伪潜育土季节性滞水条件下大冷杉毫根动态的研究(Abies grandis Lindl.)

本文对一个25年生大冷杉林在伪潜育土至45cm矿质土壤里,从1987年晚秋滞水期至1988年生长旺盛期的毫根量动态及化学组成变化进行了研究。 滞水期土壤中死根量(5558kg DS/ha)显著高于活根量(3594kg DS/ha)。生长旺盛期初,活根量增加约50％,死根量降低约27％。经过夏季至生长旺盛期末,活根量仍略有增加,死根量继续降低。毫根化学组成分析显示,滞水期活根中K、Mg及Zn离子含量显著低于生长旺盛期,Mn离子含量则明显高于生长旺盛期。这一结果表明,除了与季节性相关的生长节奏因素外,大冷杉毫根生物量的变化主要是由滞水状况所致。     

鼎湖山某些植物群落根系生物量及其氮素动态

 本文用挖土柱及埋土柱法测定了鼎湖山生物圈保护区季风常绿阔叶林,黄果厚壳桂、鼎湖钓樟群落的根系生物量和年生长量。用自动离子分析仪分析了根的含氮量并研究了根系的氮素动态。结果表明,根系生物量(t／ha)为35.43,其中活根26.63,死根8.8;根的生长量(kg／ha·a)是3.74。根库贮氮量(kg／ha)为279.23,其中活根库为202.25,死根库为76.98;每年新生根系积累的氮素为57.55kg／ha。每年新生根系生产量及其氮素积累量占整个根库生物量及其氮素贮量的百分率分别为10.6及20.6,根库年生长量及其氮素积累的比率均较高,群落正处在生长发育盛期。     

鼎湖山某些植物群落根系生物量及其氮素动态

本文用挖土柱及埋土柱法测定了鼎湖山生物圈保护区季区常绿阔叶林,黄果厚壳桂,鼎湖钓樟群落的根系生物量和年生长量,用自动离子分析仪分析了根的含氮量并研究了根系的氮素动态,结果表明：根系生物量（t/ha)为35．43,其中活根26．63,死根8．8,根的生长量（kg/ha.a) 是3．74,根库贮氮量（kg/ha)为279．23,其中活根库为202．25,死根率为76．98,每年新生根系积累的氮素为57．55kg/ha,每年新生根系生产量及其氮素积累量占整个根库生物量及其氮素贮量的百分率分别为10．6及20．6,根库年生长量及其氮素积累的纟率较高,群落正处在生长发育盛期。     

大熊猫栖息环境的森林凋落物动态研究

本文以王朗自然保护区冷杉、云杉暗针叶林为对象,在定位测定森林凋落量及其动态和枯枝落叶贮量的基础上,研究了凋落物分解速率及其主要营养元素含量的变化,结果表明：(1)地表枯枝落叶总贮量变化在30.0—91.8t／ha,其中未分解层4.9—17.8,半分解层11.5—19.7,腐殖质层13.6—57.3t／ha。(2)森林凋落的枯枝落叶量因林型不同而略有差异,平均为2.8 t／ha·yr,其凋落高峰期分别在生长季开始的5月和生长季末的10月。(3)每年以凋落物形式返回林地的养分,氮为35.5kg／ha、磷为5.7kg／ha、钾为7.0kg／ha、镁为6.8kg／ha、钙为62.9kg／ha。(4)森林各种凋落物的混合物年分解率为0.3041g／g。95%的凋落物被分解需时约10年,在分解一段时间后,凋落物中的氮、钙、镁含量略有上升,钾明显减少,而磷含量变化不大。(5)森林凋落物的混合物腐解过程中,养分释放速率大小的顺序为：K>P>Mg>Ca>N,大熊猫主食竹的凋落叶则为：K>N>Ca>Mg>P。     

