内蒙古锡林河流域羊草草原植物生长旺季呼吸的影响因素分析和区分

Based on the static opaque chamber method,the respiration rates of soil microbial respiration,soil respiration,and ecosystem respiration were measured through continuous in-situ experiments during rapid growth season in semiarid Leymus chinensis steppe in the Xilin River Basin of Inner Mongolia,China. Soil temperature and moisture were the main factor affecting respiration rates. Soil temperature can explain most CO2 efflux variations (R2=0.376-0.655) excluding data of low soil water conditions. Soil moisture can also effectively explain most of the variations of soil and ecosystem respiration (R2=0.314-0.583),but it can not explain much of the variation of microbial respiration (R2=0.063). Low soil water content (≤5%) inhibited CO2 efflux though the soil temperature was high. Rewetting the soil after a long drought resulted in substantial increases in CO2 flux at high temperature. Bi-variable models based on soil temperature at 5 cm depth and soil moisture at 0-10 cm depth can explain about 70% of the variations of CO2 effluxes. The contribution of soil respiration to ecosystem respiration averaged 59.4%,ranging from 47.3% to 72.4%; the contribution of root respiration to soil respiration averaged 20.5%,ranging from 11.7% to 51.7%. The contribution of soil to ecosystem respiration was a little overestimated and root to soil respiration little underestimated because of the increased soil water content that occurred as a result of plant removal.     

共和盆地中间锦鸡儿人工林根系的分布特征

采用剖面法对青海共和盆地中间锦鸡儿（Caragana intermedia）人工林的根系进行调查,分析5 a、9 a和25 a根系的生物量、比根长和根长密度的垂直分布格局,同时测定土壤含水量的垂直变化。结果表明:①不同林龄中间锦鸡儿人工林的吸收根（d≤1 mm）和输导根（d>1 mm）的主要分布范围不同。5 a、9 a和25 a吸收根主要分布土层分别是10～30、10～50 cm和10～60 cm,输导根主要分布土层分别是10～50、10～60 cm和10～90 cm。②随着林龄的增加,根系的吸收根、输导根的总生物量、总比根长和总根长密度均显著增加（P<0.05）;各林龄根系中的吸收根比输导根具有更高的比根长和根长密度（P<0.05）。因此,吸收水分和养分的能力随着林龄增加而增大。③中间锦鸡儿人工林根系,尤其是吸收根的分布影响土壤水分变化,吸收根集中分布土层的土壤含水量显著降低。     

Influencing factors and partitioning of respiration in a Leymus chinensis steppe in Xilin River Basin, Inner Mongolia, China

Based on the static opaque chamber method, the respiration rates of soil microbial respiration, soil respiration, and ecosystem respiration were measured through continuous in-situ experiments during rapid growth season in semiarid Leymus chinensis steppe in the Xilin River Basin of Inner Mongolia, China. Soil temperature and moisture were the main factor affecting respiration rates. Soil temperature can explain most CO2 efflux variations (R2=0.376–0.655) excluding data of low soil water conditions. Soil moisture can also effectively explain most of the variations of soil and ecosystem respiration (R2=0.314–0.583), but it can not explain much of the variation of microbial respiration (R2=0.063). Low soil water content (≤5%) inhibited CO2 efflux though the soil temperature was high. Rewetting the soil after a long drought resulted in substantial increases in CO2 flux at high temperature. Bivariable models based on soil temperature at 5 cm depth and soil moisture at 0–10 cm depth can explain about 70% of the variations of CO2 effluxes. The contribution of soil respiration to ecosystem respiration averaged 59.4%, ranging from 47.3% to 72.4%; the contribution of root respiration to soil respiration averaged 20.5%, ranging from 11.7% to 51.7%. The contribution of soil to ecosystem respiration was a little overestimated and root to soil respiration little underestimated because of the increased soil water content that occurred as a result of plant removal.     

