西双版纳热带山地雨林枯落物及其土壤水文功能

研究了云南西双版纳热带不同海拔梯度山地雨林枯落物层及土壤层水文功能.结果表明: 土壤容重随着海拔的增加而降低,土壤总孔隙度、非毛管孔隙度、毛管孔隙度、土壤最大持水率、最大持水量、有效持水量和土壤含水量随海拔的增加而增加,局部有所波动;雨季前期含水量、饱和含水量和有效调蓄水空间随海拔的增加而增加,其中,饱和含水量和土壤有效调蓄水空间在不同海拔区差异均显著(P<0.05).土壤渗透性能与总孔隙度和非毛管孔隙度均呈极显著正相关关系(P<0.01),其中,非毛管孔隙对土壤渗透性的影响更为显著.不同海拔枯落物未分解层厚度均占总厚度的一半以上,枯落物厚度均表现为未分解层＞半分解层;枯落物总蓄积量和半分解层蓄积量占枯落物总蓄积量的比例均随海拔的增加而增加,说明低海拔枯落物分解速度较慢,高海拔枯落物分解速度较快.不同海拔枯落物半分解层和未分解层最大持水量、最大持水率、自然含水率、有效拦蓄率和有效拦蓄量均随海拔的增加而增加,并且各海拔未分解层均高于半分解层,而有效拦蓄量深度随海拔的增加而降低,局部有所波动.综合未分解层和半分解层的变化规律可知,高海拔拦蓄能力较强,低海拔较弱.不同海拔枯落物持水量随着浸泡时间增加而增加;枯落物吸水速率随着浸泡时间增加而降低,12 h后枯落物吸水速率逐渐趋于饱和.不同海拔枯落物持水量与浸水时间可用对数方程表示;吸水速率与浸泡时间可用冥函数方程表示.综合分析各项因子,低海拔热带山地雨林水源涵养能力普遍低于高海拔.     

Three-dimensional discrete element method for the prediction of protoplasmic seepage through membrane in a biological cell

This paper presents a three-dimensional and compressible biological cell model based on discrete element method using multiple interacting agent that represent cellular structures within a simulated environment. The cytoplasm and nucleoplasm fluid behavior in the cell is time dependent. When taking this approach, it is important to calibrate protoplasmic flow behaviors through simulation techniques such as compressing the cell and examining the agents representing the cell cytoplasm seeping between the ones representing the confining cell membrane. This type of modelling may motivate future work on simulating simultaneous operations and interactions of multiple cellular agents in an attempt to re-create and predict the appearance of complex phenomena such as protoplasmic seepage that is caused by the force actuations of neighboring cells. Seepage occurs when a cytoplasm agent passes between three membrane particles connected in a triangular network. Based on the force–deformation response of spheres having variable size and stiffness, semi-analytic expressions are developed for the force required to cause seepage and solved numerically to find the maximum resistance offered by the membrane against cytoplasm seepage. The equations are based on force equilibrium and the constitutive relations for particle contact and membrane stiffness. In multi-particle representations of an individual cell undergoing deformation, different modes of cytoplasm seepage through confining cell membranes can occur. This can be avoided if simple criteria are satisfied. These findings can lead to certain fundamental laws for the improvement of novel cell-to-organ simulation techniques based on discrete element method.     

黄顶菊凋落物分解对节肢动物群落结构的影响

选择黄顶菊(Flaveria bidentis)入侵的林地、农田、荒地、沟渠等4种生境作为调查样地, 比较黄顶菊与本地植物凋落物的分解速率及凋落物分解对节肢动物群落结构的影响。于2014年10月凋落物高峰期在各样地内分别搜集黄顶菊与本地植物的凋落物, 每种凋落物称取20 g装入尼龙网分解袋中, 放入各生境。2015年的每个月将不同生境不同处理凋落袋各取回10袋, 用Tullgren法分离节肢动物。 4种生境共捕获17,466头, 隶属8纲18目, 4种生境的优势类群皆为蜱螨目和啮目。其中, 林地、农田、荒地、沟渠4种生境处理组中节肢动物数量分别为1,698头, 1,838头, 2,631头, 3,413头, 分别比对照组高18%, 53%, 22%, 11%。多数月份黄顶菊凋落物中的节肢动物丰富度及多样性指数高于同生境对照组, 并且在黄顶菊生长盛期差异显著; 黄顶菊凋落物的分解速率高于对照植物分解速率, 且各月份凋落物分解速率动态与节肢动物数量变化动态呈显著相关。黄顶菊凋落物对节肢动物的影响与人为干扰程度有关, 这种影响在人为干扰较小的荒地与沟渠生境中更为明显。综上所述, 黄顶菊凋落物的分解改变了节肢动物群落结构, 并引起节肢动物多样性的升高。     

