Different radial growth responses to climate warming by two dominant tree species at their upper altitudinal limit on Changbai Mountain

We analyzed the influence of climate change over the past 50 years on the radial growth of two tree species: Korean pine(Pinus koraiensis) and Yezo spruce(Picea jezoensis), located on Changbai Mountain, Northeast China, using a dendrochronology approach to understand factors that limit the altitude for tree species.Elevated temperatures increased the radial growth of Korean pine and decreased that of Yezo spruce. The positive response of tree growth to hydrothermal conditions was the key reason that the upper limit of elevation of Korean pine followed the temperature fluctuation pattern.Increased temperatures and precipitation and longer growing seasons accelerated Korean pine growth. As the temperature increased, correlations between Korean pine ring-width chronology and precipitation changed from negative to positive. In Yezo spruce, increasing monthly temperatures and inadequate precipitation during the middle and late parts of the growing season led to narrow growth rings, whereas decreasing monthly temperatures and sufficient precipitation during the late growing season promoted growth. Rising temperatures and adequate precipitation increases Korean pine growth, possibly elevating the upper range limit in altitude for this species. In contrast,Yezo spruce growth is negatively affected by warming temperatures and limited precipitation. Under future temperature increases and precipitation fluctuations, the upper limit altitude of Korean pine can reasonably be expected to shift upward and Yezo spruce downward.

Coarse woody debris features of a warm temperate deciduous broad-leaved forest,northern China

Stocking and structural composition of a deciduous broad-leaved forest were determined to predict coarse woody debris quantity by quantifying the empirical relationships between these two attributes.The most ecologically significant families by stem density were Salicaceae,Betulaceae,Fagaceae,and Aceraceae.P opulus davidiana was the most dominant species followed by B etula dahurica,Quercus mongolica,and Acer mono.The four species accounted for 69.5%of total stems.Numerous small-diameter species characterized the coarse woody debris showing a reversed J-shaped distribution.The coarse debris of P.davidiana,B.dahurica,and Q.mongolica mainly comprised the 10–20 cm size class,whereas A.mono debris was mainly in the 5–10 cm size class.The spatial patterns of different size classes of coarse woody debris were analyzed using the g-function to determine the size of the tree at its death.The results indicate that the spatial patterns at the 0–50 m scale shifted gradually from an aggregated to a random pattern.For some species,the larger coarse debris might change from an aggregated to a random distribution more easily.Given the importance of coarse woody debris in forest ecosystems,its composition and patterns can improve understanding of community structure and dynamics.The aggregation pattern might be due to density dependence and self-thinning effects,as well as by succession and mortality.The four dominant species across the different size classes showed distinct aggregated distribution features at different spatial scales.This suggests a correlation between the dominant species population,size class,and aggregated distribution of coarse woody debris.

温带草原生态系统土壤原核生物特征对自然水分梯度的响应

土壤水分是影响生态系统功能的重要因素,其不仅可以维持微生物的活性,还可以通过改变植被多样性,控制土壤养分的扩散和运输,最终改变微生物群落。为探索土壤含水量对土壤原核生物群落的影响,本研究在中国内蒙古呼伦湖南岸的草原生态系统中建立了一个覆盖自然土壤水分梯度的研究区域,并将其细分为高含水量(4.80%±1.18%)、中含水量(2.17%±0.09%)和低含水量(1.85%±0.14%)三个梯度。环境因子是通过实地调查和实验室分析获得的。土壤原核生物是通过高通量测序技术测定的。植被特征和土壤理化性质对原核生物丰富度多样性有显著影响,其中土壤含水量是最重要的影响因素。在中含水量梯度中,差异原核生物的数量最少,且门水平原核微生物的多样性和相对丰度最高。这表明中含水量梯度下的原核生物群落的内在变异较小,整体活性较高。此外,高含水量和低含水量梯度的原核生物多样性和门水平相对丰度较低。表型预测结果表明,这两组条件下的原核微生物群落具有更强的耐受性。总之,原核生物群落对呼伦湖南岸草地生态系统的自然水分梯度有明显响应,土壤水分过高或过低都会增加原核生物的抗逆性。

温带草原退化后土壤微生物群落结构和功能的变化

草原退化是草原生产力维持面临的一个重大挑战,这一过程显著影响着草原生态系统的能量流动和土壤养分变化过程,进而直接或间接地影响着土壤微生物。我们的研究目的首先是调查不同草原退化程度(即未退化、中度退化和严重退化)如何影响着内蒙古温带草原的土壤微生物组成、多样性和功能,其次是阐明哪些生物和非生物因素导致了这些变化。我们的研究主要通过高通量测序技术分析土壤微生物的群落组成,并且采用FAPROTAX工具和FUNGuild工具分别预测细菌群落和真菌群落的功能。研究发现:草原退化显著降低了土壤细菌的多样性,但对真菌多样性影响不大。地下生物量、土壤有机碳和总氮与细菌的多样性变化呈显著正相关关系。草原退化显著增加了绿弯菌门的相对丰度(由2.48%提高到8.40%),降低了厚壁菌门的相对丰度(由3.62%降低到1.08%)。其次,草原退化也显著增加了球囊菌门的相对丰度(从0.17%提高到1.53%),降低了担子菌门的相对丰度(从19.30%降低到4.83%)。致病菌的相对丰度在草原退化过程中显著下降。此外,草原退化对土壤细菌群落的功能有显著的影响,尤其是与土壤碳氮循环相关的土壤细菌群落。我们的结果表明,土壤细菌群落对草原退化的响应比真菌群落更敏感。