Topsoil Handling and Storage Effects on Woodland Restoration in Western Australia

An analysis of the effects of topsoil handling and storage methods was undertaken to optimize the potential rehabilitation of southwest Western Australian Banksia woodland species present before site disturbance. An increase in the depth of topsoil stripped from the Banksia woodland, from 10 to 30 cm, correlated to decreasing seedling recruitment from the soil seedbank by a factor of three following in situ respreading in an area to be restored. There was no significant difference in total seedling recruitment in situ at two depths of spread, 10 cm and 30 cm. These results concur with an ex situ trial on the effects of depth of seed burial on seedling recruitment that showed most species failed to emerge from depths greater than 2 cm. In situ stockpiling of the woodland topsoil for 1 or 3 years demonstrated a substantial and significant decline in seedling recruitment to 54% and 34% of the recruitment achieved in fresh topsoil, respectively. Stripping and spreading during winter substantially depressed seedling recruitment, compared with autumn operations, as did in situ stockpiling followed by spreading in the wet season, or stockpiling in winter followed by spreading in spring. No loss in total seedling recruitment occurred when replaced topsoil and subsoil were ripped to 80 cm following spreading of topsoil in sites to be restored. Conclusions from this study are that (1) topsoil provides a useful source of seeds for rehabilitation of Banksia woodland communities in the southwest of Western Australia, (2) correct handling of the topsoil, stripped and replaced fresh and dry (autumn direct return) to the maximum depths of 10 cm, can be used to optimize revegetation of species‐rich plant communities with this type of seedbank, and (3) ripping of topsoil and subsoil to ease compaction of newly restored soils does not diminish the recruitment potential of the soil seedbank in the replaced topsoil.     

双苗春小麦胚和胚乳发育异常

用石蜡切片法观察了双苗春小麦胚和胚乳的发育;发现有许多异常现象。主要表现如下：１．双胚,发生频率约６％;２．未受精形成孤雌胚;３．胚乳中具无核细胞质泡;４．原胚时期胚囊不同程度变形、缩小。     

The reproductive potential and importance of key management aspects for successful Calluna vulgaris rejuvenation on abandoned Continental heaths

The abandonment of traditional pastoralism as well as the use of heath areas for military purposes has had a major impact on dry heaths in the Continental biogeographical region of Europe, causing severe degradation of its key species Calluna vulgaris (L.) HULL. The reproductive potential of this species in a Continental climate is assumed to be low, although there is yet no observational or experimental evidence for this. More knowledge is also needed about cost‐effective and sustainable measures to restore abandoned dry heaths in this biogeographical region, because traditional management options are often too expensive (e.g., sod‐cutting) or restricted due to environmental laws and the danger of unexploded ammunition (e.g., burning). Using as an example an 800 ha Continental heathland in Germany that has been abandoned for about two decades, we studied the reproductive potential (seed production, soil seed bank, and germination ability) of degenerate C. vulgaris stands. In addition, we conducted a comprehensive field experiment to test the effects of low‐intensity, year‐round grazing by Heck cattle and Konik horses as well as one‐time mowing and patchy exposure of bare soil on the generative rejuvenation (i.e., recruitment and survival) of degenerate C. vulgaris stands over 3 years. We used generalized linear mixed models for statistical analyses. Seed production of degenerate C. vulgaris stands was high as well as the germination ability of their seeds, being similar to Atlantic heathlands. However, soil seed‐bank densities were lower than those found in managed or abandoned Atlantic heaths. Overall seedling recruitment in the field was considerably lower in comparison with Atlantic heaths. Low‐intensity grazing or one‐time mowing did not induce a substantial increase in C. vulgaris recruitment, whereas an additional one‐time creation of bare soil patches or the one‐time creation of bare soil without subsequent management significantly facilitated seedling recruitment and survival in the first year. However, from the second year on, the positive effect of the creation of bare soil without subsequent management was no longer present. In the third year, survival of juveniles was significantly supported by low‐intensity grazing in combination with shallow soil disturbances as well as in combination with one‐time mowing and shallow soil disturbances, whereas mowing alone resulted in marginally significant lower survival. The extremely low seedling recruitment requires a careful choice of suitable management measures to promote the survival of sufficient numbers of Calluna individuals. Therefore, we recommend low‐intensity grazing with free‐ranging robust breeds and the combination of this with one‐time mowing as an effective means of supporting generative rejuvenation of C. vulgaris in degraded heaths. However, at the beginning of the restoration process, the creation of bare soil patches for seedling recruitment is crucial. For implementation into practice, we present different strategies to enhance the proportion of bare soil after long‐term abandonment of heaths when traditional management options are no longer feasible.     

