Importance of forest fragments as pollinator habitat varies with season and guild

Large areas of Western Europe are covered with intensively managed agricultural land. In these landscapes, wild pollinators depend on fragments of semi-natural habitat for foraging or reproduction. Small forest patches are often the most abundant type of semi-natural habitat in these agricultural landscapes. We investigated the role these patches play in conserving the pollinator community in intensively managed agricultural landscapes.Our survey of the pollinator community in 16 forest fragments showed that the pollinator community in the edges of small forest fragments is strongly influenced by forest and forest edge characteristics. Old forest fragments with a well-developed herb layer had more diverse bee communities than recent forests or old forests without a herb layer, but overall lower activity-abundances, while sun exposure of the forest edges had a strong positive effect on pollinater activity-abundance in general. The hoverfly community had higher activity-abundances in forest edges with a higher flower-index, while saproxylic hoverflies were caught in higher numbers in sites with a higher forest cover in the surrounding landscape.We also detected a strong seasonal effect. The effects of herb layer cover on bee species richness and activity-abundance were much stronger in spring than in summer, while bee species richness was also strongly positively correlated with forest age in spring. A strong positive correlation between pollinator species richness and sun exposure was found in summer, after canopy closure.While the sampled forest edges harbour a rich and diverse pollinator community, cavity-nesting bees were very scarce. This is probably caused by the low amount of dead wood in the studied forest fragments.We conclude that small forest fragments can play an important role in conserving the pollinator community, especially bees and saproxylic hoverflies. The importance of these forest fragments is strongest in spring, when the herb layer provides foraging resources.     

土壤呼吸的温度敏感性——全球变暖正负反馈的不确定因素

基于模型模拟结果表明,全球变暖与大气CO2浓度增加将形成正反馈关系,这种正反馈效应将明显加速21世纪的气候变暖。然而,这些模拟模型都基于一个重要假设,即不同平均驻留时间的土壤有机质分解具有相同的温度敏感性(Q10)。这一假设与酶动力学理论相悖,而且不同学者对不同质量土壤有机质分解温度敏感性的差异的认识存在严重分歧,所以,全球变暖与大气CO2浓度增加的正反馈关系的显著性仍值得商榷。围绕土壤呼吸的温度敏感性问题进行了讨论和评述,涉及1)土壤有机质分解温度敏感性争论的焦点问题;2)通过经验模型曲线拟合估计Q10值存在的分歧及Q10变异的机理解释;3)实验室土壤培养实验估计Q10值存在的问题;4)土壤培养实验中Q10值计算方法的改进。进一步深化有关土壤有机质分解温度敏感性不确定性的认识,将为今后土壤呼吸及其对气候变化响应的相关研究提供参考。     

Potential effects of warming on soil respiration and carbon sequestration in a subtropical forest

Aims

Subtropical ecosystems are receiving unprecedented changes in temperature as a consequence of anthropogenic activities, which potentially affects soil respiration (R _s) and carbon (C) sequestration. Due to the large amounts of C store and cycle in subtropical forests, investigations about how R _s and C sequestration respond to warming will be critical for our understanding of future global-scale climate and biogeochemical cycling.

Methods

In this study, we transferred soil samples and plant seedlings collected from a mixed forest to the growth chambers in two sites (300 m and 30 m a.s.l.), which induced an artificial warming of ca. 1 °C between the two corresponding forest mesocosms. We tested whether the modification of abiotic factors induced by the downward translocation could alter R _s and soil C sequestration. We also investigated the effects on the biotic factors by including root biomass and soil microbial biomass.

Results

Our results showed that R _s was greater in the warm site than in the control site, which were related to the higher aboveground biomass, litterfall and root biomass. R _s showed a significantly positive exponential relationship with soil temperature. The downward translocation tended to decrease soil C sequestration, which was attributed to the decreased C use efficiency of soil microorganisms and increased root growth under downward translocation.

Conclusion

R _s responded strongly to downward translocation, suggesting that climate warming exacerbated R _s and tended to reduce soil C sequestration. The ability of subtropical forests to act as CO₂ sink may be reduced under climate warming.

