大针茅草原地上生物量形成的规律与特点

大针茅草原能进行光合作用的时间为160—170天。地上生物量的季节生长曲线呈单峰型,适宜的收获期在8月份。地上生物量的增长与群落的高度增长呈明显相关(R=0.959)。立枯量于6月份开始出现,其增长规律与绿色量呈相反的趋势。刈割后的再生草量以春季(5月份)刈割后的产量最高。仲夏(7月份)刈割对草场生产力的威胁最大。群落产量结构的研究表明：5己于人cm以上可供牲畜采食的部分约占总产量的70—80％。     

砧板柚花粉发育过程外壁糖蛋白形成的透射电镜分析

采用细胞化学技术,经钉红对砧板袖几个不同发育阶段的花粉进行染色显示,用透射电镜对花粉外壁糖蛋白进行了细胞化学定位观察,探讨了花粉发育过程中外壁糖蛋白的发生时期及输送到花粉壁的过程。研究结果表明,花粉外壁糖蛋白在单核花粉时期由绒毡层细胞产生,并被分泌到药室内,输送到花粉外壁及萌发孔周围积累和贮存,整个过程延续到花粉成熟．     

Temporal patterns of genetic variation across a 9-year-old aerial seed bank of the shrub Banksia hookeriana (Proteaceae)

The pattern of accumulation of genetic variation over time in seed banks is poorly understood. We examined the genetic structure of the aerial seed bank of Banksia hookeriana within a single 15-year-old population in fire-prone southwestern Australia, and compared genetic variation between adults and each year of a 9-year-old seed bank using amplified fragment length polymorphism (AFLP). B. hookeriana is well suited to the study of seed bank dynamics due to the canopy storage of its seeds, and because each annual crop can be identified. A total of 304 seeds from nine crop years and five maternal plants were genotyped, along with 113 plants from the adult population. Genetic variation, as assessed by the proportion of polymorphic markers (P(p)) and Shannon's index (I), increased slightly within the seed bank over time, while gene diversity (H(j)), did not change. P(p), I, and H(j) all indicated that genetic variation within the seed bank quickly approached the maximal level detected. Analysis of molecular variance revealed that less than 4% of variation could be accounted for by variation among seeds produced in different years, whereas there was greater differentiation among maternal plants (12.7%), and among individual seeds produced by different maternal plants (83.4%). With increasing population age, offspring generated each year were slightly more outbred, as indicated by an increase in the mean number of nonmaternal markers per offspring. There were no significant differences for H(j) or I between adults and the seed bank. Viability of seeds decreased with age, such that the viability of 9-year-old seeds was half that of 2-year-old seeds. These results suggest that variable fire frequencies have only limited potential to influence the amount of genetic variation stored within the seed bank of B. hookeriana.     

Stem tissue phosphorus as an index of the phosphorus status of Banksia ericifolia L. f.

The effects of P fertilizer rate on shoot growth and the total P concentration of the whole shoot, new and mature leaves, symptom leaves and stems of Banksia ericifolia L. f., a P-sensitive species, were investigated in a six month greenhouse pot experiment. Shoot dry weight of plants growing in an Australian sedge peat, coarse sand and perlite potting mix (1:1:1) increased with up to 100 mg P L⁻¹ supplied as a six month controlled release P (0:18:0) fertilizer, but was reduced by toxicity at the highest application rate (200 mg P L⁻¹). Plants receiving this treatment developed chlorotic new and mature leaves. Leaf symptoms observed at rates of 60–100 mg P L⁻¹ were confined to old leaves and were related to the P concentration of the shoot. Growth was not affected at these rates. The P concentration of stems was strongly influenced by P supply. This tissue acted as a sink for excess P, helping to regulate the P concentration of leaves. The approximate range of P concentrations in stem tissue, associated with greater than 90% of maximum shoot dry weight, was 0.5–1.5 g P kg⁻¹ tissue dry weight. This was greater than that calculated for mature leaves (0.5–0.8 g kg⁻¹) or for whole shoots (0.5–1.2 g kg⁻¹). This wider range, and the capacity to store P in excess to requirement, makes the stem a better index tissue for plant P status than either leaves or whole shoots. This revised version was published online in June 2006 with corrections to the Cover Date.     

大针茅典型草原土壤CO2排放规律的研究

采用静态室/碱吸收法研究了内蒙古大针茅典型草原土壤呼吸的时空动态.大针茅群落地上部和地下部生物量的时空变异不同步,用地上部生物量不能很好地预测群落的根系量.群落土壤呼吸具有明显的时空动态,控制群落土壤呼吸空间变异与时间变异的因子是不同的.土壤呼吸的季节变化与地上部生物量及土壤水分状况关系密切.根据大针茅群落分别计算了大针茅群落1995、1997和1998年的年CO₂排放总量,分别为180、45.8和225gC·m^-2·a^-1,年际变异很大.过度放牧大大降低了群落的生物量,也降低了土壤CO₂排放量.讨论了建立以降水量为驱动因子的草地群落土壤呼吸动态模型的可能性.     