天然枫桦红松林凋落量动态及养分归还量

三年定位研究表明小兴安岭天然枫桦红松林年均凋落量有5.8t／ha(干重)。凋落量的季节变化格局是随着气候变冷有一明显秋季凋落高峰期(9—10月)。凋落物每年养分的归还量：Ca、N、K、Mg、P,相应为67.0、56.9、14.8、9.5、和6.6kg／ha,总计155.0kg／ha。据测定阔叶树落叶养分含量明显高于所有针叶的含量。尽管阔叶树的年凋落量仅占该混交林的年总凋落量的三分之一,阔叶树落叶仍有相当高的养分比例(43.4%)归还土壤。因此,红松林分的经营管理中,保留适当比重的阔叶树有利于土壤改良和促进林分生长。     

杨树人工林下根系的氮素循环与动态特征

研究了辽宁沈阳地区人工林杨树细根及林下草本植物根系的N循环、积累和动态变化特征。结果表明,杨树人工林分条件下活细根中N储量为20．3kg·h^-2,净积累量10kg·hm^-2,吸收量14．7kg·hm^-2,年存留量和归还量分别为9．6和5．1kg·hm^-2周转期4年,整个生长季节杨树细根中N含量与土壤中水解N、NH3-N无明显相关,杨树细根中N浓度与活细根生物量的变化趋势大体一致,两者呈显著正相关。根据杨树活细根中N含量可以估测杨树活细根生物量,该林分下的草本植物根系主要吸收NH3-N,草根中N含量浓度变化与土壤中NH3-N的变化趋势相同,两者呈显著正相关。     

北京人工侧柏林的化学元素含量特征

31年生人工侧柏（Platycladus orientalis)林内,侧柏各器官中以有机C含量最高,Ga的浓度亦大,其次为N,K,Mg,P的浓度较低,Fe的浓度相对较高,除C和Al外,大部分元素在侧柏叶中含量较多,各种灌木叶的元素浓度均高于茎,还明显地高于侧柏叶,侧柏乔木层元素积累量是以地上部分高于地下部分,51％的C被积累在树干内,其他元素在叶部最高。灌木层元素积累量除N以外,均以地下部分高于地上部分,人工林C的积累量为17000kg/ha,Ca为400kg/ha,N为104kg/ha,K为87kg/ha,Mg为30kg/ha,Al,P,Fe为11－16kg/ha,Na为2．5Ka/ha,Mn,Cu,Zn小于1kg/ha, 乔木和灌木层化学元素存留量以C最高,在乔木层Ca的存留量次之,N,K,更次之,灌木层N的存留量高于Cat K,侧柏林的元素存留量C约2700kg/ha.a,Ca 为70kg/ha.a,N和K为15－20kg/ha.a,P,F,A,M 2－5g/ha.a,其他元素存留量不到1kg/ha.a,土壤中化学元素贮存量是C＞Ca>N>Fe>Mg>K>P>Na>Al,Mn>Cu>Zn。在相同土壤条件下,各种植物对土壤元素的富集系数不同,各种灌木的元素富集系数均高于侧柏,侧柏林元素积累量,存留量与土壤元素贮存量之间具极显著相关,它们的相关系数分别为R＝0．9723（P＜0．001,n=11)和R＝0．9765(P<0.001,n=11),侧柏林对元素的需要量是C＞Ca>N>K>Mg>Fe>P>Al>Na>Mn>Cu>Zn。     

贡嘎山地区不同海拔冷杉比叶质量和非结构性碳水化合物含量变化

以贡嘎山地区磨西山谷东北坡和康定山谷西南坡为样地,研究了高山林线和低海拔冷杉休眠期和生长旺盛期针叶比叶质量和组织非结构性碳水化合物含量.结果表明:生长在温暖湿润的磨西山谷东北坡的冷杉针叶比叶质量和组织非结构性碳水化合物含量均高于炎热干燥的康定山谷西南坡;高山林线冷杉比叶质量大于低海拔冷杉;高山林线冷杉组织非结构性碳水化合物含量总体高于低海拔冷杉,且生长期比休眠期更为显著.研究结果不支持"碳供应不足导致高山林线形成"的假说.     