内蒙古羊草草原呼吸的影响因素分析和区分

利用静态暗箱-气相色谱法在植物生长旺季测算了内蒙古锡林河流域羊草草原的土壤微生物呼吸、土壤呼吸和生态系统呼吸。地温和水分是植物生长旺季呼吸最重要的影响因素。地温在水分条件适宜的情况下可以解释CO₂通量的部分变化(R² = 0.376~0.655)。土壤水分含量也可以解释土壤呼吸和生态系统呼吸的部分变化(R² = 0.314~0.583),但基本不能解释土壤微生物呼吸的变化(R² = 0.063)。即使在较高温度下,较低的土壤水分含量(≤ 5%) 也会显著的抑制CO₂排放。长期干旱后降雨使CO₂通量在高温下迅速增大。基于5 cm地温和0~10 cm土壤水分含量的双变量模型可以解释CO₂通量约70%的变化。观测期间,土壤呼吸占生态系统呼吸的比例介于47.3%~72.4%之间,平均为59.4%;根呼吸占土壤呼吸的比例介于11.7%~51.7%之间,平均为20.5%。由于植物体去除引起的土壤水分含量上升可能使我们对土壤呼吸占生态系统呼吸比例的估计略微偏高,根呼吸占土壤呼吸的比例略微偏低。     

Vertical distribution of fine roots of Tamarix ramosissima in an arid region of southern Nevada

To increase our understanding of soil water and nitrogen use strategies of invasive Tamarix ramosissima during dry seasons, the vertical distributions of fine roots and their associations with soil properties were examined in the Virgin River floodplain, southern Nevada, United States. We measured morphological traits of fine roots, such as fine-root mass density, fine-root length density, specific root length and specific root area at 10 cm increments to a depth of 2 m. Soil properties were analyzed at 20 cm increments. More than 60% of fine root length and biomass was concentrated at depths between 20 and 60 cm. Soil nitrogen (N) concentration had strong and positive relationships with fine-root mass and length densities, suggesting that the fine-root distribution may be influenced by soil N availability. A weak but positive relationship was observed between soil moisture and fine-root mass density. Soil salinity had no relationship with root morphological traits. These findings suggest that T. ramosissima fine roots may contribute to N uptake from the upper soil layers during dry seasons. This might be an important advantage over native riparian tree species in arid riparian areas of the southwestern United States.     

中亚热带米槠次生林和杉木人工林细根养分含量特征

细根(≤2 mm)在调节森林生态系统的生物地球化学循环中起着较为重要的作用,但目前对不同土层细根化学计量的认识非常有限.本研究在福建省三明陈大国有林场内对米槠次生林和杉木人工林不同土层细根养分含量特征进行了研究.结果显示:(1)杉木人工林0～10 cm、60～80 cm土层0～1 mm细根碳浓度显著高于米槠次生林,10...     

Carbon pools in an arid shrubland in Chile under natural and afforested conditions

The pattern of carbon (C) allocation among the different pools is an important ecosystem structural feature, which can be modified as a result of changes in environmental conditions that can occur gradually (e.g., climatic change) or abruptly (e.g., management practices). This study quantified the C pools of plant biomass, litter and soil in an arid shrubland in Chile, comparing the natural condition (moderately disturbed by grazing) vs. the afforested condition (two-year-old plantation with Acacia saligna (Labill.) H.L. Wendl.), each represented by a 60 ha plot. To estimate plant biomass, allometric functions were constructed for the four dominant woody species, based on the volume according to their shape, which showed high correlation (R² > 0.73). The soil was the largest C pool in both natural and afforested conditions (89% and 94%, respectively) and was significantly lower in the afforested than natural condition at all five soil depths. The natural condition had in total 36.5 ton (t) C ha⁻¹ compared to 21.1 t C ha⁻¹ in the afforested condition, mainly due to C loss during soil preparation, prior to plantation of A. saligna. These measurements serve as an important baseline to assess long-term effects of afforestation on ecosystem C pools.     

