漓江上游典型森林植被对降水径流的调节作用

利用野外同步长期定位观测林外降雨、地表径流和河川径流的方法,对漓江上游典型森林植被的生态水文过程进行观测研究。结果表明:1)流域降水年内分配极不均匀,50a年降雨量总体变化趋势不明显。林冠截留受林外降雨特征的影响,也与植被类型密切相关。2)地表径流平均滞后时间为70 min。在连续降雨的情况下,降雨滞后效应不再明显,甚至出现地表径流与降雨同步的现象,小降雨可能产生大的地表径流,从而加大流域在雨季发生洪灾的风险。3)湿季径流系数略大于旱季,干季降水量减少,且森林植被消耗大量水分,减少了枯水期径流的产生,增大发生旱灾的风险。森林植被延长河川径流持续时间,使一次持续18 d的降水过程形成的径流,在降水停止后能延续24 d。降雨后退水持续时间与前期降水及后期降水叠加有关。目的为揭示漓江上游森林植被对降水径流的调节作用,客观评估漓江上游水资源潜力、加强流域水资源管理和森林经营提供科学依据。     

不同植被类型对土壤水蚀的影响

不同植被类型对土壤水蚀的影响因子是计算土壤水蚀速率以及选择适当土地利用方式的基本参数.本文以土壤侵蚀模型中的植被因子(C因子)为指标,研究不同植被类型对土壤水蚀的影响.根据6个水土保持试验项目33个小区共195个小区年的资料,计算了剌槐、柠条、沙棘、沙棘-杨树,沙棘-油松、沙打旺、红豆草、苜蓿和草木樨等9种林草植被因子值.林地植被因子介于0.004到0.164之间,以刺槐林的C值最低.草地植被因子介于0.071到0.377之间,以第一年的草木樨C值为最高.定量对比说明林草植被的水土保持效益明显优于农作物.本项研究结果可以用于定量比较不同植被类型覆盖下的土壤流失速率,对于北方农牧交错带退耕还林还草政策的实施具有参考价值.     

模拟降雨下黄土坡面水沙过程对3种灌草植被垂直结构变化的响应

植被对坡面产流产沙过程的影响随植被类型及其垂直结构组分的变化而变化,然而这些因素如何影响坡面水沙过程却缺乏定量分析。利用野外径流小区和人工模拟降雨试验,研究了黄土丘陵区3种典型灌草（沙棘、柠条、苜蓿）及其不同垂直结构组分（叶、茎、枯落物、根系）对坡面产流和产沙过程的影响。结果表明：3种灌草均具有较好的减流减沙效益,且减沙作用强于减流作用,与裸地相比,灌草植被减少径流量32.49%-44.86%,减少侵蚀量72.99%-80.63%,降低坡面流速29.17%-45.83%。苜蓿的减流效益最佳,为44.86%,柠条的减沙效益最佳,为80.63%。3种植被的减流效益在不同产流时期差异明显,从产流初期到中期和后期逐渐减少,减沙效益在不同产流时期则没有明显变化。植被垂直结构不同组分对于减流减沙效益的相对贡献与其形态特征以及其空间分布方式有着密切的关系。地上部分对于减流效益和减速效益有较大的相对贡献率,平均为75.42%和68.38%,而不同植被茎、叶和枯落物的相对贡献具有一定的差异。根系则发挥较大的减沙作用,平均相对贡献为78.44%。植被垂直结构组分越完整,减流减沙效益越显著。研究对黄土丘陵区水土保持、植被恢复和建设提供重要的科学依据和理论指导。     

