中亚热带常绿阔叶林不同演替阶段土壤呼吸及其温度敏感性的变化

为探明中亚热带地区常绿阔叶林演替序列土壤呼吸(R_s)的变化趋势及其影响机制, 在福建省建瓯市万木林自然保护区选取演替时间分别为15年(演替初期)、47年(演替中期)和110年(演替后期)三个不同演替阶段, 进行了为期1年的野外原位观测。结果发现: 演替初期、中期和后期的R_s分别为2.38、3.32和3.91 µmol·m ^-2·s ^-1, 温度敏感性(Q₁₀值)分别为2.64、1.97和1.79; 与演替初期相比, 演替后期的R_s显著增加64.29%, Q₁₀值显著降低32.30%; 不同演替阶段R_s的季节变化模式相似, 温度和含水量可分别解释季节变化的69.5% (初期)、81.9% (中期)和61.3% (后期); 回归分析发现, R_s与凋落物年归还量、细根生物量和土壤全氮和土壤有机质碳含量显著正相关。表明本研究区内植被演替促进了土壤碳排放, 降低了土壤呼吸的温度敏感性; 土壤碳输入增加、养分含量的提高和细根生物量增大是中亚热带常绿阔叶林R_s随演替进程逐渐增大的主要原因。     

Effects of nitrogen addition on soil respiration of Rhododendron simsii shrubland in the subtropical mountainous areas of China

Aims As the second largest C flux between the atmosphere and terrestrial ecosystems, soil respiration plays a vital role in regulating atmosphere CO₂ concentration. Therefore, understanding the response of soil respiration to the increasing nitrogen deposition is urgently needed for prediction of future climate change. However, it is still unclear how nitrogen deposition influences soil respiration of shrubland in subtropical China. Our objectives were to explore the effects of different levels of nitrogen fertilization on soil respiration, root biomass increment, and litter biomass, and to analyze the relationships between soil respiration and soil temperature and moisture.
Methods From January 2013 to September 2014, we conducted a short-term simulated nitrogen deposition experiment in the Rhododendron simsii shrubland of Dawei Mountain, located in Hunan Province, southern China. Four levels of nitrogen addition treatments (each level with three replicates) were established: control (CK, no nitrogen addition), low nitrogen addition (LN, 2 g·m^-2·a^-1), medium nitrogen addition (MN, 5 g·m^-2·a^-1) and high nitrogen addition (HN, 10 g·m^-2·a^-1). Soil respiration was measured by LI-8100 soil CO₂ efflux system. At the same time, we measured root biomass increment and litter biomass in each plot.
Important findings Soil respiration exhibited a strong seasonal pattern, with the highest rates found in summer and the lowest rates in winter. Annual accumulative soil respiration rate in the CK, LN, MN and HN was (2.37 ± 0.39), (2.79 ± 0.42), (2.26 ± 0.38) and (2.30 ± 0.36) kg CO₂·m^-2, respectively. Annual mean soil respiration rate in the CK, LN, MN and HN was (1.71 ± 0.28), (2.01 ± 0.30), (1.63 ± 0.27) and (1.66 ± 0.26) μmol CO₂·m^-2·s^-1, respectively, and it was 17.25% higher in the LN treatment compared with CK (p = 0.06). The root biomass increment was increased by LN, MN, and HN treatments by 18.36%, 36.49% and 61.63%, respectively, compared to CK. The litter biomass was increased by LN, MN, and HN treatments by 35.87%, 22.17% and 15.35%, respectively, compared with CK. Soil respiration exhibited a significant exponential relationship with soil temperature (p < 0.01, R² is 0.77 to 0.82) and a significant linear relationship with soil moisture at the depth of 5 cm (p < 0.05, R² is 0.10 to 0.15). The temperature sensitivity (Q₁₀) value of CK, LN, MN and HN plots was 3.96, 3.60, 3.71 and 3.51, respectively. These results suggested that nitrogen addition promoted plant growth and decreased the temperature sensitivity of soil respiration. The increase of root biomass under N addition may be an important reason for the change of soil respiration in the study area.     

Soil C mineralization and temperature sensitivity in alpine grasslands of the Qinghai-Xizang Plateau

