Land desertification is one of the most serious ecological and environmental crises in the world today. China is one of the countries with the largest and most prominent degree of harm in the existing desertification land area in the world. The area threatened by land desertification in the country is about 2.622 million km2, accounting for 27.3% of the national land area, and there are "eight major deserts" and "four major sandy lands" in the arid and semi-arid areas in the north.
The Horqin Sandy Land is a key area for desertification control in China. It is located in the transition zone from the XiliaoHe Plain to the Mongolian Plateau, in the marginal region of a temperate monsoon climate, with an average annual precipitation of 280 mm and an average annual potential evaporation of more than 2300 mm. Historically, it was once an excellent pasture with abundant water and grass and many lakes, but since modern times, after more than a century of wasteland reclamation and overgrazing, coupled with the influence of warm and dry climate, the current desertification land area in the Horqin region has reached 63,600 km2, which is the largest sandy land in China, of which the area of mobile sand dunes accounts for more than 30% of the total area, and it is also one of the main sources of aeolian sand in the Beijing-Tianjin-Hebei region.
By planting artificial sand fixing shrubs or restoring natural vegetation, some of the mobile sand dunes can be restored to fixed sand dunes, effectively controlling the expansion of desertification land.
The Institute of Forestry and Soil Science of the Chinese Academy of Sciences (now the Institute of Applied Ecology, Chinese Academy of Sciences) has been engaged in research and experimental demonstration of land desertification control since the 1950s, and in 1975, the Ulan-Aodu Desertification Research and Experimental Station was established in the western part of the Horqin Sandy Land, assisting Weng NiuTe Banner in Chifeng City to carry out the construction of sand fixing shrub vegetation and the implementation of the restoration project of degraded grassland, making contributions to the local desertification control and ecological environment improvement.
Construction project of artificial sand fixation shrub forest in Horqin Sandy Ong Niu Te Banner
Shrubs and soil feedback each other, driving the restoration of dune vegetation
Moisture is the most important limiting factor for plant survival in sandy environments. The success of the restoration of artificial sand fixing shrub vegetation mainly depends on two aspects: one is the soil moisture status of the sand dune itself, and the other is the accurate selection of sand fixing shrubs that can adapt to the corresponding water conditions.
During the succession of dune vegetation restoration, there is a strong interaction between vegetation and soil. For example, in the Horqin Sandy Land Flowing Dune Vegetation Restoration Project, Hedysarum fruticosum Pall. Caragana microphylla Lam.) It is a pair of "old partners" of Sand Fixation.
In the early stages, mangosteen astragalus grows rapidly and acts as a pioneer shrub for sand fixation to quickly limit dune flow. However, as the dunes gradually fixed and the soil moisture decreased, the growth and survival of the shrub was gradually limited, and its dominant position was replaced by the more drought-tolerant small-leaf golden pheasant.
This interaction between shrubs and soil forms an important basis for community succession during dune vegetation restoration.
Dune vegetation restores the growth performance of two commonly used artificial sand fixing shrubs at different stages
Under severe drought stress, tissue dehydration will induce cavitation embolism in the xylem of sand fixing shrubs, and the water transport function will decrease or even be lost. The shrub's ability to survive drought conditions is closely related to its ability to avoid embolism that leads to failure in hydraulic transmission. This ability is related to the resistance of xylem cavitation on the one hand, but also depends on its ability to regulate leaf transpiration and avoid drying and dehydration.
The moisture conditions of sand dunes have strong heterogeneity in time and space, and it is of great significance to clarify the water physiological differences of sand fixing shrubs, which is of great significance for the screening of shrubs in sand fixation engineering.
The process of cavitation embolism induced by the huge water column under drought stress
Sand fixing shrubs: early "taking", late "conservative"
Recently, researchers from the Plant Physiological Ecology Group, desertification control group and Argentine National Science and Technology Research Council of Shenyang Institute of Ecology have carried out cooperative research, relying on the Ulan Aodu Desertification Experimental Station of Shenyang Institute of Ecology, to study the hydraulic structure characteristics and water use strategies of commonly used local sand fixing shrubs in Horqin Sandy Land, in order to clarify the environmental adaptability differences and physiological mechanisms of different shrubs.
Collaborative research team on water physiology of sand fixing shrubs
Researchers have found that in the early stage of vegetation restoration with relatively good soil moisture conditions, sand fixation pioneer shrubs adopt a "acquisition-type" water use strategy, which has high water conduction efficiency and photosynthetic carbon assimilation ability, so as to achieve faster growth, rapid occupation of habitats and play a role in restricting dune flow, and faster growth rate is also an important mechanism for coping with the risk of sand burial.
In the later stages of recovery with poor soil moisture conditions, the dominant shrub species on the fixed sand dunes adopted a "conservative" water use strategy, with low water transfer efficiency but higher xylem cavitation resistance, so they were able to survive stably on the fixed sand dunes for a long time.
Differences in water conduction (left) and water use (right) of several typical sand-fixing shrubs at different stages of dune vegetation restoration
The results were recently published in Land Degradation and Development and Forest Ecology and Management, respectively. The relevant results can better follow the principle of "suitable land and suitable species" in the process of sandy vegetation restoration, and provide a basic scientific basis for the sustainable management of windproof sand fixation shrub forests.
Author: Gong Xuewei, Guo Jingjing, Hao Guangyou
Source: Shenyang Institute of Applied Ecology, Chinese Academy of Sciences