Effects of sand burial depth on the root system of Salix cheilophila seedlings in Mu Us Sandy Land, Inner Mongolia, China

Salix cheilophila Schneid. is a naturally occurring Salix species in Mu Us Sandy Land, Inner Mongolia, China. We focused on the morphological adaptability of S. cheilophila to sand dune burial. For morphological measurements, 32 S. cheilophila seedlings were removed from a community which was in the process of being buried by a shifting sand dune. Each seedling collected included the entire root system. We measured the number, length, and biomass of the adventitious roots, primary lateral roots, and taproot, and compared the morphological characteristics of the root system, including adventitious roots, for seedlings buried to various levels in the sand. The growth range of adventitious roots increased as the length of the buried portion of the main shoot increased. In addition, the total dry weight of all current-year shoots tended to increase gradually with increasing total dry weight of the adventitious roots. These results suggest that S. cheilophila tends to make use of the sedimentary sand layer that accompanies shifting sand dunes. However, there was no correlation between biomass or number of adventitious roots and the length of the buried part of the main shoot. Thus, S. cheilophila does not grow adventitious roots proportional to the buried part. These morphological characteristics of the root system, including the adventitious roots, may indicate that S. cheilophila has poor morphological adaptability to sand dune burial.     

Does tree species composition affect soil CO<Subscript>2</Subscript> emission and soil organic carbon storage in plantations?

Key message

Mixed tree plantations are potential silvicultural systems to increase soil carbon storage through altering litter and root inputs and soil physiochemical properties.

Abstract

Afforestation and reforestation are major strategies for global climate change mitigation. Different tree species composition can induce diverse changes in soil CO₂ emission and soil carbon sequestration in tree plantation. This study employed three plantations of monoculture and mixed Pinus yunnanensis and Eucalyptus globulus to estimate the effect of tree species composition on soil CO₂ emission and soil organic carbon storage in subtropical China. We found that tree species composition had a significant effect on the soil CO₂ emission and soil organic carbon storage. Soil CO₂ emission was lower in the mixed plantation than in the P. yunnanensis plantation, whereas it was higher than in the E. globulus plantation. Differences in soil CO₂ emission among the three plantations were determined by leaf litterfall mass, fine root biomass, soil available nitrogen, pH, soil bulk density, and soil C:N ratio. Soil organic carbon storage was 34.5 and 23.2 % higher in the mixed plantation than in the P. yunnanensis and E. globulus plantations, respectively. Higher soil organic carbon stock in the mixed plantation was attributed to lower C/N ratio of leaf litter and soil, greater fine root biomass and soil organic carbon content, and lower soil CO₂ emission. We conclude that mixed tree plantation can enhance soil carbon sequestration, but can decrease or increase soil CO₂ emission through altering litter and root inputs and soil physiochemical properties.

     

干热河谷印楝和大叶相思人工林根系生物量及其分布特征

以元谋干热河谷10年生印楝和大叶相思为研究对象,采用分层挖掘法对印楝纯林、大叶相思纯林及印楝×大叶相思混交林根系生物量及其分布特征进行研究.结果表明:印楝×大叶相思混交林根系总生物量为2.707 t/hm2,介于印楝纯林(2.264t/hm2)和大叶相思纯林(3.405 t/hm2)之间.混交林内主根总生物量为1.057 t/hm2,为印楝纯林和大叶相思纯林的69.9％和69.7％,而除粗根外,混交林内其它径级的侧根(中根、小根和细根)生物量均介于印楝纯林和大叶相思纯林之间,分别为印楝纯林的228.7％、120.1％、450.0％,为大叶相思纯林的71.3％、65.8％和48.8％.干热河谷印楝和大叶相思人工林根系在土壤表层分布比例大,尤其足0-0.2 m土层内,其根系生物量占根系总生物量的63.6％-76.3％.根系垂直累积生物量与土壤深度可用二次方程拟合,拟合方程的二阶导数表明,垂直方向上,印楝纯林根系分布较混交林均匀,而混交林较大叶相思纯林均匀.     

