Low light availability affects leaf gas exchange,growth and survival of Euterpe edulis seedlings transplanted into the understory of an anthropic tropical rainforest

Euterpe edulis Mart. (Arecaceae) is a threatened palm tree of the Brazilian Atlantic Rainforest understory with fundamental importance for the restoration of degraded forest environments. We assessed the leaf gas exchange, growth and survival of E. edulis seedlings transplanted at three different forest sites (S1, S2 and S3) in the same area in which cocoa trees had been cultivated in a rustic agroforestry system. Measurement was carried out during the first year after seedling transplantation. The sites were characterised according to canopy openness (CO) and total daily photosynthetic photon flux density (PPFD). Average CO and PPFD values were 13.3%, 8.0% and 6.7%, and 3.34, 2.79 and 0.62 mol m^?2 d^?1 for S1, S2 and S3, respectively. A progressive decline in seedling survival was observed in all sites throughout the experiment. At 387 d after planting, survival at S1, S2 and S3 was 57%, 44% and 37%, respectively. The gross light-saturated photosynthetic rate (A_max), leaf area and plant biomass were significantly higher (P < 0.05) in S1 and S2 when compared with S3. The values of dark respiration rate (R _d) and photosynthetic compensation irradiance (I _c) were sufficiently low for a positive carbon balance. Notwithstanding, the interpretation of results of microclimate variables together with leaf gas exchange and growth variables indicated that seedlings at all sites were in a suboptimal condition to achieve A_max, which is probably the main cause of the dramatic decline in the seedlings’ survival throughout the first year after transplantation. From a practical point of view, if the values of CO and PFD are lower than 10% and 3 mol m^?2 d^?1, respectively, it is suggested that the transplanting of E. edulis seedlings to the understory of abandoned agroforestry systems be accompanied by cultural practices, such as the thinning and pruning of tree tops.     

Germination and seedling growth of <Emphasis Type="Italic">Dimorphandra jorgei</Emphasis> MF Silva and <Emphasis Type="Italic">Swartzia macrostachya</Emphasis> Benth. var. <Emphasis Type="Italic">riedelii</Emphasis> Cowan

Dimorphandra jorgei MF Silva (Caesalpinaceae) and Swartzia macrostachya Benth. var. riedelii Cowan (Fabaceae) are tree species from the southern Bahian Atlantic Forest, identified for the restoration of degraded areas. The objective of this research is to study their seed germination and seedling growth to develop simple methods for seedling production in small scale nurseries. Because the species have distinct dormancy and germination characteristics, the seeds were submitted to different treatments. D. jorgei seeds were immersed in hot water, scarified and stored for 12 weeks in the laboratory environment (25°C). S. macrostachya seeds were submitted to different combinations of drying and storage in the laboratory environment or refrigerator (4°C). Seedlings were submitted to two light treatments for 3 months: partial shade (52% of full sun) and full shade (12% of full sun). In D. jorgei, the highest germination occurred for scarified seeds (87%) and for seeds stored for 12 weeks and then scarified (69%). In S. macrostachya the undried control seeds had the highest germination, followed by that of the refrigeration storage treatment, without predrying (99% and 97%, respectively). The average values for the growth parameters were greater in full shade for D. jorgei, while S. macrostachya seedlings showed greater growth rates in partial shade. Two months growth is recommended before D. jorgei seedlings are of the sufficient size and leaf number for field planting. On the other hand, a period of 4 months is recommended for S. macrostachya, due to its relatively slow growth.     

