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。     

杉木,火力楠纯林及混交林细根周转的研究

系统研究了杉木、火力楠纯林及混交林细根生物量、生产力及年周转率。结果表明,杉木、火力楠纯林及混交林活细根生物量分别为８８０、３０３５和１５６０ｋｇ．ｈａ＾－１;死细根生物量为２３５、３９８和５６５ｋｇ．ｈａ＾－１;细根年周转率为１．２９、１．４２和１．４０;年生产量为１１３７、４３１８和２１７９ｋｇ．ｈａ＾－１;年死亡量为４９７．５９５和１１４９ｋｇ．ｈａ＾－１,分别相当于林分枯枝落叶年凋落量为３     

拉萨河谷杨树人工林细根的生产力及其周转

通过土钻取样和分解袋法对拉萨河谷杨树人工林细根的生长和周转进行了测定.结果表明,在该地区杨树人工林生态系统中,约80%的细根集中分布在0～30cm土壤表层中;接近树木一侧的活(死)细根生物量均高于外侧,但二者未达到显著的差异;在生长季期间,活细根生物量平均为2.576 t · hm-2,死细根生物量平均为1.566 t · hm-2,生长高峰出现在生长季初期.经估算,拉萨河谷杨树人工林细根年生长量为3.030 t · hm-2,年周转率为1.18次;但受高原低温的影响,细根分解缓慢,分解系数k平均为0.0007～0.0008.细根的这种生长特征是杨树对高原地区短暂生长季节和雨热同季气候条件的一种适应性表现.     

武夷山甜槠林细根生物量和生长量研究

对武夷山甜槠林细根生物量和生长量的季节动态及其在不同群落发育阶段下的变化进行了初步研究,并对细根在养分归还中的作用进行了分析．结果表明,甜槠成熟林细根生物量为１０．６４５ｔ·ｈｍ－２,生长量为７．３７１５ｔ·ｈｍ－２·ａ－１,分解量为４．６７７５ｔ·ｈｍ－２·ａ－１,年周转率０．６９次;细根生物量和生长量随林龄增长的变化模式为单峰型曲线,生物量至３４龄时达到最大值,生长量至群落郁闭阶段（５８龄）达到最大值;甜槠成熟林中,通过细根死亡的Ｎ素归还量占群落年归还总量的４９．５％,多于凋落物途径,Ｐ、Ｍｇ归还量所占比例为４２．３％和２８．９％,略低于凋落物途径;Ｋ、Ｃａ归还以降水淋溶为主,其次是凋落物途径,而细根途径仅占总归还量的１９．３％和９．２％．     

长白山阔叶红松林细根周转的研究

系统研究了长白山阔叶红松林细根生物量、生产力、年周转率及其在净生产力分配中的作用,生物量调查结果表明,阔叶红松林活细根的生物量为5049kg.ha~(-1),死细根生物量的平均值为1883kg.ha~(-1),细根的年周转率为0.96,年生产量为4860kg.ha~(-1),约占总净初级生产力的19.40％,年死亡量为2343kg.ha~(-1),相当于阔叶红松林枯枝落叶年凋落量的60％,由此提出了森林凋落物应包括枯枝落叶和根系凋落物的论点。     

三峡库区马尾松人工林细根生产和周转

2011年3-12月,采用连续根钻法和分解袋法,研究了三峡库区20年生马尾松人工林细根的季节动态,计算了细根的年生产量和周转率.结果表明:三峡库区马尾松人工林细根(＜2 mm)年均生物量为146.98 g·m-2,其中活细根年均生物量(102.92 g·m-2)远大于死细根生物量(44.06 g·m-2);不同径级细根现存量的时间动态不同,＜1 mm根系季节动态较为明显,整体呈单峰型曲线;马尾松人工林细根(＜2 mm)的年生产量为104.12 g·m-2·a-1,年周转率为1.05 a-1,其中＜1 mm和1～2 mm的年生产量分别为58.35和45.77 g·m-2·a-1,周转率为1.41和0.69 a-1.     