陕北黄土高原柠条灌丛穿透雨特征与影响因素

穿透雨是降雨再分配的主要组分,对干旱半干旱区的土壤水分补给和植被生长具有关键作用。灌丛穿透雨的影响机制特别是植被特征对穿透雨的影响需要进一步的定量研究,且目前对穿透雨空间异质性与聚集效应的研究相对较少。以陕北黄土高原典型灌丛—柠条为研究对象,于2016年对六道沟小流域柠条冠层下8个方位的穿透雨以及降雨和植被因子进行系统观测,分析穿透雨量、穿透雨率、穿透雨空间变异和聚集效应的变化特征,辨识影响穿透雨的主要降雨和植被因子,并建立相应的定量关系。结果表明:次降雨下柠条的穿透雨量、穿透雨率和空间变异系数平均值分别为11.88 mm、75.71%和21.80%。穿透雨量主要由降雨量决定,随降雨量增加而线性增加(R~2=0.99)。穿透雨率和空间变异系数主要受降雨量和降雨强度影响,穿透雨率随降雨量和I_30增加而呈对数增加(R~2=0.71和0.54),渐进值约为95%,而穿透雨空间变异系数则随降雨量和I_30增加而呈幂函数递减(R~2=0.71和0.60),稳定值约为10%。冠层厚度和枝倾角是影响穿透雨的主要植被因子,并分别呈显著的线性负相关和正相关(P0.05)。柠条穿透雨具有一定的聚集效应,平均发生频率为8.53%,且聚集效应在大雨量、高雨强和长历时降雨事件中更加明显。     

两种温带落叶阔叶林降雨再分配格局及其影响因子

林冠对降雨的再分配是森林生态系统的重要生态水文过程,影响着生态系统生物地球化学循环。于2012年5—10月连续测定帽儿山森林生态站的两种温带天然次生林型——蒙古栎林和杂木林的林外降雨、穿透雨及树干径流,旨在量化其降雨再分配过程及其影响因素。结果表明:蒙古栎林的平均穿透雨、树干径流、林冠截留分别占同期林外降雨的76%、7%和17%;杂木林分别占85%、5%和10%。根据模型估算,当降雨量分别超过1.0mm和0.7mm时蒙古栎和杂木林开始出现穿透雨;当降雨量超过3.0mm开始出现树干径流。当降雨量超过5.6mm,树干径流体积会随着树木胸径的增加而显著增加;而当降雨量低于5.6mm则出现相反趋势。穿透雨、树干径流及林冠截留的绝对量均随降雨量的增大而显著增加,但其占降雨量的比例却表现出不同的变化趋势。穿透雨量的空间变异随降雨量和降雨强度的增大显著减小。两种林型的降雨再分配格局因受降雨量、降雨强度等降雨特征和林冠结构的影响而产生差异。     

马占相思人工林和果园地表径流规律的对比研究

基于连续 5年的观测 ,对比研究了马占相思人工林和果园两种地表类型上地表径流的各自特点 ;讨论了季节性地表径流的差异与系统水分结构问题 ;探讨了根据实际资料求取发生地表产流的降雨量临界值的方法 ,此方法以综合考虑未发生产流的最大降雨量和已发生产流的最小降雨量为基础 ;并得到了如下的一些结果 :1)本区域不同强度的大气降水频度分布比较均匀 ,但降水量主要由少数几场特大降水带来 ,并且降水量的季节分配极不平均 ,湿季 (4～ 9月 )降水量占全年的 85 .5 %。 2 )地表径流的季节差异更大 ,果园在湿季的地表径流量占全年的93.8% ,马占相思林占 95 .1% ,作者认为在降水量存在较大干湿季差别的地区 ,对于越难于发生地表径流的下垫面 ,这个值会越高。3)马占相思地表径流系数在逐年减小 ,果园的变化较大。4)一次性降雨量对地表径流量的影响在这两种地表类型上都很明显 (r>0 .85 ) ;一次性降雨强度对地表径流的影响只有在中等降雨量 (6～ 16 mm)下才表现明显 (r>0 .87) ,对于较小和较大降水量 ,径流量与降雨强度关系都不大 ;径流系数受一次性降雨强度的影响很明显 (林地 r>0 .92 ,果园 r>0 .77)。 5 )马占相思和果园一次性“最大可能”地表径流产流的雨量临界值 ,分别为5 .1m m和 2 .8mm。     

