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Contrasting effects of precipitation and fertilization on seed viability and production of Stipa krylovii in Mongolia

In drylands, primary production is predominantly limited by water availability; however, there is evidence for co-limitation by nutrients.We tested whether improved water and nutrient availability facilitate reproduction of dominant steppe species, and studied the effects of increased moisture and fertilization on seed production of the steppe grass Stipa krylovii. Effects of water availability on seed production and seed viability were investigated in a large-scale study on three sites with decreasing precipitation in Mongolia, over three to five consecutive years. In dry southern Mongolia, we additionally conducted an in situ irrigation and fertilization experiment to clarify the role of environmentally induced effects on seed production. Seed viability of S. krylovii was negatively correlated with annual precipitation over five years at the driest study site. The relation between annual precipitation and seed viability in the large-scale study was not as clear, however, in the two moister regions there was a trend of lower seed viability. Experimental irrigation also significantly decreased seed viability and seed mass. Seed production per hectare was not affected by irrigation, while fertilization resulted in a more than fivefold increase in both seed weight and number of viable seeds. The underlying mechanisms for these unexpected results were not investigated. However, a switch from cleistogamous pollination under dry conditions to less effective cross-pollination in moist years may be an explanation. Our data indicate that plant reproduction may show complex and unexpected reactions, and that nutrient limitation must be considered in global change scenarios even for dry regions.

In Trockengebieten ist die Primärproduktion vor allem durch Wasserverfügbarkeit limitiert, es gibt jedoch auch Hinweise auf eine Ko-Limitierung durch Nährstoffe. Wir haben getestet, ob sich Wasser- und Nährstoffverfügbarkeit auf die Reproduktion eines dominanten Steppengrases auswirken. Dazu untersuchten wir die Auswirkung unterschiedlicher Bewässerung und Düngung auf die Samenproduktion und–qualität der Federgrasart Stipa krylovii. Den Effekt der Wasserverfügbarkeit testeten wir in einem großräumigen Vergleich abnehmender Niederschläge in der Mongolei; die Messungen liefen über drei bis fünf aufeinanderfolgende Jahre. Darüber hinaus führten wir in der südlichen Mongolei, im trockensten der drei Untersuchungsgebiete, ein in situ Experiment mit Beregnung und Düngung durch, um die Rolle von umweltinduzierten Effekten auf die Samenproduktion zu analysieren.



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