中国南方3种主要人工林生物量和生产力的动态变化

基于中国南方杉木、马尾松、桉树3种主要人工林的幼龄林、中龄林、近熟林、成熟林、过熟林5个不同年龄各3块1000 m2样地(共计45块)的建立和调查,采用样木回归分析法(乔木层)和样方收获法(灌木层、草本层、地上凋落物)获取不同林型不同林龄径级样木和其它基本数据,探讨了3种人工林各组分各层次林分生物量和生产力的分配特征及随林龄的变化规律,结果表明,林分生物量和生产力与林龄密切相关,增长模型的拟合度均较高,相关显著;杉木、马尾松、桉树人工林的生物量随林龄的增长呈增加趋势,成熟林的生物量分别为192.30、191.53、105.77 Mg/hm2,其中活体植物分别占95.76%—98.39%、75.01%—99.14%、85.60%—97.61%;生物量的层次分配乔木层占绝对优势,并随年龄而增加,其它层次所占比例较小,总体趋势为凋落物草本层灌木层;乔木层的器官分配以干所占比例最高,杉木、马尾松、桉树分别占54.89%—75.97%、49.93%—83.10%、51.07%—98.48%,随年龄的增加而增加,根的比例次之,枝叶所占比例较小,随林龄而下降;灌木层器官分配以枝的相对生物量较大,草本层的地上和地下分配规律不明显;与其它森林类型相比,杉木和马尾松的生物量处于中上游水平,桉树的生物量较低,但3种人工林的生产力均很高,分别为12.37、8.98、21.10 Mg hm-2a-1,均是光合效率高、固碳潜力大的中国南方速生丰产优良造林树种。     

高寒沙地乌柳防护林碳库随林龄的变化

植被恢复是改善脆弱生态系统的有效方式。长期的植被恢复能够提高沙地生态系统的服务功能。以青海共和高寒沙地不同林龄乌柳(Salix cheilophila)防护林生态系统为研究对象,研究植被恢复过程中植被碳库与土壤碳库的动态变化,探讨乌柳防护林生态系统的碳汇功能。结果表明:随林龄增加,乌柳各组分碳浓度变化规律并不显著(P0.05),而碳贮量显著增加(P0.05),且不同林龄乌柳各组分碳库的分配比例不同,树干碳贮量占林分碳贮量的百分比最高。各林龄(6、11、16、21a)乌柳林碳贮量分别为4.95、9.93、14.67 t/hm2和21.99 t/hm2。土壤碳库随植被恢复时间的增加而增加,各林龄土壤碳库(0—200cm)分别为9.54、13.03、17.18和19.05 t/hm2。较之6、11a土壤碳库增加26.78%,16a较之11a提高24.16%,21a较16a提高9.82%。地被物层(植被残体)固碳量分别为0.27、0.29、0.33、0.43 t/hm2。不同林龄乌柳林生态系统碳库分别为14.76、23.25、32.18 t/hm2和41.48 t/hm2。各林龄乌柳植被层碳库分别占该林龄总碳库的33.54%、42.71%、45.59%和53.01%,土壤碳库分别占该林龄总碳库的64.63%、56.04%、53.39%和45.93%,而地被物层分别占该林龄总碳库的1.83%、1.25%、1.03%和1.03%。较之恢复前的,各林龄碳库依次增加57.05%、36.52%、27.75%和22.42%。植被恢复各阶段年净碳累积速率分别为1.41、1.70、1.79、1.86 t C hm-2a-1。乌柳防护林生态系统具有"碳汇"功能。     

