高寒草甸土壤呼吸及其组分对氮添加的响应

本研究比较了青藏高原高寒草甸土壤呼吸速率(Rs)、自养呼吸速率(Ra)和异养呼吸速率(Rh)随施氮梯度的变化,揭示土壤呼吸及其组分变化的主要影响因素,为评价未来氮沉降背景下高寒草甸土壤碳释放提供科学依据。于2014年在四川红原青藏高原高寒草甸建立长期氮素添加平台,采取完全随机区组试验设计,设置0(N0,对照)、2(N2)、4(N4)、8(N8)、16(N16)和32 g N·m^-2·a^-1(N32)6个水平氮素添加控制实验。于2020年生长季对Rs、Ra和Rh进行监测。结果表明：施氮显著降低了土壤呼吸及其组分(P<0.05),且Ra的下降幅度大于Rh,导致Rh/Rs随施氮水平逐渐上升;不同施氮处理下Ra和Rh与土壤温度均呈显著的指数正相关(P<0.05);施氮降低了Ra的温度敏感性(Q₁₀),但提高了Rh的Q₁₀值;土壤呼吸各组分与土壤湿度的关系均不显著,但土壤温度和土壤湿度双因子模型对Ra和Rh的解释度高于单因素模型。本研究揭示了高寒草甸土壤呼吸及其组分对氮添加的响应特征及机制,可为评...     

南亚热带森林土壤碳库稳定性与碳库管理指数对模拟酸雨的响应

通过对土壤总有机碳(SOC)、易氧化有机碳(ROC_(333)、ROC_(167)、ROC_(33))、颗粒有机碳(POC)、微生物量碳(SMBC)、溶解性有机碳(DOC)的测定,探讨模拟酸雨(pH 3.0、pH 3.5、pH 4.0、对照CK)对鼎湖山三个不同演替阶段森林(季风常绿阔叶林、针阔混交林、马尾松针叶林)土壤碳库稳定性及碳库管理指数的影响。结果表明:模拟酸雨增加了总有机碳的含量和各组分活性有机碳的含量(P0.05),但酸雨在一定程度上抑制了土壤中微生物量与活性。土壤中各组分活性有机碳与总有机碳呈显著相关,其中ROC_(333)和POC的含量与SOC关系最为密切,相关系数分别为0.853、0.846;碳库管理指数(CMI)结果表明,碳库活度(L)及碳库活度指数(LI)随森林的正向演替有下降的趋势,CPI与CMI呈现相反的趋势。在土壤有机碳及部分活性碳组分增加,碳库活性降低的前提下,土壤碳库稳定性增加。从各项指标的变化幅度可以得出:南亚热带森林土壤随森林群落正向演替而对模拟酸雨响应有更加敏感的趋势,各指标间的敏感性表现为CMIR_(333)POCSMBCR_(167)R_(33)LIDOCCPISOC。     

长期不同植被覆盖对黑土团聚体内有机碳组分的影响

为探究黑土团聚体内土壤有机碳(SOC)的“分馏”特征, 揭示不同植被覆盖下土壤团聚体的固碳机制, 该文以中国科学院海伦农业生态系统国家野外综合研究站内不同植被覆盖(草地、农田和裸地)长期定位实验的土样为研究对象, 利用团聚体湿筛分组、有机碳物理和化学分组相结合的方法, 研究了黑土团聚体及其内部的碳密度和腐殖质组分的碳分配特征。研究发现, 黑土经过不同植被覆盖31年后, 长期草地覆盖使土壤表层SOC、全氮(TN)含量显著增加, 农田和无植被覆盖的裸地SOC含量减少, 且在裸地显著降低。3种处理中, 2-0.25 mm (含2 mm, 下同)粒级团聚体均为优粒级。土壤团聚体的稳定性顺序为草地>农田>裸地。草地覆盖使土壤大团聚体的比例和有机碳库增加, 微团聚体和粉黏粒所占比例和碳库均减少, 说明草地覆盖促进了土壤大团聚体形成, 土壤固碳能力显著增强。而农田和裸地因外源碳投入少, 有机碳含量均是微团聚体>大团聚体>粉黏粒, SOC主要分布在微团聚体中。不同植被覆盖处理对土壤团聚体内密度组分和腐殖质各组分碳的富集“分馏”作用很明显, 与农田和裸地相比, 长期草地植被覆盖处理>2 mm和2-0.25 mm粒级团聚体中轻组碳含量富集的较多, 2-0.25 mm粒级团聚体中富里酸、胡敏酸和胡敏素的碳富集均最高, 而农田和裸地促进了微团聚体内腐殖质碳的富集。草地覆盖显著增加了大团聚体内活性有机碳组分, 来源于植物的碳首先进入到大粒径的团聚体中, 使土壤团聚结构显著改善, 农田和无植被覆盖的裸地土壤中轻组碳含量显著降低, 团聚体内有机碳以重组碳和胡敏素为主, 稳定化程度更高。     

