Linking tree growth and intra-annual density fluctuations to climate in suppressed and dominant Pinus sylvestris L. trees in the forest-steppe of Southern Siberia

Climate change affects forest dynamics with potential consequences for essential ecosystem services. The retrospective analysis of secondary growth unveils the effect of climate on forests. However, most tree-ring studies focus on dominant trees, and less is known about the climatic response of their neighbor suppressed trees. We evaluated the influence of tree social status (dominant/suppressed) on climate response in Pinus sylvestris L. trees from two sites with contrasting water availability conditions in the forest-steppe ecotone in southern Siberia. Tree-ring width and intra-annual density fluctuations (IADFs) were used as proxies. Late spring to early summer conditions were the main climate drivers in both tree social status, but the climate response of suppressed trees was stronger and had a longer time window (May-June). IADFs’ occurrence was controlled by temperature and its frequency was modulated by local conditions, being more common at the dry site, with tree status just marginally significant. Our results suggest that under the projected warmer and drier climate, suppressed trees in southern Siberia will be prone to increased water shortage, leading to possible higher mortality of more sensitive suppressed trees, with potential consequences for carbon sequestration in the forest-steppe ecosystems in southern Siberia.     

森林固碳释氧服务价值与异养呼吸损失量评估

固碳释氧是森林最重要的生态系统服务之一,将森林碳收支与固碳释氧服务价值评估相结合对于准确评估生态系统服务价值具有重要意义。应用森林碳收支模型(CBM-CFS3),分别基于净初级生产力(NPP)和净生态系统生产力(NEP)评估了2009—2030年湖北省兴山县森林生态系统总、净固碳释氧服务价值的时空动态,量化了异养呼吸造成的固碳释氧服务价值损失。模拟期间兴山县森林生态系统NPP逐渐增加(0.46—0.70 Tg/a),NEP由0.12 Tg/a先增加至0.21 Tg/a,然后逐渐下降至0.18 Tg/a;所对应的森林总、净固碳释氧服务价值范围分别为7.59—11.53亿元/a和2.21—3.70亿元/a。异养呼吸逐年增加,导致固碳释氧价值每年损失平均值为7.29亿元/a或4509元hm~(-2) a~(-1),约占总价值的68.6%。兴山县东南部异养呼吸造成的森林固碳释氧服务价值损失较高,而中部及西南部森林净固碳释氧价值较高。模拟期间兴山县森林为碳汇,稳定地提供固碳释氧服务。与NPP相比,使用NEP评估固碳释氧服务价值更为合理。忽视异养呼吸将严重高估森林生态系统固碳释氧服务价值;因而必须将物质循环过程与生态系统服务评估相结合,以降低评估结果的不确定性、提高生态系统服务的评估能力。     

长江三峡库区土地利用/覆盖的长期变化

了解土地利用/覆盖的时空变化有助于揭示气候变化和人类活动对生态系统的影响,是开展生态系统管理的重要前提.长江三峡库区是我国重要的生态脆弱区,环境变化影响的复杂性显著,但目前对此仍缺乏系统了解.本文通过解译Landsat时序遥感影像,获取三峡库区土地利用/覆盖数据,研究土地利用/覆盖构成结构及其分布的长期时空变化特征,以揭示三峡库区土地利用/覆盖的演变规律,为深入了解生态脆弱区生态系统变化复杂性和区域生态系统管理提供科学依据.结果表明: 1990—2015年间,三峡库区土地利用/覆盖结构的空间异质性和变化显著,农田面积比例由66.2%降至40.4%,林地面积比例由31.3%增至53.5%,库区由农业景观转变为以森林、灌木林等为主的林地景观,建设用地和水体逐渐增加;林地逐渐向库区中部扩张,建设用地点状扩张;海拔500～1000 m和坡度15°～25°区域林地面积比例增长最明显,针叶林、针阔混交林和灌木林等植被类型增长最快.研究期间,三峡水库建设和各类生态恢复工程的实施促使区域土地利用/覆盖结构呈阶段性变化,总体表现为生态恢复趋势.积极的生态恢复措施有助于消减工程建设对区域生态环境的负面影响.     

引入固氮树种对辽东落叶松人工林土壤团聚体氨基糖的影响

土壤微生物残留物是稳定性碳库的重要组分,然而固氮树种引入对落叶松人工林土壤团聚体微生物残留物分布的影响还不清楚.为了阐明固氮树种对不同团聚体粒级内微生物残留物分布的影响,本研究以氨基糖作为微生物残留物的生物标识物,比较了辽东日本落叶松人工纯林和落叶松与固氮树种赤杨混交林土壤团聚体氨基糖的分布特征.结果表明: 赤杨引入不影响团聚体氨基糖的分布,但显著提高了团聚体氨基糖含量.与纯林相比,混交林土壤不同团聚体各粒级总氨基糖含量增加1.3～1.7倍.其中,混交林土壤团聚体内总氨基糖增加量的66.5%～66.9%来自氨基葡萄糖,30.0%～30.6%来自氨基半乳糖,2.5%～3.2%来自胞壁酸.赤杨引入显著提高了>2000 μm和<250 μm团聚体中的氨基葡萄糖/胞壁酸值,但不影响250～2000 μm粒级团聚体中真菌和细菌残留物的相对贡献.此外,赤杨引入增加了土壤不同团聚体内的氨基糖对土壤有机碳的贡献,但不影响团聚体粒级之间的微生物贡献,说明赤杨对微生物贡献的影响存在空间均一性.     

