Litter and its interaction with standing vegetation affect seedling recruitment in Tibetan alpine grasslands

Background: Seedling recruitment is widely recognised to be important in the maintenance of diversity and coexistence of species. It is not clear how local abiotic factors mediated by litter and biotic interactions influence plant species recruitment in alpine grasslands.

Aims: To determine how litter and standing vegetation affected seedling recruitment in plant communities in Tibetan alpine grasslands.

Methods: Seedling recruitment was quantified in response to experimental treatments: (1) removal of standing vegetation and litter; (2) removal of standing vegetation with litter intact; (3) intact standing vegetation and removal of litter and (4) control: intact standing vegetation and litter.

Results: Litter removal increased seedling numbers, while standing vegetation removal had no effect. An interaction between litter and standing vegetation removal marginally increased seedling number. Species richness of seedlings was not related to either litter removal or standing vegetation removal. Species composition of seedling differed significantly between removal of both litter and standing vegetation and control.

Conclusions: Litter and its interaction with standing vegetation has an important role in affecting plant species recruitment in this alpine plant community. In contrast, biotic interactions, such as competition or facilitation from standing vegetation, appear to have only minor effects on recruitment.     

茄子嫁接苗与自根苗光合特性比较

对茄子嫁接苗与自根苗的光合生理特性进行了比较研究。结果表明,不同时期嫁接苗功能叶片的净光合速率（Pn）均显著高于自根苗;茄子嫁接苗与自根苗功能叶片的Pn日变化均呈“双峰”曲线,但嫁接苗的“午休”程度较自根苗轻;嫁接苗比自根苗有较低的光补偿点（LCP）和CO2补偿点（CCP）,较高的光饱和点（LSP）和CO2饱和点（CSP）;有较低的光合冷限温度和较高的光合热限温度,光合最适温度两者之间没有明显的差别;有较高的光饱和、CO2饱和及最适温度时的Pn;嫁接苗Pn高是因为嫁接苗胞间的光合反应的底物浓度大（Ci高）,表观量子效率（AQY）、羧化效率（CE）和光合能力（A350）高的缘故。     

四种沙埋深度对羊草种子出苗和幼苗生长的影响

模拟羊草种子自然埋藏深度状况,设计了0、1、2和3cm共4种沙埋深度实验,研究了其出苗率及幼苗生长对沙埋深度的响应。结果表明,羊草种子出苗率随埋深的增加呈下降趋势,0cm时出苗率最高为89.3%,1和2cm时分别为81.5%和78.5%,3cm时最低(73.5%),与前三者具有显著差异。埋深对地上株高生长动态的影响主要表现在,播种后25d,0～2cm处理的羊草幼苗地上株高均高于3cm处理;播种后36d,4种处理的地上株高没有显著差异。此外,随着埋深的增加,羊草幼苗的根长、根数、根冠比呈先上升后下降趋势,叶片数呈下降趋势,绝对株高则呈上升趋势。表明1～2cm沙埋深度更适宜于羊草种子出苗及幼苗生长,而0或3cm埋深不利于其出苗和幼苗生长。     

不同育苗方式对移栽后侧柏和白榆幼苗根系生长的影响

不同类型苗木,具有不同的根系结构特征,其根系结构也将影响林木的生长和恢复生态系统的稳定性。以侧柏和白榆为研究对象,对移栽18个月后的种基盘苗与营养钵苗根系的生长进行了调查。结果表明:侧柏种基盘苗的总根长和平均直径比营养钵苗分别增加了316.20 cm和0.05mm,白榆苗则分别增加了651.54 cm和0.88mm。侧柏和白榆种基盘苗的根系表面积比营养钵苗分别增加了40.05%和73.04%。侧柏种基盘苗的根系总体积与营养钵苗的差异不显著,而白榆种基盘苗的根系总体积则比营养钵苗增加了54.70%。侧柏和白榆营养钵苗的一级侧根数量大于种基盘苗,增幅分别为42.31%和30.65%。对于侧柏来说,营养钵苗的根尖总数比种基盘苗的增加324个,但白榆苗差异不显著。各种处理的幼苗总根长与根系表面积都有显著相关性,但与根体积不具有显著相关性。营养钵苗的根系平均直径和根尖数量具有相对独立性,而种基盘的根系平均直径与总根长以及根体积均表现为显著相关。种基盘苗能提高侧柏、白榆幼苗的根冠比,促进幼苗株高、地径和主根的生长。采用种基盘苗进行植被恢复,由于其具有较大的根表面积和根长度,林木便具有了较大的吸收水分和营养的能力,以及较高的固结表层土壤能力。     

