Johannes Max

Priority effects caused by plant order of arrival affect below‐ground productivity

Plant species that arrive first in the system can affect assembly (priority effects). However, effects of order of arrival of different plant functional groups (PFGs) on root development have not yet been investigated under field conditions. We measured standing and fine root length density in the first and third year of a grassland field experiment. We wanted to know if manipulating PFG order of arrival would affect root development, and if priority effects are modulated by soil type. Sowing legumes first created a priority effect that was found in the first and third year, with a lower standing root length density in this treatment, even though the plant community composition was different in each of the studied years. Fine root length density was not affected by order of arrival, but changed according to the soil type. Synthesis. We found strong evidence that sowing legumes first created a priority effect below-ground that was found in the first and third year of this field experiment, even though the functional group dominance was different in each of the studied years.

Der Einfluß von Bodenbearbeitung und N-Düngung auf die Verteilung von 14C-markierten Assimilaten auf Sproß und Wurzel sowie auf die Rhizodeposition bei Winterraps

Rhizodeposition is considered to be an important source for soil organic carbon. Increased root turnover rates may be a mechanism employed by plants to respond to nutrient limiting conditions. Estimation of rhizodeposition for field-grown oilseed-rape plants (Brassica napus L.) using 14C-pulse labelling technique was the objective of our present work. Treatments consisted of two soil tillage systems (ploughing/surface tillage, ‘Horsch’) and two N rates (0 and 240 kg N/ha). Soil, roots, and shoot were sampled three weeks after labelling and also at the end of the growing season. Rhizodepostion was calculated from the decrease in 14C activity between the sampling dates. Under high N supply retranslocation of assimilates, an increase of root 14C-content which is incompatible with our methodical approach was observed. Therefore, a second experiment was conducted, combining pulse-labelling and ingrowth-core techniques to calculate the transfer of mobile 14C-labelled assimilates to newly formed roots. It is concluded that rhizodeposition accounted for up to 90% of total carbon allocation to the roots (high N supply and ploughing). N supply and soil tillage had pronounced effects on 14C partitioning within the shoot and also high N supply as well as ploughing resulted in reduced 14C allocation to generative organs.