壤养分和微生物群落的影响

降雨是黄土高原地区土壤水分的最主要来源。为探明降雨减少对黄土高原半湿润区土壤养分和土壤微生物群落的影响，以刺槐人工林为研究对象，通过搭设透光遮雨板将部分穿透雨导流至样地外，实施了4年减少总降雨输入约47%的处理，测定了在不同降雨条件下林地的土壤养分含量、土壤微生物多样性及群落结构特征，分析了土壤养分和土壤微生物对降雨减少的响应。结果表明：减雨处理4年后(1)处理样地土壤有机碳、全氮、全磷含量均低于对照样地，全氮含量差异达到显著水平(P<0.05)。(2)对照样地生长季和非生长季土壤微生物多样性差异不显著，减雨处理样地非生长季的细菌均匀度显著低于处理样地生长季和对照样地非生长季(P<0.05);降雨减少对细菌和真菌的群落结构有显著影响(P<0.05),降雨减少显著降低了酸杆菌门(Acidobacteria)的相对丰度，提高了放线菌门(Actinobacteria)、绿弯菌门(Chloroflexi)、子囊菌门(Ascomycota)和被孢霉门(Mortierellomycota)的相对丰度(P<0.05)。(3)土壤有机碳、全氮含量与部分细菌相对丰度显著相关，土壤...     

北京西山地区油松林水文过程中营养元素迁移特征

对北京西山地区31a油松林降水化学进行定位监测与分析.结果表明：（1）大气降水流经油松林过程中,其营养元素（除Na^＋外）的浓度出现梯度变化：树干茎流高于穿透雨高于大气降水,并且有明显的月际变化,表明从林冠、树干淋洗大量的营养元素,林冠和树干中养分元素迁移是森林生态系统养分循环重要的组成部分.（2）营养元素变化中,浓度差异变化较大的元素是NO3^--N和K^＋,NO3^--N在穿透雨和树干茎流的浓度分别是大气降水的4.4倍、9.9倍,它们中的K^＋浓度分别为大气降水的4.1倍和8.1倍.（3）降水经过油松林,养分淋溶总量为54.12kg hm^-2,淋溶量较多的元素是Ca和K,淋溶强度最大的元素是K^＋.（4）北京西山地区大气降水输入林地的养分66.38kg hm^-2,较多的元素是Ca、N.降水经过油松林输入林地养分总量为120.50kg hm^-2,Ca元素最高,为61.22kg hm^-2,其次是N元素（NH4^＋-N＋N3^--N）,为31.34kg hm^-2,K元素为16.49kg hm^-2,Mg元素为8.11kg hm^-2,Na元素最少,为3.34kg hm^-2.     

Nutrient cycling in Pinus sylvestris stands in eastern Finland

Nutrient cycling within three Pinus sylvestris stands was studied in eastern Finland. The aim of the study was to determine annual fluxes and distribution of N, P, K, Ca, Mg, Zn, Fe, B, and Al in the research stands. Special emphasis was put on determining the importance of different fluxes, especially the internal cycle within the trees in satisfying the tree nutrient requirements for biomass production. The following nutrient fluxes were included, input; free precipitation and throughfall, output; percolation through soil profile, biological cycle; nutrient uptake from soil, retranslocation within trees, return to soil in litterfall, release by litter decomposition. The distribution of nutrients was determined in above- and belowground tree compartments, in ground and field vegetation, and in soil.The nitrogen use efficiencies were 181, 211 and 191 g of tree aboveground dry matter produced per g of N supplied by uptake and retranslocation in the sapling, pole stage and mature stands, respectively. Field vegetation was more efficient in nitrogen use than trees. Stand belowground/aboveground and fine root/coarse root biomass ratios decreased with tree age. With only slightly higher fine root biomass, almost three times more nitrogen had to be taken-up from soil for biomass production in the mature stand than in the sapling stand.The annual input-output balances of most nutrients were positive; throughfall contained more nutrients than was lost in mineral soil leachate. The sulphate flux contributed to the leaching of cations, especially magnesium, from soil in the mature stand.Retranslocation supplied 17–42% of the annual N, P and K requirements for tree aboveground biomass production. Precipitation and throughfall were important in transferring K and Mg, and also N in the sapling stand. Litterfall was an important pathway for N, Ca, Mg and micro nutrients, especially in the oldest stands.     