黄土区次降雨条件下林地径流和侵蚀产沙形成机制——以人工油松林和次生山杨林为例

以黄土区两种常见森林植被(次生山杨林和人工油松林)长期定位观测试验为基础,从水量平衡和径流产沙机理出发,分析了次降雨条件下两种林地和荒地坡面产流产沙过程.结果表明,次降雨量在5.0～50.0 mm范围内,油松林和山杨林的林冠和枯枝落叶层总截留率分别为15.45%～56.80%和20.56%～47.81%,且随降雨量的增大而减小.与荒坡地相比,林地土壤入渗性能显著增强,尤其是0～20cm土层.分析表明,在一般降水条件下林地无径流产生;而在降雨雨强为2.5 mm·min^-1和历时30 min条件下,山杨林地无地表径流产生,荒坡地的径流流速和径流挟沙浓度均为油松林地的23.5倍,而其径流剪切力和径流能量均为后者的8倍;油松林地的径流量和产沙量比荒地分别减少了87.6%和99.4%,与径流小区多年(1988～2000)观测平均值(分别为87.0%和99.9%)相近.     

黄土区次降雨条件下林地径流和侵蚀产沙形成机制

以黄土区两种常见森林植被(次生山杨林和人工油松林)长期定位观测试验为基础,从水量平衡和径流产沙机理出发,分析了次降雨条件下两种林地和荒地坡面产流产沙过程.结果表明,次降雨量在5.0～50.0 mm范围内,油松林和山杨林的林冠和枯枝落叶层总截留率分别为15.45%～56.80％和20.56%～47.81％,且随降雨量的增大而减小.与荒坡地相比,林地土壤入渗性能显著增强,尤其是0～20 cm土层.分析表明,在一般降水条件下林地无径流产生;而在降雨雨强为2.5 mm·min^-1和历时30 min条件下,山杨林地无地表径流产生,荒坡地的径流流速和径流挟沙浓度均为油松林地的23.5倍,而其径流剪切力和径流能量均为后者的8倍;油松林地的径流量和产沙量比荒地分别减少了87.6%和99.4%,与径流小区多年(1988～2000)观测平均值(分别为87.0%和99.9%)相近.     

黄土区次降雨条件下林地径流和侵蚀产沙形成机制——以人工油松林和次生山杨林为例

以黄土区两种常见森林植被(次生山杨林和人工油松林)长期定位观测试验为基础,从水量平衡和径流产沙机理出发,分析了次降雨条件下两种林地和荒地坡面产流产沙过程.结果表明,次降雨量在5.0～50.0 mm范围内,油松林和山杨林的林冠和枯枝落叶层总截留率分别为15.45%～56.80%和20.56%～47.81%,且随降雨量的增大而减小.与荒坡地相比,林地土壤入渗性能显著增强,尤其是0～20cm土层.分析表明,在一般降水条件下林地无径流产生;而在降雨雨强为2.5 mm·min^-1和历时30 min条件下,山杨林地无地表径流产生,荒坡地的径流流速和径流挟沙浓度均为油松林地的23.5倍,而其径流剪切力和径流能量均为后者的8倍;油松林地的径流量和产沙量比荒地分别减少了87.6%和99.4%,与径流小区多年(1988～2000)观测平均值(分别为87.0%和99.9%)相近.     

不同植被类型对土壤水蚀的影响

不同植被类型对土壤水蚀的影响因子是计算土壤水蚀速率以及选择适当土地利用方式的基本参数。本文以土壤侵蚀模型中的植被因子(C因子)为指标，研究不同植被类型对土壤水蚀的影响。根据6个水土保持试验项目33个小区共195个小区年的资料，计算了刺槐、柠条、沙棘、沙棘一杨树，沙棘一油松、沙打旺、红豆草、苜蓿和草木樨等9种林草植被因子值。林地植被因子介于O．004到O．164之间，以刺槐林的C值最低。草地植被因子介于O．071到O．377之间，以第一年的草木樨c值为最高。定量对比说明林草植被的水土保持效益明显优于农作物。本项研究结果可以用于定量比较不同植被类型覆盖下的土壤流失速率，对于北方农牧交错带退耕还林还草政策的实施具有参考价佰。     