缓/控释复合肥料对土壤氮素库的调控作用

采用小麦盆栽生物试验、实验室化学分析和仪器分析方法研究了缓/控释复合肥料(SRF)对土壤氮素养分库中不同组分(微生物量氮、固定态铵、NH4+-N、NO3--N、铵离子周转库)动态变化的影响及其与小麦吸收氮素养分的关系。结果表明,在小麦分蘖初期,SRF处理土壤微生物量氮、NH4+-N含量较普通复合肥料(CCF)低,此后整个小麦生育期的土壤微生物量氮、NH4+-N含量的总体变化趋势以SRF处理高于CCF处理,其中SRF处理的小麦土壤NH4+-N含量较CCF处理高108.1%—271.7%;在小麦生长前期,SRF处理土壤固定态铵含量较CCF低;在小麦生长中期,SRF处理土壤固定态铵含量较CCF处理高;与CCF处理比较,SRF处理小麦土壤硝态氮含量经历先升高后降低、在生育后期又升高的趋势。在小麦生育前期,CCF处理土壤"铵离子周转库"由371.3 mg/kg降至259.1 mg/kg;SRF处理土壤"铵离子周转库"由306.5 mg/kg升至324.5 mg/kg。在小麦需氮量较高的拔节期,CCF处理土壤"铵离子周转库"与前一次之差值仅为34.18 mg/kg,而SRF处理则达到77.21 mg/kg,表明小麦生育前期SRF土壤"铵离子周转库"能够固定更多的铵离子,降低铵离子的损失;在小麦需氮量较高的时期,"铵离子周转库"则释放更多的铵离子以供给小麦吸收利用。小麦生长初期CCF处理释放养分速率较快,小麦植株吸氮量高于SRF处理;生长中、后期SRF处理释放养分量较CCF处理高,此阶段小麦吸氮量以SRFCCF。不同处理对小麦吸氮量的影响与对小麦生物量变化是基本一致的,即初期以CCFSRF,中后期以SRFCCF,收获期SRF处理较CCF处理分别提高小麦生物量15.32%、吸氮量13.51%。相关分析表明,小麦生物试验中SRF处理土壤微生物量氮、固定态铵以及"铵离子周转库"的动态变化与小麦吸氮量之间达到显著或极显著负相关关系(r=-0.8728*—-0.9006**),SRF调控土壤氮素库的能力较CCF更强,能更好的协调土壤氮素养分供应与小麦氮素需求间的动态平衡和提高肥料氮素利用效率。     

施氮量对夏玉米根际和非根际土壤酶活性及氮含量的影响

在华北平原潮土上进行田间试验,研究施氮量对夏玉米根际和非根际土壤酶活性及氮含量的影响.结果表明: 不同施氮水平下土壤酶活性均表现出一致的季节性变化趋势.与不施氮处理相比,施氮处理能显著提高根际和非根际土壤硝态氮含量及根际土壤铵态氮含量,显著增强土壤几丁质酶、β-葡萄糖苷酶、纤维素酶和木聚糖酶活性.在整个玉米生育期内,非根际土壤硝态氮含量显著高于根际土壤;非根际土壤铵态氮含量在灌浆期显著高于根际土壤,但在苗期和完熟期则显著低于根际土壤;根际土壤几丁质酶、β-葡萄糖苷酶、纤维素酶和木聚糖酶活性都显著高于非根际土壤.施氮对土壤有机质含量没有显著影响;在0～180 kg·hm^-2施氮范围内,施氮可明显增加土壤全氮含量,但当施氮量超过180 kg·hm^-2时,土壤全氮含量则明显下降.综上,适量施氮能显著增强土壤酶活性,提高土壤全氮含量,改善土壤生化性质.     