青藏高原具有独特的海拔、气候和生态系统类型, 弄清其土壤有机质分解及其温度敏感性对于揭示青藏高原土壤碳储量变化及其碳汇功能具有重要意义。该文利用青藏高原西北部草地的11个封育-自由放牧成对草地, 通过测定不同温度(5、10、15、20和25 ℃)培养下的土壤碳矿化速率, 探讨了土地利用方式对该地区土壤碳矿化及其温度敏感性的影响。实验结果表明: 温度对青藏高原高寒草地的土壤碳矿化具有显著影响, 温度越高土壤碳矿化量越大。从东至西, 土壤碳矿化量逐渐降低。草地土壤碳矿化量与土壤有机碳和土壤全氮含量显著正相关; 即土壤有机碳和土壤全氮含量越高, 土壤碳矿化量就越高。土地利用方式对土壤碳矿化的温度敏感性(Q₁₀)无显著影响, Q₁₀值变化范围为1.4-2.4; 其中, 放牧草地Q₁₀的平均值为1.83, 封育草地Q₁₀的平均值为1.86。此外, Q₁₀与土壤有机碳和土壤全氮含量无显著的相关关系, 也无明显的空间格局。放牧和封育对青藏高原高寒草地土壤碳矿化的温度敏感性无显著影响, 为深入分析青藏高原土壤碳汇功能及其对未来气温升高的响应提供了重要的理论依据。     

Effects of tree species on soil organic carbon density: A common garden experiment of five temperate tree species

Aims Forest trees alter litter inputs, turnover and rhizospheric activities, modify soil physical, chemical and biological properties, and consequently affect soil organic carbon (SOC) storage and carbon sink strength. That how to select appropriate tree species in afforestation, reforestation and management practices is critical to enhancing forest carbon sequestration. The objective of this study was to determine the effects of tree species on SOC density and vertical distributions.Methods A common garden experiment with the same climate, soil, and management history was established in Maoershan Forest Ecosystem Station, Northeast China, in 2004. The experimental design was a completely randomized arrangement with twenty 25 m × 25 m plots, consisting of monocultures of five tree species, including white birch (Betula platyphylla), Manchurian walnut (Juglans mandshurica), Manchurian ash (Fraxinus mandshurica), Dahurian larch (Larix gmelinii), and Mongolian pine (Pinus sylvestris var. mongolica), each with four replicated plots. A decade after the establishment (2013-2014), we measured carbon density and related factors (i.e., bulk density, total nitrogen concentration, microbial biomass carbon, microbial biomass nitrogen, pH value) in soils of the 0-40 cm depth for these monocultures. Important findings Results showed that tree species significantly influenced the SOC density in the 0-40 cm depth (p < 0.05). SOC density in the 0-10 cm depth varied from 2.79 to 3.08 kg·m^-2, in the order of walnut > ash> birch > larch > pine, in the 10-20 cm depth from 1.56 to 2.19 kg·m^-2, in the order of pine > walnut > ash > birch > larch, in the 20-30 cm depth from 1.17 to 2.10 kg·m^-2, and in the 20-40 cm depth from 0.84 to 1.43 kg·m^-2. The greatest SOC density occurred in the birch stands in the 20-40 cm depth. The vertical distributions of SOC density varied with tree species. The percentage of SOC in the 0-10 cm depth over the total SOC in the soil profile was significantly higher in the walnut and larch stands than in others, while the percentage of SOC in the 20-40 cm depth over the total SOC was highest in the birch stands. SOC concentration and soil bulk density differed significantly among the stands of different tree species, and were negatively correlated. SOC density was positively correlated with soil microbial biomass and soil pH in the walnut, ash, and larch stands, and with total nitrogen density in all the stands. We conclude that tree species modifies soil properties and microbial activity, thereby influencing SOC density, and that different patterns of vertical distributions of SOC density among monocultures of different tree species may be attributed to varying SOC controls at each soil depth.     

Allocation of mass and stability of soil aggregate in different types of Nei Mongol grasslands

Aims Soil aggregate is an important component of soil structure, playing an important role in the physical and biological protection mechanism of soil organic carbon (SOC) through isolating SOC from microorganisms. As far as we know, there are few studies, however, on exploring the spatial distribution of soil aggregate at the regional scale. Our objective was to investigate the mass allocation and stability of soil aggregate in different types of Nei Mongol grasslands. Methods We have established 78 sites with a size of 10 m × 10 m across the transect of Nei Mongol grasslands and collected soil samples from different soil depth up to 1 m. We used wet sieving method to separate different sizes of aggregate partition and used mean mass diameter (MMD) and geometric mean diameter (GMD) in order to evaluate the stability of soil aggregate. The two-way ANOVA was used to test the difference of mass percentage and stability of soil aggregate in different grassland types and soil depths. In addition, a linear regression analysis was used to analyze the correlations of mass percentage and stability of soil aggregate with both mean annual precipitation (MAP) and mean annual temperature (MAT). Important findings The results showed that the mass percentages of soil aggregate were highest in meadow steppe, while almost equal in typical steppe and desert steppe. However, no significant patterns were found along the soil depth. The mass percentage of soil aggregate fractions were positively correlated with MAP in all soil layers, but negatively correlated with MAT except the layer of 70-100 cm. For the stability of soil aggregate, at 0-10 and 10-20 cm, MMD and GMD of meadow steppe were significantly greater than those of typical and desert steppes, whereas no significant differences among three grassland types were found for other soil layers. Besides, MMD and GMD in meadow steppe and typical steppe gradually decreased along the soil depth.     