福建省中部地区抗寒速生尾巨桉优株筛选

本文通过自然选择与优势木选择方法,选择了适生性状良好的尾巨桉品种的多个优良单株。根据不同选择标准,筛选出抗寒适生优良单株21株,抗寒速生优势木单株13株;对所选单株采用无性系繁殖方法,利用1000mg/L ABT生根粉处理所选择优良单株的穗条,用营养袋扦插培育无性系种苗,并建立无性系采穗圃和优良单株基因库。     

巨桉人工林地土壤微生物类群的生态分布规律

研究了四川省洪雅县巨桉人工林地土壤微生物数量及其类群分布规律.结果表明,洪雅县巨桉人工林地土壤微生物数量具有明显的季节变化,各样地均以秋季最多,达到17.42×10⁶CFU·g^-1,春季次之,夏季最少.土壤微生物主要集中在0～20cm的土层,随着土层的加深,微生物数量迅速减少;在0～60cm土层,同一类群微生物数量变动范围较大,其中好气性细菌0.31×10⁶～14.39×10⁶CFU·g^-1,放线菌0.06×10⁶～0.79×10⁶CFU·g^-1,真菌0.02×10⁶～0.07×10⁶CFU·g^-1,厌氧细菌0.07×10⁶～3.22×10⁶CFU·g^-1.巨桉人工林地微生物以细菌为主要类群,占微生物总数的92.83%以上,其次是放线菌和真菌,其微生物组成结构合理.与青冈次生林和农耕地相比,巨桉人工林地微生物数量远远高于青冈次生林地,有利于土壤微生物生长.细菌生理类群的Simpson多样性指数和Shannon-Wiener多样性指数分别达到0.773和1.896.     

不同密度巨桉人工林林下植物多样性及根际土壤化感物质

为探究巨桉人工林林下植物多样性的影响因素,选择四川省丹棱县4和8年生不同密度(1200、1600和2000株·hm^-2)巨桉人工林为对象,研究林下植物多样性和根际土壤酚类化感物质。结果表明: 共发现植物45种,隶属于33科44属;随林龄增加和林分密度降低,巨桉人工林林下植物种类增加且重要值分布更为均匀;各林分植物生活型以高位芽植物为主。4年生林地灌木Shannon指数和Margalef指数在1600株·hm^-2下显著升高,4年生林地除Margalef指数外其余草本多样性指数及8年生林地草本Pielou指数随林分密度降低均显著升高;灌木Shannon指数及Margalef指数在1200株·hm^-2下8年生林地显著高于4年生林地。根际土壤中鉴定出5种酚类化感物质,4年生林地根际土壤中水杨酸浓度在1600株·hm^-2下显著降低,5,7-二羟基黄酮浓度随林分密度降低而显著降低;水杨酸浓度在8年生林地根际土壤中随林分密度降低显著升高;水杨酸浓度在2000株·hm^-2下4年生林地显著高于8年生林地,在1600株·hm^-2下相反;5,7-二羟基黄酮浓度在1200株·hm^-2下8年生林地显著高于4年生林地。冗余分析(RDA)结果表明,土壤pH、容重、有机质、全磷、全氮及化感物质是林下植物多样性的主要环境影响因子。适度延长轮伐期、调节林分密度以改善林内微环境、缓冲巨桉的化感作用,可促进林下植被发育。     

不同放牧强度下内蒙古温带典型草原优势种植物防御策略

放牧是草原的主要利用方式, 但对牧草造成了一定的生物胁迫。面对生存压力, 牧草会通过调节初级与次级代谢过程启动防御机制。该研究以内蒙古温带典型草原优势种植物为研究对象, 通过测定其在5个放牧水平下不同营养器官中的次级代谢产物及木质素等含量, 探讨大针茅(Stipa grandis)和羊草(Leymus chinensis)的各营养器官在防御机制中的角色及其碳氮权衡策略。结果表明: 面对放牧胁迫, 大针茅和羊草会产生大量的单宁、总黄酮、酚类以及生物碱等次级代谢产物, 并以叶片为主要的合成及储存器官。中度放牧使羊草的化学防御机制得到较充分的诱导及表达。但二者地上部分木质素含量并无显著增加, 因此, 二者在避牧性机制上更倾向于化学防御而非机械防御。由于羊草有更高的氮利用效率, 这使得羊草可以通过碳氮两种代谢途径进行防御, 但大针茅在生长初期并不能将氮高效地分配到化学防御中。大针茅和羊草在生长初期面对轻度放牧胁迫, 较多的资源仍然用于初级代谢, 增加了植物耐牧性。因此, 轻度放牧有利于提高牧草的碳氮资源利用效率、提高生态系统生产力及稳定性。