Effects of soil flooding on leaf gas exchange and growth of two neotropical pioneer tree species

Schinus terebinthifolius Raddi (Anacardiaceae) and Rapanea ferruginea (Ruiz & Pavon) Mez (Myrsinaceae) are two neotropical pioneer trees with wide geographical distribution in South America, highly degree of adaptation to different soil conditions and intense regeneration in areas with anthropic activities. With the aim to recommend the use Schinus and Rapanea in gallery forest restoration programs, we conducted an experiment with the objective to analyze the capacity of these two pioneer trees to tolerate soil flooding, mainly by accessing the effects of flooding on leaf gas exchange, growth and dry matter partitioning. Seedling survival throughout the 56-day flooding period were 100 and 90% for Schinus and Rapanea, respectively. The mean values of stomatal conductance (g_s) and net photosynthesis (A) observed in the control seedlings were, respectively, 0.4 mol m^–2s^–1 and 14 mmolm^–2s^–1, for Schinus, and 0.5 mol m^–2s^–1 and 14 mmolm^–2s^–1, for Rapanea. On day 20 flooding reduced gs and A by 36 and 29% in Schinus, and 81 and 61% in Rapanea. At the end of the experiment, significant decreases were also observed for root and whole plant biomass, in both species. Based on the results, we concluded that seedlings of Schinus and Rapanea can survive and grow throughout a medium period of soil waterlogging, in spite of the alterations observed in their physiological behavior, such as the decreases in stomatal conductance and in whole plant biomass.     

Water table decline alters growth and survival of Salix gooddingii and Tamarix chinensis seedlings

In the western United States, many native riparian forests are declining downstream from dams and diversions, primarily due to a lack of successful regeneration of native species. Conceptual models have been described that incorporate stream flow characteristics that promote successful regeneration of western riparian Populus seedlings. However, these models need to be calibrated for additional species and specific stream characteristics. In this study, we examined the growth and survival of two dominant Sonoran desert riparian tree species, a native Salix gooddingii, and an exotic, Tamarix chinensis, to simulated water table declines at rates of 0, 1, 2, and 4 cm/day. Salix seedlings performed best in the 0 cm/day treatment in which the soil was saturated and showed decreasing survival and growth with increasing rates of water table decline. Root-to-shoot ratios were high for Salix, but root elongation rates were low with an emphasis on lateral root development. This root growth pattern may be an adaptation to habitat where Salix typically grows, near the stream channel where the water table is shallow but the likelihood of flood scour is high. Lateral root development may help to protect Salix seedlings from late season flood scour. Tamarix seedlings showed consistently high survival across all treatments and had the greatest growth in the 0 and 1 cm/day treatments. Tamarix seedlings had greater root elongation rates in response to water table decline relative to the control, with the greatest elongation in the 1 cm/day treatment. Greater root elongation rates and higher drought tolerance allowed Tamarix seedlings to persist in dry soils where Salix seedlings died. Differences in growth and survival of these two species in response to water table decline will need to be incorporated into management practices to promote successful native riparian tree regeneration.     

Growth and photosynthetic responses of Gallesia integrifolia (Spreng.) Harms and Schinus terebinthifolius Raddi seedlings in dense shade

We analyzed the growth and photosynthetic behavior of Gallesia integrifolia (‘pau-d’alho’) and Schinus terebinthifolius (‘aroeirinha’) under shade, seeking to obtain ecophysiological information for introducing seedlings of those species in previously established cacao agroforestry systems. Considering that light intensity under the shade of cacao trees varied between 5 and 10% daylight, 5 months old seedlings were exposed to four irradiance levels (25, 17, 10 and 5% daylight) for 92 days. With shade increase both species displayed trends of decrease leaf mass per unit leaf area, leaf area per plant (LA), relative growth rate (RGR) and net assimilation rate (NAR), and increase leaf area ratio (LAR). The mean values of light-saturated net photosynthetic rate (P _nmax) in 25 and 5% daylight were 12.8 and 8.0 μmol CO₂ m⁻² s⁻¹ for G. integrifolia and 17.9 and 7.4 μmol CO₂ m⁻² s⁻¹, respectively, for S. terebinthifolius. Based on the measurements of photosynthetic photon flux density and estimated values of photosynthetic saturated irradiance (Is) we concluded that, in all shaded conditions, the leaves of both species were under sub optimal light conditions to reach P _nmax. In spite of the lowest P _nmax values, RGR and NAR were significantly higher for G. integrifolia in all irradiance levels. Differences in growth rates can be explained by the higher values of LA, LAR and leaf mass ratio (LMR), as well as by the lower values of Is, photosynthetic compensation irradiance and dark respiration rates observed for G. integrifolia. Even though seedlings of G. integrifolia presented higher capacity to adapt under conditions of dense shade, we concluded that both species were under stress conditions induced by shade in light environments below 25% daylight. On a practical point of view it is possible to conclude that seedlings of both species should be introduced in light gaps, formed after the fall of big trees, or in places in which cacao trees are cultivated using large plant spacing.     

