水分条件和冻融循环对科尔沁沙地不同土地利用方式土壤呼吸的影响

在东北半干旱地区的科尔沁沙地,秋冬与冬春季节由温度变化引起的土壤冻融对CO2排放具有显著影响,研究水分和冻融的交互作用对土壤呼吸的影响具有重要意义.以科尔沁沙地樟子松疏林草地、农田和草地为研究对象,通过冻融模拟实验分析水分和冻融循环对不同土地利用方式土壤呼吸的影响.结果表明,水分条件、土地利用方式和冻融循环均对土壤呼吸影响显著.冻融前草地土壤呼吸显著大于疏林草地和农田,冻融期疏林草地土壤呼吸显著大于农田,而冻融后草地土壤呼吸速率显著大于疏林草地.80％田间持水量时3种土地利用方式的土壤呼吸速率显著大于60％田间持水量时土壤呼吸速率;在培养期内(20 d),60％田间持水量时疏林草地、农田和草地的土壤CO2释放量分别为21.535、19.908和25.037 g CO2·m-2,80％田间持水量时分别为26.407、29.447和36.246g CO2·m-2.     

Effects of soil phosphorus availability,temperature and moisture on soil respiration in Eucalyptus pauciflora forest

Rates of soil respiration (CO₂ efflux) were measured for a year in a mature Eucalyptus pauciflora forest in unfertilized and phosphorus-fertilized plots. Soil CO₂ efflux showed a distinct seasonal trend, and average daily rates ranged from 124 to 574 mg CO₂ m^–2 hr^–1. Temperature and moisture are the main variables that cause variation in soil CO₂ efflux; hence their effects were investigated over a year so as to then differentiate the treatment effect of phosphorus (P) nutrition.Soil temperature had the greatest effect on CO₂ efflux and exhibited a highly significant logarithmic relationship (r² = 0.81). Periods of low soil and litter moisture occurred during summer when temperatures were greater than 10 °C, and this resulted in depression of soil CO₂ efflux. During winter, when temperatures were less than 10 °C, soil and litter moisture were consistently high and thus their variation had little effect on soil CO₂ efflux. A multiple regression model including soil temperature, and soil and litter moisture accounted for 97% of the variance in rates of CO₂ efflux, and thus can be used to predict soil CO₂ efflux at this site with high accuracy. Total annual efflux of carbon from soil was estimated to be 7.11 t C ha^–1 yr^–1. The model was used to predict changes in this annual flux if temperature and moisture conditions were altered. The extent to which coefficients of the model differ among sites and forest types requires testing.Increased soil P availability resulted in a large increase in stem growth of trees but a reduction in the rate of soil CO₂ efflux by approximately 8%. This reduction is suggested to be due to lower root activity resulting from reduced allocation of assimilate belowground. Root activity changed when P was added to microsites within plots, and via the whole tree root system at the plot level. These relationships of belowground carbon fluxes with temperature, moisture and nutrient availability provide essential information for understanding and predicting potential changes in forest ecosystems in response to land use management or climate change.     

Response of soil bacterial communities to moisture and grazing in the Tibetan alpine steppes on a small spatial scale

As the Third Pole of the world, the Tibetan Plateau provides a typical alpine grassland environment for soil bacteria with its unique frigid and arid climate. Owing to clear changes in spatial moisture and increased grazing intensity, moisture and livestock grazing have become key factors influencing the microbial communities. Accordingly, we investigated the diversity and composition of soil bacteria in a selected alpine grassland within the dual gradients of moisture and grazing using high-throughput sequencing. Our results showed that grazing changed the soil bacterial diversity and composition, whereas moisture only influenced the relative abundance of the segmental community at the small spatial scale. Species richness was found to be increased by moderate grazing compared with that by high or low-grazing intensity. The relative abundance of dominant species and β-diversity of soil bacteria both showed differences with heavy, moderate, and low grazing. Some dominant bacteria were altered with the moisture content. However, there were no significant differences according to the moisture gradient in terms of the overall bacterial β diversity and composition. These results might be taken account into the small spatial scale as well as the compensation of grazing to moisture on this scale. This work provides new insights into the soil bacterial response to moisture gradients and grazing intensity in alpine steppe habitat.     