宁南山区不同恢复年限柠条林土壤养分及有机碳组分变化特征

植被恢复能有效改善土壤质量,促进土壤有机碳(SOC)的固存。本研究以宁南山区0～100 cm土层不同恢复年限(16、28、38年)柠条林为研究对象,以农田和天然草地作为对照,分析了土壤养分及有机碳组分沿剖面分布特征及其对恢复年限的响应。结果表明：1)SOC、土壤全氮(TN)、全磷(TP)、颗粒态有机碳(POC)和矿物结合态有机碳(MAOC)含量以及颗粒态有机碳占总有机碳的比例(POC/SOC)均随土层深度增加而降低,而矿物结合态有机碳占总有机碳的比例(MAOC/SOC)呈相反趋势;2)随着柠条恢复年限的增加,SOC、TN、TP、C∶P、N∶P、POC和MAOC含量逐渐降低,C∶N无显著变化,POC/SOC先增后减,MAOC/SOC先减后增;3)在3种土地类型中,POC、MAOC与SOC之间均呈极显著正线性相关关系,且SOC的增加主要依赖于MAOC的增加。天然草地和柠条林地土壤SOC、TN、TP、POC和MAOC含量均显著高于农田。综上,柠条林地土壤养分及POC、MAOC含量随着恢复年限增加逐渐降低;与农田相比,天然草地和柠条林地维持和提高土壤养分及碳储存的能力较高。     

围栏封育对黄河源区斑块化退化高寒草甸碳交换及其组分的影响

为明确围栏封育对斑块化退化高寒草甸净生态系统碳交换(NEE)不同组分的影响，本研究选取青藏高原黄河源区斑块化退化高寒草甸进行围封试验，设置4个围封年限(1、2、5、11 a)和1个正常放牧对照，研究NEE及组分对不同围封年限的响应。结果表明，围封5 a退化高寒草甸总初级生产力(GPP)和生态系统呼吸(ER)显著大于正常放牧、围封1 a、2 a和11 a,围封2 a和5 a退化高寒草甸NEE显著小于正常放牧、围封1 a和11 a样地(P<0.01),其他NEE组分对不同围封年限的响应情况不一致。植被自养呼吸(Ra)、根系呼吸(Rr)和土壤异养呼吸(Rh)占ER的比例在不同围封年限间差异显著(P<0.01)。此外，土壤温度与NEE呈二次曲线的关系，与ER以及除Rh以外的其他呼吸组分呈指数关系，土壤含水量与NEE、GPP、ER、土壤呼吸(Rs)、Ra、Rr呈线性关系(P<0.05)。全氮、全磷、生物量和NEE及组分存在显著的相关关系。说明围封5 a能显著提高退化草地的土壤养分和固碳功能，并能维持草地生产力，无需进行长期围封。     

