干旱河谷-山地森林交错带土壤水分与养分特征

Soil nutritional properties and moisture gradient of the ecotone between dry valley and montane forest of the Minjiang River

干旱河谷-山地森林交错带(EDM)在延伸亚高山森林生态功能,抑制干旱河谷上延等发挥着重要且不可替代的作用。研究了交错带邻近生态系统干旱河谷(DV)、亚高山森林(SF)以及交错带内(EDMⅠ、EDMⅡ、EDM)3个土层(L1、L2、L3)土壤水分及养分特征,结果表明,(1)相比于DV,EDM具有更好的土壤水环境,并为植物生长提供更多的可吸收磷,但未表现出更好的土壤氮素环境;SF则是山地垂直带谱中土壤水环境和养分环境最好的区域。(2)交错带内由于主要植物种类及其群落结构组成不同,土壤水、肥环境仍存显著差异。(3)海拔梯度上,L1中土壤水分与氨态氮相关性不显著,与其它养分均极显著相关(P<0.01)。L3中,速效养分均与土壤水分相关性不显著;剖面层次上,EDM和EDMⅠ不同层次的土壤养分与土壤水均未表现出显著相关性,而在EDMⅡ和SF却表现出显著相关。

The ecotone between dry valley and subalpine forest（EDM） does not only play principle and non-substitute roles in inhabiting the expansion of dry valle（DV） and extending the ecological functions of subalpine forest（SF）,but also is one of the important residential areas for Zang and Qiang minorities,and is always the primary ecological restoration region after ＂5.12＂ Wengchuan Earthquake.The soil moisture and nutrient is one of the main limiting factors on plants growth in arid and semiarid areas,and is also the key issues in ecological restoration on earthquake-damaged ecosystem at EDM.Many previous studies have been documented the soil physical properties,plant photosynthesis characteristics,water use efficiency and nutrient use efficiency of native plants in this ecotone system.However,most of these researches have a comprehensive knowledge on EDM as an extending areas of dry valley according to the results from controlled experiments such as water controlling and nutrient supplying,little attention have been paid to soil nutrient properties along soil moisture gradient caused by natural physiognomy and climate（altitude,precipitation,species） as well as present vegetation.Therefore,the spatial heterogeneity of five plots（i.e.DV,SF,EDMⅠ,EDMⅡ,EDM） and three layers（i.e.L1,L2,L3） of soil were selected in the present study.Soil moisture（volumetric water content）,was monitored using 6050X3K1 time-domain reflectrometry（TDR） in a representative date.At the same time,soil nutrient characteristics,including soil organic matter（SOM）,nitrate nitrogen（NN）,ammonium nitrogen（AN）,total nitrogen（TN）,available phosphorus（AP）,total phosphorus（TP）,were also investigated respectively.The results indicate that,soil water content in the same layer have significant gradient spatial heterogeneity at different plots and increase with the increase of altitudes,showed the order as： DVEDMEDMⅠEDMⅡSF,but soil water content in different layers are non-significant in the same plot except SF.And what＇s more,outside of EDM,total carbon was highest in the subalpine forest（16.59 mg/kg,18.28 mg/kg,10.06 mg/kg）,at an intermediate level in the EDM（7.32 mg/kg,3.30 mg/kg,2.56 mg/kg）,and it was lowest in the dry valley（4.24 mg/kg.4.18 mg/kg,4.92 mg/kg）.Meanwhile,EDM,Comparing to DV,can supply more suitable soil phosphorus environment,but did not represent nitrogen accumulation.Furthermore,inside of EDM,the moisture and nutrition of soil showed significant difference due to the difference of plant species and communities structure.For soil profile of each pedon,soil water in L1,within the altitudinal gradient,observed significant correlation with nutrition except nitrate nitrogen（P0.01）.The available nutrition all showed no sigificant correlation in L3.By contrast,the correlation between soil water and nutrition of different layer in the same site（i.e.EDM,EDMⅠ） was not significant.Comprehensively understanding,soil is pivotal in determining the construction and the development of plants communities and is always a difficult scientific issue in restoration of fragile dry valley ecosystems due to their extreme climates.The research suggested that EDM has better soil water and some nutrient environmen（e.g.phosphorus） than dry valley and has more frequent fluctuating and exchange of nutrients,which could plays an ecological carrier function in inhabiting the expansion of dry valley.Though instantaneous measurements of soil nutrient along soil water gradient are essential,researches about the transformation and exchanging as well as redistributing of nutrient and water are also needed.