Seed mass and seedling establishment after fire in Ku‐ring‐gai Chase National Park,Sydney, Australia

Abstract Relationships between seed mass and several aspects of plant regeneration ecology were investigated in a post‐fire environment in Ku‐ring‐gai Chase National Park near Sydney, Australia. We found a significant positive relationship between seed mass and time to seedling emergence (P < 0.001) and a strong negative relationship between seed mass and time between emergence and production of the first true leaf (P < 0.001). Surprisingly, we found no relationship between seed mass and seedling establishment (P = 0.21). It seems most likely that this lack of relationship is a result of the many stochastic factors affecting seedling establishment during any given recruitment episode at any given site. A cause of mortality was assigned to 56% of the 781 seedlings that died during the present study. There was no relationship between cause of death and seed mass (P = 0.28). Of the seedlings for which the cause of death was known, 57% were killed by herbivory and 21% were killed by drought. Seedling–seedling competition affected only one species.     

Restoration of a Restinga Sandy Coastal Plain in Brazil: Survival and Growth of Planted Woody Species

In this article we report the results of an experiment introducing 17 native shrub and tree species into a Brazilian restinga (i.e., coastal sandy plain vegetation). Restingas have been affected by human impact for about 8,000 years, and human occupation for housing, tourism, and land speculation has recently increased in such a way that there is a need for conservation of remnant patches and restoration of degraded areas throughout the coast to protect biodiversity. Our study site is a remnant located in Rio de Janeiro, the second largest city in the country, and has been subjected in the past to deforestation, man‐made fire, and sand extraction. Although trees and shrubs predominantly compose natural restinga vegetation, local vegetation after impact was replaced by an exotic grass cover, which meant a drastic reduction in species richness. Thus, in this experiment we removed the grass cover, introduced shrub and tree species, and monitored survival and growth of 20 plants per species for 2 years. Despite the adversities imposed by the nutrient‐poor sandy soil, 70% of the species showed high survival percentage and considerable growth. This report on restoration initiatives in the restingas points out the viability of shrub and tree plantation following exotic grass removal as a strategy to restore Brazilian coastal vegetation.     

增产菌对棉花苗期病害的抑制效果及其机制的研究

在棉田覆膜栽培和温室盆栽条件下,对增产菌抑制棉苗病害的效果和机制进行了研究。增产菌处理过的田块,棉苗根病减轻8.8—9.2％,复合死苗率减轻43.4％。其机制为:根际微生物群落发生变化,导致害菌减少益菌增加,而且植株体内的过氧化物酶活性及其同功酶活性增强,同功酶还出现二条新谱带;再者根际土壤酶活性也增强,提高了土壤速效养分的供应。     

长白山暗针叶林苔藓植物群落特征与林木更新的关系

暗针叶林是长白山亚高山地区的主要森林植被,林下苔藓植物资源极其丰富,有些地段苔藓盖度可达80％以上。苔藓植物作为暗针叶林的主要活地被物,其对林木更新的影响不容忽视。研究了苔藓植物的盖度和厚度对暗针叶林主要树种更新的影响。对苔藓层盖度及厚度与主要针叶树种及亚乔木树种幼苗数量的相关关系分析发现,当苔藓盖度大于40％或厚度大于4cm时,苔藓层对红松、臭冷杉、花楷槭幼苗数量的负面影响较明显;而在苔藓厚度小于4cm时,苔藓层有利于花楷槭和花楸幼苗数量的增加;对苔藓层盖度及厚度与针叶树幼苗高度的相关关系分析发现,一定盖度和厚度的苔藓层对幼苗高生长有积极作用,但其影响程度在各树种间有明显差异。     