格氏栲天然林与人工林细根生物量、季节动态及净生产力

通过对福建三明格氏栲天然林及在其采伐迹地上营造的33年生格氏栲人工林和杉木人工林细根分布、季节动态与净生产力进行的为期3a(1999～2001)的研究,结果表明,格氏栲天然林、格氏栲和杉木人工林活细根生物量分别为4.944t/hm2、3.198t/hm2和1.485t/hm2,死细根生物量分别为3.563t/hm2、2.749t/hm2和1.287t/hm2;死细根生物量占总细根生物量的比例分别为41.9%、46.2%和46.4%;<0.5mm细根生物量占总细根生物量的比例分别为31.2%、29.4%和69.9%。3种林分活细根生物量和死细根生物量季节间差异显著(P<0.05),但年份间差异则不显著(P>0.05);活细根生物量最大值均出现在3月份,最小值一般出现在5～7月份或11～翌年1月份间。0～10cm表土层格氏栲天然林活细根生物量高达295.65g/m2,分别是格氏栲人工林和杉木人工林的2.4倍和8.1倍;该层格氏栲天然林活细根生物量占全部活细根生物量的59.8%,均高于格氏栲人工林(39.07%)和杉木人工林(24.51%)。格氏栲天然林、格氏栲人工林和杉木人工林细根分解1a后的干重损失率分别为68.34%～80.13%、63.51%～77.95%和47.69%～60.78%;年均分解量分别为8.747、5.143和2.503t/hm2;死亡量分别为8.632、5.148和2.492t/hm2;年均净生产量分别为8.797、5.425和2.513t/hm2,年周转速率分别为1.78、1     

帽儿山温带落叶阔叶林细根生物量、生产力和周转率

细根在森林生态系统能量流动与物质循环中占有重要地位,但其生物量、生产和周转测定尚存在很大的不确定性,而且局域尺度空间变异机制尚不清楚。本研究分析了帽儿山温带天然次生林活细根生物量和死细根生物量在0～100 cm剖面的垂直分布与0～20 cm细根的季节动态、生产力和周转率,对比了采用连续根钻法(包括决策矩阵法和极差法)和内生长袋(直径3和5 cm)估测细根生产力和细根周转率,并探讨了可能影响细根的林分因子。结果表明: 76.8%的活细根生物量和62.9%的死细根生物量均集中在0～20 cm土层,随着深度增加,二者均呈指数形式减少。活细根生物量和死细根生物量的季节变化不显著,可能与冬季几乎无降雪而夏季降雨异常多有关。2种直径内生长袋估计的细根生产力无显著差异;对数转换后决策矩阵、极差法和内生长法估计的细根生产力和细根周转率差异显著。随着土壤养分增加,活细根生物量和死细根生物量比值显著增加,死细根生物量显著减少,但活细根生物量、细根生产力和细根周转率均无显著变化;细根周转率与前一年地上木质生物量增长量呈显著正相关,但与当年地上木质生物量增长量无显著相关关系。     

长白山几种主要森林群落木本植物细根生物量及其动态

2005年在长白山北坡选择5种垂直植被带典型植物群落类型阔叶红松林、白桦林、山杨林、云冷杉林和岳桦林,利用钻取土芯法对细根分布及细根生物量进行了研究.研究结果表明,不同森林群落细根现存生物量存在一定的差异,其中白桦林最高,月平均细根现存生物量为5.1340 t/hm^2、其次为云冷杉林（5.0530 t/hm^2）、岳桦林（4.9255 t/hm^2）、阔叶红松林（4.4919 t/hm^2）和山杨林（3.9372 t/hm^2）;不同群落细根现存量月动态变化也有较大差异,月均最高最低相差阔叶红松林约为72﹪、白桦林近73﹪、山杨林26﹪、云冷杉林56﹪、岳桦林144﹪.在生长季节内不同群落细根发生和死亡也是不均匀的,春季所有群落都会产生大量的细根,一些群落在初秋（9月份）出现另一个较高的峰值,同时发现每次细根大量发生后,都随之产生大量细根的死亡,生长季末群落死亡细根生物量往往是最高的.调查群落72.9﹪以上的细根集中于土壤表层0～10cm的范围内,不同群落略有差别,在所研究的5种森林群落中,不同月份0～10cm土层中细根生物量几乎都表现出白桦林＞阔叶红松林＞云冷杉林＞岳桦林＞山杨林.     

