FT-IR study of the changes in carbohydrate chemistry of three New Jersey pine barrens leaf litters during simulated control burning

Low intensity control burns are a standard fuel reduction management tool used in pine barrens ecosystems. Periodic disturbances through fire can be an important influence on the cycling of nutrients within the ecosystem. Previous studies have shown that the inorganic chemistry of leaf litter residues differs with increasing temperature. Our study compared chemical changes in white oak (Quercus alba), pitch pine (Pinus rigida) and black huckleberry (Gaylussacia baccata), characteristic of the New Jersey pine barrens, during thermal decomposition using FT-IR spectroscopy. Three replicates of senescent leaf material were ground and separately heated for 2 h at: 100, 200, 300, 400 and 550 °C. These temperatures are representative of the range seen in fuel reducing prescribed burns in the pine barrens. Unburned litter of each species was used as a control. An optimization process using varying amounts of KBr and oak litter was performed to develop favorable FT-IR spectral conditions for a sample to KBr ratio of 0.75%. Chemometric analysis of the FT-IR spectra using principal component analysis (PCA) was used to analyze the changes in carbohydrate chemistry of each litter plant species (leaf litter species) at each temperature. In general, it appears that there is clear separation of leaf litter species at the different combustion temperatures. Infrared spectroscopy illustrated that all three species shared wavenumbers characteristic of the primary components of leaves such as cellulose, lignin and hemicellulose. Results from the PCA indicated separation of litter species and species by combustion temperature. PC axis 1 corresponds to the effects of temperature on leaf litter species and PC axis 2 separates the leaf litter species. At the low temperatures (control-200 °C), oak, pine and huckleberry litter species separated from each other. Wavenumbers that contributed to the separation of species at low temperatures belonged to functional group stretching frequencies of outer surface waxes, basic sugars, fatty acids and aldehydes. It appears that oak had more IR bands specific to suberin content. Convergence of these species occurs at 300 °C. Complexity of chemical composition decreases at this particular temperature as is shown by the decrease in wavenumber richness when compared to litters at low and high temperatures. Oak, pine and huckleberry had similar IR spectra showing bands belonging to outer surface wax content, pectin, lignin and hemicellulose. With increasing temperatures (400-550 °C), differences between litter species increased slightly. Plant material was reduced to similar composition due to thermal decomposition, which consisted of inorganic materials such as carbonate, phosphate and sulfate ions and possible fused aromatics.     

不同机械处理对白栎种子萌发的影响

为有效解决白栎(Quercus fabri Hance)种子延迟萌发和出苗不整齐的问题,研究了不同机械处理(对照、去碗疤、去皮、去皮及切除1/2子叶、去皮及切除2/3子叶)对白栎种子萌发和生长的影响。结果表明:(1)去皮、去皮及切除1/2子叶处理的种子根的平均萌发时间分别比对照显著缩短39 d和36 d,芽的平均萌发时间分别比对照显著缩短52 d和51 d,根的萌发整齐性指数分别显著提高0.3和0.2,芽的萌发整齐性指数均显著提高0.4,2个处理显著增加了白栎种子出根率(平均增加57.8%)与萌芽率(平均增加33.3%),去皮处理促进了根的生长(增加3.0 cm);(2)去皮及切除2/3子叶处理显著缩短了白栎种子根和芽的平均萌发时间(分别缩短36 d和50 d),提高了萌发整齐性指数(分别提高0.2和0.4)和生根率(均增加26.7%),但萌芽率、根长和苗高均与对照无显著差异;(3)去碗疤处理显著降低了白栎种子根和芽的平均发芽时间(分别缩短16 d和21 d),但萌发整齐性指数、出根率、萌芽率、根长和苗高均没有显著变化。因此,去皮和去皮及切除1/2子叶处理效果较好,能有效促进白栎种子萌发和整齐性出苗,对白栎的育苗工作有重要的实践意义。     

Effects of mixing radiata pine needles and understory litters on decomposition and nutrients release