长期不同植被覆盖对黑土团聚体内有机碳组分的影响

为探究黑土团聚体内土壤有机碳(SOC)的"分馏"特征,揭示不同植被覆盖下土壤团聚体的固碳机制,该文以中国科学院海伦农业生态系统国家野外综合研究站内不同植被覆盖(草地、农田和裸地)长期定位实验的土样为研究对象,利用团聚体湿筛分组、有机碳物理和化学分组相结合的方法,研究了黑土团聚体及其内部的碳密度和腐殖质组分的碳分配特征。研究发现,黑土经过不同植被覆盖31年后,长期草地覆盖使土壤表层SOC、全氮(TN)含量显著增加,农田和无植被覆盖的裸地SOC含量减少,且在裸地显著降低。3种处理中, 2–0.25 mm (含2 mm,下同)粒级团聚体均为优粒级。土壤团聚体的稳定性顺序为草地农田裸地。草地覆盖使土壤大团聚体的比例和有机碳库增加,微团聚体和粉黏粒所占比例和碳库均减少,说明草地覆盖促进了土壤大团聚体形成,土壤固碳能力显著增强。而农田和裸地因外源碳投入少,有机碳含量均是微团聚体大团聚体粉黏粒, SOC主要分布在微团聚体中。不同植被覆盖处理对土壤团聚体内密度组分和腐殖质各组分碳的富集"分馏"作用很明显,与农田和裸地相比,长期草地植被覆盖处理2 mm和2–0.25 mm粒级团聚体中轻组碳含量富集的较多, 2–0.25 mm粒级团聚体中富里酸、胡敏酸和胡敏素的碳富集均最高,而农田和裸地促进了微团聚体内腐殖质碳的富集。草地覆盖显著增加了大团聚体内活性有机碳组分,来源于植物的碳首先进入到大粒径的团聚体中,使土壤团聚结构显著改善,农田和无植被覆盖的裸地土壤中轻组碳含量显著降低,团聚体内有机碳以重组碳和胡敏素为主,稳定化程度更高。     

模拟酸雨对鼎湖山季风常绿阔叶林土壤呼吸的初期影响

通过在鼎湖山季风常绿阔叶林(季风林)进行野外模拟酸雨试验,对不同酸雨强度处理下的林地土壤呼吸速率进行原位测定,探讨酸雨对南亚热带森林土壤呼吸的初期影响。结果表明:在两年的测定周期内,4个酸雨水平:CK(pH值4.5左右的天然湖水)、T1(pH值4.0)、T2(pH值3.5)和T3(pH值3.0)处理下的年平均土壤呼吸速率分别为(3.07±0.08)、(3.06±0.17)、(2.78±0.29)和(2.56±0.08)μmol·m~(-2)·s~(-1),其中T3处理显著低于CK和T1处理(P0.05),说明模拟酸雨抑制了季风林土壤呼吸。这种抑制作用大体上随处理时间的延长而逐渐显著,处理间的差异只在测定周期的第二年达到显著水平,且抑制作用的差异显著性只出现在湿季(P0.05)。模拟酸雨对土壤呼吸的抑制作用可能与其胁迫下土壤酸化而导致土壤微生物异养呼吸及凋落物CO_2释放量下降有关。表现为模拟酸雨导致土壤pH值降低,使得土壤酸化加剧;降低了土壤微生物量碳、氮含量,抑制了微生物活性;提高了凋落物质量残留率,抑制了凋落物分解。还与土壤呼吸结果相对应,上述指标对模拟酸雨的响应也大体上随处理时间的延长而逐渐显著。另外,土壤呼吸温度敏感系数Q_(10)值随处理pH值降低有下降的趋势,表明酸雨处理在一定程度上降低了土壤呼吸的温度敏感性。     

广西喀斯特移民迁入区土地利用变化对土壤有机碳和全氮储量的影响

土地利用变化是影响土壤碳、氮循环的重要因素,也是研究全球气候变化的热点.本研究基于固定深度法(FD)和等效质量法(ESM),从森林开垦和退耕还林还草两个角度探讨喀斯特移民迁入区土地利用变化对土壤有机碳(SOC)和全氮(TN)储量的影响.结果表明: 原始森林被开垦为草地、桉树林和农田后,SOC和TN储量均显著减少;基于FD方法计算的SOC和TN储量分别损失了47.4%、41.6%,而通过ESM方法计算的SOC和TN的损失率分别为54.8%、49.7%.农田撂荒为草地及种植桉树后,SOC和TN储量显著增加;基于FD方法计算的SOC和TN储量提高了60.5%、49.7%,通过ESM方法计算的SOC和TN分别增加85.5%和70.8%.FD方法忽略了土地利用变化后土壤容重的差异,而森林开垦后会显著增加土壤容重,因此,FD方法高估了SOC和TN储量;农田恢复后土壤容重减小,FD方法则会低估SOC和TN储量的增加.建议相关研究选择ESM方法测算土地利用变化对SOC和TN储量的影响.     

