The importance of early season precipitation conditioning sub-mediterranean grassland responses to rainfall variation

Background & Aims: Climate change will likely modify patterns of precipitation, with an expected increase in frequency and magnitude of extreme events. The Mediterranean area seems to be very sensitive to such events, but their effect on ecosystem services, such as plant productivity, is widely unknown. Here we evaluate the short-term effect of an experimental precipitation gradient on the above ground net primary productivity (ANPP) of mesic and xeric sub-Mediterranean grassland systems over two consecutive years. Study sites: Torricchio Nature Reserve, Central Apennines, Italy. Mesic (north-facing) and xeric (south-facing) grasslands are differentiated in geophysical and edaphic properties. Methods: In both systems, a gradient of declining precipitation was obtained using additional rainfall, ambient rainfall and reduced rainfall for two years (2011, 2012). ANPP of the system as well as its functional groups was measured after the period of rainfall manipulation. An increase of ANPP and its variability with rainfall availability in each study year was analysed with monotonic trend tests (Jonckheere-Terpstra Test, Neuhauser-Hothorn Test) Main Results & Interpretations: A significant increase of the ANPP due to increased rainfall appeared only in the mesic system in the year 2012. This response was driven by the increased productivity of perennial forbs while grasses showed little changes. Comparing our findings of two different climatic years we conclude that positive effects of an increased precipitation on ANPP could be weakened by dry springs which might influence plant growth of the entire growing season. In sum, precipitation variation can have noticeable implications for sub-Mediterranean montane grassland productivity depending on local functional group composition and the amount of early season precipitation on ANPP.