The invasive grass,Melinis minutiflora,inhibits tree regeneration in a Neotropical savanna

Abstract Exotic grasses are becoming increasingly abundant in Neotropical savannas, with Melinis minutiflora Beauv. being particularly invasive. To better understand the consequences for the native flora, we performed a field study to test the effect of this species on the establishment, survival and growth of seedlings of seven tree species native to the savannas and forests of the Cerrado region of Brazil. Seeds of the tree species were sown in 40 study plots, of which 20 were sites dominated by M. minutiflora, and 20 were dominated by native grasses. The exotic grass had no discernable effect on initial seedling emergence, as defined by the number of seedlings present at the end of the first growing season. Subsequent seedling survival in plots dominated by M. minutiflora was less than half that of plots dominated by native species. Consequently, at the end of the third growing season, invaded plots had only 44% as many seedlings as plots with native grasses. Above‐ground grass biomass of invaded plots was more than twice that of uninvaded plots, while seedling survival was negatively correlated with grass biomass, suggesting that competition for light may explain the low seedling survival where M. minutiflora is dominant. Soils of invaded plots had higher mean Ca, Mg and Zn, but these variables did not account for the higher grass biomass or the lower seedling survival in invaded plots. The results indicate that this exotic grass is having substantial effects on the dynamics of the tree community, with likely consequences for ecosystem structure and function.     

Effects of nutrient additions on plant biomass and diversity of the herbaceous-subshrub layer of a Brazilian savanna (Cerrado)

The Brazilian Cerrado is a diversity hotspot due to its high level of endemism and rapid loss of habitats. It is estimated that the number of herbaceous species is four times higher than that of woody species. Increasing levels of nitrogen additions to natural ecosystems have been indicated as a determinant of biodiversity loss. We investigated the effects of nutrient additions on the productivity (aboveground and belowground) and on diversity of the herbaceous-subshrub layer of a Brazilian savanna (cerrado stricto sensu). The experiment was carried out in the IBGE Ecological Reserve, near Brasília, Brazil. Between 1998 and 2006, N, P, N plus P, or Ca were applied to sixteen 225 m² plots, arranged in a completely randomized design. Aboveground biomass was compared 1 year after the first fertilization and 10 years later. Floristic diversity was significantly different (P < 0.01) between the treatments. The highest and lowest species richness were presented in control and NP, respectively. The addition of P alone or in combination with N induced invasion by Melinis minutiflora (exotic C₄ grass). The aboveground biomass of this species was higher in NP and P plots. In the N treatment, Echinolaena inflexa (native C₃ grass) presented elevated cover and biomass but M. minutiflora was absent. The invasion by alien species resulted in negative impacts on native grass species. Besides changes in aboveground biomass, addition of N and P also led, although to a lesser extent, to changes in the root morphology and biomass, but these responses were modulated by seasonal variation in soil moisture. The results suggest that environmental changes in nutrient availability can lead to important consequences for diversity and functioning of this savanna where the numerous rare species have more chance to persist under dystrophic conditions as some species that tend to be dominant would be less competitive.     

Effects of an African grass invasion on Hawaiian shrubland nitrogen biogeochemistry

African perennial C₄ grasses are highly successful invaders in Hawaiian ecosystems. We examined the effects of African molasses grass (Melinis minutiflora Beauv.) on Hawaiian shrubland nitrogen (N) dynamics without the influence of fire disturbance. Vegetation tissue carbon and nitrogen chemistry, soil inorganic N pools, net N mineralization rates, and total soil N were studied in three adjacent areas: a monospecificMelinis grassland, a mixed grass/shrubland mosaic, and an un-invaded shrubland.Melinis plots within the mosaic area exhibited the largest inorganic N pools and fastest net N mineralization rates, but were temporally variable with grass phenology. Un-invaded shrubland plots contained the smallest inorganic N pools and lowest net N mineralization rates. Grass foliar C:N and litter C:N were lower than those of common shrubland species, providing one possible link between species and ecosystem N dynamics at this site. The combined effects of N cycle modification, successful light competition, and fire-cycle enhancement make the invasion ofMelinis a significant perturbation to Hawaiian shrubland ecosystem function and successional dynamics. ei]Section editor H Lambers     