杉木观光木混交林细根的分布

对27年生混交比例为2行杉木和1行观光木的混交林和杉木纯林群落细根分布的研究表明,杉木和观光行间的杉木细根密度虽比极木行间的低8．5％,但观光木细根密度则高152．09％,其细根总密度比杉木与杉木行间的大10．43％。混交林中杉木各径级活动根密度呈单峰型分布,均以5－10cm土层最大,而观光木各径级各活细根主要分布在0－10cm土层内。纯林杉木各径活细根密度亦基本呈单峰型分布,但峰值出现在10－20cm或20－30cm土层。不同树种不同径级死细根的分布均与其各自的活细根分布相似。混交林中灌木细根密度在30－40cm的土层最大,而纯林中的灌木细根集中于0－10cm的表土层;混交林和纯林中的草木细根均集中在0－5cm土层。与纯林的相比,混交林中杉木细根主要分布的土层明显上移,表层土壤细根所占比重增大,有利于更好利用土壤养分和提高群落生产力。     

华西雨屏区香樟人工林土壤表层细根生物量和碳储量

2010年11月-2011年12月, 研究了华西雨屏区31年生香樟人工林土壤表层(0～30 cm)细根生物量及碳储量.结果表明: 香樟人工林土壤0～30 cm层细根总生物量(活根+死根)和碳储量的平均值分别为1592.29 kg·hm^-2和660.68 kg C·hm^-2,其中活细根贡献率分别为91.1%和91.8%.随着土壤深度的增加,香樟1～5级活细根和死细根的生物量及碳储量均显著减少;随着根序等级的升高,香樟活细根生物量及碳储量显著增加.香樟细根总生物量及碳储量均在秋季最高、冬季最低,死细根生物量及碳储量为冬季最高、夏季最低;1级根和2级根生物量及碳储量均在夏季最高、冬季最低,而3~5级根则为秋季最高、冬季最低.土壤养分和水分的空间异质性是导致细根生物量和碳储量变化的主要原因.     

Biomass, morphology and nutrient contents of fine roots in four Norway spruce stands

Fine root systems may respond to soil chemical conditions, but contrasting results have been obtained from field studies in non-manipulated forests with distinct soil chemical properties. We investigated biomass, necromass, live/dead ratios, morphology and nutrient concentrations of fine roots (<2 mm) in four mature Norway spruce (Picea abies [L.] Karst.) stands of south-east Germany, encompassing variations in soil chemical properties and climate. All stands were established on acidic soils (pH (CaCl₂) range 2.8–3.8 in the humus layer), two of the four stands had molar ratios in soil solution below 1 and one of the four stands had received a liming treatment 22 years before the study. Soil cores down to 40 cm mineral soil depth were taken in autumn and separated into four fractions: humus layer, 0–10 cm, 10–20 cm and 20–40 cm. We found no indications of negative effects of N availability on fine root properties despite large variations in inorganic N seepage fluxes (4–34 kg N ha⁻¹ yr⁻¹), suggesting that the variation in N deposition between 17 and 26 kg N ha⁻¹ yr⁻¹ does not affect the fine root system of Norway spruce. Fine root biomass was largest in the humus layer and increased with the amount of organic matter stored in the humus layer, indicating that the vertical pattern of fine roots is largely affected by the thickness of this horizon. Only two stands showed significant differences in fine root biomass of the mineral soil which can be explained by differences in soil chemical conditions. The stand with the lowest total biomass had the lowest Ca/Al ratio of 0.1 in seepage, however, Al, Ca, Mg and K concentrations of fine roots were not different among the stands. The Ca/Al ratio in seepage might be a less reliable stress parameter because another stand also had Ca/Al ratios in seepage far below the critical value of 1.0 without any signs of fine root damages. Large differences in the live/dead ratio were positively correlated with the Mn concentration of live fine roots from the mineral soil. This relationship was attributed to faster decay of dead fine roots because Mn is known as an essential element of lignin degrading enzymes. It is questionable if the live/dead ratio can be used as a vitality parameter of fine roots since both longevity of fine roots and decay of root litter may affect this parameter. Morphological properties were different in the humus layer of one stand that was limed in 1983, indicating that a single lime dose of 3–4 Mg ha⁻¹ has a long-lasting effect on fine root architecture of Norway spruce. Almost no differences were found in morphological properties in the mineral soil among the stands, but vertical patterns were apparently different. Two stands with high base saturation in the subsoil showed a vertical decrease in specific root length and specific root tip density whereas the other two stands showed an opposite pattern or no effect. Our results suggest that proliferation of fine roots increased with decreasing base saturation in the subsoil of Norway spruce stands.     

