利用1:5万土壤数据库估算浙江省土壤有机碳密度及储量

土壤有机碳库作为陆地生态系统中重要的碳库之一,对于温室效应和全球变化研究具有重要意义.利用浙江省1:5万土壤数据库,对浙江省277个土种0～100cm土层的有机碳密度进行估算,分析了全省土壤有机碳密度和储量,以及各主要土壤类型有机碳密度和分布.结果表明:浙江省土壤有机碳密度值主要集中在5～10kg·m-2;山香灰土有机碳密度最高,为52.80kg·m-2,清水砂最低,为1.82kg·m-2;红壤和水稻土土类土壤有机碳储量最大,两者之和占浙江省土壤有机碳总储量的63.8%;浙江省土壤总面积为100784.19km2,土壤有机碳储量为875.42×106t,土壤有机碳平均密度为8.69kg·m-2.通过叠加数字高程模型分析,发现土壤有机碳密度随高程、坡度和坡向的变化均呈现明显的变化趋势.     

利用1∶5万土壤数据库估算浙江省土壤有机碳密度及储量

土壤有机碳库作为陆地生态系统中重要的碳库之一,对于温室效应和全球变化研究具有重要意义.利用浙江省1∶5万土壤数据库,对浙江省277个土种0～100 cm土层的有机碳密度进行估算,分析了全省土壤有机碳密度和储量,以及各主要土壤类型有机碳密度和分布.结果表明： 浙江省土壤有机碳密度值主要集中在5～10 kg·m^-2;山香灰土有机碳密度最高,为52.80 kg·m^-2,清水砂最低,为1.82 kg·m^-2;红壤和水稻土土类土壤有机碳储量最大,两者之和占浙江省土壤有机碳总储量的63.8%;浙江省土壤总面积为100784.19 km²,土壤有机碳储量为875.42×10⁶ t,土壤有机碳平均密度为8.69 kg·m^-2.通过叠加数字高程模型分析,发现土壤有机碳密度随高程、坡度和坡向的变化均呈现明显的变化趋势.     

西双版纳热带季节雨林与橡胶林土壤呼吸

季节雨林和橡胶(Hevea brasiliensis)林是西双版纳热带森林生态系统中原始林和大面积种植人工林的两种代表类型。热带季节雨林层次结构复杂,多样性丰富,而橡胶林结构简单,乔木层只有橡胶树1种。应用碱吸收法,研究了这两种植被类型土壤呼吸速率、地下5 cm土壤温度、气温和土壤含水率的季节变化规律,以及土壤呼吸速率与地下5 cm土壤温度、气温和土壤含水率的关系。结果表明:1)季节雨林和橡胶林土壤呼吸速率、土壤温度、气温和土壤含水率都有明显的季节变化,而且两种林型的变化趋势基本一致;2)季节雨林和橡胶林土壤呼吸速率与地下5 cm土壤温度和气温之间具有显著的指数相关关系,显著水平达1%,与地下5 cm温度的相关性(r²分别为0.87和0.82)明显高于与气温的相关性(r²分别是0.80和0.72);3)季节雨林和橡胶林土壤呼吸速率与土壤含水率具有显著的线性相关(r²分别是0.73和0.63),显著水平达1%;4)橡胶林的土壤呼吸速率明显高于季节雨林,这与两种林型的结构有关;5)季节雨林和橡胶林土壤呼吸的Q₁₀分别为2.16和2.18,比文献报道的热带土壤的Q₁₀(1.96)稍高。     

