Effects of litter on establishment of grassland plant species: the role of seed size and successional status

Abstract Litter layers have a negative effect on seedling recruitment in many ecosystems. Successional fen grasslands are characterized by the built-up of litter layers which might be a key-factor influencing species composition and diversity during succession. Seed size is thought to be an important feature for the regeneration niche of species. Large seed size has been shown to be of advantage for germination and establishment under shaded conditions and beneath litter layers and thus for late-successional species. We investigated the effects of litter (control, litter layer of 3 cm and 8 cm) on seedling recruitment in 35 grassland species varying in seed size and successional status and on the abiotic conditions temperature, light quantity and light quality. Furthermore, we analyzed the species' light requirement for germination and its relation to seed size, successional status and establishment beneath litter. Light quantity was significantly lower beneath litter (reduction of 78% and 91% beneath 3 cm and 8 cm litter, respectively). The R/FR-ratio decreased from 1.2 without litter to 0.8 and 0.6 in presence of 3 cm and 8 cm litter. Seedling recruitment of 33 species was hampered by a litter layer. Establishment in presence of litter was positively related to seed size (r = 0.62, p We conclude that species-specific effects on seedling establishment are mainly due to differences in seed mass, successional status, and light requirement for germination and that these factors thus influence species composition and diversity during abandoned fen grassland succession. Nach der Nutzungsaufgabe ist die Sukzession auf Feuchtgrunland-Brachen durch die Bildung machtiger Streuauflagen gekennzeichnet. Durch Effekte auf Keimung und Etablierung beeinflusst die Streuauflage die Artenzusammensetzung und -vielfalt und wird deshalb als ein Schlusselfaktor fur die Vegetationsentwicklung angesehen. In einem Gewachshaus-Experiment wurde der Einfluss unterschiedlicher Streumachtigkeiten (Kontrolle, 3 cm und 8 cm) auf die abiotischen Faktoren Temperatur, Lichtintensitat und Lichtqualitat sowie auf die Keimlingsetablierung von 35 Grunlandarten untersucht. Die ausgewahlten Arten unterscheiden sich hinsichtlich ihres Samengewichts (von 0,1 bis 4,8 mg) sowie ihres Verhaltens im Sukzessionsverlauf (Arten fruher sowie spater Sukzessionstadien). Weiterhin wurden die Zusammenhange zwischen der Lichtbedurftigkeit der Keimung und dem Samengewicht, dem Verhalten im Sukzessionsverlauf und der Keimlingsetablierung unter Streuauflagen analysiert. Unter den Streuvarianten war die Lichtintensitat signifikant niedriger als in der Kontrolle (Reduktion um 78% und 91% unter 3 und 8 cm Streuauflage). Das Hellrot/Dunkelrot-Verhaltnis sank von 1,2 ohne Streuauflage auf 0,8 und 0,6 unter 3 bzw. 8 cm Streumachtigkeit. Die Keimlingsetablierung von 33 Arten wurde durch die Streu signifikant verringert. Die Etablierung von Arten mit einem hohen Samengewicht wurde weniger durch die Streuauflagen beeinflusst als diejenige kleinsamiger Arten (r = 0,62, p Die Ergebnisse zeigen, dass die artenspezifischen Unterschiede hinsichtlich der Keimlingsetablierung unter Streuauflagen im Wesentlichen durch die Faktoren Samengewicht, Lichtbedurftigkeit fur die Keimung sowie das Sukzessionsverhalten erklart werden konnen und dass diese Eigenschaften somit die Artenzusammensetzung und -vielfalt wahrend der Sukzession auf Feuchtgrunland-Brachen beeinflussen.

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