三峡库区马尾松细根生产和周转及其影响因子

采用连续根钻法、分解袋法、分室通量模型法计算三峡库区马尾松细根的年生产量和周转率,分析细根生产量和周转率与各影响因子的关系.结果表明: 马尾松<0.5、0.5～1和1～2 mm细根年均生物量分别为0.29、0.59、0.76 t·hm^-2,细根年生产量分别为0.13、0.49、0.37 t·hm^-2,细根年周转率分别为1.49、1.01、0.40 a^-1.各影响因子对不同径级细根生产与周转的影响不同.土壤温度、土壤钙含量显著影响<0.5 mm细根生产量与细根周转,且土壤温度解释生产量和周转率32.8%和25.0%的变异,土壤钙含量解释65.6%和73.1%的变异;细根生物量与细根生产量呈显著正相关,细根生物量分别解释<0.5、0.5～1和1～2 mm细根生产量41.0%、41.1%和54.5%的变异;细根P、K含量与<0.5 mm细根生产量具有显著相关性,分别解释<0.5 mm细根生产量32.2%、39.2%的变异.<0.5 mm细根与各影响因子的关系最为密切,土壤温度、土壤钙含量是细根生物量的主要影响因子.     

Nitrate-reducing capacity of roots and nodules ofAlnus rubra and roots ofPseudotsuga menziesii

Summary Nitrate-reducing capability was demonstrated for root segments of red alder and, at more than twice that rate, for alder nodules. Root segments of Douglas-fir failed to reduce nitrate despite various treatments designed to induce such activity. The reported response of Douglas-fir to nitrate fertilizer may be ascribed either to microbial assimilation of nitrate ions with subsequent liberation of ammonium in the soil or to nitrate assimilation by fungi that form mycorrhizae with Douglas-fir roots.     

Flavonoids from shoots, roots and roots exudates of Brassica alba

Analysis of extracts obtained from shoots, roots and exudates of Brassica alba revealed the presence of 3,5,6,7,8-pentahydroxy-4'-methoxy flavone in shoots, as well as 2',3',4',5',6'-pentahydroxy chalcone and 3,5,6,7,8-pentahydroxy flavone in roots and exudates. Apigenin was also found in the shoots and roots, but not in the root exudates.     

Lipids in hairy roots and non-Agrobacterium induced roots of Crambe abyssinica

Hairy root cultures of Crambe abyssinica were obtained through infection of leaves with two wild-type agropine strains of Agrobacterium rhizogenes. The efficiency of transformation was about 16 %. The presence of T-DNA from A. rhizogenes in the hairy roots genome was confirmed by PCR using specific primers for rolB and rolC genes. Selected clones of hairy roots and non-Agrobacterium induced roots from sterile cultures were used for analyses of acyl-lipids. The total amount of acyl-lipids per mg of dry weight was similar in both the non-Agrobacterium induced roots and the hairy roots in good physiological condition, and ranged from 38 to 53 nmol. However, in the clones which showed symptoms of ageing, the lipid content was severely reduced. Also the lipid composition of hairy roots appears to be similar to the composition of non-transformed roots. Polar lipids were the dominant class of lipids in both types of roots (about 75 %). Furthermore, we found diacylglycerols, free fatty acids (FFA), triacylglycerols, sterol esters, and an unidentified lipid class. The dominant fatty acids in the lipids of both types of roots were α-linolenic acid, palmitic acid, and linoleic acid (over 12 % of total FA). Among the lipids of both hairy roots and non-Agrobacterium induced roots of C. abyssinica, an unidentified FA was found (over 16 % of total FAs). The present study is the first example of establishment of hairy roots cultures of C. abyssinica. It also includes the first analysis of the lipids in hairy roots and non-Agrobacterium induced roots of this species.     

