Experimental Precipitation Reduction Slows Down Litter Decomposition but Exhibits Weak to No Effect on Soil Organic Carbon and Nitrogen Stocks in Three Mediterranean Forests of Southern France

Abstract

Forest ecosystems are some of the largest carbon (C) reservoirs on earth. Pinus halepensis Mill., Quercus ilex L. and Quercus pubescens Willd. represent the dominant tree cover in the Mediterranean forests of southern France. However, their contributions to the French and global forest C and nitrogen (N) stocks are frequently overlooked and inaccurately quantified and little is known about to what extent the ongoing climate change can alter these stocks. We quantified the soil organic C (SOC) and N (SN) stocks in Mediterranean forests dominated by these tree species and evaluated to what extent an experimental precipitation reduction (about −30% yearly) affects these stocks and the litter decomposition efficiency. Litter mass losses were 55.7, 49.8 and 45.7% after 24 months of decomposition in Q. ilex, Q. pubescens and P. halepensis forests, respectively, and were 19% lower under drier climatic conditions. The SOC stocks were 14.0, 16.7 and 18.5 Mg ha−1 and the SN stocks were 0.70, 0.93 and 0.88 Mg ha−1 in Q. ilex, Q. pubescens and P. halepensis forests, respectively. The shallowness and stoniness of these Mediterranean forests could explain these limited stocks. By distinguishing the organic from the organo–mineral layer, we showed 74% less SOC in the organic layer of the P. halepensis forest under drier conditions, while no difference was detected in the organo–mineral layer or in the two oak forests. This last finding deserves further investigation and points out the necessity to distinguish the organic from the organo–mineral layer to detect the first impacts of climate change on SOC stocks.

Amplified Drought Alters Leaf Litter Metabolome, Slows Down Litter Decomposition, and Modifies Home Field (Dis)Advantage in Three Mediterranean Forests

“…On average, P. halepensis , Q. ilex , and Q. pubescens lost 42%, 50%, and 52% of initial litter mass after 2 years of field exposure, respectively. These rates of litter decomposition are similar to those reported in other studies from Mediterranean forested ecosystems [ 36 , 40 , 70 ]. It was reported that around 50% of the mass was lost for Q. pubescens after 25 months of field exposure [ 71 ].…”

Building forests for the future

“…The results reported above come predominantly from studies of forests under existing climate conditions. To study the dynamics of forest under changed climate, experiments modifying temperature (Rustad et al., 2001), water availability (e.g., Santonja et al., 2022), or atmospheric composition (Norby et al., 2016; United States Department of Energy, 2020) are required. Of these environmental modification experiments, Free‐Air CO 2 Enrichment (FACE) is the most technically difficult for mature forest stands and also tests the most direct physiological connection between forest productivity and the human‐perturbed atmosphere (i.e., changing atmospheric CO 2 as a substrate for photosynthesis and, hence, the terrestrial food web).…”

The Effects of Stand Development Stages on Soil Carbon and Nitrogen Stocks in Black Pine, Scots Pine and Fir Stands in Türkiye

“…Therefore, soils are the largest carbon reservoirs of the terrestrial carbon cycle (Das 2019;Ozlu et al, 2022). The residence or accumulation time of C in the soil is longer than that in vegetation (Santonja et al 2022). The soil holds this large carbon stock and prevents the accumulation of carbon dioxide in the atmosphere, which will increase the problem of climate change (Poeplau et al, 2021).…”