Seedling tolerance to cotyledon removal varies with seed size: A case of five legume species

It is generally accepted that seedlings from large seeds are more tolerant to defoliation than those from small seeds due to the additional metabolic reserves present in the large seeds. However, information on the effects of amount of seed reserves (cotyledon removal) from seedlings resulting from large vs. small seeds on seedling growth and long‐term survival in the field is limited. Five legume species with different sizes of seeds were sown in the field and none, one, or both cotyledons removed 7 days after seedling emergence. Seedling biomass, relative growth rate (RGR) and survival were determined at different time. Cotyledon removal, species, and their interaction had significant effects on seedling growth and survival. During the period between 33 and 70 days, seedlings from large seeds had a significantly lower RGR than those from small seeds. Biomass, RGR, and survival of seedlings from large seeds were significantly reduced by removal one or both cotyledons, whereas those of seedlings from small seeds were not affected. Seed energy reserves are more important for the early growth of seedlings from large seeds than for those from small seeds. The overall effect of cotyledon removal on growth and survival varies with seed size (i.e., energy reserves) with seedlings from small seeds being less sensitive than those from large seeds under field conditions.     

Differential response of Scots pine seedlings to variable intensity and ratio of red and far‐red light

We investigated the response to increasing intensity of red (R) and far‐R (FR) light and to a decrease in R:FR ratio in Pinus sylvestris L. (Scots pine) seedling. The results showed that FR high‐irradiance response for hypocotyl elongation may be present in Scots pine and that this response is enhanced by increasing light intensity. However, both hypocotyl inhibition and pigment accumulation were more strongly affected by the R light compared with FR light. This is in contrast to previous reports in Arabidopsis thaliana (L.) Heynh. In the angiosperm, A. thaliana R light shows an overall milder effect on inhibition of hypocotyl elongation and on pigment biosynthesis compared with FR suggesting conifers and angiosperms respond very differently to the different light regimes. Scots pine shade avoidance syndrome with longer hypocotyls, shorter cotyledons and lower chlorophyll content in response to shade conditions resembles the response observed in A. thaliana. However, anthocyanin accumulation increased with shade in Scots pine, which again differs from what is known in angiosperms. Overall, the response of seedling development and physiology to R and FR light in Scots pine indicates that the regulatory mechanism for light response may differ between gymnosperms and angiosperms.     

Idiosyncratic phenomenon of regeneration from cotyledons in the idiot fruit tree,Idiospermum australiense

Idiospermum australiense (Diels) S. T. Blake, is a rare species that produces very large diaspores (up to 225 g) comprising 2–6 cotyledons. Anecdotal evidence suggested that each cotyledon within the diaspore could develop an independent root/shoot axis in natural populations and under glasshouse conditions. To investigate this potential, 13 diaspores were collected. Six diaspores were kept intact and cotyledons in the remaining seven were separated, planted into soil and scored for germination. All shoots were allowed to grow for 12 weeks. To test for differences in growth response from seedlings emerging from intact diaspores and single cotyledons, plant height, shoot mass, stem mass, leaf mass and total leaf area were compared between groups using both absolute values and values standardized to initial reserve mass. To examine the effects of reserve mass in more detail, height to stem mass, leaf mass to stem mass and specific leaf area was also compared between groups. All intact cotyledons and 24 of the 27 single cotyledons produced a functional root/shoot system. Time to germination was not different between groups. Shoot mass, stem mass and leaf mass were significantly greater in intact diaspores than in single cotyledons, although no difference was found in any parameter when standardized to initial reserve mass. Shoots arising from individual cotyledons were significantly taller per gram initial weight, because of a significantly greater relationship between height and stem mass. Shoots arising from single cotyledons also had a significantly greater investment in leaf mass per unit stem mass, even though there was no difference in specific leaf area between groups. Thus, seedlings arising from individual cotyledons grew relatively taller and produced a greater area of leaf tissue relative to stem than those arising from intact diaspores.     