施肥对落叶松和水曲柳人工林土壤呼吸的影响

 以落叶松（Larix gmelinii）和水曲柳（Fraxinus mandshurica）人工林为研究对象,采用动态气室法（LI-6400-09叶室连接到LI-6400便携式CO₂/H₂O分析系统）对两种林分的土壤呼吸速率进行了观测,探讨了细根生物量、根中氮含量与土壤呼吸速率的关系,以及施肥对细根生物量、根中氮含量和土壤呼吸速率的影响。结果表明：1）施肥导致落叶松和水曲柳林分的活细根生物量降低18.4％和27.4％, 死细根生物量分别降低了34.8％和127.4 ％;2）施肥使落叶松和水曲柳林地土壤呼吸速率与对照相比分别减少了34.9％和25.8％;3 ）施肥对根中氮含量没有显著影响;4）落叶松和水曲柳林地的土壤呼吸与土壤温度表现出相同的季节变化,两种林分的土壤呼吸速率与地下5和10 cm处的温度表现出明显的指数关系 ,其相关性R²=0.93～0.98。土壤呼吸温度系数Q₁₀的范围在2.45～3.29。 施肥处理对Q₁₀没有产生影响,施肥处理导致细根生物量减少可能是引起林地土壤呼吸速率下降的主要原因。     

不同树龄杨树人工林的根系呼吸季节动态

根系呼吸是准确评估森林生态系统土壤碳收支的一个重要依据。基于LI-COR-6400-09土壤呼吸系统连续2a测定的3个生长阶段杨树人工林的根系呼吸数据,分析了根系呼吸的季节变化规律及树龄、土壤水热因子和细根生物量对它的影响。结果表明:3个不同树龄人工林的根系呼吸速率均呈明显的季节变化,最大值出现在夏初,最小值出现在秋末,基本上与表层土壤温度的季节变化相一致。根系呼吸的峰值早于土壤温度和细根生物量的峰值,说明林木根系的季节生长节律、地下碳分配模式都可能影响根系呼吸的季节变化。2年生人工林的根系呼吸速率最高,平均为3.78μmolCO2m-2s-1,并随树龄增长呈下降趋势。3个树龄人工林根系呼吸占土壤呼吸的比例介于38.6%-58.0%之间,且2年生人工林最大。不同林龄之间根系呼吸的差异主要与根系的生长周转速率及代谢活性随生长阶段的变化有关。总的来说,表层土壤温度和细根生物量的协同作用可解释根系呼吸速率变化的76%。此外在评估一个轮伐期内的根系呼吸强度时,应考虑不同生长阶段对它的影响。     

间伐对川西亚高山粗枝云杉人工林细根生物量及碳储量的影响

以川西亚高山50年生粗枝云杉(Picea asperata)人工林为研究对象, 探讨了间伐对粗枝云杉人工林1-5级细根生物量及碳储量的影响。结果表明: 粗枝云杉人工林细根生物量和碳储量随根序等级的增加而显著增加(p < 0.05), 5级根序中1级根生物量及碳储量最小, 5级根生物量及碳储量最大。与对照(间伐0%)相比, 间伐对粗枝云杉人工林林分细根生物量及碳储量有显著影响(p < 0.05); 而对单株细根生物量影响不一, 间伐10%和20%与对照没有显著性差异(p > 0.05)。间伐显著影响生物量在各根序中的分配, 随着间伐强度的增加, 1、2级细根中生物量分配比例增加, 1级细根的生物量增加幅度最大; 3-5级细根的生物量分配比例减小, 5级细根减少幅度最大。其中, 间伐50%显著减少了细根在下层(20-40 cm)土壤中的生物量比例(p < 0.05), 但与间伐20%和30%无显著差异(p > 0.05)。     

广西不同林龄杉木、马尾松人工林根系生物量及碳储量特征

为了解不同林龄杉木、马尾松人工林地地下根系生物量及碳储量特征,以广西杉木、马尾松主产区5个不同林龄阶段(幼龄林、中龄林、近熟林、成熟林、过熟林)的人工林为研究对象,采用全根挖掘法和土钻法获取标准木根系生物量、灌草根系生物量和林分细根生物量,并测定其碳含量,分析其不同林龄阶段地下根系生物量和碳储量分配特征。结果表明:杉木、马尾松林地下根系总生物量分别在9.06—31.40Mg/hm~2和7.91—53.40Mg/hm~2之间,各林龄阶段根系总生物量总体上呈现随林龄增加而增加的趋势,杉木林细根生物量随林龄的增加呈现出先减后增的趋势,马尾松呈现出逐渐减小的趋势;林分各层次根系碳含量表现为乔木灌木草本、细根;杉木、马尾松地下根系碳储量变化趋势与生物量变化趋势相同,杉木、马尾松林不同林龄阶段各层次根系和土壤细根总碳储量分别在7.56—21.97Mg/hm~2和8.86—29.95Mg/hm~2之间;地下根系碳储量总体上以乔木根系占优势,且随林龄的增大其比例呈增加的趋势。     