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.     

Variation in Canopy Litterfall Along a Precipitation and Soil Fertility Gradient in a Panamanian Lower Montane Forest

Fertilization experiments in tropical forests have shown that litterfall increases in response to the addition of one or more soil nutrients. However, the relationship between soil nutrient availability and litterfall is poorly defined along natural soil fertility gradients, especially in tropical montane forests. Here, we measured litterfall for two years in five lower montane 1‐ha plots spanning a soil fertility and precipitation gradient in lower montane forest at Fortuna, Panama. Litterfall was also measured in a concurrent nitrogen fertilization experiment at one site. Repeated‐measures ANOVA was used to test for site (or treatment), year, and season effects on vegetative, reproductive and total litterfall. We predicted that total litterfall, and the ratio of reproductive to leaf litterfall, would increase with nutrient availability along the fertility gradient, and in response to nitrogen addition. We found that total annual litterfall varied substantially among 1‐ha plots (4.78 Mg/ha/yr to 7.96 Mg/ha/yr), and all but the most aseasonal plot showed significant seasonality in litterfall. However, litterfall accumulation did not track soil nutrient availability; instead forest growing on relatively infertile soil, but dominated by an ectomycorrhizal tree species, had the highest total litterfall accumulation. In the fertilization plots, significantly more total litter fell in nitrogen addition relative to control plots, but this increase in response to nitrogen (13%) was small compared to variation observed among 1‐ha plots. These results suggest that while litterfall at Fortuna is nutrient‐limited, compositional and functional turnover along the fertility gradient obscure any direct relationship between soil resource availability and canopy productivity.     

杉木人工林生态系统水文学过程的养分特性

根据5a定位观测的数据,对湖南会同24～28a生的杉木人工林生态系统各水文学过程中的养分特性进行了研究。结果表明：林冠降水是杉木人工林生态系统养分输入的重要来源,其中Ca的养分含量最高,P的含量最低。林内穿透水各养分元素的含量明显高于林冠降水中养分的含量。除Ca外,树干茎流中其它养分元素的含量为林冠降水的6倍以上。可见,林内穿透水和树干茎流是杉木林生态系统内养分循环的重要组成部分,有利于提高系统的养分利用率。地表径流中除硝态氮外,各元素的含量与穿透水的含量接近,其中P、Na和K三种元素的含量较低,但未超过林冠降水中养分元素含量。地下径流中N和K的含量较低,而Ca的含量与林冠降水相比没有差异。因而地表径流和地下径流不可避免的造成生态系统的养分损失,但24～28a生杉木林生态系统的调控能力较强,地表径流和地下径流量较小,生态系统的养分损失也相对较小,养分为净积累。不同季节之间水文学过程中养分元素含量存在一定程度的差异。降水形态、雷电和地形等要素影响养分元素含量。硝态氮在冰雹中未检出,而在雨水中的含量是雪水的2倍。铵态氮、K和Mg等元素在雨水中的含量最高。P和Ca以雪水的含量最高,与雨水和冰雹相比不存在数量级差异。雷电明显增加降水中养分的含量,特别是林冠上层的低空放电使降水中N的含量增加3～5倍。由于山谷和山麓的立地条件较好,其穿透水中养分含量比山坡的高,山谷与山麓的大致相等。在采集水样进行养分分析时,应考虑降水时间、降水形态和地形等因子的影响。     

Solute fluxes in throughfall and stemflow in four forest ecosystems in northwest Amazonia