A microcosm experiment was conducted to understand the impacts of mixing radiata pine (Pinus radiata D. Don) needle litter and understory (gorse—Ulex europaeus L., broom—Cytisus scoparius L., bracken—Pteridium aquilinum L., and lotus—Lotus pedunculatus L.) litter materials on decomposition and nutrient release dynamics. Mixing of pine needle litter with understory litter material had significant impacts on both the rate of decomposition and nutrient release patterns of pine litter as well as that of the understory species. Incubation in microcosms over 10 months resulted in significantly lower mass loss of radiata pine needle litter mixed with broom and lotus litters (35.8±8.4 and 41.3±0.8%, respectively) than pure pine needle litter (63.5±2.3%). Mixing with pine needle litter significantly increased the mass loss of broom (53.1±6.1%) compared to that of pure broom (30.2±1.0%). Significant transfers of nutrients, especially of magnesium and potassium, were observed in litter mixture treatments. Concentration of K in litter materials was found to be the most limiting factor for the decomposing microorganisms in the present study. The findings of this study suggest that management of understory litter composition via weed control could be used to manipulate carbon turnover and nutrient release in the forest floor. Also, initial selection of understory species will be important and could be managed.     

Earthworm-mediated maternal effects on seed germination and seedling growth in three annual plants

Many ecological studies have pointed out maternal effects in plants and shown that plant maternal environment influences germination of their seed and subsequent seedling growth. However, few have tested for maternal effects induced by soil macroorganisms. We tested whether two earthworm species (Aporrectodea caliginosa and Lumbricus terrestris) trigger such maternal effects on seed germination and seedling growth of three plant species (Veronica persica, Poa annua and Cerastium glomeratum). Our results show that, through maternal effects, A. caliginosa enhanced seed germination (V. persica and P. annua) and seedling growth (C. glomeratum and P. annua) while L. terrestris reduced seed germination only in V. persica. In some cases, the increase in germination rates of seeds produced in the presence of earthworms was associated with a reduction of nitrogen content in seeds. These results show that earthworms induce maternal effects in plants and that the size and direction of these effects depend on the combination of plant and earthworm species.     

Time of seed collection and germination in rocket, Erucavesicaria (L.) Cav. (Brassicaceae)

The increasing importance of rocket Erucaspp. as a leaf and oil crop, and especially as a Fourth Generationvegetable, calls for a better understanding of several basic aspectsof its biology. Knowledge on seed germination behaviour is necessaryto optimize the management of the plant in the field and inseedbanks. Seed germination of several samples of rocket was assayedin the laboratory under different incubation conditions. Germinationin the two studied populations was fairly high, ranging from68% to 96%. However, remarkable variation was foundwithin one of them according to the date of collection of the sample,ranging from 78–96% for those collected in summer(LG1 and LG2) to 21–29% for that collected inautumn (LG3). Neither time of storage nor GA₃treatments had any significant effect on this low percentage, whichcould only be significantly improved with scarification, up to47% by dry heat and up to 66% by immersion in liquidnitrogen. Dormancy and low seed viability probably originating fromeffects of environmental factors during seed formation and maturationseem to play a role in the low germination percentage of sampleLG3.     

Crude extract of Astragalus mongholicus root inhibits crop seed germination and soil nitrifying activity

Astragalus mongholicus has been of medicinal use within the traditional Chinese system for centuries. However, little information is available on its allelopathic effects on other crop plants and soil biochemical properties. Field experiment showed that the extracted residues of A. mongholicus root inhibited seed germination of wheat. Inhibition of seed germination was further confirmed in laboratory using the same crude extract. When the crude extract was applied to soil at various rates and incubated for 30 days, soil urease activity and denitrifying enzyme activity were significantly increased while soil nitrification rate was significantly decreased at 10% amendment rate as compared to the control. Soil respiration rate was significantly increased by the crude extract when measured at the start of incubation but returned to basal levels after 30 days of incubation. The crude extract supplemented to NB medium significantly decreased the colony numbers of Agrobacterium tumefaciens C58, Paraccocus denitrificans and soil bacteria. The stimulating effects of crude extract observed in the amended soil was attributed to the easily-available carbohydrates in the extract, which might served as external energy sources for heterotrophic microbial activities. It was concluded that A. mongholicus contained some compounds that inhibited seed germination, soil nitrification and bacterial growth in general. Possible links between allelochemicals responsible for the inhibitory effects observed in the present study and the medically bioactive compounds are discussed based on information reported in other fields. Further work is needed to specify and verify the allelochemicals produced by this herbal plant.     