西双版纳热带季节雨林与橡胶林土壤呼吸的季节变化

采用挖壕沟法与红外气体分析法,研究了西双版纳热带季节雨林和人工橡胶林内土壤呼吸包括根系呼吸、异养呼吸的干湿季动态变化.结果表明：季节雨林内土壤呼吸和异养呼吸速率均显著大于橡胶林(P＜0.01),但根系呼吸差异不显著;土壤温湿度是呼吸速率变化的主要影响因子,季节雨林和橡胶林内土壤呼吸和异养呼吸速率均为雨季＞干热季＞雾凉季,但季节雨林内根系呼吸为雨季＞雾凉季＞干热季,而橡胶林内为雾凉季＞雨季＞干热季;季节雨林内根系呼吸对土壤呼吸的贡献率(29%)小于橡胶林(42%,P＜0.01),而季节雨林内异养呼吸对土壤呼吸的贡献率为71%、橡胶林为58%;当5 cm土壤温度在12 ℃～32 ℃范围内变化时,季节雨林内土壤呼吸及根系呼吸、异养呼吸的Q₁₀值均大于橡胶林,且异养呼吸的Q₁₀值最大而根系呼吸的Q₁₀值最小.     

青海省森林土壤有机碳氮储量及其垂直分布特征

森林土壤在调节森林生态系统碳、氮循环和减缓全球气候变化中起着关键的作用。但是,由于林型、林龄以及环境因子(海拔)的差异,至今对于森林土壤碳、氮储量的估算依然存在极大的不确定性。因此,利用森林土壤实测数据估算了青海森林土壤有机碳、氮密度和碳、氮储量,分析了土壤有机碳、氮密度的垂直分布格局。结果表明:1)土壤有机碳密度随海拔的增加呈单峰曲线变化,在海拔3100—3400 m达到最大34.33 kg/m~2;氮密度随海拔的增加而增加,范围为1.39—2.93 kg/m~2。2)在0—30 cm土层,土壤有机碳、氮密度均随土层的增加而降低,范围分别为3.84—4.63 kg/m~2、0.22—0.27 kg/m~2。3)青海省森林土壤碳储量为1098.70 Tg,氮储量为61.78 Tg。4)海拔与氮含量和密度之间存在极显著正相关关系(P0.01,P0.01)。土层深度与有机碳含量存在极显著负相关关系(P0.01);与有机碳密度、氮密度存在极显著正相关关系(P0.01,P0.01)。说明海拔和土层是影响青海省森林土壤有机碳、氮分布的关键因子。     

基于1∶100万土壤数据库的中国土壤有机碳密度及储量研究

基于中国1∶100万土壤数据库,利用土壤有机碳储量和碳密度的空间化表达和计算方法研究中国土壤有机碳密度及储量.土壤空间数据库包含926个土壤类型单元,690个土属类型,94 000多个图斑;土壤属性数据库收录了7 292个全国各类型土壤的剖面数据,包括81个土壤属性字段.研究采用“土壤类型GIS连接法”实现土壤剖面有机碳密度与图形图斑连接,通过制图单元碳储量求和得出全国或者区域碳储量,并利用面积平均法计算全国及各类型土壤的有机碳平均密度.结果表明,中国的土壤面积共有928.10×10⁴ km²,有机碳储量为89.14 Pg (1 Pg=10¹⁵ g),土壤平均碳密度9.60 kg·m^-2,是目前与真值最为接近的研究结果.     

松嫩平原玉米带土壤碳氮储量的空间特征

利用第二次全国和县级土壤普查的382个典型土壤剖面资料和1∶50万数字化土壤图建立土壤剖面空间数据库,利用土壤类型法估算松嫩平原玉米带土壤碳、氮储量,分析土壤有机碳、氮密度的空间分布特征,探讨土壤有机碳、氮密度与土壤类型和土地利用类型之间的关系.结果表明:松嫩平原玉米带土壤有机碳、氮储量分别为(163.12±26.48)Tg和(9.53±1.75)Tg,土壤碳、氮储量主要集中在草甸土、黑钙土和黑土等土类中.土壤有机碳、氮密度分别为5.51～25.25和0.37～0.80kg·m-2,土壤C/N值大致在7.90～12.67.土壤有机碳、氮密度的空间分布均表现为东部和北部高、西部低.在不同土地利用类型中,旱田土壤的有机碳密度最高,为(19.07±2.44)kg·m-2;林地土壤的氮密度最高,为(0.82±0.25)kg·m-2;水田土壤的碳、氮密度均较低.     