模拟降雨对西双版纳热带次生林和橡胶林土壤呼吸的影响

降雨作为一个重要的环境因子,对土壤呼吸具有重要的影响。研究土壤呼吸与降雨的关系,对准确估算大气中的CO2含量具有重要意义。本研究通过人工模拟降雨事件,应用野外原位测定方法,测量了热带次生林和橡胶林土壤呼吸速率、地下5cm土壤温度和土壤含水量的变化,以探究热带两种主要植被类型的土壤呼吸、土壤温度、土壤含水量对旱季单次降雨事件的响应过程与规律。研究发现,在旱季连续一周没有降雨的情况下,人工模拟降雨事件使土壤呼吸在降雨后的2h内被迅速激发,次生林的土壤呼吸最大达到11.15 μmolCO2·m-2·s-1,是对照的近7倍;橡胶林的土壤呼吸最大达到了15.88 μmolCO2·m-2·s-1,是对照的近11倍。随后激发效应迅速降低,尤其是橡胶林,在人工模拟降雨6h后处理与对照间无显著差异。人工模拟降雨前两种林型的土壤含水量与对照相比均无显著性差异,人工模拟降雨后的2d内土壤含水量均显著高于对照;人工模拟降雨前后土壤温度与对照相比均无显著性差异。本研究结果支持了"Birch effect",2种主要热带林型在旱季时期,由于单次降雨事件激发而释放到大气中的CO2是降雨前的数倍。     

Spatio-temporal variation of rhizosphere soil microbial abundance and enzyme activities under different vegetation types in the coastal zone,Shandong, China

In coastal sandy soils, the establishment of a plant cover is fundamental to avoid degradation and desertification processes. A better understanding of the ability of plants to promote soil microbial process in these conditions is necessary for successful soil reclamation. The current study was to investigate the ability of four different plant species to regenerate the microbiological processes in the rhizosphere soil and to discuss which species were the most effective for the reclamation of the coastal zone. The rhizosphere soils were studied by measuring microbial abundance (bacteria, fungi, actinomycetes, and ammonifiers), enzyme activities (invertase, catalase, urease, and phosphatase) and their relationship. Microbial abundance greatly varied among rhizospheres of different plant species (p < 0.05). Phragmites australis supported the highest amount of bacterial, actinomycetes, and ammonifiers abundance, and Echinochloa crusgalli supported the highest fungi abundance. In addition, the significant differences in rhizosphere enzyme activities of different plant species were also observed. There was a significant linear correlation between rhizosphere soil microbial abundances and enzyme activities between bacteria and urease and between fungi and catalase, but no such significant relationship was found between all rhizosphere soil microbial abundance and phosphatases. It was concluded that different plant species in coastal areas have different rhizosphere soils due to the impact of the different root exudates and plant residues of the microbial properties. In addition, natural grasslands (P. australis and E. crusgalli) are the most effective for revegetating coastal sandy soils.     

不同温度条件下土壤水分对羊草幼苗生长特性的影响

采用生长箱控制方法,研究了羊草幼苗生长对5个温度和5个水分梯度的响应。结果表明,不同温度改变了羊草生物量对土壤水分变化的响应类型。在20～26℃下羊草植株生物量对土壤水分的响应曲线呈三次多项式或抛物线变化规律,而在29～32℃下为指数方程。在温度较低或适度时,轻度乃至中度干旱有促进生长的作用,但在温度较高时轻度干旱及比其程度更高的干旱显著地影响羊草的生长,表明羊草在较高温度下对水分更加敏感。在适当的温度下(26℃),羊草根的贡献率或根冠比与土壤水分呈直线关系。高温加强了干旱对羊草幼苗生长的抑制作用,表明高温降低了羊草对干旱的适应能力。     

