柠条细根的分布和动态及其与土壤资源有效性的关系

Effects of soil resource availabilities on vertical distribution and dynamics of fine roots in a Caragana korshinskii plantation

受土壤资源有效性时空异质性的影响,植物细根会表现出明显的垂直分布和季节变化特征。揭示这些特征对认识细根的养分和水分吸收规律,预测C在地下的分配特点具有重要意义。运用Minirhizotron技术对晋西北黄土丘陵区30a生柠条(Caragana korshinskiiKom.)人工灌木林0—100 cm土层深度范围内细根的根数密度(FRD,根/cm2)、根长密度(FRLD,根/cm2)、平均直径(FRDi,mm)和根面积指数(FRAI,mm2/cm2)的垂直分布特征和季节动态进行了一个生长季的观测,分析了这些参数与土壤温度、水分和有效氮的关系。结果表明:(1)FRD、FRLD和FRAI均表现随土层深度增加而先增大后减小,且最大值均出现在40—80 cm土层,而表层0—20 cm最小;FRDi表现随土层深度增加而减小(除80—100 cm土层外),其中表层0—20 cm最大,而60—80 cm土层最小;(2)受土壤资源有效性季节变化的影响,FRD、FRLD和FRAI在不同土层(除0—20 cm外)表现相似的季节动态,即随季节变化而先增大后减小,春季小而秋季大;FRDi则表现随季节变化由粗逐渐变细的过程,春季最粗而秋季最细;(3)各细根参数与土壤温度、水分和有效氮在各土层存在不同程度的相关性。简单相关分析表明,细根的季节性变化主要受土壤温度和水分的影响,有效氮的影响不明显。表层(0—20 cm)主要受土壤水分影响,而在中下层(20—100cm)则主要受土壤温度的影响。各土层细根与土壤有效资源间的相关性反映了细根功能的季节性差异。综合分析表明,细根各参数季节变化的54.0%—98.6%是由土壤温度和水分的相互作用引起的。

The distribution of fine roots is closely related to soil resource availability.The characterization of vertical distribution and seasonal changes of the fine roots are essential for ecologists to further understand the rules of water and nutrient absorption for plant fine roots.They may also benefit the estimation of belowground carbon allocation of plants.In this study,we investigated the vertical distribution and seasonal dynamics of fine root density（FRD,N/cm2）,fine root length density（FRLD,mm/cm2）,mean fine root diameter（FRDi,mm） and fine root area index（FRAI,mm2/cm2） in 0-100cm soil profile（0-20,20-40,40-60,60-80 and 80-100cm soil layers,respectively） in a 30-year old Caragana korshinskii plantation located in the loess hilly region,northwest Shanxi Province,China by using minirhizotron techniques.Soil properties such as soil temperature,moisture and soil nitrogen availability were measured during the experiment.The correlations of soil properties with fine root parameters of FRD,FRLD,FRDi and FRAI were analyzed.The results showed that：（1） The highest values of FRD,FRLD and FRAI all appeared in 40-60cm soil layer;and the lowest values occurred in 0-20cm soil layer.Significant differences were found for each of them among the five soil layers（P0.05）.However,FRDi became small with soil depth increase,and the difference was insignificant among five soil layers（P0.05）.（2） A similar seasonal trend was found for FRD,FRLD or FRAI among different soil layers except for 0-20cm soil layer because of the seasonal change of soil resource availability.The highest values of FRD,FRLD and FRAI all occurred in autumn,and the smallest ones of them all appeared in spring.However,FRDi became finer from spring to autumn.For 80-100cm soil layer,the values of each fine root parameter in March（spring） had significant differences from those in August and September（autumn）（P0.01）.However,the values of each parameter for nine months（Mar.-Nov.） showed various levels of significances in their differences for other soil layers.（3）Pearson correlation analysis indicated that the seasonal change of fine roots was significantly influenced by soil temperature and moisture,respectively,and to a lesser extent,by soil nitrogen availability.Soil moisture had a significant influence on FRD,FRLD and FRAI in 0-20cm soil layer（r=-0.729——0.914,P0.05）.In 20-100 cm soil layers,soil temperature played a major role,and showed a significance increase with the soil depth increment（r=-0.028-0.832,P0.05）.Functional variation of fine roots was different in among soil layers and seasons.Multiple correlation analysis showed that the effects of soil temperature and soil moisture on fine roots were more significant than those of soil temperature and soil nitrogen availability,or soil moisture and soil nitrogen availability in each soil layer.The seasonal interaction of soil temperature with soil moisture can explain 54.0%-98.6% of the seasonal variation of FRD,FRLD,FRDi and FRAI.These results suggested that soil resource availability was closely related to the vertical distribution and seasonal changes of fine roots,and soil temperature and moisture together had a great influence on fine root distribution in the loess hilly region.