氮磷富集对森林土壤碳截存的影响研究进展

Effects of Nitrogen and Phosphorus Enrichment on Carbon Sequestration in Forest Soils: A Review

大气氮磷沉降增加森林土壤养分的可利用性,改变底物的化学质量、土壤微生物组成和功能,进而影响土壤有机质的储量与稳定性。然而,现有研究主要集中在氮素富集对自然森林生态系统碳截存的影响,有关磷富集以及氮磷交互对人工林土壤有机碳(SOC)截存的影响及其微生物学机制尚不清楚。本文综述了氮磷富集对森林土壤碳转化和净交换通量、土壤有机质(SOM)的激发效应、SOM组成与稳定性以及介导碳转化功能微生物群落的影响,并指出各个研究环节的不足,包括:(1)森林土壤碳通量及其组分对氮磷富集的非线性响应方程及临界阈值尚未确定;(2)氮磷富集对森林SOM激发效应的影响程度与潜在机制知之甚少;(3)SOM的物理-化学协同稳定机制研究不够深入;(4)土壤活性微生物群落组成、SOM化学结构与SOC累积之间的耦联关系尚不清晰。据此,指出未来研究重点与研究思路:基于多水平氮磷添加控制试验和^(13)C标记培养实验,利用原位监测、土壤化学(^(13)C-NMR和Py-GC/MS)、宏基因组测序的分子生物学方法,重点研究氮磷添加及其交互作用对人工林土壤碳排放与流失通量、微生物激发效应、SOM组成与化学稳定性以及功能微生物群落组成的影响,确定土壤碳输出通量对氮磷添加的非线性响应方程与氮沉降临界负荷,阐明分解微生物群落组成与土壤碳转化及稳定性的耦联关系,揭示氮磷交互影响人工林土壤碳积累与损耗的微生物学机制。研究结果有助于控制森林尤其是人工林土壤碳损失,有效降低陆地"氮促碳汇"评估的不确定性,并可为森林生态系统应对全球变化提供科学依据。

Atmospheric nitrogen(N)and phosphorus(P)deposition increases soil nutrients available for plants,change chemical quality of the substrates,as well as composition and function of the soil microorganisms,thereby affecting storage and stability of the soil organic matter(SOM)in forest soils.However,the studies reported in the literature focused mainly on effects of N enrichment on carbon(C)sequestration in natural forest ecosystems,with little eyesight on effects of P enrichment and interaction of N and P on soil organic carbon(SOC)sequestration of in artificial forests as well as their microbiological mechanisms.In this paper,a review is presented of effects of N and P enrichment on C transformation and net C exchange fluxes,priming effect of SOM,chemical composition and stability of SOM,and composition and functions of microbial communities mediating C turunover in forest soils;moreover,the authors also shed light on deficiencies in the present researches,as follows.(1)Nonlinear response equations of soil C flux and its components in response to N and P enrichment in forest soils as well as their critical thresholds have not yet been determined;(2)Little is known about effects of N and P enrichment on priming effect of SOM in forest ecosystems and microbial mechanisms;(3)In-depth researches on mechanism of the physicochemical synergic stabilization of SOM under N and P enrichment are far from sufficient;and(4)It is still unclear how composition of soil active microbial community and SOM chemical structure is related to SOC accumulation.Therefore,the authors hold that future researches should foucs on the following aspects:Based on the established multi-level N and P addition and 13C-labeled incubation experiments,effects of N and P addition and their interaction on soil C emission and loss fluxes,microbial priming effect,composition and chemical stability of SOM,and functional microbial community composition are to be determined using the techniques of in-situ monitoring,soil chemistry(13C-NMR and Py-GC/MS),and macrogenomics of molecular biology,etc.Besides,more efforts should be laid on(1)defining the nonlinear equations for responses of soil C emission and loss to N and P addition as well as critical loads of atmospheric N and P depositions;(2)elucidating coupling relationships between composition of the soil decomposing microbial community and SOC transformation and stability;and(3)exposing microbial mechanisms responsible for the effects of N and P interaction on soil C accumulation and depletion in forest ecosystems,especially in subtropical plantations.All the findings in this review will help control C losses from forest soils,reduce uncertainties in assessing'N promoted C sink'in terrestrial ecosystems,and hence provide a scientific basis for subtropical plantations or forest ecosystems to deal with global change.