Effects of submergence in water on seed germination and vigor of the Copaifera lucens （Fabaceae） seedlings

We analyzed the tolerance of Copaifera lucens seeds to sub- mersion in water to assess the use of this species for direct seeding in riparian forest restoration programs. Seeds were submerged in water for 2, 4, 8, 16 and 32 days or not submerged （control = 0 days of submer- gence）. For the control and at the end of each period of submersion, germination and seedling vigor tests were carried out. For germination tests, seeds were sown in plastic pots containing sand and kept in labora- tory conditions. The percentage of seed germination, the germination rate and the average germination time were analyzed. For seedlings, total biomass, leaf area, leaf mass per area and leaf area ratio were analyzed. Submersion time drastically affected the dissolved oxygen content and seed germination. Between 4 and 8 days of submersion there was a de- crease from 83.8% to 15.6% in the germination percentage. No seed germination occurred after 16 days of submersion. Although there was a significant decrease in the percentage of seed germination between 4 and 8 days of submersion, seedling vigor was not affected. Seeds of this species were partially tolerant to submersion in water, suggesting that C. lucens is a promising species for direct seeding in riparian forest restora- tion projects.     

Influence of light availability on growth, leaf morphology and plant architecture of beech ( Fagus sylvatica L.), maple ( Acer pseudoplatanus L.) and ash ( Fraxinus excelsior L.) saplings

In a field study, we measured saplings of beech, ash and maple growing in a fairly even-aged mixed-species thicket established by natural regeneration beneath a patchy shelterwood canopy with 3–60% of above canopy radiation reaching the saplings. Under low light conditions, maple and ash showed a slight lead in recent annual length increment compared with beech. With increasing light, ash and maple constantly gained superiority in length increment, whereas beech approached an asymptotic value above 35% light. A suite of architectural and leaf morphological attributes indicated a more pronounced ability of beech to adapt to shade than ash and maple. Beech displayed its leaves along the entire tree height (with a concentration in the middle crown), yielding a higher live crown ratio than ash and maple. It allocated biomass preferentially to radial growth which resulted in low height to diameter ratios, and expressed marked plagiotropic growth in shade indicating a horizontal light-foraging strategy. In addition, beech exhibited the highest specific leaf area, a greater total leaf area per unit tree height, a slightly greater leaf area index, and a greater plasticity to light in total leaf area. Ash and maple presented a “gap species” growth strategy, characterized by a marked and constant response in growth rates to increasing light and an inability to strongly reduce their growth rates in deep shade. In shade, they showed some plasticity in displaying most of their leaf area at the top of the crown to minimize self-shading and to enhance light interception. Through this, particularly, maple developed an “umbrella” like crown. These species-specific responses may be used for controlling the development of mixed-species regeneration in shelterwood systems.     

不同连作土壤处理对再植水蜜桃苗生长状况及光合特性的影响

为了比较分析不同连作土壤处理水蜜桃再植苗的生长状况及其对主要营养元素的吸收差异,以探讨连作土壤对再植桃苗生长的影响机制,设置了4个土壤处理即重茬土(T_1)、重茬土+生石灰(T_2)、重茬土+活性炭(T_3)、重茬土+微生物肥(T_4)进行试验,分别测定了再植桃苗的生物量、气体交换参数、光合色素含量、叶绿素荧光参数及各组织中N、P的含量。试验结果表明:T_1处理的再植桃苗生长缓慢,其生物量最低,T_2、T_3和T_4处理则均明显地促进了再植桃苗的生长,其中T_4处理的长势最佳;T_1处理的再植桃苗其生长受到抑制,其影响因素为叶片气孔关闭和光合色素合成受阻、P元素缺乏等非气孔因素;T_4处理可促进再植桃苗叶片光合色素的合成,能明显提高其净光合速率,使其光合机构分配到光化学反应中的光能明显增多,光能利用效率明显提高,各组织中的P含量明显增加。研究结果表明:连作条件下再植桃苗的生长受到明显抑制,但施入微生物肥能有效缓解连作土壤对再植桃苗生长的伤害。     