The contribution of throughfall and stemflow as pathways for solute inputs into the forest floor in four mature forests in northwest Amazonia was investigated. Total solute inputs, resulting from the changes of atmospheric deposition after rainfall passes through the forest canopy, are presented in the form of throughfall and stemflow nutrient inputs and their possible sources are discussed. Throughfall is by far the most important solute input into the forest floor of the forests studied. On average, it represents about 98% of the total solute inputs. Although trends in solute enrichment varied among the forests, there is a general tendency in all ecosystems towards a distinct enrichment of SO₄, K, Cl, NO₃ and NH₄ in throughfall and stemflow and a small increase of protons, Mn, orthoP and Fe. When comparing the net enrichment between the forests, the relative increase of solutes in throughfall and stemflow was higher in the flood plain and low terrace than in the high terrace and sedimentary plain forests. While highest values for total cation inputs were observed in the flood plain, the low terrace showed the highest value for total inorganic anions. The length of the antecedent dry period was the main factor affecting throughfall and stemflow composition, concentrations increasing with increasing length. A second, less important factor was the amount of throughfall and stemflow, which showed a poor and negative correlation with solute concentrations. The increased activity of frugivores in the canopy during fruiting periods seemed to lead to temporary increased solute concentrations in throughfall and stemflow as a result of the wash off of deposited faecal materials and detritus in the canopy. Leaching from leaves and wash off of exudes, of solutes deposited on the foliage after evaporation of intercepted rainfall and of dry deposited materials were all found to contribute to the concentration of solutes in the throughfall and stemflow. Gross rainfall enrichment after passing the forest canopy, mainly by nutrient leaching, is considerably lower than the amounts of nutrients released in litterfall implying a tight nutrient cycling and nutrient conserving mechanisms by forests studied.     

Nutrient cycling and nitrogen mineralization in eucalypt forests of south-eastern Australia

Summary Nutrient pools in litter and soil and the major nutrient transfers and additions in rainfall, throughfall and litterfall were measured in eight mature, undisturbed eucalypt forests covering a range of species, climate, productivity and soil type. Litterfall is the major pathway for the return of N, P, Ca and usually Mg, to the soil. The forests covered almost the range of litterfall reported for eucalypt forests and, in conjunction with published data, litterfall was strongly related to climatic variables. Extractable P in the soil and P concentrations in litter and litterfall were significantly higher in two sub-alpine forests (Eucalyptus pauciflora andE. delegatensis) than in all other forests. In general, nutrient turnover, particularly N turnover, was related to the rate of organic matter turnover. Rates of organic matter turnover in these forests and in other studies of eucalypts were correlated with climatic conditions using the simple climatic scalar developed by Vitousek. Nitrogen turnover, especially that proportion cycling via leaf litterfall is primarily a function of organic matter turnover, but litter quality appears also to have an influence.     

模拟降雨减少对马尾松人工林凋落物量及其化学性质的短期影响

为研究气候变化背景下降水格局变化对森林生长和碳固持的影响,2012年在我国南亚热带地区选择广泛分布的马尾松(Pinus massoniana)人工林为研究对象,分别设置3块20 m×20 m的模拟降雨减少50%和对照样地,每个样地随机设置5个距地面40 cm的1 m×1 m的凋落物收集框,2016年1—12月每隔1月收集各样地林冠层凋落物,比较研究减水处理对凋落物组分产量和基本化学性质的短期影响。结果表明:马尾松人工林针叶凋落物量及其所占比例显著高于其他凋落物组分(P0.05),减雨处理对马尾松人工林凋落叶和总量无显著影响(P0.05)。与对照相比,减雨处理分别增加凋落针叶含碳量和凋落果含氮量27.4 g/kg和5.1 g/kg,以及凋落针叶的木质素含量、阔叶纤维素含量和皮半纤维素含量3.9%、5.2%和4.0%(P0.05),但显著降低凋落皮碳、纤维素含量和凋落果的碳氮比(P0.05)。凋落物N、P含量具有协同性,含碳量与木质素含量显著正相关(P0.05)。模拟降雨减少处理初期并未显著改变南亚热带马尾松人工林总凋落物量,但增加了凋落针叶的木质素含量和含碳量。本研究预示短期穿透雨减少可能降低南亚热带马尾松人工林凋落物的分解能力,由此降低马尾松人工林土壤中凋落物源性碳的输入量。