Stress responses of native and exotic grasses in a Neotropical savanna predict impacts of global change on invasion spread

Communities subject to stress, including those with low invasibility, may be dominated by exotic generalist species. African grasses are aggressive invasive species in Neotropical savannas, where their response to abiotic stress remains unknown. We assessed the role of waterlogging and canopy closure on the presence, abundance and reproductive tillering of African and native grasses in a Neotropical savanna in southeastern Brazil. We obtained abundance and reproductive tillering data of exotic (Melinis minutiflora, Melinis repens and Urochloa decumbens) and common native grasses in 20 sites. We also determined the groundwater depth, soil surface water potential and canopy cover at these sites. The grass species generally had a low frequency and performed poorly where soil remained waterlogged throughout the year, except for two native species. Most native species were exclusive to either well‐drained savannas or better drained wet grasslands. However, two species (Loudetiopsis chrysothrix and Trachypogon spicatus) occurred in both vegetation types. Two exotic species (M. minutiflora and M. repens) were less common but demonstrated reasonable performance in wet grasslands, possibly due to their root system plasticity. Furthermore, U. decumbens had a lower occurrence, density and reproductive tillering at these sites, but was successful at sites where the groundwater level was slightly deeper. Although the favourable water regime in the savannas increases their invasibility in general, resistance to invasion by African grasses may be greater at microsites with high canopy closure, where these species showed lower performance and did not affect the abundance of co‐occurring native grasses. In summary, the Brazilian savanna becomes more susceptible to the spread of African grasses when disturbances decrease canopy closure or lower rainfall associated with climate change reduces the average groundwater depth and consequently releases invasive species from soil waterlogging in grasslands.     

Growth energetics of juvenile herring,Clupea harengus L.: food conversion efficiency and temperature dependency of metabolic rate

The relationship between rates of food consumption (C) and somatic growth (G) and the effect of temperature (T) on rates of mass lost during food deprivation were examined in 9–10 cm total length (TL) [1.0–1.5 g dry mass (DM)] juvenile Atlantic herring (Clupea harengus L.) in the laboratory. One feeding‐growth trial was conducted at 16°C using groups of herring feeding on known rations of brine shrimp (Artemia spp.) nauplii to quantify gross and net growth efficiency. Rates of mass lost by groups of herring (a proxy for metabolic rate, M) were measured in trials conducted at 9.7, 14.2 and 17.9°C. Gross growth efficiency (GGE = 100*G*C^?1) at 16°C was 25% at the highest rations (5.8–6.6% DM). The maintenance ration (C_main = C at zero G) was equal to 432 J*fish^?1*d^?1 or 2.0% DM*d^?1. At 16°C, net growth efficiency (100*G*(C?C_main)^?1) was 42%. The nucleic acid content (RNA‐DNA ratio, RD) in herring muscle tissue was strongly related to somatic growth (G, % DM*d^?1 = ?0.36*RD² + 3.21*RD ?3.92, r² = 0.90, P < 0.05, n = 8 groups). The effect of T (9.7–17.9°C) on M was described by a second order polynomial equation M = ?1.24*T + 38.2*T ? 218 (J*g DM^?1*d^?1) and M = ?10*T + 310*T ? 1815 (J*fish^?1*d^?1). This was the first study to investigate the influence of temperature on the metabolic rate of juvenile Atlantic herring under stress‐free conditions in the laboratory and provides the first estimates of gross and net growth efficiency for this species feeding on live prey.     