红豆和白扁豆种子萌发和生长对盐胁迫的响应及其生理机制

为探讨红豆和白扁豆种子萌发及幼苗生长对盐胁迫的响应及其生理机制,以红豆品种‘渝红豆2号’和传统白扁豆品种为材料,分别用不同浓度NaCl （0 mmol·L^-1、20 mmol·L^-1、40 mmol·L^-1、60 mmol·L^-1、80 mmol·L^-1、100 mmol·L^-1）溶液处理种子,测定不同NaCl浓度胁迫下红豆和白扁豆种子的发芽指标及幼苗生长指标、叶片丙二醛（MDA）含量、超氧化物歧化酶（SOD）和过氧化物酶（POD）活性,分析NaCl胁迫对红豆和白扁豆种子萌发及幼苗生长的影响。结果表明：1）随NaCl浓度增加,红豆和白扁豆种子发芽率、发芽势、发芽指数和活力指数均呈下降趋势。当NaCl浓度为80 mmol·L^-1时,白扁豆发芽势、发芽指数、活力指数降为0,红豆的发芽势、发芽指数、活力指数分别为20.00%、2.00、0.83;NaCl浓度为100 mmol·L^-1时,红豆的发芽率为16.67%,但白扁豆为0,这表明在盐胁迫下红豆较白扁豆具有更高的萌发能力。2）红豆与白扁豆相对盐害率随NaCl浓度的增加而增加,当NaCl浓度为80 mmol·L^-1和100 mmol·L^-1时,白扁豆相对盐害率为96.58%和96.67%,红豆相对盐害率为47.05%和83.18%,说明红豆受盐害程度较低。3）红豆与白扁豆幼苗胚根、胚芽及鲜重均随NaCl浓度增加而下降。NaCl浓度为100 mmol·L^-1时,白扁豆胚根长为0,红豆胚根长为0.23 cm。4）随NaCl浓度升高,红豆和白扁豆叶片的MDA含量均增加,造成细胞膜透性逐渐增大,但是红豆幼苗MDA积累量低于白扁豆,这表明红豆叶片细胞膜损伤较小。5） NaCl胁迫下,红豆与白扁豆SOD活性均显著升高,但红豆SOD活性显著高于白扁豆;NaCl胁迫下,POD活性显著升高,但白扁豆POD活性显著下降。研究发现红豆可通过提高SOD和POD活性以降低细胞膜氧化伤害,减少MDA积累量,进而提高种子萌发能力。在相同浓度NaCl胁迫下红豆较白扁豆有更高的耐盐性,能更好地适应盐胁迫环境。     

Nutrient utilization by pine seedlings and soil microbes in oligotrophic pine barrens forest soils subjected to prescribed fire treatment

The purpose of this greenhouse experiment was to examine the short-term effects of competition between pine seedlings and the soil microbial biomass in sandy oligotrophic pine barrens upland forest soils subjected to varying levels of prescribed fire severity. Pine seedling growth performance, microbial biomass nitrogen, extractable soil nutrients and leaching loss from the soil were determined, throughout a single growing season following fire treatment. Replicate soil cores exposed to three levels of fire severity were maintained in a greenhouse with or without a pine seedling. Throughout the following growing season replicate cores from each treatment were harvested and analyzed monthly. The data allowed testing for two main effects: soil fire treatment and tree presence/absence. In no instance was a significant fire treatment X tree presence/absence interaction found. Our results indicate that biological activity strongly influences soil conditions. Reduced microbial activity resulted from the interaction of soil microbial biomass and an individual pine seedling. Increased plant growth performance correlates with reduced soil mineral nitrogen concentration and decreased pH. At the levels of fire severity utilized in this experiment immobilization due to biological uptake and abiotic soil fixation prevented significant leaching losses above that of unburned control samples. In the oligotrophic, pine barrens soils, nitrogen and phosphorus mineralized by fire are largely conserved by biological processes. These results also suggest that plant growth is subject to limitation by phosphorus availability in these soils.     