Responses of soil moisture to precipitation pattern change in semiarid grasslands in Nei Mongol,China

Aims Under global climate change, precipitation patterns were predicted to change with larger seasonal and annual variations and more extreme events in the semiarid regions of northern China. Water availability is one of the key limited factors in semiarid grasslands. Changes in precipitation patterns will inevitably affect ecosystem structure and function through soil water condition. Our objective was to investigate the response of soil water content to changes of precipitation pattern, especially its pulse response to precipitation events.
Methods Two semiarid steppe sites (Duolun and Xilinhot) in Nei Mongol were chosen and meteorological stations were installed to monitor precipitation and soil volumetric water content (VWC) at five soil depths (0-10 cm, 10 cm, 20 cm, 30 cm, 50 cm) from 2006 to 2013. The pulse response of VWC at 0-10 cm to an individual precipitation event was simulated by an exponential equation.
Important findings Significant seasonal and inter-annual variations of VWC were observed at the Duolun and Xilinhot sites. VWC at 50 cm soil layer in Xilinhot showed an obvious increase during the early spring due to the influences of snow melting. Mean surface (0-10 cm soil layer) VWC was significantly correlated with annual precipitation across eight years, but VWC in the deeper soil layers (10-50 cm) were not impacted by precipitation. We also found that the precipitation event larger than 2 mm could induce a significant increase in surface (0-10 cm soil layer) VWC, and could be regarded as an effective precipitation in this region. The maximum increment of surface VWC after the events and lasting time (T_lasting) were determined by the event size, while showed negatively linear correlations with the initial soil water content before the events. Vegetation development (leaf area index) did not show significant impacts on the responses of surface soil moisture to precipitation pulses. The infiltration depth of rain water was also determined by rain size and pre-event soil moisture. In average, soil water can infiltrate 1.06 cm and 0.79 cm deeper in Duolun and Xilinhot with 1 mm more precipitation, respectively. Therefore, our results suggest that the event size and pre-event soil moisture were the most important factors affecting response patterns of soil moisture to rain events in semiarid ecosystems.     

Stoichiometric characteristics of carbon,nitrogen and phosphorus in Phyllostachys edulis forests of China

Aims Stoichiometric ratios of carbon (C), nitrogen (N) and phosphorus (P) are important characteristics of the ecological processes and functions. Studies on population ecological stoichiometry can refine the content of flora chemometrics, determine the limited nutrient, and provide data for process-based modeling over large scale. Phyllostachys edulis is an important forest type, whose area accounts for 74% of total bamboo forest area in Southern China. However, little is known about the ecological stoichiometric in P. edulis. This study aimed to reveal C:N, C:P and N:P stoichiometry characteristics of the “plant-soil-litter” continuum and to provide a better understanding nutrient cycling and stability mechanisms in P. edulis forest in China. Methods The data were collected from the published literature containing C、N、P content in leaf or surface soil (0-20 cm) or littefall in P. edulis forests. Important findings 1) The leaf C, N, P content were estimated at 478.30 mg·g^-1, 22.20 mg·g^-1, 1.90 mg·g^-1 in P. edulis, and the corresponding C: N, C: P and N: P were 26.80, 299.60 and 14.40, respectively. Soil C, N, and P content in 0-20 cm were 21.53 mg·g^-1, 1.66 mg·g^-1, 0.41 mg·g^-1, with ratios of 14.20 for C:N, 66.74 for C:P and 4.28 for N:P. The C, N and P contents were 438.49 mg·g^-1, 13.39 mg·g^-1, 0.86 mg·g^-1 for litterfall, with the litter C:N, C:P and N:P being 25.53, 665.67, 22.55, respectively. 2) In the plant-soil-litter system in P. edulis forest, leaf had higher C:N, litter had higher C:P and N:P, while soil were the lowest. The N, P resorption rate was 39.68% and 54.74%, indicating that P. edulis forest growth and development was constrained by P or by both of N and P in China. 3) N content and N:P in leaf showed a tendency to increase with latitude, while the C:N of leaf declined with latitude. N:P of leaf increased with longitude, but the P content and the C:N of leaf showed a opposite trend. C: N of soil increased with longitude, whereas the N content of soil declined longitude. The N content of litter declined with longitude. 4) The leaf N content was negatively correlated with mean annual temperature and mean annual precipitation, but being more sensitive to temperature than precipitation. The positive correlations between N content and latitude support “Temperature-Plant Physiological” hypothesis, reflecting an adaptive strategy to environmental conditions.     

