Are regional precipitation–productivity relationships robust to decadal-scale dry period?

降水-生产力的空间关系是否稳定不变？ 降水是全球陆地生态系统中植被生长和净初级生产力的主要驱动因素。因此,探究降水和生产力关系有助于深入了解气候变化如何改变生态系统功能。降水-生产力的空间关系在全球不同草地上非常相似,但在连续多年气候异常的情况下,这种关系是否会发生变化以及如何变化尚不清楚。本研究利用 利用中国北方温带草地长达10年低于多年平均降水的时期,基于遥感植被指数数据,量化了区域尺度上降水-植被生产力关系在持续多年的干湿期之间将如何变化。结果表明,在连续10年的干期,降水-生产力空间相关性急剧下降,而该空间关系的下降主要是由于不同草原类型对干旱的响应在空间上存在高度的异质性,即不同生态系统对干旱的响应程度存在差异。因此,如果未来气候变化进一步加剧全球草地的干旱,那么基于历史时期(平水期)得到的降水-生产力空间关系推测区域尺度植被生产力可能导致误差。     

Greater soil microbial biomass loss at low frequency of N addition in an Inner Mongolia grassland

低频率的氮添加使内蒙古草原土壤微生物生物量碳出现更大幅度下降 土壤微生物生物量在生物地球化学循环过程中至关重要,是土壤碳固持的前体物质。人为氮输入深刻地改变了草地土壤微生物生物量。然而,传统氮沉降模拟实验仅通过低频率的氮添加进行,与持续高频率的自然氮沉降相比,对土壤微生物生物量的影响可能存在差异。不同频率的氮添加对土壤微生物生物量的影响尚缺乏可靠的数据支撑。本研究通过在不同的氮添加速率(0–50 g N m−2 yr−1)下,控制氮添加频率(每年2次和12次),研究了土壤微生物生物量碳对不同氮添加频率的响应。研究结果表明,在两种氮添加频率下,随着施氮水平的提高,土壤微生物生物量碳逐渐降低。然而,在低施氮频率下,土壤微生物生物量的下降幅度更大,这说明传统的氮添加实验可能高估了氮沉降对土壤微生物生物量的影响。在低施氮频率下,土壤酸化、无机氮积累、碳氮失衡、地下净初级生产力分配减少和真菌细菌比例降低等情况加剧,导致微生物生物量出现较大幅度下降。在未来研究中,为可靠预测氮沉降对草地生态系统土壤微生物功能和碳循环的影响,不仅要考虑氮添加的剂量,还需要考虑氮添加的频率。     

Forest Structure and Primary Productivity in a Bornean Heath Forest

Aboveground forest structure, biomass, and primary productivity in a tropical heath forest in Central Kalimantan (Indonesian Borneo) were examined using data from 1-ha plots and stand-level allometric equations developed from harvested tree samples. The study site experienced a severe drought in 1997–1998 associated with the El Niño Southern Oscillation event. The drought effect on heath forest productivity was also assessed by evaluating changes in wood mass increment rates. Allometric relationships suggested that heath forest trees had leaves with smaller specific leaf area (SLA), and large heath forest trees allocate more to leaf mass compared to mixed dipterocarp forest trees. Aboveground biomass (for trees ≥ 4.8 cm DBH) in two 1-ha plots, P1 and P4, totaled 244.8 and 232.0 Mg/ha. Aboveground wood mass increment rate was –0.1 and 4.7 Mg/ha/yr in P1 and P4 during the drought period (from February to August 1998), while it quickly recovered to 8.1 and 8.5 Mg/ha/yr during the post-drought period (from August 1998 to August 1999 for P1 and from August 1998 to November 1999 for P4). This suggests a severe impact of the drought on heath forest productivity. Leaf characteristics of heath forest such as small SLA and long-lived leaves probably play a significant role in effective assimilation and maintenance of heath forest productivity under stressful conditions.     

Physiological adaptability of three mangrove species to salt stress

The impact of salinity on three arboreal mangrove plants, Sonneratia apetala (Sa), S. caseolaris (Sc) and Rhizophora stylosa (Rs), was studied. The three mangrove species were treated with different salinity levels over a three-month period. The response and adaptation of these three mangrove species to salinity were shown to be different. Net photosynthesis rate, stomata conductance and transpiration rate of leaves decreased and soluble sugar content in leaves increased, with salt concentration in all three mangrove species. The malondial dehyde (MDA) content in stems and leaves of Sa and Sc somewhat decreased when the salinity was lower than 10, but rapidly increased with increasing salt concentration. The MDA content in stems and leaves of Rs increased only when salinity was greater than 40. No changes were observed in the MDA content of roots in the three mangrove species. The adaptabilities of Sa and Sc to salt tolerance were limited. The more salt tolerant the mangrove Rs, the more likely the free oxygen radicals were eliminated through the increase in activity of superoxide dismutase (SOD). Results of this experiment identified salinity levels best suited for the growth and metabolism of the species, which provides information necessary for maintaining mangrove forestation along the South China coast.     