     

寒温针叶林土壤呼吸作用的时空特征

利用Li-6400便携式CO2分析系统对寒温针叶林土壤呼吸作用观测数据分析表明,土壤呼吸作用日、季动态均呈单峰型变化,日最大值出现在16:00左右,与5 cm土壤温度日动态相似,滞后于气温日动态变化;月最大值出现在8月份,2006年和2007年分别为8.19 和6.89 μmol CO2 m-2 s-1。日、季土壤呼吸作用与土壤温度的相关性均好于气温。土壤呼吸作用存在较大的空间变异性,一天内3:00 am、7:00 am和11:00 am的土壤呼吸作用变异系数分别为35.5%、27.6%和23.0%,根系和凋落物与土壤呼吸作用表现出相似的空间变异性,其中细根与土壤呼吸作用的相关性最好。     

Contrasting mechanisms underlie short‐ and longer‐term soil respiration responses to experimental warming in a dryland ecosystem

Soil carbon losses to the atmosphere through soil respiration are expected to rise with ongoing temperature increases, but available evidence from mesic biomes suggests that such response disappears after a few years of experimental warming. However, there is lack of empirical basis for these temporal dynamics in soil respiration responses, and for the mechanisms underlying them, in drylands, which collectively form the largest biome on Earth and store 32% of the global soil organic carbon pool. We coupled data from a 10 year warming experiment in a biocrust‐dominated dryland ecosystem with laboratory incubations to confront 0–2 years (short‐term hereafter) versus 8–10 years (longer‐term hereafter) soil respiration responses to warming. Our results showed that increased soil respiration rates with short‐term warming observed in areas with high biocrust cover returned to control levels in the longer‐term. Warming‐induced increases in soil temperature were the main drivers of the short‐term soil respiration responses, whereas longer‐term soil respiration responses to warming were primarily driven by thermal acclimation and warming‐induced reductions in biocrust cover. Our results highlight the importance of evaluating short‐ and longer‐term soil respiration responses to warming as a mean to reduce the uncertainty in predicting the soil carbon–climate feedback in drylands.     

Representative estimates of soil and ecosystem respiration in an old beech forest

Respiration has been proposed to be the main determinant of the carbon balance in European forests and is thus essential for our understanding of the carbon cycle. However, the choice of experimental design strongly affects estimates of annual respiration and of the contribution of soil respiration to total ecosystem respiration. In a detailed study of ecosystem and soil respiration fluxes in an old unmanaged deciduous forest in Central Germany over 3 years (2000–2002), we combined soil chamber and eddy covariance measurements to obtain a comprehensive picture of respiration in this forest. The closed portable chambers offered to investigate spatial variability of soil respiration and its controls while the eddy covariance system offered continuous measurements of ecosystem respiration. Over the year, both fluxes were mainly correlated with temperature. However, when soil moisture sank below 23 vol.% in the upper 6 cm, water limitations also became apparent. The temporal resolution of the eddy covariance system revealed that relatively high respiration rates occurred during budbreak due to increased metabolic activity and after leaf fall because of increased decomposition. Spatial variability in soil respiration rates was large and correlated with fine root biomass (r ² = 0.56) resulting in estimates of annual efflux varying across plots from 730 to 1,258 (mean 898) g C m⁻² year⁻¹. Power function calculations showed that achieving a precision in the soil respiration estimate of 20% of the full population mean at a confidence level of 95%, requires about eight sampling locations. Our results can be used as guidelines to improve the representativeness of soil respiration measurements by nested sampling designs, being applied in long-term and large-scale carbon sequestration projects such as FLUXNET and CarboEurope.     

哀牢山亚热带常绿阔叶林森林土壤温湿特征及其对温度升高的响应

为把握土壤温度对未来全球气候变暖的响应程度,评估气候变暖对亚热带森林土壤呼吸的影响,利用在哀牢山亚热带常绿阔叶林中设置的土壤增温和土壤呼吸人工控制实验2011—2013年的实测数据,通过分析,得到如下结果:环境温度的升高不会改变林内的近地层气温、土壤温度和土壤含水量的年变化和日变化规律;冬季和夜间增温效应大于夏季和昼间;增温会导致土壤含水量降低,雨季的效应大于干季;增温导致的升温效应和降低土壤水分效应具有一定的年变化,但是基本没有日变化;所设置的人工增温控制实验的年平均增温在2.0℃左右,所设置人工控制实验可以达到5 cm土壤增温2.0℃的设计要求,可为其后探讨土壤呼吸对温度升高的响应提供良好的基础保证。     

A distinct seasonal pattern of the ratio of soil respiration to total ecosystem respiration in a spruce-dominated forest