Responses of soil extracellular enzyme activities to carbon input alteration and warming in a subtropical evergreen broad-leaved forest

土壤胞外酶来源于土壤微生物、植物和动物, 是土壤生物地球化学过程的积极参与者, 在森林生态系统的物质循环和能量流动过程中扮演着重要角色。为探明土壤胞外酶活性对碳输入变化及增温的响应, 该研究基于长期增温、去除地表凋落物(以下简称去凋)和切根处理的云南哀牢山亚热带常绿阔叶林控制实验平台, 研究了不同处理(对照、去凋、切根、切根并增温)下表层矿质土壤(0-5和5-10 cm)与碳氮磷获取相关的胞外酶活性, 包括多酚氧化酶(POX)、过氧化物酶(PER)、β-葡萄糖苷酶(BG)、β-1,4-N-乙酰氨基葡萄糖苷酶(NAG)和酸性磷酸酶(AP)。结合铵态氮(NH₄⁺-N)含量、硝态氮(NO₃^--N)含量、溶解有机碳(DOC)含量、溶解总氮(DN)含量、土壤含水量(SWC)等相关指标, 探讨凋落物碳输入、根系碳输入和温度变化对土壤胞外酶活性及其生态化学计量特征的影响。研究结果表明: 在对照样方, 除POX外其余酶活性均为0-5 cm层显著高于5-10 cm层。与对照相比, 长期的凋落物去除显著降低了0-5 cm层土壤AP和BG活性, 对NAG、PER和POX活性则无显著影响; 长期切根处理显著降低了0-5 cm层土壤BG活性, 但提高了两个土层PER活性; 长期切根并增温处理显著降低了0-5 cm层AP和BG活性, 对其余酶活性无显著影响。冗余分析结果显示SWC和NH₄⁺-N含量是驱动土壤酶活性变化的重要因子。本研究为该生态系统土壤碳氮磷生物地球化学关键过程对全球变化的响应提供了土壤酶学的依据。     

Soil organic carbon density and influencing factors in tropical virgin forests of Hainan Island,China

Aims
Estimating soil organic carbon (SOC) density and influence factors of tropical virgin forests in Hainan Island provide new insight in basic data for SOC pool estimation and its dynamics study.
Methods
The main distribution areas of tropical virgin forests in Jianfengling (JFL), Bawangling (BWL), Wu- zhishan (WZS), Diaoluoshan (DLS), Yinggeling (YGL) of Hainan Island were selected, and soil samples (0-100 cm) were sampled and analyzed. SOC density was estimated by soil vertical fitting method and soil stratification method to discover the distribution characteristics of soil organic carbon in tropical virgin forests of Hainan Island.
Important findings
Results showed that: (1) The average SOC density using soil vertical fitting method in JFL, BWL, WZS, DLS and YGL was 14.98, 18.46, 16.48, 18.81, 16.66 kg·m^-2, respectively, which was significantly higher (p < 0.05) than the estimated average SOC density using soil stratification method in these areas (14.73, 16.24, 15.50, 16.91, 15.03 kg·m^-2, respectively). It is better to use soil vertical fitting method for SOC density estimation when the soil was natural without disturbance. (2) The proportion of SOC content in the first 0-30 cm depth interval out of SOC in the whole 0-100 cm soil profiles in JFL, BWL, WZS, DLS and YGL was 50.50%, 48.56%, 43.49%, 47.37%, 42.88%, respectively. (3) SOC density was significantly negative correlated with Shannon-Wiener index, Simpson index, species richness, and soil bulk density; and was significantly positive correlated with altitude, soil porosity, and soil nitrogen. However, SOC density was not significantly correlated to slope, biomass, average diameter at breast height, or average height. (4) Our study area Hainan was located in low latitude area with high rainfall and high temperature, which accelerated the decomposition of organic matter and nutrient recycling, resulting in significantly lower SOC densities in this tropical virgin forests of Hainan Island than the average value in China.     

Characteristics of soil water distribution and evaluation of recharge rate under different grazing history in the Xilin Gol Steppe