科尔沁沙地不同土地利用类型土壤化学计量特征

土壤碳(C)、氮(N)、磷(P)化学计量是衡量土壤质量及生态系统元素限制的重要指标,探讨土地利用和土层深度对土壤化学计量特征的影响有利于揭示科尔沁沙地土壤元素循环规律。本研究以科尔沁沙地5种土地利用类型(灌溉农田、旱作农田、沙质草地、固定沙丘、流动沙丘)土壤为对象,分析不同土地利用类型和不同土层土壤有机碳(SOC)、全氮(TN)、全磷(TP)含量及其化学计量特征。结果表明: 1)科尔沁沙地0～10 cm SOC(3.23 g·kg^-1)、TN(0.37 g·kg^-1)、TP(0.15 g·kg^-1)含量及化学计量比(C:N、C:P、N:P分别为9.07、25.56、2.97)远低于中国陆地土壤。2)土地利用变化显著改变了SOC、TN、TP含量及其化学计量特征,0～100 cm SOC、TN、TP含量均表现为灌溉农田>沙质草地>旱作农田>固定沙丘>流动沙丘;沙质草地、灌溉农田、旱作农田C:N显著高于固定沙丘和流动沙丘,沙质草地、固定沙丘、灌溉农田、旱作农田C:P显著高于流动沙丘,5种土地利用类型N:P无显著差异。3)随土层深度增加,沙质草地、固定沙丘、灌溉农田、旱作农田SOC和TN含量显著降低,流动沙丘SOC、TN含量和C:P在各土层间无显著差异;总体上,各土地利用类型TP含量和C:N受土层影响较小;沙质草地、固定沙丘、灌溉农田、旱作农田C:P和沙质草地N:P随土层深度增加而降低。4)SOC、TN、TP、C:N与中砂粒、细砂粒、土壤容重呈显著负相关,与黏粉粒和极细砂粒呈显著正相关。沙漠化导致科尔沁沙地SOC和养分流失,加剧土壤N缺乏,水肥投入有助于耕地维持相对较高的土壤养分水平。     

桂北喀斯特山区不同植被类型土壤碳库管理指数的变化特征

以广西北部喀斯特石山地区不同植被类型(青冈栎次生林、灌丛、马尾松林、竹林、草地、农田、裸地)土壤为研究对象,探讨植被类型对活性有机碳库以及土壤碳库管理指数的影响,为喀斯特山区生态环境建设提供依据。结果表明:1)青冈栎次生林土壤碳储量、全氮含量、速效氮含量显著高于其他植被,土壤容重小于除农田以外的其他植被类型; 2)不同植被类型下土壤有机碳(SOC)、活性有机碳(LOC)含量均随土层深度的增加而降低,0～40cm土层SOC含量为1.07～29.76 g·kg~(-1),大小关系表现为青冈栎次生林灌丛马尾松林竹林草地农田裸地; LOC含量为0.58～13.77 g·kg~(-1),表现为青冈栎次生林灌丛马尾松林竹林农田草地裸地; LOC/SOC表现为青冈栎次生林最小,农田最大; 3)土壤碳库管理指数随土层深度的变化为先减小后增加再减小的趋势,0～40 cm土层CPMI平均值表现为青岗栎次生林灌丛马尾松林农田竹林草地裸地; 4)土壤植被类型、土层深度以及二者的交互作用对土壤碳库管理指数及碳库特征具有显著影响。本研究表明,增加植被覆盖以及减少人为活动的干扰,能提高土壤有机碳含量,有利于维持桂北喀斯特山区土壤碳库的稳定性。     

Variations in the nitrogen saturation threshold of soil respiration in grassland ecosystems