基于1∶100万土壤数据库的中国土壤有机碳密度及储量研究

基于中国1∶100万土壤数据库,利用土壤有机碳储量和碳密度的空间化表达和计算方法研究中国土壤有机碳密度及储量.土壤空间数据库包含926个土壤类型单元,690个土属类型,94000多个图斑;土壤属性数据库收录了7292个全国各类型土壤的剖面数据,包括81个土壤属性字段.研究采用“土壤类型GIS连接法”实现土壤剖面有机碳密度与图形图斑连接,通过制图单元碳储量求和得出全国或者区域碳储量,并利用面积平均法计算全国及各类型土壤的有机碳平均密度.结果表明,中国的土壤面积共有928.10×104km2,有机碳储量为89.14Pg(1Pg=1015g),土壤平均碳密度9.60kg.m-2,是目前与真值最为接近的研究结果.     

热带季节雨林和人工橡胶林林冠截留雾水的比较研究

利用 4a( 1 999～ 2 0 0 2 )的雾水截留观测资料 ,对西双版纳热带季节雨林和人工橡胶林林冠截留雾水进行了研究。热带季节雨林和人工橡胶林全年由林冠截留的雾水分别达 89.4± 1 3.5 mm和 1 8.6± 2 .5 mm(平均值±标准差 ) (雾季各占 62 .9%± 4.8%和 91 .9%± 6.3% ) ,分别占全年降水量的 4.9%± 1 .7%和1 .1 %± 0 .2 %。年雾水截留量与年降雨量呈负相关关系。月雾水截留量与月均最低气温呈显著的负相关 ,与月均相对湿度、月均 0∶ 0 0～ 1 0∶ 0 0风速呈显著的正相关。热带季节雨林全年 68%± 5 %、人工橡胶林40 %± 4%的有雾天气里可以收集到雾水 (分别为 0 .38± 0 .2 7mm/ d和 0 .2 4± 0 .1 2 mm/ d) ,且日雾水截留量与气温和风速呈显著的相关 ,即 :气温越低、风速越大 ,日雾水截留量越多。对本地区热带季节雨林生态系统的健康生长和维持而言 ,雾及雾水极大的弥补了降雨量的不足 ,雾的这种作用在降雨量少的年份似乎更为重要     

东北次生杨桦林土壤碳氮动态特征

土壤分级组分是研究其碳氮动态的基础,次生杨桦林作为东北地区主要的天然林类型,目前相关数据的欠缺状态要求对此进行深入研究。为此,采集0—10cm、10—20cm、20—30cm长白山次生杨桦林土壤,通过土壤颗粒组分物理化学分级方法,将土壤分成5种组分:沙和稳定团聚体土壤组分(SA)、酸不溶土壤组分(AI)、易氧化土壤组分(EO)、颗粒态土壤组分(P)和可溶性土壤组分(S),进而分析了不同组分的质量分数、碳氮含量、碳氮分配比例及红外光谱5类官能团相对含量,旨在探讨次生杨桦林土壤固碳、氮供应机制。结果显示,接近90%的土壤质量集中在稳定组分AI(66.21%)和SA(22.11%)上,导致稳定组分中碳截获量最大(占土壤总碳量的2/3),而且其C/N比活跃组分(P和EO)大2—9倍;与碳不同,由于活跃组分中N含量比稳定组分大4—80倍,致使活跃组分P和EO氮的分配比例最大,分别占土壤总氮的33.1%和26.0%;除了占土壤质量很少的P和S外,组分间以及组分内的碳氮间多具有显著相关关系。这种土壤碳、氮在不同组分间贮存方式的差异使得土壤碳储存稳定性更高、而N肥力供应更快速。伴随不同组分碳氮储存的变化,不同组分间红外官能团存在显著差异,AI组分中绝大多数官能团相对含量均最低,而P和S组分中绝大多数官能团相对含量均较高,绝大多数官能团相对含量与碳含量、氮含量呈现显著的正相关关系,反映了官能团具有维持土壤碳氮的功能。同时,官能团与土壤C/N具有显著相关关系,反映出组分官能团相对含量的高低具有指示组分化学活性高低的作用。研究发现对于林分土壤的碳截获与氮供应的机制阐明具有重要的科学意义,这为深入了解东北次生杨桦林碳氮动态及对未来气候的响应提供基础数据。     