壳聚糖对不同种源柠条种子发芽及其酶活性的影响

用不同浓度壳聚糖乙酸溶液分别对陕西省的吴起县和榆林市榆阳区两个产地的柠条种子浸种处理,以清水浸种处理为对照,调查种子发芽及幼苗生长特性,并测定了萌发过程中种子α-淀粉酶、脱氢酶、过氧化物酶、过氧化氢酶活性。结果表明,壳聚糖能促进柠条种子的萌发,缩短发芽时间;随着处理浓度的增大,各项发芽指标及各种酶活性先升高后降低,且不同种源柠条种子对壳聚糖浓度的反应不同。当壳聚糖浓度为0.5%时,榆阳柠条种子的发芽率是对照的1.2倍,平均发芽速率缩短0.9d,各种酶活性比对照显著提高,处理效果最佳。当壳聚糖浓度为1.0%时,吴起柠条种子发芽率比照提高13%,平均发芽速率缩短1.7d,各种酶活性比对照显著提高,处理效果最佳。当壳聚糖浓度达到1.5%时,对榆阳柠条种子的萌发有一定的抑制作用,而对吴起柠条种子萌发无抑制作用。壳聚糖对柠条幼苗的生长也有一定的影响,表现在幼苗的根长、苗高、干重、鲜重和叶绿素含量均显著高于对照,吴起柠条和榆阳柠条最佳的处理浓度分别为1.0%和0.5%。     

紫外辐射增加对作物种子发芽及幼苗生长的影响

研究了ＵＶ－Ｂ紫外辐射增加对作物种子萌发及幼苗生长的影响,试验结果表明：ＵＶ－Ｂ增加能显著延缓种子发芽进程和幼苗生长,不同作物对ＵＶ－Ｂ增加的敏感程度不同,作物幼苗在三叶期前地上部与地下部对ＵＶ－Ｂ增加的敏感程度相近。     

Provenance variation in seed germination and seedling growth of Acacia nilotica ssp. indica in India

Summary Acacia nilotica ssp. indica, a multipurpose tree species occurs throughout semi-arid India. The present study reports the variation in seed germination and seedling growth of 21 sites (provenances) collected between the latitude 11°N and 31°23N, and 19 m to 650 m altitude throughout India. There were significant differences (P<0.05) between the sites for seed germination that varied from 16 to 90% in the incubator, and 14 to 84% in the nursery. Significant variations were also observed in seedling growth up to 28 days in the incubator. There was no significant relationship between seed germination and seedling growth and the latitude or longitude of the original seed source. However, in general the South Indian provenances showed lower germination as compared to North Indian provenances. The observations are important for selection of vigorous provenances concerning seed germination and early seedling growth.     

Mineralization of forest litter nutrients by heat and combustion

Temperature dependant mineralization dynamics during fire of litter species characteristic of the New Jersey pine barrens was determined. Senescent leaf material of pitch pine (Pinus rigida), white oak (Quercus alba) and black huckleberry (Gaylusssacia baccata) were collected at the time of abscission; sorted, ground and oven-dried at 70 °C. Replicate samples were then heated for 2 h at: 70, 100, 200, 300, 400, and 550 °C. Mass loss and total nitrogen and total phosphorus concentration of the heated material were determined. Additional samples of the residual material were extracted with deionized water, and the filtrate was assayed for the anions: , , ; and cations: , K⁺, Mg⁺⁺, and Ca⁺⁺.By heating leaf litter over a range of temperatures, to simulate the heterogeneous nature of forest litter burning, we identified patterns of nutrient mineralization characteristic of specific temperatures, some of which were common to all three litter species and others unique to individual species. In general, it appears that black huckleberry leaf litter was the most nutrient rich and the most labile. In huckleberry litter, there was a large reserve of soluble nitrogen, sulfur, phosphate, calcium and magnesium that became available upon heating to 200 °C. Pitch pine litter was the most nutrient poor, and the rates of nutrient mineralization were also generally the lowest of the three species studied. White oak litter nutrient concentration and rates of mineralization along the temperature gradient were intermediate. For all three litter species examined organic and inorganic nitrogen losses due to volatilization were >99% upon heating to 550 °C, and soluble magnesium concentrations declined significantly at temperatures of 300 °C, despite having a volatilization temperature greater than 1100 °C. Under the temperature range employed, heating of leaf litter resulted in little volatilization loss of phosphorus; however, the amount of soluble phosphate phosphorus was much lower in all three litter types at temperatures of 300 °C and above. With increasing temperatures, inorganic phosphate ions presumably became bound to cations in the ash, forming insoluble metal phosphates. The dramatic increase of the ratio of total phosphorus to soluble inorganic phosphate at higher temperatures, the loss of soluble magnesium above 300 °C, and the near complete loss of nitrogen at 550 °C suggests that after intense fires availability of these minerals may be dramatically reduced.     