Annual budgets and fitted temperature response curves for soil respiration and ecosystem respiration provide useful information for partitioning annual carbon budgets of ecosystems, but they may not adequately reveal seasonal variation in the ratios of these two fluxes. Soil respiration (R_s) typically contributes 30–80% of annual total ecosystem respiration (R_eco) in forests, but the temporal variation of these ratios across seasons has not been investigated. The objective of this study was to investigate seasonal variation in the R_s/R_eco ratio in a mature forest dominated by conifers at Howland, ME, USA. We used chamber measurements of R_s and tower‐based eddy covariance measurements of R_eco. The R_s/R_eco ratio reached a minimum of about 0.45 in the early spring, gradually increased through the late spring and early summer, leveled off at about 0.65 for the summer, and then increased again to about 0.8 in the autumn. A spring pulse of aboveground respiration presumably causes the springtime minimum in this ratio. Soil respiration ‘catches up’ as the soils warm and as root growth presumably accelerates in the late spring, causing the R_s/R_eco ratios to increase. The summertime plateau of R_s/R_eco ratios is consistent with summer drought suppressing R_s that would otherwise be increasing, based on increasing soil temperature alone, thus causing the R_s/R_eco ratios to not increase as soils continue to warm. Declining air temperatures and litter fall apparently contribute to increased R_s/R_eco ratios in the autumn. Differences in phenology of growth of aboveground and belowground plant tissues, mobilization and use of stored substrates within woody plants, seasonal variation in photosynthate and litter substrates, and lags between temperature changes of air and soil contribute to a distinct seasonal pattern of R_s/R_eco ratios.     

Effects of experimental drought on soil respiration and radiocarbon efflux from a temperate forest soil

Soil moisture affects microbial decay of SOM and rhizosphere respiration (RR) in temperate forest soils, but isolating the response of soil respiration (SR) to summer drought and subsequent wetting is difficult because moisture changes are often confounded with temperature variation. We distinguished between temperature and moisture effects by simulation of prolonged soil droughts in a mixed deciduous forest at the Harvard Forest, Massachusetts. Roofs constructed over triplicate 5 × 5 m² plots excluded throughfall water during the summers of 2001 (168 mm) and 2002 (344 mm), while adjacent control plots received ambient throughfall and the same natural temperature regime. In 2003, throughfall was not excluded to assess the response of SR under natural weather conditions after two prolonged summer droughts. Throughfall exclusion significantly decreased mean SR rate by 53 mg C m^?2 h^?1 over 84 days in 2001, and by 68 mg C m^?2 h^?1 over 126 days in 2002, representing 10–30% of annual SR in this forest and 35–75% of annual net ecosystem exchange (NEE) of C. The differences in SR were best explained by differences in gravimetric water content in the Oi horizon (r²=0.69) and the Oe/Oa horizon (r²=0.60). Volumetric water content of the A horizon was not significantly affected by throughfall exclusion. The radiocarbon signature of soil CO₂ efflux and of CO₂ respired during incubations of O horizon, A horizon and living roots allowed partitioning of SR into contributions from young C substrate (including RR) and from decomposition of older SOM. RR (root respiration and microbial respiration of young substrates in the rhizosphere) made up 43–71% of the total C respired in the control plots and 41–80% in the exclusion plots, and tended to increase with drought. An exception to this trend was an interesting increase in CO₂ efflux of radiocarbon‐rich substrates during a period of abundant growth of mushrooms. Our results suggest that prolonged summer droughts decrease primarily heterotrophic respiration in the O horizon, which could cause increases in the storage of soil organic carbon in this forest. However, the C stored during two summers of simulated drought was only partly released as increased respiration during the following summer of natural throughfall. We do not know if this soil C sink during drought is transient or long lasting. In any case, differential decomposition of the O horizon caused by interannual variation of precipitation probably contributes significantly to observed interannual variation of NEE in temperate forests.     

