Heinz Coners

The Kobresia pygmaea ecosystem of the Tibetan highlands – Origin, functioning and degradation of the world's largest pastoral alpine ecosystem: Kobresia pastures of Tibet

With 450,000 km2Kobresia (syn. Carex) pygmaea dominated pastures in the eastern Tibetan highlands are the worlds largest pastoral alpine ecosystem forming a durable turf cover at 3000-6000 m a.s.l. Kobresias resilience and competitiveness is based on dwarf habit, predominantly below-ground allocation of photo assimilates, mixture of seed production and clonal growth, and high genetic diversity. Kobresia growth is co-limited by livestock-mediated nutrient withdrawal and, in the drier parts of the plateau, low rainfall during the short and cold growing season. Overstocking has caused pasture degradation and soil deterioration over most parts of the Tibetan highlands and is the basis for this man-made ecosystem. Natural autocyclic processes of turf destruction and soil erosion are initiated through polygonal turf cover cracking, and accelerated by soil-dwelling endemic small mammals in the absence of predators. The major consequences of vegetation cover deterioration include the release of large amounts of C, earlier diurnal formation of clouds, and decreased surface temperatures. These effects decrease the recovery potential of Kobresia pastures and make them more vulnerable to anthropogenic pressure and climate change. Traditional migratory rangeland management was sustainable over millennia, and possibly still offers the best strategy to conserve and possibly increase C stocks in the Kobresia turf.

Fine Root Abundance and Dynamics of Stone Pine (Pinus cembra) at the Alpine Treeline Is Not Impaired by Self-shading

Low temperatures are crucial for the formation of the alpine treeline worldwide. Since soil temperature in the shade of tree canopies is lower than in open sites, it was assumed that self-shading may impair the trees’ root growth performance. While experiments with tree saplings demonstrate root growth impairment at soil temperatures below 5–7°C, field studies exploring the soil temperature – root growth relationship at the treeline are missing. We recorded soil temperature and fine root abundance and dynamics in shaded and sun-exposed areas under canopies of isolated Pinus cembra trees at the alpine treeline. In contrast to the mentioned assumption, we found more fine root biomass and higher fine root growth in colder than in warmer soil areas. Moreover, colder areas showed higher fine root turnover and thus lower root lifespan than warmer places. We conclude that P. cembra balances enhanced fine root mortality in cold soils with higher fine root activity and by maintaining higher fine root biomass, most likely as a response to shortage in soil resource supply. The results from our study highlight the importance of in situ measurements on mature trees to understand the fine root response and carbon allocation pattern to the thermal growth conditions at the alpine treeline.

Water sources of plant uptake along a salt marsh flooding gradient

Salt marsh plants are affected by regular tidal inundation exposing them to saline water as a potential water source. This study aimed at quantifying the water uptake of plants depending on their distance from the sea and exploring plant responses to changing inundation regimes. We used stable isotope ratios (δ18O) to determine the proportions of seawater and precipitation water used by three salt marsh species (Spartina anglica, Atriplex portulacoides and Elytrigia atherica) from a German North Sea coast salt marsh. Additionally, A. portulacoides was transplanted to experimental islands at three elevation levels to investigate its plasticity in water use in the course of future sea level rise. We found a marked gradient in plant seawater use from the lowermost pioneer zone (79–98% seawater uptake by S. anglica) to the lower marsh (61–95% by A. portulacoides) and the upper marsh (25–39% by E. atherica). Seasonal differences in water use were not pronounced, likely due to the absence of longer dry periods during summer in these temperate salt marshes. Contradicting our expectation, roots in deeper soil showed higher water uptake rates per fine root mass than topsoil roots suggesting effective root adaptation to the anoxic subsoil. Transplanted A. portulacoides plants significantly increased the uptake of seawater with increasing inundation indicating flexibility in the use of water sources by this species which may facilitate acclimation to rising sea levels. We conclude that the zonation of salt marsh vegetation reflects the availability of water sources along the inundation gradient.