Effects of phenolic acids on seed germination and seedling growth in soil

Summary It is commonly assumed that the adverse effect of plant residues on crop yields is largely or partly due to phytotoxic compounds leached from these residues or produced by their decomposition. There has been substantial support for the hypothesis that the phytotoxic compounds responsible for reduced crop yields are phenolic acids such as p-coumaric acid, p-hydroxybenzoic acid, and ferulic acid. To test the validity of this hypothesis, we studied the effects of nine phenolic acids (caffeic acid, chlorogenic acid, p-coumaric acid, ellagic acid, ferulic acid, gallic acid, p-hydroxybenzoic acid, syringic acid, and vanillic acid) on (1) seed germination of corn (Zea mays L.), barley (Hordeum vulgare L.), oats (Avena sativa L.), rye (Secale cereale L.), sorghum [Sorghum bicolor (L.) Moench], wheat (Triticum aestivum L.), and alfalfa (Medicago sativa L.) on germination paper and soil, (2) seedling growth of alfalfa, oats, sorghum, and wheat on germination paper and soil, and (3) early plant growth of corn, barley, oats, rye, sorghum, and wheat in soil. The results showed that although the phenolic acids tested affected germination and seedling growth on germination paper, they had no effect on seed germination, seedling growth, or early plant growth in soil even when the amounts applied were much greater than the amounts detected in soil. We conclude that the adverse effect of plant residues on crop yields is not due to phenolic acids derived from these residues.     

模拟干旱和盐碱胁迫对碱蓬、盐地碱蓬种子萌发的影响

为研究干旱和盐碱胁迫对碱蓬(Suaeda glauca)、盐地碱蓬(Suaeda salsa)种子萌发的影响,比较碱蓬和盐地碱蓬逆境生理特性的异同,本研究利用PEG6000、NaCl和Na_2CO_3分别模拟干旱、盐和碱胁迫,配制相同渗透势的PEG6000、NaCl、Na_2CO_3处理液,以蒸馏水处理为对照,对碱蓬、盐地碱蓬种子的萌发与胚的生长进行比较研究。结果表明:1)低渗处理(-0.46 MPa)对碱蓬、盐地碱蓬种子的萌发无显著影响;高渗处理(-1.38MPa、-1.84 MPa)抑制碱蓬、盐地碱蓬种子的萌发。2)当溶液渗透势相等时,NaCl处理下碱蓬种子的萌发率显著大于PEG、Na_2CO_3处理;而等渗PEG、NaCl、Na_2CO_3处理对盐地碱蓬种子萌发率的影响无显著差异。3)PEG、NaCl、Na_2CO_3处理组碱蓬、盐地碱蓬种子的最终萌发率与对照无显著差异。4)在幼苗形成阶段,PEG、Na_2CO_3处理对碱蓬、盐地碱蓬胚的抑制作用显著大于等渗NaCl处理。5)碱蓬、盐地碱蓬胚的生长对NaCl、Na_2CO_3胁迫的响应存在差异。-0.92 MPa NaCl处理抑制碱蓬胚的生长,却对盐地碱蓬产生促进作用;-0.46 MPa Na_2CO_3处理对碱蓬胚的抑制作用小于盐地碱蓬。综合分析表明:碱蓬、盐地碱蓬均具有很强的抗盐性。在种子萌发阶段,碱蓬种子的抗旱、抗碱能力低于盐地碱蓬;在幼苗形成阶段,碱蓬胚的抗盐性小于盐地碱蓬,但对轻度碱胁迫的抗性高于盐地碱蓬。     

The effect of mixing ground leaf litters to soil on the development of pitch pine ectomycorrhizal and soil arthropod communities in natural soil microcosm systems