模拟增温对土壤呼吸影响机制的研究进展与展望

土壤呼吸是土壤碳库向大气碳库输入的主要途径,而温度升高会影响土壤呼吸从而改变全球碳平衡.据预测在21世纪末,全球平均地表温度将升高0.3～4.8 ℃,因此野外自然条件下的模拟增温试验对土壤呼吸的影响是全球变化研究的热点之一.本文综述了不同时空格局下土壤呼吸对模拟增温的响应特征,指出短期增温能提高土壤呼吸,而长期增温下无统一规律,并且不同生态系统之间也存在差异;重点讨论了模拟增温对土壤呼吸的影响机制,指出增温能直接影响土壤呼吸,同时增温也能通过影响土壤水分、盐分、土壤理化性质等环境因子以及光合作用、凋落物等生物因子对土壤呼吸产生间接影响;另外,分析了土壤呼吸对增温产生适应性的形成机制,主要包括微生物、根、酶的温度适应性、水分限制、氮素过量以及呼吸底物限制.在此基础上对今后的研究方向加以展望:加强根际微生态系统的研究;重点研究不对称增温下土壤呼吸的特征及机制;关注典型物候期和不同季节典型天气土壤呼吸的测定;构建土壤呼吸响应模拟增温试验的研究网络,进行联网试验.     

森林土壤有机碳分解对模拟增温的响应

由化石燃料燃烧和土地利用变化引起的全球气候变暖是地球上最严重的人为干扰之一,对陆地生态系统结构和功能产生重要的影响。土壤有机碳（SOC）是陆地生态系统最大的碳库,其微小变化都会影响全球碳平衡和气候变化。近30年来,国内外学者在不同森林生态系统相继开展了野外模拟增温对SOC分解的影响及其调控机制研究。基于在全球建立的26个野外模拟气候变暖实验平台,系统分析增温对森林生态系统SOC分解的影响格局和潜在机制,发现增温通常促进森林SOC的分解,对气候变暖产生正反馈作用。然而,因增温方式和持续时间、土壤微生物群落结构和功能的多样性、SOC结构和组成的复杂性、植物-土壤-微生物之间相互作用以及森林类型等不同而存在差异,导致人们对森林SOC分解响应气候变暖的程度及时空格局变化缺乏统一的认识,且各类生物和非生物因子的相对贡献尚不清楚。基于已有研究,从土壤微生物群落结构和功能、有机碳组分以及植物-土壤-微生物互作3个方面构建了气候变暖影响SOC分解的概念框架,并进一步阐述了今后的重点研究方向,以期深入理解森林生态系统碳-气候反馈效应,为制定森林生态系统管理措施和实现"碳中和"提供科学依据。1）加强模拟增温对不同森林生态系统（特别是热带亚热带森林生态系统） SOC分解的长期观测研究,查明SOC分解的时空动态特征;2）加强土壤微生物功能群与SOC分解之间关系的研究,揭示SOC分解对增温响应的微生物学机制;3）形成统一的SOC组分研究方法,揭示不同碳组分对增温的响应特征和机制;4）加强森林生态系统植物-土壤-微生物间相互作用对模拟增温的响应及其对SOC分解调控的研究;5）加强模拟增温与其他全球变化因子（例如降水格局变化、土地利用变化、大气氮沉降）对SOC分解的交互作用,为更好评估未来全球变化背景下森林土壤碳动态及碳汇功能的维持提供理论基础。     

氮添加对多伦草原土壤微生物呼吸及其温度敏感性的影响

人类活动导致氮和磷输入到草原生态系统,对土壤有机碳循环产生影响,但是土壤微生物呼吸(Soil microbial respiration,Rs)及其温度敏感性(Q₁₀)对于氮沉降和磷有效性增加的响应还存在争议。因此,依托多伦草原氮添加样地(0、50 kg N hm^-2 a^-1和100 kg N hm^-2 a^-1),并添加磷进行室内恒温培养(10℃和15℃),研究氮添加和磷有效性增加对Rs及其Q₁₀的影响。结果发现:氮添加显著降低胞壁酸含量和显著增加真菌丰富度(Fungal richness, F-richness)。与N0处理相比,N50和N100处理使累积呼吸量显著降低了61.2%和67.1%,但Q₁₀显著升高了32.7%和50.8%;磷有效性增加没有对累积呼吸量及其Q₁₀产生显著影响。逐步回归结果表明,F-richness和pH值分别是累积呼吸量及其Q₁₀最重要的影响因子。研究表明氮添加...     