显脉金花茶的光合生理特性研究

采用LI-6400便携式光合测定系统(Li-Cor Inc., USA)对显脉金花茶光合特性进行研究。结果表明：(1)在夏季,显脉金花茶叶片的P_n日变化呈单峰曲线,最高峰出现在中午11：00。其最大净光合速率（P_max）为3.81 μmol·m^-2·s^-1、光饱和点（LSP）为459.9 μmol·m^-2·s^-1、光补偿点（LCP）为6.9 μmol·m^-2·s^-1。显脉金花茶的光饱和点和光补偿点都比较低,表明其是一种阴生植物。（2）在控制光照强度和温度的条件下,CO₂浓度小于800 μmol·mol^-1,P_n几乎呈直线上升,升高CO₂浓度可使显脉金花茶的净高合速率增大,提高了叶片对光能的利用率。其叶片CO₂饱和点(CSP)大约在1 200 μmol·mol^-1左右,CO₂的补偿点（Г^*）为70.1 μmol·mol^-1,最大羧化速率（V_cmax）为17.5 μmol·m^-2·s^-1,最大电子传递速率（J_max）为40 μmol·m^-2·s^-1。     

Relations between carbon dioxide fluxes and environmental factors of Kobresia humilis meadows and Potentilla fruticosa meadows

Carbon dioxide fluxes of Kobresia humilis and Potentillafruticosa shrub meadows,two typical ecosystems in the Qinghai-Tibet Plateau,were measured by eddy covariance technology and the data collected in August 2003 were employed to analyze the relations between carbon dioxide fluxes and environmental factors of the ecosystems.August is the time when the two ecosystems reach their peak leaf area indexes and stay stable,and also the period when the net carbon absorptions of Kobresia humilis and Potentilla photo flux densities (PPFD),the carbon dioxide-uptake rate of the Kobresia humilis meadow is higher than that of the Potentilla fruticosa shrub meadow;where the PPFD are rates of the two ecosystems declined as air temperature increased,but the carbon dioxide uptake rate of the Kobresia humilis meadow decreased more quickly (-0.086) than that of the Potentilla fruticosa shrub meadow (-0.016).Soil moistures exert influence on the soil respirations and this varies with the vegetation type.The daily carbon dioxide absorptions of the ecosystems increase with increased diurnal temperature differences and higher diurnal temperature differences result in higher carbon dioxide exchanges.There exists a negative correlation between the vegetation albedos and the carbon dioxide fluxes.     

Land use intensification increasingly drives the spatiotemporal patterns of the global human appropriation of net primary production in the last century

Land use has greatly transformed Earth's surface. While spatial reconstructions of how the extent of land cover and land-use types have changed during the last century are available, much less information exists about changes in land-use intensity. In particular, global reconstructions that consistently cover land-use intensity across land-use types and ecosystems are missing. We, therefore, lack understanding of how changes in land-use intensity interfere with the natural processes in land systems. To address this research gap, we map land-cover and land-use intensity changes between 1910 and 2010 for 9 points in time. We rely on the indicator framework of human appropriation of net primary production (HANPP) to quantify and map land-use-induced alterations of the carbon flows in ecosystems. We find that, while at the global aggregate level HANPP growth slowed down during the century, the spatial dynamics of changes in HANPP were increasing, with the highest change rates observed in the most recent past. Across all biomes, the importance of changes in land-use areas has declined, with the exception of the tropical biomes. In contrast, increases in land-use intensity became the most important driver of HANPP across all biomes and settings. We conducted uncertainty analyses by modulating input data and assumptions, which indicate that the spatial patterns of land use and potential net primary production are the most critical factors, while spatial allocation rules and uncertainties in overall harvest values play a smaller role. Highlighting the increasing role of land-use intensity compared to changes in the areal extent of land uses, our study supports calls for better integration of the intensity dimension into global analyses and models. On top of that, we provide important empirical input for further analyses of the sustainability of the global land system.     

辽西樟子松人工林净生态系统碳交换

樟子松是三北地区造林的主要树种之一,研究樟子松人工林净生态系统碳交换(NEE)及其影响要素对理解我国人工林碳平衡有重要意义。本研究以辽西樟子松人工林为对象,采用涡度相关系统及其配套设备于2020年对樟子松人工林NEE和环境要素进行了原位连续观测。结果表明: 在0.5 h尺度上,1—12月夜间为碳源,白天为碳汇,且受干旱影响5—8月下午碳吸收受到明显抑制。在日尺度上,受干旱影响,控制夜间NEE季节动态的主要要素为土壤温度和土壤湿度,控制白天NEE季节动态的主要要素为土壤湿度和饱和水汽压差;土壤干旱时降水可促进夜间和白天NEE,并导致光合呼吸参数升高。在月尺度上,白天NEE与表观量子利用效率和最大光合速率均呈显著负相关,当空气温度小于5 ℃时,10 ℃生态系统呼吸和生态系统呼吸温度敏感性随空气温度降低而呈线性增加。2020年辽西樟子松人工林NEE积累量为-145.17 g C·m^-2,表现为弱碳汇。     

荒漠短命植物地上和地下生产力对极端干旱和降水的响应

在古尔班通古特沙漠南缘沙垄4个坡位和坡向,设置减少65%和增加65%生长季降水量以模拟极端干旱和极端降水事件,研究极端干旱和极端降水事件对沙垄不同坡位和坡向短命植物层片生产力的影响。结果表明: 极端干旱使地上净初级生产力和地下净初级生产力分别显著降低48.8%和13.7%,极端降水使地上净初级生产力和地下净初级生产力分别显著增加37.9%和23.2%。地上净初级生产力对极端干旱和极端降水的敏感性(0.26和0.21 g·m^-2·mm^-1)显著强于地下净初级生产力的敏感性(0.02和0.03 g·m^-2·mm^-1)。沙垄东坡地上净初级生产力(24.22 g·m^-2)和地下净初级生产力(5.77 g·m^-2)与西坡相比显著增大29.7%和71.7%,而地上净初级生产力和地下净初级生产力对降水变化的敏感性在不同坡位和坡向之间差异不显著。