有机物料中有机碳和有机氮的分解进程及分解残留率

在中国科学院沈阳生态站(埋袋法)和海伦站(砂滤管法)研究了不同有机物料中有机碳和有机氮的矿化进程、分解残留率和C/N的动态变化.结果表明:有机物料中有机碳和有机氮的分解进程可分为快、慢2个阶段;各有机物料中有机氮的矿化速率均明显低于有机碳,因而其残留率高于有机碳;有机物料C/N的下降速率也可分为快、慢2个阶段.经3～5年分解后,各种有机物料残留物的C/N趋于稳定:低C/N有机物料(猪粪)残留物的C/N值接近土壤腐殖质的C/N,约为10,已完成其腐殖化过程;高C/N有机物料残留物的C/N值处于适宜微生物活动的25左右,利于增加土壤有机质、培肥土壤.     

根系分泌物C∶N对刺槐林地土壤理化特征和土壤呼吸的影响

为探究根系分泌物C∶N对土壤养分循环及微生物活性的影响,本研究以黄土高原人工刺槐林为对象,在生境条件基本一致的15、25、35、45 a刺槐林地取原位土壤,通过模拟不同C∶N的根系分泌物(只添加N、C∶N=10、C∶N=50、C∶N=100和只添加C)添加至土壤,以去离子水作为对照,分析根系分泌物C∶N对土壤碳、氮、磷、pH值等理化特征和土壤呼吸的影响。结果表明: 1)有机碳含量与根系分泌物C∶N呈正相关,根系分泌物C∶N=10时土壤有机碳(SOC)分解较快,高根系分泌物C∶N(C∶N=100)能延缓SOC分解,而只添加C处理对SOC无显著影响。2)不同C∶N根系分泌物处理对全氮的影响不明显,碳添加能促进微生物对铵态氮的吸收,氮添加能促进铵态氮的硝化,随着根系分泌物C∶N增加,土壤中铵态氮含量下降。3)氮添加会导致土壤pH值下降,增加土壤全磷含量。4)刺槐林地土壤呼吸值与根系分泌物C∶N呈正相关,随着C∶N增加,根系分泌物对25和35 a人工刺槐林土壤呼吸的促进作用更显著。综上,根系分泌物C∶N值越高,对人工刺槐林土壤呼吸的促进作用越显著。研究结果进一步加深了对森林根系-土壤-微生物互作过程的认识。     

Effects of forest management on soil N cycling in beech forests stocking on calcareous soils