黄土高原西部3个降水量梯度近成熟油松人工林碳库特征

森林在陆地生态系统吸收碳素方面起着主要作用,了解其固碳特征对研究地区之间的碳循环至关重要。油松人工林是黄土高原地区一种典型的退耕还林树种,研究其固碳特征有利于综合分析评价油松人工林的生态效益。为了研究黄土高原西部地区油松人工林碳储量及碳密度空间分布特征因降水量不同引起的差异,以黄土高原西部地区3个典型栽培区域的近成熟油松人工林为对象,研究了群落内各组成部分的生物量和碳库特征。乔木层生物量的估算采用以胸径和树高为基础变量的生物量方程,灌木、草本、凋落物采用样方收获法,土壤碳库依据土壤剖面(1 m)和土钻取样相结合的方法测算。结果表明:在兰州官蘑滩地区(372 mm)、太子山(519 mm)和小陇山(632 mm)3个不同降水量区域,油松人工林生物量碳密度分别为(49.08±2.86)t/hm~2、(73.90±9.36)t/hm~2和(82.55±7.36)t/hm~2。小陇山地区的生态系统总碳密度和生物量碳密度与兰州地区存在显著性差异。在3个不同降水量区域,土壤有机碳密度仅在表层土壤(0—10 cm)差异达到显著水平(P0.05),而土壤总碳密度间差异未达到显著水平(P0.05)。黄土高原半干旱区近成熟油松人工林的生物量碳密度与年均降水量间呈现出显著正相关关系。在半干旱地区,降水量可能成为影响油松人工林生产力和碳固存的关键因素。     

Biomass accumulation and carbon storage of four different aged Sonneratia apetala plantations in Southern China

The objectives of this study were to examine plant biomass accumulation and carbon (C) storage in four different aged Sonneratia apetala plantations in the Leizhou Bay in South China. The allometric equations using diameter at breast height (DBH) and height (H) were developed to quantify plant biomass. The total forest biomass (TFB) of S. apetala plantation at 4, 5, 8, and 10 years old was 47.9, 71.7, 95.9, and 108.1 Mg ha^?1, respectively. The forest biomass C storage in aboveground (AGB) and roots at 4, 5, 8, and 10-year plantation was 19.9, 32.6, 42.0, 49.0 Mg ha^?1, respectively. Soil organic C (SOC) on the top 20 cm of sediments increased by 0.3, 6.8, 27.4, and 35.0 Mg ha^?1after 4, 5, 8, and 10 years of reforestation, respectively. The average annual rate of total carbon storage (TCS) accumulation at 4, 5, 8, and 10-year S. apetala plantation was 5.0, 7.9, 8.7, and 8.4 Mg ha^?1 yr^?1, respectively. The TCS values in this study were underestimated because we only estimated SOC storage on the top 20-cm sediments in these plantations. This study suggests these young S. apetala plantations have the characteristics of fast growth, high biomass accumulation, and high C storage capacity, especially in sediments. They sequestrated C at a high but varying rate over time. The large-scale reforestation of S. apetala plantations in the open coastal mudflats in southern China has great potential to sequestrate more C as well as restore the degraded coastal land. The potential ecological issues associated with the increasing monoculture plantations were discussed. More long-term monitoring and research are needed to further evaluate biomass and C accumulation of S. apetala plantations over time as well as how the increasing distribution of this monoculture plantation will influence the few native mangrove remnants.     