Potentiality of Different Seed Priming Agents to Mitigate Cold Stress of Winter Rice Seedling

Seed priming has proved to be an effective pre-germination seed invigoration technique for different crops to improve seed and seedling performance under different abiotic stresses. In Bangladesh, winter rice is very often exposed to cold waves just after sowing in the nursery bed resulting in poor seed germination and seedling emergence, yellowish and thin seedlings production, and a very low survival rate. Seed priming may mitigate the cold stress during seed germination and seedling emergence and helps in the quality seedling production of winter rice. To evaluate the efficacy of different seed priming techniques in increasing seedling emergence, growth, vigor and survivability of winter rice cultivars under cold stress, a pot experiment was conducted at the Department of Agronomy, Bangladesh Agricultural University during December 2018 to January 2019. The experiment comprised two factors, (A) Winter rice variety namely, i) BRRI dhan29 and ii) BRRI dhan36; (B) Seed priming agent namely i) Control (no priming), ii) 20000 ppm NaCl, iii) 30000 ppm NaCl, iv) 20000 ppm KCl, v) 30000 ppm KCl, vi) 20000 ppm CaCl₂, vii) 30000 ppm CaCl₂, viii) 50 ppm CuSO₄, ix) 75 ppm CuSO₄, x) 10000 ppm ZnSO₄, xi) 15000 ppm ZnSO₄, xii) 2 ppm Na₂MoO₄, xiii) 3 ppm Na₂MoO₄, xiv) 100 ppm PEG (Polyethylene glycol 4000) and xv) 150 ppm PEG. Seeds were sown on two different dates viz., 1st December and 1st January so that seedlings are exposed to cold stress at different stages. The experiment was laid out in a completely randomized design (CRD) with three replications. Results indicated that (in most of the cases) seed priming has a positive impact on seedling emergence rate (%), root length, shoot length, root shoot ratio, root dry weight, shoot dry weight, seedling dry weight and survival rate (%). Among the priming agents, KCl and CaCl₂ performed best; while priming with NaCl and PEG showed no advantages over no priming for both the sowing dates. In general, BRRI dhan36 performed better than BRRI dhan29 in terms of seedling growth because of its higher tolerance to cold stress. But, both the varieties performed similarly in terms of emergence rate and survival rate. Thus, priming is an effective tool to increase seed germination, better seedling growth, and higher seedling survivability of winter rice under cold stress, and KCl (20000 ppm) or CaCl₂ (20000 ppm) can be considered as a viable priming agent.     

Establishment of Fabaceae Tree Species in a Tropical Pasture: Influence of Seed Size and Weeding Methods

The successful establishment of trees in pastures may be related to species, seed size, and weed control treatments. This study experimentally evaluated the emergence, establishment after 2 years, and growth of individuals of 7 tree species with different seed sizes sowed under three weeding methods (no weeding, grasses clipped, and grasses removed). The experiment was carried out in a tropical abandoned pasture in Midwestern Brazil, dominated by the exotic invasive grass Urochloa brizantha. The effect of seed size on seedling emergence was significant and was more intense in the no weeding and weeding treatment plots than in grasses clipped. Furthermore, an increase in seed size resulted in an increase in the probability of establishment of tree species, although this pattern also differed among weeding treatments. The increase in seed size reflected negatively on tree growth in the absence of grasses, whereas in the presence of grasses there was an inverse relationship. The experimental results suggested that the use of seeds of different sizes for direct seeding in pastures is a possible strategy of Fabaceae tree species reintroduction in pastures within the Cerrado. Fabaceae species with seeds larger than 100 mg can establish in areas with no weeding, whereas species with seeds smaller than 50 mg can establish preferentially in areas with weeding, growing faster than larger ones. Thus, weeding strategies can determine the success of direct seeding of different species in restoration projects of tropical pastures.     