The effects of forest management (thinning) on gross and net N conversion, the balance of inorganic N production and consumption, inorganic N concentrations and on soil microbial biomass in the Ah layer were studied in situ during eight intensive field measuring campaigns in the years 2002–2004 at three beech (Fagus sylvatica L.) forest sites. At all sites adjacent thinning plots (“T”) and untreated control plots (“C”) were established. Since the sites are characterized either by cool-moist microclimate (NE site and NW site) or by warm-dry microclimate (SW site) and thinning took place in the year 1999 at the NE and SW sites and in the year 2003 at the NW site the experimental design allowed to evaluate (1) short-term effects (years 1–2) of thinning at the NW site and (2) medium-term effects (years 4–6) of thinning under different microclimate at the SW and NE site. Microbial biomass N was consistently higher at the thinning plots of all sites during most of the field campaigns and was overall significantly higher at the SWT and NWT plots as compared to the corresponding untreated control plots. The size of the microbial biomass N pool was found to correlate positively with both gross ammonification and gross nitrification as well as with extractable soil NO₃⁻ concentrations. At the SW site neither gross ammonification, gross nitrification, gross ammonium (NH₄⁺) immobilization and gross nitrate (NO₃⁻) immobilization nor net ammonification, net nitrification and extractable NH₄⁺ and NO₃⁻ contents were significantly different between control and thinning plot. At the NET plot lower gross ammonification and gross NH₄⁺ immobilization in conjunction with constant nitrification rates coincided with higher net nitrification and significantly higher extractable NO₃⁻ concentrations. Thus, the medium-term effects of thinning varied with different microclimate. The most striking thinning effects were found at the newly thinned NW site, where gross ammonification and gross NH₄⁺ immobilization were dramatically higher immediately after thinning. However, they subsequently tended to decrease in favor of gross nitrification, which was significantly higher at the NWT plot as compared to␣the␣NWC plot during all field campaigns after␣thinning except for April 2004. This increase␣in␣gross nitrification at the NWT plot (1.73 mg N kg⁻¹ sdw day⁻¹ versus 0.48 mg N kg⁻¹ sdw day⁻¹ at the NWC plot) coincided with significantly higher extractable NO₃⁻ concentrations (4.59 mg N kg⁻¹ sdw at the NWT plot versus 0.96 mg N kg⁻¹ sdw at the NWC plot). Pronounced differences in relative N retention (the ratio of gross NH₄⁺ immobilization + gross NO₃⁻ immobilization to gross ammonification + gross nitrification) were found across the six research plots investigated and could be positively correlated to the soil C/N ratio (R = 0.94; p = 0.005). In sum, the results obtained in this study show that (1) thinning can lead to a shift in the balance of microbial inorganic N production and consumption causing a clear decrease in the N retention capacity in the monitored forest soils especially in the first two years after thinning, (2)␣the resistance of the investigated forest ecosystems to disturbances of N cycling by thinning may vary with different soil C contents and C/N ratios, e. g. caused by differences in microclimate, (3) thinning effects tend to decline with the growth of understorey vegetation in the years 4–6 after thinning.     

Land-use change effects on soil C and N transformations in soils of high N status: comparisons under indigenous forest, pasture and pine plantation

Globally, land-use change is occurring rapidly, and impacts on biogeochemical cycling may be influenced by previous land uses. We examined differences in soil C and N cycling during long-term laboratory incubations for the following land-use sequence: indigenous forest (soil age = 1800 yr); 70-year-old pasture planted after forest clearance; 22-year-old pine (Pinus radiata) planted into pasture. No N fertilizer had been applied but the pasture contained N-fixing legumes. The sites were adjacent and received 3–6 kg ha^–1 yr^–1volcanic N in rain; NO₃ ^–-N leaching losses to streamwater were 5–21 kg ha^–1 yr^–1, and followed the order forest < pasture = pine. Soil C concentration in 0–10 cm mineral soil followed the order: pasture > pine = forest, and total N: pasture > pine > forest. Nitrogen mineralization followed the order: pasture > pine > forest for mineral soil, and was weakly related to C mineralization. Based on radiocarbon data, the indigenous forest 0–10 cm soil contained more pre-bomb C than the other soils, partly as a result of microbial processing of recent C in the surface litter layer. Heterotrophic activity appeared to be somewhat N limited in the indigenous forest soil, and gross nitrification was delayed. In contrast, the pasture soil was rich in labile N arising from N fixation by clover, and net nitrification occurred readily. Gross N cycling rates in the pine mineral soil (per unit N) were similar to those under pasture, reflecting the legacy of N inputs by the previous pasture. Change in land use from indigenous forest to pasture and pine resulted in increased gross nitrification, net nitrification and thence leaching of NO₃ ^–-N.     