Plant functional traits and soil microbial biomass in different vegetation zones on the Loess Plateau

Plant functional traits built the relationships between plant diversity, species composition, and physiology along with the environmental changes, thus influencing soil microbial community. As the sensitivity indicators, soil microbial biomass and plant functional traits responses soil micro-organism and plant characteristics in direct way. Ten plant functional traits of 149 species and soil microbial biomass (carbon, nitrogen, and phosphorus) were analyzed across the different vegetation types (forest, forest-steppe, and steppe) that are divided by environmental gradient (temperature and precipitation), aimed to find the correlations among them. Our results confirmed the greatest values of plant functional traits (except the leaf density and the fine root density) that were distributed in the steppe zone, mainly due to the different mean annual temperature and mean annual precipitation conditions. For different plant growth forms, the plant functional traits were significant differences among the vegetation zones. The advantages of higher rate nutrient cycling, plentiful biomass supplements, and favorite habit conditions lead to the forest-steppe zone with the highest C_mic and N_mic concentrations. The canonical correlation analysis indicated that leaf nitrogen, root nitrogen, and fine root densities were correlated with root exudate and tissue which affected the concentrations of soil organic carbon (SOC) and total nitrogen (N), consequently impacting soil microbial biomass carbon (C_mic) and soil microbial biomass nitrogen (N_mic). Soil is the medium that connects micro-organism and plant root system that influenced leaf nitrogen, root nitrogen, and fine root density of plant functional traits, the concentrations of SOC and total N that plant feedback are consequently influencing C_mic and N_mic.     

Estimation of carbon allocation to the roots from soil respiration measurements of oil palm

CO₂ flux from the soil was measured in situ under oil palms in southern Benin. The experimental design took into account the spatial variability of the root density, the organic matter in the soil-palm agrosystem and the effect of factors such as the soil temperature and moisture.Measurements of CO₂ release in situ, and a comparison with the results obtained in the laboratory from the same soil free of roots, provided an estimation of the roots contribution to the total CO₂ flux. The instantaneous values for total release in situ were between 3.2 and 10.0 mol CO₂ m^-2 s^-1. For frond pile zones rich in organic matter, and around oil palm trunks, root respiration accounted for 30% of the efflux when the soil was at field capacity and 80% when the soil was dry with a pF close to 4.2. This proportion remained constant in interrow zones at around 75%, irrespective of soil moisture.Subsequently carbon allocation to the roots was determined. Total CO₂ release over a year was 57 Mg of CO₂ ha^-1 yr^-1 (around 1610 g of C per m² per year), and carbon allocation to the roots was approximately 53 Mg of CO₂ ha^-1 yr^-1 of which approximately 13 Mg CO₂ ha^-1 yr^-1 (25%) was devoted to turn-over and 40 Mg CO₂ ha^-1 yr^-1 (75%) to respiration.     

Seasonal changes in the contribution of root respiration to total soil respiration in a cool-temperate deciduous forest

A trenching method was used to determine the contribution of root respiration to soil respiration. Soil respiration rates in a trenched plot (R _trench) and in a control plot (R _control) were measured from May 2000 to September 2001 by using an open-flow gas exchange system with an infrared gas analyser. The decomposition rate of dead roots (R _D) was estimated by using a root-bag method to correct the soil respiration measured from the trenched plots for the additional decaying root biomass. The soil respiration rates in the control plot increased from May (240–320 mg CO₂ m^–2 h^–1) to August (840–1150 mg CO₂ m^–2 h^–1) and then decreased during autumn (200–650 mg CO₂ m^–2 h^–1). The soil respiration rates in the trenched plot showed a similar pattern of seasonal change, but the rates were lower than in the control plot except during the 2 months following the trenching. Root respiration rate (R _r) and heterotrophic respiration rate (R _h) were estimated from R _control, R _trench, and R _D. We estimated that the contribution of R _r to total soil respiration in the growing season ranged from 27 to 71%. There was a significant relationship between R _h and soil temperature, whereas R _r had no significant correlation with soil temperature. The results suggest that the factors controlling the seasonal change of respiration differ between the two components of soil respiration, R _r and R _h.     