Snag Benchmarks and Treatment Options for Mixed‐Pine Forest Restoration in Eastern Upper Michigan

Snags (dead‐standing trees) are biological legacies that remain after disturbances in forests. We enhanced the ecological underpinnings of snag management within the context of mixed‐pine forest restoration in the northern Lake States by quantifying characteristics of live trees and snags within eighty-five 500‐m² plots at Seney National Wildlife Refuge (NWR) in eastern Upper Michigan. Study plots represented reference conditions (i.e. no past harvesting, relatively unaltered fire regime) and altered (i.e. harvested, altered fire regime) conditions. We also compared three treatments for creating snags from live trees. Snags were found in 87% of the reference plots and 85% of the altered plots. The only snag variables that differed between plot types were mean snag basal area, which was greater in altered plots (Student's t‐test, p = 0.04), and mean percent total basal area of snags (greater in reference plots, p = 0.06). The composition of snags differed only in the 10‐ and 25‐cm diameter classes (Multi‐Response Permutation Procedure, p < 0.10). The percentage of snags that developed into the most advanced decay class (DC) differed among treatments after 4 years (χ² = 16.49, p < 0.01), with 26% of girdled trees, 3% of prescribed fire trees, and zero topped trees reaching DC5. Logistic regression illustrated that the influence of predictor variables on DC development varied by species and treatment. The findings from this study, past studies, and ongoing projects at Seney NWR are directly applicable to innovative management of snags in mixed‐pine forests.     

Effect of Soil Slope on the Appearance of Mycobacterium avium subsp. paratuberculosis in Water Running off Grassland Soil after Application of Contaminated Slurry

The study assessed the effect of soil slope on Mycobacterium avium subsp. paratuberculosis transport into rainwater runoff from agricultural soil after application of M. avium subsp. paratuberculosis-contaminated slurry. Under field conditions, 24 plots of undisturbed loamy soil 1 by 2 m² were placed on platforms. Twelve plots were used for water runoff: 6 plots at a 3% slope and 6 plots at a 15% slope. Half of the plots of each slope were treated with M. avium subsp. paratuberculosis-contaminated slurry, and half were not treated. Using the same experimental design, 12 plots were established for soil sampling on a monthly basis using the same spiked slurry application and soil slopes. Runoff following natural rainfall was collected and analyzed for M. avium subsp. paratuberculosis, coliforms, and turbidity. M. avium subsp. paratuberculosis was detected in runoff from all plots treated with contaminated slurry and one control plot. A higher slope (15%) increased the likelihood of M. avium subsp. paratuberculosis detection but did not affect the likelihood of finding coliforms. Daily rainfall increased the likelihood that runoff would have coliforms and the coliform concentration, but it decreased the M. avium subsp. paratuberculosis concentration in the runoff. When there was no runoff, rain was associated with increased M. avium subsp. paratuberculosis concentrations. Coliform counts in runoff were related to runoff turbidity. M. avium subsp. paratuberculosis presence/absence, however, was related to turbidity. Study duration decreased bacterial detection and concentration. These findings demonstrate the high likelihood that M. avium subsp. paratuberculosis in slurry spread on pastures will contaminate water runoff, particularly during seasons with high rainfall. M. avium subsp. paratuberculosis contamination of water has potential consequences for both animal and human health.     

Throughfall,stemflow and interception of rainwater in an evergreen broadleaved forest

In order to analyze the dyanmics of heavy metals in a forest ecosystem, throughfall and stemflow were collected for individual rain showers in an evergreen broad-leaved forest dominated byCastanopsis cuspidata. The relation between throughfall (or stemflow) (Px) and gross rainfall (P) was approximated by a linear regression equationPx=a(P-b). The values of coefficient “a” were 0.32–2.02 for throughfall at each sampling point and the mean values for 1976 and 1977–1978 were 0.682 and 0.767, respectively. The stemflow volume differed widely among individual trees, depending mainly on the tree form of each species. In particular, the tree form ofPasania edulis was found to be especially suited to collecting stemflow. OneP. edulis tree collected 64% of the rainwater that fell onto its crown as stemflow. The ratio of stemflow to gross rainfall decreased in summer resulting from an increase in leaf biomass and an increase in air temperature. In fact, the values of coefficient “a” for mean stemflow per unit area were 0.180 for summer and 0.229 for other seasons in 1976, and 0.145 for summer and 0.155 for other seasons in 1977–1978 for different sampled trees.     