The addition of leaf litter to soil influences both the nutrients and polyphenols of soil. It is likely that contrasting nutrient and polyphenolic composition of different plant litters may affect plant growth, mycorrhizal and soil arthropod communities. We report results from a microcosm experiment of effects of incorporation of three single leaf litter species and a mixture of all three on pitch pine seedling growth, their ectomycorrhizal community and soil arthropod community. The three litter species (pine, oak and huckleberry) represent co-dominant species within the New Jersey pine barrens ecosystem. We show that the leaf litters have different composition of nutrients and polyphenols, with rooting matrix containing pine litter having lower inorganic nitrogen content (1.6 μg g⁻¹) than oak (19.9 μg g⁻¹) and huckleberry (4.4 μg g⁻¹), but oak litter having the highest extractable phosphorus (13.3 cf. 0-0.08 μg g⁻¹) and total phenol content and lowest condensed tannin content. These differences were imparted to rooting matrix of homogenized humic (Oa) layer of pine barrens soil to which milled leaf litter was added and used in the microcosms. Pitch pine seedlings grew significantly better in un-amended rooting matrix (0.33±0.02 g) than any of the litter treatments (0.15±0.02-0.17±0.01 g) and tissue P concentrations tracked phosphate concentrations in the rooting matrix. Total P accumulation into plant tissue was higher in oak than control, attributable to a significantly higher (P<0.05) accumulation in roots (3.3±0.19 mg g⁻¹) compared to other species (1.1±0.04-2.3±0.08 mg g⁻¹). No relationship was seen between tissue N concentration and soil N, but seedlings growing in huckleberry litter amended soil accumulated less N than control. The effect of leaf litters on the ectomycorrhizal community composition were determined by PCA (first two axes accounted for 81% of the variance) and stepwise multiple regression analysis. These analyses showed that huckleberry leaf litter had a significant impact on mycorrhizal community composition with morphotypes Cg and DB being more abundant in the presence of huckleberry litter (178±13 cf. 68±15-106±15 for Cg and 141±11 cf. 88±23-111±18 for DB) and its influence of elevating nitrate nitrogen, organic nitrogen, total phenols and protein precipitation content of the rooting matrix. Mycorrhizal morphotypes BS and SB were significantly more abundant in the community where these soil factors were low in the absence of leaf litter addition. Total ectomycorrhizal abundance was negatively related to hydrolysable tannin concentration in the rooting matrix (r²=0.132, P<0.05). There was no influence of leaf litter type on mite density (dominated by non-burrowing phthiracarids), but collembolan density (dominated by Folsomia spp) showed a greater than threefold reduction in population density in the presence of leaf litter (F=6.47, P<0.05). Collembolan density was positively correlated with mycorrhizal morphotypes GS and SB (P<0.05) and negatively related to morphotypes DB (P<0.05) and soil extractable NH₄-N (P<0.05), suggesting a possible selection of fungal species in their diet and a relationship between collembola and nitrification.     

种子引发对盐胁迫下高粱种子萌发及幼苗生长的影响

以“Tx623A”ד89-363”(Sb1, 耐盐性较弱)和“黑30A”ד大粒早”(Sb2, 耐盐性较强)2 个高粱杂交组合为试验材料, 利用100 mmol·L^-1?NaCl 溶液对种子进行引发处理。采用营养液沙培试验, 设4 个NaCl 浓度(0、50 mmol·L^-1、100 mmol·L^-1和150 mmol·L^-1)模拟盐胁迫, 研究种子引发处理对盐胁迫下高粱种子萌发及幼苗生长的影响。结果表明: 随着盐胁迫强度增加, 无论经引发处理还是未经引发处理2 个高粱杂交组合种子的出苗时间均明显延迟, 出苗率和成苗率下降, 幼苗生长受到抑制, 物质积累减少。同等盐胁迫强度下,引发处理与未引发处理相比, 种子出苗时间缩短, 出苗率和成苗率提高, 幼苗地上部分干、鲜重和地下部分干、鲜重增加, 光合色素含量升高, Na⁺/K⁺值显著降低。由此得出, 种子引发处理可以不同程度地促进盐胁迫下高粱种子萌发, 减轻盐胁迫对幼苗的伤害, 促进幼苗生长, 提高耐盐性; 耐盐性不同的品种引发效果存在差异, 对耐盐性较弱的品种引发效果更好。     