Light Response of Seedlings of a Central African Timber Tree Species,Lophira alata (Ochnaceae), and the Definition of Light Requirements

Light is of primary importance in structuring tropical tree communities. Light exposure at seedling and adult stages has been used to characterize the ecological profile of tropical trees, with many implications in forest management and restoration ecology. Most shade‐tolerance classification systems have been proposed based on empirical observations in a specific area and thus result in contradictions among categories assigned to a given species. In this study, we aimed to quantify the light requirements for seedling growth of a Central African timber tree, Lophira alata (Ochnaceae), taking into account effects of population origin. In two controlled experiments: a light response experiment and a comparative population experiment, conducted in southwestern Cameroon, using seeds collected from four populations (three from Cameroon and one from Gabon), we examined the quantitative responses to irradiance of seedlings. After 2 years, mortality was very low (<3%), even in extremely low irradiance. Growth and biomass allocation patterns varied in response to light, with intermediate irradiance (24–43%) providing optimal conditions. Light response differed between populations. The Boumba population in the northeastern edge of the species' distribution exhibited the highest light requirements, suggesting a local adaptation. As a result of positive growth at low irradiance and maximum growth at intermediate irradiance, we concluded that L. alata exhibits characteristics of both non‐pioneer and pioneer species. Implications of our results to propose an objective way to assign the light requirement for tropical tree species are discussed.     

草木灰对四种松属种子发芽和幼苗生长的影响

火干扰不仅影响森林生态系统的结构与功能,而且影响群落更新与演替。为了研究草木灰对4种松属种子萌芽和幼苗生长的影响,在湖南省株洲市黄丰桥林场采集马尾松、云南松、湿地松和火炬松种子,以马尾松次生林火烧迹地的草木灰为基质,设置对照和3个草木灰处理,进行播种试验及生长观测。结果表明:(1)草木灰处理下4个物种的种子发芽率比对照试验低,并呈现随草木灰含量的增加而降低的趋势,低草木灰含量处理马尾松种子发芽率不及对照一半,中、高草木灰含量处理发芽率更低;云南松、湿地松和火炬松种子发芽率规律类似于马尾松,而高草木灰含量处理发芽率为0。(2)培养皿播种平均发芽时间比花盆播种长,无论草木灰处理还是培养条件(培养皿或花盆),马尾松和云南松种子平均发芽时间比湿地松和火炬松短。(3)4个物种种子播种14周后,对照试验中马尾松和云南松幼苗死亡率最低,而火炬松和湿地松幼苗死亡率相对增加。(4)播种14周后不同试验处理4个物种幼苗生长差异不明显。火炬松、湿地松、云南松和马尾松幼苗的单株平均干重分别达0.038、0.031、0.027、0.024 g。各物种叶干重按降序排列依次是火炬松(0.026 g)湿地松(0.019 g)云南松(0.017 g)马尾松(0.016 g),根和茎的干重比重相当,约占对应物种幼苗叶干重的三分之一。研究表明以草木灰为培养基质,马尾松和云南松种子的发芽率较高,平均发芽时间较短,更适合作为火烧迹地植被恢复先锋树种,为火干扰后选择人工促进天然更新树种提供参考。     

Maize w3 disrupts homogentisate solanesyl transferase (ZmHst) and reveals a plastoquinone‐9 independent path for phytoene desaturation and tocopherol accumulation in kernels

Maize white seedling 3 (w3) has been used to study carotenoid deficiency for almost 100 years, although the molecular basis of the mutation has remained unknown. Here we show that the w3 phenotype is caused by disruption of the maize gene for homogentisate solanesyl transferase (HST), which catalyzes the first and committed step in plastoquinone‐9 (PQ‐9) biosynthesis in the plastid. The resulting PQ‐9 deficiency prohibits photosynthetic electron transfer and eliminates PQ‐9 as an oxidant in the enzymatic desaturation of phytoene during carotenoid synthesis. As a result, light‐grown w3 seedlings are albino, deficient in colored carotenoids and accumulate high levels of phytoene. However, despite the absence of PQ‐9 for phytoene desaturation, dark‐grown w3 seedlings can produce abscisic acid (ABA) and homozygous w3 kernels accumulate sufficient carotenoids to generate ABA needed for seed maturation. The presence of ABA and low levels of carotenoids in w3 nulls indicates that phytoene desaturase is able to use an alternate oxidant cofactor, albeit less efficiently than PQ‐9. The observation that tocopherols and tocotrienols are modestly affected in w3 embryos and unaffected in w3 endosperm indicates that, unlike leaves, grain tissues deficient in PQ‐9 are not subject to severe photo‐oxidative stress. In addition to identifying the molecular basis for the maize w3 mutant, we: (1) show that low levels of phytoene desaturation can occur in w3 seedlings in the absence of PQ‐9; and (2) demonstrate that PQ‐9 and carotenoids are not required for vitamin E accumulation.