Responses of Root Growth of Alhagi sparsifolia to Different Simulated Groundwater Depths in the Taklimakan Desert

Root system is the most important organ in plants for the absorption of water and nutrients. In arid lands, the availability of water and nutrients to plants largely depends on the environmental conditions, as well as the size, morphology and competitiveness of the root system. Groundwater is one of the main water sources for natural vegetation in arid areas, and changes in the depth of the groundwater table have a profound effect on the growth and morphological distribution of plant roots.

The Taklimakan Desert is one of the most arid areas in the world. Several dominant perennial species at the fringe of the Taklimakan Desert need to be in contact with groundwater if they are to survive, whereas the roots of seedlings must reach the limits of water capillary action if their root systems are not to be threatened by soil drought.

Alhagi spp. are perennial, leguminous and lignified herbs growing in deserts and semi-deserts. In the Taklimakan Desert, the survival and growth of A. sparsifolia must largely depend on groundwater resources. Therefore, Prof. ZENG Fanjiang et al. investigated the response characteristics of the root growth and the distribution of one-year-old A. sparsifolia seedlings to different groundwater depths in the southern fringe of the Taklimakan Desert. The ecological adaptability of the root systems of A. sparsifolia seedlings was examined using the artificial digging method.

The results showed that A. sparsifolia seedlings adapted to an increase in groundwater depth mainly through increasing the penetration depth and growth rate of vertical roots. The vertical roots grew rapidly when soil moisture content reached 3%–9%, but slowly when soil moisture content was 13%–20%. The vertical roots stopped growing when soil moisture content reached 30% (the critical soil moisture point).

The morphological plasticity of roots is an important strategy used by A. sparsifolia seedlings to obtain water and adapt to dry soil conditions. When the groundwater table was shallow, horizontal roots quickly expanded and tillering increased in order to compete for light resources, whereas when the groundwater table was deeper, vertical roots developed quickly to exploit space in the deeper soil layers.

The decrease in groundwater depth was probably responsible for the root distribution in the shallow soil layers. Root biomass and surface area both decreased with soil depth. One strategy of A. sparsifolia seedlings in dealing with the increase in groundwater depth is to increase root biomass in the deep soil layers. The relationship between the root growth/distribution of A. sparsifolia and the depth of groundwater table can be used as guidance for harvesting A. sparsifolia biomass and managing water resources for forage grasses. It is also of ecological significance as it reveals how desert plants adapt to arid environments.

The study entitled “Responses of root growth ofAlhagi sparsifoliaShap. (Fabaceae) to different simulated groundwater depths in the southern fringe of the Taklimakan Desert, China” was published in Journal of Arid Land in 2013, 5(2): 220-232.