由人类活动所导致的锡林郭勒草原草场退化、土地沙化等问题日趋严重, 区域土壤水资源评价及其科学管理显得尤为重要。为确定锡林郭勒典型草原不同放牧条件对深层土壤剖面水分动态及降水入渗补给的影响, 选取1979年以来禁牧(UG79)、1999年以来禁牧(UG99)和持续放牧(CG) 3个小区6个土壤剖面, 基于不同深度土层的质量含水量、Cl ^-浓度等数据, 分析了放牧对深层土壤水分特征的影响, 且利用氯质量平衡法估算了降水入渗补给量。结果表明: 1)禁牧可以提高土壤含水量, 且禁牧时间越长, 效果越显著, 尤以表层最为明显。整个土壤剖面(0-5 m)土壤质量含水量的平均值表现为UG79 > UG99 > CG, 但各处理间差异不显著; 0-2 m UG79处理土壤剖面质量含水量分别比UG99和CG处理高26.6%和33.7%, 储水量分别高87.19 mm和82.52 mm, 且UG79处理与UG99、CG差异显著, 但UG99与CG之间差异不显著; 除局部地区受土壤颗粒组成影响含水量不同外, 各处理2-5 m土层含水量和储水量差异较小; 2)不同处理土壤含水量影响因素不同, 0-2 m土层含水量主要受地表植被状况和土壤性质的综合影响, 而2-5 m土层则主要受土壤颗粒组成的影响, 但随着禁牧年限的增加, 土壤有机质(SOM)含量对土壤水分的影响越来越大。UG79整个土壤剖面含水量与土壤颗粒含量和SOM含量呈极显著相关关系, UG99与CG处理0-2 m含水量与SOM含量呈极显著相关关系, 2-5 m土壤含水量与土壤颗粒含量呈极显著相关关系, 而与SOM含量相关性不显著; 3)氯质量平衡法估算得出年降水入渗补给率为UG79 > UG99 > CG, 35年和15年禁牧分别将降水入渗补给率提高了130.2%和44.5%; 考虑干沉降的不确定性, 研究区年降水入渗补给率为1.95-7.61 mm·a ^-1, 仅占年降水量的0.55%-2.13%。总之, 禁牧能够增加土壤含水量和储水量, 增加降水对土壤水分的补给, 但降水不是该区地下水的主要补给源。     

Early responses of vegetation and soil organic carbon to waterlogging and winter wildfire on abandoned red paddy soils

为了探明积水和冬季火烧对弃耕红壤稻田地表植被和土壤有机碳的影响, 该实验设置了对照(无人为干扰)、积水、冬季火烧和积水-冬季火烧4个不同处理, 采用样方法对样地植物的高度、密度、盖度及物种组成进行了调查。地上部分生物量采用收获法进行测定, 根系采用土柱法获取, 弃耕前后土壤有机碳含量的测定采用K₂Cr₂O₇外加热法。结果表明: 1)积水和冬季火烧对红壤稻田弃耕早期物种组成、丰富度、均匀度及多样性具有重要的影响。双穗雀稗(Paspalum paspaloides)和水竹叶(Murdannia triquetra)是积水条件下的优势种, 而柔枝莠竹(Microstegium vimineum)是冬季火烧条件下的优势种, 大狼杷草(Bidens frondosa)是积水和冬季火烧条件下的共优种。2)分布在0-5 cm表层土壤中的根系占0-20 cm深度土壤中根系的66.50%-80.34%。样地在积水条件下, 2011-2013年0-20 cm深度的土壤根系生物量分别高出对照样地的49.84%、73.34%和28.94%。3)冬季火烧可以提高样地的物种多样性和增加地上部分生物量, 2011-2013年冬季火烧样地分别高出对照样地的25.74%、64.30%和50.24%。4)与稻田弃耕前土壤有机碳含量逐渐上升趋势相反, 稻田弃耕6年后, 对照、积水、冬季火烧和积水-冬季火烧样地中土壤有机碳含量分别降低11.16%、18.99%、9.17%和19.12%, 并且在积水条件下土壤有机碳含量降低更明显(p < 0.05)。研究结果表明, 红壤稻田弃耕后地表植被物种组成、地上和地下生物量、土壤有机碳含量与积水和冬季火烧关系密切(p < 0.05)。     

Soil respiration features of mountain meadows under four typical land use types in Zhaosu Basin

为探讨不同土地利用方式对新疆昭苏天山北坡山地草甸土壤呼吸速率的影响, 于2015年和2016年的4月底至9月初, 用土壤呼吸测量仪对补播草地(RG)、豆禾混播草地(LG)、围封草地(NG)和农田(CR)的土壤呼吸进行测定, 并分析了影响土壤呼吸速率的土壤生物和水热因子。结果表明: 1)土壤呼吸速率在2015年NG和CR呈现双峰值, RG和LG呈现单峰曲线, 各处理均在8月达到最大值。2016年各处理峰值出现的时间不同, RG和LG在6月底达到最大值, NG和CR在7月底达到最大值; 监测期内平均土壤呼吸速率由大到小依次为: NG > RG > CR > LG。2)各样地土壤呼吸速率与土壤温度呈指数正相关关系; 土壤含水量与土壤呼吸的关系可能由于此地段常年湿润, 土壤含水量较高, 从而抑制土壤呼吸, 土壤呼吸与土壤体积含水量呈线性负相关关系; 土壤呼吸的温度敏感指数(Q₁₀)大小为NG > CR > RG > LG。3)不同处理的土壤微生物以细菌为主, 放线菌次之, 真菌居第三, 各样地总微生物生物量为: NG > RG > CR > LG, 与各样地平均土壤呼吸速率大小一致, 拟合分析显示RG土壤呼吸与放线菌呈显著的线性相关关系, LG土壤呼吸与细菌和放线菌呈显著线性相关关系。不同处理微生物生物量碳平均含量为CR > NG > LG > RG, 拟合分析显示RG与CR的土壤呼吸速率与微生物生物量碳呈显著线性相关关系, 其中CR的土壤呼吸速率与微生物生物量碳极显著相关; 4)各样地酶活性与土壤呼吸的相关关系分析显示, 只有蛋白酶和蔗糖酶与土壤呼吸有相关关系, 而蔗糖酶对土壤呼吸的影响更大。豆禾混播草地和补播草地相对于围封草地和农田, 土壤呼吸速率显著降低, 草地土壤的固碳能力显著提高。     