Effects of soil moisture content and temperature on methane uptake by grasslands on sandy soils

Aerobic grasslands may consume significant amounts of atmospheric methane (CH4). We aimed (i) to assess the spatial and temporal variability of net CH4 fluxes from grasslands on aerobic sandy soils, and (ii) to explain the variability in net CH4 fluxes by differences in soil moisture content and temperature. Net CH4 fluxes were measured with vented closed flux chambers at two sites with low N input on sandy soils in the Netherlands: (i) Wolfheze, a heather grassland, and (ii) Bovenbuurtse Weilanden, a grassland which is mown twice a year. Spatial variability of net CH4 fluxes was analysed using geostatistics. In incubation experiments, the effects of soil moisture content and temperature on CH4 uptake capacity were assessed. Temporal variability of net CH4 fluxes at Wolfheze was related to differences in soil temperature (r2 of 0.57) and soil moisture content (r2 of 0.73). Atmospheric CH4 uptake was highest at high soil temperatures and intermediate soil moisture contents. Spatial variability of net CH4 fluxes was high, both at Wolfheze and at Bovenbuurtse Weilanden. Incubation experiments showed that, at soil moisture contents lower than 5% (w/w), CH4 uptake was completely inhibited, probably due to physiological water stress of methanotrophs. At soil moisture contents higher than 50% (w/w), CH4 uptake was greatly reduced, probably due to the slow down of diffusive CH4 and O2 transport in the soil, which may have resulted in reduced CH4 oxidation and possibly some CH4 production. Optimum soil moisture contents for CH4 uptake were in the range of 20 – 35% (w/w), as prevailing in the field. The sensitivity of CH4 uptake to soil moisture content may result in short-term variability of net atmospheric CH4 uptake in response to precipitation and evapotranspiration, as well as in long-term variability due to changing precipitation patterns as a result of climate change.     

Response of soil respiration to soil temperature and moisture in a 50-year-old oriental arborvitae plantation in China

China possesses large areas of plantation forests which take up great quantities of carbon. However, studies on soil respiration in these plantation forests are rather scarce and their soil carbon flux remains an uncertainty. In this study, we used an automatic chamber system to measure soil surface flux of a 50-year-old mature plantation of Platycladus orientalis at Jiufeng Mountain, Beijing, China. Mean daily soil respiration rates (R(s)) ranged from 0.09 to 4.87 μmol CO(2) m(-2) s(-1), with the highest values observed in August and the lowest in the winter months. A logistic model gave the best fit to the relationship between hourly R(s) and soil temperature (T(s)), explaining 82% of the variation in R(s) over the annual cycle. The annual total of soil respiration estimated from the logistic model was 645±5 g C m(-2) year(-1). The performance of the logistic model was poorest during periods of high soil temperature or low soil volumetric water content (VWC), which limits the model's ability to predict the seasonal dynamics of R(s). The logistic model will potentially overestimate R(s) at high T(s) and low VWC. Seasonally, R(s) increased significantly and linearly with increasing VWC in May and July, in which VWC was low. In the months from August to November, inclusive, in which VWC was not limiting, R(s) showed a positively exponential relationship with T(s). The seasonal sensitivity of soil respiration to T(s) (Q(10)) ranged from 0.76 in May to 4.38 in October. It was suggested that soil temperature was the main determinant of soil respiration when soil water was not limiting.     