Accumulation of soil carbon under elevated CO2 unaffected by warming and drought

Elevated atmospheric CO₂ concentration and climate change may substantially alter soil carbon (C) dynamics, which in turn may impact future climate through feedback cycles. However, only very few field experiments worldwide have combined elevated CO₂ (eCO₂) with both warming and changes in precipitation in order to study the potential combined effects of changes in these fundamental drivers of C cycling in ecosystems. We exposed a temperate heath/grassland to eCO₂, warming, and drought, in all combinations for 8 years. At the end of the study, soil C stocks were on average 0.927 kg C/m² higher across all treatment combinations with eCO₂ compared to ambient CO₂ treatments (equal to an increase of 0.120 ± 0.043 kg C m^?2 year^?1), and showed no sign of slowed accumulation over time. However, if observed pretreatment differences in soil C are taken into account, the annual rate of increase caused by eCO₂ may be as high as 0.177 ± 0.070 kg C m^?2 year^?1. Furthermore, the response to eCO₂ was not affected by simultaneous exposure to warming and drought. The robust increase in soil C under eCO₂ observed here, even when combined with other climate change factors, suggests that there is continued and strong potential for enhanced soil carbon sequestration in some ecosystems to mitigate increasing atmospheric CO₂ concentrations under future climate conditions. The feedback between land C and climate remains one of the largest sources of uncertainty in future climate projections, yet experimental data under simulated future climate, and especially including combined changes, are still scarce. Globally coordinated and distributed experiments with long‐term measurements of changes in soil C in response to the three major climate change‐related global changes, eCO₂, warming, and changes in precipitation patterns, are, therefore, urgently needed.     

Effects of biochar addition on dynamics of soil respiration and temperature sensitivity in a Phyllostachys edulis forest

Aims Recent studies have shown that artificial addition of biochar is an effective way to mitigate atmospheric carbon dioxide concentrations. However, it is still unclear how biochar addition influences soil respiration in Phyllostachys edulis forests of subtropical China. Our objectives were to examine the effects of biochar addition on the dynamics of soil respiration, soil temperature, soil moisture, and the cumulative soil carbon emission, and to determine the relationships of soil respiration with soil temperature and moisture.Methods We conducted a two-year biochar addition experiment in a subtropical P. edulis forest from 2014.05 to 2016.04. The study site is located in the Miaoshanwu Nature Reserve in Fuyang district of Hangzhou, Zhejiang Province, in southern China. The biochar addition treatments included: control (CK, no biochar addition), low rate of biochar addition (LB, 5 t·hm^-2), medium rate of biochar addition (MB, 10 t·hm^-2), and high rate of biochar addition (HB, 20 t·hm^-2). Soil respiration was measured by using a LI-8100 soil CO₂ efflux system.Important findings Soil respiration was significantly reduced by biochar addition, and exhibited an apparent seasonal pattern, with the maximum occurring in June or July (except LB in one of the replicated stand) and the minimum in January or February. There were significant differences in soil respiration between the CK and the treatments. Annual mean soil respiration rate in the CK, LB, MB and HB were 3.32, 2.66, 3.04 and 3.24 μmol·m^-2·s^-1, respectively. Compared with CK, soil respiration rate was 2.33%-54.72% lower in the LB, 1.28%-44.21% lower in the MB, and 0.09%-39.22% lower in the HB. The soil moisture content was increased by 0.97%-75.58% in LB, 0.87%-48.18% in MB, and 0.68%-74.73% in HB, respectively, compared with CK. Soil respiration exhibited a significant exponential relationship with soil temperature and a significant linear relationship with combination of soil temperature and moisture at the depth of 5 cm; no significant relationship was found between soil respiration and soil moisture alone. The temperature sensitivity (Q₁₀) value was reduced in LB and HB. Annual accumulative soil carbon emission in the LB, MB and HB was reduced by 7.98%-35.09%, 1.48%-20.63%, and -4.71%-7.68%, respectively. Biochar addition significantly reduced soil carbon emission and soil temperature sensitivity, highlighting its role in mitigating climate change.     

Enhanced root exudation stimulates soil nitrogen transformations in a subalpine coniferous forest under experimental warming

