Radial stem growth dynamics and leaf emergence in Corylus avellana L. differ from Corylus colurna L

It has been reported that in multi-stem individuals of C. avellana, leaf emergence occurs about one month before the radial stem growth onset. This pattern appears to be different compared to other broad-leaf woody plants, in which the two processes are generally synchronous. Thus, it might be hypothesized that there is a different strategy of carbon use in polycormic (multi-stemmed) species. We hypothesize that C. colurna, a monocormic (single stem) species of the same genus, often used as rootstock, should behave as other broad-leaf woody plants, with radial growth and leaf emergence occurring at the same time. To test this hypothesis, we compared the radial stem growth and leaf emergence timing in C. colurna and C. avellana Tonda Romana (TR). In 2021, we installed a set of dendrometers and monitored phenology and growth of the two species in central Italy: C. colurna in the didactic lab of Perugia University (Deruta, PG) and C. avellana TR in a private commercial orchard that was part of the PANTHEON project (Nepi, VT). Meteorological parameters were collected as well. The daily radial growth was fit with the Gompertz function to find the timing of onset and maximum growth (Tp). Notes on vegetative phenology were collected weekly. The results showed that in C. avellana TR there is a one-month lag between leaf emergence and radial stem growth onset as previously observed in other C. avellana cultivars. On the contrary, in C. colurna leaf emergence and radial stem growth onset were temporally matched. These results highlight how Corylus polycormic species fractionate the timing of carbon use, while the monocormic concentrates the resource allocation in a single time slot. In a low-disturbed environment the monocormic might be better performing, while the polycormic strategy might cope better in unstable climates. Still, a more extended trial including multiple C. avellana cultivars and C. colurna, as well as C. avellana grafted on C. colurna rootstock in the same location, will add further evidence on the resource allocation strategy.