Over the last century, anthropogenic activities have increased nitrogen (N) deposition considerably, which significantly affects ecosystem processes and has the potential to induce N saturation in the future. The continuous increase in N deposition may cause a non-linear response in soil respiration (Rs), an important component of carbon (C) cycling. However, little is known about N saturation threshold of soil respiration. In this study, we conducted coordinated experiments in four grassland types across northern China with four N addition levels to explore patterns in the Rs saturation threshold. Our results showed that an Rs saturation threshold generally exists in grassland ecosystems in response to N addition gradients. The N saturation threshold of Rs occurred at an average rate of 50 kg N ha⁻¹ yr⁻¹, but varied widely with grassland type; the N saturation threshold occurred at rates of 100, 50, 50, and 25 kg N ha⁻¹ yr⁻¹ in the alpine meadow, meadow steppe, typical steppe, and desert steppe, respectively. Autotrophic respiration (Ra) and heterotrophic respiration (Rh) responded to N addition gradients differently. Ra increased initially and became saturated at a rate of 50 kg N ha⁻¹ yr⁻¹ and declined thereafter. In contrast, Rh decreased monotonically after N addition. Structural equation models further confirmed that the effects of N addition gradients on Rs were primarily determined by the non-linear response of belowground biomass. Interestingly, the compiled global dataset showed that the N saturation threshold of Rs increased with precipitation and soil moisture. These findings indicate that the stimulating effect of N deposition on Rs and Ra might diminish with increasing N deposition in the future, especially in dry grassland ecosystems.

     

Spatially explicit estimate of nitrogen effects on soil respiration across the globe

Soil respiration (Rs), as the second largest flux of carbon dioxide (CO₂) between terrestrial ecosystems and the atmosphere, is vulnerable to global nitrogen (N) enrichment. However, the global distribution of the N effects on Rs remains uncertain. Here, we compiled a new database containing 1282 observations of Rs and its heterotrophic component (Rh) in field N manipulative experiments from 317 published papers. Using this up-to-date database, we first performed a formal meta-analysis to explore the responses of Rs and Rh to N addition, and then presented a global spatially explicit quantification of the N effects using a Random Forest model. Our results showed that experimental N addition significantly increased Rs but had a minimal impact on Rh, not supporting the prevailing view that N enrichment inhibits soil microbial respiration. For the major biomes, the magnitude of N input was the main determinant of the spatial variation in Rs response, while the most important predictors for Rh response were biome specific. Based on the key predictors, global mapping visually demonstrated a positive N effect in the regions with higher anthropogenic N inputs (i.e., atmospheric N deposition and agricultural fertilization). Overall, our analysis not only provides novel insight into the N effects on soil CO₂ fluxes, but also presents a spatially explicit assessment of the N effects at the global scale, which are pivotal for understanding ecosystem carbon dynamics in future scenarios with more frequent anthropogenic activities.     

模拟酸雨对土壤呼吸影响的研究进展

土壤呼吸是陆地生态系统与大气环境之间进行碳交换的主要途径,在全球碳循环和碳平衡中占有极其重要的地位。全球变化背景下,由于人类活动而导致日益严重的酸雨问题,其对土壤呼吸的影响越来越受到国内外学者的广泛关注。酸雨导致土壤酸化,对土壤微生物代谢活动、植物地上地下生长以及凋落物分解等产生影响,进而影响土壤呼吸。该文综述了模拟酸雨对森林生态系统和农田生态系统土壤呼吸影响的三种结果,即抑制、促进和无影响;酸雨影响土壤呼吸的差异受到酸雨酸性、酸雨处理持续时间以及植被类型、植物生长季节、植被演替阶段以及土壤理化性质等生物和非生物因素的综合影响。低强度和高强度酸雨都倾向于降低土壤呼吸的温度敏感性(Q_(10))。从影响土壤呼吸的四个关键的生物因子,即光合作用、凋落物、微生物、根系生物量,分析了模拟酸雨影响土壤呼吸的潜在机制;但是酸雨影响土壤呼吸的过程复杂,使得土壤呼吸对酸雨的部分响应机理仍存在不确定性。在此基础上总结了现有研究存在的不足,提出了今后需要给予重点关注的四个方面的研究:(1)不同类型生态系统对酸雨响应的研究;(2)土壤各组分呼吸对酸雨响应的研究;(3)模拟酸雨与其他外界因素的共同作用研究;(4)与土壤呼吸相关的生物因子对酸雨响应的研究。     

Contrasting responses of heterotrophic and autotrophic respiration to experimental warming in a winter annual‐dominated prairie