Effects of pre- and post-planting shading on growth of container Norway spruce seedlings

Norway spruce (Picea abies (L.) Karst.) is shade-tolerant and sensitive to high irradiance, summer frosts and winter desiccation, which can impair its reforestation success. In this study, artificial pre- and post-planting shading was examined to determine their effects on post-planting shoot and root growth as well as the vigor of one- and two-year-old Norway spruce seedlings. Three planting experiments were carried out on open nursery fields (Exp. 1, 2) and on a mounded forest clearcut in central Finland (Exp. 3). Before planting, the seedlings were stored over winter either in a freezer or on open fields under snow cover. For two weeks prior to planting, half of the seedlings were placed in the open and the other half under a horizontal shade netting (light transmittance 56 %) (Exp. 1, 2). All seedlings were planted with or without a vertical post-planting shade, which was located on the southern side. Post-planting shading enhanced shoot growth and reduced damage (better visual vigor and needle color and less pine-weevil damage) on Norway spruce seedlings for at least two years after planting (Exp. 2, 3). Those seedlings, that had been stored over winter in the open and kept in shade prior to planting seemed to benefit most from post-planting shading (Exp. 2). However, post-planting shading may give variable results, depending on the seedling quality and weather conditions after planting, and may even reduce shoot growth if no pre-planting shading is used (Exp. 1). Shoot growth may also be improved at the expense of root growth (Exp. 3). The costs of manufacturing and installing post-planting shades may limit their use in practice, for example, to selected regeneration sites where there is high risk of frost damage but where no alternative silvicultural procedure (shelterwood or nurse crop) has been used.     

Effects of different soil treatments on growth and net nitrogen uptake of newly planted Picea abies (L.) Karst. seedlings

Five soil treatments in a 4-year-old clearcut in southern Sweden affected biomass increase and net nitrogen uptake by planted Norway spruce (Picea abies (L.) Karst.) seedlings through their on net mineralisation and root growth. The patch soil treatments studied were: (i) soil inversion in an old clearcut; (ii) mineral soil from the clearcut remaining, (iii) mineral soil from the clearcut with fertiliser application during the first season; (iv) mineral soil from a nearby uncut forest replacing the clearcut mineral soil; and (v) an untreated control. Growth increased in seedlings in treatments (i) and (iii), but growth in soil treatments with humus removal was not better than that of seedlings in untreated soil. High N uptake early in the first growing season resulted in increased growth during this season in contrast to late N uptake that resulted in a high N concentration in the seedlings after the first growing season. This in turn led to a high growth rate during the next growing season. Generally, both root growth and net N mineralisation were positively correlated to N uptake in the soil treatments. Therefore, a combination of low net N mineralisation and poor root growth as a result of high soil density appears to explain the low N uptake in seedlings in undisturbed soil. The importance of competition with field vegetation for N and water was not clear. Net mineralisation was larger in soil treatments where the humus layer was retained than where it was removed. Net N mineralisation in soil from old clearcuts was the same as in soil from fresh clearcuts.     

Effects of light radiation intensity on photosynthetic characteristics and water use efficiency of Platycladus orientalis and Pinus tabulaeformis seedlings

