Ecological and functional roles of mycorrhizas in semi-arid ecosystems of Southeast Spain

Mycorrhizas are worldwide symbiotic associations established between certain soil fungi and most vascular plants and are fundamental in optimizing plant fitness and soil quality. Mycorrhizal symbioses improve the resilience of plant communities against environment stresses, including nutrient deficiency, drought and soil disturbance. Since these stresses are paramount in the degradation of semi-arid ecosystems in the SE Spain, a series of basic, strategic and applied studies have been made to ascertain how the activity and diversity of mycorrhizal fungi affect plant community composition, structure and dynamics in this region. These investigations are reviewed here in terms of: (i) analysing the diversity of mycorrhizal fungi; (ii) assessing the ecological and functional interactions among plant communities and their associated mycorrhizal fungal populations; and (iii) using mycorrhizal inoculation technology for the restoration of degraded semi-arid areas in Southeast Spain. Disturbance of the target semi-arid ecosystems decreases the density and diversity of mycorrhizal fungust populations. Nevertheless, the mycorrhizal propagules do not disappear completely suggesting a certain degree of stress adaptation, and these remaining, resilient ecotypes are being used as plant inoculants. Numerous field experiments, using plant species from the natural succession inoculated with a community of indigenous mycorrhizal fungi, have been carried out in revegetation projects in the semi-arid Iberian Southeast. This management strategy improved both plant development and soil quality, and is a successful biotechnological tool to aid the restoration of self-sustaining ecosystems. However, despite a 20-year history of this work, we lack a comprehensive view of the mycorrhizal potential to improve the composition, diversity, structure and functionality of drought-adapted plant communities in the Region.     

洱海四种沉水植物对弱光环境的适应性比较

水下弱光环境是水生态系统沉水植被恢复面临的常见问题,因此研究沉水植物在弱光胁迫下的适应性是必要的.本研究以云南大理州洱海南部重度退化的湖区(惯称湖心平台,曾分布有大面积沉水植物)作为实验地点,选取4种沉水植物——苦草(Vallisneria natans)、轮叶黑藻(Hydrilla verticillata)、穗花狐...     

Recovery of topsoil physicochemical properties in revegetated sites in the sand-burial ecosystems of the Tengger Desert, northern China

Recovery in soil properties and processes after sand burial in the Tengger Desert, northern China, was documented at five different-aged revegetated sites (1956, 1964, 1973, 1982, and 1991) and at a reference site with native vegetation, which had never been damaged by sand burial and was enclosed for grazing. The proportions of silt and clay, depth of topsoil and biological soil crusts, and concentrations of soil organic C, K, total N and total P increased with years since revegetation. Most characteristics of topsoil (0–5 cm) characteristics had recovered to 60% of those measured at the reference site by 50 years after sand-binding vegetation had been established. Exceptions were electrical conductivity and contents of sand, silt, CaCO₃ and organic C, which recovered to 20–40% of the values at the reference site. The difference in annual recovery rates of soil properties between the two most recently revegetated sites (0–14 years) was greater than the difference between the two oldest revegetated sites (43–50 years). Best-fit asymptote models showed that the estimated times for the soil properties in the 50-year-old site to reach the same levels as in the reference site (i.e. an undisturbed, native steppified desert ecosystem) would be between 23 and 245 years, but for some properties even maximum recovery after > 50 years still fell significantly short of the level at the reference site. These results suggest that soil recovery is a slow process in an extremely arid desert environment, and therefore the conservation of soil habitat is a crucial issue for land managers.     

李氏禾的水土保持特性及其在新丰江水库消涨带的应用

通过在新丰江水库岸坡消涨带植被恢复的试验研究,说明李氏禾具有抗旱耐淹耐瘠的生物学特性.保证李氏禾在水淹之前具有足够长的生长期,并采取适当的技术措施使其正常生长,水库消涨带植被恢复的问题就可以解决.对李氏禾在水库岸坡消涨带植被恢复中减少坡面径流,防止水土流失,改善生态环境,提升景观价值等进行了探讨,并提出李氏禾用于植被恢复进一步工作的设想.     

Effects of forest land management on erosion and revegetation after the eruption of Mount St. Helens

The 1980 eruption of Mount St. Helens covered soils with a tephra blanket and killed the forest tree cover in a 550 km² area. After the eruption, rates of sheetwash and rill erosion, and plant cover were measured on tephra-covered hillslopes which had been subject to three land-management practices: grass seeding; scarification, and salvage logging. On rapidly-eroding hillslopes subject to grass seeding, limited plant covers were established only after erosion had declined sharply. Logging of trees downed by the eruption and scarification of previously logged surfaces slowed erosion, although the effect was small because erosion rates had already slowed substantially by the time these two practices were implemented. The factors controlling erosion, revegetation, and their relative timing at Mount St. Helens are similar to those following explosive volcanic eruptions elsewhere, suggesting that grass seeding is not likely to be effective at slowing erosion following most tephra eruptions, and that early mechanical disturbance could be an effective erosion-control measure. The results also indicate that even without deliberate conservation measures, processes which mechanically disturb a surface layer of low hydraulic conductivity (such as frost-action or trampling) can radically reduce runoff and erosion before revegetation has an important effect.     