Understanding how soil respiration (Rs) and its source components respond to climate warming is crucial to improve model prediction of climate‐carbon (C) feedback. We conducted a manipulation experiment by warming and clipping in a prairie dominated by invasive winter annual Bromus japonicas in Southern Great Plains, USA. Infrared radiators were used to simulate climate warming by 3 °C and clipping was used to mimic yearly hay mowing. Heterotrophic respiration (Rh) was measured inside deep collars (70 cm deep) that excluded root growth, while total soil respiration (Rs) was measured inside surface collars (2–3 cm deep). Autotrophic respiration (Ra) was calculated by subtracting Rh from Rs. During 3 years of experiment from January 2010 to December 2012, warming had no significant effect on Rs. The neutral response of Rs to warming was due to compensatory effects of warming on Rh and Ra. Warming significantly (P < 0.05) stimulated Rh but decreased Ra. Clipping only marginally (P < 0.1) increased Ra in 2010 but had no effect on Rh. There were no significant interactive effects of warming and clipping on Rs or its components. Warming stimulated annual Rh by 22.0%, but decreased annual Ra by 29.0% across the 3 years. The decreased Ra was primarily associated with the warming‐induced decline of the winter annual productivity. Across the 3 years, warming increased Rh/Rs by 29.1% but clipping did not affect Rh/Rs. Our study highlights that climate warming may have contrasting effects on Rh and Ra in association with responses of plant productivity to warming.     

Changes in soil organic carbon of terrestrial ecosystems in China: A mini-review

The present study provides an overview of existing literature on changes in soil organic carbon (SOC) of various terrestrial ecosystems in China. Datasets from the literature suggest that SOC stocks in forest, grassland, shrubland and cropland increased between the early 1980s and the early 2000s, amounting to (71±19) Tg·a⁻¹. Conversion of marshland to cropland in the Sanjiang Plain of northeast China resulted in SOC loss of (6±2) Tg·a⁻¹ during the same period. Nevertheless, large uncertainties exist in these estimates, especially for the SOC changes in the forest, shrubland and grassland. To reduce uncertainty, we suggest that future research should focus on: (i) identifying land use changes throughout China with high spatiotemporal resolution, and measuring the SOC loss and sequestration due to land use change; (ii) estimating the changes in SOC of shrubland and non-forest trees (i.e., cash, shelter and landscape trees); (iii) quantifying the impacts of grassland management on the SOC pool; (iv) evaluating carbon changes in deep soil layers; (v) projecting SOC sequestration potential; and (vi) developing carbon budget models for better estimating the changes in SOC of terrestrial ecosystems in China.     

典型森林和草地生态系统呼吸各组分间的相互关系

生态系统呼吸是陆地生态系统碳收支的重要组成部分,分析其组分间的相互关系对理解生态系统呼吸过程和精确评价生态系统碳收支具有重要意义,也是当前碳循环研究工作的一大难点。本研究利用ChinaFLUX的长白山温带针阔混交林（CBS）,鼎湖山亚热带常绿阔叶林（DHS）和海北灌丛草甸（HBGC）三个典型生态系统的通量观测数据,采用经验统计方法,分析了其在中国典型生态系统中的适用性及敏感性,揭示了生态系统呼吸各组分的动态变化特征及相互关系。结果表明：采用本研究中的呼吸组分拆分方法所获结果与理论推测及实测数据大致相同,拆分结果对净初级生产力与总初级生产力的比值（NPP/GPP）较为敏感,NPP/GPP变化0.1时,自养呼吸在生态系统呼吸中的比例（Ra/RE）改变0.05。各生态系统中,生态系统呼吸及其组分在年内均表现出明显的单峰型变化特征,在夏季生长旺盛的时节达到最大值。异养呼吸与生态系统呼吸的比值（Rh/RE）也具有明显的季节变化,但在生态系统间表现出明显差异,CBS和HBGC分别表现出先增大后减小和先减小后增大的变化趋势,DHS则相对稳定,在0.5附近波动, Ra/RE的季节动态与Rh/RE相反。在年总量上,HBGC主要通过异养呼吸向大气排放CO2,异养呼吸占生态系统呼吸的60%,而CBS和DHS的自养呼吸和异养呼吸所占比重大致相似,异养呼吸占生态系统呼吸的49%。这说明,该统计学模型可以用来进行生态系统呼吸组分的拆分,进而可以为生态系统碳循环过程的精细研究提供参考数据,但今后应加强NPP/GPP的测定,以提高生态系统呼吸拆分的精度。     

Soil Respiration and Organic Carbon Dynamics with Grassland Conversions to Woodlands in Temperate China