The effect of soil warming on bulk soil vs. rhizosphere respiration

There has been considerable debate on whether root/rhizosphere respiration or bulk soil respiration is more sensitive to long-term temperature changes. We investigated the response of belowground respiration to soil warming by 3 °C above ambient in bare soil plots and plots planted with wheat and maize. Initially, belowground respiration responded more to the soil warming in bare soil plots than in planted plots. However, as the growing season progressed, a greater soil-warming response developed in the planted plots as the contribution of root/rhizosphere respiration to belowground respiration declined. A negative correlation was observed between the contribution of root/rhizosphere respiration to total belowground respiration and the magnitude of the soil-warming response indicating that bulk soil respiration is more temperature sensitive than root/rhizosphere respiration. The dependence of root/rhizosphere respiration on substrate provision from photosynthesis is the most probable explanation for the observed lower temperature sensitivity of root/rhizosphere respiration. At harvest in late September, final crop biomass did not differ between the two soil temperature treatments in either the maize or wheat plots. Postharvest, flux measurements during the winter months indicated that the response of belowground respiration to the soil-warming treatment increased in magnitude (response equated to a Q ₁₀ value of 5.7 compared with ∼2.3 during the growing season). However, it appeared that this response was partly caused by a strong indirect effect of soil warming. When measurements were made at a common temperature, belowground respiration remained higher in the warmed subplots suggesting soil warming had maintained a more active microbial community through the winter months. It is proposed that any changes in winter temperatures, resulting from global warming, could alter the sink strength of terrestrial ecosystems considerably.     

Temperature and substrate controls on intra-annual variation in ecosystem respiration in two subarctic vegetation types

Arctic ecosystems are important in the context of climate change because they are expected to undergo the most rapid temperature increases, and could provide a globally significant release of CO₂ to the atmosphere from their extensive bulk soil organic carbon reserves. Understanding the relative contributions of bulk soil organic matter and plant‐associated carbon pools to ecosystem respiration is critical to predicting the response of arctic ecosystem net carbon balance to climate change. In this study, we determined the variation in ecosystem respiration rates from birch forest understory and heath tundra vegetation types in northern Sweden through a full annual cycle. We used a plant biomass removal treatment to differentiate bulk soil organic matter respiration from total ecosystem respiration in each vegetation type. Plant‐associated and bulk soil organic matter carbon pools each contributed significantly to ecosystem respiration during most phases of winter and summer in the two vegetation types. Ecosystem respiration rates through the year did not differ significantly between vegetation types despite substantial differences in biomass pools, soil depth and temperature regime. Most (76–92%) of the intra‐annual variation in ecosystem respiration rates from these two common mesic subarctic ecosystems was explained using a first‐order exponential equation relating respiration to substrate chemical quality and soil temperature. Removal of plants and their current year's litter significantly reduced the sensitivity of ecosystem respiration to intra‐annual variations in soil temperature for both vegetation types, indicating that respiration derived from recent plant carbon fixation was more temperature sensitive than respiration from bulk soil organic matter carbon stores. Accurate assessment of the potential for positive feedbacks from high‐latitude ecosystems to CO₂‐induced climate change will require the development of ecosystem‐level physiological models of net carbon exchange that differentiate the responses of major C pools, that account for effects of vegetation type, and that integrate over summer and winter seasons.     

华西雨屏区苦竹人工林土壤呼吸各组分特征及其温度敏感性

通过在华西雨屏区苦竹(Pleioblastus amarus)人工林内建立固定样地、定期监测等方法,研究该人工林生态系统土壤呼吸各组分特征及其温度敏感性.结果表明:2010年2月-2011年1月,苦竹林平均土壤呼吸速率为1.13 μmol·m-2·s-1,仲夏最高,深冬最低;凋落物层、无根土壤和植物根系对苦竹林土壤呼吸的贡献率分别为30.9％、20.8％和48.3％,各呼吸组分的季节动态均与土壤总呼吸类似,并与温度和凋落量等因素相关;苦竹林土壤总呼吸(RST)、凋落物层CO2排放(RSL)、无根土壤CO2排放(RSS)和植物根系呼吸(RSR)的年碳排放量分别为4.27、1.32、0.87和2.08 MgC· hm-2 ·a-1;土壤总呼吸及其各组分与凋落量呈显著正线性相关,与土壤10 cm温度和气温均呈显著正指数相关;基于土壤温度计算的RST、RSL、RSS和RSR的Q10值分别为2.90、2.28、3.09和3.19,凋落物层CO2排放的温度敏感性显著低于总呼吸和其他各组分.     