地膜/网纱覆盖对冬季菠萝园小环境及菠萝生长和果实品质特性的影响

为探明地膜/网纱覆盖在菠萝冬季防寒中的作用,以露地(NF)栽培为对照,设置地膜+网(FM+GC)、地膜(FM)及露地+网(NF+GC)3种处理,研究了地膜/网纱覆盖对冬季菠萝园小环境温湿度、光照强度、土壤温度的调控效应,及其对冬季菠萝植株、果实生长,果实品质形成等的影响。结果显示,(1)与露地对照相比,地膜+网、地膜及露地+网处理均提高了小环境的空气温度;地膜+网、露地+网均提高了空气湿度,而地膜处理在10:00前可提高空气湿度,11:30后会降低;地膜+网、露地+网处理均降低了光照强度,但地膜处理则可略微提高光照强度;地膜+网、地膜及露地+网处理均提高了土壤温度。(2)地膜+网、地膜及露地+网处理的植株新抽叶片数增多,新抽叶片长度增加,果实单果重及纵、横径提高,但可溶性固形物、可滴定酸含量及固/酸比变化不明显。(3)地膜+网、地膜处理的菠萝果实果皮的L*、a*、b*值提高,而露地+网处理的则降低;地膜+网处理的菠萝果肉L*、a*、b*值提高,而地膜处理的果肉L*值提高,a*、b*值却降低;露地+网处理的菠萝果肉L*、a*、b*值均降低。(4)地膜+网处理的果实酯类香气物质总相对含量降低,烯类总相对含量提高;而地膜、露地+网处理的则相反。研究表明,地膜/网纱覆盖促进了冬季菠萝植株及果实的生长,对果实品质无显著影响,但网纱覆盖对菠萝果实色泽、香气物质有一定的影响。     

火烧对黔中喀斯特山地马尾松林土壤理化性质的影响

在黔中喀斯特山地马尾松人工次生林内取样分析火烧和对照样地间土壤理化指标的变化,研究了火烧对林地土壤理化性质的影响。结果表明马尾松火烧林地表层土壤毛管孔隙度和总孔隙度升高、最大持水量和最小持水量增加,土壤密度和非毛管孔隙度降低、土壤质量含水量和体积含水量减少;土壤有机质、全N量、全P量、全K量,水解N量、有效P量、速效K量、交换性盐基量和pH值增大,阳离子交换量降低。林火对马尾松林地土壤主要理化指标影响的趋势为或表层土壤影响率大于剖面影响率、或表层土壤影响率小于剖面影响率,不同指标在土壤剖面的变化趋势或增加、或降低,对数或幂函数拟合曲线均达相关显著性水平。火烧和对照样地间的表层土壤理化指标变化主要反映了林火影响,近岩层土壤理化指标变化主要是成土母质在空间上的分异,也受生物的影响。乔木层植株死亡率同表层土壤最大持水量、最小持水量、有机质量和全N量的正相关性显著,同土壤密度的负相关性显著;灌木层植株死亡率同表层土壤密度正相关性显著,同毛管孔隙度、总孔隙度、质量含水量、最大持水量、最小持水量、有机质量、全N量、全P量和速效K量的负相关性达显著或极显著水平;灌木层生物损失量同表层土壤密度和有机质量正相关显著,同速效K量的负相关性显著,枯物层生物损失量同pH值的正相关性显著。火烧马尾松林分平均胸径同表层土壤密度正相关性显著,同毛管孔隙度、总孔隙度、质量含水量、最大持水量、最小持水量和有机质量的负相关性显著。