Ecophysiological Responses to Rainfall Variability in Grassland and Forests Along a Latitudinal Gradient in Italy

Adriano Conte,Costantino Sirca,Flavia Savi,Silvano Fares,Leonardo Montagnani,Francesco Mazzenga,Luca Salvati,Giorgio Matteucci,Edoardo Cremonese,Serena Marras,Donatella Spano,Marta Galvagno

doi:10.3389/ffgc.2019.00016

Abstract

In the Mediterranean region, ecosystems are severely affected by climate variability. The Italian Peninsula is a hot spot for biodiversity thanks to heterogeneous landscape and Mediterranean, Continental, and Alpine climates hosting a broad range of plant functional types along a limited latitudinal range from 40' to 46' N. In this study we applied a comparative approach integrating descriptive statistics, time series analysis, and multivariate techniques to answer the following questions: (i) do the climatic variables affect GPP, Reco, WUE and ET to a similar extent among different sites? (ii) Does a common response pattern exist among ecosystems along a latitudinal gradient in Italy? And, finally (iii) do these ecosystems respond synchronically to meteorological conditions or does a delayed response exists? Six sites along a latitudinal, altitudinal and vegetational gradient from semi-arid (southern Italy) to a mountainous Mediterranean site (central Italy) and sub-humid wet Alpine sites (northern Italy) were considered. For each site, carbon and water fluxes and meteorological data collected during two hydrologically-contrasting years (i.e. a dry and a wet year) were analysed. Principal Component Analysis was adopted to identify temporal and spatial variations in Gross Primary Productivity (GPP), Ecosystem Respiration (Reco), Water Use Efficiency (WUE) and Evapotranspiration (ET). The model outlined differences among Mediterranean semi-arid, Mediterranean mountainous, and Alpine sites in response to contrasting precipitation regimes. GPP, Reco, WUE and ET increased up to 16, 19, 25 and 28 %, respectively in semi-arid Mediterranean sites and up to 15, 32, 15 and 11%, respectively in Alpine sites in the wet year compared to the dry year. Air temperature was revealed to be one of the most important variables affecting GPP, Reco, WUE and ET in all the study sites. While relative air humidity was more important in southern Mediterranean sites, global radiation was more significant in northern Italy. Our work suggests that a realistic prediction of the main responses of Italian forests under climate change should also take in account delayed responses due to acclimation to abiotic stress or changing environmental conditions.

Highlights

Air temperatures and rainfalls are among the major climatic drivers of the terrestrial carbon cycle, and climate change can strongly affect ecosystem processes such as photosynthesis and respiration (Griffin and Prager, 2017)
The vegetation at the sites is represented by maquis, a holm oak forest, a beech forest, a spruce forest, a subalpine grassland, and a larch forest, for Capo Caccia, Castelporziano, Collelongo, Renon, Torgnon grassland and Torgnon forest sites, respectively
A mixed analysis strategy grounded on exploratory multivariate statistics (Principal Component Analysis, PCA), correlation techniques and multiple regression models, was adopted in this study with the aim to identify a relatively large number of contextual variables considered as candidate predictors of the eco-physiological processes investigated here (Colantoni et al, 2016)

Summary

INTRODUCTION

Air temperatures and rainfalls are among the major climatic drivers of the terrestrial carbon cycle, and climate change can strongly affect ecosystem processes such as photosynthesis and respiration (Griffin and Prager, 2017). By means of the increase in the occurrence of extreme heat and drought events, a substantial drying and warming of ecosystems in Mediterranean regions is expected (Gouveia et al, 2017; Paeth et al, 2017) Different patterns of these changes are expected for the various microclimates that characterize the Italian peninsula (Chelli et al, 2017). The responses of variables such as WUE and, more generally, Gross Primary Productivity (GPP), Ecosystem respiration (Reco), and Evapotranspiration (ET) to weather variability and changes in climate regimes at ecosystem level can be studied with the eddy covariance technique. We took advantage of an important anomaly observed in the Italian peninsula in 2014, marked by a very cool and wet summer, in particular in the northern part of Italy, where monthly precipitations in July were 84% above the mean for the years 1982–2013 (NIMBUS, 2015; Ratna et al, 2017), preceded by a moderately dry year (2013), to test the following hypotheses: (i) Do the climatic variables affect GPP, Reco, WUE, and ET to a similar extent among different sites? (ii) Does a common response pattern exist among ecosystems along a latitudinal gradient in Italy? (iii) Is the statistical prediction of GPP, Reco, WUE, and ET behavior improved taking account of both synchronic and delayed vegetation responses to meteorological variables?

MATERIALS AND METHODS

RESULTS

CONCLUSIONS