Responses of dominant desert species <Emphasis Type="Italic">Artemisia ordosica</Emphasis> and <Emphasis Type="Italic">Salix psammophila</Emphasis> to water stress

Morphology, biomass accumulation and allocation, gas exchange, and chlorophyll fluorescence were compared for one-year-old seedlings of Salix psammophila and Artemisia ordosica, two dominant desert species, in response to two water supplies (equivalent to 315.0 mm for present precipitation in growing season and to 157.5 mm for future decreasing precipitation) during 105 d. For both species, photochemical efficiency of photosystem 2 (F_v/F_m), net photosynthetic rate, transpiration rate, stomatal conductance, biomass accumulation in different organs, tree height, number of leaves, and leaf area were reduced in response to the decrease in water supply. For both species, instantaneous water use efficiency was not affected by the water deficit. However, diurnal patterns of gas exchange and biomass allocation were affected in different ways for the two species, with notably a decrease in specific leaf area and an increase in root : shoot ratio for S. psammophila only. Overall, S. psammophila was more responsive to the decreasing precipitation than A. ordosica.     

松材线虫侵染的马尾松人工林细根形态及生物量分异特征

中龄林的马尾松受松材线虫侵染后,林木生长、生理生化指标、群落多样性等会发生异质性变化,但是,针对患病林木地下细根的响应尚不清楚。本研究以松材线虫疫区患病马尾松和健康马尾松为研究对象,采用土柱法,分0-15 cm和15-30 cm土层,对细根进行分级研究,定量分析1-5级细根的形态、生物量以及养分元素,探讨松材线虫侵染的马尾松人工林细根形态、生物量以及养分元素的分异特征。结果表明:(1)患病马尾松人工林细根的健康状态与根长密度、生物量呈极显著正相关(P<0.01),低级根(如1级根)患病后,响应会更加强烈。(2)马尾松人工林患病后,细根有效磷、速效钾浓度会显著降低(P<0.05),而全氮、钙浓度会显著升高(P<0.05)。(3)松材线虫病使林分的土壤有机质含量显著高于健康林分(P<0.05),而土壤速效钾含量会显著低于健康林分(P<0.05)。以上结果表明,松材线虫侵染的马尾松人工林会在细根形态、细根养分和土壤养分上会发生特异性响应,揭示了松材线虫病对马尾松人工林地下细根的影响,旨在为松材线虫病防治提供一定参考。     

Effects of Sewage Sludge Application on Biomass Production and Concentrations of Cd,Pb and Zn in Shoots of <Emphasis Type="Italic">Salix</Emphasis> and <Emphasis Type="Italic">Populus</Emphasis> Clones: Improvement of Phytoremediation Efficiency in Contaminated Soils

Fast-growing clones of Salix and Populus species have been studied for phytoremediation of soils contaminated by risk elements (REs) using short-rotation coppice plantations. Biomass yield, accumulation and removal of RE (Cd, Pb and Zn) by highly productive willow (S1—(Salix schwerinii × Salix viminalis) × S. viminalis, S2—Salix × smithiana) and poplar (P1—Populus maximowiczii × Populus nigra, P2—P. nigra) clones were investigated with and without sewage sludge (SS) application. The precise field experiment was established in April 2008 on moderately Cd-, Pb- and Zn-contaminated soil. Initially, shoots were harvested after four seasons in February 2012 and then after two more seasons in February 2014. The application of SS limited plant growth during the first years of the experiment in the majority of treatments, mainly due to weed competition and higher concentrations of available soil nutrients causing lower yields than those of control (C) treatments. Well-developed roots were able to take advantage of SS applications, and shoot yield was mainly higher in SS treatments in the second harvest, reaching up to 15 t dry matter (DM)?ha^?1. Willows performed better than poplars. Application of SS reduced RE shoot concentrations compared to the C treatment. The removal of RE was significantly higher in the second harvest for all clones and elements (except the P2 clone), and the biomass yield was the major driving force for the amount of RE removed by shoots. Well-developed plantations of fast-growing trees showed better suitability for the phytoextraction of moderately contaminated soils for Cd and partly for Zn but not for Pb, which was less available to plants. From the four tested clones, S2 showed the best removal of Cd (up to 0.94 %) and Zn (up to 0.34 %) of the total soil element content, respectively, and this clone is a good candidate for phytoextraction. SS can be a suitable source of nutrients for Salix clones without any threat to the food chain in terms of biomass contamination, but its application to the soil can result in an increased incidence of some weeds during the first years of plantation.     