中亚热带森林土壤微生物群落多样性随海拔梯度的变化

运用Biolog EcoPlate技术, 对武夷山不同海拔植被带(常绿阔叶林(EBF)、针叶林(CF)、亚高山矮林(DF)、高山草甸(AM))土壤微生物群落多样性差异进行了研究。结果表明: 不同海拔植被带土壤微生物群落功能多样性差异显著。土壤平均颜色变化率(AWCD)随培养时间延长而逐渐增加, 同一深度土层的AWCD值随海拔升高而逐渐降低, 大小顺序依次为EFB > CF > DF > AM。同一海拔植被带, 不同深度土层的AWCD值总体趋势依次为0-10 cm > 10-25 cm > 25-40 cm。土壤微生物群落Simpson指数、Shannon-Wiener指数、丰富度指数和McIntosh指数的总体趋势为EBF最高, CF和DF次之, AM最低。不同海拔植被带土壤微生物对不同碳源利用强度存在较大差异, 其中EBF利用率最高, AM利用率最低, 碳水化合物和羧酸类碳源是各海拔植被带土壤微生物的主要碳源。主成分分析结果表明, 从31个因素中提取的与碳源利用相关的主成分1、主成分2分别能解释变量方差的75.27%和16.14%, 在主成分分离中起主要贡献作用的是胺类和氨基酸类碳源。土壤微生物群落多样性随着海拔上升、土层加深而逐渐下降的原因, 可能是生物量、林分凋落物、土壤养分、微小动物、植物根系等多种因素共同作用的结果。     

氮硅添加对青藏高原高寒草甸土壤氮矿化的影响

为了解全球气候变化背景下氮沉降对土壤氮矿化的影响及硅添加对土壤氮矿化的促进作用, 该试验设置不同浓度的氮肥单独添加(0、20、40、60 g·m ^-2, 分别为对照CK、N20、N40、N60)以及与硅肥配施(硅酸4 g·m ^-2, Si4), 测定不同处理下0-20、20-40、40-60 cm土层土壤硝态氮含量、铵态氮含量、净硝化速率、净氨化速率以及净矿化速率。结果显示: (1)单独添加氮肥, 各土层土壤硝态氮和铵态氮含量均随处理浓度的增加而增加, 0-20 cm土层N20、N40、N60处理下土壤硝态氮和铵态氮分别较CK增加63.48%、126.04%、247.03%和80.66%、152.52%、244.56%; 随着土层深度增加, 土壤硝态氮、铵态氮含量均有下降, 20-40、40-60 cm土层较0-20 cm土层硝态氮含量分别平均减少53.90%、76.05%, 铵态氮含量分别平均减少48.62%、68.23%。(2)土壤净硝化速率、净氨化速率及净矿化速率随着氮肥浓度增加均呈上升趋势。相同氮肥添加浓度下, 土壤净硝化速率、净氨化速率和净矿化速率随着土层深度增加逐渐下降(除CK外)。(3)与单独添加氮肥比较, 氮硅肥配施, 土壤氮含量有显著提高, 在0-20 cm土层硝态氮和铵态氮较CK分别增加98.78%、192.62%、330.16%和99.96%、195.82%、306.32%, 20-40、40-60 cm土层也有类似趋势。同时, 氮硅配施促进了土壤氮矿化行为, 在0-20 cm土层, N60Si4处理下的土壤净硝化速率、净氨化速率较单独施氮时分别增加35.88%、27.41%。以上结果表明, 与单独氮肥添加相比, 氮硅配施不但能提高土壤氮含量, 而且能促进土壤氮的矿化作用, 对大气氮沉降有一定的缓解作用。     

Geostatistical analysis of spatial variations in leaf traits of woody plants in Tiantong,Zhejiang Province