栓皮栎叶片δ13C和δ15N的纬向趋势及其影响因子

以东亚广布种栓皮栎为例,通过对南北样带(26°-40° N)上7个群体的调查取样,并结合2个生活史阶段,探讨栓皮栎碳氮同位素比值随纬度环境的变异规律.结果表明: 在纬向梯度上,栓皮栎叶片δ¹³C和δ¹⁵N随纬度的增加分别呈现非线性的增加和下降趋势,且成年树叶片δ¹³C和δ¹⁵N均显著高于幼树;同时,树龄和纬度对叶片δ¹⁵N和δ¹³C均无显著交互作用,表明栓皮栎幼树和成年树纬向环境变化的响应较为一致.随机森林模型结果显示,栓皮栎叶片δ¹⁵N主要受土壤养分,如土壤有机质、磷和氮含量的影响,而叶片δ¹³C主要受水分因子,如空气相对湿度、降水量等的影响.     

以小时为步长的大兴安岭典型林分地表死可燃物含水率模型预测及外推精度

地表死可燃物含水率是火险天气和火行为预报中的重要指标.本研究基于时滞平衡含水率法(Nelson和Simard方法)及气象要素回归方法,于2010年9—10月对黑龙江省大兴安岭地区盘古林场不同郁闭度的山杨-白桦混交林、红皮云杉纯林,以及采伐迹地(原1∶1樟子松-白桦混交林)地表死可燃物含水率进行以小时为步长的连续测定,建立其预测模型,得到预测误差,并使用相应的模型对其他林分地表死可燃物含水率进行外推精度分析.结果表明:采用Nelson平衡含水率法构建的地表死可燃物含水率变化模型的平均绝对误差、平均相对误差和均方误差根(0.0154、0.104和0.0226)低于Simard法(0.0185、0.117和0.0256)和气象要素回归法(0.0222、0.150和0.0331).在外推效果方面,气象要素回归法的平均绝对误差、平均相对误差和均方误差根(0.0410、0.0300和0.0740)低于Simard法(0.610、0.492和0.846),但前两者均高于Nelson法(0.034、0.021和0.0660),说明以小时为步长的时滞平衡含水率法,尤其是Nelson法适用于大兴安岭地区所测林分.外推虽不能降低误差,但有助于提高现有模型应用至不同林分条件或大尺度范围内的地表死可燃物含水率预测精度和利用率.模型建模和外推误差与不同树种和郁闭度条件差异有关,研究时应根据不同林分和地点选择合适的平衡含水率模型.     

细胞外Ba2+对大鼠心肌细胞L型钙通道的影响

目的：观察细胞外Ba²⁺对记录大鼠心肌细胞L型钙通道的影响。方法：采用急性酶解分离法获得大鼠的单个心肌细胞,使用全细胞膜片钳技术记录L型钙通道电流。采用Ba²⁺替换台式液中的Ca²⁺和直接向台式液中加入Ba²⁺（0~8 mmol/L）,观察峰值电流15 min内的变化,数据采用5个以上细胞进行重复。结果：（1）台式液中的Ca²⁺被Ba²⁺替换后,L型钙通道电流的失活速率明显减慢（P<0.01）;在台式液中加入少量Ba²⁺（0.2,0.4 mmol/L）时L型钙通道电流的失活速率无明显改变（P>0.05）,加入0.8 mmol/L Ba²⁺时失活速率明显减慢（P<0.05）。（2）与正常台式液比较,在细胞外液中加入Ba²⁺（0.2,0.4 mmol/L）峰值电流衰减减弱,其中10 min和15 min两个时间点衰减差异明显（P<0.01）。（3）在细胞外液中加入Ba²⁺可下移电流电压曲线,改变翻转电位,减弱丹酚酸A对钙电流的抑制强度,使量效关系曲线右移。结论：在细胞外液中加入一定浓度的Ba²⁺,能够减弱全细胞膜片钳技术记录大鼠心室肌细胞L型钙通道时出现的峰值电流衰减,改变通道的电压依赖特性,影响药物量效关系。     

Cellulose oxygen isotopic composition of teak (Tectona grandis) collected from Java Island: a tool for dendrochronological and dendroclimatological analysis

The oxygen isotopic composition (δ¹⁸O) of tree-ring cellulose has been recognized as a powerful tool for dendroclimatological and dendrochronological investigations in Asia. Only a few studies of cellulose δ¹⁸O so far published, however, have been conducted in Indonesia, and the spatial coherence of cellulose δ¹⁸O has yet to be clarified. In this study we measured cellulose δ¹⁸O of teak (Tectona grandis) collected from four sites on Java Island to evaluate the similarity between the different teak δ¹⁸O values and the potential for using teak δ¹⁸O both as a climate proxy and as a tool for cross-dating. Cellulose δ¹⁸O time series of Javanese teaks were found to be significantly correlated in all of the comparisons between sites, even between sites separated by a distance as great as 400 km. While significant correlations did not appear in the ring width data between our samples (expressed population signal (EPS) = 0.64; Rbar = 0.23; sample depth = 10), they were found between the cellulose δ¹⁸O values (EPS = 0.89; Rbar = 0.58; sample depth = 10). These results suggest that teak δ¹⁸O variations have higher spatial coherence and might be a useful tool for cross-dating. A significant negative correlation was observed between cellulose δ¹⁸O and the relative humidity/precipitation during the rainy season, indicating that the cellulose δ¹⁸O of Javanese teak is an effective proxy for relative humidity/precipitation during the rainy season. Cellulose δ¹⁸O was found to be positively correlated with precipitation during the dry season preceding the growing season, whereas it showed no correlations with the temperature and Palmer Drought Severity Index (PDSI), the key constraints of δ¹⁸O on the Indochina Peninsula.