Large seasonal changes in Q10 of soil respiration in a beech forest

We analyzed one year of continuous soil respiration measurements to assess variations in the temperature sensitivity of soil respiration at a Danish beech forest. A single temperature function derived from all measurements across the year (Q₁₀ = 4.2) was adequate for estimating the total annual soil respiration and its seasonal evolution. However, Q₁₀'s derived from weekly datasets ranged between three in summer (at a mean soil temperature of 14 °C) and 23 in winter (at 2 °C), indicating that the annual temperature function underestimated the synoptic variations in soil respiration during winter. These results highlight that empirical models should be parameterized at a time resolution similar to that required by the output of the model. If the objective of the model is to simulate the total annual soil respiration rate, annual parameterization suffices. If however, soil respiration needs to be simulated over time periods from days to weeks, as is the case when soil respiration is compared to total ecosystem respiration during synoptic weather patterns, more short‐term parameterization is required. Despite the higher wintertime Q₁₀'s, the absolute response of soil respiration to temperature was smaller in winter than in summer. This is mainly because in absolute numbers, the temperature sensitivity of soil respiration depends not only on Q₁₀, but also on the rate of soil respiration, which is highly reduced in winter. Nonetheless, the Q₁₀ of soil respiration in winter was larger than can be explained by the decreasing respiration rate only. Because the seasonal changes in Q₁₀ were negatively correlated with temperature and positively correlated with soil moisture, they could also be related to changing temperature and/or soil moisture conditions.     

Response of ecosystem carbon exchange to warming and nitrogen addition during two hydrologically contrasting growing seasons in a temperate steppe

A large remaining source of uncertainty in global model predictions of future climate is how ecosystem carbon (C) cycle feedbacks to climate change. We conducted a field manipulative experiment of warming and nitrogen (N) addition in a temperate steppe in northern China during two contrasting hydrological growing seasons in 2006 [wet with total precipitation 11.2% above the long‐term mean (348 mm)] and 2007 (dry with total precipitation 46.7% below the long‐term mean). Irrespective of strong intra‐ and interannual variations in ecosystem C fluxes, responses of ecosystem C fluxes to warming and N addition did not change between the two growing seasons, suggesting independence of warming and N responses of net ecosystem C exchange (NEE) upon hydrological variations in the temperate steppe. Warming had no effect on NEE or its two components, gross ecosystem productivity (GEP) and ecosystem respiration (ER), whereas N addition stimulated GEP but did not affect ER, leading to positive responses of NEE. Similar responses of NEE between the two growing seasons were due to changes in both biotic and abiotic factors and their impacts on ER and GEP. In the wet growing season, NEE was positively correlated with soil moisture and forb biomass. Negative effects of warming‐induced water depletion could be ameliorated by higher forb biomass in the warmed plots. N addition increased forb biomass but did not affect soil moisture, leading to positive effect on NEE. In the dry growing season, NEE showed positive dependence on grass biomass but negative dependence on forb biomass. No changes in NEE in response to warming could result from water limitation on both GEP and ER as well as little responses of either grass or forb biomass. N addition stimulated grass biomass but reduced forb biomass, leading to the increase in NEE. Our findings highlight the importance of changes in abiotic (soil moisture, N availability) and biotic (growth of different plant functional types) in mediating the responses of NEE to climatic warming and N enrichment in the semiarid temperate steppe in northern China.     

