Conversion of Natural Evergreen Broadleaved Forests Decreases Soil Organic Carbon but Increases the Relative Contribution of Microbial Residue in Subtropical China

Liuming Yang,Quancheng Wang,Xiaojian Zhong,Chengfang Lin,Silu Chen,Yusheng Yang,Zhijie Yang,Yan Li

doi:10.3390/f10060468

Abstract

It has been recognized that land use change affects soil organic carbon (SOC) dynamics and the associated microbial turnover. However, the contribution of microbial residue to SOC storage remains largely unknown in land use change processes. To this end, we adopted a “space for time” approach to examine the dynamics of SOC and amino sugars, which was a biomarker of microbial residue C, in different natural forest conversions. Three typical converted forests were selected: an assisted natural regeneration (ANR) and two coniferous plantations of Cunninghamia lanceolata (Lamb.) Hook (Chinese fir) and Pinus massoniana Lamb. (pine) each. All of these were developed at the same time after the harvest of an old natural forest and they were used to evaluate the effects of forest conversions with contrasting anthropogenic disturbance on SOC and microbial residue C, along with the natural forest. Natural forest conversion led to an approximately 42% decrease in SOC for ANR with low anthropogenic disturbance, 60% for the Chinese fir plantation, and 64% for the pine plantation. In contrast, the natural forest conversion led to a 32% decrease in the total amino sugars (TAS) for ANR, 43% for the Chinese fir plantation, and 54% for the pine plantation at a soil depth of 0–10 cm. The ratios of TAS to SOC were significantly increased following natural forest conversion, with the highest ratio being observed in the Chinese fir plantation, whereas the ratios of glucosamine to muramic acid (GluN/MurA) were significantly decreased in the two plantations, but not in ANR. The contents of SOC, individual amino sugar, or TAS, and GluN/MurA ratios were consistently higher at a soil depth of 0–10 cm than at 10–20 cm for all of the experimental forests. Redundancy analysis showed that microbial residue C was significantly correlated with SOC, and both were positively correlated with fine root biomass, annual litterfall, and soil available phosphorus. Taken together, our findings demonstrated that microbial residue C accumulation varied with SOC and litter input, and played a more important role in SOC storage following forest conversion to plantations with higher anthropogenic disturbance.

Highlights

The decomposition, transformation, and stabilization of soil organic carbon (SOC) are the consequence of microbial growth and activity, which is a process that is associated with proliferation, metabolism, and mortality of microorganisms
The converted forests had experienced several forest management disturbances before our experiment, and the present study showed that natural forest conversion has a profound effect on soil C stocks in the subtropical forest, which cannot be recovered to a pre-harvest level, even after over 40 years of forest regrowth
0–10 cm soil depth in the converted forest, whereas no significant difference between the natural forest and converted forests occurred for the 10–20 cm soil depth (Figure 3). These results indicate the slower loss of microbial residue C than other soil C fractions following forest conversions, which suggests that microbial residue, as a refractory C, plays an important role in SOC storage, in the surface

Summary

Introduction

The decomposition, transformation, and stabilization of soil organic carbon (SOC) are the consequence of microbial growth and activity, which is a process that is associated with proliferation, metabolism, and mortality of microorganisms. More and more attention has been paid to microbial residue in recent studies, which demonstrated that senesced microbial biomass may play a much greater role in the stabilization of soil C pools than that previously considered [1,2,3,4]. It is critical to elucidate the response of soil microbial residue to global change, as well as the underlying mechanisms driving its transformation, to better understand global biogeochemical cycles and improve current global C cycle models [5,6]. There are a number of studies exploring the effects of global change on soil microbial residue. Liang and Balser observed that warming and N deposition reduced microbial residue contribution to the soil C pool [8]. To the best of our knowledge, studies investigating the effects of forest conversion on microbial residue contribution to soil C sequestration are lacking

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