高寒沙地乌柳(Salix cheilophila)林根系分布特征

对青海共和高寒沙地植被恢复区不同林龄(6年、11年、16年和21年)乌柳(Salix cheilophila)人工防护林根系分布及根量进行了调查、测定,同时测定了土壤有机质含量的垂向变化。结果表明:①不同林龄乌柳林根系主要由中根和细根构成,其数目占土壤剖面根系总数的90%以上,其中又以直径小于2.0mm细根所占比例最高,细根占剖面根系总数的50%以上;②各林龄乌柳根系在0~50cm土层分布较为集中,在30cm以下土层,根量随深度的增加逐渐减少,6年生乌柳林根系垂直分布在0~130cm,20年生乌柳可达200cm,随植被恢复时间的增长,各林龄根量显著增加(p0.05);③各林龄乌柳林有明显发达的垂直主根,属典型的垂直状根系,随植株不断生长,根系表现出深根性;④以不同深度根系重量作为解释变量,以土壤有机质含量作为响应变量,回归结果显示不同林龄乌柳林根系重量显著影响土壤有机质含量(p0.001),这也为评价沙地植被改良土壤功能提供了依据。     

Herbaceous layer development during spring does not deplete soil nitrogen in the Portuguese montado

Nitrogen (N) content in the soil and in the herbaceous biomass were monitored during spring of 2004-2006 to determine how the herbaceous layer development influences soil N availability in the montado ecosystem of southern Portugal. Highest (246.6 ± 52.7 g m⁻²) and lowest (123.2 ± 89.5 g m⁻²) peak biomass occurred in 2006 and 2005 respectively. Total soil N within the top 20 cm soil profile ranged between 0.2 ± 0.1% in February and 0.41 ± 0.2% in May, while available soil N was lowest (5 ± 2 μg g⁻¹soil) in February but increased three-to-five fold in March and was >17.5 μg g⁻¹soil at senescence in May. Significant (p < 0.001) increase in total N in the aboveground pool occurred between February and May. There was however, no decay in soil N content. Instead, the herbaceous vegetation enhanced soil N input and N retention in the ecosystem. Most of the herbaceous plants were annuals with large reserves of organic N at senescence, which returned to the soil as detritus. The herbaceous vegetation is a critical component of the montado that contributes to N recharge and cycling within the ecosystem.     

中国亚热带地区造林对土壤碳周转的影响

Afforestation in China’s subtropics plays an important role in sequestering CO2 from the atmosphere and in storage of soil carbon (C). Compared with natural forests,plantation forests have lower soil organic carbon (SOC) content and great potential to store more C. To better evaluate the effects of afforestation on soil C turnover,we investigated SOC and its stable C isotope (δ13C) composition in three planted forests at Qianyanzhou Ecological Experimental Station in southern China. Litter and soil samples were collected and analyzed for total organic C,δ13C and total nitrogen. Similarly to the vertical distribution of SOC in natural forests,SOC concentrations decrease exponentially with depth. The land cover type (grassland) before plantation had a significant influence on the vertical distribution of SOC. The SOC ?13C composition of the upper soil layer of two plantation forests has been mainly affected by the grass biomass 13C composition. Soil profiles with a change in photosynthetic pathway had a more complex 13C isotope composition distribution. During the 20 years after plantation establishment,the soil organic matter sources influenced both the δ13C distribution with depth,and C replacement. The upper soil layer SOC turnover in masson pine (a mean 34% of replacement in the 10 cm after 20 years) was more than twice as fast as that of slash pine (16% of replacement) under subtropical conditions. The results demonstrate that masson pine and slash pine plantations cannot rapidly sequester SOC into long-term storage pools in subtropical China.     

Effects of Pinus sylvestris var. mongolica afforestation on soil phosphorus status of the Keerqin Sandy Lands in China