In order to offer a scientific basis for cultivation and management of forests, effects of light radiation intensity on photosynthetic characteristics and water use efficiency of Platycladus orientalis and Pinus tabulaeformis were studied under different soil moisture contents. By adopting artificial control methods to soil moisture, and under simulated photosynthetic radiation (SPR), the net photosynthetic rate (P _N), transpiration rate (T _r), water use efficiency (WUE) and intercellular CO₂ concentration (C _i) of Platycladus orientalis and Pinus tabulaeformis in the semi-arid region of the Loess Plateau, were studied. Results are as follows: within the photon range of 0–2,200 μmol/(m²·s), P _N, T _r and WUE were enhanced with an increase in SPR in both species. P _N and WUE of Platycladus orientalis and Pinus tabulaeformis, however, declined with continued increase in SPR. P _N, T _r, WUE and light saturation point (LSP) of Platycladus orientalis were higher than those of Pinus tabulaeformis, while light compensation point (LCP) of Platycladus orientalis was lower than that of Pinus tabulaeformis at the same soil moisture content. The efficiency of light energy utilization of Platycladus orientalis was higher than that of Pinus tabulaeformis; P _N, T _r and C _i of Platycladus orientalis and Pinus tabulaeformis were enhanced by increasing soil moisture content, whereas WUE declined. At soil moistures of 7.90%, 13.00% and 19.99%, LSP of Platycladus orientalis was 1,275, 1,450 and 1,675 μmol/(m²·s) respectively, and LCP was 42, 25 and 13 μmol/(m²·s) respectively, with corresponding maximal net CO₂ photosynthetic rates (P _max) of 3.04, 4.06 and 5.53 μmol/(m²·s). At soil moistures of 7.83%, 13.04% and 20.15%, the LSP of Pinus tabulaeformis was 1,100, 1,325 and 1,500 μmol/(m²·s) respectively, and LCP was 60, 30 and 23 μmol/(m²·s), with P _max of 1.08, 3.35 and 4.36 μmol/(m²·s) respectively. __________ Translated from Science of Soil and Water Conservation, 2006, 4(3): 108–113 [译自: 中国水土保持科学]     

NaCl和Na_2CO_3胁迫对枸杞幼苗生长和光合特性的影响

以黑果枸杞‘黑杞1号’和宁夏枸杞‘宁杞7号’的1年生幼苗为试材,用NaCl和Na_2CO_3溶液进行处理,研究盐胁迫条件下,枸杞幼苗生长、光合作用和叶绿素荧光参数的变化。结果表明,2种枸杞在NaCl和Na_2CO_3胁迫下,幼苗生长、光合作用和叶绿素荧光参数的变化趋势基本相同,但不同盐不同品种间幼苗生长、光合作用和叶绿素荧光参数值存在差异。生长特性方面,盐胁迫主要影响株高和基径;在光合和叶绿素荧光特性方面,盐胁迫主要影响的参数有P_n、G_s、C_i、T_r、Ф_(PSⅡ)、F_o、F_m、F_v/F_m、C_(qP)、C_(qN)、叶绿素a含量、叶绿素b含量、总叶绿素含量,其中,P_n、G_s、C_i、F_o、C_(qP)、Ф_(PSⅡ)和总叶绿素含量与对照相比差异显著,T_r、F_m、F_v/F_m、C_(qN)、叶绿素a含量和叶绿素b含量与对照相比无显著差异。NaCl胁迫后,‘黑杞1号’和‘宁杞7号’幼苗的生长量、光合速率分别在1.3 mol·L~(-1)和1.2 mol·L~(-1)时达到最高值,在1.5 mol·L~(-1)时,达到耐盐极限值;Na_2CO_3胁迫后,‘黑杞1号’和‘宁杞7号’幼苗的生长量、光合速率在0.1 mol·L~(-1)时达到最高值,分别在0.4 mol·L~(-1)和0.5 mol·L~(-1)达到耐盐极限值。所以,‘黑杞1号’耐盐能力强于‘宁杞7号’,且Na_2CO_3对枸杞幼苗影响显著大于NaCl。     