Main determinants of forest soil respiration along an elevation/temperature gradient in the Italian Alps

The main determinants of soil respiration were investigated in 11 forest types distributed along an altitudinal and thermal gradient in the southern Italian Alps (altitudinal range 1520 m, range in mean annual temperature 7.8°C). Soil respiration, soil carbon content and principal stand characteristics were measured with standardized methods. Soil CO₂ fluxes were measured at each site every 15–20 days with a closed dynamic system (LI‐COR 6400) using soil collars from spring 2000 to spring 2002. At the same time, soil temperature at a depth of 10 cm and soil water content (m³ m^?3) were measured at each collar. Soil samples were collected to a depth of 30 cm and stones, root content and bulk density were determined in order to obtain reliable estimates of carbon content per unit area (kg C m^?2). Soil respiration and temperature data were fitted with a simple logistic model separately for each site, so that base respiration rates and mean annual soil respiration were estimated. Then the same regression model was applied to all sites simultaneously, with each model parameter being expressed as a linear function of site variables. The general model explained about 86% of the intersite variability of soil respiration. In particular, soil mean annual temperature explained the most of the variance of the model (0.41), followed by soil temperature interquartlile range (0.24), soil carbon content (0.16) and soil water content (0.05).     

鄂东南低丘马尾松林和枫香林土壤异养呼吸及温湿度敏感性

采用野外监测方法,研究了鄂东南低丘地区主要森林类型枫香林和马尾松林土壤异养呼吸、土壤温湿度的年动态;并通过室内试验研究了土壤呼吸随土壤深度的变化以及表层土壤(0～5 cm)异养呼吸的温湿度敏感性,建立了表层土壤异养呼吸的温湿度响应模型,探讨全球温暖化对该区土壤异养呼吸的潜在影响.结果表明:枫香林和马尾松林0～5 cm土壤呼吸速率分别是5～10 cm、10～15 cm层的2.39、2.62倍和2.01、2.94倍,说明土壤异养呼吸主要发生在土壤表层(0～5 cm);枫香林和马尾松林0～5 cm、5～10 cm及10～15 cm土壤的Q10分别是2.10、1.86、1.78和1.86、1.77、1.44;枫香林和马尾松林表层土壤呼吸对温度(T)的响应符合指数模型[R=αexp(βT)],对湿度(W)的响应符合二次函数模型(R=a+bW+cW2);0～5 cm土壤对温湿度双因子的响应符合lnR=a+bW+cW2+dT+eT2模型,且异养呼吸对湿度的响应具有温度依赖性,即在高温下敏感,低温下敏感性下降;应用表层土壤异养呼吸温湿度模型预测枫香林和马尾松林土壤异养呼吸年动态及总量,枫香林土壤异养呼吸量的模拟值比实测值略高...     

Differential responses of auto‐ and heterotrophic soil respiration to water and nitrogen addition in a semiarid temperate steppe

Evaluating how autotrophic (SR_A), heterotrophic (SR_H) and total soil respiration (SR_TOT) respond differently to changes of environmental factors is critical to get an understanding of ecosystem carbon (C) cycling and its feedback processes to climate change. A field experiment was conducted to examine the responses of SR_A and SR_H to water and nitrogen (N) addition in a temperate steppe in northern China during two hydrologically contrasting growing seasons. Water addition stimulated SR_A and SR_H in both years, and their increases were significantly greater in a dry year (2007) than in a wet year (2006). N addition increased SR_A in 2006 but not in 2007, while it decreased SR_H in both years, leading to a positive response of SR_TOT in 2006 but a negative one in 2007. The different responses of SR_A and SR_H indicate that it will be uncertain to predict soil C storage if SR_TOT is used instead of SR_H to estimate variations in soil C storage. Overall, N addition is likely to enhance soil C storage, while the impacts of water addition are determined by its relative effects on carbon input (plant growth) and SR_H. Antecedent water conditions played an important role in controlling responses of SR_A, SR_H and the consequent SR_TOT to water and N addition. Our findings highlight the predominance of hydrological conditions in regulating the responses of C cycling to global change in the semiarid temperate steppe of northern China.