AimsExploring spatial variations in leaf traits and their relationships with environmental properties is crucial for understanding plant adaptation strategies and community assembly. This study aimed to reveal how leaf traits varied spatially and the role of environmental factors.MethodsThe study was conducted in a 5-hm² forest plot in Tiantong, Zhejiang Province. Three leaf traits, including individual leaf area (ILA), specific leaf area (SLA), and leaf dry matter content (LDMC) were measured for 20253 individual trees with diameter at breast height (DBH) ≥1 cm. Soil properties measured included contents of soil total nitrogen, soil total phosphorus, soil total carbon, soil pH value, soil volumetric water content, bulk density, and humus depth. Topographic variables measured included elevation, slope and convexity. We used geostatistical analysis to reveal spatial variations of the three leaf traits. Relationships between leaf variability and environmental factors were analyzed using principal component analysis (PCA) and Pearson’s correlation.Important findings Spatial variability followed the order of ILA > SLA > LDMC. Spatial autocorrelation of three leaf traits was weak within a distance of 5.16 m. The optimal model of the semi-variogram function was Gaussian model for ILA, and exponential model for SLA and LDMC. ILA showed the largest variability at the direction of northeast-southwest, and smallest variability at the direction of northwest-southeast. In contrast, SLA and LDMC had the highest variability at the direction of northwest-southeast and least variability at the direction of northeast-southwest. There were significantly negative relationships between ILA and topographic factors (r = -0.12, p < 0.0001), and between SLA and soil nutrients (r = -0.16, p < 0.0001). In contrast, LDMC was positively correlated with soil nutrients (r = 0.13, p < 0.0001). Relative to soil nutrients, topographic factors affected much more variations in ILA, SLA and LDMC at the direction of northeast-southwest. Distinctly, at the direction of northwest-southeast, variability of ILA was affected mainly by topographic factors, while soil nutrients resulted in the most variability of SLA and LDMC. In conclusion, leaf traits varied considerably with spatial direction in the studied forest plot. Associations between leaf traits and topographic factors and soil nutrients indirectly indicated effects of environmental filtering on community assembly.     

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。     

东北温带次生林与落叶松人工林的土壤呼吸

2006年5—10月,使用Li-6400-09土壤呼吸系统测定了黑龙江省帽儿山地区温带次生林转化为落叶松人工林后土壤呼吸速率(Rs)的变化.结果表明:次生林与落叶松人工林土壤呼吸速率的日变化均呈单峰型曲线,与地温的日变化趋势相似.测定期间内,次生林和落叶松人工林Rs的变化范围分别为0.43~7.26μmol CO2.m-2.s-1和0.63~4.70μmol CO2.m-2.s-1,最大值出现在7—8月,最小值出现在10月.5—8月,次生林的Rs明显高于落叶松人工林.次生林和落叶松人工林枯落物层呼吸速率的季节变化范围分别为-0.65~1.26μmol CO2.m-2.s-1和-0.43~0.47μmol CO2.m-2.s-1.两林分中的Rs与土壤温度均呈明显的指数相关,且与5 cm深地温相关最紧密.用5 cm地温估算的次生林和落叶松人工林Q10分别为3.61和3.07.次生林的Rs与10~20 cm土壤含水率相关显著,而落叶松人工林的Rs与土壤含水率无明显相关.     

戈壁灌丛堆周边地表土壤颗粒的空间异质特征

研究戈壁地区单个灌丛及其下沙堆这一有机整体对周边土壤风蚀的抑制能力, 对加强相关地区的植被类型及其空间配置格局的防沙效应研究十分重要, 可为荒漠化监测的评价和制定科学的防治措施提供参考。该文利用数字图像处理技术, 获取吉兰泰盐湖北部戈壁上单个白刺(Nitraria tangutorum)灌丛沙堆和沙冬青(Ammopiptanthus mongolicus)灌丛沙堆周边地表不同土壤风蚀颗粒的百分含量; 并采用经典描述性统计及地统计学方法, 对各类土壤风蚀颗粒百分含量的水平空间异质性进行分析。结果表明: (1)灌丛基部和下风向是细物质积累区, 以灌丛堆为中心向外, <0.42 mm的细颗粒含量呈减少趋势; 而且细物质积累的最大值出现在白刺灌丛的迎风侧附近, 沙冬青样地则相反, 出现在灌丛的背风侧附近。在沙源物质有限的戈壁中, 白刺的防风固沙作用集中体现在灌丛附近, 其水平空间尺度范围不及沙冬青, 这亦是白刺样地粗粒化程度高于沙冬青样地的原因。(2)白刺和沙冬青灌丛附近地表中粒径>0.84 mm (不可蚀)、0.84-0.42 mm (半可蚀)及<0.42 mm (高度可蚀)颗粒的空间异质性尺度分别为17.80 m、66.63 m、8.41 m和9.82 m、15.33 m、14.91 m, 均超出了灌丛冠幅覆盖范围, 空间自相关部分比例C/(C₀ + C)在63.40%-99.96%之间, 由此推断灌丛沙堆附近的风沙流特征是造成相应尺度内土壤颗粒空间异质性的主要因子。(3)高度可蚀颗粒的空间异质性尺度略大于灌丛平均间距(8.77 m包括灌丛半径), 从防止土壤风蚀来看, 这说明研究区内的建群种灌丛间存在一定程度的相互促进关系, 有利于该区植被的稳定与发展。     

