Productivity of reed (Phragmites australis Trin. ex Steud.) in continental-arid NW China in relation to soil, groundwater, and land-use

Reed ( Phragmites australis Trin. ex Steud.) is a cosmopolitan plant species which can build up large stands in wetlands, floodplains, and on sites where groundwater is available. Phragmites australis provides many ecosystem services, such as the production of raw material (e.g. house construction or organic fuel). In the desert regions of Central Asia, reed occurs along river, e.g. the Tarim, Syr Darya, Amu Darya, and serves as fodder plant and raw material for construction and paper production. In those arid regions, reed occurs on submerged sites as well as non-flooded sites in a wide variety of phenotypes, ranging from so-called „giant reed“ (2-4 m high) to dwarf-like thorny reed not exceeding 40 cm stem length. We investigated the net primary production of the different phenotypes and their distribution with regard to soil and groundwater salt content and regarding grazing. The phenotypes were characterized through stem length, stem diameter, number of leaves per stem length, leaf weight ratio, leaf length, and leaf width. The net primary production reached 6,004 kg/ha·a on a non-grazed site, which is submerged for one month in late summer. The depth of the closed capillary fringe before onset of the flood was 2.2 m. The electric conductivity at the closed capillary fringe (determined from a water saturated soil extract) was 2 mS/cm. Stem length and stem diameter did not decrease with increasing soil and groundwater salt content, as expected. Conversely, stem length and stem diameter decreased and leaf weight ratio increased with increasing grazing intensity. Thus, grazing turned reed into dwarf-like thorny phenotypes. Non-grazed reed stands are the most productive ecosystems of the riparian vegetation at the Tarim and have a high potential to be used as raw material plant. We conclude that biomass harvesting could be an alternative to grazing with regard to sustainable land use.

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