Biomass Harvest from Natural Willow Rings around Prairie Wetlands

The study followed the harvest of natural willow from three wetlands using a prototype modified agricultural round baler nicknamed a Bio-Baler. The study reports fuel characteristics and combustion testing of biomass harvested from natural willow rings. Composition of native willow species in the harvested willow rings was determined. We specifically measured regrowth of the biomass and number of regenerated stems per stump 1 year after harvest to determine how different willow species responded to mechanical biomass cutting with the Bio-Baler. The results of combustion testing for the natural willow were essentially similar to those with “conventional” wood chips or planted willows. The ash content was approximately 1.65%, slightly lower than for planted willow plantations. The calorific value of the natural willow was 19.6 MJ kg^?1 (dry basis) similar to what is expected for wood and planted willow. Four Salix species (Salix bebbiana Sarg., Salix petiolaris Sm., Salix eriocephala Michx., and Salix discolor Muhl) were identified in the willow rings. Stem biomass increased for all species except S. bebbiana after willow was harvested with the Bio-Baler. Overall, willow regeneration was not affected by mechanical harvesting compared to hand cutting. Regenerated stem density was 93 stems per square meter for mechanically harvested stumps compared to 105 stems per square meter for hand-pruned stumps. Based on the results, biomass harvested from natural willow rings has acceptable fuel characteristics when compared to purpose-grown willows and mechanical harvest with a Bio-Baler does not have a negative effect on willow regeneration.     

Biomass Accumulation and Carbon Sequestration in Four Different Aged Casuarina equisetifolia Coastal Shelterbelt Plantations in South China

Thousands of kilometers of shelterbelt plantations of Casuarina equisetifolia have been planted to protect the southeast coastline of China. These plantations also play an important role in the regional carbon (C) cycling. In this study, we examined plant biomass increment and C accumulation in four different aged C. equisetifolia plantations in sandy beaches in South China. The C accumulated in the C. equisetifolia plant biomass increased markedly with stand age. The annual rate of C accumulation in the C. equisetifolia plant biomass during 0–3, 3–6, 6–13 and 13–18 years stage was 2.9, 8.2, 4.2 and 1.0 Mg C ha⁻¹ yr⁻¹, respectively. Soil organic C (SOC) at the top 1 m soil layer in these plantations was 17.74, 5.14, 6.93, and 11.87 Mg C ha⁻¹, respectively, with SOC density decreasing with increasing soil depth. Total C storage in the plantation ecosystem averaged 26.57, 38.50, 69.78, and 79.79 Mg C ha⁻¹ in the 3, 6, 13 and 18- yrs plantation, with most of the C accumulated in the aboveground biomass rather than in the belowground root biomass and soil organic C. Though our results suggest that C. equisetifolia plantations have the characteristics of fast growth, high biomass accumulation, and the potential of high C sequestration despite planting in poor soil conditions, the interactive effects of soil condition, natural disturbance, and human policies on the ecosystem health of the plantation need to be further studied to fully realize the ecological and social benefits of the C equisetifolia shelterbelt forests in South China.     

Root biomass distribution of planted <Emphasis Type="Italic">Haloxylon ammodendron</Emphasis> in a duplex soil in an oasis: desert boundary area

Duplex soils, consisting of a sandy surface soil (A-horizon) and silty-clay subsoil (B-horizon), occur in a boundary area between oasis and desert in northwestern China and create a challenging habitat for restoration of plant growth. We conducted an experiment in a 10-year-old H. ammodendron plantation forest to determine the influence of physical properties of duplex soil on water infiltration and plant root growth. We used a trenching method to assess root biomass, and classified roots into two diameter classes: fine (<2 mm) and coarse (>2 mm). Following a 26.7 mm rain event, water infiltrated to the B- horizon; further deep percolation was hindered by low hydraulic conductivity, so that B horizon remained at high available soil moisture for an extended period of time. Root biomass increased rapidly in, or very close to the B horizon, especially for coarse roots. The subsoil formed a barrier to root penetration, but may also reflect the accumulation of water resources at the boundary between the A- and B-horizon. Shoot growth and root distribution, shrub height and canopy area, and total root biomass were negatively correlation with depth to the B horizon, and that was reflected by quadratic functions. We conclude that the texture and structure of duplex soils influenced the soil environment for water infiltration and storage, indicating that the B-horizon underlying sand in duplex soils is advantageous for the growth, and development of planted sand-stabilizing vegetation. These results have important implications for sustainable development of sand-fixing plantations in desert ecosystems.     

