[Spatial variations and its influencing factors of soil carbon and nitrogen on the southern foot of Taihang Mountains, China]. / å¤ªè¡Œå±±å—éº“å¡é¢åœŸå£¤ç¢³æ°®ç©ºé—´å˜å¼‚æ€§åŠå ¶å½±å“å› ç´ .

As an important ecological barrier for the North China Plain, research on the spatial variations of soil nutrients in the southern foot of the Taihang Mountains is of great significance for the forestry ecological construction in this rocky mountainous area. With the typical slopes (the artificial forestland and the natural wild slope) of the southern foot of the Taihang Mountains as the research objects, we used the grid method to arrange sampling points, and combined classical statistics, geostatistics and constrained sorting methods to analyze the spatial variations of soil nutrients. The results showed that: 1) soil total carbon (TC) contents were 6.80-57.05 g·kg-1, and the total nitrogen (TN) contents were 0.74-3.93 g·kg-1. The coefficients of variation of both soil TC and TN were 25.0%-52.8%, belonging to the moderate degree of variation, which were caused by the combination of random and structural factors. The spatial aggregation of soil nutrients decreased with increasing lag distances. 2) The contents of soil nutrients had increasing trends from the top to the bottom of the slopes, with high nutrient values appearing at the bottom of the slopes. 3) The soil bulk density, gravel content, vegetation coverage, and soil water content were the main factors affecting the spatial variability of soil TC and TN on the southern foot of the Taihang Mountains. 4) Soil water content was the main factor affecting soil nutrients at the natural wild slope, but not at the artificial forestland.

[Spatial distribution of plant diversity in shrub layer of Quercus variabilis plantation and its relationship with light environment]. / æ “çš®æ Žäººå·¥æž—çŒæœ¨å±‚æ¤ç‰©å¤šæ ·æ€§çš„ç©ºé—´åˆ†å¸ƒåŠå ¶ä¸Žå ‰çŽ¯å¢ƒçš„å ³ç³».

We analyzed the spatial heterogeneity of plant species diversity in shrub layers and its relationship with light environment in Quercus variabilis plantation and Q. variabilis-Platycladus orientali mixed forest, following the method of geostatistics. The results showed that plant species diversity indices (Shannon H, Simpson Ds, Margalef Ma) of shrub layers in Q. variabilis plantation were significantly lower than that in Q. variabilis-P. orientalis mixed forest. The variation ranges and spatial autocorrelation distances of plant species diversity index in Q. variabilis plantation were higher than that in Q. variabilis-P. orientalis mixed forest, with lower spatial homogeneity but stronger spatial dependence. The plant species diversity indices of H, Ds and Ma structural ratios of shrub layers in Q. variabilis pure forest were 44.2%-49.7%, with moderate spatial autocorrelation. The structure ratios of H, Ds and Ma in Q. variabilis-P. orientalis mixed forest were 1.5%-3.3%, with strong spatial autocorrelation. The spatial distribution of biodiversity showed obvious strip-like gradient trend in Q. variabilis plantation and patchy gradient change in Q. variabilis-P. orientalis mixed forest, suggesting that the spatial continuity of plant species of shrub layers was worse in Q. variabilis-P. orientalis mixed forest and that the spatial variation was stronger than that in Q. variabilis pure forest. Results of correlation analysis and stepwise regression analysis showed that the total light and plant canopy openness were the most significant factors affecting plant species diversity of shrub layers in both forest types. Light environment formed by plant canopy structure played a crucial part in maintaining plant diversity in shrub layer.

[Distribution characteristics of surface soil organic carbon and total nitrogen in forest plantation of hilly area of Taihang Mountains, Chin]. / å¤ªè¡Œå±±ä½Žå±±ä¸˜é™µåŒºäººå·¥æž—è¡¨å±‚åœŸå£¤æœ‰æœºç¢³å’Œå ¨æ°®åˆ†å¸ƒç‰¹å¾.

To explore the effects of forest types and slope positions on the content of soil organic carbon (SOC) and total nitrogen (TN) in the lower hilly area of Taihang Mountains, we examined the distribution pattern of SOC and TN contents in Quercus variabilis plantation (Qo), and Platycladus orientalis plantation (Po), and abandoned land (Al). The results showed that in the same forest type or slope position, the contents of SOC and TN gradually decreased with increasing soil depth. Under different slope conditions, the contents of SOC and TN showed the tendency of upper-slope (U) > middle-slope (M) > lower-slope (L) in the planted forests (Qo and Po), but showed the tendency of L>U>M in Al. Under different forest types, the contents of SOC and TN in the U and M showed the trend of Qo>Po>Al. At the LS, the contents of SOC and TN of Al were the highest. The C/N ratio followed an order of Qo>Po> Al at U and M, while Qo>Al> Po at L. Within the same forest type, C/N of different slopes was different, but not significant. Our results suggested that the adaptability of the Qo plantation is the best in the lower hilly area of Taihang Mountains.

Demographic expansion of two Tamarix species along the Yellow River caused by geological events and climate change in the Pleistocene.

The geological events and climatic fluctuations during the Pleistocene played important roles in shaping patterns of species distribution. However, few studies have evaluated the patterns of species distribution that were influenced by the Yellow River. The present work analyzed the demography of two endemic tree species that are widely distributed along the Yellow River, Tamarix austromongolica and Tamarix chinensis, to understand the role of the Yellow River and Pleistocene climate in shaping their distribution patterns. The most common chlorotype, chlorotype 1, was found in all populations, and its divergence time could be dated back to 0.19 million years ago (Ma). This dating coincides well with the formation of the modern Yellow River and the timing of Marine Isotope Stages 5e-6 (MIS 5e-6). Bayesian reconstructions along with models of paleodistribution revealed that these two species experienced a demographic expansion in population size during the Quaternary period. Approximate Bayesian computation analyses supported a scenario of expansion approximately from the upper to lower reaches of the Yellow River. Our results provide support for the roles of the Yellow River and the Pleistocene climate in driving demographic expansion of the populations of T. austromongolica and T. chinensis. These findings are useful for understanding the effects of geological events and past climatic fluctuations on species distribution patterns.