滇南热带季节雨林和橡胶林对降雨侵蚀力的减缓效应

降雨是影响土壤侵蚀的主要因素,降雨侵蚀力通常用降雨动能和一段时间的最大雨强的乘积表示,简化的计算也可用日降雨量估算。本文选取昆-曼国际大通道滇南段旷地4个气象站(勐腊、勐仑、景洪、思茅)以及1个人工林(橡胶林)和1个热带季节雨林的日降雨量资料,计算了降雨侵蚀力以及随季节变化的规律,比较了森林破坏对降雨侵蚀力的影响。结果表明,昆-曼国际大通道滇南段旷地的降雨侵蚀力干季均较小,雨季逐渐增大,在7、8月达最大;旷地的降雨侵蚀力明显大于橡胶林和热带季节雨林,其差值在干季较小,雨季显著;旷地的年降雨侵蚀力可达到橡胶林的1.8倍以上,是热带季节雨林的2.3倍以上;而月降雨侵蚀力差异最大可达6~7倍;此外橡胶林和热带季节雨林降雨侵蚀力干季相差不大,而雨季橡胶林降雨侵蚀力明显大于热带季节雨林。说明了水土保持效果橡胶林和热带季节雨林比旷地要好,而热带季节雨林的效果要比橡胶林好;森林破坏将极大地增加降雨侵蚀力,加速水土流失。     

不同林龄落叶松人工林土壤微生物生物量碳氮的季节变化

为从土壤微生物生物量角度分析不同林龄落叶松人工林的土壤肥力状况,对辽宁东部山区两种林龄(9年生,幼龄林;43年生,成熟林)落叶松人工林不同土层(腐殖质层和矿化层)微生物生物量碳、氮季节变化进行了监测,并分析了微生物生物量碳氮的季节变化与土壤养分及水分的关系.结果表明:两种林龄落叶松腐殖质层微生物生物量碳、氮含量均高于矿化层;在腐殖质层,幼龄林微生物生物量碳、氮含量高于成熟林.方差分析表明,在春、秋季节,同一土层两林龄土壤微生物生物量碳、氮含量之间差异达到显著水平(P<0.01).在观测的3个季节内,幼龄林腐殖质层的微生物生物量碳基本无变化,而成熟林的微生物生物量碳在秋季达到最高;两种林龄落叶松微生物生物量氮均在夏季达到最高.在矿化层,两种林龄落叶松微生物生物量碳、氮均在秋季达到最大.相关分析发现,微生物生物量碳、氮之间以及土壤微生物生物量碳、氮与土壤有机碳、全氮呈显著正相关,而与土壤水分无相关性;另外,落叶松人工林内的灌木种类和数量以及季节性温度变化对土壤微生物生物量碳氮也有影响.上述结果表明,研究区域土壤微生物生物量碳、氮的季节波动与土壤养分状况密切相关,幼龄林土壤养分状况优于成熟林.     

Litter type control on soil C and N stabilization dynamics in a temperate forest

While plant litters are the main source of soil organic matter (SOM) in forests, the controllers and pathways to stable SOM formation remain unclear. Here, we address how litter type (¹³C/¹⁵N‐labeled needles vs. fine roots) and placement‐depth (O vs. A horizon) affect in situ C and N dynamics in a temperate forest soil after 5 years. Litter type rather than placement‐depth controlled soil C and N retention after 5 years in situ, with belowground fine root inputs greatly enhancing soil C (x1.4) and N (x1.2) retention compared with aboveground needles. While the proportions of added needle and fine root‐derived C and N recovered into stable SOM fractions were similar, they followed different transformation pathways into stable SOM fractions: fine root transfer was slower than for needles, but proportionally more of the remaining needle‐derived C and N was transferred into stable SOM fractions. The stoichiometry of litter‐derived C vs. N within individual SOM fractions revealed the presence at least two pools of different turnover times (per SOM fraction) and emphasized the role of N‐rich compounds for long‐term persistence. Finally, a regression approach suggested that models may underestimate soil C retention from litter with fast decomposition rates.