Soils are the largest terrestrial carbon store and soil respiration is the second-largest flux in ecosystem carbon cycling. Across China''s temperate region, climatic changes and human activities have frequently caused the transformation of grasslands to woodlands. However, the effect of this transition on soil respiration and soil organic carbon (SOC) dynamics remains uncertain in this area. In this study, we measured in situ soil respiration and SOC storage over a two-year period (Jan. 2007–Dec. 2008) from five characteristic vegetation types in a forest-steppe ecotone of temperate China, including grassland (GR), shrubland (SH), as well as in evergreen coniferous (EC), deciduous coniferous (DC) and deciduous broadleaved forest (DB), to evaluate the changes of soil respiration and SOC storage with grassland conversions to diverse types of woodlands. Annual soil respiration increased by 3%, 6%, 14%, and 22% after the conversion from GR to EC, SH, DC, and DB, respectively. The variation in soil respiration among different vegetation types could be well explained by SOC and soil total nitrogen content. Despite higher soil respiration in woodlands, SOC storage and residence time increased in the upper 20 cm of soil. Our results suggest that the differences in soil environmental conditions, especially soil substrate availability, influenced the level of annual soil respiration produced by different vegetation types. Moreover, shifts from grassland to woody plant dominance resulted in increased SOC storage. Given the widespread increase in woody plant abundance caused by climate change and large-scale afforestation programs, the soils are expected to accumulate and store increased amounts of organic carbon in temperate areas of China.     

Seasonal Changes in Soil Respiration with An Elevation Gradient in <i>Abies nephrolepis</i> (Trautv.) Maxim. Forests in North China

Soil respiration (Rs) plays an important role in regulating carbon cycle of terrestrial ecosystems and presents temporal and spatial heterogeneity. Abies nephrolepis is a tree species that prefers the cold and wet environment and is mainly distributed in Northeast Asia and East Asia. The Rs variations of Abies nephrolepis forests communities are generally environmental-sensitive and can effectively reflect the adaptive responses of forest ecosystems to climate change. In this study, the growing-seasonal variations of Rs, soil temperature, soil water content and soil properties of Abies nephrolepis forests were analyzed along an altitude gradient (2000, 2100, 2200 and 2300 m) over two years on Wutai Mountain in North China. As the main results showed, soil respiration keeps the same change trend as soil temperature and reached peaks in July at 2000 m in 2019 and 2020. During 26^th July to 25^th October in 2019 and 27^th May to 23^rd October in 2020, on the whole, the soil temperature independently explained 76.2% of Rs variations while the soil water content independently explained 26.8%. Soil temperature and soil water content jointly explained 81.8% of Rs variations. Soil properties explained 61.8% and 69.6% of Rs variation in 2019 and 2020, respectively. Soil organic carbon content and soil enzyme activity had the signifi- cant (P < 0.01) negative and positive relationships, respectively, with Rs variation. With altitudes evaluated from 2000 to 2300 m, soil respiration temperature sensitivity (Q₁0) and the soil organic carbon content increased by 12.4% and 10.4%, respectively, while invertase activity, cellulase activity and urease activity dropped by 41.2%, 29.45% and 38.19%, respectively. The results demonstrate that (1) soil temperature is the major factor affecting Rs variations in Abies nephrolepis forests; (2) weakened microbial carbon metabolism in high-altitude areas results in the accumulation of soil organic carbon; (3) with a higher Q₁, forest ecosystems in high-altitude areas might be more easily affected by climate change; (4) climate warming might accelerate the consumption of soil organic carbon sink in forest ecosystems, especially in high-altitude areas.     

土地利用变化对土壤有机碳的影响研究进展

土壤有机碳是陆地碳库的重要组成部分,也是当前全球碳循环和全球变化研究的热点。土地利用/覆被变化及土地管理变化通过影响土壤有机碳的储量和分布,进而影响温室气体排放和陆地生态系统的碳通量。研究土地利用变化影响下的土壤有机碳储量及其动态变化规律,有助于加深理解全球气候变化与土地利用变化之间的关系。在阅读国内外有关文献的基础上,分别从土地利用及其管理方式变化的角度,概括了土地利用变化对土壤有机碳的影响过程与机理;针对当前研究的两大类方法,即实验方法和模型方法,分类详细介绍了它们各自的特点以及存在的一些问题。在此基础上,提出今后土地利用变化对土壤有机碳影响研究的发展趋势。