Hydrological responses and soil erosion potential of abandoned cropland in the Loess Plateau, China

Recent changes in hydrological processes and soil erosion in the Loess Plateau, China, are immediate responses to cropland abandonment for revegetation, which lead to a long-term decrease in runoff generation and soil erosion. However, detailed hydrological responses and soil erosion changes have not been clearly evaluated. In this study, two issues were focused on the plot scale. The first issue relates to changes in vegetation cover and soil properties during the early stages of revegetation. Given the occurrence of soil compaction, it was hypothesized that runoff increased during this period and the soil erosion did not significantly decline, even though vegetation increased. The second issue is the effect of scale on runoff and soil erosion. Three plot groups of three vegetation types and two restoration stages were established for comparative experiments. The results from these experiments confirmed that the soil compaction occurred during revegetation in this region. Greater runoff was produced in plot group that experienced both a longer restoration time and with higher vegetation cover (such as Groups 2 and 3 in this study) than that with a shorter restoration time and lower vegetation cover (Group 1). In addition, the total soil loss rates of all plot groups were rather low and did not significantly differ from each other. This indicates that a reduction in runoff generation and soil erosion, as a result of revegetation, was limited in the early stages of restoration following the cropland abandonment. With increasing plot area, the runoff coefficient decreased for the plot group with a longer revegetation time (Groups 2 and 3), but gently increased for the one with a shorter restoration time (Group 1). In Groups 2 and 3, soil loss rate decreased when plot area enlarged. In Group 1, it decreased before a plot area threshold of 18 m² was exceeded. However, the increase occurred when plot area crossed the threshold value. In conclusion, the high vegetation cover alone did not lead to reduction in the runoff coefficient during the early stages of revegetation. When evaluating hydrological and soil erosion responses to revegetation, the soil compaction processes should be considered. Additionally, the effect of scale on runoff and soil erosion was found to be dependent on restoration extent, and thus on restoration time.     

Changes in land cover and shallow landslide activity: A case study in the Spanish Pyrenees

The Pyrenees, like many other mountain areas in Europe, have experienced depopulation and land abandonment during the 20th century. This has encouraged vegetation recovery in formerly occupied areas, including reforestation to promote woodland. The objective of this study is to analyse the effects of these changes on shallow landsliding, a process responsible for erosion and land degradation in many mountain areas. A sequence of aerial images reveals a slight decrease in the landslide occurrence rate in the last half of the 20th century and a parallel increase in the landslide extinction rate, i.e. the rate at which evidence of landslide activity is removed by vegetation colonisation. A logistic regression routine was used to assess the influence of land use and vegetation recovery in the occurrence of shallow landslides. The result shows that the former arable fields on the valley slopes still facilitate landsliding, even after land abandonment and revegetation by shrubs or trees. A shift in the topographic location of landslides was also detected, pointing to an increased importance of water redistribution in the slopes after prolonged rainfall periods.     

Research Progress and Perspectives on Biodiversity Conservation and Restoration of Coal Mine Reclamation Area

Biodiversity provides many ecosystem functions and services in the coal mine areas and plays an important role in improving the environment and sustainable development of mining area. From the view of coal mining-damage-the whole process of reclamation, the biodiversity conservation planning and biodiversity survey, monitoring and evaluation technology were briefly introduced before coal exploiting. The main contents for biodiversity conservation and technology including the protection of topsoil seed bank, soil fauna, biological soil crusts and optimization techniques of concurrent mining and reclamation during coal mining and the operational phase were elaborated. The key factors affecting biodiversity restoration in land reclamation stage were analyzed. The research on soil improvement and revegetation was discussed. Finally, the development direction of research about conservation and restoration of biodiversity in land reclamation of coal mine were proposed. It may provide some ideas for further promoting the research in this area.     

Vegetation diversity and its application in sandy desert revegetation on Tibetan Plateau

The dry and cold Tibetan Plateau is, by its nature, sensitive to desertification, and now human impacts and overexploitation makes things worse. One of the most important things involved in combating desertification is to stabilize mobile sandy land and facilitate revegetation. A study was conducted on shifting sand dunes of Tibetan Plateau to investigate the relationships among sand control, vegetation restoration and diversity dynamics of seed plant species. It was found that a positive correlation lay between sand stabilizing shrubs (Caragana korshinskii and Artemisia ordosica) and Leymus secalinus, a species of dominant and perennial grass in well-restored vegetation, but a negative correlation occurred between those shrubs and Agriophyllum arenarium indicator of shifting dunes. Secondly, sand stabilization facilitated revegetation, and total cover and cover of L. secalinus rose continuously from the beginning of restoration, but diversity indices showed a complex tendency. Based on these results, it was reasoned that on alpine shifting dunes of desertified regions, continual sand drifting caused by gales was the limiting factor for plant to survival. If sand barriers were established, sand drifting would be effectively controlled, then many native plant species could colonize shifting dunes gradually, so the process of revegetation was facilitated.