张广才岭西坡不同起源林分土壤碳收支机制研究

对五常凤凰山林场皆伐迹地上45年生不同起源（人工更新、人天混更新、天然更新）形成的次生阔叶林、落叶松与阔叶树混交林和人工更新土壤碳输入和输出的季节动态进行研究,探讨不同起源对林分土壤碳收支的影响。结果表明：（1）不同起源土壤有机碳含量为针阔混交林显著高于落叶松纯林(P＜0.05),次生阔叶林居中,且与二者差异不显著（P＞0.05）;（2）不同起源林分叶凋落物总量表现出次生阔叶林＞针阔混交林＞落叶松纯林,且次生阔叶林显著高于落叶松纯林（P＜0.05）;（3）3种起源林分凋落物分解速率顺序为次生阔叶林>针阔混交林>落叶松纯林;（4）不同起源林分不同季节土壤呼吸速率均以次生阔叶林最高,落叶松人工林最低;（5）不同起源林分土壤微生物生物量碳（MBC）、土壤易氧化碳（ROC）6~10月平均值表现出针阔混交林>次生阔叶林>落叶松纯林,而土壤水溶性有机碳（WSOC）则为次生阔叶林>针阔混交林>落叶松纯林;（6）不同起源林分凋落物分解失重率与3种土壤活性碳的相关性均显著（P<0.05）,土壤呼吸速率与ROC和WSOC呈极显著负相关（P<0.01）。综合分析土壤碳收支过程表明,人天混更新更利于土壤碳的周转和贮存。     

The effect of litter type and macrofauna community on litter decomposition and organic matter accumulation in post-mining sites

Field microcosms consisting of mineral soil (spoil substrate) and two types of litter taken either from an unreclaimed site with spontaneously developed vegetation (mostly Salix caprea) or from an alder plantation (a mixture of Alnus glutinosa and A. incana) were exposed in spontaneously developed or reclaimed sites at a post-mining heap near Sokolov (Czech Republic) for one year. The litter types differed remarkably in C:N ratio which was 29 for spontaneous litter and 14 for alder litter. The two microcosm types were either accessible or not accessible to soil macrofauna. The effect of macrofauna exclusion on soil mixing was complex and depended on litter quality and the site that determined soil fauna composition. In reclaimed sites where macrofauna was dominated by saprophags, mainly earthworms, the macrofauna access increased soil mixing. In sites where predators dominated, the macrofauna exclusion probably suppressed fragmentation and mixing activity of the mesofauna.     

神农架常绿落叶阔叶混交林凋落物动态及影响因素

凋落物是陆地生态系统的重要组成部分, 凋落物动态特征可以反映出生态系统的存在状况以及环境对植被的影响作用。为探究北亚热带常绿落叶阔叶混交林凋落物产量及现存量的动态及其影响因素, 该研究观测了神农架地区一处典型植被2009-2015年的凋落物产量及现存量, 据此分析其动态特征及其与气象因素的关系。研究结果表明: 该森林凋落物平均年产量及现存量分别为5.94 t·hm ^-2和10.46 t·hm ^-2, 2009至2014年均无明显年际变化趋势, 但在2015年均显著降低, 且当年倒春寒天数显著高于其他年份; 季节动态变化呈现双峰型, 峰值分别出现在3-5月和10月; 凋落物月产量与当月的前第1-4个月的月平均气温正相关, 与当月的前第8-10个月的月平均气温负相关, 且与当月的前第6-7及第10个月的月平均相对湿度负相关; 凋落物产量季节性指数平均值为0.032, 与年平均气温显著正相关。可见, 长时间倒春寒现象会显著影响凋落物年产量及现存量, 月平均气温和相对湿度对凋落物产量季节动态的影响有明显的滞后性, 且年平均气温对北亚热带主要森林类型的凋落物产量季节性指数有显著影响。     