镉胁迫对10种月季生长及光合特性的影响

采用盆栽模拟试验的方法,研究了质量分数为1 mg/kg镉（Cd）胁迫对10个月季品种叶、茎、根生长及光合特性的影响。结果表明,不同的月季品种对Cd胁迫的反应不同。与对照相比,Cd胁迫对大游行、伊丽莎白女王、奥赛娜、第一夫人的根、茎、叶生长及光合特性主要产生抑制作用,其中第一夫人所受抑制作用最大;在Cd胁迫下,维西利亚和彩虹的根、茎、叶生长及光合特性几乎不受影响;而Cd胁迫对尼科尔、阿比沙莉卡、冰山、御用马车的根、茎、叶生长及光合特性产生了一定程度促进作用,其中冰山和御用马车所受促进作用较大。由此可知,冰山和御用马车对Cd胁迫环境的适宜性较强,是较好的耐Cd污染的月季品种。     

Effects of nitrogen content on growth and hydraulic characteristics of peach （Prunus persica L.） seedlings under different soil moisture condi- tions

A pot experiment was conducted to investigate the effects of nitrogen content [N1(no fertilizer), N2(0.15 g?kg–1), and N3(0.3 g?kg–1)] on the growth and the hydraulic characteristics of peach seedlings under different soil moisture conditions(W1, W2 and W3, in which the soil water content was 45% to 55%, 60% to 70%, and 75% to 80% of the field water capacity, respectively) by using a specialized high pressure flow meter with a root chamber and a coupling, which was connected to plant organs. Leaf area and leaf hydraulic conductivity(KL) increased significantly in the seedlings because of increased soil moisture and N content. KL increased with leaf area. A linear correlation was documented between KL and leaf area. KL was higher in the morning and began to decline sharply after 16:00, at which KL declined after an initial increase. Soil moisture and N content enhanced shoot(Ks) and root(Kr) hydraulic conductivities, thereby improving the low soil moisture condition to a large extent. Ks and Kr of the seedlings were reduced by 32% and 27% respectively in N1, and by 14.7% and 9.4%, respectively in N2, and both in W1, compared with the control treatment. N3 had no significant effect on Ks and Kr under similar conditions. Linear negative correlations were observed between Kr and the excised root diameter as well as between Ks and the shoot stem diameter. The shoot-to-root ratio increased with increase in N content. The shoot-to-root ratio in N3 was increased by 14.37%, compared with N1 in W1 as well as by 12% and 4.39% in W2 and W3, respectively. Knowledge of the effects of soil moisture and N fertilizer on hydraulic characteristics and growth is important. Our results provide basic guidelines for the implementation of water-saving irrigation and fertilization management of nursery stock.     

Effects of a deep container on morpho-functional characteristics and root colonization in Quercus suber L. seedlings for reforestation in Mediterranean climate

In the last decades, reforestation and afforestation programs are being carried out mainly with containerized seedlings. Container design determines the morphological and physiological characteristics of seedlings. However, container characteristics are often the same for plant species with very different growth strategies. The most commonly used nursery containers are relatively shallow and limit tap root growth; consequently, species relying on the early development of a long tap root to escape drought, such as those of the Quercus genus, might need to be cultivated in deep containers. The aim of this paper was to compare the morphological and physiological characteristics of Quercus suber L. seedlings cultivated in shallow containers (CCS-18, depth 18 cm) with seedlings cultivated in deep containers (CCL-30, depth 30 cm). Both container types used were made of high-density polyethylene, cylindrical in shape, open-bottomed, with a diameter of 5 cm, two kinds of vertical ribs on the inside wall showing a cultivation density of 318 seedlings/m². At the end of nursery culture, the seedlings cultivated in the CCL-30 deep container presented a longer tap root, higher shoot and root biomass and higher Dickson Quality Index (DQI). Moreover, the CCL-30 seedlings showed a higher root growth capacity (RGC), they reached deep substrate layers faster and they presented higher root hydraulic conductance. These morpho-functional advantages improved the CCL-30 seedling water status, which was expressed by higher stomatal conductance during an imposed drought period.     