Few studies have considered the effects of afforestation on soil phosphorus (P) status in semiarid regions such as the Keerqin Sandy Lands in China, though plantations have been widely established on P-deficient sandy soils to control wind-induced desertification. Phosphorus fractions and acid phosphomonoesterase (AP) activities were compared in the rhizosphere and bulk soils (0–5 and 5–20 cm) under Mongolian pine (Pinus sylvestris L. var. mongolica Litv.) plantations of different ages (15, 22, and 30 years old) and in bulk soils under grasslands to understand soil P behavior with Mongolian pine plantation development and to find out major factors controlling soil P cycling. Stand age and rhizosphere processes had similar effects on the soil P fractions. Labile inorganic P and phosphate absorbed on aluminum and iron oxides were not affected by stand age and rhizosphere processes. Rhizosphere effects of Mongolian pine accelerated the mineralization of organic P by increasing microbial and AP activities. Soil P properties in bulk and rhizosphere soils changed similarly with plantation development. In the first 15 years after afforestation, total organic P, calcium phosphate, labile organic P, microbial biomass P (MBP) concentrations, and AP activities were reduced sharply. About 73% of the reduction in total P came from mineralization of organic P and 24% came from solubilization of calcium phosphate. From 15 to 22 years onward, soil total organic P and calcium phosphate decreased gradually and labile organic P, MBP, and AP activities increased greatly, whereas total inorganic P remained constant. The results suggest that soil P pool was depleted with Mongolian pine plantation development, especially in the early stage. As the dominant form of soil P, organic P was the main source of available P and associated biological processes controlled soil P cycling under Mongolian pine plantations. To ensure sustainability of pine plantations, it is imperative that soil fertility is conserved by adding fertilizer, thinning, and protecting litterfall.     

Effects of Forest Types and Environmental Factors on Soil Microbial Biomass in a Coastal Sand Dune of Subtropical China

Coastal sand dune ecosystems generally have infertile soil with low water-holding capacity and high salinity. However, many plant species have adapted to the harsh sand environment along the southeastern coast of China. Studying the microbial biomass in such an ecosystem can improve our understanding of the roles that microbes play in soil fertility and nutrient cycling. We investigated the differences in soil microbial biomass carbon (MBC) and nitrogen (MBN) contents and their seasonal dynamics in five forest types (a secondary forest and plantations of Casuarinas, Pine, Acacia, and Eucalyptus). The results indicated that the seasonal variations of soil MBC and MBN contents in all five forest stands were higher in spring and winter, but lower in summer and autumn. The MBC content was lower in the Casuarinas plantation than in the other plantations in the same soil layer. However, no significant differences were observed in MBN contents among the different forest types. The MBC and MBN concentrations were positively correlated with soil moisture, but negatively correlated with soil temperature. The MBC and MBN contents also decreased with increasing soil depth. Across all soil layers, secondary forest had the highest MBC and MBN concentrations. Our study also showed that the MBC and MBN contents were positively affected by total soil carbon (TC), pH, and litter N content, but were negatively impacted by soil bulk density and litter C content. Moreover, the MBN content was positively correlated with root N content. In summary, environmental factors and the differences in litter and fine roots, soil nutrient contents, as well as the soil physical and chemical properties caused by different tree species collectively affected the concentrations of the soil MBC and MBN.     

老龄杉木人工林生态系统碳库及分配

对福建省南平市安曹下87年生的杉木人工林碳库及其分配进行研究．采用分层切割法和相对生长方程计算乔木层生物量,样方收获法测定林下植被生物量、枯枝落叶层和粗木质残体现存量,CN元素分析仪测定碳含量,研究结果表明：老龄杉木人工林生态系统碳库为287.89t·hm^-2,其中乔木层碳库占生态系统碳库的68.18％,矿质土壤层碳库占26.39％,而林下植被层、枯枝落叶层和粗木质残体碳库所占比例之和不超过6％。老龄杉木林的干材（干＋皮）碳库占乔木层碳库的79．61%。87年生与40年生杉木人工林碳库很接近,前者比后者仅高出7．15％,主要是因为两者占生态系统主体的乔木层碳库和土壤层碳库很接近,前者分别仅高出后者的4．51％和10．39％,前者林下植被层和粗木质残体碳库较大,分别是后者的2．05倍和2．80倍,而枯枝落叶层碳库则低于后者。因此,老龄阶段杉木人工林生态系统碳库增幅不大,但在碳库分配上变化明显。     

干旱区不同土地利用方式下土壤呼吸日变化差异及影响因素

利用开路式土壤碳通量测量系统-LI-8100对塔里木河下游6种土地利用方式下土壤呼吸速率的日变化进行了野外定位测量,并就水热因子及土壤理化性质对土壤日呼吸速率差异的影响进行了分析。结果表明,梨园、弃耕地、棉田、人工林、草地和天然林土壤呼吸速率日变化均呈单峰曲线,土壤日呼吸速率差异显著。大气温度和土地利用方式是造成土壤日呼吸差异的主要因素,其中土地利用方式通过改变地表温度、土壤水分、电导率、pH、盐分含量及机械组成等影响土壤日呼吸速率。     