落叶松人工林细根动态与土壤资源有效性关系研究

树木细根在森林生态系统C和养分循环中具有重要的作用。由于温带土壤资源有效性具有明显的季节变化, 导致细根生物量、根长密度 (Rootlengthdensity, RLD) 和比根长 (Specificrootlength, SRL) 的季节性变化。以 17年生落叶松 (Larixgmelini) 人工林为研究对象, 采用根钻法从 5月到 10月连续取样, 研究了不同土层细根 (直径≤ 2mm) 生物量、RLD和SRL的季节动态, 以及这些根系指标动态与土壤水分、温度和N有效性的关系。结果表明 :1) 落叶松细根年平均生物量 (活根 +死根 ) 为 189.1g·m-2 ·a-1, 其中 5 0 %分布在表层 (0~ 10cm), 33%分布在亚表层 (11~ 2 0cm), 17%分布在底层 (2 1~ 30cm) 。活根和死根生物量在 5~ 7月以及 9月较高, 8月和 10月较低。从春季 (5月 ) 到秋季 (10月 ), 随着活细根生物量的减少, 死细根生物量增加 ;2 ) 土壤表层 (0~ 10cm) 具有较高的RLD和SRL, 而底层 (2 1~ 30cm) 最低。春季 (5月 ) 总RLD和SRL最高, 分别为 10 6 2 1.4 5m·m-3 和 14.83m·g-1, 到秋季 (9月 ) 树木生长结束后达到最低值, 分别为 2 198.2 0m·m-3 和 3.77m·g-1;3) 细根生物量、RLD和SRL与土壤水分、温度和有效N存在不同程度的相关性。从单因子分析来看, 土壤水分和有效N对细根的影响明显大于温度, 对活根的影响大于死根。由于土壤资源有效性的季节变化, 使得C的地下分配格局发生改变。各土层细根与有效性资源之间的相关性反映了细根功能季节性差异。细根 (生物量、RLD和SRL) 的季节动态 (5 8%~ 73%的变异 ) 主要由土壤资源有效性的季节变化引起。     

遮荫对水曲柳幼苗细根衰老的影响

细根周转对森林生态系统碳地下分配和养分循环具有重要影响,而衰老是细根周转过程中最重要的阶段。根据“源-汇”理论,细根衰老受碳向细根分配的影响。为此,该研究通过控制水曲柳(Fraxinus mandshurica)苗木向根系的碳分配的遮荫处理试验,采用树木生理分析技术,重点研究了在光合产物供应停止情况下水曲柳幼苗根系的生理变化(即根尖、1级根到3级根的细胞活力、可溶性糖含量、可溶性蛋白含量和膜透性的变化)。目的是从生理水平上证实:1)碳分配对细根衰老产生怎样的影响;2)细根衰老的顺序是否与分支顺序相反。实验结果表明,遮荫处理使细根活力、可溶性糖含量、可溶性蛋白含量显著降低和膜透性增大,导致细根出现明显衰老。从根系顶端向基部随着根序增加,细胞活力、可溶性糖含量和可溶性蛋白含量提高,膜透性降低,从生理水平上表明细根衰老具有逐渐变化的顺序性,并且这种顺序性与根发育的顺序性相反。     