Restoring Western (Basalt) Plains grassland. 2. Field emergence, establishment and recruitment following direct seeding

Summary   Both reservation of small remnants and ecological restoration of degraded areas will be crucial if the Victorian Western (Basalt) Plains grassland community is to be conserved in the long term. This study examined the potential of direct seeding as a technique for grassland restoration by recording the initial establishment and subsequent recruitment success of 64 (predominantly perennial) grassland species direct sown onto a constructed site. Forty-three (67%) of the sown species emerged and established during the 2-year study and a further three species were recorded in subsequent years. In the second year, 32 species increased their number either through seedling or vegetative recruitment and 30 species dispersed beyond their original sown plot. Seed size was not correlated with field emergence but life form did influence initial field success for some groups. The finding that many species are able to establish and recruit under the study conditions supports the need for further investigation of direct seeding in the restoration of grassland communities.     

Magnetic treatment of irrigation water and snow pea and chickpea seeds enhances early growth and nutrient contents of seedlings

The effects of magnetic treatment of irrigation water and snow pea (Pisum sativum L var. macrocarpon) and Kabuli chickpea (Cicer arietinum L) seeds on the emergence, early growth and nutrient contents of seedlings were investigated under glasshouse conditions. The treatments included (i) magnetic treatment of irrigation water (MTW), (ii) magnetic treatment of seeds (MTS), (iii) magnetic treatment of irrigation water and seeds (MTWS) and (iv) no magnetic treatment of irrigation water or seeds as control treatment. A magnetic treatment device with two permanent magnets (magnetic induction: 3.5-136 mT) was used for the above treatments. Seeds were sown in washed sand and seedlings were harvested at 20 days. The results showed that MTW led to a significant (P < 0.05) increase in emergence rate index (ERI; 42% for snow pea and 51% for chickpea), shoot dry weight (25% for snow pea and 20% for chickpea) and contents of N, K, Ca, Mg, S, Na, Zn, Fe and Mn in both seedling varieties compared to control seedlings. Likewise, there were significant increases in ERI (33% for snow peas and 37% for chickpea), shoot dry weight (11% for snow pea and 4% for chickpea) and some nutrients of snow pea and chickpea seedlings with MTS in comparison with the controls. The results of this study suggest that both MTW and MTS have the potential to improve the early seedling growth and nutrient contents of seedlings.     

槟榔苗期主要病虫害为害症状及防治方法

槟榔幼苗健壮程度直接影响槟榔植株前期的生长速度、中后期的果品品质及最终的果实产量.本文综述了槟榔幼苗期发生的主要生理性病害(白化、日灼、肥害)、侵染性病害(炭疽病、大茎点霉叶斑病、枯萎病)以及虫害(椰圆蚧、基斑毒蛾、斑腿蝗虫、红蜘蛛、黑刺粉虱)的发生症状、防治方法等.根据槟榔育苗期病虫害的发生规律,探索各种病害、虫害的防治方法,以期为槟榔苗期病虫害防治提供参考.     

