@article{0a00dc2c40a9474b80470e647f6327b7,
title = "Depth-driven responses of microbial residual carbon to nitrogen addition approaches in a tropical forest: Canopy addition versus understory addition",
abstract = "Canopies play an important role in nitrogen (N) redistribution in forest ecosystems, and ignoring the canopy's role might bias estimates of the ecological consequences of anthropogenic atmospheric N deposition. We investigated the effects of the approach of N addition (Canopy addition vs. Understory addition) and level of N addition (25 kg N ha−1yr−1 vs. 50 kg N ha−1yr−1) on microbial residual carbon (MRC) accumulation in topsoil and subsoil. We found that the response of MRC to both approach and level of N addition varied greatly with soil depth in a tropical forest over eight years of continuous N addition. Specifically, N addition enhanced the accumulation of fungal and total MRC and their contribution to soil organic C (SOC) pools in the topsoil, whereas it decreased the contribution of fungal and total MRC to SOC in the subsoil. The contrasting effects of N addition on MRC contribution at varying soil depths were associated with the distinct response of microbial residues production. Understory N addition showed overall greater effects on MRC accumulation than canopy N addition did. Our results suggest that the canopy plays an important role in buffering the impacts of anthropogenic atmospheric N deposition on soil C cycling in tropical forests. The depth-dependent response of microbial residues to N addition also highlights the urgent need for further studies of different response mechanisms at different soil depths.",
keywords = "Canopy nitrogen addition, Microbial residual carbon, Nitrogen addition, Soil depth, Tropical forest, Understory nitrogen addition",
author = "Luhui Kuang and Zhijian Mou and Yue Li and Xiaofei Lu and Yuanwen Kuang and Jun Wang and Faming Wang and Xi'an Cai and Wei Zhang and Shenglei Fu and Dafeng Hui and Hans Lambers and Jordi Sardans and Josep Pe{\~n}uelas and Hai Ren and Zhanfeng Liu",
note = "Funding Information: This work was supported by the Key-Area Research and Development Program of Guangdong Province (No. 2022B1111230001 ), the National Natural Science Foundation of China (No. 42177289 and No. 42007045 ), the Youth Innovation Promotion Association CAS ( 2019340 ), the Spanish Government projects PID2019-110521 GB-I00 and PID2020115770RB-I , Fundaci{\'o}n Ram{\'o}n Areces project CIVP20A6621 and Catalan government project ( SGR2017-1005 ). Funding Information: Partially contrary to our first hypothesis, we found that eight years of N addition in a tropical forest tended to increase microbial biomass and activity and greatly increased fungal MRC contribution in the topsoil (Fig. 5a). However, partially supporting our first hypothesis and fully supporting our third hypothesis, we found that N addition significantly decreased soil MRC contribution in the subsoil, in contrast with that in the topsoil (Fig. 5b). Previous studies on topsoil (0–10 or 0–20 cm) of N-saturated tropical and subtropical forests have also shown that fungal MRC contribution is more sensitive to N addition than bacterial, but N addition tends to decrease the fungal MRC contribution (Kjoller et al., 2012; Zhang et al., 2016; Ma et al., 2020a, 2020b), which is contrary to our results. Nitrogen addition might decrease MRC contribution to SOC via inhibiting microbial activity and biomass (Lu et al., 2021d), or might decrease the accumulation and contribution of MRC in the SOC pool via increasing bioavailable soil N, microbial biomass, and enzyme activity (Chen et al., 2020; Ma et al., 2020b). The divergent response of MRC contribution to SOC under N addition among sampling depths, suggests that the mechanism driving the response of MRC to N addition differs between topsoil and subsoil.This work was supported by the Key-Area Research and Development Program of Guangdong Province (No. 2022B1111230001), the National Natural Science Foundation of China (No. 42177289 and No. 42007045), the Youth Innovation Promotion Association CAS (2019340), the Spanish Government projects PID2019-110521 GB-I00 and PID2020115770RB-I, Fundaci{\'o}n Ram{\'o}n Areces project CIVP20A6621 and Catalan government project (SGR2017-1005). Publisher Copyright: {\textcopyright} 2023 Elsevier Ltd",
year = "2023",
month = aug,
day = "15",
doi = "10.1016/j.jenvman.2023.118009",
language = "English",
volume = "340",
journal = "Journal of Environmental Management",
issn = "0301-4797",
publisher = "Academic Press",
}