季节性雪被对天山雪岭云杉凋落叶分解和碳氮磷释放的影响

季节性雪被下显著的冻融格局差异可能对干旱区山地森林凋落叶分解过程产生重要影响, 但一直未见深入研究。2015年10月至2016年10月, 采用凋落物分解袋法, 研究了天山典型树种雪岭云杉(Picea schrenkiana)凋落叶在季节性雪被覆盖下的3个关键时期(冻融期、深冻期、融冻期)以及生长季(生长季早期和生长季末期)的分解动态和碳、氮、磷释放特征。结果表明: (1)经过一年的分解, 不同雪被厚度下雪岭云杉凋落叶分解率为24.6%-29.2%, 且存在显著性差异。分解系数k值厚雪被覆盖最大, 无雪被覆盖最小。(2)冬季雪被覆盖期雪岭云杉凋落叶分解对当年分解总量的贡献达46.0%- 48.5%, 其中对冻融期凋落叶分解影响较为明显。(3)随着凋落叶的分解, 雪岭云杉凋落叶氮含量总体呈增加趋势; 碳含量和碳氮比大致呈下降趋势, 在深冻期和生长季末期不同雪被处理下碳含量呈显著性差异; 而凋落叶磷含量呈不规则变化趋势, 且在冻融期和融冻期不同雪被厚度下呈显著性差异。(4)整个雪被覆盖季节凋落叶氮元素表现为富集, 碳和磷元素表现为释放; 其中, 在融冻期薄雪被和中雪被处理下碳元素富集率最大, 在冻融期薄雪被、中雪被和厚雪被处理下, 融冻期无雪被和厚雪被下以及生长季早期中雪被和厚雪被下氮元素富集率最大, 而雪被对凋落叶磷释放的影响不显著。     

凋落物去除和添加处理对典型草原生态系统碳通量的影响

为揭示凋落物去除和添加处理对草原生态系统碳通量的影响, 2013和2014年连续两年在成熟群落围封样地进行凋落物去除实验、在退化群落放牧样地进行凋落物添加实验, 并运用静态箱法探讨碳通量变化规律并分析其主要影响因子。结果表明: 两种群落的净生态系统CO₂交换(NEE)有明显的季节性变化。对成熟群落而言, 去除50%凋落物显著增加了NEE, 去除100%凋落物显著降低了NEE, 而对生态系统总初级生产力(GEP)和生态系统呼吸(ER)均无显著影响; 对退化群落而言, 凋落物添加显著增加了GEP和NEE, 而对ER无显著影响。两种群落的GEP与10 cm土壤温度显著正相关, 但NEE和GEP的变化规律与土壤温度相反, 与10 cm土壤湿度相同。由此可见, 凋落物去除和添加处理对生态系统碳通量的影响主要是改变土壤湿度和地上生物量,而不是改变土壤温度。该研究为合理利用凋落物改善草地生态系统管理和促进草地恢复提供了理论依据。     

Refining the cheatgrass–fire cycle in the Great Basin: Precipitation timing and fine fuel composition predict wildfire trends

Larger, more frequent wildfires in arid and semi‐arid ecosystems have been associated with invasion by non‐native annual grasses, yet a complete understanding of fine fuel development and subsequent wildfire trends is lacking. We investigated the complex relationships among weather, fine fuels, and fire in the Great Basin, USA. We first modeled the annual and time‐lagged effects of precipitation and temperature on herbaceous vegetation cover and litter accumulation over a 26‐year period in the northern Great Basin. We then modeled how these fine fuels and weather patterns influence subsequent wildfires. We found that cheatgrass cover increased in years with higher precipitation and especially when one of the previous 3 years also was particularly wet. Cover of non‐native forbs and native herbs also increased in wet years, but only after several dry years. The area burned by wildfire in a given year was mostly associated with native herb and non‐native forb cover, whereas cheatgrass mainly influenced area burned in the form of litter derived from previous years’ growth. Consequently, multiyear weather patterns, including precipitation in the previous 1–3 years, was a strong predictor of wildfire in a given year because of the time needed to develop these fine fuel loads. The strong relationship between precipitation and wildfire allowed us to expand our inference to 10,162 wildfires across the entire Great Basin over a 35‐year period from 1980 to 2014. Our results suggest that the region's precipitation pattern of consecutive wet years followed by consecutive dry years results in a cycle of fuel accumulation followed by weather conditions that increase the probability of wildfire events in the year when the cycle transitions from wet to dry. These patterns varied regionally but were strong enough to allow us to model annual wildfire risk across the Great Basin based on precipitation alone.