华西雨屏区香樟人工林土壤表层细根生物量和碳储量

2010年11月-2011年12月, 研究了华西雨屏区31年生香樟人工林土壤表层(0～30 cm)细根生物量及碳储量.结果表明: 香樟人工林土壤0～30 cm层细根总生物量(活根+死根)和碳储量的平均值分别为1592.29 kg·hm^-2和660.68 kg C·hm^-2,其中活细根贡献率分别为91.1%和91.8%.随着土壤深度的增加,香樟1～5级活细根和死细根的生物量及碳储量均显著减少;随着根序等级的升高,香樟活细根生物量及碳储量显著增加.香樟细根总生物量及碳储量均在秋季最高、冬季最低,死细根生物量及碳储量为冬季最高、夏季最低;1级根和2级根生物量及碳储量均在夏季最高、冬季最低,而3~5级根则为秋季最高、冬季最低.土壤养分和水分的空间异质性是导致细根生物量和碳储量变化的主要原因.     

Ecosystem carbon storage and soil organic carbon stability in pure and mixed stands of Cunninghamia lanceolata and Michelia macclurei

Background and aims

Across the world, about 264 million ha forest plantations are monospecific. This practice has been found to cause site productivity and soil fertility decline in the regions where forests have been harvested several times. To mitigate these problems, mixed-species plantations, especially with broadleaved and coniferous species, are preferred. Understanding the effects of introducing broadleaved tree in monospecific coniferous plantation on ecosystem carbon (C) storage and soil organic C (SOC) stability is critical to improve our understanding of forest C sequestration and C cycle.

Methods

Plots were established in subtropical plantations with a randomized block design to examine the influence of introducing Michelia macclurei trees into pure Cunninghamia lanceolata plantation on biomass C storage, SOC storage of total, labile, and recalcitrant fractions (0–40 cm depth), and SOC stability.

Results

Introducing M. macclurei trees increased biomass C by 17.9 % and 14.2 % compared with monospecific C. lanceolata and M. macclurei plantations, respectively. Storage of different SOC fractions was not significantly different between monospecific C. lanceolata and mixed plantations. SOC stability in bulk soils was not affected, although it differed in 10–20 cm and 20–40 cm soil depth among three plantations.

Conclusions

Mixed species plantations can increase C sequestration, and in the subtropical forest ecosystem examined this was mainly attributed to an increase in biomass C.     

Biometric-based estimation of net ecosystem production in a mature Japanese cedar (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis>) plantation beneath a flux tower

Quantification of carbon budgets and cycling in Japanese cedar (Cryptomeria japonica D. Don) plantations is essential for understanding forest functions in Japan because these plantations occupy about 20% of the total forested area. We conducted a biometric estimate of net ecosystem production (NEP) in a mature Japanese cedar plantation beneath a flux tower over a 4-year period. Net primary production (NPP) was 7.9 Mg C ha⁻¹ year⁻¹ and consisted mainly of tree biomass increment and aboveground litter production. Respiration was calculated as 6.8 (soil) and 3.3 (root) Mg C ha⁻¹ year⁻¹. Thus, NEP in the plantation was 4.3 Mg C ha⁻¹ year⁻¹. In agreement with the tower-based flux findings, this result suggests that the Japanese cedar plantation was a strong carbon sink. The biometric-based NEP was higher among most other types of Japanese forests studied. Carbon sequestration in the mature plantation was characterized by a larger increment in tree biomass and lower mortality than in natural forests. Land-use change from natural forest to Japanese cedar plantation might, therefore, stimulate carbon sequestration and change the carbon allocation of NPP from an increment in coarse woody debris to an increase in tree biomass.