Root dynamics in plant and ratoon crops of sugar cane

The root system of a sugar cane crop on an Ultisol in northeastern Brazil was examined throughout the plant and first ratoon crop cycles, using both coring and minirhizotron methods. Total root masses (living plus dead, 0.9–1.1 kg m^-2) and live root lengths (14.0–17.5 km m^-2) were greater during the ratoon cycle than at the end of the plant cane cycle (0.75 kg m^-2 and 13.8 km m^-2, respectively). Root die-back during the two weeks following ratoon harvest was estimated to be 0.15 kg m^-2, about 17% of the total root mass. Root die-back after the plant cane harvest was lower because fire was not used at this harvest and soil humidity was higher under the accumulated litter. A small amount of fine roots proliferated in the litter layer, amounting to 1% of the total mass and 3% of the total length. Root turnover could not be accurately assessed from minirhizotron observations due to variation in the relationship between coring data and the minirhizotron data with both time and soil depth.     

Vertical distribution of fine roots in relation to soil factors in Pinus tabulaeformis Carr. forest of the Loess Plateau of China

Growth and vertical distribution of fine root closely depend on soil resource availability. Better understanding of relationships of root profile with vertical distribution of available soil resource and soil characteristics can allow ecologists to predict the fine root distribution on the scales ranging from individual plants to vegetation communities. The objective of the study was to understand the fine root mass density (FRMD), fine root length density (FRLD), fine root area density (FRAD), mean root diameter and specific root length (SRL), vertical distribution in soil profile and their relation with soil environment factors in semiarid and arid Loess Plateau of China. The vertical fine root distribution and soil bulk density, soil moisture and soil inorganic N in 0-60 cm soil profile (0–15, 15–30, 30–45 and 45–60 cm intervals) were investigated by soil coring methods in three Pinus tabulaeformis Carr. forests chosen at three locations. The fine root density parameters (FRMD, FRLD and FRAD) and SRL peaked in the most upper soil layer (0–15 cm interval) and decreased with increased soil depth. The results provided a strong support that soil water rather than soil inorganic N is a key control on fine root distribution in the Loess Plateau. With increased soil moisture, the root mass, length and SRL increased and the mean root diameter decreased. The effects of soil bulk density on the fine root parameters were consistent with those of the soil water. An unexpected result was obtained about the relationships between soil organic N and the root distributions and occurrences because of no differences among the soil depth intervals in soil inorganic N content. It might be associated with severe soil water deficit limiting soil nitrogen utilization efficiency in arid Loess Plateau.     

Edaphic Factors are a More Important Control on Surface Fine Roots than Stand Age in Secondary Tropical Dry Forests

Although there are generalized conceptual models that predict how above and belowground biomass increase during secondary succession after abandonment from agriculture, there are few data to test these models for fine roots (defined as ≤2 mm diameter) in tropical forests. We measured live and dead fine roots (0–10 cm depth) in 18 plots of regenerating tropical dry forest in Costa Rica that varied in age from 5 to 60 yrs, as well as in soil properties. We predicted that both stand age and soil fertility would affect fine roots, with greater values in older forests on low fertility soils. Across two sampling dates and locations, live fine roots varied from 0.35 to 3.53 Mg/ha and dead roots varied from 0.15 to 0.93 Mg/ha. Surprisingly, there was little evidence that surface fine roots varied between sampling dates or in relation to stand age. By contrast, total, live, and dead fine roots averaged across sampling dates within plots were negatively correlated with a multivariate index of soil fertility (Pearson correlations coefficients were ?0.64, ?0.58, and ?0.68, respectively; P < 0.01) and other individual edaphic variables including pH, silt, calcium, magnesium, nitrogen, and phosphorus. These results suggest that soil fertility is a more important determinant of fine roots than forest age in tropical dry forests in Costa Rica, and that one‐way these plant communities respond to low soil fertility is by increasing fine roots. Thus, simple conceptual models of forest responses to abandonment from agriculture may not be appropriate for surface fine roots.