Direct seeding of Quercus robur L. for reforestation: The influence of mechanical site preparation and sowing date on early growth of seedlings

Compared with conventional planting, direct seeding of Quercus spp. is a method that can reduce the costs of reforestation considerably. However, interference from natural vegetation and predation on acorns contribute to regeneration failures. Mechanical site preparation has the potential to reduce both these problems. To study the influence of sowing date and of different mechanical site preparation treatments on early seedling growth, an experiment was carried out in storm-felled areas, formerly Norway spruce forests, in southern Sweden from May 2006 to September 2008. Five treatments were applied and acorns were planted in May and July 2006. The treatments were: disc trenching, patch scarification, topsoil removal, mounding and an undisturbed control. A delay of less than two months in seeding resulted in the equivalent of one year's growth reduction with respect to oak seedling's height and biomass. This could be explained by delayed emergence of seedlings, and by the dry conditions during summer seeding. The seedlings only exhibited a weak positive biomass growth response following disc trenching, patch scarification and top soil removal. In the latter case this might be explained by increased soil compaction and extensive removal of the humus layer. Site preparation by mounding resulted in good vegetation control, an increased biomass growth response and deeper seedling roots. In this treatment, we found high relative light levels near seedlings, reduced soil moisture and dry bulk density of the soil and higher soil temperatures. One or more of these environmental factors could have influenced the growth response. Whether this increased early growth rate persists throughout young stand development is, however, uncertain.     

Effects of silicon-rich soil amendments on growth,mortality and bark feeding damage of Sitka spruce (Picea sitchensis) seedlings under field conditions

Alternative methods of protection are required against feeding by the large pine weevil (Hylobius abietis) on the bark of conifer seedlings. Silicon (Si) has been shown to enhance the resistance of plants to insect herbivores. This study investigated the effects of low doses of Si-rich soil amendments on growth, mortality and bark feeding damage of Sitka spruce (Picea sitchensis) seedlings. Two-year old seedlings were grown, individually, in soil taken from a tree nursery treated with coal ash, peat ash, rice husk ash, slag, sodium metasilicate or a commercially available Si fertiliser (Pro-Tekt) and planted out on two reforestation sites in Ireland. Seedlings grew well (about 20% growth in terms of height, 66% in root collar diameter, after two growing seasons), and Si-rich amendments did not have a significant effect on growth or mortality. Bark feeding damage on Si-treated seedlings did not vary significantly from control seedlings. Bark Si concentrations were not significantly larger in treated seedlings than in control seedlings, but control seedlings already had comparatively high bark Si concentrations (560?mg?kg^?1 dry tissue). In conclusion, Sitka spruce seedlings grown in the presence of Si-rich soil amendments prior to planting did not show greater resistance to weevil feeding under the present conditions.     

烂皮病菌侵染对新疆杨光合特性及碳水代谢的影响

目的 研究烂皮病菌侵染对新疆杨叶片光合响应以及水分代谢特征的影响,探讨病菌侵染下杨树光合作用与水分代谢之间的相关性,为杨树烂皮病的发生及控制提供理论及实验依据。 方法 以1年生新疆杨为植物材料,采用枝干表皮微环割方法接种烂皮病菌,研究烂皮病菌侵染10～30天新疆杨的叶片气体交换、叶绿素荧光、根部非结构性碳水化合物以及叶片正午水势等指标,分析蒸腾速率、正午水势分别与气孔导度以及水汽压亏缺之间的关系。 结果 与环割对照相比,烂皮病菌侵染显著降低新疆杨叶片的净光合速率（62.45%～91.05%）、气孔导度（64.19%～87.43%）、光系统Ⅱ的最大光化学效率（19.13%～42.79%）、实际光化学效率（46.04%～69.93%）、电子传递速率（52.58%～68.03%）等参数;显著抑制新疆杨叶片最大净光合速率（76.94%）、光饱和点（40.40%）及表观量子效率（46.09%）,并显著升高暗呼吸速率（82.14%）及光补偿点（242.42%）。烂皮病菌侵染显著降低根部可溶性糖（35.06%～44.50%,20～30天）及淀粉含量（35.77%～58.39%,10～30天）。烂皮病菌侵染显著抑制叶片的蒸腾速率（57.36%～80.49%）、水分利用效率（24.92%～70.55%）以及升高水汽压亏缺（13.59%～33.65%）和叶片正午水势（39.74%,20天）。相关性分析结果表明蒸腾速率与气孔导度呈正相关,与水汽压亏缺呈负相关;叶片正午水势与气孔导度及水汽压亏缺均无线性关系,烂皮病菌侵染导致的气孔关闭与叶片水分状况无关。 结论 烂皮病菌侵染下新疆杨叶片净光合速率降低的主要原因是叶片光能转化、光合电子传递及光能利用受阻。烂皮病菌侵染并未造成新疆杨叶部水分胁迫,甚至有一定的改善作用;同时,影响寄主根系的碳积累,导致根部非结构性碳水化合物含量始终在胁迫初期时的水平。     