Reintroduction of Wild Lupine (Lupinus perennis L.) Depends on Variation in Canopy,Vegetation, and Litter Cover

We experimentally examined the effects of canopy, vegetation, and leaf litter cover on the demography of Wild lupines (Lupinus perennis) in a central North American oak savanna spanning 9 years. We also compared the distribution of Wild lupine across the landscape to results predicted by the demographic experiments. With less canopy cover, soil temperatures were warmer and seedlings emerged earlier. Seedling survival increased 14% with each additional leaf grown. Seedling survival was four times greater in openings and partial shade than in dense shade. Seedling survival was also influenced by interactions between canopy cover and vegetation cover, between canopy cover and leaf litter, and among canopy cover, vegetation cover, and litter cover. In openings, seedlings had higher survival when vegetative cover was present, suggesting a positive shading effect on survival, but with greater canopy cover vegetative cover reduced survival. Seedling survival was greater for plants that experienced herbivory, a result that was probably related to plant size and quality rather than having been eaten. Survival of lupines to 9 years after seed planting was greatest in the partial shade, moderate in openings, and least in dense shade. Wild lupine cover across the landscape was greatest when litter cover was low and canopy cover and ground layer cover were moderate. Reduction of canopy cover by burning or cutting, and reduction of leaf litter by prescribed burning will benefit the reintroduction of Wild lupine by increasing light, reducing litter cover, and creating disturbances; however, the reduction of vegetation cover in openings may hinder lupine reintroduction.     

五种荒漠植物幼苗出土及生长对沙埋深度的响应

研究了红砂、泡泡刺、花棒、白刺和沙拐枣5种荒漠优势植物的幼苗出土和生长对沙埋的响应,判断了幼苗的生长特征能否预测植物的定植能力。进行了0、1、2、3、5cm和8cm等6个沙埋深度处理,每个处理5个重复。结果表明：每种植物的出苗率都随着沙埋深度的增加而降低,而且遵循着指数方程关系。红砂种子的最佳沙埋深度应为0-1cm,3cm已是出苗和存活的最大沙埋深度;泡泡刺、花棒和白刺种子的最佳深埋深度为0—3cm;沙拐枣在0—8cm各个深度都有出苗现象,且出苗率没有显著差异,但8cm深度的出苗率只有4％,最佳沙埋深度约为5cm。幼苗的生长高度受沙埋深度的影响显著,在同一时间,幼苗的最大生长高度并不在0cm表层,但红砂幼苗除外。泡泡刺、花棒和白刺在0—3cm的沙埋深度的幼苗生长高度大于5-8cm沙埋深度的生长高度,但沙拐枣幼苗在5cm深度的生长高度最大。5种荒漠植物幼苗的生物量受沙埋深度的影响不显著。在同一沙埋深度下,红砂的绝对高度生长率明显低于其余4种植物,沙拐枣的绝对高度生长率高于其余4种植物幼苗;5种植物的相对高度生长率对沙埋深度的响应并不敏感。绝对高度生长率与相对高度生长率并不能预示幼苗存活成功率。     

Does a latitudinal gradient in seedling survival favour larger seeds in the tropics?

The mean size of seeds produced by plants at the equator is two to three orders of magnitude higher than the mean size of seeds produced by plants at 60°. We compiled data from the literature to assess the possibility that this latitudinal gradient in seed size allows species to cope with more difficult seedling establishment conditions in tropical environments. We found no relationship between latitude and seedling survival through 1 week (P = 0.27, n = 112 species). There was also no evidence that a larger seed mass is required to gain a given level of seedling survival in tropical environments (P = 0.37, n = 112 species), and no relationship between latitude and the duration of the juvenile period (P = 0.57, n = 132 species). Thus, our results are not compatible with the idea that seedling establishment is more difficult in the tropics.     

不同罗汉果品种组培苗产量与质量性状的比较研究

以罗汉果组培苗的单株产量、果实大小、罗汉果总皂苷以及皂苷V的含量作为罗汉果药材产量和质量的评价指标,通过田间随机区组试验对不同罗汉果品种组培苗产量进行统计分析,并采用分光光度法和HPLC法分别对罗汉果总皂苷和罗汉果皂苷V的含量进行测定。结果显示,不同罗汉果品种组培苗在产量和质量性状上有显著差异。青皮果组培苗的产量较高,果实较大,罗汉果总皂苷和皂苷V含量也较高,适于大面积推广。