侧柏与其他树种枯落叶混合分解对养分释放的影响

以黄土高原的主要人工林树种侧柏为对象,通过采集侧柏及其他拟混交的8个树种的当年枯落叶,以无林荒草地腐殖质层土壤作为分解介质,在室内将侧柏与不同树种枯落叶剪碎后以一定比例混合装入尼龙网袋并埋人盛土培养钵中,进行恒温恒湿下连续345 d分解培养试验,测定分解前后枯落叶质量及养分含量的变化.结果表明:(1)在枯落叶分解释放养分元素中,K最活跃而易于释出,p一般比较迟钝而难以释出,C、N居中并具有一定的释出同步性,且各种养分的周转期约为1～2a.(2)与侧柏枯落叶混合分解后,在对C释放的影响中白榆表现为促进作用,紫穗槐、白桦和辽东栎表现为抑制作用;在对N释放的影响中小叶杨表现为促进作用,白桦、辽东栎和紫穗槐表现为抑制作用;在对P释放的影响中除小叶杨、白榆不明显之外均表现为抑制作用;在对K释放的影响中白榆表现为促进作用,紫穗槐表现为抑制作用.(3)应用主成分分析法分析不同树种枯落叶混合分解对C、N、P、K释放的综合影响结果表明,与侧柏枯落叶混合分解后总体上促进养分释放的树种以白榆、小叶杨最显著,其次为柠条和辽东栎;而总体上抑制养分释放的树种以紫穗槐的作用最强,白桦、沙棘和刺槐的作用较弱.     

三七连作土壤对其种子萌发及幼苗生长的影响

为明确三七连作的障碍效应,以不同连作年限及不同空间分布的土壤为基质,通过发芽和幼苗生长试验,研究了连作土壤对三七种子萌发及幼苗生长的影响。结果表明:①与新土相比,连作土壤处理下三七种子萌发的最大速度加快,种子的发芽势变化不大,而发芽率、发芽指数和快速发芽期则明显呈降低或变短的趋势;②随土壤连作年限的增加,三七幼苗的成苗率和株高均显著下降(p0.05);③与根区外土相比,根区土和根区下土显著降低了三七种子的发芽势、发芽率和发芽指数,对种子萌发的最大速度也呈降低作用,但却使三七幼苗的地上生物量明显增加。连作土壤对三七种子的萌发及幼苗的生长均表现明显的障碍效应,化感(自毒)作用可能是造成三七连作障碍的原因之一。     

氮素对NaCl胁迫下甜高粱种子萌发及芽苗生长与生理的影响

为了研究NaCl胁迫下氮肥对甜高粱种子萌发及芽苗生长和生理特性的影响,探索提高甜高粱耐盐能力的措施,室内设置不同盐分浓度、不同氮源及浓度条件下甜高粱萌芽试验。结果表明:NaCl胁迫和不同氮源对甜高粱发芽和芽苗生长的影响各有不同。NaCl浓度对甜高粱种子萌发有显著影响,在甜高粱芽苗生长阶段,通过提高保护酶活性和渗透调节物质而增强耐盐伤害能力是有限的。100 mmol.L 1NaCl胁迫下,根系POD活性最低,而叶片MDA积累量、可溶性糖含量、POD活性最高,受盐害程度最大。没有盐胁迫情况下增加不同氮源及氮量对甜高粱根叶生理特性的影响差异显著,当氮浓度在20 mmol.L 1时,细胞受伤害程度最低,生长最好。不同形态氮源对甜高粱发芽和幼苗生长的影响差异明显,NH4Cl的促进效果优于KNO3。在100mmol.L 1的NaCl胁迫下,施加铵态氮或硝态氮源均可以增强甜高粱芽苗期的POD活性,减少MDA积累,从而缓解盐胁迫带来的伤害。研究表明采取适当的氮肥调控措施可以提高甜高粱的耐盐能力。     

长江三角洲地区麻栎和栓皮栎蒸腾规律及其对气候因子的响应

森林蒸腾在维系森林生态系统水量平衡上起着重要作用,研究麻栎和栓皮栎的蒸腾耗水规律,有助于了解栎林的水文过程和水量平衡.采用热扩散探针法,对江苏省句容市麻栎和栓皮栎林蒸腾速率进行连续观测,研究蒸腾速率在晴天、阴天和雨天的日变化特征,以及不同天气下气候因子对蒸腾速率的影响机制.结果表明,麻栎和栓皮栎蒸腾速率日变化在晴天、阴...