Despite the perceived importance of exudation to forest ecosystem function, few studies have attempted to examine the effects of elevated temperature and nutrition availability on the rates of root exudation and associated microbial processes. In this study, we performed an experiment in which in situ exudates were collected from Picea asperata seedlings that were transplanted in disturbed soils exposed to two levels of temperature (ambient temperature and infrared heater warming) and two nitrogen levels (unfertilized and 25 g N m^?2 a^?1). Here, we show that the trees exposed to an elevated temperature increased their exudation rates I (μg C g^?1 root biomass h^?1), II (μg C cm^?1 root length h^?1) and III (μg C cm^?2 root area h^?1) in the unfertilized plots. The altered morphological and physiological traits of the roots exposed to experimental warming could be responsible for this variation in root exudation. Moreover, these increases in root‐derived C were positively correlated with the microbial release of extracellular enzymes involved in the breakdown of organic N (R² = 0.790; P = 0.038), which was coupled with stimulated microbial activity and accelerated N transformations in the unfertilized soils. In contrast, the trees exposed to both experimental warming and N fertilization did not show increased exudation rates or soil enzyme activity, indicating that the stimulatory effects of experimental warming on root exudation depend on soil fertility. Collectively, our results provide preliminary evidence that an increase in the release of root exudates into the soil may be an important physiological adjustment by which the sustained growth responses of plants to experimental warming may be maintained via enhanced soil microbial activity and soil N transformation. Accordingly, the underlying mechanisms by which plant root‐microbe interactions influence soil organic matter decomposition and N cycling should be incorporated into climate‐carbon cycle models to determine reliable estimates of long‐term C storage in forests.     

Response of soil surface CO2 flux in a boreal forest to ecosystem warming

Soil surface carbon dioxide (CO₂) flux (R_S) was measured for 2 years at the Boreal Soil and Air Warming Experiment site near Thompson, MB, Canada. The experimental design was a complete random block design that consisted of four replicate blocks, with each block containing a 15 m × 15 m control and heated plot. Black spruce [Picea mariana (Mill.) BSP] was the overstory species and Epilobium angustifolium was the dominant understory. Soil temperature was maintained (～5 °C) above the control soil temperature using electric cables inside water filled polyethylene tubing for each heated plot. Air inside a 7.3‐m‐diameter chamber, centered in the soil warming plot, contained approximately nine black spruce trees was heated ～5 °C above control ambient air temperature allowing for the testing of soil‐only warming and soil+air warming. Soil surface CO₂ flux (R_S) was positively correlated (P < 0.0001) to soil temperature at 10 cm depth. Soil surface CO₂ flux (R_S) was 24% greater in the soil‐only warming than the control in 2004, but was only 11% greater in 2005, while R_S in the soil+air warming treatments was 31% less than the control in 2004 and 23% less in 2005. Live fine root mass (< 2 mm diameter) was less in the heated than control treatments in 2004 and statistically less (P < 0.01) in 2005. Similar root mass between the two heated treatments suggests that different heating methods (soil‐only vs. soil+air warming) can affect the rate of decomposition.     

Effects of in situ experimental air warming on the soil respiration in a coastal salt marsh reclaimed for agriculture

Background and Aims

The reclamation of natural salt marshes for agricultural use is expected to profoundly influence the effects of predicted global warming on the carbon balance of coastal areas globally. This study was undertaken to understand the potential for soil respiration changes in a disturbed coastal ecosystem under future atmospheric warming

Methods

An in situ simulated warming experiment was conducted in a reclaimed salt marsh on Chongming Island in the Yangtze Estuary, China. Open-top chambers (OTCs) were applied to simulate air-warming conditions.

Results

Based on the 2-year study, we found the following: (1) Averaged across the entire study period, the OTCs significantly increased the mean air temperature by 1.53?±?0.17 °C. (2) The air warming resulted in no significant stimulation of the mean soil respiration averaged across the entire study period. Warming had no significant effect on soil respiration in the growing season, but it markedly reduced soil respiration by 16 % in the non-growing season. (3) Air warming had no significant effect on the mean soil temperature or volumetric moisture at a 5 cm depth, but it increased the mean soil porewater salinity by 119 % averaged across the entire study period. (4) Air warming had no significant effect on total organic carbon, total nitrogen or the molar C/molar N ratio of the soil in the uppermost 10 cm layer during the 2 years of soil respiration measurement. The warming treatment also had no significant effect on aboveground biomass or fine root (<2 mm) density during the second year of soil respiration measurement. (5) Soil temperature accounted for 81.0 % and 79.0 % of the temporal variations of soil respiration in the control (CON) and elevated temperature (ET) plots, respectively. No significant correlation between soil volumetric moisture and soil respiration was observed in either CON or ET. Soil porewater salinity was positively correlated with soil respiration in CON, but such a positive correlation was not found in ET. No change of the temperature sensitivity of soil respiration (Q ₁₀ value) was observed.

Conclusions

Based on above results, we speculate that soil porewater salinity was the key factor controlling the effects of air warming on soil respiration in the reclaimed salt marsh. Our results suggest that an air warming of approximately 1.5 °C over the next few decades may not lead to a higher soil respiration in reclaimed salt marshes.