Effects of treeshelters and polyethylene mulch sheets on survival and growth of cork oak (Quercus suber L.) seedlings planted in northwestern Tunisia

Success of plantation establishment depends on the ability of seedlings to withstand animal browsing and competition from vegetation. This study in northwestern Tunisia examined the influence of browsing protection and vegetation control on seedling mortality, diameter, and height growth components of an evergreen sclerophyllous oak species, cork oak (Quercus suber L.) for the first 2 years after planting (2005 and 2006). Browsing protection was controlled by varying both treeshelter type (non-vented, vented, and control) and height (1.2-m and 1.8-m tall). Competing vegetation was controlled through increasing sizes of square-shaped black polyethylene mulch sheets: 0 m, 0.7 m, 1 m and 1.3 m large. Seedling mortality rate was relatively low during the first year (9%) and was not affected by any of the studied factors. During the following year, mortality was lower for seedlings in both types (non-vented and vented) of 1.2-m tall treeshelters than for unsheltered ones. Mortality was only slightly higher for 1.8-m tall shelters than for 1.2-m shelters. Compared to unsheltered seedlings, basal diameter was reduced during both seasons for seedlings inside non-vented treeshelters (1.2-m and 1.8-m tall), whereas for vented shelters it was reduced during the first year and then increased during the second year. Height growth was positively affected by tree shelters during both years. Seedlings inside non-vented 1.8-m tall shelters were the tallest having an average height of up to 140 cm at the end of the second year, while the unsheltered seedlings had only an average height of up to 42 cm. The greater height of the sheltered seedlings was attributed to the increase of: (1) the number of shoot flushes yearly established on the main stem (up to three), and (2) the length of all the growth units produced during each flush. Seedlings inside vented shelters had balanced growth with a low proportion of seedlings unable to support themselves without a stake (7%). However, non-vented shelters had unbalanced height and diameter growths resulting in both a higher height-to-diameter ratio and in a higher proportion of seedlings having stability problems (47%). Polyethylene mulch sheets did not affect early survival, seedling basal diameter, or number of shoot flushes established yearly, but did slightly improve seedling height at the end of the second season, mostly due to the significant improvement in shoot elongation of the first flush. Results suggest that both 1.8 m treeshelters and plastic mulches may enhance the growth of cork oak seedlings planted on harsh sites in northwestern Tunisia.     

泥炭、风化煤改良风沙土促进樟子松幼苗生长的研究

利用盆栽试验,研究施入不同比例的泥炭、风化煤对风沙土的改良作用及其促进樟子松幼苗生长的效果,并初步分析了两种有机物料的作用机理。试验结果表明,泥炭和风化煤都显著地改良了风沙土的理化性质,随着施入量的增加,两者对风沙土的影响都表现出土壤pH值下降、持水量增加、养分含量提高,且泥炭的效果普遍比风化煤的效果要好;两者均促进了樟子松幼苗生长。不同含量的泥炭对促进樟子松幼苗生长(苗高、地径、根长、生物量)的效果表现为8%>10%>5%>2%>0。不同含量的风化煤对高生长的影响依次是5%>8%>10%>2%>0,对地径生长的影响依次为5%>8%>2%>10%>0,对生物量的影响依次为5%>2%>8%>10%>0。总的来看,泥炭的效果比风化煤好。结合樟子松在沙地中的生长特性,推断泥炭和风化煤中含有微量抑制樟子松生长的物质,并提出8%的泥炭与风沙土之比是促进沙地樟子松幼苗生长的最佳配比。