Changes in ecosystem carbon stocks following grassland afforestation of semiarid sandy soil in the southeastern Keerqin Sandy Lands, China

The ecological consequences of grassland afforestation in arid/semiarid sandy regions are not well known with respect to tree species and stand age. The present study quantifies the changes in above- and belowground carbon (C) stocks following afforestation in the southeastern Keerqin Sandy Lands with species of Mongolian pine and poplar. We studied 15-, 24-, and 30-year-old Mongolian pine plantations, 7-, 11-, and 15-year-old poplar plantations, and adjacent grasslands. The results show that total ecosystem C stocks increased following grassland afforestation. Aboveground C stocks increased at a rate of 2.75 Mg C ha⁻¹ yr⁻¹ in the poplar plantations, and 1.06 Mg C ha⁻¹ yr⁻¹ in the Mongolian pine plantations. Mineral soil C stocks decreased during the early stage of forest establishment, but recovered with increasing stand age. Root C stock increased significantly in the Mongolian pine plantations, but the poplar plantations showed no such increase relative to the grassland. Our results indicate that afforestation of the grassland in the southeastern Keerqin Sandy Lands would sequester more C than would continuous grassland. Tree species selection and stand developmental age should be considered in planning future afforestation projects.     

Reducing topsoil salinity and raising carbon stocks through afforestation in Khorezm, Uzbekistan

Agricultural mismanagement of irrigated drylands results in severe soil degradation. Afforestation is an option for ameliorating such degraded land. We evaluated the impact afforestation has on the topsoil (0-20 cm) of salinized degraded cropland in regards to salinity, aggregate stability, and soil organic carbon (SOC) stocks in Uzbekistan, Central Asia. The effects of tree plantations established under either furrow or drip irrigation were studied four years following afforestation and two years after irrigation ceased. For comparative study we also sampled fallow land, land with 80 years of tree growth, natural forest, desert ecosystems, and paddy rice fields. Initial furrow irrigation showed to be most effective in improving soil fertility after four years of afforestation; the respective plantations of Populus euphratica and Ulmus pumila showed significant levels of reduced soil salinity and increased aggregate stability and improved SOC stocks. The comparison of the long-term afforested land with the short-term equivalent suggested a C sequestration rate of 0.09-0.15 t C ha⁻¹ year⁻¹. The SOC stocks of the long-term afforestation site exceeded those of the native forest. Hence, a rehabilitation of salt-affected cropland is feasible following the conversion into occasionally irrigated tree plantations, although it takes decades to reach steady-state conditions.     

Effects of afforestation on soil carbon turnover in China’s subtropical region

Afforestation in China’s subtropics plays an important role in sequestering CO2 from the atmosphere and in storage of soil carbon (C). Compared with natural forests, plantation forests have lower soil organic carbon (SOC) content and great potential to store more C. To better evaluate the effects of afforestation on soil C turnover, we investigated SOC and its stable C isotope (δ13C) composition in three planted forests at Qianyanzhou Ecological Experimental Station in southern China. Litter and soil samples were collected and analyzed for total organic C, δ13C and total nitrogen. Similarly to the vertical distribution of SOC in natural forests, SOC concentrations decrease exponentially with depth. The land cover type (grassland) before plantation had a significant influence on the vertical distribution of SOC. The SOC δ13C composition of the upper soil layer of two plantation forests has been mainly affected by the grass biomass 13C composition. Soil profiles with a change in photosynthetic pathway had a more complex 13C isotope composition distribution. During the 20 years after plantation establishment, the soil organic matter sources influenced both the δ13C distribution with depth, and C replacement. The upper soil layer SOC turnover in masson pine (a mean 34% of replacement in the 10 cm after 20 years) was more than twice as fast as that of slash pine (16% of replacement) under subtropical conditions. The results demonstrate that masson pine and slash pine plantations cannot rapidly sequester SOC into long-term storage pools in subtropical China.     