Changes of the relationships between soil and microbes in carbon,nitrogen and phosphorus stoichiometry during ecosystem succession

AimsThe carbon (C), nitrogen (N) and phosphorus (P) stoichiometry (C:N:P) of soil profoundly influences the growth, community structure, biomass C:N:P stoichiometry, and metabolism in microbes. However, the relationships between soil and microbes in the C:N:P stoichiometry and their temporal dynamics during ecosystem succession are poorly understood. The aim of this study was to determine the temporal patterns of soil and microbial C:N:P stoichiometry and their relationships during ecosystem succession.MethodsAn extensive literature search was conducted and data were compiled for 19 age sequences of successional ecosystems, including 13 forest ecosystems and 6 grassland ecosystems, from 18 studies published up to May 2016. Meta-analyses were performed to examine the sequential changes in 18 variables that were associated with soil and microbial C, N and P contents and the stoichiometry. Important findings (1) There was no consistent temporal pattern in soil C:N along the successional stages, whereas the soil C:P and N:P increased with succession; the slopes of the linear relationships between soil C:N:P stoichiometry and successional age were negatively correlated with the initial content of the soil organic C within given chronosequence. (2) There was no consistent temporal pattern in microbial C:N:P stoichiometry along the successional stages. (3) The fraction of microbial biomass C in soil organic C (qMBC), the fraction of microbial biomass N in soil total N, and the fraction of microbial biomass P in soil total P all increased significantly with succession, in consistency with the theory of succession that ecosystem biomass per unit resource increases with succession. (4) The qMBC decreased with increases in the values of soil C:N, C:P, or N:P, as well as the stoichiometric imbalances in C:N, C:P, and N:P between soil and microbes (i.e., ratios of soil C:N, C:P, and N:P to microbial biomass C:N, C:P, and N:P, respectively). The C:N, C:P, and N:P stoichiometric imbalances explained 37%-57% variations in the qMBC, about 7-17 times more than that explainable by the successional age, illustrating the importance of soil-microbial C:N:P stoichiometry in shaping the successional dynamics in qMBC. In summary, our study highlights the importance of the theories of ecosystem succession and stoichiometry in soil microbial studies, and suggests that appropriately applying macro-ecological theories in microbial studies may improve our understanding on microbial ecological processes.     

北方农牧交错带温性盐碱化草地土壤呼吸对不同形态氮添加和刈割的响应

农牧交错带草地生态系统兼受农业和牧业的影响, 属于脆弱生态系统, 尤其是养分贫瘠的盐碱化草地, 其生态系统结构和功能对外界干扰的响应更加强烈。位于晋西北地区的农牧交错带盐碱化草地, 地理位置独特, 区别于天然牧区草地生态系统。由于毗邻农田, 农业氮肥的过量使用促进了活性氮气体排放, 同时使得农牧交错带草地土壤碳氮循环发生改变。刈割是北方农牧交错草地生态系统的主要管理方式, 为了深入探究氮添加和刈割管理方式对农牧交错带草地碳循环的影响, 进一步厘清该区域草地生态系统的碳动态问题, 该研究设置了一个不同形态氮添加和刈割的裂区实验, 测定土壤呼吸对不同形态氮肥添加和刈割的响应, 为进一步科学管理该区域草地提供可靠的依据。实验样地位于山西省右玉县境内的“山西农业大学农牧交错带草地生态系统野外观测研究站”, 于2017年设置不同形态氮添加和刈割处理, 实验处理包括对照(不刈割和刈割)、尿素添加、缓释尿素添加、刈割+尿素添加、刈割+缓释尿素添加, 每种处理6个重复, 共36个小区。在不同处理条件下测定土壤呼吸速率、土壤温度、土壤水分、土壤微生物生物量、土壤无机氮含量、植物地上和地下生物量, 并计算土壤累积碳排放量及CO₂通量。研究结果表明: (1)短期(2017-2018年)尿素和缓释尿素的添加显著提高了该地区土壤呼吸速率和土壤累积碳排放量。与添加缓释尿素相比, 添加尿素处理下的土壤呼吸速率和累积碳排放量更高; (2)刈割显著降低土壤呼吸速率和累积碳排放量; (3)短期氮添加和刈割的交互作用对土壤呼吸速率没有显著影响。因此, 短期氮添加促进了北方农牧交错带盐碱化草地土壤碳释放, 刈割抑制土壤呼吸, 降低了累积碳排放量, 这可能是由于刈割移除地上植物, 减少了凋落物的输入, 底物减少导致土壤微生物活性降低。但是随着处理时间的延长, 氮添加和刈割对该农牧交错带盐碱化草地土壤碳动态的影响还有待进一步探究和发现。