鼎湖山季风常绿阔叶林枯落物层自然含水量的长期动态变化

[目的]枯落物层自然含水量是林地环境特征的重要方面,探究枯落物层自然含水量长期动态及其影响机制对认知森林生态系统的水源涵养功能及森林立地环境变化具有重要意义。[方法]本文以鼎湖山国家级保护区内严格保护下的季风常绿阔叶林为研究对象,按照中国生态系统研究网络台站标准化的观测规范,对森林枯落物层自然含水量长期观测(2005—2018年),探究该地带性顶极森林枯落物层自然含水量的长期动态及其环境影响机制。[结果]鼎湖山地区多年平均降雨量1 975.6 mm,年均蒸发量1 117.3 mm,降雨丰富,热量输入稳定,雨热同期特征显著。地带性顶极森林群落季风常绿阔叶林的枯落物层现存量的多年均值为126.0g·m^(-2),干季期间现存量(130.3 g·m^(-2))略高于湿季(121.6 g·m^(-2));枯落物层自然含水量的多年均值为89.5%,湿季(103.2%)显著高于干季(75.8%),且湿季期间枯落物层含水量的变异系数(19.6%)显著低于干季(35.9%)。此外,相较于同期表层土壤(0~15 cm)的变化,枯落物层自然含水量的变异系数(30.1%)显著高于土壤水分的相应变异(11.6%),表明枯落物层对外界环境变化更具敏感性。进一步分析表明,降雨量、空气相对湿度、蒸发量、饱和水汽压差和土壤水分条件均显著影响着枯落物层自然含水量的变化,尤其是湿季期间空气相对湿度以及干季期间空气相对湿度和降雨量对枯落物层自然含水量变化表现出主导作用。[结论]鼎湖山季风常绿阔叶林的枯落物层自然含水量整体处于较高水平,枯落物层具有重要的稳定森林生态系统内部环境以及指示森林立地环境变化等的水文生态功能。

Effect of Simulated Acid Rain on Potential Carbon and Nitrogen Mineralization in Forest Soils

Acid rain is a serious environmental problem worldwide. In this study, a pot experiment using forest soils planted with the seedlings of four woody species was performed with weekly treatments of pH 4.40, 4.00, 3.52, and 3.05 simulated acid rain (SAR) for 42 months compared to a control of pH 5.00 lake water. The cumulative amounts of C and N mineralization in the five treated soils were determined after incubation at 25 ℃ for 65 d to examine the effects of SAR treatments. For all five treatments, cumulative CO2-C production ranged from 20.24 to 27.81 mg kg-1 dry soil, net production of available N from 17.37 to 48.95 mg kg-1 dry soil, and net production of NO-3 -N from 9.09 to 46.23 mg kg-1 dry soil. SAR treatments generally enhanced the emission of CO2-C from the soils; however, SAR with pH 3.05 inhibited the emission. SAR treatments decreased the net production of available N and NO3-N. The cumulative CH4 and N2O productions from the soils increased with increasing amount of simulated acid rain. The cumulative CO2-C production and the net production of available N of the soil under Acmena acuminatissima were significantly higher (P ≤ 0.05) than those under Schima superba and Cryptocarya concinna. The mineralization of soil organic C was related to the contents of soil organic C and N, but was not related to soil pH. However, the overall effect of acid rain on the storage of soil organic matter and the cycling of important nutrients depended on the amount of acid deposition and the types of forests.

二次妊娠产妇胎膜早破危险因素及其妊娠结局研究分析

目的分析二次妊娠产妇胎膜早破危险因素及其妊娠结局.方法选取180例二次妊娠产妇胎膜早破患者作为此次研究的研究对象,将其视为观察组,另取同时期,我院收治的180例二次妊娠产妇胎膜未破产妇作为对照组,对两组产妇的资料进行回顾性分析.结果年龄、生殖道感染以及文化程度等七项因素是影响产妇二次妊娠胎膜早破出现的主要因素,在观察组和对照组两组患者的妊娠结局中,观察组事件的发生率要高于对照组,显示二次妊娠胎膜早破会对产妇的妊娠结局产生明显的影响,差异具有统计学意义(P<0.05).结论在临床二次妊娠产妇中,胎膜早破将会对产妇的分娩方式以及妊娠结局造成明显的影响,让产妇的剖宫产率提高,为了保证产妇的健康可以从这些角度出发,保证产妇和胎儿的健康.

增温对南亚热带森林土壤磷形态的影响及其对有效磷的贡献

磷(P)是森林生态系统生产力的重要限制性元素。土壤磷的有效性取决于磷的存在形态及其转化过程。目前有关增温如何调控磷形态转化过程,从而促进土壤有效磷含量增加的机制尚未明确。该研究以南亚热带森林为研究对象,采用沿海拔高度从300 m下降至30 m以模拟温度自然上升的方法,采集该林型0–10、10–20、20–40 cm的土壤,并用适用于酸性土壤的连续浸提方法分离不同形态磷,研究增温对土壤不同形态磷含量的影响,探讨土壤不同形态磷与有效磷的关系,识别对土壤有效磷在增温背景下增加有重要贡献的磷组分。结果表明增温使0–10cm的无机钙磷(Ca-Pi)及20–40cm的无机铁磷(Fe-Pi)和总无机磷含量分别显著增加了65.5%、17.9%和18.5%,但对总有机磷及各有机磷组分含量均无显著影响。土壤不同形态磷与有效磷含量的相关分析表明,有效磷与无机态的不同形态磷及有机铝磷、有机铁磷含量均显著正相关,其中与Fe-Pi含量的相关性最强。通过土壤不同形态磷与有效磷含量的通径分析进一步发现,无机铝磷、Fe-Pi是土壤磷转化过程中的重要中间过渡性磷组分,且Fe-Pi是促进有效磷含量增加最重要的直接贡献磷组分。结合前期研究结果,增温可能增大了凋落物磷对土壤磷的输入,还可能强化了土壤的吸附和沉淀过程,使得更多进入到土壤的溶解态磷转化为Ca-Pi、Fe-Pi等缓效磷源,其中Fe-Pi可能成为南亚热带森林在气候变暖背景下最重要的有效磷来源。

Responses of Soil Acid Phosphomonoesterase Activity to Simulated Nitrogen Deposition in Three Forests of Subtropical China

Soil acid phosphomonoesterase activity (APA) plays a vital role in controlling phosphorus (P) cycling and reflecting the current degree of P limitation. Responses of soil APA to elevating nitrogen (N) deposition are important because of their potential applications in addressing the relationship between N and P in forest ecosystems. A study of responses of soil APA to simulated N deposition was conducted in three succession forests of subtropical China. The three forests include a Masson pine (Pinus massoniana) forest (MPF)-pioneer community, a coniferous and broad-leaved mixed forest (MF)-transition community and a monsoon evergreen broad-leaved forest (MEBF)-climax community. Four N treatments were designed for MEBF: control (without N added), low-N (50 kg N ha-1 year-1), and medium-N (100 kg N ha-1 year-1) and high-N (150 kg N ha-1 year-1), and only three N treatments (i.e., control, low-N, medium-N) were established for MPF and MF. Results showed that soil APA was highest in MEBF, followed by MPF and MF. Soil APAs in both MPF and MF were not influenced by low-N treatments but depressed in medium-N treatments. However, soil APA in MEBF exhibited negative responses to high N additions, indicating that the environment of enhanced N depositions would reduce P supply for the mature forest ecosystem. Soil APA and its responses to N additions in subtropical forests were closely related to the succession stages in the forests.