Auxin binding in roots: A comparison between maize roots and coleoptiles

Auxin binding onto membrane fractions of primary roots of maize seedlings has been demonstrated using naphth-1yl-acetic acid (NAA) and indol-3yl-acetic acid (IAA) as ligands. This binding is compared with the already well characterized interaction between auxins and coleoptile membranes. The results indicate that while kinetic parameters are of the same order for root and coleoptile binding, a number of differences occur with respect to location in cells and relative affinity. The possible significance of the existence of such binding sites in root cells is discussed in relation to auxin action.Abbreviations 4-Cl-PA 4-chlorophenoxyacetic acid - EDTA ethylene diamine tetracetic acid - IAA indol-3yl-acetic acid - MCPA 2-methyl-4-chlorophenoxyacetic acid - NAA naphth-1yl-acetic acid - 2-NAA naphth-2yl-acetic acid - Tris 2-amino-2-(hydroxymethyl) propane-1,3 diol - TIBA 2,3,5 triiodobenzoic acid - NPA naphthylphthalamic acid - PCIB 4-chlorophenoxyisobutyric acid - PCPP 4-chlorophenoxyisopropionic acid - 2,4-D 2,4-dichlorophenoxyacetic acid     

Development and function ofAzospirillum-inoculated roots

Summary The surface distribution ofAzospirillum on inoculated roots of maize and wheat is generally similar to that of other members of the rhizoplane microflora. During the first three days, colonization takes place mainly on the root elongation zone, on the base of root hairs and, to a lesser extent, on the surface of young root hairs.Azospirillum has been found in cortical tissues, in regions of lateral root emergence, along the inner cortex, inside xylem vessels and between pith cells. Inoculation of several cultivars of wheat, corn, sorghum and setaria with several strains ofAzospirillum caused morphological changes in root starting immediately after germination. Root length and surface area were differentially affected according to bacterial age and inoculum level. During the first three weeks after germination, the number of root hairs, root hair branches and lateral roots was increased by inoculation, but there was no change in root weight. Root biomass increased at later stages. Cross-sections of inoculated corn and wheat root showed an irregular arrangement of cells in the outer layers of the cortex. These effects on plant morphology may be due to the production of plant growth-promoting substances by the colonizing bacteria or by the plant as a reaction to colonization. Pectic enzymes may also be involved. Morphological changes had a physiological effect on inoculated roots. Specific activities of oxidative enzymes, and lipid and suberin content, were lower in extracts of inoculated roots than in uninoculated controls. This suggests that inoculated roots have a larger proportion of younger roots. The rate of NO^– ₃, K⁺ and H₂PO^– ₄ uptake was greater in inoculated seedlinds. In the field, dry matter, N, P and K accumulated at faster rates, and water content was higher inAzospirillum-inoculated corn, sorghum, wheat and setaria. The above improvements in root development and function lead in many cases to higher crop yield.     

Random roots and lineage sorting

Lineage sorting has been suggested as a major force in generating incongruent phylogenetic signal when multiple gene partitions are examined. The degree of lineage sorting can be estimated using the coalescent process and simulation studies have also pointed to a major role for incomplete lineage sorting as a factor in phylogenetic inference. Some recent empirical studies point to an extreme role for this phenomenon with up to 50-60% of all informative genes showing incongruence as a result of lineage sorting. Here, we examine seven large multi-partition genome level data sets over a large range of taxonomic representation. We took the approach of examining outgroup choice and its impact on tree topology, by swapping outgroups into analyses with successively larger genetics distances to the ingroup. Our results indicate a linear relationship of outgroup distance with incongruence in the data sets we examined suggesting a strong random rooting effect. In addition, we attempted to estimate the degree of lineage sorting in several large genome level data sets by examining triads of very closely related taxa. This exercise resulted in much lower estimates of incongruent genes that could be the result of lineage sorting, with an overall estimate of around 10% of the total number of genes in a genome showing incongruence as a result of true lineage sorting. Finally we examined the behavior of likelihood and parsimony approaches on the random rooting phenomenon. Likelihood tends to stabilize incongruence as outgroups get further and further away from the ingroup. In one extreme case, likelihood overcompensates for sequence divergence but increases random rooting causing long branch repulsion.