不同年龄杉木人工林土壤无机氮比较研究

在福建南平杉木林中心产区,选取11、21、28、40、88年生杉木人工林以及采伐迹地、杂木林为研究对象,研究不同年龄杉木林土壤无机氮的差异．结果表明：不同年龄杉木林土壤NH4^＋-N含量差异显著,以21年生的杉木人工林最高（11．91±0．43mg·kg^-1）,其他的为88年生的（8．33±0．38mg·kg^-1）〉28年生的（8．19±0．25mg·kg^-1）〉11年生的（5．65±0．17mg·kg^-1）〉40年生的（5．63±0．38mg·kg^-1）;NO3^--N含量较低（3．15～4．11mg·kg^-1）,且没有显著差异,这与杉木林所处的生长阶段、土壤理化性质有关．杉木林取代杂木林后,NH4^＋-N和NO3^--N含量都有所下降;采伐迹地土壤NH4^＋-N（19．74±1．44mg·kg^-1）和NO3^--N（18．05±0．72mg·kg^-1）含量远高于88年生的杉木林,分别是88年生的2．37和4．60倍．本地区无机氮含量较低,NH4^＋-N占无机氮的比例为60．0％～74．3％,NH4^＋-N为无机氮的主要形态．     

High belowground biomass allocation in an upland black spruce (Picea mariana) stand in interior Alaska

The root system of forest trees account for a significant proportion of the total forest biomass. However, data is particularly limited for forests in permafrost regions. In this study, therefore, we estimated the above- and belowground biomass of a black spruce (Picea mariana) stand underlain with permafrost in interior Alaska. Allometric equations were established using 4–6 sample trees to estimate the biomass of the aboveground parts and the coarse roots (roots >5 mm in diameter) of P. mariana trees. The aboveground biomass of understory plants and the fine-root biomass were estimated by destructive sampling. The aboveground and coarse-root biomasses of the P. mariana trees were estimated to be 3.97 and 2.31 kg m^?2, respectively. The aboveground biomass of understory vascular plants such as Ledum groenlandicum and the biomass of forest floor mosses and lichens were 0.10 and 0.62 kg m^?2, respectively. The biomass of fine roots <5 mm in diameter was 1.27 kg m^?2. Thus, the above- and belowground biomasses of vascular plants in the P. mariana stand were estimated to be 4.07 and 3.58 kg m^?2, respectively, indicating that belowground biomass accounted for 47% of the total biomass of vascular plants. Fine-root biomass was 36% of the total root biomass, of which 90% was accumulated in the surface organic layer. Thus, this P. mariana stand can be characterized as having extremely high belowground biomass allocation, which would make it possible to grow on permafrost with limited soil resource availability.     

腾格里沙漠东南缘不同年代固沙区根系分布

2010年8月,选择腾格里沙漠东南缘1964年、1981年和1990年建立的人工固沙区为对象,以流动沙丘和邻近的天然植被区为对照,利用根钻取样法研究了不同年代固沙植被区根系的3.0 m剖面的分布特征。结果表明：单位土地面积上<1 mm的活根、全部活根、<1 mm的死根和全部死根的重量密度和长度密度在不同样地间存在着显著差异(p<0.05);流沙、1990年、1981年、1964年固沙区和天然植被区全部活根重量密度分别为2.9±2.2、164.7±46.5、461.3±83.6、440.4±81.8 g·m-2和350.0±132.5 g·m-2,5个样地全部死根重量密度分别为4.9±2.8、58.7±16.8、390.9±57.9、492.5±252.2 g·m-2和214.4±29.9 g·m-2;根长密度也表现为相似的变化趋势。单位土壤体积的根系重量密度和长度密度随着土层加深而递减,植被区0~1.0 m土壤层活根的累积重量密度和长度密度在全部活根中的比例均超过70.0%,其中以天然植被区最大,流沙区则不超过25%;死根也表现为相似的趋势,只是比例有所降低。根鞘占全部根系生物量的比例非常不稳定,流沙区的最大,为94.3%,而1981年植被区的只有0.5%,1964年、1990年固沙区和天然植被区分别为29.9%,70.3%和58.9%。