Litter traits and rainfall reduction alter microbial litter decomposers: the evidence from three Mediterranean forests

Abstract

The objective of the study was to evaluate changes in microbial communities with the predicted arrival of new species to Mediterranean forests under projected intensification of water stress conditions. For that, litter from three Mediterranean forests dominated respectively by Quercus pubescens Willd., Quercus ilex L. and Pinus halepensis Mill. was collected, and placed to their ‘home’ forest but also to the two other forests under natural and amplified drought conditions (i.e. rainfall reduction of 30%). Quantitative PCR showed that overall, actinobacteria and total bacteria were more abundant in Q. pubescens and Q. ilex than in P. halepensis litter. However, the abundance of both groups was dependent on the forest sites: placement of allochthonous litter to Q. pubescens and P. halepensis forests (i.e. P. halepensis and Q. pubescens, respectively) increased bacterial and fungal abundances, while no effect was observed in Q. ilex forest. P. halepensis litter in Q. pubescens and Q. ilex forests significantly reduced actinobacteria (A/F) and total bacteria (B/F) to fungi ratios. The reduction of rainfall did not influence actinobacteria and bacteria but caused an increase of fungi. As a result, a reduction of A/F ratio is expected with the plant community change towards the dominance of spreading P. halepensis under amplified drought conditions.

Soil fauna drives vertical redistribution of soil organic carbon in a long‐term irrigated dry pine forest

“…Meta-analysis of decomposers activity in response to drought showed large variability among functional groups and individual species, with soft-bodied fauna undergoing water stress sooner than microbial activity (Manzoni et al, 2012). In agreement with our study, microbial decomposers were only weakly affected by drier conditions (Aupic-Samain et al, 2021;Pereira et al, 2019), while soil fauna groups playing a key role in litter fragmentation and incorporation processes, such as Collembola, Oribatida, and Lumbricidae, were found to be highly responsive to drought (Aupic-Samain et al, 2021;Lindberg et al, 2002;Stevnbak et al, 2012). Among these, Collembola are particularly sensitive to desiccation due to their permeable cuticle (Kaersgaard et al, 2004;Peguero et al, 2019).…”

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

“…After 24 months of the experiment, P. halepensis showed a lower litter decomposition rate compared with the two oak species. The lower litter quality of pine needles compared with oak leaves can explain this difference in decomposition rates [50][51][52][53]. Indeed, P. halepensis needle litter exhibits higher C:N and C:P ratios and lower water-holding capacity (WHC) than Q. ilex and Q. pubescens leaf litters [53].…”

Soil biota response to experimental rainfall reduction depends on the dominant tree species in mature northern Mediterranean forests

“…In temperate forest ecosystems, bacteria and fungi are often positively correlated with soil water availability (e.g., Pflug and Wolters, 2001;Taylor and Wolters, 2005;Lensing and Wise, 2007). In Mediterranean ecosystems, in contrast, the regular summer droughts could have select adapted phenotypes among microbial species (Criquet et al, 2000;Pereira et al, 2019), leading to only weak or an absence of drought effect on soil bacterial and fungal communities (Wilkinson et al, 2002. Sherman et al, 2012.…”